Impact of Retarded Spark Timing on Engine Combustion,
Hydrocarbon Emissions, and Fast Catalyst Light-Off
by
Brian E. Hallgren
B.S., Mechanical Engineering
Binghamton University, 1998
S.M., Mechanical Engineering
Massachusetts Institute of Technology, 2000
Submitted to the Department of Mechanical Engineering in Partial
Fulfillment of the Requirements for the Degree of
DOCTOR OF PHILOSOPHY
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
February 2005
MASSACHUSETTS INSTITUTE
OF TECHNOLOGY
©2005 Massachusetts Institute of Technology
All Rights Reserved
MAY 0 5 2005
I IBRARIES
Signature of Author ...........
Department of Mechanical Engineering
October 18, 2004
Certified by ..........................................
John B. Heywood
Professor of Mechanical Engineering
Thesis Supervisor
A ccepted by .......................................
.........................................
Lallit Anand
Chairman, Department Committee on Graduate Students
BARKER
2
In memory of my father
3
4
Impact of Retarded Spark Timing on Engine Combustion,
Hydrocarbon Emissions, and Fast Catalyst Light-off
by
Brian E. Hallgren
Submitted to the Department of Mechanical Engineering on
October 18, 2004 in partial fulfillment of the requirements
for the Degree of Doctor of Philosophy
ABSTRACT
An experimental study was performed to determine the effects of substantial spark retard
on engine combustion, hydrocarbon (HC) emissions, feed gas enthalpy, and catalyst light-off.
Engine experiments were conducted at cold engine conditions for various ignition timings and air/
fuel ratios. Chemical and thermal energy of the exhaust gas was tracked from cylinder-exit to the
catalytic converter inlet using a variety of experimental techniques. Time-resolved exhaust port
and exhaust runner hydrocarbon concentrations were converted to an exhaust HC mass flow rate
and compared to time-averaged downstream HC levels. Quenching experiments quantified
cylinder-exit HC emissions by rapidly cooling exhaust gas at the valve seats, effectively freezing
HC oxidation reactions.
Combustion stability was observed to decrease as the phasing of the 50% mass fraction
burned location occurred later in the expansion stroke. A thermodynamic burn rate analysis
indicated combustion was complete by exhaust valve opening with spark timings as late as 200
after top-dead-center (ATDC). Engine operation with a relative air/fuel ratio 10% lean of
stoichiometric resulted in the lowest observed tailpipe-out HC emissions. Retarded spark timings
increased exhaust system oxidation, with port HC oxidation ranging from 15% to 37% with
additional HC reductions (40-50%) in the runner for ATDC spark timings. Catalyst light-off times
were reduced by 5 seconds and cumulative catalytic converter-in HC emissions were reduced by
44% prior to light-off.
A phenomenological model of exhaust system oxidation was developed to provide insight
into HC burn-up with late combustion phasing. A detailed chemical kinetic mechanism was
coupled with an exhaust flow model and exhaust thermal model. The hydrocarbon tracking and
exhaust gas quenching experiments provided initial conditions for a reacting plug flow model. The
predicted exhaust HC reaction rates were found to be strongly coupled with exhaust gas
temperature and the hydrocarbon species used to represent unburned fuel. The analysis showed
that most of the oxidation occurred early in the exhaust period when gas temperatures exceeded
1300K.
Thesis Supervisor: John B. Heywood
Title: Professor of Mechanical Engineering
6
TABLE OF CONTENTS
AB STR AC T ...........................................................................................................................
5
TABLE OF C ONTENTS.........................................................................................................
7
LIST O F F IGUR ES................................................................................................................
11
LIST OF TABLES..............................................................................................................
21
N OM ENCLATURE............................................................................................................
23
CHAPTER 1:
INTRODUCTION............................................................................................
1.1
OVERVIEW ....................................................................................
1.1.1
BACKGROUND AND MOTIVATION ....................................
1.1.2
PREVIOUS W ORK..............................................................
1.2
RESEARCH OBJECTIVES ..................................................................
1.2.1
OVERVIEW ........................................................................
1.2.2
EXPERIMENTAL ................................................................
1.2.3
M ODELING........................................................................
25
25
25
26
27
27
27
28
CHAPTER 2:
EXPERIMENTAL APPARATUS AND PROCEDURES......................................
2.1
SINGLE-CYLINDER ENGINE ............................................................
2.1.1
ENGINE-DYNAMOMETER.................................................
2.1.2
ENGINE CONTROL UNIT ...................................................
2.1.3
CYLINDER PRESSURE MEASUREMENTS............................
2.1.4
INTAKE CHARGE MOTION CONTROL PLATE (CMCP)........
2.1.5
DATA ACQUISITION SYSTEM............................................
2.1.6
EXPERIMENTAL CONDITIONS ...........................................
2.1.7
HYDROCARBON EMISSIONS MEASUREMENTS ..................
RELATIVE AIR/FUEL RATIO .............................................
2.1.8
2.1.9
AIR AND FUEL MASS FLOW RATES ................................
2.1.10 TEMPERATURE MEASUREMENTS......................................
2.1.11 EXHAUST GAS QUENCHING SETUP ..................................
2.1.12 SECONDARY AIR INJECTION SETUP.................................
2.2
MULTI-CYLINDER ENGINE ............................................................
2.2.1
ENGINE-DYNAMOMETER.................................................
2.2.2
EXHAUST SYSTEM OVERVIEW ..........................................
2.2.3
ENGINE SUB-SYSTEMS AND INSTRUMENTATION................
2.2.4
DATA ACQUISITION SYSTEM............................................
2.2.5
MODULAR DEVELOPMENT SYSTEM HARDWARE ................
2.2.6
MODULAR DEVELOPMENT SYSTEM SOFTWARE...............
2.2.7
IN-CYLINDER PRESSURE MEASUREMENTS ..........................
2.2.8
ENGINE TEST CONDITIONS AND PROCEDURE ..................
2.2.9
FAST-RESPONSE EMISSIONS ANALYZERS .........................
29
29
29
29
29
30
31
31
31
33
33
33
34
35
35
35
36
36
38
39
39
39
40
40
CHAPTER 3:
SINGLE-CYLINDER EXPERIMENTAL RESULTS..........................................
COMBUSTION CHARACTERISTICS ...................................................
3.1
3.1.1
COMBUSTION STABILITY.....................................................
3.1.2
BURN RATE ANALYSIS OVERVIEW ...................................
COMBUSTION DURATION AND PHASING .............................
3.1.3
43
43
43
44
46
7
3.2
3.3
3.4
3.5
3.6
3.7
CHAPTER 4:
EXHAUST GAS TEMPERATURES ....................................................
48
DOWNSTREAM TIME-AVERAGED HYDROCARBON EMISSIONS ......... 50
TIME-RESOLVED HYDROCARBON CONCENTRATION ..................... 52
3.4.1
O VERVIEW .......................................................................
52
3.4.2
EFFECT OF RETARDED SPARK TIMING ............................
53
3.4.3
EFFECT OF FLUID TEMPERATURES ......................................
55
ANALYSIS OF TIME-RESOLVED HC MEASUREMENTS....................55
3.5.1
O VERVIEW .......................................................................
55
3.5.2
ENGINE SIMULATION MODEL ...........................................
57
3.5.3
TIME-RESPONSE HC MEASUREMENTS ............................
59
3.5.4
PORT AND RUNNER HC MASS FLOW RATE ..................... 60
QUENCHING EXPERIMENTS ............................................................
64
SECONDARY AIR INJECTION ..........................................................
69
O VERVIEW .......................................................................
3.7.1
69
3.7.2
FIXED ENGINE RELATIVE AIR/FUEL RATIO......................69
3.7.3
TIMED SECONDARY AIR INJECTION..................................... 70
3.7.4
HC EMISSIONS FEED GAS SENSIBLE ENTHALPY................. 71
MULTI-CYLINDER EXPERIMENTAL RESULTS...............................................
4.1
ENGINE STARTUP OVERVIEW.........................................................
4.2
COMBUSTION CHARACTERISTICS...................................................74
4.2.1
COMBUSTION STABILITY .................................................
4.2.2
BURN RATE ANALYSIS ....................................................
4.3
EXHAUST EMISSIONS .....................................................................
4.3.1
TIME-RESOLVED CO AND HC EMISSIONS........................
4.3.2
CUMULATIVE CO AND HC MASS EMISSIONS .....................
4.3.3
CYLINDER-TO-CYLINDER MALDISTRIUBTION ....................
4.4
EXHAUST FEED GAS AND LIGHT-OFF............................................
4.4.1
FEED GAS EMISSIONS AND ENTHALPY .............................
4.4.2
CATALYST LIGHT-OFF TIMES..........................................87
73
73
74
76
78
78
80
81
86
86
CHAPTER 5:
EXHAUST SYSTEM M ODEL .......................................................................
89
5.1
O VERVIEW ......................................................................................
89
5.2
PLUG FLOW SUB-MODEL ..............................................................
90
5.2.1
M ASS ELEMENTS .................................................................
90
5.2.2
INITIAL CONDITIONS ........................................................
91
5.3
EXHAUST SYSTEM HEAT TRANSFER SUB-MODEL.........................93
5.3.1
O VERVIEW .......................................................................
93
5.3.2
EXHAUST RUNNER ...............................................................
95
5.3.3
AVERAGE EXHAUST HEAT TRANSFER COEFFICIENT...........'95
5.3.4
EXHAUST HEAT TRANSFER MODEL VALIDATION ............ 96
5.4
HYDROCARBON OXIDATION SUB-MODEL ....................................
99
5.4.1
O VERVIEW .......................................................................
99
5.4.2
HYDROCARBON SPECIES...................................................
99
5.4.3
CHEMICAL KINETIC MECHANISM ......................................
101
5.4.4
CHEMICAL KINETIC MODEL ..............................................
102
5.4.5
BURNT GAS RADICAL CONCENTRATION ........................... 103
CHAPTER 6:
M ODELING RESULTS ................................................................................
6.1
SINGLE-CYLINDER ENGINE .............................................................
8
105
105
6.2
6.3
6.4
CHAPTER 7:
105
6.1.1
EXHAUST PORT AND RUNNER OXIDATION.......................
109
MODEL SENSITIVITY .......................................................................
109
GAS TEMPERATURE ...........................................................
6.2.1
6.2.2
EXHAUST SYSTEM TEMPERATURE..................................... 110
110
6.2.3
MASS ELEMENTS ...............................................................
111
6.2.4
MIXTURE OF HYDROCARBONS...........................................
113
CARBON MONOXIDE OXIDATION....................................................
113
6.3.1
SECONDARY AIR INJECTION ..............................................
115
EXTENSION TO MULTI-CYLINDER ENGINE .....................................
6.4.1
EXHAUST FLOW AND HEAT TRANSFER ............................. 115
115
6.4.2
EXHAUST COMPOSITION ....................................................
6.4.3
EXHAUST SYSTEM OXIDATION..........................................
118
SUMMARY AND CONCLUSIONS..................................................................
EXPERIMENTS..................................................................................
7.1
7.1.1
SINGLE-CYLINDER ENGINE................................................
7.1.2
MULTI-CYLINDER ENGINE.................................................
7.2
EXHAUST OXIDATION MODEL ........................................................
REFERENCES.....................................................................................................................
APPENDIX A: BURN
A .I
A .2
A .3
A .4
RATE ANALYSIS PROGRAM .............................................................
ENERGY EQUATION.........................................................................
RESIDUAL G AS ESTIMATION ...........................................................
IN-CYLINDER HEAT TRANSFER .......................................................
EXHAUST GAS PROPERTIES.............................................................
121
121
121
122
123
125
127
127
127
127
128
APPENDIX B: MDS SYSTEM INSTRUCTIONS....................................................................
B.1 MDS FILE BOOT AND DOWNLOAD.................................................
B.2 AIR/FUEL RATIO CALIBRATION MODIFICATION.............................
B.3 SPARK, RPM, AND IAC CALIBRATION MODIFICATION..................
129
129
130
132
APPENDIX C: SINGLE-CYLINDER DATA ..........................................................................
C .I
D ATA TABLES .................................................................................
135
135
C.1.1
C.1.2
C.2
C.3
C.4
C.5
EXHAUST TEMPERATURES ..............................................................
137
WITH CHARGE MOTION CONTROL PLATE (CMCP).......... 137
C.2.1
C.2.2
WITHOUT CHARGE MOTION CONTROL PLATE (CMCP) ... 138
BURN RATE ANALYSIS: 900, 400, AND 200 C ................................. 139
TIME-RESOLVED HC MEASUREMENTS: 900 C FLUIDS ................... 140
HYDROCARBON MASS FLOW RATES ..............................................
141
C.5.1
PORT AND RUNNER EMISSION: SP = 150 BTDC................ 141
C.5.2
PORTANDRUNNEREMISSION: SP=BTDC ................ 142
C.5.3
C.5.4
C.6
C.7
200 C FLUIDS, 3.0 BAR NET-IMEP, 1500 RPM, W/CMCP135
900 C FLUIDS, 3.0 BAR NET-IMEP, 1500 RPM, w/CMCP136
PORT AND RUNNER EMISSION: SP = -1O BTDC .............. 143
PORT AND RUNNER EMISSION: SP = -150 BTDC .............. 144
CYLINDER-EXIT QUENCHING ..........................................................
SECONDARY AIR EXPERIMENTS......................................................
C.7.1
HC FLOw RATE AND EGTS: SP = 150 BTDC...................
9
145
146
146
APPENDIX D: MULTI-CYLINDER STARTUP DATA: 1 TO 20 SECONDS.............................. 149
149
''.......................
= 00)'.''.
BASELINE CALIBRATION: 00 (AOSp
D.1
CYLINDER PRESSURE, RPM, MAP, SPARK, AND A/F ....... 149
D. 1.1
D. 1.2 HC CONCENTRATIONS AND EGT ......................................
150
D.2 SPARK TIMING MODIFICATION: -5* (AOspA
= -50).......................151
D.2.1
CYLINDER PRESSURE, RPM, MAP, SPARK, AND A/F ....... 151
152
D.2.2
HC CONCENTRATIONS AND EGT ......................................
SPARK TIMING MODIFICATION: -10* (AOSPARK = -100)................... 153
D.3
D.3.1
CYLINDER PRESSURE, RPM, MAP, SPARK, AND A/F ....... 153
D.3.2
HC CONCENTRATIONS AND EGT ......................................
154
= -150)................... 155
D.4 SPARK TIMING MODIFICATION: -150 (AOspA
D.4.1
CYLINDER PRESSURE, RPM, MAP, SPARK, AND A/F....... 155
D.4.2
HC CONCENTRATIONS AND EGT ......................................
156
157
APPENDIX E: ENGINE SIMULATION .................................................................................
157
SINGLE-CYLINDER ENGINE .............................................................
E.1
E.1.1
VALVE LIFT AND DISCHARGE COEFFICIENTS....................157
158
M ULTI-CYLINDER ENGINE ..............................................................
E.2
158
E.2.1
GT-POWER ENGINE SIMULATION......................................
E.2.2
VALVE LIFT AND DISCHARGE COEFFICIENTS....................159
APPENDIX F: EXHAUST OXIDATION M ODEL...................................................................
INITIAL MODEL INPUT CONDITIONS ...............................................
F.1
F.2
HEAT TRANSFER M ODEL ................................................................
F.3
CHEMKIN SOFTW ARE ......................................................................
F.4
SINGLE-CYLINDER ENGINE .............................................................
F.4.1
SPARKTIMING = 15* BTDC AND X = 1.0 .........................
F.4.2
SPARK TIMING = 00 BTDC AND X = 1.0 ...........................
SPARK TIMING =-15 0 BTDC AND A = 1.0 ........................
F.4.3
161
161
162
164
168
168
170
172
LIST OF FIGURES
Figure 1.1
Cumulative engine-out and tailpipe-out HC emission over an FTP-75 for a sixcylinder SI engine ..........................................................................................
26
Figure 2.1
Intake charge motion control plate (CMCP) with 67% asymmetrical area
reduction for the single cylinder engine..........................................................30
Figure 2.2
Fast-response HC analyzer probe sampling locations for single-cylinder
experiments. Exhaust port and runner probes 7 cm and 37 cm from exhaust valves,
12
respectively .....................................................................................................
Figure 2.3
Schematic of probes located at the exhaust valve seats utilized for quenching and
34
secondary air injection experiments...............................................................
Figure 2.4
Overview of gas delivery system equipment used for quench gas and secondary
35
air experim ents ..............................................................................................
Figure 2.5
Active three-way catalyst (serial no: XX90IJP) specifications ......................
37
Figure 2.6
Figure 2.6 Schematic of fast-response NDIR sampling head ........................
40
Figure 3.1
COV of Net-IMEP as a function of spark timing with and without intake charge
motion control plate (CMCP) for three relative air/fuel ratios. Data shown for 3.0
43
bar Net-IMEP, 1500 RPM, and 20' C fluids .................................................
Figure 3.2
In-cylinder pressure, cumulative mass fraction burned (MFB) and instantaneous
MFB rate as a function of crank angle for three spark timings. Operating
conditions: 3.0 bar Net-IMEP, 1500 RPM, ? = 1.0, with charge motion (CMCP)
and 20' C fluids...............................................................................................
45
Figure 3.3
Combustion durations as a function of spark timing for different relative air/fuel
ratios and fluid temperatures without charge motion control plate (CMCP) at 3.0
bar Net-IM EP and 1500 RPM ........................................................................
46
Figure 3.4
Combustion duration as a function of spark timing for different relative air/fuel
ratios and fluid temperatures with charge motion control plate (CMCP) at 3.0 bar
Net-IM EP and 1500 RPM ...............................................................................
47
Figure 3.5
Location of 50% MFB as a function of spark timing without charge motion control
plate (CMCP) for various relative air/fuel ratios and fluid temperatures at 3.0 bar
Net-IM EP and 1500 RPM ...............................................................................
47
Figure 3.6
Location of 50% MFB as a function of spark timing with charge motion control
plate (CMCP) for various relative air/fuel ratios and fluid temperatures at 3.0 bar
Net-IM EP and 1500 RPM ...............................................................................
48
Figure 3.7
Thermocouple measured port exit exhaust gas temperature as a function of 50%
MFB location for various relative air/fuel ratios with and without the charge
motion control plate (CMCP) and 20'C fluids ...............................................
49
11
Figure 3.8
Converter-in sensible enthalpy rate as a function of COV of Net-IMEP for
different relative air/fuel ratios with and without the charge motion control plate
(C M C P)............................................................................................................
50
Figure 3.9
Steady-state hydrocarbon mass flow rate as function of spark timing for different
relative air/fuel ratios and fluid temperatures. Data shown for 3.0 bar Net-IMEP
and 1500 RPM with charge motion (CMCP)......................................................51
Figure 3.10 Steady-state HC flow rate and emission index HC emissions as a function of 50%
MFB location for various relative air/fuel ratios and fluid temperatures at 3.0 bar
Net-IMEP, 1500 RPM, with charge motion (CMCP)...................................... 52
Figure 3.11
Typical time-resolved HC concentration profile measured in the exhaust port, 7cm
from the exhaust valves. Major features shown and noted during gas exchange,
from exhaust valve opening (EVO) to exhaust valve closing (EVC)............. 53
Figure 3.12 In-cylinder pressure and exhaust port and runner time-resolved HC concentration
measurements for three different spark timings (Sp = 150, 0', and -16' BTDC) at
54
3.0 bar Net-IMEP, X=1.0, CMCP, and 20' C fluids ........................................
Figure 3.13 In-cylinder pressure and time-resolve HC concentration measured in the port and
runner for 90', 40', 20' C fluid temperatures, spark timing = -1 BTDC, X=1.0,
and without charge motion (CMCP)..............................................................56
Figure 3.14 Overview of mass plug flow model used for analysis of time-resolved HC
36
concentrations ................................................................................................
Figure 3.15 Engine cycle simulation thermodynamic model of open system, including
crevices, work transfer to piston, and heat transfer to cylinder boundaries........57
Figure 3.16 GT-Power model of single-cylinder engine with intake and exhaust system.....58
Figure 3.17 Port exit exhaust mass flow rate and exhaust gas temperature predicted by the
engine model at the exit of the exhaust valves versus crank angle for various spark
timings at 3.0 bar Net-IMEP, 1500 RPM, ? = 1.0, and 20' C fluids .............. 59
Figure 3.18 Spatial and cyclic variations of the time-resolved HC measurements in the exhaust
port, 7 cm from exhaust valves at several port-exit locations........................60
Figure 3.19 Model results from analysis of HC measurements. GT-Power simulation results of
in-cylinder pressure and exhaust mass flow rate at the port exit and runner.
Measured HC concentration and resulting HC mass flow rate computed by a plug
61
flow model .......................................................................................................
Figure 3.20 Steady-state HC emissions as a function of spark timings measured in three
62
locations under X = 1.0, 20' C fluids ..............................................................
Figure 3.21
Emission index HC emissions as a function of location of 50% MFB for different
63
exhaust locations under X = 1.0 and 200 C fluids ..........................................
Figure 3.23
Steady-state HC emissions as a function of spark timing for three different
locations under X = 1.1 and 200 C fluids........................................................63
Figure 3.24 Emission index HC emissions as a function of the location of 50% MFB for three
different locations under X = 1.1 and 200 C fluid ..........................................
64
Figure 3.25 Phasing of quench gas injection as a function of crank angle. Data shown with incylinder pressure and solenoid trigger signal for 3.0 bar Net-IMEP, 150 BTDC
spark tim ing, and X = 1.0 ................................................................................
65
Figure 3.26
Change in HC and NOX emissions as a function of the ratio of mass of quench gas
to mass of charge (mCo2Quench/mChargeair+fue) for three spark timings with k = 1.0
and 20' C fluids...............................................................................................
66
Figure 3.27
Steady-state HC emissions as a function of spark timing at four locations (cylinder
exit, port exit, runner, and mixing tank) under X = 1.0 and 20' C fluids............67
Figure 3.28 Emission index HC emissions as a function of 50% MFB location at four locations
under X = 1.0 and 20 * C fluids ........................................................................
67
Figure 3.29
Steady-state HC emissions as a function of spark timings at four locations under
, = 1.1 and 20 C fluids .................................................................................
68
Figure 3.30
Emission index HC emissions as a function of 50% MFB location at four locations
for ? = 1.1 and 20 C fluids ............................................................................
68
Figure 3.31
Exhaust secondary air injection experiments conducted at an engine relative air/
fuel ratio of 0.85 (kengine) as a function of with exhaust relative air/fuel ratio. Data
shown for 00 BTDC spark timing and 20' C fluids ........................................
70
Figure 3.32 Hydrocarbon flow rate and runner exhaust gas temperatures as a function of
various secondary air injection timings for a fixed engine (Xengine = 0.85) and
exhaust stoichiometry (Xexhaust = 1.2). Data shown for 3.0 bar Net-IMEP, 1500
RPM , and 20 C fluids ...................................................................................
71
Figure 3.33 Normalized HC flow rate as a function of normalized sensible feed gas enthalpy
rate for three spark timings. Data shown for 1= 1.0, 1.1, and secondary air injection
(SAI) at a fixed engine relative air/fuel ratio (kengine = 0.85) with exhaust
enleanment from Xexhaust = 0.85 to 1.4 Shown with respect to X = 1.0 and 150
BTDC spark timing baseline condition, 3.0 bar Net-IMEP, 1500 RPM, and 200 C
flu ids....................................................................................................................72
Figure 4.1
Baseline calibration MAP, RPM, spark timing, and relative air/fuel ratio as a
function of time after crank. Data from an ambient startup under idle load and
speed conditions...............................................................................................
73
Figure 4.2
Spark timing as a function of time after startup for various spark modifications
(AOspark) ------------------------------------------------..............................................................
75
Figure 4.3
Measured UEGO relative air/fuel ratio (k) as a function of cycle no. after engine
startup. Data shown for accelerated closed loop control compared to baseline
calibration ............................................................................................................
75
Figure 4.4
COV of Net-IMEP as a function modified spark timing, 4 to 20 seconds after
crank (130 cycles). In-cylinder pressure data acquired from all four cylinders at
idle speed and load conditions following an ambient start .............................
76
13
Figure 4.5
Location of 50% MFB as a function of cycle no. after 200 C startup. Data shown
for various spark timing modifications under idle speed and load conditions.... 77
Figure 4.6
Combustion duration (10-90%) as a function of cycle number after 200 C startup.
Data shown for various spark timing modifications under idle speed and load
conditions .......................................................................................................
77
Figure 4.7
Cylinder no. 4 port exit and converter-in hydrocarbon concentrations (ppmc1) for
the first 20 seconds following a 20' C start. Baseline timing and fueling calibration
under idle load and speed conditions ..............................................................
78
Figure 4.8
Cylinder no. 4 pressure, CO, C0 2 , and HC time-resolved concentrations measured
at the exhaust port exit of cylinder no. 4 as a function of crank angle (CA). Data
shown for three different spark modifications (absolute spark timings: 30, -1', -6'
BTDC) from cycle 200 to 210, stoichiometric closed loop control and idle speed
and load conditions (2.3 bar Net-IMEP, 1000 RPM, X=1.0).Grayed areas show
period of exhaust flow .....................................................................................
79
Figure 4.9
Cylinder no. 4 exhaust port and converter-in mass flow rates and exhaust gas
temperatures as a function of engine crank angle (CA). Data predicted by the
engine simulation for baseline timing and fueling calibration under idle load and
speed conditions ..............................................................................................
80
Figure 4.10 Cumulative, 1 to 20 seconds, ambient startup CO and HC mass emissions
measured at the exhaust port exit of cylinder no. 4 and converter-inlet as a function
of modified spark timing under idle speed and load conditions (Port exit emissions
are scaled by a factor of 4 for comparison to catalytic converter-in levels).......81
Figure 4.11 Cylinders no. 3 and no. 4 in-cylinder pressure, CO, C0 2, and CO + CO 2 timeresolved concentrations measured at the exhaust port as a function of crank angle
(CA). Data shown from cycle 200 to 210 after startup, absolute spark timing 3'
BTDC, stoichiometric closed loop control, and idle speed and load conditions.
Grayed areas show period of exhaust flow .....................................................
82
Figure 4.12 Cylinder no. 3 and no.4 in-cylinder pressure and port exit time-resolved HC
concentrations as a function of crank angle (CA). Data shown from cycle 200 to
210 after startup, absolute spark timing -4' BTDC, stoichiometric closed loop
control, and idle speed and load conditions (2.3 bar Net-IMEP, 1000 RPM, X =
1.0).Grayed areas show period of exhaust flow..............................................83
Figure 4.13 Port exit measured exhaust gas temperatures and relative air/fuel ratios (Q)
calculated from time-resolved CO and CO 2 measurements for cylinders no. 3 and
no. 4 as a function of modified spark timing. Data shown for idle load and speed
conditions under closed loop stoichiometric control .....................................
84
Figure 4.14
Spark-ignition engine exhaust gas CO 2 and CO concentration data as a function of
relative air/fuel ratio.......................................................................................
84
Figure 4.15 Converter-in CO + 02 emissions and emission index HC levels as a function of
intake MAP. Data shown for stoichiometric closed loop control and 200 C idle
speed and load conditions (2.3 bar Net-IMEP, 1000 RPM, X = 1.0). CO+0 2
concentration shown with and without oxygen concentration corrections due to
HC em issions .................................................................................................
85
14
Figure 4.16 Measured exhaust gas and component temperatures as a function of time after
crank. Data shown for baseline timing and fueling calibration under idle load and
86
speed conditions ...............................................................................................
Figure 4.17 Cumulative converter-in feed gas HC emissions as a function of cumulative
converter-in sensible enthalpy. Data shown for 1 to 20 seconds following an
ambient startup for four spark timing modifications (AOsp) under idle speed and
87
load conditions .................................................................................................
Figure 4.18 Cumulative HC mass emissions prior to catalyst light-off as a function of light-off
time following an ambient start. Data shown for various spark modifications
(AOSP) under idle speed and load conditions (Light-off defined as 50% reduction
88
in HC em issions).............................................................................................
Figure 5.1
Plug flow exhaust oxidation sub-model flowchart with linked engine predicted
cylinder-exit conditions, heat transfer, and chemical kinetic mechanism .......... 89
Figure 5.2
Diagram of exhaust port and runner zones .....................................................
Figure 5.3
Simulation of single-cylinder exhaust mass flow versus crank angle after exhaust
valve opening. Exhaust mass modeled using two elements; mass from
compressible blown process and incompressible displacement....................... 91
Figure 5.4
Mass element model details ............................................................................
Figure 5.5
Cylinder-exit initial conditions for plug flow model. Data shown from engine
92
simulation predictions and experimental results .............................................
Figure 5.6
Mole fraction of exhaust gas composition for highly diluted reactive mixture of
93
hydrocarbons ....................................................................................................
Figure 5.7
Thermocouple measured exhaust gas and component temperatures for 150,00, and
-15' BTDC spark timings. Steady-state warmed-up exhaust system with 20' C
94
fluids, 3.0 bar Net-IMEP, 1500 RPM, and), = 1.0 ........................................
Figure 5.8
Average port (left) and runner (right) heat transfer coefficient as a function of
spark timings. Data shown for mass elements from exhaust blowdown and
96
displacem ent process......................................................................................
Figure 5.9
Schematic of exhaust port and runner temperature validation of heat transfer submodel. Exhaust port and runner HC oxidation modeled as a heat addition per unit
97
length ..................................................................................................................
90
91
Figure 5.10 Instantaneous exhaust gas, runner wall and thermocouple temperature as a
function of time. Thermocouple response data shown for hot exhaust component
98
temperatures ....................................................................................................
Figure 5.11
Thermocouple exhaust gas temperatures, measured versus modeled, for various
spark timings. Comparison includes heat released due to exhaust system HC bum98
up .........................................................................................................................
Figure 5.12 Cold-start SI engine-out speciated HC emissions for initial 63 seconds of engine
100
operation using Japanese dom estic fuel............................................................
15
Figure 5.13 Variation in engine-out hydrocarbon composition as a function of time during
w arm -up ............................................................................................................
100
Figure 5.14 Hydrocarbon oxidation pathways .....................................................................
102
Figure 6.1
Relative port, runner, and total exhaust system HC oxidation as a function of spark
timing and relative air/fuel ratio. Data shown for 3.0 bar Net-IMEP, 1500 RPM,
200 C fluids, with intake charge motion (CMCP).............................................
106
Figure 6.2
Measured port and runner exhaust gas temperature as a function of spark timing
and relative air/fuel ratio. Data shown for 3.0 bar Net-IMEP, 1500 RPM, 200 C
fluids, with intake charge motion (CMCP).......................................................
106
Figure 6.3
Measured and predicted fraction of port reacted hydrocarbons (left) and exhaust
port time averaged and enthalpic gas temperatures (right) as a function of spark
tim ing. Data show n for ) = 1.0 .........................................................................
107
Figure 6.4
Measured and predicted fraction of port reacted hydrocarbons (left) and exhaust
port time averaged and enthalpic gas temperatures (right) as a function of spark
tim ing. Data show n for k = 1.1 .........................................................................
107
Figure 6.5
Measured and predicted fraction of runner reacted hydrocarbons (left) and exhaust
runner time averaged and enthalpic gas temperatures (right) as a function of spark
timing. Data shown for k = 1.0, 3.0 bar Net-IMEP, and 1500 RPM ................ 108
Figure 6.6
Measured and predicted fraction of runner reacted hydrocarbons (left) and exhaust
runner time averaged and enthalpic gas temperatures (right) as a function of spark
timing. Data shown for k = 1.1, 3.0 bar Net-IMEP, and 1500 RPM ................ 108
Figure 6.7
Effect of gas temperature on exhaust HC oxidation predictions. Data shown with
respect to baseline gas temperatures .................................................................
109
Figure 6.8
Effect of cold (20' C) exhaust component temperature on predicted HC oxidation.
Data shown for different ignition timings (Sp) with respect to baseline HC mixture
and hot stabilized component temperatures ......................................................
110
Figure 6.9
Effect of the number exhaust mass elements on predicted exhaust HC oxidation.
Data shown with respect to 2 mass element baseline condition ....................... Ill
Figure 6.10 Hydrocarbon mole fraction composition for three cases. Data shown for case 1
with the baseline HC mixture, case 2 is 100% iso-octane, and case 3 contains 55%
ethylene, 35% pentane, and 10% methane........................................................
112
Figure 6.11
Calculated half-lives (T 5 0 ) of various hydrocarbon mixtures as a function of
temperature for exhaust residence times. Data shown for ? = 1.0, 1% HC gas
m ixture ..............................................................................................................
112
Figure 6.12 Effect of HC mixture on predicted exhaust HC oxidation. Data shown with respect
to baseline mixture: 44% ethylene, 26% methane, 17% n-pentane, 9% toluene, and
4% iso-octane ....................................................................................................
113
Figure 6.13 CO oxidation reaction mechanisms ..................................................................
16
114
Figure 6.14 CO oxidation time constant as a function of exhaust relative air/fuel ratio (X) Data
shown for three different spark timings (exhaust gas temperatures)................ 114
Figure 6.15 Measured time averaged and predicted adiabatic enthalpic runner gas
temperatures as a function of exhaust relative air/fuel ratio Q) ....................... 115
Figure 6.16 Cylinder no. 4 port exit and collector-in exhaust mass flow rate as a function of
116
crank angle ........................................................................................................
Figure 6.17 Cylinder no. 4 port exit and collector-in exhaust gas temperature as a function of
116
crank angle ........................................................................................................
Figure 6.18 Diagram of multi-cylinder exhaust system with runner collector mixing ........ 117
Figure 6.19
Cylinder relative air/fuel ratio as a function of distance from exhaust valves.. 117
Figure 6.20
Measured and predicted fraction of runner reacted hydrocarbons (left) and exhaust
runner time averaged and enthalpic gas temperatures (right) as a function of spark
timing. Data shown for idle speed and load conditions, 1 to 20 seconds after 200
C startup. Model initial conditions based upon air/fuel ratio data from cylinder
119
nos. 3 and 4 .......................................................................................................
Figure B.2.1 Air/fuel ratio as a function time with noted calibration tables controlling A/F ratio.
Closed loop operation with the exhaust gas oxygen sensor (02) noted in top of
13 1
figure .................................................................................................................
Figure B.3.1 Spark timing as a function of time after crank..................................................
133
Figure C.2.1 Port exit and runner exhaust gas temperatures as function of the location of the
50% mass fraction burned (MFB) for 200 C and 90' C fluid temperatures and
various relative air/fuel ratios. Data shown for 3.0 bar Net-IMEP, 1500 RPM, with
137
intake charge motion control plate (CMCP).....................................................
Figure C.2.2 Port exit and runner exhaust gas temperatures as function of the location of the
50% mass fraction burned (MFB) for 200 C and 90' C fluid temperatures and
various relative air/fuel ratios. Data shown for 3.0 bar Net-IMEP, 1500 RPM,
138
without intake charge motion control plate (CMCP)........................................
Figure C.4.1 Cumulative mass fraction burned (MFB) and instantaneous MFB rate as a
function of crank angle for 900, 400, and 200 C fluids. Operating conditions: 3.0
bar Net-IMEP, 1500 RPM, ?, = 1.0, spark timing = -1' BTDC, without charge
139
m otion (C M C P).................................................................................................
Figure C.5.1 In-cylinder pressure and exhaust port and runner time-resolved HC concentration
measurements for three different spark timings (Sp = 15', -P , and -16' BTDC),
140
X=1.0, CMCP, and 900 C fluids ........................................................................
Figure C.6.1 Model results from analysis of time-resolved HC measurements. GT-Power
simulation results of in-cylinder pressure (upper left) and exhaust mass flow rate
at the port exit and runner (upper right). Measured HC concentrations (lower left)
and predicted HC mass flow rate (lower right). Data shown for 150 BTDC spark
tim ing, ? = 1.0, and 200 C fluids.......................................................................141
17
Figure C.6.2 Model results from analysis of time-resolved HC measurements. GT-Power
simulation results of in-cylinder pressure (upper left) and exhaust mass flow rate
at the port exit and runner.(upper right). Measured HC concentrations (lower left)
and predicted HC mass flow rate (lower right). Data shown for -' BTDC spark
timing, k = 1.0, and 200 C fluids.......................................................................
142
Figure C.6.3 Model results from analysis of time-resolved HC measurements. GT-Power
simulation results of in-cylinder pressure (upper left) and exhaust mass flow rate
at the port exit and runner.(upper right). Measured HC concentrations (lower left)
and predicted HC mass flow rate (lower right). Data shown for -10' BTDC spark
tim ing, k = 1.0, and 200 C fluids......................................................................
143
Figure C.6.4 Model results from analysis of time-resolved HC measurements. GT-Power
simulation results of in-cylinder pressure (upper left) and exhaust mass flow rate
at the port exit and runner.(upper right). Measured HC concentrations (lower left)
and predicted HC mass flow rate (lower right). Data shown for -15' BTDC spark
tim ing, X = 1.0, and 20' C fluids.......................................................................144
Figure C.7.1 Change in HC and NOx emissions as a function of the ratio of mass of quench gas
to mass of charge (mco2Quench/MChargeair+fue) for three spark timings with X = 1.0
and 900 C fluids.................................................................................................145
Figure C.8.1 Port exit and runner EGTs and tailpipe-out HC flow rate as a function of exhaust
relative air/fuel ratio. Data shown for continuos secondary air injection at a fixed
engine relative air/fuel ratio (kengme = 0.85) and 150 BTDC spark timing ...... 146
Figure C.8.2 Port exit and runner EGTs and tailpipe-out HC flow rate as a function of exhaust
relative air/fuel ratio. Data shown for continuos secondary air injection at a fixed
engine relative air/fuel ratio (Xengine = 0.85) and 00 BTDC spark timing ........ 146
Figure C.8.3 Port exit and runner EGTs and tailpipe-out HC flow rate as a function of exhaust
relative air/fuel ratio. Data shown for continuos secondary air injection at a fixed
engine relative air/fuel ratio (kengine = 0.85) and -15' BTDC spark timing ..... 147
Figure D.l.1 In-cylinder pressure, RPM, MAP, spark timing, and lambda (1) as a function of
time after ambient startup. Data shown for baseline spark and fuel calibration
(AOspark = 00). Calculated Net-IMEP and COV of Net-IMEP, averaged RPM,
MAP, spark timing, and X, for 1 to 20 seconds after crank. ............................. 149
Figure D.1.2 Time-resolved port exit (FFID #1) and converter-in (FFID #2) HC concentrations,
port exhaust gas temperature (EGT), and exhaust component temperatures as a
function of time after ambient startup. Data shown for baseline spark and fuel
calibration (AOspark = 00). Calculated sensible enthalpy and averaged HC
concentrations for 1 to 20 seconds after crank..................................................
150
Figure D.2.1 In-cylinder pressure, RPM, MAP, spark timing, and lambda (k) as a function of
time after ambient startup. Data shown for -5' spark timing modification (AOspark
= -50). Calculated Net-IMEP and COV of Net-IMEP, averaged RPM, MAP, spark
timing, and k, for 1 to 20 seconds after crank..................................................
151
18
Figure D.2.2 Time-resolved port exit (FFLD #1) and converter-in (FFID #2) HC concentrations,
port exhaust gas temperature (EGT), and exhaust component temperatures as a
function of time after ambient startup. Data shown -5' spark modification (AOspark
= -5O). Calculated sensible enthalpy and averaged HC concentrations for 1 to 20
152
seconds after crank. ..........................................................................................
Figure D.3.1 In-cylinder pressure, RPM, MAP, spark timing, and lambda (1) as a function of
time after ambient startup. Data shown for -10' spark timing modification (AOspark
= -10*). Calculated Net-IMEP and COV of Net-IMEP, averaged RPM, MAP,
spark timing, and X, for 1 to 20 seconds after crank. ....................................... 153
Figure D.3.2 Time-resolved port exit (FFID #1) and converter-in (FFID #2) HC concentrations,
port exhaust gas temperature (EGT), and exhaust component temperatures as a
function of time after ambient startup. Data shown -10' spark modification
(AOspark = -10o). Calculated sensible enthalpy and averaged HC concentrations for
154
1 to 20 seconds after crank. ..............................................................................
Figure D.4.1 In-cylinder pressure, RPM, MAP, spark timing, and lambda (1) as a function of
time after ambient startup. Data shown for -15* spark timing modification (AOspark
= -15'). Calculated Net-IMEP and COV of Net-IMEP, averaged RPM, MAP,
spark timing, and k, for 1 to 20 seconds after crank......................................... 155
Figure D.4.2 Time-resolved port exit (FFID #1) and converter-in (FFID #2) HC concentrations,
port exhaust gas temperature (EGT), and exhaust component temperatures as a
function of time after ambient startup. Data shown -15' spark modification
(AOspark = -15o). Calculated sensible enthalpy and averaged HC concentrations for
156
1 to 20 seconds after crank................................................................................
Figure F. 1.1 Exhaust gas hydrogen (H 2 ) as a function of CO concentration ........................
161
Figure F.2.1 Schematic of type-k thermocouple and radiation shielding for measuring exhaust
162
gas temperature ................................................................................................
Figure F.3.1 SENKIN sub-model flowchart overview ..........................................................
164
Figure F.3.2 Port, runner, and calculated burn-up exhaust gas temperature as a function of
combustion phasing (location of 50% MFB). Burn-up temperatures are based
upon complete oxidation of HC without the effects of heat transfer in the runner.
Data shown for 3.0 bar Net-IMEP, 1500 RPM, 20' fluids, k = 1.0 with charge
165
m otion (C M C P).................................................................................................
Figure F.3.3 Hydrocarbon mass flow rate as a function of distance from exhaust valve seats for
three spark timings. Data shown for 3.0 bar Net-IMEP, 1500 RPM, k = 1.0, with
charge m otion (CMCP).....................................................................................
166
Figure F.3.4 Super-equilibrium exhaust gas radical concentrations. Volume-time dependent
Senkin calculation from the end of combustion to exhaust valve opening....... 167
Figure F.4.1 Time histories of cylinder-exit temperature, velocity, mass flow, and hydrocarbon
mass emissions as a function of crank angle. Data shown for k = 1.0 and spark
168
tim ing = 15 0 B TD C ...........................................................................................
19
Figure F.4.2 Mass element temperature and exhaust gas mole fraction histories as a function of
time for a highly diluted reactive mixture. Data shown for X = 1.0 and spark timing
= 15' B TD C ......................................................................................................
169
Figure F.4.3 Time histories of cylinder-exit temperature, velocity, mass flow, and hydrocarbon
mass emissions as a function of crank angle. Data shown for X=1.0 and spark
tim ing = 0 B TD C .............................................................................................
170
Figure F.4.4 Mass element temperature and exhaust gas mole fraction histories as a function of
time for a highly diluted reactive mixture. Data shown for X = 1.0 and spark timing
= 0 B TD C ........................................................................................................
17 1
Figure F.4.5 Time histories of cylinder-exit temperature, velocity, mass flow, and hydrocarbon
mass emissions as a function of crank angle. Data shown for X=1.0 and spark
tim ing = -15 B TD C .........................................................................................
172
Figure F.4.6 Mass element temperature and exhaust gas mole fraction histories as a function of
time for a highly diluted reactive mixture. Data shown for X = 1.0 and spark timing
= -15 B TD C .....................................................................................................
173
20
LIST OF TABLES
Table 2.1
Single-cylinder engine specifications .......................................................
29
Table 2.2
Indolene fuel properties (UTG-96)..........................................................
32
Table 2.3
Multi-cylinder engine specifications........................................................
37
Table 5.1
Nusselt number correlations for exhaust blowdown and exhaust displacement
period..........................................................................................................
95
Table 5.2
Nusselt number correlations for exhaust runner with argument factors pulses
and pipe bends..........................................................................................
95
Table A.4.1 Viscosity (ip), thermoconductiveity (k), and ratio of specific heat capacities (y)
coefficient....................................................................................................
128
21
22
NOMENCLATURE
ABBREVIATIONS:
ABDC
A/F
ATDC
BBDC
BDC
BTDC
CA
CMCP
COV
CVI
DAQ
DOHC
ECM
ECU
EGR
EOC
EV
EVC
EVO
FFID
FID
FNDIR
FTP
HC
IAC
IMEP
MAP
MBT
MDS
MFB
NDIR
NOX
OSC
PC
PFI
ppmci
PVC
RPM
SI
TDC
UEGO
ULEV
WOT
after bottom-dead-center
air/fuel ratio
after top-dead-center
before bottom-dead-center
bottom-dead-center
before top-dead-center
crank angle
charge motion control plate
coefficient of variation
closed valve injection
data acquisition
dual overhead camshafts
engine control module
engine control unit
exhaust gas recirculation
end of combustion
exhaust valve
exhaust valve closing
exhaust valve opening
fast flame ionization detector
flame ionization detector
fast non-dispersive infrared
federal test procedure
hydrocarbons
idle air control
indicated mean effective pressure
manifold air pressure
maximum break torque
modular development system
mass fraction burned
non-dispersive infrared
oxides of nitrogen
oxygen storage capacity
personal computer
port fuel injected
parts per million - single carbon atom
positive crankcase ventilation
revolutions per minute
spark-ignition
top-dead-center
universal exhaust gas oxygen
ultra-low-emission vehicle
wide open throttle
23
SYMBOLS:
mol
ms
Nu
Q
discharge coefficient
specific heat at constant pressure
relative spark timing modification
crank angle
ratio of specific heats
convective heat transfer coefficient
relative air/fuel ratio
mole
millisecond
Nusselt number
ohm
Pd
Palladium
Pr
Pt
Re
Rh
p
Sp
wt
Prandtl number
Platinum
Reynolds number
Rhodium
density
spark
weight
Cd
Cp
AOsp
0
y
he
24
CHAPTER 1
INTRODUCTION
1.1 OVERVIEW
1.1.1 BACKGROUND AND MOTIVATION
Use of catalytic converters for aftertreatment is an effective means of reducing tailpipe-out
hydrocarbon (HC) emissions from spark-ignition engines (SI). However, a sizeable amount (70 90%) of the total hydrocarbon emissions during the Federal Test Procedure (FTP) cycle are
emitted during the first several seconds of operation before the catalyst reaches light-off
temperature (~300' C), Fig. 1.1. During a cold-start, fuel evaporation is poor and fuel enrichment
is necessary to ensure a robust combustion event. Exhaust aftertreatment is not effective until
light-off temperatures are achieved. Furthermore, light-off temperatures for aged catalysts can
increase by 50' C [1]. Significant HC emissions reductions can be attained by reducing tailpipeout hydrocarbons before catalyst activation and reducing the time required for light-off.
Numerous sources of hydrocarbon emissions exist for SI engines; mass trapped in crevice
volumes, wall quenching during flame propagation, outgasing of HC from in-cylinder deposits and
oil layer, and liquid wetting of in-cylinder surfaces. As the flame propagates outward from the
ignition source, in-cylinder pressure rises increasing the mass fraction of unburned fuel trapped in
crevice volumes. Boundary layers also form on the cylinder liner, piston top, and cylinder head
due to heat transfer from the high temperature unburned mixture to the combustion chamber
surfaces, quenching chemical reactions and leaving a thin layer of unburned reactants. During the
expansion stroke, post-flame oxidation can consume hydrocarbons as crevice volumes and fuel
trapped in deposits are released and mix with the high temperature burnt gases. Additional incylinder and exhaust system oxidation occurs as the bulk gases are expelled during the exhaust
process.
Engine operation with aggressively retarded spark timings from maximum brake torque
(MBT) timings has proven effective in achieving both of these requirements. Phasing the
combustion process later in the expansion stroke decreases the amount of useful work extracted
25
from the burnt gases, resulting in higher exhaust gas temperatures and increased post-flame
oxidation rates. Additionally, lower in-cylinder peak pressures reduce the mass of unburned
mixture trapped in crevices that escape oxidation during flame propagation and exit as HC
emissions. However, there are limitations to late combustion phasing; with substantial spark
retard, flame propagation occurs in a rapidly expanding volume, increasing cycle-to-cycle
variations and reducing engine efficiency. Excessively high exhaust gas temperatures, greater than
10500 C, can lead to thermal deactivation and degraded catalyst performance [2].
Chrysler 3.8 L Engine
100
-
94% of HC Emissions
CA
80
0
E
W
U
120 seconds
60
40
---
i
Engine-out (FTP)
Tailpipe-out (FTP)
E
20
-
8.8% of HC Emissions
I
0
0
500
1000
Landsberg, MIT
Source: G.
I
1500
2000
Time (sec)
Figure 1.1
Cumulative engine-out and tailpipe-out HC emission over an FTP-75 for a sixcylinder SI engine.
1.1.2 PREvious WORK
Post-flame hydrocarbon oxidation in the exhaust system of spark ignition engines has
been the focus of previous research. Caton et al. [3] performed exhaust port temperature
quenching experiments to determine the impact of relative air/fuel ratios, speed, load, spark
advance, and compression ratio on HC oxidation. By rapidly cooling the exhaust gas close to the
exhaust valve, hydrocarbon oxidation reactions were frozen and the resulting HC concentration
was quantified. Exhaust port oxidation ranged from 2% to 70% depending upon exhaust gas
26
temperatures, port residence time, and oxygen concentration. Similar research by Russ et al. [4,5]
quantified combustion and emission characteristics under cold engine conditions with retarded
spark timings. The primary cause of cycle-to-cycle variations with late spark ignition was late
combustion phasing, quantified by the location of the 50% mass fraction burned. With close to
stoichiometric operation, flame quenching, misfires, and prior cycle effects were not observed [5].
1.2 RESEARCH OBJECTIVES
1.2.1 OVERVIEW
Exhaust system oxidation under cold engine conditions is not well understood. Limited
experimental data exists that tracks the thermal and chemical energy from cylinder-exit to the first
brick of the catalyst. The trade-off between cold start tailpipe-out HC emissions and heating of the
catalyst is done empirically. Therefore, experiments were designed to quantify the effect of cold
engine conditions on engine combustion, HC emissions, and catalyst light-off with late spark
timing. The work described herein quantifies and provides additional insight into processes that
occur with spark timings aggressively retarded from MBT. With increased interest in reducing HC
emissions following startup, engine experiments focused on ambient (200 C) engine conditions. A
variety of experimental techniques and equipment was utilized to quantify engine exhaust
emission. Fast-response exhaust gas analyzers, exhaust gas quenching and secondary air injection
experiments provided a detailed understanding of the thermal and chemical energy of the feed gas
from cylinder-exit to the inlet of the catalytic converter.
1.2.2 EXPERIMENTAL
Numerous HC tracking experiments were conducted over a range of spark timings and
relative air/fuel ratios under ambient engine conditions. Time-resolved and time-averaged HC
measurements provided exhaust system HC flow rates at various exhaust locations. Likewise,
quenching experiments injected carbon dioxide at the exit plane of the exhaust valves, rapidly
cooling the exhaust gas and effectively freezing HC reaction rates. These experiments yielded
valuable information regarding the extent of HC emissions exiting the cylinder with late
combustion phasing. Additionally, secondary air injection into the exhaust system was also
27
explored. The engine was operated rich of stoichiometric and air was introduced into the exhaust
system to promote oxidation. Exothermic reactions coupled with the increased mass flow rate of
feed gas to the catalyst resulted in reduced converter-in HC emissions and increased enthalpy rates
supplied to the catalyst. These experiments guided the modeling effort and were used to verify
sub-models.
1.2.3 MODELING
The hydrocarbon oxidation in the engine exhaust system was modeled as a 1-D quasisteady reacting flow. Engine experiments and various diagnostic tools provided exhaust gas
thermodynamic properties and compositions. A phenomenologically based model of the HC
oxidation and catalyst feed gas enthalpy was developed, providing an interpretive tool for
assessing exhaust system behavior during engine warm-up period. The model was coupled with a
heat transfer subroutine and a time-dependent reacting plug flow model with inputs from an engine
cycle simulation and experimental results. The chemical kinetic mechanism was selected from
literature and found to provide agreement when compared to the experiments. The model provided
quantitative information on the extent of exhaust oxidation and the state of the feed gas supplied to
the catalyst.
28
CHAPTER 2
EXPERIMENTAL APPARATUS AND PROCEDURES
2.1 SINGLE-CYLINDER ENGINE
2.1.1 ENGINE-DYNAMOMETER
Steady-state experiments were performed using a single-cylinder Ricardo Hydra MKIII
spark ignition engine fitted with a modified Volvo B5254 head. The head was port fuel injected
(PFI) with 4-valves and a pent-roof combustion chamber geometry. The engine crankshaft was
coupled to a Eaton dynamometer (6000 series) with absorbing and motoring capability.
Table 2.1
Single-cylinder engine specifications.
Sin le Cylinder Engine Specifications
487
Displacement Volume (cc)
54
Clearance Volume (cc)
83
Bore (mm)
90
Stroke (mm)
158
Connecting Rod (mm)
1
Wrist Pin Offset (mm)
10:1
Compression Ratio
4v DOHC
Valve Train
IVO 00 BTDC I IVC 600 ABDC
Valve Timing
EVO 440 BBDC I EVC 8* ATDC
2.1.2 ENGINE CONTROL UNIT
Fuel injection and spark timing were controlled by a MoTeC M4 engine control unit
(ECU). The system utilized speed-density tables allowing for precise control of fuel injector pulse
width and coil discharge. A standalone personal computer linked to the ECU allowed for the realtime adjustment of spark timing and fueling.
2.1.3 CYLINDER PRESSURE MEASUREMENTS
The engine was equipped with an in-cylinder piezoelectric pressure transducer (Kistler
6125A) coupled to a charge amplifier (Kistler 5010B) yielding a voltage output. The transducers
gain was statically calibrated at several pressures utilizing a dead weight tester. Referencing of in-
29
cylinder pressure was obtained by an absolute pressure transducer (Omega PX176 Series) located
around
in the intake plenum. The acquired in-cylinder pressure data was averaged over 200 CA
bottom-dead-center (BDC) during the compression stroke and scaled to reflect an absolute
by
pressure. Proper crank angle phasing and transducer linearity was checked periodically
motoring the engine at WOT and plotting cylinder pressure and cylinder volume on a log-log
scale.
The pressure transducer was side mounted between the exhaust and intake valves. The
by the
transducer was found to have problems related to thermal shock (a phenomena caused
to the
deformation of the transducer diaphragm when heat transfer occurs from the flame front
late in
transducer face resulting in thermal strain). This resulted in erroneous measurements noted
the expansion process and required the use of a flame arrestor over the exposed tip to decrease
measurement error.
2.1.4 INTAKE CHARGE MOTION CONTROL PLATE (CMCP)
Engine combustion stability was improved by use of an intake charge motion control plate
(CMCP). The charge motion control plate (CMCP) was installed in the plane of the intake port,
cross
downstream of the fuel injector, Fig. 2.1. The asymmetrical CMCP reduced the port
the
sectional area by approximately 67%, but did not impede the fuel spray targeting footprint of
to
injector. The plate increased the in-cylinder tumble torque moment by a factor of 4 compared
have a
flow levels generated without the port area reduction [6]. The intake CMCP was found to
angle
negligible impact on in-cylinder swirl. Burning velocity was increased and the crank
location of the spark retard ignition timing limit was extended.
CMCP:
2/3 Area Reduction
Asymmetrical
Figure 2.1
Intake charge motion control plate (CMCP) with 67% asymmetrical area
reduction for the single cylinder engine.
30
2.1.5 DATA ACQUISITION SYSTEM
All signals were acquired using a National Instruments data acquisition (DAQ) board
(PCI-6024E) capable of 8-channels of differential voltage input. The data acquisition system was
triggered from an 1* incremental encoder coupled to the crankshaft. A superimposed 5-volt spike
on the pressure data was used to mark BDC of the compression stroke. A dedicated PC running
LabView software was used to create a virtual instrument (VI) for data scaling, processing, and
logging. Post processing of data was carried out using custom scripts written in MatLab software.
2.1.6 EXPERIMENTAL CONDITIONS
The engine was operated at 1500 RPM and a net indicated mean effective pressure (NetIMEP) of 3.0 bar. Spark timing and relative air/fuel ratio sweeps were performed under steadystate conditions with fixed fluid (coolant and oil) temperatures of 200, 400, and 90' C. The coolant
temperature was that of the cylinder head and liner. The exhaust system was not externally cooled
and was allowed to reach a hot stabilized temperature. All engine testing was conducted with
reference gasoline, Indolene (UTG-96), Table 2.2.
2.1.7 HYDROCARBON EMISSIONS MEASUREMENTS
Hydrocarbon emissions were measured via a Cambustion HFR-400 fast-response flame
ionization detector (FID) with a time response (10-90%) of approximately 1 millisecond. Heated
transfer sample lines (TSL-H) with a hole diameter of 0.026" were located at the exit of the
exhaust port and runner, at distances of 7 cm and 37 cm, respectively, from the exhaust valve seats,
Fig. 2.2. The TSL-H had a transient time of approximately 3 milliseconds. The runner probe
location was located at a distance similar to the catalytic converter inlet on a modern multicylinder engine. The fast-response FID instrument was setup as follows for all exhaust system
investigations; heated line controller for the sampling probes (TSL-H): 1800 C, fast FID sampling
head temperature (HSM): 300* - 3500 C, CP VAC: 100 mmHg, AP FID: 330 mmHg. The
instrument was calibrated before and after each experiment using 1500 ppmc 3 (4500ppmci)
propane (C 3H8 ) span gas and zeroed with nitrogen (N 2) gas.
31
Table 2.2
Indolene fuel properties (UTG-96) [7].
UTG-96
Property
Copper Corrosion. 3 h at 50 *C
API Gravity at 60 *F
Specific Gravity at 60/60 *F
Oxidation Stability
Carbon Density
Existent Gum, mg/100 mL
Lead Content, g/gal
Sulfur Content. wt %
Phosphorus. g/gal
Total Alcohol Content. vol %
Reid Vapor Pressure at 100 OF. psia
Research Octane Number
Motor Octane Number
Sensitivity
Distillation Range at 760 mmHg. OF
Initial Boiling Point
10%
50%
90%
End Point
Composition. vol %
Olefins
Aromatics
Saturates
Heat of Combustion, Net, Btu/lb
Carbon Content. wt %
Hydrogen Content. wt %
Anti-Knock Index, (R+M)/2
Typical Value
1
59.8
0.740
1440+
2420
1.0
0.001
0.005
0.001
0.00
9.0
96.1
87.0
9.0
Specification
1 max
58.7-61.2
0.734 - 0.744
1440 min
2401 - 2441
5 max
0.05 max
0.1 max
0.005 max
0.00 max
8.7 - 9.2
96.0 min
91
128
220
309
409
75 - 95
120-135
200-230
300 - 325
415 max
5
28
67
18400
86.5
13.5
92.0
10 max
35 max
Remainder
7.5 min
Test Method
ASTM D 130
ASTM D 1250
ASTM D 4052
ASTM D 525
Calculated
ASTM D 381
ASTM D 3237 Modifie<
ASTM D 3120
ASTM D 3231
EPA Procedure 10
ASTM D 323
ASTM D 2699
ASTM D 2700
Calculated
ASTM D 86
ASTM D 1319
ASTM D 3338
Calculated
Runner
Port
Pr-U
Figure 2.2
Fast-response HC analyzer probe sampling locations for single-cylinder
experiments. Exhaust port and runner probes 7 cm and 37 cm from exhaust
valves, respectively.
32
Time-averaged downstream HC emissions were sampled from a well-mixed, large
volume, pulse-damping tank located 120 cm from the exhaust valves and quantified with a second
FID (Rosemount Analytical Inc., Model 402) having a response time of several seconds. The FID
was calibrated with 1500ppmc3 ( 4 50 0 ppmcl) propane and zeroed with nitrogen. The analyzer's
oven temperature and heated sampling line were both set to 1900 C to eliminate condensation
before reaching the FID chamber.
2.1.8 RELATIVE AIR/FUEL RATIO
Exhaust gas relative air/fuel ratio was recorded using a universal exhaust gas oxygen
(UEGO) sensor (Horiba MEXA- I10) approximately 60 cm downstream from the exhaust valves.
The Horiba UEGO had response time of approximately 100 ms and was calibrated in atmospheric
air prior to engine testing.
2.1.9 AIR AND FUEL MASS FLOW RATES
Intake air was measured by a Ricardo viscous flow meter (laminar flow element) equipped
with a differential pressure transducer (Omega PX- 176). The mass flow rate was then calculated
from the volume flow rate based on ambient temperature and pressure. Fuel flow rates were
obtained by flow testing the injector at various pulse widths and fuel rail pressures. Agreement
within 2% was achieved between the UEGO measured air/fuel ratio and the calculated air/fuel
ratio from fuel flow and air flow measurements.
2.1.10 TEMPERATURE MEASUREMENTS
Time-averaged exhaust gas temperatures were measured with chromel-alumel (type-K)
exposed junction thermocouples (0.8-mm bead diameter). The junctions were shielded with
stainless steel sheaths to eliminate errors due to radiant heat transfer. The shielded thermocouples
had a response time (10-90%) of approximately 1 second. Additional thermocouples were used to
record exhaust system component temperatures, including the port manifold flange and runner
outer walls. Temperatures of the fuel, coolant, oil, and inlet air were also monitored and recorded
during engine testing.
33
2.1.11 EXHAUST GAS QUENCHING SETUP
An adaptor plate was installed between the exhaust manifold and cylinder head that
allowed for the installation of four small tubes (outer diameter: 0.125", inner diameter 0.105")
adjacent to the exit plane of the exhaust valves. A 35 mm section ofjet holes (2 mm in diameter)
discharged quench gas in a lateral flow field at the cylinder-exit plane, Fig. 2.3. Pulse flow control
of quench gas was regulated by two solenoid valves triggered by an external control system.
Upstream and downstream pressure and temperature histories were monitored and recorded by the
DAQ system. High-pressure bottled gas injection ensured flow interruption did not occur during
the exhaust blow down process. However, due to the required quench gas flow rate, an
accumulator tank and heated gas regulators were needed to prevent icing, Fig. 2.4.
A7
Probe
Flange adaptor
E
E
-35mm
2 mm
Figure 2.3
Schematic of probes located at the exhaust valve seats utilized for quenching and
secondary air injection experiments.
34
During quenching experiments, carbon dioxide was utilized due to its high specific heat
and ability to be quantified using an exhaust gas analyzer. Carbon dioxide (C0 2) levels in the
exhaust were measured far down stream from the exhaust valves (120 cm) using a non-dispersive
infrared (NDIR) detector (Rosemount 440). Water vapor was removed from the exhaust gas and
the instrument was calibrated with 10% and 20% CO 2 and zeroed with nitrogen. However,
subsequent dilution of the exhaust gas with nitrogen (N 2 ) was required to achieve readings within
the CO 2 analyzer's range. The oxides of nitrogen (NOx) were also monitored using a
chemiluminnescence detector (Thermo Environmental Instruments Model 10A) and calibrated
with 998ppm nitrogen oxide (NO) and nitrogen gas.
--
Accumulator
To Probes
CO
Figure 2.4
CO
Heaters
Solenoid Valves
Overview of gas delivery system equipment used for quench gas and secondary
air experiments.
2.1.12 SECONDARY AIR INJECTION SETUP
In order to investigate methods to increase feed gas sensible enthalpy and decrease
converter-in HC emissions, experiments using the single-cylinder engine were conducted at fuel
rich engine air/fuel ratios with secondary air injected at the exhaust valve seats. The same
experimental setup outlined in Sec. 2.1.11 was used and CO2 was replaced by compressed dry air.
2.2 MULTI-CYLINDER ENGINE
2.2.1 ENGINE-DYNAMOMETER
A 2003 model year, 2.2 liter L61 Ecotec (GMX357) engine was chosen to investigate
exhaust system oxidation during the first 20 seconds of operation following a cold-start. The
engine was coupled to an eddy current, absorbing only, dynamometer (Froude Consine AE-80).
35
This test setup used the engine's starter motor for "crank" and "run" operation with full control
over the engine control module (ECM). Additional engine details are given in Table 2.3.
2.2.2 EXHAUST SYSTEM OVERVIEW
The multi-cylinder engine's exhaust system consisted of a cast iron manifold, a three-way
catalytic converter, muffler, and gate valve set to achieve a desired exhaust back pressure (350 kPa
at WOT, 5600 RPM). The exhaust manifold and cylinder head were equipped with passages for
secondary air operation, but this air system was not utilized in the experiments. Three catalysts
were supplied with the engine; an inert catalyst (substrate only, no precious metals or oxygen
storage capacity) and two active Ultra-Low-Emission Vehicle (ULEV) catalysts. The active
catalysts were dyno-aged 100 hours to simulate 50,000 vehicle miles.
Each converter had a total volume of 82 cubic inches and was 4.2 inches in diameter with
600 cells per inch. The inert and active catalyst, XX9901JP, had a substrate wall thickness of
0.0043 inches, the other active catalyst, XX9901JQ, had a substrate thickness of 0.0035 inches.
The active catalysts were composed of two bricks; the first was 2 inches in length and loaded with
3.5 grams of Palladium (Pd). The second brick was 4 inches in length and loaded with 1.5 grams of
Platinum (Pt) and 0.31 grams of Rhodium (Rh). The second brick also contained a washcoat with
oxygen storage capacity (OSC). The active catalyst XX9901JP was used to investigate light-off
times for four different spark timing strategies. A thermocouple was embedded mid-brick and
along the centerline of the catalyst and an additional thermocouple measured the catalyst shell
temperature. Pre-catalyst and post-catalyst gas samples were acquired approximately 4.8 inches
from the bricks.
2.2.3 ENGINE SUB-SYSTEMS AND INSTRUMENTATION
The engine coolant system was a closed looped system driven by an internal water pump
that circulated fluid through the block and cylinder head. The thermostat was removed and the
heater core was modified to eliminate the recirculation of coolant within the cylinder head and
block. Coolant exited the head and flowed to an external water pump installed in the engine's
cooling circuit. This allowed for maximum heat rejection rates when the engine was not in
operation. The pump outlet was connected to an external head exchanger and to a coolant reservoir
36
tank before being routed back to the engine. Coolant temperature was varied via a setpoint
controller that actuated a valve allowing for plant water to flow through an external heat
exchanger. The engine's oil was not externally cooled and its temperature was measured in the oil
pan.
Table 2.3
Multi-cylinder engine specifications.
Ecotec Endine Specfications
2189
1-3-4-2
65
86
94.6
146.5
0.8
10:1
Displacement Volume (cc)
Firing Order
Clearance Volume (cc)
Bore (mm)
Stroke (mm)
Connecting Rod (mm)
Wrist Pin Offset (mm)
Compression Ratio
16v DOHC
IVO 7- BTDC I IVC 560 ABDC
EVO 680 BBDC I EVC 160 ATDC
Valve Train
Valve Timing
First Brick
Li: 2 in
3
Vi: 27.2 in
Pd: 3.5g
.4 -, A
Second Brick
L 2 : 4 in
3
V 2 : 54.4 in
Pt: 1.5g
Rh: 0.31g
Washcoat with OSC
Exhaust Flow
0
4.8 in
PA
Sample Point
A
fI
A
3
: 82 in
a: 4.2 in 2
Cells. 600/in
Wall: 0.0043 in
V
Serial No.: XX9901JP
Figure 2.5
Active three-way catalyst (serial no: XX901JP) specifications.
37
The engine was operated with the positive crankcase ventilation (PCV) system in place
and did not use an external exhaust gas recirculation (EGR) system. The engine had a returnless
fuel injection system which required a constant fuel rail pressure of 52 psig. Fuel was supplied by
external fuel pump with an inline filter, accumulator, and pressure regulator. The line return from
the fuel regulator was directed through an external heat exchanger and back to the fuel tank. The
regulator outlet was connected to the fuel injector rail. Fuel flow was estimated from the pulse
width durations.
The intake system was modified to contain a damping tank and a thermal mass flowmeter
(EPI, Series 8000 MP) to measure inducted air flow. Throttle position was varied using a stepper
motor (Pacific Scientific SinMax 1.80 motor with 5230 indexer/driver) connected via a cable to the
engine's throttle body. Incremental movement of the throttle was adjusted by two momentary
contact switches with a selectable stepping rate.
Exhaust air/fuel ratio was monitored with a UEGO sensor (Horiba MEXA-700) located at
the manifold collector. A pressure transducer (OMEGA PX- 176) was installed in the intake
plenum that provided better transient response compared to the OEM MAP transducer used for the
ECM. All gas temperatures were measured with chromel-alumel (type-K), 0.8-mm exposed
junction thermocouples with custom radiation shielding. Other thermocouples were installed
throughout the engine setup to measure various fluid and metal temperatures.
2.2.4 DATA ACQUISITION SYSTEM
The data acquisition (DAQ) system utilized two DAQ boards from National Instruments
installed in a personal computer. The first card (PCI-6071E) acquired 32 differential channels of
high speed signals. The second card (PCI-6024E) was used with a multiplexing chassis (SCXI1000) and a 32 channel thermocouple module (SCXI- 1102) to capture temperature data from typeK thermocouples. The two boards were operated at different speeds; high speed data was captured
once per engine crank angle degree, while temperature data was acquired once per engine
revolution (at top-dead-center of cylinders no. 1 and no. 4). Both DAQ cards were triggered from
signals provided by an incremental encoder (BEI Series H25E) coupled to the engine's crankshaft.
A dedicated PC computer using LabView software was used to create a virtual instrument for data
38
scaling, processing, and logging. Post processing of data was carried out using custom MatLab
scripts.
2.2.5 MODULAR DEVELOPMENT SYSTEM HARDWARE
The Delco Modular Development System (MDS) was used to control and modify the
engine control module (ECM). Specific ECM operations were monitored and recorded by the
MDS. This system provided the user control of parameters including the change of calibration data
by read only memory (ROM) emulation. A PC was connected to the MDS stack that allowed for
internal and external data logging. The stack was composed of several units. The main instrument
unit (MIU) was the core of the MDS system and contained two main processors. The computer
interface buffer internal logging (CIBIL) provided MDS communication with a computer. The
analog conversion module (ACM) contained 8-BNC outputs and 2 instantaneous switches scaled
from 0 to 5 volts. A 1MB GMPX Pod was connected to the X-pod that interfaced with the ECM
and allowed the ECM's EPROM to be flashed for standalone ECM operation. The shell program
allowed the user to have full access to lookup tables and relevant environmental variables. Realtime monitoring and modification of several parameters (RPM, MAP, spark timing, air/fuel ratio,
idle air control (IAC) valve position) was accomplished by using the MDS's external display unit
(DU).
2.2.6 MODULAR DEVELOPMENT SYSTEM SOFTWARE
Full control of the engine was possible using the Delphi Electronics Instrument Tool Suite
(ITS) running the Saturn Legacy Software. File handling between the computer and MDS unit was
achieved using the ITS software. The program CalTools was used to modify ECM parameters and
lookup table variables. For more detailed information regarding the MDS software refer to the Sec.
B. 1 in the Appendix.
2.2.7 IN-CYLINDER PRESSURE MEASUREMENTS
Each cylinder was fitted with an in-cylinder pressure transducer (Kistler 6125A). The
cylinder head passage sleeve incorporated an eight-hole flame arrester to minimize the occurrence
of thermal shock. The transducers were periodically cleaned of carbon deposits and re-calibrated
39
after 10-15 hours of service to minimize erroneous readings. Proper crank angle phasing and
transducer linearity was checked periodically by disabling the cylinder's fuel injector and
motoring the cylinder of interest, while firing the remaining three cylinders. Transducer calibration
and pressure referencing was conducted as outlined in Sec. 2.1.3.
2.2.8 ENGINE TEST CONDITIONS AND PROCEDURE
Vehicle data provided by General Motors indicated that during the park idle period of the
FTP test (0-15 seconds), the baseline calibration produced a Gross-IMEP of 3.0 bar and 1000 RPM
(0.40-0.45 bar MAP and 6' BTDC spark timing). Therefore, the target load and speed for all
experiments with the multi-cylinder engine was 2.3 bar Net-IMEP and 1000 RPM.
All engine tests were conducted with Indolene (Table 2.2) at approximately 200 C
conditions. Engine speed and load were not regulated by the dynamometer controller (Digalog
Series 1022A) due to the unstable transient control of the dyno-engine system during startup RPM
flare. The required engine idle load was achieved by utilizing engine accessories with the
dynamometer coupled but not absorbing power from the engine. A hydraulic power steering pump
and alternator were added to the engine setup to simulate park idle load conditions observed during
the first 15 seconds of the FTP test. The power steering pump was throttled to 800 psig by use of a
needle valve. The low pressure line was routed through a heat exchanger before returning oil to the
reservoir tank. The regulated 14.7 volt output from the alternator was isolated from the 12 volt
battery bus by a zener diode and connected to bank of power watt resistors totaling 0.2 Q (three 0.6
Q resistors in parallel). After each engine startup test, metal temperatures throughout the engine
and exhaust system were force cooled to ambient temperatures before another experiment was
performed.
2.2.9 FAST-RESPONSE EMISSIONS ANALYZERS
The fast-response FID was utilized to measure HC emissions in the exhaust port of
cylinder no. 4 and at the inlet and outlet of the catalytic converter. The instrument was calibrated
and setup according to the specifications outlined in Sec. 2.1.7.
In order to provide additional insight into exhaust system oxidation, a fast-response nondispersive infrared (NDIR) detector (Cambustion NDIR-500) was used to evaluate exhaust gas CO
40
and CO 2 concentrations. The instrument used two independent sampling heads and heated probes;
CO and CO 2 concentrations were simultaneously measured from one sample head. The NDIR500's miniaturized sample chamber operated at sub-atmospheric pressure. Sample gas from the
engine's exhaust system passed through narrow heated capillaries directly into the sample chamber
where the gas was subjected to IR radiation. An IR detector was located below the emitter, with
optical filters mounted on a chopping wheel that supplied a reference signal, Fig. 2.6. The system
corrected for slight changes in temperature and IR emitter/detector signal strength. The optical
windows of the emitter and detector were cleaned following 3 to 4 ambient starts. The fast-NDIR
system had an overall response time (10-90%) of approximately 20 ms.
Temperature
Controlled Body
Sapphire Windows
-4
.
-
Pressure measure
Vac control bleed air
Inipacter
Sample Gas
Window
Figure 2.6
cleaning access
-
R-
oVacuum
a
TO Vac Pumnp
mesh
r
Schematic of fast-response NDIR sampling head from Cambustion [8].
41
42
CHAPTER 3
SINGLE-CYLINDER EXPERIMENTAL RESULTS
3.1 COMBUSTION CHARACTERISTICS
3.1.1 COMBUSTION STABILITY
As combustion was phased later in the cycle, spark retard was limited by combustion
stability, quantified by the coefficient of variation (COV) in net indicated mean effective pressure
(Net-IMEP). Cycle-to-cycle variations in the combustion process were caused by several factors:
variations in relative air/fuel ratio around the spark plug, mixture motion variations, and residual
gas fraction [16]. With aggressive spark retard, slower burning cycles result in a loss of efficiency
as combustion occurred in a rapidly expanding volume. Figure 3.1 shows COV in the Net-IMEP as
a function of various spark timings and relative air/fuel ratios with and without the charge motion
control plate (CMCP) installed in the intake port.
3.0 bar Net IMEP, 1500 RPM, 200 C
18
CMCP
16
*
A2
I
NoCMCP
Xx=1.0
0
X=1.1
.2n
I
I
I
I
A
A AA
14
-0
A
12
A
A
0 0
0
-
C
10
0
A
-
A
z
0
8
A
0
0
0*
AO
0
6
0-
A
4.
0 0
A
2
-
A
0
OE
20
15
*
35
30
25
0 0
U
0-:4
. .
10
5
0
-5
I I-
-10 -15
-20
Spark Timing (0 BTDC)
Figure 3.1
COV of Net-IMEP as a function of spark timing with and without intake charge
motion control plate (CMCP) for three relative air/fuel ratios. Data shown for 3.0
bar Net-IMEP, 1500 RPM, and 200 C fluids.
43
The data shown in Fig. 3.1 was analyzed for 400 cycles with no recorded misfires or
partial burns.
Significant
improvements
in combustion
stability were achieved
for all
stoichiometries with the use of the charge motion control plate. Typically, under fuel lean
conditions, increased charge mixture variations and slower flame speeds worsen combustion
stability. However, additional charge motion provided by the intake CMCP was observed to extend
the misfire spark retard limit of the engine under lean, 200 C fluid conditions. A similar plate
geometry was used by Takahashi et al. to alter charge motion with spark timing retardation based
upon the combustion stability limit [22]. Combustion stability improved allowing for addition
spark retarded further reducing HC emissions and increasing exhaust gas temperature. The CMCP
was also thought to cause redistribution of liquid fuel in-cylinder. Liquid fuel has been shown to
increase HC emissions by a factor of 3 to 7 per unit mass of fuel depending upon the location of
liquid in-cylinder [23]. Enhanced in-cylinder motion has also been observed to increase post-flame
oxidation transport rates [22].
3.1.2 BuRN RATE ANALYSIS OVERVIEW
A single-zone thermodynamic burn rate analysis incorporating the effects of residuals,
heat transfer, and crevices was used to quantify combustion characteristics with late spark timings
[9]. The burn rate analysis used a single zone energy model of the in-cylinder contents to
determine the energy released from acquired in-cylinder pressure data, Eq. (3.1). The ratio of
specific heats (y) during the compression and expansion stroke was a linear function of
temperature, equivalence ratio, and residual gas fraction. During combustion the ratio of specific
heats was an averaged constant with 100 CA transition period at the start and end of combustion.
Total crevice volume was estimated to be equal to 2% of the clearance volume. Heat transfer was
handled by the Woschni correlation with the Cl coefficient equal to 1.7 and the gas expansion
velocity constant, C2, fixed at 1.0. For more information on the Woschni correlation refer to the
Sec. A.2 of the Appendix.
aQChemlical
0
-I
lP.
0
1_ p + 8 QCevice
IV2
y00
00
44
+ 0 QHT
0
(3.1)
where:
Qc,
0
y
p
V
Qc,,,,
Q,.
fuel chemical energy
crank angle
ratioof specific heat
cylinderpressure
cylinder volume
energy in crevices
heat transfer
In-cylinder pressure data, cumulative mass fraction burned (MFB), and instantaneous
MFB data for three different spark timings (15', -1*, and -16' BTDC) at 3.0 bar Net-IMEP, 1500
shown
RPM, X = 1.0, without charge motion (CMCP) and 20* C fluids for 15 consecutive cycles is
MFB
in Fig. 3.2. Due to the occurrence of thermal shock observed in the pressure data, cumulative
profiles had an upward sloping tail noted after the end of the main flame propagation. As a result,
the crank angle location at the end of combustion (EOC) was used as a reference point in reporting
the
combustion phasing and combustion duration. The EOC point was determined when
is
instantaneous MFB rate fell below a threshold value (10-4 per crank angle). The location of EOC
noted in Fig. 3.2
Sp= -16* BTDC
Sp =-1* BTDC
Sp =15' BTDC
20
-15
15
-10
-
10
5
a-0
5
10.8-
77
0-8
-0.6
J
LL0.4
End of
0.2
0.0
End of
Contshon
0.0
0.05
0.04
0.03
0.02
U
EVO
EV0
EVO
0.6
1.0
*
*'
Conusfoiin
-
-
p
If-
:
0.04
0.03
0.02
-
0.01
5
-0.01
-25
0.01
0.00
0.00i
0
25
50
75
CA (* ATDC)
Figure 3.2
125
7
100
125
.
-25
0
25
50
75
CA (*ATDC)
100
125
-25
0
25
1 i1
.
50
-
- -0.01
75
100
CA (- ATDC)
In-cylinder pressure, cumulative mass fraction burned (MFB) and instantaneous
MFB rate as a function of crank angle for three spark timings. Operating
conditions: 3.0 bar Net-IMEP, 1500 RPM, X = 1.0, with charge motion (CMCP)
and 20' C fluids.
45
125
3.1.3 COMBUSTION DURATION AND PHASING
The flame-development angle (0-10% energy-release fraction), rapid-burning angle (1090% energy-release fraction), and location of the 50% energy-released fraction were investigated
with and without the charge motion charge plate (CMCP) at various fluid temperatures, retarded
spark timings, and stoichiometries, Figs. 3.3 - 3.6. Increased charge motion (CMCP) was found to
decrease the crank angle location of the 50% MFB and shorten the 10-90% burn duration, as
shown in Figs. 3.4 and 3.6, respectively. Under all test conditions, combustion was found to be
complete before exhaust valve opening (EVO).
,
50
90* C Fluids 20* C
*
x=1.0 0
0,
ma 40
RPM
,3.0 bar n-imep. 1500
A
=1.1
0
x=1.2
A
A
0
0
0
*
-
13
30
0
-
0
0-10%
20
.2
E
0
-10
0
10
20
30
-20
7
6
0A
0
)A
0
&A3
AA
I
10-90%
20
2YlJ M
30
20
0
10
-10
-:
-20
Spark Timing (* BTDC)
Figure 3.3
Combustion durations as a function of spark timing for different relative air/fuel
ratios and fluid temperatures without charge motion control plate (CMCP) at 3.0
bar Net-IMEP and 1500 RPM.
46
3.0 bar n-imep, 1500 RPM, CMCP
A
50
20* C
0o
90* C Fluids
X==1.0
o
4
A
0)
0A
=1 .2
0-00-
30
496oE
.
0
2
0-10%
[.
0
C:
-20
-10
0
10
20
30
7fl
0
0
60
50
10-90%
40
A
A
30
co
A&
20
0
a
0:1-
-20
-10
0
10
20
30
0 3
00o2o
Spark Timing (* BTDC)
Figure 3.4
Combustion duration as a function of spark timing for different relative air/fuel
ratios and fluid temperatures with charge motion control plate (CMCP) at 3.0 bar
Net-IMEP and 1500 RPM.
3.0 bar n-imep, 1500 RPM
90
Fluids
1.0
I x
90* C
80
F-
S
A
A
20* C
[3
=1.1
= 1.2
0
70
E
AO
0 A
0
i- 60
-
Il e
A
0
A
A-. o
50
-0
LO
0
-A
A
0
A
40
A
A
30
0
0
0
-1
20
2-21-02
0
30
20
0
10
-10
-
-20
Spark Timing (0 BTDC)
Figure 3.5
Location of 50% MFB as a function of spark timing without charge motion
control plate (CMCP) for various relative air/fuel ratios and fluid temperatures at
3.0 bar Net-IMEP and 1500 RPM.
47
3.0 bar n-imep, 1500 RPM, CMCP
90
900 C Fluids 20* C
8W-
8
A
S70
-
-.
x=1.1o
0N
X=1.2
-
-Ao
AO
160
A
LL
C'
3< -E-0
0
A
-
'
0 30
0
0
5-19/20.02
0
I
f
30
20
0
10
-10
- 1
-20
Spark Timing (0 BTDC)
Figure 3.6
Location of 50% MFB as a function of spark timing with charge motion control
plate (CMCP) for various relative air/fuel ratios and fluid temperatures at 3.0 bar
Net-IMEP and 1500 RPM.
3.2 EXHAUST GAS TEMPERATURES
Exhaust gas temperatures were measured at port exit and compared to the 50% MFB
location as shown in Fig. 3.7. Data was acquired for various relative air/fuel ratios with and
without intake charge motion (CMCP) at 200 C fluids. Gas temperatures were observed to increase
linearly with combustion phasing (location of 50% MiFB). At an equivalent phasing, a
stoichiometric air/fuel ratio had the highest burn gas temperature. In addition, the CMCP
decreased gas temperature between 30-lOOK for an equivalent combustion phasing, which was
attributed to the increased in-cylinder heat transfer during combustion.
48
3.0 bar Net-IMEP, 1500 RPM, 200 C Fluids
1200
w/CMCP
w/o CMCP
x= 1.0 1
)Li=A 1.1. 0C
£ 1100
U
0
a 40
0
('3
(D 1000
CL
E
900
I
F
A0
0
A
A
00
A
-r-
w
-t
0
Q_
800
0 18
I
0
10
I
20
.
a
.
30
I
40
.
I
50
.
I
i
S
60
70
80
90
Location of 50% MFB (0 ATDC)
Figure 3.7
Thermocouple measured port exit exhaust gas temperature as a function of 50%
MFB location for various relative air/fuel ratios with and without the charge
motion control plate (CMCP) at 3.0 bar Net-IMEP, 1500 RPM, and 20* C fluids.
Feedgas sensible enthalpy rate (kJ/s) as a function of the coefficient of variation (COV) in
the Net-IMEP was also investigated, Fig. 3.8. Tailpipe-out HC emissions can be dramatically
reduced if the catalytic converter can reach light-off temperature faster following engine startup.
Under stoichiometric engine operation and equivalent combustion stability (a COV in Net-IMEP
of approximately 10%) the CMCP allowed for additional spark retard which increased the sensible
enthalpy rate more than 60% (3 U/s to 5 kJ/s).
49
3.0 bar Net-IMEP,
5.5
5.0 -
2
4.5 -
1500 RPM, 20 C Fluids
.. If'IkACD
-d-fAI'D
A1.2
A
0.0
4.00
0
W 3.5
ai)
0
C
0
2 5
C 2.0
.
-
t2.0
A*
2
>
A
A
0
A
1.0
0
2
4
6
8
10
12
a
14
16
COV of Net-IMEP (%)
Figure 3.8
Converter-in sensible enthalpy rate as a function of COV of Net-IMEP for
different relative air/fuel ratios with and without the charge motion control plate
(CMCP).
3.3 DOWNSTREAM TIME-AVERAGED HYDROCARBON EMISSIONS
To achieve the same engine load (Net-IMEP) with late spark timing, the engine's mass
flow rate was increased to offset the reduced work extracted per cycle. Therefore, the meaningful
representation of the HC emissions is the total engine-out hydrocarbon flow rate. Fig. 3.9 shows
HC emissions with the CMCP and 200 C fluids. Engine-out HC levels were observed to reach
a
minimum for X = 1.0 and X = 1.1. Several mechanisms were responsible for the trends shown
in
Fig. 3.9. As spark was slewed from MBT to after-top center timings, rising burned
gas
temperatures increased the rate of post-flame hydrocarbon oxidation. Lower in-cylinder
peak
combustion pressures reduced the mass fraction of HC trapped in crevice volumes that
escaped
oxidation during flame propagation. However, over the range of spark timings tested, manifold
air
pressure (MAP) was varied from 0.3 bar to wide open throttle (WOT), in order to maintain
constant Net-IMEP, changing the mass and temperature of trapped residual gases. As spark
retard
is increased, blowdown pressures and mass flow rates increase, resulting in reduced
exhaust port
50
residence times. Higher intake port pressures diminish back-flow during the valve overlap period
and impeded fuel vaporization with 20' C fluids. Mixture preparation was adversely affected and
resulted in additional liquid fuel entering the cylinder, increasing HC emissions.
Slightly lean of
stoichiometric (X = 1.1) resulted in the lowest observed HC mass flow rate, corresponding to
exhaust conditions in which additional molecular oxygen was present while maintaining high
burned gas temperatures.
3.0 bar Net IMEP, 1500 RPM, 200 C, CMCP
8
90" C Fluids 200 C
~ =1.0 0
a.)
1.2
%
X
E
0
A
-
a)
D
o
0
0
a)
0
0 0
-60
U-
A0A
-
A
a)
CO
AU
*
*
9A
A
5-20-02
0
20
15
10
5
0
-5
-10
-15
-20
Spark Timing (0 BTDC)
Figure 3.9
Steady-state hydrocarbon mass flow rate as function of spark timing for different
relative air/fuel ratios and fluid temperatures. Data shown for 3.0 bar Net-IMEP
and 1500 RPM with charge motion (CMCP).
Tailpipe-out HC mass flow rate (mg/sec) and the HC emission index (gHC/kgFuel) are
shown with respect to combustion phasing (crank angle location of 50% MFB) in Fig. 3.10. This
figure shows the observed changes in HC emissions due to variation in fluid temperatures and
relative air/fuel ratios. At a fluid temperature of 200 C and at the most aggressive retarded spark
timing, approximately 1% of the fuel mass injected exited the tailpipe as HC emissions. Under
51
fully warmed-up conditions (900 C) approximately 0.2% of the injected fuel exited the tailpipe as
HC emissions.
CD
0o
8
3.0 bar n-ineD. 1500 RPM. CMCP
7
.
6
a)
01
X=1.2
AA
5
4
3
D
0-000
-
0
A
00
I
X=1.0
Xx=1.1
20 0 C
0
0
A
2
*
uA
EA ,A
1
0
0
100
80
60
40
20
0
90 C
s
35
30
0
0
W,
*
20
Ma
E
Ui
=1.0
00
25
OIL
0
15
OA
0
A
0
A
L
*
A
5
*A"
0
0
20
20 0 C
0
0
10
.Am
60
40
90 0 C
.
80
100
Location of 50% MFB (0 ATDC)
Figure 3.10 Steady-state HC flow rate and emission index HC emissions as a function of 50%
MFB location for various relative air/fuel ratios and fluid temperatures at 3.0 bar
Net-IMEP, 1500 RPM, with charge motion (CMCP).
3.4 TIME-RESOLVED HYDROCARBON CONCENTRATION
3.4.1
OVERVIEW
To better understand exhaust system oxidation, crank angle-resolved HC concentrations
were recorded at the exit of the exhaust port and in the exhaust runner. Figure 3.11 shows a typical
crank angle-resolved HC concentration measured in parts per million of carbon atoms (ppmcI) at
the exit of the exhaust port, 7 cm from the exhaust valves (EV). At the time of exhaust valve
opening (EVO), an initial peak was observed during the blow-down phase as head gasket, spark
plug, and valve seat crevice gases were exhausted. As the blow-down process continues, there was
a rapid decrease in concentration as the bulk of the burnt gases were expelled. As in-cylinder
52
pressure equilibrates during exhaust displacement, an increase in HC levels was observed. This
feature was attributed to several possible mechanisms: a period of flow reversal, release of HC
from the piston top land crevice, and out-gassing of HC from lubricant on the liner and in-cylinder
deposits. Near the end of the exhaust stroke, the cylinder-wall HC boundary layer was shed,
resulting in a vortex that was expelled near the end of the exhaust process, increasing the observed
HC concentration. This was followed by a brief period of back-flow during valve overlap prior to
exhaust valve closing (EVC) [10].
3000
Valve/Head Crevices
2500
Port: 7-cm from EV
& Valve Leakage
E 2000
Valve
Overlap
Port
0.
-
Residuals
Is
land crevice
Oil/deposit out gassing
Burned Gas Core
1500
0
0
EV-
1000
500
EVO
Boundary layer
rollup vortex
0
350
400
450
500
550
600
CA (deg)
Figure 3.11 Typical time-resolved HC concentration profile measured in the exhaust port, 7
cm from the exhaust valves. Major features shown and noted during gas
exchange, from exhaust valve opening (EVO) to exhaust valve closing (EVC).
3.4.2 EFFECT OF RETARDED SPARK TIMING
Figure 3.12 shows cylinder pressure measurements and crank angle-resolved HC
concentration measured at the exit of the exhaust port, 7 cm from the exhaust valves (EV). Each
column of graphs represents specific spark timings under stoichiometric (X = 1.0) and ambient
fluid (20 C) conditions. Grayed areas in Fig. 3.12 show the exhaust flow period from exhaust
valve opening (EVO) to exhaust valve closing (EVC). The first row of graphs represents measured
53
in-cylinder pressure acquired over several cycles. Notice that with top-center-center (TDC) spark
timing two distinct peaks are evident, the first due to piston motion and the second due to
combustion. Fixed engine load testing required additional mass flow, resulting in greater
compression stroke and exhaust blowdown pressures as ignition was retarded.
The second row of graphs shows HC concentrations (ppmcI) measured in the exhaust port
at a distance 7 cm from the exhaust valve seats. The grayed area again represent the period of
exhaust flow. However, there was a phase delay due to the transport time within the exhaust and
sampling system, in addition to a characteristic response time associated with the FFID. Note that
the exhaust transport delay became smaller with increasing spark retard as the mass flow rate and
in-cylinder pressures at EVO increase. For each of the three different spark timings, there was a
general trend in the time history of HC concentration measured in the exhaust port. During the
period of no exhaust flow, relatively high (5000 - 7000 ppmci) HC concentrations were observed
for all spark timings and were attributed to stagnant residuals from a previous cycle.
1.0, 3.0 bar n-imep, 1500 RPM, 20* C
24
-
24
-
20
In-cylinder pressure
16
Sp=15"BTDC
ln-;yIinder pressure
Sp = 'BTDC
20
In-cylinder pressure
Sp= 16 BTDC
16
12
12
8
8
a-4
Sf4
0
0
10000
E
. 10000
Port: 7-cm from EV
Sp 150 BTDC
80
Port 7-cm from EV
Sp = 0' BTDC
-
~
8000
~
5b 1
6000
0
0
4000
r
HPort 7-cm fromn EV
6000
- 4000
I
I
2000
1 -124 - I A 1
7000
E
Runner: 37-cm from EV
Sp =0* BTDC
7
6000
7000
1~7
6000
Runner 37-,cm from EV
SPI-16*Bi0j
-
5000
4000
3000
4
)
110
Runner- 37-cm from EV
Sp = 15* BTDC
00
100
2000
200
300
400 500
CA (0 ABDC)
~2000
1000
0
600 700
0
100
200
300
400
500 600 700
r*EV
CA (- ABDC)
0
100 200
300
400
500
600 700
CA (0 ABDC)
Figure 3.12 In-cylinder pressure and exhaust port and runner time-resolved HC concentration
measurements for three different spark timings (Sp = 150, 00, -16' BTDC) at 3.0
bar Net-IMEP, X = 1.0, CMCP, and 200 C fluids.
54
The last row in Fig. 3.12 shows HC concentration measured in the exhaust runner at a
distance of 37 cm from the exhaust valve seats. Stagnant residual HC emissions were observed to
decrease with spark retardation. During the exhaust process, depicted within the grayed areas, the
HC signature was different from the signal measured in the exhaust port due to gas phase reactions
within the exhaust system. As the majority of the burned gases were expelled, a single peak in the
HC concentration was detected.
As spark timing was retarded, shown in the second and third columns of Fig. 3.12, the
exhaust transport delay decreased as additional charge mass was required to achieve the fixed NetIMEP. As combustion was phased later in the cycle, peak in-cylinder combustion pressures were
reduced, decreasing the mass loading of HC in crevice volumes. The trend was observed in the
first HC peak measured in the exhaust port, the magnitude of which decreased with spark
retardation.
3.4.3 EFFECT OF FLUID TEMPERATURES
Additional experiments with the fast-response FID were conducted at three different fluid
temperatures, 200, 40*, and 90* C at a fixed spark timing (-1 BTDC) and Net-IMEP (3.0 bar), Fig.
3.13. In all three cases, the exhaust system was not externally cooled and was at a hot stabilized
operating temperature which was approximately equal for all engine tests. The lowest HC
concentrations were observed in the port and runner under fully warmed-up conditions ( 9 0 ' C
fluids).
3.5 ANALYSIS OF TIME-RESOLVED HC MEASUREMENTS
3.5.1 OVERVIEW
As described in Section 3.4, time-resolved measurements provided insight into HC
concentration levels at various exhaust locations with spark retardation. However, in order to
achieve the same Net-IMEP as combustion was phased later in the cycle, the engine's mass flow
rate was increased to offset the reduction in work extracted from the burnt gases. Changes in
exhaust mass flow rate were addressed to better interpret the results from the time-resolved HC
concentrations. To accomplish this, a simple plug flow model was developed that calculated the
55
mass flow rate of HC at the exit of the exhaust port and in the exhaust runner, Fig. 3.14. In order to
perform the analysis at each engine operating condition, burn rate information was required and
obtained from in-cylinder pressure data. Next, an engine and exhaust simulation model was
developed using the results from the burn rate analysis. The simulation provided exhaust gas
conditions that were required by the plug flow model. Data from the fast-response FID was then
combined with the plug flow model, yielding a HC mass flow rate.
900 C Fluids
6
4
i~12
0
8
6
4
2
EVC 541
TOC{
{C
EV0316
20* C Fluids
400 C Fluids
6
1~
4- -1.
4
2 -0
8
6
16
1
14-
EVC548
TOO
WBC
-
2
TDC
-
4 .
2-
L~....J
__
00
L
18()00
EV03eV*
EV03W
TM
E
EVC5W8
BDC
8.
6 .
4
4
A
EV0316
12
10
1500a
12000
30,
X33
20C
0
10C
1 750
EC61W
-EV3w
0.E
- .v
-
s
4600
EVC5W
BM0
-M
Tan fmfm EV
Ponr:
9000
1 - 1
,
Port' E
7-EmCmm
01L
-
20(
7500EV3
11500
15(
0 L0
0
40
0
100
200
300
A
500
400
000
700
0
100
200
300
CA(
(0ABC)
400
500
000
0
700
BDC)
200
100
300
400
500
CA (* AJBC)
Figure 3.13 In-cylinder pressure and time-resolve HC concentration measured in the port and
runner for 90', 400, 200 C fluid temperatures, spark timing = -1 BTDC, X = 1.0,
and without charge motion (CMCP).
n-Cylinder
pressure
Output
Sub-Models
Experiments
7
Burn Rate
GT Power
Mass
Anilysis
Simulation
Flow
S mp
Pg
F
'
HC Mass
7
Flow Rate
FFID HC
Concentration
Figure 3.14 Overview of mass plug flow model used for analysis of time-resolved HC
concentrations.
56
600
700
3.5.2 ENGINE SIMULATION MODEL
GT-Power, engine simulation software from Gamma Technologies, was applied to model
the engine and exhaust system. The cycle simulation was based upon one-dimensional gas
dynamics incorporating the effects of fluid flow and heat transfer. In-cylinder contents were
modeled in a two-zone thermodynamic state (burned and unburned) with a variable volume. The
model included the effects of heat transfer to the cylinder boundaries, work transfer to the piston,
and mass trapped in crevice volumes. The cycle simulation required user inputs such as 10-90%
combustion duration, 50% MFB location, RPM, MAP, relative air/fuel ratio, and engine surface
temperatures.
Mo
Q
BURNED ZONE
W
UNBURNED ZONE
Figure 3.15Engine cycle simulation thermodynamic model of open system, including
crevices, work transfer to piston, and heat transfer to cylinder boundaries.
The engine exhaust system was modeled as a series of pipes and junctions, Fig. 3.16. The
I-D flow code simultaneously solved the continuity, momentum, and energy equations, Eqs. (3.2),
(3.3), and (3.4). Pipe and junction elements were discretized into numerous volumes with
boundary conditions that were used to obtain a flow solution. Each pipe element was scaled with a
friction multiplier, heat transfer multiplier, and pressure loss coefficient. Friction losses were based
upon the Reynolds number and the surface roughness of the walls. Established heat transfer
coefficients were dependent upon fluid velocity, thermo-physical properties, and the wall surface
57
finish. Intake and exhaust valve discharge coefficient and lift profile were inputted by the user. For
more information regarding GT-Power's engine simulation, refer to Gamma Technologies user's
manuals.
0
S)
ex t
n-.7
1
13
in_port in-Val
k
_run25
L
1
2
Wid
ex_Val
ex_ry ner_
o
0
1
0
1
2
19cn-f rom-EV
1
ortank tank
ex-ben
0
ex
Engine
exit
0
ru ner_2
ATM
33cn-from-EV exrunner_3
Figure 3.16 GT-Power model of single-cylinder engine with intake and exhaust system.
dm
Emflx
-=
dt
d(me)
di
d(mflx)-
dpA+
dV+
dt
E
boundaries
E(mflx*H)-hA(T,,-Ta.,,)
(3.3)
boundaries
(mflx*u)-4C
boundaries
dx
dt
where:
mflx
m
V
p
p
A
e
H
boundary mass flux
mass ofvolume
volume
pressure
density
flow area
internal energy
total enthalpy
hg
heat transfercoefficient
U
u
C1
C,
D
dx
dp
velocity at center ofvolume
velocity at boundary
skin friction coeficient
pressure loss coefficient
equivalent diameter
thickness of mass element
pressure differential acrossdx
58
2
D
C
pu
(I2~
A
~
(3.4)
From the simulation, the exhaust temperature, mass flow rate, and velocity were
determined and shown in Fig. 3.17. Highest exhaust gas temperatures were observed during the
blowdown phase of the exhaust process. The mass flow rate was observed to be highest during the
initial blowdown period and gradually decreased until a period of back-flow was observed due to
the single cylinder exhaust dynamics. The outflow of exhaust gas continued during the
displacement process with a slight flow reversal noted during the valve overlap period.
GT-Power Simulation 3.0 bar Net-IMEP, 1500 RPM, ) =1.0, 20* C fluids
0.08
--- Sp = 150 BTDCa)
0.06
0)
0.04
----
0.02
Sp=-15BTDC
-
-
0.00
a)
-0.02
cai
2400
2100
a)
CL
1800
1500
E 1200
a)
I-
900
-C
X
W
600
300
120
150
180 210
240
270
300
330
360
390
CA (deg ATDC)
Figure 3.17 Port exit exhaust mass flow rate and exhaust gas temperature predicted by the
engine model at the exit of the exhaust valves versus crank angle for various
spark timings at 3.0 bar Net-IMEP, 1500 RPM, X = 1.0, and 200 C fluids.
3.5.3 TIME-RESPONSE HC MEASUREMENTS
Due to the fast time transient response of the FFID, a small sample of gas was required to
determine HC concentrations. To ensure the point measurement was representative of the entire
cross section, additional experiments were performed to ensure spacial HC uniformity at the
farthest upstream sampling location, 7 cm from the exhaust valves. Four different sample locations
were investigated along the exit plane of the exhaust port for 10 consecutive cycles, Fig. 3.18.
59
Cyclical and spacial variations were not observed during the period of exhaust flow and all fastresponse FID measurements were assumed to be representative of the entire cross section.
3.0 bar n-imep, Sp 12* BTDC, 1500 RPM, 200 C, CMCP
7000
6000
-
5000
1000
-
P2
3b5
2000
#0
0
20
1E
0
rI
7 cm froeas
exas ports
Exhaus
measuredhexhaustot ad7cm from
3.5.4 PORT AND RUNNER
0
0
0
0
0
voalvsa evrlprteiooctos
alved
C seratons,
andcaladx
HC MASS FLOW RATE
Results from the cycle simulation were analyzed in conjunction with the time-resolved HC
measurement to obtain instantaneous HC mass flow rates in the exhaust port and runner. Figure
3.19 contains four sub-charts: in-cylinder pressure measured experimentally and calculated by the
cycle simulation, exhaust port and runner instantaneous mass flow rate from the simulation,
measured exhaust port and runner time-resolved HC concentrations, and calculated exhaust port
and runner instantaneous HC flow rate. The time-resolved HC measurements were time (crank
angle) aligned for transport and time response delays. Overall HC measurement delays varied
from 25* to 85' CA due to changes in exhaust blowdown pressures as spark timing was retarded
and engine mass flow rates increased.
A simple flow model was developed in MatLab assuming pure displacement plug flow of
the exhaust mass. The mass of HC contained in each mass element was calculated from
experimental and computational data yielding an instantaneous HC mass flow rate during the
60
period of exhaust flow. Steady-state HC flow rates were obtained by integrating the instantaneous
HC flow from EVO to EVC.
GT Power simulated exhaust flow rate
*
18
Simulation
Port (7-cm from EV)
Runner (37-cm from EV)
100
Data
-
16
so
14
60
12
1:
-2
10
40
-k-
8
20
6
0
4
2
0
-20
500
300
4
CA (dog)
200
1
Measured FFID Signal (tay
6
350
700
CA (dog)
Hydrocarbon flow rate
Corrected)
10000
9000
5000
7000
(3Z
Location:
Port
Runner
EVO HC
3576
1626
ResiduaEM
7625
2218
Delay (CA):
45.7
55.7
500
450
400
250
g
1
6000
0V 5000
I
200
Port HC
150
RunnerHC
M
A 100
mg/a):9.35-Std:
1.2
-
(mg/s):4.51.Std:1
(glaee):
s.5
0
I
4000
50
3000
2000
0
1000
350
450
400
350
500
450
400
500
CA (dog)
CA (deg)
Figure 3.19 Model results from analysis of HC measurements. GT-Power simulation results
of in-cylinder pressure and exhaust mass flow rate at the port exit and runner.
Measured HC concentration and resulting HC mass flow rate computed by a plug
flow model.
Exhaust port exit and runner HC emissions are shown in Figs. 3.20-3.23 for two relative
air/fuel ratios and various combustion phasings. Time-averaged HC emissions measured in the
exhaust tank (120 cm from EV) are shown for comparison. Hydrocarbon levels calculated in the
port and runner by the FFID ieasurements agreed quantitatively with the time-averaged
measurements; the highest emissions were observed at the port exit and decreased with distance
from the exhaust valves. The fraction of hydrocarbons oxidized in the exhaust port reached a
maximum with top-center spark timings. HC oxidation rates in the runner were modest (10%) with
150 and 0' BTDC spark timings and became significant (40-50%) with additional spark
retardation (-15' BTDG). Total exhaust system oxidation increased with later spark timings, and
61
reached a maximum (68%) for -15' BTDC spark timing and stoichiometric engine operation.
Exhaust runner oxidation was not observed to be significant until after TDC spark timings, Figs,
3.26 and 3.28. However, when port exit HC emissions were expressed as a percentage of the fuel
injected, HC emissions remained constant at approximately 3%, independent of combustion
phasing and stoichiometry.
3.0 bar n-imep, A= 1.0, 1500 RPM, 20* C, CMCP, GT-Power
S14
E2
Port Exit (7-cm)
|
Runner (37-cm)
-
0)
2J Exhaust Tank (120-cm)
E
-/71
0
Ca
0
6
0
GC13
(D3
~0
I
-
24 U
15
........ L..z..
10
5
-
0
..... i
-5
.
-10
-15
-20
Spark Timing (0 BTDC)
Figure 3.20 Steady-state HC emissions as a function of spark timings measured in three
locations under X = 1.0, 201 C fluids.
62
3.0 bar n-tmep, X = 1.0, 1500 RPM, 20* C, CMCP, GT-Power
45
40
5-2 E Port Exit (7-cm)
EM Runner (37-cn)
-
Tank (120-cm)
-Exhaust
35
30
0)
25
C)
I
0)
20
0
I
15
-
L..-..J-
L
-
-
10
5
0
70
60
50
40
30
20
10
80
Location of 50% MFB (0 ATDC)
Figure 3.21 Emission index HC emissions as a function of location of 50% MFB for different
exhaust locations under X = 1.0 and 20' C fluids.
3.0 bar n-imep, X
14
D
Cl)
S- Port (7-cm)
EM Runner (37-cm)
Exhaust Tank (120-cm)
0)
12
0
1.1, 1500 RPM, 20* C, CMCP, GT-Power
10
CO
,-,~
c0
0
/
cc
8 6
14
Ca
£
2
Ca
.0(D
0CO 20
15
10
5
0
-5
-10
-15
-20
Spark Timing (0 BTDC)
Figure 3.22 Steady-state HC emissions as a function of spark timing for three different
locations under X = 1.1 and 200 C fluids.
63
3.0 bar n-imep, A= 1.1, 1500 RPM, 20* C, CMCP, GT-Power
.
45
5-20-2
Z
40 -Z3
Port (7-cm)
Runner (37-cm)
Exhaust Tank (120-cm)
35
30
/
025
0
27
X 15/
4)
10
5
0
10
20
30
40
50
60
70
80
Location of 50% MFB (0 ATDC)
Figure 3.23 Emission index HC emissions as a function of the location of 50% MFB for three
different locations under X = 1.1 and 200 C fluid.
3.6 QUENCHING EXPERIMENTS
In order to determine the extent of HC oxidation within the exhaust port, cylinder-exit HC
emissions were investigated using exhaust quenching experiments. Hydrocarbon reactions were
frozen by rapidly reducing exhaust gas temperatures at the exit plane of the exhaust valves with
CO 2. Timed injection of quench gas prevented artificial cooling of the exhaust port and valves,
reduced exhaust back pressure, and minimized changes to residual gas temperature and
composition. However, response times of the solenoid valves controlling the injection of CO 2 was
limited, and the quench gas could not be phased directly with the exhaust event, Fig. 3.24. As a
result, the mass of quench gas per cycle (mCO2Quench) included the mass injected while the
exhaust valves were closed (displacing gas in the exhaust system) and the mass injected during the
exhaust process (mixing with burnt gases exiting the cylinder). Experiments were performed using
fixed CO 2 injection durations and timings that were optimized for a stable and repeatable injection
event. Although the engine was operated at high intake manifold pressure, back-flow of CO 2 into
the cylinder during valve overlap was a concern. Increased residual gas dilution with CO 2 would
64
raise the specific heat of the residual gas, reducing peak combustion temperatures and lowering
NOX emissions. Therefore, NOX emissions were monitored under quenching and non-quenching
conditions to assess any back-flow impact.
3.0 bar n-imep, 1500 RPM, Sp 15* BTDC, ; = 1.0, 90* C
24
Cylinder Pressure
Probes A
- - - Probes B
- -Trigger
5
-
22
CU
20
.0
18
CU
.
4
_
C
16
3
W
14
U)
12
28 0
-N
10
8
.
6
4
.v
-
0
0
2
0
00
200
400
600
800
1000
1200
CA (deg)
Figure 3.24 Phasing of quench gas injection as a function of crank angle. Data shown with incylinder pressure and solenoid trigger signal for 3.0 bar Net-IMEP, 150 BTDC
spark timing, and X = 1.0.
Cylinder-exit HC and NOX emissions with quenching were normalized with equivalent
non-quenching values. Figure 3.25 shows quenching experiments conducted for three spark
timings under stoichiometric and 20' C fluid conditions. Results were expressed as a ratio of the
mass of CO 2 injected to the mass of fuel and air entering the cylinder. The amount of quenching
gas was increased until cylinder-exit HC emissions were found to reach a plateau. In all cases, this
cylinder-exit HC emissions plateau was obtained while altering NOX levels by less than 10%.
65
3.0 bar n-imep, 1500 RPM, ? = 1.0, 20* C, CMCP
3.5
SSp: 15
2.5
BTDC
Sp: 0* BTDCp:-15* BTDC
3.0
-
A
128%
C
2.0
A 1.5
I
0
1.0
0
0*
0
I
-
I
- --- ---
A/A'
-0.5
4-
-0.05
*
-0.10
o
-0.25
I
I
-1
A-
A-
0
-0.15
-
I
*
4)
Z
-
A
eA
0.00
z
-
3450%
0.5
0.0
,
'
-A-
37%
I
-0.30
0.0
0.5
1.5
1.0
2
mCO uench
2.0
2.5
/ mChargea,~e
Figure 3.25 Change in HC and NO, emissions as a function of the ratio of mass of quench
gas to mass of charge (mCO2Quench/mChargeair+fueI) for three spark timings
with X = 1.0 and 20 C fluids.
Results from the quenching experiments provided cylinder-exit HC emissions and
hydrocarbon tracking information reported as both steady-state HC flow rate and emission index,
at the four exhaust locations; cylinder-exit, port exit, runner, and exhaust tank can be found in
Figs. 3.26 and 3.27, respectively, for stoichiometric (X = 1.0) operation. Additional exhaust HC
tracking information for X = 1.1 is shown in Figs 3.28 and 3.29.
66
3.0 bar n-imep, I = 1.0, 1500 RPM, 20* C, CMCP, GT-Power
I
.
.-
25
I 202
5-2M.2
0
Cylinder Exit
Port Exit (7-cm)
M Runner (37-cm)
[= Exhaust Tank (120-cm)
20 -
E0
0)
-0 15 L)
0
2o
777
10
W
5
I
I
15
O0
20
5
10
0
Spark Timing
-5
I
-10
-15
-20
(0 BTDC)
Figure 3.26 Steady-state HC emissions as a function of spark timing at four locations
(cylinder exit, port exit, runner, and mixing tank) under X = 1.0 and 200 C fluids.
3.0 bar n-imep, I = 1.0, 1500 RPM, 20* C, CMCP, GT-Power
65
60
-
Cylinder Exit
5202
22Port Exit (7-cm)
Runner (37-cm)
55 -
Exhaust Tank (120-cm)
50
-
-\
-s 40
C-
35
-ZZ
30
25
Z
-
-N
45
-
-
20
15
10
5
0
10
20
30
40
50
60
70
80
Location of 50% MFB (0 ATDC)
Figure 3.27 Emission index HC emissions as a function of 50% MFB location at four
locations under ? = 1.0 and 200 C fluids.
67
3.0 bar n-imep, k = 1.1, 1500 RPM, 20'
20
18
C, CMCP, GT-Power
Cylinder Exit
Port Exit (7-cm)
Runner (37-cm)
Exhaust Tank (120-cm)
E
0) 16
14
0
12
ca
10
8
0(U
Ox
-
6
4
I-
20
01
20
10
15
5
0
-5
-10
-15
-20
Spark Timing (0 BTDC)
Figure 3.28 Steady-state HC emissions as a function of spark timings at four locations under
X = 1.1 and 200 C fluids.
3.0 bar n-imep, k = 1.1, 1500 RPM, 20* C, CMCP, GT-Power
65
60
55
-
Cylinder Exit
Port (7-cm)
IZZRunner (37-cm)
{E2Exhaust Tank (I120-cm)
20-03
~
-
-
50
-
E
45 -
-
40
35
o 30
O
25
(D 20
15
10
5
0
10
20
30
40
50
60
70
80
Location of 50% MFB (0 ATDC)
Figure 3.29 Emission index HC emissions as a function of 50% MFB location at four
locations for k = 1.1 and 20' C fluids.
68
3.7 SECONDARY AIR INJECTION
3.7.1 OVERVIEW
Several technologies exist that assist in reducing engine-out HC levels and improve
catalyst light-off times. One such strategy involves the use of secondary air injection (SAI) into the
exhaust port to accelerate converter warm-up. This mode of operation requires the engine to be
operated under fuel-rich conditions forming reactive partially oxidized products in the exhaust gas:
hydrogen (H 2), carbon monoxide (CO) and hydrocarbons (HC). When mixed with air in the
exhaust port, exothermic reactions occur, raising gas temperatures and reducing converter-in
emissions. Fuel-rich engine operation also results in a more robust and stable combustion,
allowing for additional spark retardation from MBT. Previous studies have investigated the
importance of proper air delivery systems and exhaust manifold designs [11-13]. Mixing rates and
residence times within the exhaust system have a dramatic impact on converter-in HC emissions
and catalyst light-off times [12]. Large heat losses per unit length of exhaust reduces exhaust gas
temperatures and results in longer ignition delays of the reactive components.
3.7.2 FIXED ENGINE RELATIVE AIR/FUEL RATIO
Experiments were conducted at the same fixed engine torque (3.0 bar Net-IMEP), and
fixed engine relative air/fuel ratio (Xengine = 0.85), with the secondary air injected at the exhaust
valve seats. The setup was not equipped with a catalytic converter. Therefore, a distance of 37 cm
from the exhaust valve seats was selected to represent the flow length of the catalyst inlet on a
modern multi-cylinder engine. Exhaust relative air/fuel ratio (Xexhaust) was varied experimentally
as CO and HC emissions and exhaust gas temperatures were quantified. In Fig. 3.30, air was
continuously injected at the valve seats as exhaust stoichiometry was varied. Port temperatures
decreased due to burnt gases mixing with the injected air. Exothermic reactions at the runner
location raised the exhaust gas temperature, as the secondary air oxidized CO, H 2, and HC. A
trade-off existed between exhaust gas temperature and HC emissions. Excessive secondary air
over-cooled the mixture, quenched reactions rates, and resulted in higher HC emissions and lower
exhaust gas temperatures.
69
Engine X = 0.85, Sp = 00 BTDC, 3.0 bar n-imep, 1500 RPM
0.125
1
6
5
0.100
4
W)
0.075
_
CD
0
o
'
0.050 -
600 -
0U
585
a)
570
(D
555 -
E
a)
-
540
0
.
a.. C-,mrunner
.-
.
-u-Ts
,
*------
-
+-T
525 510
0.9
0.8
-
1.1
1.0
1.2
1.3
1.4
Exhaust k
Figure 3.30 Exhaust secondary air injection experiments conducted at an engine relative air/
fuel ratio of 0.85 (Xengine) as a function of with exhaust relative air/fuel ratio.
Data shown for 3.0 bar Net-IMEP, 1500 RPM, 00 BTDC spark timing, and 200 C
fluids.
3.7.3 TIMED SECONDARY AIR INJECTION
Comparisons of different pulsed air injection events and continuous air injection was
investigated for a single engine operating condition and a fixed mass of secondary air (Xexhaust ~
1.2, spark timing 0' BTDC). Injection event "B", as illustrated in Fig. 3.31, was timed to be in
phase with the exhaust blow-down process. The remaining pulsed injections were phased in
increments of 1800 CA with respect to the exhaust valve opening event. Continuous air injection,
compared to phased injection, was found to yield the highest exhaust gas temperatures and lowest
HC levels measured in the exhaust runner with the setup used in these experiments.
70
Engine X = 0.85, Exhaust x = 1.2, Sp = 00 BTDC
40
_CO
Exhaust
-
30
-Air In. A
Air Inj.B
Air Ini.C..
Air Inj. D
-
as
-
20
0
-
I'J-
10
C -0)
In
I
-
0
100
-_.
200
300
-
400
500
-
600
700
CA (0 ABDC)
600
---
MI
C:
550
Cn
E
- 500
o
(D
\g--
450
~~-0
400
0
C=
CD
350
I
A
I
I
I
C
I
Continuou s
Air Injection Timing
Figure 3.31 Hydrocarbon flow rate and runner exhaust gas temperatures as a function of
various secondary air injection timings for a fixed engine (Xengine = 0.85) and
exhaust stoichiometry (Xexhaust = 1.2). Data shown for 3.0 bar Net-IMEP, 1500
RPM, and 200 C fluids.
3.7.4 TAILPIPE-OUT HC EMISSIONS AND FEED GAS SENSIBLE ENTHALPY
Relative magnitudes of well downstream HC emissions and sensible enthalpy flow rates
with aggressive spark retardation were compared with SAI engine operation in Fig. 3.32. Results
were shown relative to a stoichiometric base case with a 150 BTDC spark timing. For the SAI
tests, exhaust stoichiometry was varied from a relative air/fuel ratio of 0.85 to 1.4. Use of SAI
yielded the lowest HC emission and highest enthalpy rates for a fixed level of spark retardation..
With aggressive (-15* BTDC) spark retard, SAI operation was observed to reduce HC flow rates
approximately 60% while increasing the sensible enthalpy flow by a factor of 3.8 compared to the
baseline conditions.
71
3.0 bar n-imep, 1500 RPM, 20* C
1.4
XExhaust
=0.85
0
0
-1.2
1.0
S
-
Sp= 15* BTDC
0
0
0.8
Sp
T
0'
BTD C
Sp=-15*BTDC
O
V
0.6
0.4
A
F
0.2
0.5
*
A
1.0
5
7 = 0.85 w/SA
X=1.0
.1
1.5
X Exhaust=1.
2.5
2.0
mC(Ttalyst - Tmbient) / [mC
-tayst -
I.
I
3.0
3.5
4.0
Tamvtient)l 7.=1.0, 15* BTDC
Figure 3.32 Normalized HC flow rate as a function of normalized sensible feed gas enthalpy
rate for three spark timings. Data shown for X = 1.0, 1.1, and secondary air
injection (SAI) at a fixed engine relative air/fuel ratio (Xengine = 0.85) with
exhaust enleanment from Xexhaust = 0.85 to 1.4 Shown with respect to X = 1.0 and
15' BTDC spark timing baseline condition, 3.0 bar Net-IMEP, 1500 RPM, and
200 C fluids
72
CHAPTER 4
MULTI-CYLINDER EXPERIMENTAL RESULTS
4.1 ENGINE STARTUP OVERVIEW
Ambient startup is a complicated process that requires delivery of an adequate relative air/
fuel ratio around the spark plug gap for a robust combustion event during engine cranking. Upon
the first cylinder firing, the engine accelerates, resulting in an RPM flare and a rapid decrease in
intake manifold pressure. During this transient period, spark timing is advanced as engine speed
and in-cylinder exhaust gas residuals increase. Several parameters (MAP, RPM, spark timing, and
relative air/fuel ratio) were acquired during the first 20 seconds following an ambient startup and
are shown in Fig. 4.1. Due to RPM flare and the complex nature of the startup event, emissions
from the first second of engine operation (noted in the grayed areas of Fig. 4.1) was excluded from
the analysis and no attempt was made at altering the first second "crank" and "run" fueling or
timing strategy.
200 C startup, Baseline Calibration, 2.3 bar Net-IMEP
1.0
0.9
18
0.8
14
16
Z 0.7
-
20
M
0.6
12 C)
-10
RPM
-
86
CL 0.5
2 0.41
0.3
MAP
2
0
0.2
1.2
30
25
20
15 -1.0
o
1.1
-2
0.9
10
*-
S
.
-
0.7
-
-5
-15
0
0.6
Spark
- --
cc-10
2
4
6
8
10
12
14
16
18
0.5
20
Time after crank (sec)
Figure 4.1
Baseline calibration MAP, RPM, spark timing, and relative air/fuel ratio as a
function of time after crank. Data from an ambient startup under idle load and
speed conditions.
73
During a typical 200 C (ambient) start, the baseline calibration resulted in an idle speed of
approximately 1000 RPM and TDC (00 BTDC) spark timing, 5 seconds after engine cranking.
Net-IMEP averaged 2.3 bar with 4% COV and an 8% Net-IMEP imbalance cylinder-to-cylinder.
Multi-cylinder experiments focused on the initial 1-20 seconds of operation following an ambient
start. During this transient warm-up period, combustion stability, HC, CO, and CO 2 emissions, and
feed gas enthalpy were evaluated for four late spark timing strategies.
Spark timing "blend" and "run" tables were modified using Caltools software and
uploaded to the ECM using the MDS. Spark timings during the engine cranking period were not
modified, only the magnitude of spark timings during the "blend" and "run" period were altered
and the trajectory remained the same. All calibration changes were referred to as spark
modifications (AOsp) and were slewed relative to the baseline calibration spark timing, A0~s = 00,
observed in the stock ECM file, Fig. 4.2. Fueling "blend" and "fast choke" tables and the idle air
control (IAC) stepper position tables were varied in order to maintain the same air/fuel ratio as the
engine's mass flow was adjusted during open loop operation. Default air/fuel feedback control was
established in 20 seconds (~200 engine cycles) after startup. Accelerated closed loop control was
achieved in approximately 10 seconds by pre-heating the exhaust gas oxygen (EGO) sensor before
startup and making appropriate changes to the calibration file, Fig 4.3. Test-to-test variations in
air/fuel ratio was 14.6 ± 0.5.
4.2 COMBUSTION CHARACTERISTICS
4.2.1 COMBUSTION STABILITY
The extent of late combustion phasing was limited by the COV of the Net-IMEP. As spark
timing was retarded from the baseline calibration, there was a noticeable decrease in idle quality
and an increase in the engine's noise, vibration, and harshness (NVH). Therefore, at each of the
four different spark modification, combustion stability was investigated during a quasi-steady idle
period (second 4 to second 20 after startup) that contained approximately 130 engine cycles. Spark
timings were modified (AOSP = -50, -100, and -15') with respect to the baseline (A0~s
= 00) ECM
calibration tables. Under idle load conditions, the baseline spark timing yielded a COV of NetIMEP of approximately 4% across all four cylinders. Combustion stability decreased as
74
combustion was phased later in the expansion stroke; a COV of 8% was observed with the most
aggressive retarded spark timing modification, AOsp = -15'.
200 C startup, Idle load
30
--
a
----
251
rk =
- - -- AID
-- --
-20
------ AO
00
= -5*
=-spark
10
pr = -15*
15
0
CD 10
C
E5
0
w
ji11 0kf
It
C,
-5
-10
- .
-U
-15
0
10
5
20
15
Time After Startup
Figure 4.2
Spark timing as a function of time after startup for various spark modifications
(AOspark).
20" C startup, Idle load
1.05
1.00
0.95
0.90
0
0 0.85
0.80
0.75
0.70 0.65
0.60
Baseline Calibration (20 sec)
Accel. Closed Loop (10 sec)
---. I
0
20
.
I
40
,
I
60
,
I
80
I
,
100
.
I
120
.
I
140
.
I
160
-.
I
180
Cycle No. After Startup
Figure 4.3
Measured UEGO relative air/fuel ratio (X) as a function of cycle no. after startup.
Data shown for accelerated closed loop control compared to baseline calibration.
75
12
1
2.3 bar Net-IMEP, Idle Load, 200 C startup
1
N
Cyl
Cyl
A Cyl
v Cyl
10 -
#1
#2
#3
#4
4
A
I--4 to 20 sec after crank (130 cycles)
2-
0
0
-5
-10
-15
Modified Spark Timing (AOSP)
Figure 4.4
COV of Net-IMEP as a function modified spark timing, 4 to 20 seconds after
crank (130 cycles). In-cylinder pressure data acquired from all four cylinders at
idle speed and load conditions following an ambient start.
4.2.2 BURN RATE ANALYSIS
Burn rate analysis was conducted on from second I to second 20 following ambient
startup. The location of the 50% MFB and 10-90% combustion duration were obtained from incylinder pressure data acquired from cylinder no. 4. During the quasi-steady idle period, after 60
engine cycles, the 50% MFB location increased with the level of spark retardation. With very late
spark timings, large variations in the location of the 50% MFB was observed as combustion was
phased later in a rapidly expanding cylinder volume, Fig. 4.5. As expected, the 10-90%
combustion duration was observed to increase with increasing spark retardation, Fig. 4.6.
76
200 C startup, Idle load
90
1 to 20 sec after crank
o
AO =0*
80
AO = -50
AO Op = -10 0
A = -15*
.
A
F
70
IV
V
vV
-
0
VV
0'
LL 60
V
V
V V~
V~0V
~
V
V
-
V
V
0
7
COD~
-0
7
o
LO
A
-
50
A
c2
oAc
2
0
-C
0
0 40
-
121
D1,
1
0
0
0
12
13
-123
3U
~ ~
I~
61
1
1 2a:]
n
0
1
1
12J12
12
12
-1
0
20
0
20
40
60
80
100
120
140
160
180
Cycle No. After Startup
Figure 4.5
Location of 50% MFB as a function of cycle number after 200 C startup. Data
shown for various spark timing modifications under idle speed and load
conditions.
1 '
i
20* C startup, Idle load
'
1*'
I'I*
'
I'
70 1 to 20 sec after crank
O SP = 0*
A6 = -5'
AO= -10'
AO = -15*
65 60--
0 55
I
-
cap
E
50
045 *00
E
=340 O)
o
cnV
V
'V
A
V
-,
35V-
.
.
V21-f
1 12
-
I .
I
2
zz,
E: 120
121
12
-
025
20
-
1[
I
0
*
I
I
20
40
*
I
60
*
80
100
*I
I
I
120 140 160
*
0
180
Cycle No. After Startup
Figure 4.6
Combustion duration (10-90%) as a function of cycle number after 200 C startup.
Data shown for various spark timing modifications under idle speed and load
conditions.
77
4.3 EXHAUST EMISSIONS
4.3.1 TIME-RESOLVED CO AND HC EMISSIONS
Time-resolved cylinder no. 4 port exit and converter-in HC concentration measurements
were taken for the first 20 second of engine operation, Fig. 4.7. Port HC levels were constituently
higher than converter-in levels due to exhaust system oxidation and contribution from the other
three cylinders.
200 C startup, Baseline Calibration, 2.3 bar Net-IMEP
30000
25000
E
Port Cyl #4
----Converter-in
20000
Cs
15000
%
-T"
w
w
0
10000
5000
n
0
2
4
6
8
10
12
14
16
18
20
Time after crank (sec)
Figure 4.7
Cylinder no. 4 port exit and converter-in hydrocarbon concentrations (ppmCl)
for the first 20 seconds following a 200 C start. Baseline timing and fueling
calibration under idle load and speed conditions.
Experiments were conducted to evaluate HC and CO emission levels at the exhaust port
exit of cylinder no. 4 for various spark timings. The engine was operated under idle speed and load
conditions (1000 RPM and 2.3 bar Net-IMEP) following an ambient startup. In-cylinder pressure
and emission levels from cycle 200 to 210 were investigated at three spark timings; 3*, -I*, and -6*
BTDC under stoichiometric closed loop control. The results are shown in Fig. 4.8, all
78
concentrations were measured on a wet basis and the grayed areas represent the period of exhaust
flow.
Spark = 3* BTDC (eO ,=
Spark = -1 BTDC (0 >d= -5*)
0*)
Spark = -6' BTDC (0
12
-~
8
-15*)
FCy1#4
12
-
Cf4
0
1.5
-Port0Cy
1
- 1.5
-
#4
I
PoyCyl #4
- 1.0
~
0.5
0.5
~
Port Cyl #4
0.0
*'
14.0
14.0
-
13.5
-13.5
Por Cyl#4
13.0
' 13.0
12.5 -
-
0.0"-
-
-
-
-
-
.0
Port Cyl#4-
3200
~I3200
3200
6 2800
E 2400
2000
r 1600
12.5
--1235
Port Cyl#4
2400
2000
-Portcy*#
-
-
0
100 200 300 400 500 600 700
CA (deg)
Figure 4.8
0
100
200
300
400
CA (deg)
500
600
700
0
100 200 300 400 500
CA (deg)
1600
600 700
Cylinder no. 4 pressure, CO, C0 2, and HC time-resolved concentrations
measured at the exhaust port exit of cylinder no. 4 as a function of crank angle
(CA). Data shown for three different spark modifications (absolute spark
timings: 30, -P', -6' BTDC) from cycle 200 to 210, stoichiometric closed loop
control and idle speed and load conditions (2.3 bar Net-IMEP, 1000 RPM, X =
1.0).Grayed areas show period of exhaust flow.
As the spark timing is retarded from the baseline value (30
BTDC), port exit CO
concentrations decreased from a peak of 1.3% to 0.8% during the exhaust flow period. However,
as the spark timing is further retarded, from -1' to -60 BTDC, CO levels observed at the port exit
increase to approximately 1%. There are several plausible mechanisms for the changes in CO
levels observed in Fig 4.8; port oxidation rates, port residence time, and in-cylinder air-fuel nonuniformities.
The last row of graphs in Fig. 4.8 depicts port exit HC concentrations decreasing as
combustion was phased later in the engine cycle. Baseline spark timings yield HC concentrations
on the order of 3000 ppmcI and decline with increasing spark retard. However, recall that as spark
timing was retarded, the mass flow rate through the engine increases to maintain the same torque
output. Thus, a decrease in HC concentration could be offset by an increase in HC mass emissions.
79
4.3.2 CUMULATIVE
CO AND HC MASS EMISSIONS
In order to investigate the impact of late combustion phasing, cumulative feed gas
emissions were evaluated from the first second to the twentieth second following engine startup.
Cumulative emissions were calculated based upon a simple plug flow model outlined in Sec. 3.5.
Instantaneous mass flow rates and exhaust gas temperature predicted by the multi-cylinder engine
simulation are shown in Figs. 4.9. Cumulative HC and CO mass emissions as a function of spark
timing modifications is shown in Fig. 4.10. Port exit emissions from cylinder no. 4 were scaled by
a factor of four for comparison to converter-in levels. Port exit CO emissions reached a minimum
following the baseline calibration and then increased with additional spark retardation. Port exit
HC emissions were also observed to increase linearly with spark retardation. Converter-in
emissions contained emission levels from all four cylinders.
GT-Power Simulation 2.3 bar Net-IMEP, 1000 RPM
0.10
0.08
0.06
0.04
a
cr0.02
0.00
U--0.02
-0.04-0.06
1800
1600
-
__
1600
1400 -----
T
Port Cyl #4
Converter-in
C1200C.
1000
E
800
-7
600
x
400
120
150
180 210
240
270
300 330
360
390
CA (deg ATDC)
Figure 4.9
Cylinder no. 4 exhaust port and converter-in mass flow rates and exhaust gas
temperatures as a function of engine crank angle (CA). Data predicted by the
engine simulation for baseline timing and fueling calibration under idle load and
speed conditions.
80
1 to 20 sec After Startup, Idle Conditions
-j 5.0
0
o 4.0
Co
3.0
E 3.
0
o------
2.0
.S
1.0
-i"- Port Cyl #4 (x4)
o-- Converter-in
E
S0.0
0.7
0.6
HC
.0 0.5
0.4
w
o0.3
0.2
.T 0.1
E nn
0
0 -----------Port Cyl #4 (x4)
--
o-- Converter-in
0
-5
-10
-15
Modified Spark Timing from Baseline (A0spar)
Figure 4.10 Cumulative, 1 to 20 seconds, ambient startup CO and HC mass emissions
measured at the exhaust port exit of cylinder no. 4 and converter-inlet as a
function of modified spark timing under idle speed and load conditions (Port exit
emissions are scaled by a factor of 4 for comparison to converter-in levels).
4.3.3 CYLINDER-TO-CYLINDER MALDISTRIBUTION
The multi-cylinder engine was subject to cylinder-to-cylinder variations in air flow and
fuel injection. These imbalances led to cylinder-to-cylinder fuel maldistriubtion and in-cylinder
fuel stratification, resulting in higher HC and CO emissions. Incomplete mixing of fuel and air
within each cylinder also led to differences in residual gas composition [14,15]. Equilibrium
concentrations of the main exhaust gas species (CO, CO2 , H20, H2, and 02) is a function of air/
fuel ratio. For a stoichiometric mixture, CO 2 concentration reached a maximum with negligible
concentrations of 02 and CO. Rich of stoichiometric, CO concentration increases linearly with
increasing equivalence ratio. Likewise, lean of stoichiometric, 02 concentrations increase linearly
with decreasing equivalence ratio. Therefore, fuel maldistriubtion was indicated by CO 2
concentration and the linear combination of CO and 02 concentrations. Utilizing the fast-response
NDIR instrument, exhaust port exit CO and CO 2 concentrations were quantified under
81
stoichiometric engine operation. Figure 4.11 shows in-cylinder pressure, CO, C0 2, and CO + CO 2
concentrations for cylinders no. 3 and no. 4 for a spark timing of 3' BTDC under idle speed and
load conditions.
Spark = 3' BTDC (O,=
Spark =30 BTDC (0s-= 0)
12
4
Cy #3
8
cyI #
8
:3
-
-
cO 4
4
a-s
_0
1
0
2.0
2.0
1.5
1.5
01.0
1.0
0 0.5
0.5
O0
0*)
12
0.0
0.0
13.5
13.5
-
13.0
13.0
--
012.5
-
PortCyl#4
o1.5
12.0
I
+ 13.5
15.00
0
0
I
0
0
014.25
12.05
Port Cy
1#3
0
*
I
I
I
I~
.
I
~
I
*
I
.Yr~rTw
-T
j.JjW
~A
Port Cyl #4
" 14.25
0
.0
+ 13.50
0
o 12.75
0
100 200 300 400 500
I
0
600 700
100
*
I
*
I.
I
200 300 400
500 600
700
CA (deg)
CA (deg)
Figure 4.11 Cylinders no. 3 and no. 4 in-cylinder pressure, CO, C0 2 , and CO + CO 2 timeresolved concentrations measured at the exhaust port as a function of crank angle
(CA). Data shown from cycle 200 to 210 after startup, absolute spark timing 30
BTDC, stoichiometric closed loop control, and idle speed and load conditions
(2.3 bar Net-IMEP, 1000 RPM, X = 1.0).Grayed areas show period of exhaust
flow.
in CO
The grayed areas of in Fig. 4.11 show the period of exhaust flow with an observed increases
for each
concentrations from cylinder no. 3 compared to cylinder no. 4, CO + CO 2 was plotted
no. 4 were
cylinder to check the balance of carbon. Port exit HC emissions for cylinders no. 3 and
observed to vary by approximately 500 ppmcI during the exhaust flow period, Fig. 4.12.
82
t
Spark = -4* BTDC (0
Spark = -40 BTDC (0.
*",= -100)
10
10
Cyl #43
8
CyI #
8
6
6 -CL
a)
c
= -10*)
4
-
2
2
0
0
3"0
3000 -
2750
2750
Port Cyl #4
2500
02500
0
6 2250
CL
C
0: 2000-
0
1750-1500
1500
0
100 200
300
400
500
0
600 700
100
200
300
400
500
600
70(0
CA (deg)
CA (deg)
HC
Figure 4.12 Cylinder no. 3 and no.4 in-cylinder pressure and port exit time-resolved
to
200
cycle
from
shown
Data
concentrations as a function of crank angle (CA).
loop
closed
stoichiometric
BTDC,
210 after startup, absolute spark timing -4"
control, and idle speed and load conditions (2.3 bar Net-IMEP, 1000 RPM, X =
1.0).Grayed areas show period of exhaust flow.
Data from the time-resolved CO and CO2 measurements was used to estimate cylinder-togas
cylinder relative air-fuel ratio. Figure 4.13 shows cylinder no. 3 and no. 4 port exit exhaust
cylinder's
temperature (EGT) and relative air-fuel ratio (X) as a function of spark timing. Each
relative air-fuel ratio was calculated from exhaust gas equilibrium concentrations of CO and C0 2,
the
see Fig. 4.14. Cylinder no. 4 was observed to runner slightly lean of stoichiometric and have
highest measured port exit EGT.
83
2.3 bar Net-IMEP, Idle Load, 200 C, X = 1.0
1.14
-
900
---Cyl#3 --0-I
1.12
1.10
10''
1.08
800
1.06
0.0
a-
-
1.04
~~
700
W"
0
1.02
(0
0.
0
0
3
1.00 0
0
0
(D,
0
0.98
600
0.96
-0
----.
-''
-~o
90
0
0.94
500
0.92
'
"
0
-5
-10
0.90
-15
Modified Spark Timing (Ao,)
Figure 4.13 Port exit measured exhaust gas temperatures and relative air/fuel ratios (k)
calculated from time-resolved CO and CO 2 measurements for cylinders no. 3 and
no. 4 as a function of modified spark timing. Data shown for idle load and speed
conditions under closed loop stoichiometric control.
14
I
I
I
10
I
8
12 I
6
10
-
I
2
I
C4J
0
-
CO
()
0
O
4
0-
8
2
-
6
0
0.8
0.9
1.0
1.1
1.2
Relative air/fuel ratio (k)
Figure 4.14 Spark-ignition engine exhaust gas CO 2 and CO concentration data as a function
of relative air/fuel ratio.
84
Relative air-fuel ratio non-uniformities and HC emissions were investigated at the
collector inlet as a function of manifold air pressure (MAP) under stoichiometric operation, Fig.
4.15. The fuel maldistriubtion parameter, CO + 02, was corrected for hydrocarbons and was
observed to increase with increasing MAP. Hydrocarbon emissions, expressed as a fraction of the
fuel injected, decreased with increasing MAP. Figure 4.15 suggests that with increasing MAP (and
increasing spark retardation) mixture preparation worsens and results in an increases in cylinderto-cylinder air-fuel variations under idle speed and load conditions.
Converter-in Emissions, 2.3 bar Net-IMEP, 1000 RPM, X = 1.0
.JA
-- HC -corrected- -o- -HC - uncorrected
2.5
10
2.0
--1.5
0
0
1.0
-
-
01
0.5
-
0.0
80
I
I
I
I
I
75
70
U
U
65
0Y)
60
3:
55
Z)
U
*
50
40
0.
38
0.40
I
I
I
0.42
0.44
0.46
0.48
0..50
MAP (bar)
Figure 4.15 Converter-in CO + 02 emissions and emission index HC levels as a function of
intake MAP. Data shown for stoichiometric closed loop control and 200 C idle
speed and load conditions (2.3 bar Net-IMEP, 1000 RPM, X = 1.0). CO+0 2
concentration shown with and without oxygen concentration corrections due to
HC emissions.
85
4.4 EXHAUST FEED GAS AND LIGHT-OFF
4.4.1 FEED GAS EMISSIONS AND ENTHALPY
Exhaust gas temperatures were measured at the exit of the exhaust port at all four cylinder,
Fig. 4.16. In addition, converter-in and converter-out EGTs, brick temperatures, and skin
temperatures were recorded for the first 20 seconds of engine operation. During this time period,
metal skin and component temperatures were observed to vary less than 200 C.
200 C startup, Baseline Calibration, 2.3 bar Net-IMEP
j
600
*-
500
I-
-
Cy #1
Port Cyl #2.----- Port Cyl #3
Port Cy#4
-- Converter-in
700
-Port
....-.
C 400
w
300
200
o 100
0
250
00
(200
s
a
sesil
w r
211
-e Cat d1 Brick
-- Cat 2' Brick
WCat
Shell
--
150
-
Exh Collector Skin
Exh Runner Skin-
Converter-out EGT
C100
E50
0
-0
2
4
6
8
10
12
14
16
18
20
Time after crank (sec)
Figure 4.16 Measured exhaust gas and component temperatures as a function of time after
crank. Data shown for baseline timing and fueling calibration under idle load and
speed conditions.
Cumulative converter-in feed gas HC emissions as a function of cumulative sensible
enthalpy for four different spark modifications was investigated from second I to 20 following an
ambient (20' C) startup. With the most aggressive retarded spark modification (A~spark = - 15*),
sensible enthalpy supplied to the catalyst was increased by a factor of three and HC emissions
were reduced by 23%, Fig. 4.17.
86
200 C startup, Idle load
0.350
1 to 20 sec after crank
E AO
00
0.325
u0
C
AO
09
A
UI)
u) 0.300
V
spa =-
A Ospark
-50
AO spark = -10"
1
AOs
= -15*
We
o 0.275
3:
A
co)
A
0.250
V
V
LL. 0.225
(D
0.200
E
o
0.175 1
0.00
0
2
4
6
8
10
12
14
Cumulative Converter-in Sensible Enthalpy (kJ)
Figure 4.17 Cumulative converter-in feed gas HC emissions as a function of cumulative
converter-in sensible enthalpy. Data shown for 1 to 20 seconds following an
ambient startup for four spark timing modifications (AOSP) under idle speed and
load conditions.
4.4.2 CATALYST LIGHT-OFF TIMES
A decrease in exhaust gas temperature can be offset by an increase in oxygen
concentration of the feedgas which has a large impacts on the low-temperature activity of the
catalyst. The 50% light-off temperature was observed to decreased greatly with late ignition
timings. Lean relative air/fuel ratio reduces engine-out hydrocarbons but increases combustion
instability. Increased oxygen concentration in the feedgas has been to have a favorable effect on
lowering the catalyst light-off temperatures with catalysts having a high Pd content [22]. However,
lean mixtures require advancement of ignition timing which results in lower exhaust gas
temperatures.
Cumulative feed gas HC emissions versus catalyst light-off time was investigated for
various late spark timings, Fig. 4.18. Catalyst light-off was defined as the 50% conversion
efficiency of hydrocarbons (lHC = 50%). Light-off experiments were conducted with a 50k mile
aged ULEV catalyst (serial no: XX901JP). Hydrocarbon concentrations were monitored pre-
87
catalyst and post-catalyst utilizing the fast-response FID analyzer. Compared to the baseline spark
timing (AOspark = 00), engine operation with aggressive spark retardation (AOspark = 15') reduced
cumulative converter-in HC emissions, prior to catalyst light-off, by 40% and decreased light-off
times by approximately 5 seconds.
200 C startup, Idle load
0.50
50k Catalyst (100 hrs)
N A
0.45
0.40
C
00
pak
*
AO
A
AO
= -100
v
AO
=
=
-50
-15*
0
E 0.35
w
D
0.30
V
ID
0.25
E 0.00
V
V
0'3
0 23
24
25
26
27
28
29
30
Catalyst Light-off Time (sec) [T1HC = 50%]
Figure 4.18 Cumulative HC mass emissions prior to catalyst light-off as a function of lightoff time following an ambient start. Data shown for various spark modifications
(A0SP) under idle speed and load conditions (Light-off defined as 50% reduction
in HC emissions).
88
CHAPTER 5
EXHAUST SYSTEM MODEL
5.1 OVERVIEW
Time-resolved cylinder-exit exhaust gas temperature, velocity, and mass flow rate
gas
histories were required for the modeling investigation. The thermodynamic state of exhaust
was difficult to measure experimentally therefore, a cycle simulation and exhaust flow simulation
was used to determine the gas state. The exhaust system was modeled as 1-D quasi-steady
was
compressible flow, additional details are provided in Sec. 3.5.2. Exhaust gas composition
of exhaust CO2 , CO, and HC
and direct measurements
estimated from stoichiometry
concentrations. The predicted and measured parameters were used as inputs to drive a plug flow
model of the exhaust system. Exhaust flow, heat transfer, and a detailed chemical kinetic
air/
mechanism were coupled to predict exhaust oxidation as a function spark timing and relative
fuel ratio, Fig. 5.1. The oxidation model employed a two zone, exhaust port and runner, system,
each zone had a specific exhaust geometry and heat transfer correlation, Fig. 5.2.
No of Plugs
n
T
linder-out Conditions
(GT-Power)
mExh
mHC
-
Initial Plug Conditions
A/F
T, H20, CO,, H,, CO, 02 N2, HC
/ Exhaust Geometry
at Zone 'X
Heat Transfer
Auto-ignition Sub-Model
(Senkin)
Chemical
Mechanism
I,
-
Plug 'n' State at Zone X
L, D
n
Figure 5.1
p. V, T, X,
n+1
n+..
Plug flow exhaust oxidation sub-model flowchart with linked engine predicted
cylinder-exit conditions, heat transfer, and chemical kinetic mechanism.
89
ViY
Runner
Port
Figure 5.2
Diagram of exhaust port and runner zones.
5.2 PLUG FLOW SUB-MODEL
5.2.1 MAss ELEMENTS
Plug flow was used to model the transport and chemical reactions of exhaust gas from
of
cylinder-exit to converter-in. The systems was characterized by linear flow rates without zones
5.3.
recirculation. Cylinder-exit gas out flow was discretized into two constant mass elements, Fig.
The first element contained mass expelled during the compressible blowdown period (EVO to 250
ABDC) and the second mass element held mass from the incompressible displacement period (260
ABDC to EVC). Each element was an isolated moving control volume with infinitely fast mixing;
mass
uniform properties with no temperature, pressure, or concentration gradient. The center of
was
and evolution of species were tracked and the linear distance traveled by each mass element
converted to time from bulk momentum averaged velocity measurements predicted by the engine
simulation. As each mass segment evolved, heat transfer to the inner pipe wall was modeled, but
no interactions were allowed between elements, Fig. 5.4.
90
30
2k1
I
I
I
25
Element 1: Compressible blowdown
Element 2: Incompressible displacemenjt
U) 620
CU
W 15
0
C')
co
Cl)
ca
-5
BDC
700
600
500
400
300
2001
EVC
100
0
CA after EVO (deg)
Figure 5.3
Simulation of single-cylinder exhaust mass flow versus crank angle after exhaust
valve opening. Exhaust mass modeled using two elements; mass from
compressible blown process and mass from incompressible displacement.
Exhaust
T
Ucond
OP
i
§ZiPpp
W-------
- -- ---- ---
------Vi
P
M
0
Tgi
Y
- +
V
Mass Element
Figure 5.4
Mass element model details.
5.2.2 INITIAL CONDITIONS
An engine-exhaust simulation generated crank angle (time) histories of mass flow rate,
velocity, and temperature for various engine conditions and exhaust locations. The results were
discretized into two mass elements, Fig. 5.5. Each element had an enthaplic temperature (Eq.
91
F.1.2), momentum averaged velocity (Eq. F.1.3), and exhaust gas composition obtained from the
HC tracking experiments and estimations based on stoichiometry and carbon monoxide (CO) and
carbon dioxide (GO 2 ) measurements.
Exhaust quenching experiments quantified cylinder-exit HC emissions. However, unlike
the time-resolved port and runner measurements, quenching experiments provided an integrated
total. Therefore, cylinder-exit emissions were assumed to have the same profile, but different
magnitude, of HC emissions as the time-resolved exhaust port measurements. Likewise, exhaust
gas hydrogen (H 2) levels were estimated from CO concentrations, Fig. F. 1.1. The highly diluted
reactive mixture contained N 2 , CO 2 , H 2 0, 02, CO, H 2 , HC, and combustion radicals, Fig. 5.6.
These initial conditions and compositions were used to drive the exhaust plug flow oxidation
model.
90 F
400
75
YXHC plug1 X HCplug 2
E
45
E
000
3D
-L
(-D
15-
0
T
plugI
plug2
0
25
80
X MexP
20
60
1
Y,Mexpug 2
15
40
4D
00
VVplug
-20
100
150
1
V
Vplug 2
_________
200
250
300
350
400
Figure 5.5
100
150
200
250
300
350
400
CA (deg)
CA (deg)
Cylinder-exit initial conditions for plug flow model. Data shown from engine
simulation predictions and experimental results.
92
77;1
1.0
N
0.9
2
HC
H 20
H
C
0 0.8
2
CO2
U,
U-
Co
0.7
ffit
MI
Radicals
.--
0.6
0.5
0.o
Figure 5.6
I
I
Case 1
4
Mole fraction of exhaust gas composition for highly diluted reactive mixture of
hydrocarbons.
5.3 EXHAUST SYSTEM HEAT TRANSFER SUB-MODEL
5.3.1 OVERVIEW
Heat transfer was separated into two zones exhaust port and exhaust runner region. The
exhaust port contained regions of complex flows and heat transfer processes. In order to simplify
Eq.
the analysis, convective exhaust port heat transfer was approximated as quasi-steady and 1-D,
F.2.5.
Exhaust port and runner heat transfer was perpendicular
to wall surfaces and
circumferentially uniform. Exhaust component wall temperature fluctuations during the exhaust
and
blowdown period were assumed to have a negligible impact. Therefore, time-averaged port
inner
runner outer wall temperatures was measured, Fig. 5.7, and conductive heat transfer from the
to outer pipe layer was calculated, Eq. F.2.6.
93
3.0 bar n-imep, 1500 RPM, 20 C, X= 1.0, CMCP
900
11 Port Exit Gas [7-cm from EV]
800
I
Flange Surface
E= Runner Gas [37-cm from EV]
=Z Runner Surface
700
600
0
500
.
-1.
&T400
(D
E 300
200
100
15
Spark Timing
Figure 5.7
-15
0
(0 BTDC)
Thermocouple measured exhaust gas and component temperatures for 150,00,
and -15* BTDC spark timings. Steady-state warmed-up exhaust system with 20'
C fluids, 3.0 bar Net-IMEP, 1500 RPM, and X = 1.0.
Depending upon the exhaust valve lift, different mechanisms governed the heat transfer
process in the exhaust port. Caton et aL. [26] noted exhaust port heat transfer for the blowdown
process (low valve lift) was dominated by large scale motion and approximated as convergent,
conical jet flow. High jet velocities produced large scale eddies in the exhaust port, that scaled
approximately with half the port's diameter. [26]. The Nusselt number (Nu) was calculated from a
simple power law empirical correlation using the Reynolds number (Re) based on half of the port's
diameter and a Prandtl number (Pr) of 0.65. During the exhaust displacement period, the Nusselt
number was established from turbulent pipe flow correlations (Pr = 0.65) with empirical constants
CI and C2 for developing flow and pipe roughness. A summary of exhaust port Nusselt number
correlations used during the two exhaust periods is shown in Table 5.1.
94
Table 5.1
Nusselt number correlations for exhaust blowdown and exhaust displacement
period [26].
Exhaust Port s
Nusseft No.
Exhaust Period
Nu 1 = 0.4*Re
Blowdown
0
6
Nu 2 = 1.0{0.0194*C1*C2*ReD 0.8
Displacment
5.3.2 EXHAUST RUNNER
Previous investigation observed that large scale motion was not a significant feature 3
valve diameters downstream from the exhaust valves [26]. Therefore, an empirical convective heat
transfer coefficient for the exhaust runner was calculated using a Nusselt-Reynolds number
correlation for turbulent, fully developed pipe flow. Effects of exhaust pulsations and pipe bends
were accounted for by augmenting factors Fpulse and Fbend, respectively, and used to modify the
Nusselt number, Table 5.2 [27].
Table 5.2
Nusselt number correlations for exhaust runner with argument factors pulses and
pipe bends [26,27].
Exhaust Runner
NUnunner =
1.0{0.0194*C1*C2*ReD 0.8
1.6s Fpe <3.0
214
Fb~, = Nube"t =1+
Re*'4 dbn
Nu
b
5.3.3 AVERAGE EXHAUST HEAT TRANSFER COEFFICIENT
The average exhaust port and runner heat transfer coefficients for mass elements expelled
during the blowdown and displacement process are given in Fig. 5.8. Port heat transfer coefficient
was approximately twice that of the runner for TDC and after ignition timings. Higher engine mass
flow rates with late combustion phasing, resulted in higher velocities and increased exhaust heat
transfer coefficients.
95
Exhaust Port
3500
Exhaust Runner
800
2Z Blowdown Element
700 -
Z] Displacement Element
3000 _
[
Z Blowdown Element
~ Displacement Element
E
60060
C0
0
2500
0
02000
00 15)
-00I
C
F0 1500
B
g (300
pa
500
0 0
-
-400
1b
o
0
~200
=3
0D
40
V
500
~100-0
500
0
0
15
Figure 5.8
Spark Timing
-
Spark Timing
(0 BTDC)
-15
0
15
-15
0
(0 BTDC)
Average port (left) and runner (right) heat transfer coefficient as a function of
spark timings. Data shown for mass elements from exhaust blowdown and
displacement process.
5.3.4 ExHAuST HEAT TRANSFER MODEL VALIDATION
After modeling the cylinder-exit temperatures, energy released from exhaust HC bum-up
2
5.9.
was added as an internal heat source per unit length (W/m ) to the port and runner, Fig.
at
Experimental thermocouple measurements provided time-averaged exhaust gas temperatures
gas
the port exit and runner. Utilizing the engine-exhaust simulation's instantaneous enthalpic
temperatures, the response of the thermocouple sensors were modeled, Fig. 5.10. An energy
transfer
balance was derived for the model assuming lumped capacitance with convective heat
dominating, Eq. F.2.4. For the multi-cylinder engine undergoing a transient startup, the dominant
The
heat transfer rate to the thermocouple was controlled primarily by the Reynolds number.
of
thermocouples were observed to have a first-order time constant with a response time (10-90%)
angle
approximately 1 second. The response of the thermocouples was estimated from crank
transfer
resolved enthalpic temperature data from the model. Port and runner exhaust system heat
multipliers, Cl and C2, and augmentation factors, Fpulse and Fbend, were adjusted until agreement
within AT = 50 K was achieved between temperatures predicted by the time-averaged
96
thermocouple sensor model and direct time-averaged temperature measurements from the
experiments, Fig. 5.11.
There were several possible sources of error with the steady-state experimental
temperature measurements including: radiation losses, end conduction losses, and kinetic energy
gains. Only losses due to radiation were taken into account using the model simulation. The
measured temperatures were obtained by utilizing radiation shielding, thus minimizing losses (AT
= 10 K). Previous investigations by Caton et al. noted that heat transfer losses due to condition of
the wires and kinetic energy can produce measurement errors, but the combined effect was found
to be less than 10 K under similar engine operating conditions [26].
Tport
~
T runner]
j_\
runner
Figure 5.9
Schematic of exhaust port and runner temperature validation of heat transfer submodel. Exhaust port and runner HC oxidation modeled as a heat addition per unit
length. Thermocouple modeled exhaust gas temperature at port exit and runner.
97
Temperatures
3 7 5 0 Therocouple ti:runmer
ex tc2
750.0
--
625.0
-
- -i
5---.0
I---I--
----- -- -
-
375.0
Wall
Thermocouple
250.01
0.00
4.00
3.20
2.40
1,60
0.80
Time [sec]
Figure 5.10 Instantaneous exhaust gas, runner wall and thermocouple temperature as a
function of time. Thermocouple response data shown for hot exhaust component
temperatures.
5
Measured
Model
0
Sp =15 BTDC -- r-
1200 -
Sp=
10-01A-
0
BTDC -- C -
Sp =-15* BTDC----
CIS
CL0
E
<50K
~~AT
,.
-
--
'A.
-
600-A
400-
200-
0 -
0
20
40
6
80
100
120
Distance from exhaust valve seats (cm)
Figure 5.11 Thermocouple exhaust gas temperatures, measured versus modeled, for various
spark timings. Comparison includes heat released due to exhaust system HC
bum-up.
98
5.4 HYDROCARBON OXIDATION SUB-MODEL
5.4.1 OVERVIEW
During the combustion process in a spark-ignition engine, a small fraction of the fuel is
not burned during flame propagation and is stored in cold wall layers (crevices, deposits, oil films
and quench layer). These hydrocarbons emerge from different sources and mix with burned gases
during the expansion and exhaust process. Throughout the cold-start phase, over 100 HC species
of various molecular size, have been identified in exhaust gas. Speciated HC emissions for the
first 63 seconds following a cold-start from a SI engine fueled with Japanese domestic gasoline is
shown in Fig. 5.12.
Exact HC composition depends highly upon the fuel composition, air/fuel ratio, and
engine coolant temperature, but cold-start emissions have generally observed a higher weight
percentage of methane during the initial period following startup [16,17]. Weight percentages of
various hydrocarbons (methane, acetylene, and C 2 and C 4 olefins) were also observed to vary
throughout the engine warm-up period, Fig. 5.13. Kaiser et al. suggested that paraffims, olefins,
and naphthalenes fuel species were converted to low molecular weight, C 2 - C 4 , olefins by C-C
bond scission via thermal decomposition and/or H-atom abstraction during the blowdown exhaust
process [17,18]. These olefins were found to be highly reactive, thus exhaust gas reactivity
increases as the warm-up progresses [17]. Additional HC variations have been attributed to
changes in air/fuel ratio during startup, with insufficient oxygen levels promoting the formation of
methane and acetylene [18].
5.4.2 HYDROCARBON SPECIES
Previous investigations have reported that cold-start engine exhaust gas HC species can
be represented as mixture of 10 wt-% methane (CH 4 ), 30 wt-% n-pentane (C 5H 12), 30 wt-%
ethylene (C 2 H 4 ), 20 wt-% toluene (C 7Hg), and 10 wt-% other species [16-18]. Therefore, a
reactive mixture of these HC was selected to represent the unburned composition with the
following mole fractions: 44 mol-%, C 2H 4 , 26 mol-% CH 4 , 17 mol-% C5 1 2, 9 mol-% C 7H8 , and
4 mol-% of iso-octane (2,2,4-trimethylpentane, C8 H18 ).
99
Ethane(1. 3)
Propa
(1
0/1
Methane(6.5)
MTBE(7.7)
1,2,4-TMBenzene(1.1)
2,3-DMButane
Butane(1.1)
(1.3)
2M-Butane(2.7)
2-MPentane(1.4) " Pentane(1.4)
3-MPentane(1.0)
Hexane(0.9)
Xylene o-(0.8)
p-(0.7)
2,2,4-TM-Pentane
(13.0)
Heptane(1.2)
m-(1.8)
E-Benzene
M-CycHexane(0.6)
2,5-DM-Hexane(0.9)
2,4-DM-Hexane(1.0)
2,3,4-TM-Hexane(2.9)
Toluene
(10.1)
Benzene(3. 1)
Acetylene(5.4)
Ethylene(5.8)
Propene(5.3)
(wt.%)
2M-Propene(5.8)
Figure 5.12 Cold-start SI engine-out speciated HC emissions for initial 63 seconds of engine
operation using Japanese domestic fuel. Source: Yamamoto et al. [16].
100
M
w
80
70
CL
0
60
0
0.
50
w E 40
w 30
20
Ix
10
0
2.5
I
9
x 'x
X~x'
x.~
K
/7;,/"
x'x
X('
34
150
240
480
Time after cold start (sec)
Methane
Acetylene
FC 2 - C4 Olefins
L Alkylbenzenes of Unburned Fuel
[,/
Others of Unburned fuel
FTTI) Other
Figure 5.13 Variation in engine-out hydrocarbon composition as a function of time during
warm-up. Source: Kubo et al. [17].
100
5.4.3 CHEMICAL KINETIC MECHANISM
A detailed chemical kinetic mechanism with elementary reactions was selected to model
the hydrocarbon oxidation process. Comprehensive reaction mechanisms for toluene and isooctane were obtained from literature and combined to simulate hydrocarbon oxidation [24,25].
Each mechanism was validated with experimental data over a wide range premixed and nonpremixed conditions with initial pressures, temperatures, and equivalence ratios similar to those
observed in an engine exhaust system (1-45 bar, 550 - 1700K, and
1= 0.3 - 1.5). The combined
mechanisms contained 973 species and 3849 reactions and was used to model the highly diluted
autoignition chemistry.
The autoignition mechanisms contained low and high temperature pathways for the
oxidation of hydrocarbons. The low temperature mechanism was more complex than the high
temperature pathway Fig. 5.14. Low temperature ignition was initiated by H-atom abstraction or
decomposition of the parent fuel (RH) and forms alkyl radicals (R) which react with 02 to form
alkyloperoxy radicals (ROO). These radicals underwent isomerization (internal H-atom transfer)
forming hydroperoxy alkyl radicals (QOOH). Another 02 addition step led to the formation of
hydroperoxyalkylperoxy radicals (OOQOOH). Chain branching was initiated as an additional
isomerization led to the formation of carbonyl hydroperoxides (O=R'OOH) and OH radicals.
Further decomposition of carbonyl hydroperoxides yields carbonyl radicals (O=R'O) and OH
radicals. At higher temperatures, ROO decomposed back into 02 and R. Hydroperoxy radicals
(HOO)
were formed by 02 addition to H-atoms resulting from hydrogen abstraction.
Recombination of HOO radicals resulted in the formation of hydrogen peroxides (HOOH). At
high temperatures, the pool of hydrogen peroxide (HOOH) decomposes yielding two OH radicals.
The relatively large concentration of OH radicals was response for the first autoignition stage of
hydrocarbons.
101
RH
I+X
R +HX
+02
Low temperature mechanism
High temperature mechanism
1
JrOO
+HOO
ROO
I
02+
OH+
ROOH
+021
Q+
HOO
+02
+
H+Q
+RH (or HOO)
QOOH
1
1+02
RO
OOQOOH
R'(or
0 2)+ HOOH
O=R'OOH
2xOH
branching
O=R'O
Figure 5.14 Hydrocarbon oxidation pathways.
5.4.4 CHEMICAL KINETIC MODEL
Combustion simulations were conducted with Chemkin-II software package. Chemkin is
composed of the interpreter, the thermodynamic database, the linking file, and reaction
mechanism,
Fig. F.3.1.
The forward and reverse
reaction rates for each reaction and
thermodynamic database for the species were taken from the toluene and iso-octane literature.
[24,25]. The plug flow model used a zero-dimensional program called Senkin. The Senkin
application of Chemkin-11 predicted homogenous gas-phase chemical kinetic by solving a system
of time dependent energy and species conservation ordinary differential equations [23]. The
program computed the time evolution of the homogenous gas mixture in a closed system at
constant pressure (-1.013 bar). The adiabatic treatment of the gas mixture (energy equation, Eq.
F.3.1) was modified in Fortran to include the heat transfer sub-routine outlined in Sec. 5.3.4.
102
5.4.5 BURNT GAS RADICAL CONCENTRATION
Burnt gases contained radicals that were critical in the attack of hydrocarbons. Key
radicals such as hydroxyl (OH) radical, hydrogen atom (H), oxygen atom (0), hydroperoxy radical
(HOO), and hydrogen peroxide (HOOH) are responsible for chain branching, chain propagating,
and initiating steps as outlined in Sec. 5.4.3. Therefore, the mass exiting the cylinder was assumed
to contain a homogeneous mixture of unburned and burned gas, with burned gas contained radical
that underwent the time temperature and pressure histories during the expansion stroke, Fig. F.3.4.
Cylinder volume as a function of time during the expansion stroke was used to estimate the initial
super-equilibrium radical concentrations present in burnt gases. Initial pressure and temperature
were obtained at the end of the combustion process and the simulation provide an order of
magnitude estimate for the initial radical concentrations in the exhaust gas at the time of exhaust
valve openening (EVO).
103
104
CHAPTER 6
MODELING RESULTS
6.1 SINGLE-CYLINDER ENGINE
6.1.1 EXHAUST PORT AND RUNNER OXIDATION
A summary of results from single-cylinder HC tracking and exhaust gas temperatures
measurements for various spark timings and relative air/fuel ratios is shown in Figs. 6.1 and 6.2.
These results were compared to the oxidation model predictions for various spark timings and
relative air/fuel ratios, Figs. 6.3-6.6. The unburned mixture from HC sources, crevice volumes,
wall quenching, deposits, and oil layer, were assumed to contain the oxygen and nitrogen
characteristic of the overall relative air/fuel ratio. The reactive mixture was highly dilute with
burned gases containing super-equilibrium concentration of radicals formed during the expansion
process.The computation starts at exhaust valve openening with a specified initial composition and
temperature of the homogeneous mixture at constant pressure. The chemistry sub-model contained
detailed chemical reactions and evolution of all species were tracked. Total HC concentrations
(ppmcl) was obtained by summing the total mole fraction of species containing carbon (C 1 )
excluding carbon monoxide (CO) and carbon dioxide (C0 2) and is reported as the fraction of
hydrocarbon oxidized (R) in the port or runner. Generally, agreement between the port and runner
oxidation observed in the experiments and oxidation predicted by the model was better than 30%.
Measured and mass averaged (enthalpic) predicted temperatures for the exhaust port
oxidation are also shown in Fig. 6.3-6.6. Previous investigations have indicated that massaveraged
(enthalpic) temperatures are generally
10-15%
higher than the time averaged
temperatures obtained with thermocouple sensors [31]. Agreement was achieved between the
model and experiments. Coupling of gas temperature (governed by the heat transfer sub-routine)
and the rate of gas-phase chemical kinetics will be investigated in the sensitivity section. However,
high gas temperatures ensured the low temperature mechanism pathway and the negative
temperature coefficient (NTC) region were avoided.
105
3.0 bar n-imep, 1500 RPM, 20* C, CMCP
70
65
Port
-EZ
EM Runner-
60
Total-
-
55
50
-0
0
S=1.0=1.
45
40
-
-
35
0 30
-.
25
20
15
10
5
0
-15
0
15
-15
0
15
Spark Timing (* BTDC)
Figure 6.1
Relative port, runner, and total exhaust system HC oxidation as a function of
spark timing and relative air/fuel ratio. Data shown for 3.0 bar Net-IMEP, 1500
RPM, 200 C fluids, with intake charge motion (CMCP).
1000
900
3.0 bar n-imep, 1500 RPM, 20* C, CMCP
2= Port (7-cm from EV)
Runner (37-cm from EV)
-
800
CL
700
.. 0
600
-
E
a)
-
500
400
-a
300
200
100
15
0
-15
15
0
-15
Spark Timing (0 BTDC)
Figure 6.2
Measured port and runner exhaust gas temperature as a function of spark timing
and relative air/fuel ratio. Data shown for 3.0 bar Net-IMEP, 1500 RPM, 200 C
fluids, with intake charge motion (CMCP).
106
3.0 bar Net-IMEP, 1500 RPM, x = 1.0, 200 C
1.0, 20* C
3.0 bar Net-IMEP, 1500 RPM, )L
.
*.
1
*1
N
60
1200-
I
.
.
1150
50
1100
1050
0
40
1000
950
0
C
30
''
20
'
'
'
'
'
'S
'
900
t
00
S-
850
U-
800
Experiments
Model
w
*
10
U
750
* Exerimnts Timeaverged
Modl
*(Enhalp-
700
A
015
0
5
10
-5
-10
-15
6L
650:
300k
15
-20
Figure 6.3
5
10
Spark Timing (0 BTDC)
0
-10
-5
-15
-20
Spark Timing (0 BTDC)
Measured and predicted fraction of port reacted hydrocarbons (left) and exhaust
port time averaged and enthalpic gas temperatures (right) as a function of spark
timing. Data shown forX = 1.0, 3.0 bar Net-IMEP, and 1500 RPM.
3.0 bar Net-IMEP, 1500 RPM, X = 1.1, 20* C
50
--
U
*
F-
1200
3.0 bar Net-IMEP, 1500 RPM, X = 1.1, 20 C
*
.'
1
1150
-5
1100
IS
40 k
1050
0
1000
CiL
w
~30 I-
950
900
-
-
>, 20
0
-0
a-
850
-
800
Mdel(Ethap-
750
ct 10
*
*
Exeriets~
Model.
700
9
A,0
300
0
15
10
5
0
-5
-10
-15
15
-20
5
0
-5
-10
-15
-20
Spark Timing (0 BTDC)
Spark Timing (0 BTDC)
Figure 6.4
10
Measured and predicted fraction of port reacted hydrocarbons (left) and exhaust
port time averaged and enthalpic gas temperatures (right) as a function of spark
timing. Data shown for X = 1.1, 3.0 bar Net-IMEP, and 1500 RPM.
107
3.0 bar Net-IMEP, 1500 RPM, X
3.0 bar Net-IMEP, 1500 RPM, X = 1.0, 20* C
1100
Expeiments.
-I
-
50
1050
1000
eme
C
950 -
40
900
I-
0
30
0-
1.0, 20* C
1150
60
C
=
1200
0
C
cc
0
C
-U-
850 800 -
750
700
20
650
-S-
10
.
.
01
15
10
5
0
-10
-5
Experiments (Time averaged)
Model (Enthalpy)
50
.
.
I
6
*
-
550
300
10
15
-20
-15
5
0
-10
-5
-20
-15
Spark Timing (0 BTDC)
Spark Timing (0 BTDC)
Measured and predicted fraction of runner reacted hydrocarbons (left) and
exhaust runner time averaged and enthalpic gas temperatures (right) as a function
of spark timing. Data shown for X = 1.0, 3.0 bar Net-IMEP, and 1500 RPM.
Figure 6.5
3.0 bar Net-IMEP, 1500 RPM, X = 1.1, 20* C
3.0 bar Net-IMEP, 1500 RPM, X= 1.1, 20* C
1200
.
1150
60
1100
Expeiments
Model
50
0
1050
-
-
1000
950
40
900
0
00
850
0
30
800
750
0
T-
a:
20
-
-U
10
-
-0
A
15
700
U
0
650
600
a
550
* Model (Enthalpy)
Experiments (Time averaged)
500:
'I
' I.
10
5
1
0
.
.
-5
1
-10
-15
-20
30 )L
15
10
5
0
-5
-10
-15
-20
Spark Timing (0 BTDC)
Spark Timing (0 BTDC)
exhaust
Figure 6.6 Measured and predicted fraction of runner reacted hydrocarbons (left) and
spark
of
function
a
as
(right)
temperatures
gas
enthalpic
runner time averaged and
RPM.
1500
and
Net-IMEP,
bar
3.0
1.1,
=
X
timing. Data shown for
108
6.2 MODEL SENSITIVITY
6.2.1 GAS TEMPERATURE
Model predictions of the average enthalpic temperatures were investigated to insure the
model adequately predicted the heat transfer processes in exhaust port and runner. Cylinder-exit
conditions drove the heat transfer sub-routine with correlations based upon empirical data. The
model assumes that the wall boundary layer and core gases are well mixed, homogeneous in
temperature and composition. A sensitivity analysis was conducted with AT L100 K gas element
temperatures and the impact on the predicted HC burn up was evaluated, Fig. 6.7.
When temperatures were above 1400 K, hydrocarbon oxidation were consumed in
approximately 1 to 2 millisecond. Kinetic time scales were observed to be much faster than the
exhaust system residence times, that were on the order of tens of milliseconds. At the most
advanced ignition time (Sp = 150 BTDC) a 100 K increase in gas temperature promoted an
addition 25% burn up compared to the baseline condition. Likewise, a reduction of temperature
below 1100 K, resulted in longer carbon conversion times of HC to CO. These times were
observed to be longer than the exhaust port residence time of 2 ms and resulted in a 15% reduction
in HC oxidation. With aggressive spark retarded (Sp = -15* BTDC), temperature in excess of 1400
K showed modest burn up sensitivity (less than 10%) to temperature variations.
Sp = -15* BTDC
AT =+100 K
=
]AT = -100 K
Sp =00 BTDC
Sp =150 BTDC
.S . . .
-30
-20
.... . .
i.... .... . .
-10
10
0
20
30
%-Change in Baseline Oxidation with Reactive Mixture
(44% Ethylene, 26% Methane, 17% n-Pentane, 9% Toluene, 4%
Iso-octane)
Figure 6.7 Effect of gas temperature on exhaust HC oxidation predictions. Data shown with
respect to baseline gas temperatures.
109
6.2.2 EXHAUST SYSTEM TEMPERATURE
All
experiments were conducted with 200 C fluids and hot stabilized exhaust
temperatures. Depending upon air/fuel ratio and ignition timing, the hot exhaust component
temperatures ranged from 300 - 5000 C. An analysis was performed to investigate cold (200 C)
wall temperatures and the impact on the predicted HC bum-up, Fig. 6.8. Cold exhaust component
temperatures increased heat transfer rates 18 - 23%, and were found to have the most significant
(20%) impact on HC burn up for TDC spark timings. Exhaust residence times remained constant,
but reduced temperatures increased the chemical kinetic time scales for the reactions.
Cold Exhaust Wall Temperatures
Sp = -15
0
BTDC
Sp =0 BTDC
Sp =15 BTDC
-50
-40
-30
-10
-20
0
10
%-Change in Baseline Oxidation with Reactive Mixture
(44% Ethylene, 26% Methane, 17% n-Pentane, 9% Toluene, 4% Iso-octane)
Figure 6.8
Effect of cold (20 C) exhaust component temperature on predicted HC
oxidation. Data shown for different ignition timings (Sp) with respect to baseline
HC mixture and hot stabilized component temperatures.
6.2.3 MASS ELEMENTS
The mass expelled during the exhaust period was discretized into 5 and 10 independent
mass elements distributed as a function of time and compared to the baseline case of 2 elements,
Fig 6.9. An increase in the number of mass elements was observed to have no significant impact
(less than 4%) on the model's prediction of exhaust oxidation. However, the increase in the
number mass elements was found to dramatically increase the required computational time.
110
Sp = -15' BTDC
Sp = 0* BTDC
Sp = 150 BTDC
-30
-20
-10
5 Mass Elements
10 Mass Elements
10
0
20
30
%-Change in Baseline Oxidation with Reactive Mixture
(44% Ethylene, 26% Methane, 17% n-Pentane, 9% Toluene, 4% Iso-octane)
Figure 6.9
Effect of the number exhaust mass elements on predicted exhaust HC oxidation.
Data shown with respect to 2 mass element baseline condition.
6.2.4 MIXTURE OF HYDROCARBONS
Three different mixtures of hydrocarbon species representing exhaust emissions were
investigated; the baseline mole fraction mixture (case 1) of 44% ethylene, 26% methane, 17%
pentane, 9% toluene, and 4% iso-octane. Case 2 contained 100% iso-octane and case 3 was a
mixture of 55% ethylene, 35% pentane, and 10% methane, Fig. 6.10. The time for the 50%
conversion of hydrocarbons to either CO or CO 2 was calculated for each of the three cases, Fig.
6.11.
The fastest rate of fuel to carbon conversion was observed for the mixture containing the
highest concentration of ethylene and n-pentane, case 3. The paraffin (n-pentane) was found to be
less stable than the olefins (ethylene), resulting in shorter ignition delay period. Case 3 also had a
reduced mole fraction of methane,
10% compared to the baseline case of 26%. High
concentrations of methane have been observed to retard autoignition [30]. Case 2, neat iso-octane,
a branched paraffin, had the longest fuel destruction time and was attributed to the cracking
pattern. Iso-octane breaks up into iso-butene and other species that form relatively stable radicals,
III
whereas, n-alkanes fragment into ethylene which reacts very rapidly to form highly reactive
radicals such as HCO and HCHO.
1.0
C:
0
0.8
LL
/
0.6
0
C
0
.0
0.4
E.
0
0
r-
X
] Methane (CH 4)
3EEthylene (C2 H4)
~0
EMli Pentane (C.H,)
0.2
0.0
22=Toluene
(CH.)
(55o3osoane
(C.H,)
Case 3
Case 2
Case I
Hydrocarbon Mixture
Figure 6.10 Hydrocarbon mole fraction composition for three cases. Data shown for case 1
with the baseline HC mixture, case 2 is 100% iso-octane, and case 3 contains
55% ethylene, 35% pentane, and 10% methane.
1000
-
-
100
E
10
0
A
*
E
C
A
LL
0.1
A
Case 1 (baseline)
I Case 2:
ICase 3
0.01
0. 60 0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
100orr (K)
Figure 6.11 Calculated half-lives (T5 0 ) of various hydrocarbon mixtures as a function of
temperature for exhaust residence times. Data shown for X = 1.0, 1% HC gas
mixture.
112
The initial HC species selected for the modeling investigation was shown to have a
significant impact on the predicted HC bum up Fig. 6.12. The iso-octane mechanism was found to
impede HC bum-up significantly (60 - 90%) compared to the baseline HC reactive mixture,
worsening as exhaust port residence decreased with additional spark retard. The reactive mixture
of ethylene, n-pentane, and methane was observed to increase the total carbon conversion to CO or
CO 2 by 15 - 35%.
100% Iso-octane
55% Ethylene, 35% n-Pentane, 10% Methane
Sp = -150 BTDC
Sp = 0* BTDC
Sp =150 BTDC
-100-90 -80 -70 -60 -50 -40 -30 -20 -10 0
10 20 30 40
%-Change in Baseline Oxidation with Reactive Mixture
(44% Ethylene, 26% Methane, 17% n-Pentane, 9% Toluene, 4% Iso-octane)
Figure 6.12 Effect of HC mixture on predicted exhaust HC oxidation. Data shown with
respect to baseline mixture: 44% ethylene, 26% methane, 17% n-pentane, 9%
toluene, and 4% iso-octane.
6.3 CARBON MONOXIDE OXIDATION
6.3.1 SECONDARY AIR INJECTION
The oxidation of CO into CO 2 occurs relatively late in the chemical reaction scheme after
all fuel and HC intermediates are consumed. There are several mechanisms responsible for the
oxidation of CO to C0 2 , Fig. 6.13. The major pathway (CO + OH <=> CO 2 + H) for oxidation
occurs once all HC are consumed and the concentration of hydroxyl (OH) radicals increase and
converts CO into CO 2 . The characteristic times for CO oxidation computed for various exhaust
113
relative air/fuel ratios and temperatures (spark timings) are shown in Fig. 6.14. With aggressive
TDC and after ignition timings, the characteristic times for CO to CO2 conversion were found to
be less than the exhaust residence times. The CO oxidation model was also used to predict runner
exhaust gas temperatures for secondary air injection (SAI) experiments, Fig. 6.15. The calculated
adiabatic enthalpic temperatures were within range of measured time-averaged temperatures.
0+ CO(+M)
0
2
-+ CO 2 (+M)
+CO <->0+CO 2
CO+OH <-> C0 2 +H
HO 2 +CO<->OH+CO 2
Figure 6.13 CO oxidation reaction mechanisms.
100
BTDC (730K)
0Sp150
--.-
Sp
00 BTDC
(820K)
Sp -15* BTDC (100KJ)
CO)
0
10
(D
E
o
A
1=
0.8
0.9
1.0
1.1
1.2
1.3
1.4
Exhaust 1
Figure 6.14 Co oxidation time constant as a function of exhaust relative air/fuel ratio (1)
Data shown for three different spark timings (exhaust gas temperatures).
114
600
550
0
500
0-
450
ai)
E
400
-n-
l--
C
--
Measured [time ave]
[enthalpy ave, adiab]
- Model
350
300
0.9
1.0
1.1
*.A
*.
*.
.
1.2
1.3
1.4
Exhaust X
Figure 6.15 Measured time averaged and predicted adiabatic enthalpic runner gas
temperatures as a function of exhaust relative air/fuel ratio (k).
6.4 EXTENSION TO MULTI-CYLINDER ENGINE
6.4.1 EXHAUST FLOW AND HEAT TRANSFER
The single-cylinder oxidation model was extended to a four-cylinder engine configuration
in order to investigate port exit to converter-in HC burn-up. An engine simulation provided
exhaust port exit and converter inlet mass flow rates, Figs. 6.16 and 6.17. The ambient exhaust
system employed the same single-cylinder heat transfer correlations. However, the exhaust event
phasing order (1-3-4-2) resulted in overlap of the displacement and the blowdown process noted in
Fig. 6.16. Therefore, the mass elements expelled by adjacent firing cylinders were combined and
well-mixed at the runner collector, a distance halfway between the exhaust port and the inlet to the
catalytic converter, Fig. 6.18. The single lumped element was taken to have averaged properties
and was homogeneous in temperature and composition.
6.4.2 EXHAUST COMPOSITION
Cylinder-to-cylinder CO, HC, and air/fuel ratio variations were noted in the experimental
investigation of cylinder nos. 3 and 4 (Sec. 4.3.3). Exhaust gas CO and HC measurements
provided initial composition required for cylinders nos. 3 and 4. The remaining cylinders were
assumed to contain an average concentration of the measured emission levels. In order to establish
stoichiometric exhaust conditions, each cylinder was assumed to have an equivalent air flow. A
115
relative air/fuel ratio (X) of 0.94 was recorded for cylinder no. 3, 1.0 for cylinder no. 4, and 1.03
was assigned to cylinder nos. 1 and 2. Mass elements from different cylinders were lumped, wellmixed, and subjected to a step change in air/fuel ratio at the runner collector before reaching the
converter inlet, Fig. 6.19.
Cylinder #4 Exhaust
yliner #
I-oit~ltC~*4b
- -Podt
EMi Cyl
--- Catadyst CdlecWor
-
60
Cylinder #2
Blowdown
50
40
U)
-
230
0
EVC
iEVO
I
-
20
U)
C)
a10
0
'
Y
-
...
x-10
-20
ji
-30
6-7-03b1 .txt-
.
FY.
I
200
100
0
-
.
600
500
400
300
I
700
CA (deg)
Figure 6.16 Cylinder no. 4 port exit and collector-in exhaust mass flow rate as a function of
crank angle.
Cylinder #4 Exhaust
1800
-
-PortExit
CyI 4
--- Catalyst Colector
1600
0ht
~'l
EVO
EVC
.1
Cylinder #2
Blowdown
1400 1Ii
II
ii
II
Ii
a-
E
CO
0
(!J;
1200
I
/
1000
I
I
/
~
1
I
~I -
I
VI
~ /
-,
A
,~/..i
slf
I
\.,
CD
z
W
VJL-
800
w
600
.1
400
0
100
200
300
400
500
600
700
CA (deg)
Figure 6.17 Cylinder no. 4 port exit and collector-in exhaust gas temperature as a function of
crank angle.
116
Perfectly
Stirred
Reactor
-Per
Qwall
Flow
Plug
Sen
nHC
Catalyst
Exhaust Port
Figure 6.18 Diagram of multi-cylinder exhaust system with runner collector mixing.
1.04
I
I
*
.
I
I
1.03
1.02
1.01 0
ca
1.00
- --- Cyl #3
- -- Cyl#4
- --- Cyl#1 and#2
--- ---
-- - -- - ---
0.99
0.98
c:3
-
0.97
0.96
0.95
0.94
0.93
0.93 0
I
10
20
30
.
'40
I
50
Distance from Exhaust Valve Seats (cm)
Figure 6.19 Cylinder relative air/fuel ratio as a function of distance from exhaust valve seats.
117
6.4.3 EXHAUST SYSTEM OXIDATION
The model predicted port exit to converter-in HC oxidation as a function of spark
modification for two cases, Fig. 6.20. The first case used a constant relative air/fuel ratio (X = 1.0)
for all cylinders and an exhaust gas composition based on HC and CO levels measured from
cylinder no. 4. Hydrocarbon species were represented by the baseline reactive mixture (ethylene,
methane, n-pentane, toluene, iso-octane). Exhaust mass elements were phased according to the
multi-cylinder firing order and allowed to combine and mix at the runner inlet before continuing to
the converter inlet. The second case accounted for cylinder-to-cylinder exhaust gas compositional
variations. Each mass element was had a specified relative air/fuel ratio, Fig. 6.19, that was a
function of time (distance) in the plug flow model. The reactive mixture of HC was also used to
model the species present in the exhaust gas. Converter-in enthalpic exhaust gas temperatures were
computed for both cases and compared to time averaged thermocouple measurements, Fig. 6.20.
Agreement between the experiments and model was improved from 30% to 15%. using
the change in air/fuel ratio as a function of time (distance). Additional unburned fuel from cylinder
no 3. and excess oxygen from cylinder nos. 1 and 2 increased the exhaust system oxidation and
exhaust gas temperatures.
118
Idle Load, 20* C, 1 to 20 sec After Startup
I
I
I
.
1100
I
Idle Load, 20* C, I to 20 sec After Startup
.
.
.
0
60
0
1000
-
E50 -o
0
a)
> 40
o
0
W
A
c 700
N
0
-
- 30 -1L-
a)
q)600
0
a- 20 -
500
Experiments
Model (Cyl-to-Cyl)
A Model (Cyl #4).
10
0
080
800
'
'
I
0
-5
-10
A
A
Experiments (Time averaged)
Model Cyl-to-Cyl (Enthalpic)
Model Cyl #4 (Enthalpic)
400
*
'
300
0
-15
Modified Spark Timing (A0,,)
-5
1
1
-10
-15
1
Modified Spark Timing (A05 )
Figure 6.20 Measured and predicted fraction of runner reacted hydrocarbons (left) and
exhaust runner time averaged and enthalpic gas temperatures (right) as a function
of spark timing. Data shown for idle speed and load conditions, I to 20 seconds
after 200 C startup. Model initial conditions based upon air/fuel ratio data from
cylinder nos. 3 and 4.
119
120
CHAPTER 7
SUMMARY AND CONCLUSIONS
7.1
EXPERIMENTS
Experiments were performed to determine the effect of substantial ignition retard on
engine combustion, HC emissions, exhaust feed gas enthalpy, and catalyst light-off. A variety of
experimental techniques quantified hydrocarbon emissions at several exhaust locations, from
cylinder-exit to the catalytic converter inlet, for various spark timings, air/fuel ratios, and fluid
temperatures. The results from the investigations were used to develop a phenomenological model
of exhaust system oxidation.
7.1.1 SINGLE-CYLINDER ENGINE
Single-cylinder experiments were conducted to provide additional insight into combustion
characteristics and HC emission behavior with late spark timings. Detailed mapping of the
combustion process and exhaust composition were performed under fixed engine operation and
cold (200 C) fluid conditions. The following conclusions were based on the results from those
experiments.
1.
A single-zone thermodynamic burn rate analysis indicated combustion was
complete by exhaust valve opening with spark timings as late as -20* before top
dead center (BTDC). Cycle-to-cycle variations increased (up to a maximum COV
of 15%) with aggressive spark retard and were attributed to late phasing of the
combustion event in a rapidly expanding volume (50% mass fraction burned
located 730 after top-dead-center (ATDC)).
2.
For an equivalent combustion stability the use of an intake charge motion control
plate (CMCP) increased the ignition timing limit increasing feed gas enthalpy
rates to the catalyst by more than 60%.
121
3.
A relative air/fuel ratio 10% lean (k = 1.1) yielded 19% lower tailpipe-out HC
emissions than stoichiometric at the same retarded spark timing. Additional
molecular oxygen and high burnt gas temperatures increased the rate of postflame HC oxidation.
4.
Exhaust quenching experiments, using CO 2 , were conducted to evaluate HC
levels exiting the engine at the valve seats. Significant (35%) HC oxidation
occurred in the exhaust port with 00 BTDC spark timings.
4.
Mass based HC levels calculated from time-resolved HC concentrations and
quenching experiments agreed quantitatively with time-averaged HC results.
Substantial HC runner bum-up (40 - 50%) and total exhaust system oxidation (4768%) was observed with -15' BTDC spark timings.
5.
Fuel rich engine operation (Xengine = 0.85) with secondary air injection yielded the
highest catalyst feed-gas temperature, lowest HC emission, and improved
combustion stability compared to stoichiometric and lean operation. At an
equivalent exhaust relative air/fuel ratio (Xexhaust = 1.2), continuous air injected
into the exhaust system was also observed to be more effective in achieving low
tailpipe-out HC emissions and high exhaust gas temperatures than phased air
injection.
7.1.2 MULTI-CYLINDER ENGINE
Multi-cylinder startup experiments were conducted with cold metal exhaust system
temperatures. Combustion stability, feed gas enthalpy, and catalyst light-off was evaluated for
multi-cylinder engine following an ambient startup for four different spark timing modifications.
122
1.
Late spark timings were found to reduce cumulative feed gas HC emissions up to
22% and converter-in sensible enthalpy by a factor of 3 for the engine idle period
(1 to 20 seconds) following ambient start-up.
2.
Engine operation with the most aggressive ignition timing strategy, reduced the
time for catalyst light-off (1 HC=50o/) by 5 seconds (17%) and reduced cumulative
converter-in HC mass emissions prior to light-off by 44%.
3.
Cylinder-to-cylinder air/fuel ratio variations, measured by time-resolved CO and
HC concentrations, were observed to increased as combustion was phased later in
the cycle.
7.2 EXHAUST OXIDATION MODEL
Exhaust system behavior was investigated with a detailed chemical kinetic mechanism
coupled with exhaust fluid flow and exhaust heat transfer. Hydrocarbon tracking and exhaust gas
quenching experiments provided quantitative information that was used in a reacting plug flow
model. Exhaust gas parameters were obtained from an engine cycle simulation and drove the
oxidation model.
1.
Exhaust oxidation was observed to be strongly coupled with exhaust gas
temperature and hydrocarbon fuel species used to represent the unburned fuel in
the chemical mechanism. Fuel destruction times for the conversion of fuel bound
carbon to CO or CO 2 varied by two orders of magnitude depending upon the
highly diluted mixture of hydrocarbons selected.
2.
The mass during the blowdown process
had the highest observed
gas
temperatures and was observed to contain 60 - 80% of the total hydrocarbon
emissions.
123
3.
Oxidation was observed to transition from the exhaust port to the exhaust runner
as ignition timings were phased after top-dead-center. As spark timing was
retarded, the increase in engine flow rate reduced the blowdown element
residence time in the exhaust port from 2 to 0.5 ms. Exhaust gas temperatures in
excess of 1300 K resulted in chemical kinetic time scales of approximately 1 ms
and HC oxidation was observed to occur in the runner.
4.
Cold exhaust component and wall temperatures, compared to hot stabilized
temperatures, were found to increase heat transfer rates by 18 - 25% and reduce
total exhaust system oxidation between 10 - 20%.
5.
The single-cylinder model was extended to a multi-cylinder exhaust system to
investigate port-exit to converter-in HC bum-up. Overlapping port-exit exhaust
flows from adjacent firing cylinders required the model to combine mass elements
in a well-mixed region located at the runner collector.
6.
Agreement between the model and experiments was significantly improved (30%
to 15%) by including cylinder-to-cylinder variations in air/fuel ratio, HC, and CO
exhaust gas concentrations. A step change in the air/fuel ratio occurred at a
distance halfway between the exhaust port and inlet to the catalyst converter.
Additional available oxygen was introduced into fuel rich mass elements resulting
in exothermic reactions. HC bum-up was constrained to a reduced volume,
minimizing heat transfer losses and increasing reaction rates.
124
REFERENCES
1.
Eastwood, P., Critical Topics in Exhaust Gas Aftertreatment, Research Studies Press Ltd.,
UK 2000.
2.
Kollmann K., Abthoff J., and Zahn W., "Secondary Air Injection with a New Developed
Electrical Blower for Reduced Exhaust Emissions," SAE Paper 940472, 1994.
3.
Caton, J. A. and Heywood, J. B., "Models for heat transfer, mixing and hydrocarbon
oxidation in an exhaust port of a spark-ignited engine," SAE Paper 800290, 1980.
4.
Russ, S., Lavoie, G., and Dai, W., "SI Engine Operation with Retarded Ignition: Part 1 Cyclic Variations," SAE Paper 1999-01-3506, 1999.
5.
Russ, S., Thiel, M., and Lavoie, G., "SI Engine Operation with Retarded Ignition: Part 2 HC Emissions and Oxidation," SAE Paper 1999-01-3507, 1999.
6.
Goldwitz, J. "Combustion Optimization in a Hydrogen-Enhanced Lean Bum SI Engine,"
S.M. Thesis, MIT Department of Mechanical Engineering, 2002.
7.
UTG-96 Fuel Properties, Chevron Phillips Chemical Company LLC, October 2004 <http:/
/www.cpchem.com/tdsunsecured/UTG96.pdf>.
8.
Cambustion NDIR-500, October 2004 <http://www.cambustion.co.uk>.
9.
Cheung, H. M. and Heywood, J. B., "Evaluation of a One-Zone Burn-Rate Analysis
Procedure Using Production SI Engine Pressure Data," SAE Paper 932749, 1993.
10. Cheng, W.K., Summers, T., and Collings, N., "The Fast-Response Flame Ionization
Detector," Progress in Energy and Combustion Science, Volume 24, Issue 2, 1998, Pages
89-124.
11. Herrin, R.J., "The Importance of Secondary Air Mixing in Exhaust Thermal Reactor
Systems," SAE Paper 750174, 1975.
12. Borland, M. and Zhao, F., "Application of Secondary Air Injection for Simultaneously
Reducing Converter-In Emissions and Improving Catalyst Light-Off Performance," SAE
Paper 2002-01-2803, 2002.
13. Koehlen, C., Holder, E., and Vent, G., "Investigation of Post Oxidation and Its
Dependency on Engine Combustion and Exhaust Manifold Desing," SAE Paper 2002-01 -
0744, 2002.
14. Heywood, J. B., Internal Combustion Engine Fundementals, McGraw-Hill, New York,
1998.
15. Alkidas, A., "Indication of Fuel Maldistribution in Spark-Ignition Engines," American
Society of Mechanical Engineers Internal Combustion Engine Division, Vol. 24-4, 1995.
125
16. Yamamoto, S., Matsushita, K., Etoh, S., and Takaya, M., "In-line Hydrocarbon (HC)
Absorber System for Reducing Cold-Start Emissions," SAE Paper 2000-01-0892, 2000.
17. Kubo, S., Yamamoto, Kizaki, Y., Yamazaki, S., Tanaka, T., and Nakanishi, K., "Speciated
Hydrocarobn Emissions of SI Engine During Cold Start and Warm-up," SAE Paper
932706, 1993.
18. Kaiser E., Siegl, W., Cotton, D., and Anderson, R., "Effect of Fuel Structure on Emissions
from a Spark-Ignited Engine," Environ. Sci. Technol., Vol. 25 (1991) pgs. 2005-2012.
19. Kaiser, E., Siegl, W., Trinker, F., Cotton, D., Cheng, W., and Drobot, K., "Effect of
Engine Operating Parameters on Hydrocarbon Oxidation in the Exhaust Port and Runner
of a Spark-Ignited Engine," SAE Paper 950159, 1995.
20. Takahashi, H., Ishizuka, Y., Tomita, M., and Nishizawa, K., "Engine-Out and Tail-Pipe
Emission Reduction Technologies of V-6 LEVs," SAE Paper 980674, 1998.
21. Landsberg, G., Heywood, J., and Cheng, W.,
"Contribution of Liquid Fuel to
Hydrocarbon Emissions in Spark-Ignition Engines," SAE Paper 2001-01-3587, 2001.
22. Nakayama, Y., Maruya, T., Oikawa, T. Kawamata, M., Fujiwara, M., "Reduction on HC
Emission from VTEC Engine During Cold-Start Condition," SAE Paper 940481, 1994.
23. Chemkin Collection Release 3.6, "Senkin: A Program for Predicting Homogenneous GasPhas Chemical Kinetics in a Closed System with Sensitivity Analysis", October 2004
<http://www.chemkin.com>.
24. Curran, H. J., Gaffuri, P., Pitz, W. J., and Westbrook, C. K. "A Comprehensive Modeling
Study of iso-Octane Oxidation," Combustion and Flame 129:253-280 (2002).
25. Pitz, W., Seiser, R., Bozzelii, J., Seshadri, K., Chen, C., Da Costa, I., Fournet, R., Billaud,
F., Battin-Lecler, F., and Westbrook, C., "Chemical Kinetic Study of Toluene Oxidation
Under Premixed and Nonpremiexed Conditiions," Manuscript Draft.
26. Caton, J., "Heat Transfer, Mixing and Hydrocarbon Oxidation in an Engine Exhaust Port,"
Ph.D. Thesis, MIT Department of Mechanical Engineering, 1979.
27. ChanS. and Hoang, D., "Modeling of Catalytic Conversion of CO/HC in Gasoline
Exhaust at Engine Cold-Start," SAE Paper 1999-01-0452, 1999.
28. Fox, J., Cheng, W., and Heywood, J., "A Model for Predicting Residucal Gas Fraction in
Spark-Ignition Engines," SAE Paper 931025, 1993.
29. Wu, K., "Chemical Kinetic Modeling of Oxidation of Hydrocarbon Emissions in Spark
Ignition Engines," S.M. Thesis, MIT Department of Mechanical Engineering, 1994.
30. Glassman, I., Combustion, 3rd edition, Academic Press, San Diego, 1996.
31. Caton, J., "Comparisons of Thermocouple,Time-averaged and Mass-Averaged Exhaust
Gas Temperatures for a Spark-Ignited Engine," SAE Paper 820050, 1982.
126
APPENDIX A
BURN RATE ANALYSIS PROGRAM
A.1 ENERGY EQUATION
(A.1.1)
Energy Equation
0
v
y-I
Chemical -
+
"QCrevice + aQHT
00
p- V0
S00
0
where:
Q,_, fuel chemical energy
0
crank angle
y
ratio of specific heat
cylinder pressure
cylinder volume
energy in crevices
heat transfer
p
V
Q.-
A.2 RESIDUAL GAS ESTIMATION
Fox Correlation (modified for a 4-valve engine) [28]
O.F.
1.266*O.F.,
Xresdual
N
in
(A.2.1)
-0.87
D(i
-0.74
PVh J-- +0.632*
*
P
r, P h
P, ,h
O.F.= 1.45 *( 1 0 7 +7.8*AO+A2)
D
*(Lv,max*v
B
B
AO = Deg. of Valve Overlap
A.3 IN-CYLINDER HEAT TRANSFER
(A.3.1)
Woschni Correlation
dQht = A*h*
(T -T.i,)
dt
A = Heat Transfer Area
h =Convective Heat Transfer Coefficient
2PT
h = 3.56* C,* B-
w
228(S-P+uwir)+3
-05 4 6 W,8
c3
2 5 *lO*C
2
127
*TVC*
V
VdJ
I
PIVc
A.4 EXHAUST GAS PROPERTIES
Exhaust gas properties as a function of temperature [3]
x(T)=a + flT + iT
2
where:
T is degrees Kelvin (K)
Table A.4.1:
Viscosity (p), thermoconductiveity (k), and ratio of specific heat capacities (y)
coefficients (pressure of I bar and temperatures 600 - 2000K) used for Eq. A.4. 1.
Jexh
7.280E-05
3.553E-07
-4.399E-1 1
2.326E-03
7.577E-05
-6.797E-09
1.424E+00
-1.833E-04
5.024E-08
(g/cms)
k^,
(J/m*s*K)
7exh
128
(A.4.1)
APPENDIX B
MDS SYSTEM INSTRUCTIONS
B.1 MDS FILE BOOT AND DOWNLOAD
1.
Run the Delco Electronics ITS software, when prompted, keep the system
"off-line". Select "File" then "Unpack and Open" from the main menu,
open the baseline default "ColdriveR3182088.PnG" file.
2.
Select "Open" and the required engine software, boot file, and MDS file
will be copied onto the hard drive in a new directory called
"C:\s I9files\r_03_182" manually copy the baseline engine calibration file
"a3ml82dl.s19" to the "C:\sl9files\r_03_182" directory. Now select:
"File", "Open" and select the "ColdriveR3182088.prj" project file which
will be located in the "C:\s 1 9files\r_03_182\mds" directory. Select "OK"
3.
Make sure that ignition power is off to the ECM harness and disconnect
power to the MDS system. Verify that the MDS XPOD is connected to the
ECM and reconnect power to the MDS and hit the reset button on the
MDS display unit. The MDS system must be powered for the next step.
4.
Select: "Launch", "Instrument Controller Tool" and select the "Boot"
button and select "Open". This will start the Boot procedure for the MDS
system. The Boot procedure will load the MIDS system with the required
configuration files, engine software, and boot files. Note, when the boot
procedure completes the display unit (DU) should contain variable names
and when the ignition power is applied to the ECM the values for the
variable should be displayed.
129
5.
The engine calibration file will have to be downloaded next by selecting
the "Download" button on the "Instrument Controller Tool". Select the
"a3ml82dl.s19" calibration file and make sure that "Dave A File" is
selected for the Destination and "Port A" is selected for the Device. Select
"OK" when the file is selected and the file will be downloaded.
Now,
one can start the engine and view and slew the variables on the MDS
display unit update.
B.2 AIR/FUEL RATIO CALIBRATION MODIFICATION
1.
Using "Caltools", open the calibration file named "A3Ml82D1.S19"
along with the database file "C3182088.dbf'. Linear interpolation
between points is done, never edit the length of the hex file, MS Excel can
be used to modify the table. Any modifications and changes to the
calibration file should be saved under a different file name and should be
fully document by the user. The file then should be download via the ITS
shell as outlined earlier in Appendix B.1.
2.
The air/fuel ratio during a start is called with the F54C, F5 1 D and F65A
tables, Fig. B.2. 1. Table F54C determines the beginning cranking A/F
ratio as a function of start-up coolant temperature. Tables F5 ID and F65A
are the slow and fast "chokes" subtracted from the desired running A/F
ratio (KAFSTCN). They are also looked up as a function of start-up
coolant and decrement from there as a function of time. The fast "choke"
decrements 0.1 of an A/F ratio every 200 ms and the slow "choke"
decrements 0.1 of an A/F ratio every 1.4 seconds. The A/F ratio is
controlled by start-up coolant temp and time, there is no firing event-toevent control.
3.
Closed loop A/F control is achieved after 20 seconds of engine operation
and is controlled by the F124C table which commands an A/F = 14.4 in
130
order to burn an A/F = 14.6. Feed back control can be accelerated by
externally heating the exhaust gas oxygen (EGO) sensor. However, the
threshold voltage output for rich (600 mV) and lean (300 mV) excursions
much be changed by editing the KO2AMAXA table and the EGO timer
table KO2ATIME. Tables KT1A and KT2A must also be changed in
order to achieve a maximum feedback of approximately 5 seconds, Fig.
B.2.1.
The engine using a "6x" encoder system and is synchronized off a TDC
4.
marker (cylinders no. 1 and no. 4) and all injectors fire upon engine
cranking. Paired cylinders are sparked (nos. 1 & 4 and nos. 2 & 3) the
cycle position is determined from spark discharge times differences
between the two fired cylinders.
Above
Closed Loop Control:
Modul: FUELOALD
<Ku2A'' X>windpw must high or low (600mV or 300m\)orfeedbsck)
<<KO2ATChME}> timer to ldok @ 0 sensorvotage
<<KTIA>> change to 1-sec for accel foedback}
<<KT2A> {charge to I-sec for accelfeedback}
-
800MV for feedback
-
2
--
-------------------------------
Notes,
Feedback default is 20 seconds, can accel feedback by ext. supply 12v to EGO for
30-sec and change time to look at along with <<KTlA>> & <<KT2A>>.
5-sec feedback possible with method above, do not leave EGO heating more than 30sec.
Main Choke + Decay
<<F51D>>+ <<F52E>>
Fast Choke
Decay Delay
A/F
Closed Loop Control
(time vs. CLT)
<<F124C>>
(commanded 14.4 to bum 14.61
Crank to Run Blend
<<F696B>>
(% of Run A/F)
Fast Choke + Decay
<<F65A>> + <<KAFT12DC>>
Crank
<<F54C
{#
Run Flag
of ref TDCs above RPM}
Applied
Enleanment
Figure B.2.1
t
Air/fuel ratio as a function time with noted calibration tables controlling A/F
ratio. Closed loop operation with the exhaust gas oxygen sensor (02) noted in top
of figure.
131
B.3 SPARK, RPM, AND IAC CALIBRATION MODIFICATIONS
1.
Spark timing control works same way, a base value will come from F1
(latercalledKtSPRKphiFlSparkAdvance) and FlEXTA tables. It is a
function of engine speed and load. During a start some catalytic converter
light off retard will be applied and it is not a function of cylinder events,
Fig B.3.1.
2.
Cranking spark is fixed by the "calsKwSPRK-phiFTSMAdvance",
KwSPRK_nFTSMLowerLimit,
KwSPRK_n_FTSMUpperLimit,
KRPMUPS, and KRPMDNS. These five calibration variables are a spark
value, a lower window hysteresis pair and an upper window hysteresis is
pair. The window refers to where FTSM (fixed targeted spark mode) will
operate as opposed to runs spark mode. The hardware will not be able to
provide firing event-to-event control.
3.
Idle RPM is controlled by table F13 and is a function of coolant
temperature
4.
Idle air control (IAC) uses the INPTCALD module and is controlled by
two tables. Table F17A controls the IAC stepper position as a function of
coolant temperature during engine cranking and table F10B governs the
position based upon the offset to learned position. Module IDLECALD
sets the stepper stop position (maximum position is 255 counts). Note that
the engine much reach warmed-up (900 C) to learn a position.
132
IAC Controls:
Module: INPTCALD
<cF17A {cd IAC vs. CLT during crank)
FlOB>>{run lAC vs. CLT offset to leamed position}
Ile RPM:
Commanded RPM: <<F3> (CLT vs. RPM)
Module: IDLECALD
<cKIACPARK -- (stepper stop position)
SAIl
<<F100>> (Air pump on time)
Notes:
Max counts: 55
Let enne warnup to lear position
Module: AIRPCALD
<kAiRDLY>> (tume delay for SAl)
Notes: A/F not tied into SAl system, need to
adjust:<<FS1D>
IEnd
ofInjection atdle:<F1II1>I
Blend
<<F81B>>
Spark
Run: F1 Spark Advance + Modifiers
-CLO: <<Fs>> (Cat Lgt Off}
-CLT: <<F81 F>>; <<F82B>>; <<F83B>>
Run Flag
2x
6x crank encoder system
Crank
-Syncs on spark discharge time
-Startup fires all injectors
<<kwSpark-phiFrSadvance>>
{TDC to 5* BTDC)
t
Figure B.3.1
TDC 1&4
Spark timing as a function of time after crank. Tables noted
133
134
.. covco!)
Lambda
CA)
Spark
'MAP -Maimfuel
(BDC
ba),Wh~ib
(BTDC) (bar) (g/se(C)
LRuifrRunner
alknEG
EGT
41
Port
EG
EGT
Tailpipeu C
out HC
(ppm C
ssHC
Of LOc. 50%
-C
etHC
Net,
~MFB-
F
(mg/sec) (g1kg)
IMEP
(%))
('A'CrDC)
(TY,,
(11c)~
0.228
0.265
0.298
0.328
0.373
250
267
305
325
390
415
399
444
503
537
587
619
490
596
675
719
774
814
3816
2700
2031
1830
1710
1632
5.64
4.65
4.08
4.10
4.23
4.59
28.8
20.4
15.3
13.8
12.9
12.3
11
4.9
70
8.0
9.4
12.0
16
37
49
56
63
73
19
24
29
31
33
38
17
24
28
29
31
33
3.00
3.41
0.187
0.212
258
302
481
591
3621
2496
1.1
5-7
17
25
0.241
335
656
1812
14.9
9.3
2
30
0.748
0.270
0.950
4.34
4.86
5.53
0-344
354
387
412
696
747
794
1536
1329
1224
12.7
11.0
10.1
9.4
12.0
13.0
12
34
46
53
20
25
38
5.57
4.37
3.60
3.42
3.31
3.47
29.9
20.6
0.6
393
449
496
529
0.552
0.655
0.744
0.847
3.44
4.00
4.40
4.98
0.196
0.228
0.251
0.283
284
317
344
370
544
3066.
2430
2055
1611
5.38
4.97
4861
4.08
27.4
21.7
18.4
14.4
4-9
9.8
13.0
15.0
1.0
1.0
1.0
1.0
1.0
1.0
12
-1
-7
-10
-13
-17
0.48F 2.88
0.196
0.558
0.660
0.751
0.849
0.950
3.33
3.87
4.34
4.79
5.45
1.1
1.1
1.1
1.1
1.1
1.1
16
3
-3
-6
-9
-12
0.467
0.555
1.2
1.2
1.2
1.2
9
2
-1
-4
0.8W6
0.302
568
608
423
473
499
538
691
656
715
z
0i0% 10-90%
u
u
OuMr0
Oif
-(deo)
(deg)
61
69
31
134
38
32
35
37
27
42
50
58
24
28
32
35
25
3
3
4
0
(
Z
$z
C
R-*
0)
0.463
COV of
Loc.F50% 0-10% 10-90%
Our
Dur
MFB.
(deg)
(ATDC) - (den)
Port
Tailpipe-
533
605
636
687
739
788
820
700
752
794
826
860
2226
996
576
423
303
286.5
3.02
1.57
1.06
0.87
0.70
0.75
16.8
7.5
4.3
3.2
2.3
2.2
1.4
4.1
5.5
7.3
7.9
9.2
18
39
50
59
66
74
19
24
36
44
50
58
18
25
27
29
30
31
RUnner
Runner
sknn
Rune
Lambda Spark MAP Mair Mfuel wall
EGT
skin EGT
(
(
(glsec)
("BTDC) (bar) (glsec)
Q,)
EGTaiup
HC
EGI out HC
(
(
eiHC
ssHC
(mg/sec) (g/kg)
Net- .
IMEP
0
0
1.0
1.0
1.0
1.0
1.0
1.0
10
-3
-8
-13
-16
-20
0.557
0.661
0.755
0.855
0.944
2.63
3.05
3.55
3.99
4.46
5.07
0.180
0.209
0.243
0.273
0.306
0.347
282
326
355
381
393
382
1.1
1.1
0.462
0.557
0.660
0.755
0.852
2.69
3.10
3.56
4.00
4.49
0.167
0.193
0.222
0.249
0.280
487
608
669
716
753
569
662
715
757
794
2442
1002
540
352.5
288
3.37
1.59
0.99
0.72
0.66
20.1
8.3
4.5
2.9
2.4
1.0
4.5
7.3
8.6
11.0
9
34
47
56
65
19
24
32
39
47
17
25
30
33
34
11
16
0.944
5.11
0.318
267
319
350
375
382
391
z
I.
19
2
-4
-8
-12
794
826
219
0.58
1.8
11.0
73
54
35
-
1.2
8
1.2
1
-3
-7
-10
0.554
0.657
0.754
0.853
0.944
3.16
3.58
4.00
4.54
5.13
0.180
0.204
0.228
0.259
0.293
300
327
360
353
385
558
620
672
715
753
610
666
710
748
1 776
1545
855
534
382.5
295.5
2.49
1.56
1.09
0.89
13.8
7.7
4.8
3.4
2,6
4.0
7.7
10.0
12.0
15.0
28
42
52
61
69
24
28
34
41
49
25
31
36
39
40
1.1
1.1
i.2
1.2
1.2
0.77
0
0
C.2 EXHAUST TEMPERATURES
C.2.1 With Charge Motion Control Plate (CMCP)
3.0 bar n-imep, 1500 RPM, CMCP
S
I
I
*
I
*
I
*
900
"
900C
800
U 0
3 700
0E
. 600
AAO
A
0
A
0
-A
Port
U,
500
0
40
20
Runner
E X =1.0
a
X=1.2
A
A
" 400
0
Q0
0
80
60
I 0O
VU
2 800
-
A
a)
700
CL
E
C4
A
600
-
500
010
00
0
2000
A
Cu
=c 400
X
wL
*
0
20
I
*
40
I
*
60
80
1 00
Location of 50% MFB (* ATDC)
Figure C.2.1
Port exit and runner exhaust gas temperatures as function of the location of the
50% mass fraction burned (MFB) for 200 C and 900 C fluid temperatures and
various relative air/fuel ratios. Data shown for 3.0 bar Net-IMEP, 1500 RPM,
with intake charge motion control plate (CMCP).
137
C.2.2 Without Charge Motion Control Plate (CMCP)
I3.0 bar n-imep, 1500 RPM
I
900
I
I
0
900 C
800
"
CL
0
700
N 0
E
*
600
0
0J 500
A
A
0
A
0
Port
Runner
a ?=1.0 0
* X=1.1
0
0
0 A
A
400
x
w 00
A
X=1.2
A
j
Wc
0
I
I
20
40
60
80
100
-900
0
D
800
00
E
c
CL
700
E
600
H
AA
0
.
0
0
AA
CO
cai
500
X
w
2000C
AA
4
-C
0e 0
40
400
0
20
60
40
80
100
Location of 50% MFB (0 ATDC)
Figure C.2.2 Port exit and runner exhaust gas temperatures as function of the location of the
50% mass fraction burned (MFB) for 200 C and 900 C fluid temperatures and
various relative air/fuel ratios. Data shown for 3.0 bar Net-IMEP, 1500 RPM,
without intake charge motion control plate (CMCP).
138
C.3
BURN RATE ANALYSIS: 900, 40*, AND 200
C
400 C Fluids
90* C Fluids
20* C Fluids
-
1.0
-I
EVO_
0.8
V-
EV
EVO
-
0.6
0.4
End o Combusin
-i
0.2
End
of Combustion-
,End of Comnbustio
0.0
0.05
--
0.04
0.03
-0.02
-
0.01
-
-.
t---S
0.00
-0.01
0
20
40
60
80
CA (* ATDC)
100
120
1400
20
40
60
80
CA (* ATDC)
100
120
140 0
20
40
60
80
100
CA (* ATDC)
Figure C.3.1 Cumulative mass fraction burned (MFB) and instantaneous MFB rate as a
function of crank angle for 90*, 400, and 200 C fluids. Operating conditions: 3.0
bar Net-IMEP, 1500 RPM, X = 1.0, spark timing = -P BTDC, without charge
motion (CMCP).
139
120
140
C.4 TIME-RESOLVED HC MEASUREMENTS: 900 C FLUIDS
=1I., 3.0 bar nimep, 1500 RPM, 90' C
16
16
Sp =150 ETDC
212
-
=-
7-= f
BTDC-
-
~Sp=-16* ETC
- 12
.D8
8
4
-I-
0400
0
5000
Port 7-cM f
V
-Pxt 7-cm frnm EV
-
- Port 7-am from EV
- 4000
3000
2000
-
n --
1000
0
0
4000
4000
FRnner
.um ,7- .r , .
-mfrmE
Mw -Mekr
ft
E 3000
]
3000
-
2000
3a
()1000
1000
0
100
200 300 400 500 600 700 0
100 200 300 400 500 600 700 0
CA ( ABDC)
Figure C.4.1
100 200 300 400 500 600 7D
CA (0 ABDC)
In-cylinder pressure and exhaust port and runner time-resolved HC concentration
measurements for three different spark timings (Sp = 15', -1P, -16 BTDC) at 3.0
bar Net-IMEP, k = 1.0, CMCP, and 900 C fluids.
140
0
C.5 HYDROCARBON MASS FLOW RATES
C.5.1 Port and Runner Emission: Spark Timing = 15' BTDC
GT Power simulated exhaust flow rate
GT Power Simulation Analysis
Simulation
Port (7-cm from EV)
Runner (37-cm hrom EV)
30
Data
20-
25
20
Z
15-
15
10
10-
5
0
-5
000
-0
100
-10
0
10
300
200
50
40
CA (dug)
600
350
700
50
450
400
CA (dug)
Hydrocarbon flow rate
Measured FFID Signal (Tdeay Corrected)
100
8000
7000
Location:
.EVO
Dek
Port
Runner
HC_:
5260
4
esaE~c:
4697
3758
CA):
57.4
80
6
Port HC
-
Runner HC. (mgs):
40
M
E
4000
.
S-Std
(g/sec): 2.
20
0
0
(mg/s): 6.o9-Sid: 0.633
60
3000
0
2000
-20
1000
-40
350
Figure C.5.1
450
400
350
500
450
400
500
CA (dog)
CA (deg)
Model results from analysis of time-resolved HC measurements. GT-Power
simulation results of in-cylinder pressure (upper left) and exhaust mass flow rate
at the port exit and runner.(upper right). Measured HC concentrations (lower left)
and predicted HC mass flow rate (lower right). Data shown for 3.0 bar Net-IMEP,
1500 RPM., 150 BTDC spark timing, X = 1.0, and 20' C fluids.
141
C.5.2 Port and Runner Emission: Spark Timing = -1* BTDC
GT Power simulated exhaust flow rate
GT Power Simulation Analysis
-
-
Simulation
Data
I0-
Port (7-cm from EV)
Runner (37-cm from EV)
-
60
so
8
40
-
30
a
6-
20
IL
10
4-
0
2-10
0
0
100
200
400
300
CA (deg)
500
600
350
7000
450
400
500
CA (dog)
Measured FFID Signal (Tdelay Corrected)
Hydrocarbon flow rate
120
6000
Location:
Port
EVO
4515
3656
4523
286
HC.'
Residuali:
5000
Delay (CA):
Runner
50.3
100
-8
Runner HC_
68.
4000
0
Port HC_ (mg/s):
6.61-Sd: 0.448
0
(rrg/):
6.1-Sd: 0.321
0
a
3000
M...
(g/sec):
40
3.24
20
2000[
20
1000
-20
350
400
450
350
500
Figure C.5.2
450
400
500
CA (deg)
CA (deg)
Model results from analysis of time-resolved HC measurements. GT-Power
simulation results of in-cylinder pressure (upper left) and exhaust mass flow rate
at the port exit and runner.(upper right). Measured HC concentrations (lower left)
and predicted HC mass flow rate (lower right). Data shown for 3.0 bar Net-IMEP,
1500 RPM., -I' BTDC spark timing, ? = 1.0, and 200 C fluids.
142
C.5.3 Port and Runner Emission: Spark Timing
-100 BTDC
=
GT Power simulated exhaust flow rate
GT Power Simulation Analysis
Port (7-cm from EV)
Runner (37-cm from EV)
Sknulation
14
Data
A-
so
12
10
cc
8
8
6
4020
4
0
2
-20
0
100
300
200
500
400
600
-
350
700
500
450
400
CA (deg)
CA (deg)
Measured FFID Signal (Tdelay Corrected)
Hydrocarbon flow rate
8000
Location:
Port
Runner
7000
EVO HC:
4715
3179
6000
Residua
6393
3170
16
60.2
Delay (CA):
:
200
Port HC
(mg/s): 9.6-Std:
.O01
150Runner HC
(mg/s):
7.14.Std:
0.524
5000
100
0
M
4000X:
3000
(/sec): 4.43
50.
2000 -
0
1000350
450
400
350
500
CA (deg)
450
400
500
CA (deg)
Figure C.5.3 Model results from analysis of time-resolved HC measurements. GT-Power
simulation results of in-cylinder pressure (upper left) and exhaust mass flow rate
at the port exit and runner.(upper right). Measured HC concentrations (lower left)
and predicted HC mass flow rate (lower right). Data shown for 3.0 bar Net-IMEP,
1500 RPM., -10' BTDC spark timing, X = 1.0, and 200 C fluids.
143
C.5.4 Port and Runner Emission: Spark Timing = -15' BTDC
GT Power simulated exhaust flow rate
GT Power Simulation Analysis
18
-
Port (7-cm from EV)
Runner (37-cm from EV)
-
Simulation
Data
1001
16
O0
14
A
C
12
10
60
40
8
20
2-
0
-20
0
100
500
300
400
CA (deg)
200
600
700
350
450
400
500
CA (deg)
10
Hydrocarbon flow rate
Measured FFID Signal (Tdr y Corrected)
0
900 0
Location:
Port
Runner
EVO HC_:
3576
1626
7625
2218
45.7
48.8
250
700
(mg/s):
HC_ .Port
200
800
Residual
0
Delay (CA):
:
150 -
Runner HC
100-
Ma
9.35-3td: 1.2
(mgs): 4.51.Std: 1
600
EP
0.
0
0
300 0
200 0
100 0
500
0
(g/sec): 5.58
400
50
0
350
450
400
350
500
Figure C.5.4
450
400
CA (deg)
CA (deg)
Model results from analysis of time-resolved HC measurements. GT-Power
simulation results of in-cylinder pressure (upper left) and exhaust mass flow rate
at the port exit and runner.(upper right). Measured HC concentrations (lower left)
and predicted HC mass flow rate (lower right). Data shown for 3.0 bar Net-IMEP,
1500 RPM., -150 BTDC spark timing, X = 1.0, and 200 C fluids.
144
500
C.6
CYLINDER-EXIT QUENCHING
3.0 bar n-imep, 1500 RPM, X = 1.0, 90' C, CMCP
a)
0
I
'C
CT
I
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
9
A
Sp: 150 BTDC
Sp: 00 BTDC
Sp: -150 BTDC
A
A
2%
-.
1
27%A
A
A
83%
-
U
--
4 A A
0.00
U)
.
I
-
-0.05
*AA_
-0.10
x
Z -0.15
0
-
A
*
-
S -0.20
CT
x
o
z
-0.25
-0.30
0.0
0.5
1.0
1.5
2.0
2.5
mCO 2 Quench ImChargeai~fua)
Figure C.6.1
Change in HC and NOx emissions as a function of the ratio of mass of quench
gas to mass of charge (mCO 2 Quench/mChargeair+fuel) for three spark timings with
X = 1.0 and 90 C fluids.
145
C.7 SECONDARY AIR EXPERIMENTS
C.7.1 HC Flow Rate and EGTs: Spark Timing 15' BTDC
Engine X = 0.85, Sp = 150 BTDC, 3.0 bar n-imep, 1500 RPM
6.0
540
5.5
0"
530
- 5.0
-
520
4.5
510
4.0
500
.- I
-
-
490
0
0.
480
3.0
0
--
2.5
470
E
3.5 0
-
460
Ca
-TI-
--
1.5
450
440
1.0
portexit
-
-
(a
- 2.0
-......
0.5
430
-.
-
-I
I
HC
.
'b
0.0
420
0. 8
1.2
1.1
1.0
0.9
1.4
1.3
Exhaust ,
Figure C.7.1
Port exit and runner EGTs and tailpipe-out HC flow rate as a function of exhaust
relative air/fuel ratio. Data shown for continuos secondary air injection at a fixed
engine relative air/fuel ratio (engine = 0.85) and 15' BTDC spark timing.
Engine X = 0.85, Sp =
610
O' BTDC, 3.0 bar n-imep, 1500 RPM
6.0
-5.5
600
5.0
590
4.5
580
/...
A -----
-
570
a)
4.0 :1
0
3.5
560
3.0
a) 550
M.
2.5
3)
E
a)
I
0
2.0
540
1.5
runner
530
1.0
-A-
520
510
HC
0.5
I
0.8
0.9
1.0
1.1
1.2
.
I
1.3
.
I
0.0
1.4
Exhaust X
Figure C.7.2
Port exit and runner EGTs and tailpipe-out HC flow rate as a function of exhaust
relative air/fuel ratio. Data shown for continuos secondary air injection at a fixed
engine relative air/fuel ratio (kegine = 0.85) and 00 BTDC spark timing.
146
Engine X = 0.85, Sp = -150 BTDC, 3.0 bar n-imep, 1500 RPM
I
I
i
i
740
5.5
730
5.0
720
4.5
710
4.0
700
690
W~
6.0
X
0
3.5 M
A
0
3.0
680
a
670 -
E
2.5
_
660 650 640
630
1.5
runne
runnT
--
O--T
1.0
-AHC
620
0.8
aj
2.0 3
0.5
I
0.9
1.0
I
I
1.1
1.2
0.0
1.3
Exhaust X
Figure C.7.3
Port exit and runner EGTs and tailpipe-out HC flow rate as a function of exhaust
relative air/fuel ratio. Data shown for continuos secondary air injection at a fixed
engine relative air/fuel ratio (kengine = 0.85) and -15' BTDC spark timing.
147
148
APPENDIX D
MULTI-CYLINDER STARTUP DATA: 1 TO
D.1 BASELINE CALIBRATION: 00 (AOSpR =
20
SECONDS
00)
D.1.1 In-cylinder Pressure, RPM, MAP, Spark Timing, and Relative Air/Fuel Ratio
2-22-04b2a.xis
2(
7
)
crank:
I
:
20 1 Number
f Cy ):
169.5
1
-. cycles:
_7rtup
12.5
6
4
Cyl #2 nirnep (bar): .18 1 COV (%): 13
Cyl
#1 nimep (bar): 2.47
COV (%): 11
Cyl #3 rnmep (bar): 2.1
V(%): 13
Cyl #4 nimep (bar): 2.081 COV (%): 13
3
-
2
--
-
0
100
-200
CA (deg)
-100
-300
-400
-500
1
2.
Tre
(oc)astercrank:1
to:20
Mean RPM: 10241 sSt 1.9e4002
a
Mean MAP (bar): 038 1std: 0.028
8
c.o
a.
Cl!
0
5
15
10
2E
20
Time (sec)
2
20
crank: 1 to: 20
Mean Spark (dBTDC): 3.581 std: 6.3
Mean Lambda: 0.861 std: 0.072
Tine (sec) after
0
Spark
Lambda
-201
0
5
10
15
20
Time (sec)
Figure D.1.1
In-cylinder pressure, RPM, MAP, spark timing, and lambda (k) as a function of
time after ambient startup. Data shown for baseline spark and fuel calibration
(AOspu = 00). Calculated Net-IMEP and COV of Net-IMEP, averaged RPM,
MAP, spark timing, and X, for 1 to 20 seconds after crank.
149
10.5
25
D.1.2 Hydrocarbon Concentrations, Exhaust Gas and Component Temperatures
x 104
2-22-04b2a.xis
(s4
T
3E
2
nk
-T.n
:20
Slit 3.2e+=0
1.2+004
Mean F F--2 (ppmC1):
0L
0
FFID #1IFFID #2
10
5
0
15
5
20
2
20
25
Time (sac)
600500 4001
300-
-
200-
-
Cy; #1
Cyl #2
Cyl #3
Cyl #4
100 15
10
5
0
Time (sac)
400
Tkme (sac) after crank:
1 to: 20
input::
acvrier
v..
300
Sansdl. Eadial
1st Brick
2nd Brick
Post-Ca
Can
200
E
(kJ): 93.9
HC low input (g): 0.422
HC fow output (g): 0.457
100
---- - - - - - -----
0
-
-
15
10
20
Time (sac)
Figure D.1.2
and converter-in (FFID #2) HC
Time-resolved port exit (FFID #1)
concentrations, port exhaust gas temperature (EGT), and exhaust component
temperatures as a function of time after ambient startup. Data shown for baseline
spark and fuel calibration (AOspark = 00). Calculated sensible enthalpy and
averaged HC concentrations for
1 to 20 seconds after crank.
150
25
D.2 SPARK TIMING MODIFICATION: -5* (AOSPARK = -50)
D.2.1 In-cylinder Pressure, RPM, MAP, Spark Timing, and Relative Air/Fuel Ratio
2-22-04b3a.xis
Time(
7
Z
'S
r crank:
1
to: 20
Number of
Cy
12 I
Starkip
cy cs: 13
6
54-
Cyl #2 nknep (bar): 2.19 1 COV(%): 17
Cyl #1 nirep (bar): 2.
COV (%): 16
0
-100
Cyl #3 nimap (bar): 2.12\CO V (%): Ia
Cyl #4 nimep (bar): 2.12 1 COV (%): 18
3
CL
2-
1L
0
100
-300
-200
-500
-400
CA (deg)
T/e(nea)
-
-----------
-- ---
after crank: I to: 20
_____- Mean RPM: 10611
aid: 24e+002
Mean MAP (bar): 0.38 1
std: 0.034
0
0
b
(L
-RPM
MAP
02
5
Is
10
25
20
Time (sec)
2
4010
20
Tane (sec) after crank: I to: 20
Mean Spark (dBTDC): 3.761 id: 6.8
Mean Lambda: 0.871 ski: 0.086
E
Ol
Spark
Lambda
0
5
15
15
10
20
Time (sec)
Figure D.2.1
In-cylinder pressure, RPM, MAP, spark timing, and lambda (k) as a function of
time after ambient startup. Data shown for -5' spark timing modification (AOspak
= -50). Calculated Net-IMEP and COV of Net-IMEP, averaged RPM, MAP,
spark timing, and X, for 1 to 20 seconds after crank.
151
25
D.2.2 Hydrocarbon Concentrations, Exhaust Gas and Component Temperatures
2-22-04b3a.xis
X10o
3.F
2.5
E
C-
after crank:
I 6: 20
Tint (sec)
Mean FFID #1 (ppmCl): 8.16e+003
Si: 2.4e+003
Mean FFID #2 (ppmCi): 1.18+004
Sid: 3.7e+003
2
1.5
-
0
1-
FF108
FFD#2
-
0.5
0o
15
10
5
-
2
20
5
Time (sea)
GOO 500 -
400
0- 300-
-
200
---
100
0
5
0
I
10
15
Cyl #1
Cyl #2
Cyl #3
Cyl #4
25
20
Time (see)
400 -
Time (sec) after
crank: 1 to: 20
Converter input:
52
Sensible Enthapy (kJ):82.1
300-Pro-Cat
-
200-
E
HC Raw input (9): 0.409
s k
2nd Brick
Post-Cat
HC low outut (g): 0.451
Can
100
0
0
Figure D.2.2
5
15
10
20
Time (sec)
and converter-in (FFID #2) HC
Time-resolved port exit (FFID #1)
concentrations, port exhaust gas temperature (EGT), and exhaust component
temperatures as a function of time after ambient startup. Data shown -50 spark
modification (AOsPark = -50). Calculated sensible enthalpy and averaged HC
concentrations for I to 20 seconds after crank.
152
25
D.3 SPARK TIMING MODIFICATION: -100 (AOsp
10)
=
D.3.1 In-cylinder Pressure, RPM, MAP, Spark Timing, and Relative Air/Fuel Ratio
2-22-04b4a.xis
me (sac
r crank: 1 kx: 20
I Numberaf
s: 159.5 I
Startui
cycles: 125
6
4
Cy
#2 nimep (bar): 2.161 COV (%):
13
Cyl
1nwp (bar): 22
COV (%): 12
Cyl
#3 nimep (bar): 1.0
Cyl #4 nimep (bar): 2.141 COV (%): 13
7
n_
2
100
0
-100
-200
CA (dog)
-300
-400
Time
-500
(sec) after
crank: 1
Wa 20
Mean RPM: 10361 aid: 294002
a
C'
Mean MAP (bar): 0.39 1 std: 0.027
0
-C
Cr
RPM
MAP
5
0
10
20
15
25
Time (sac)
20
1111_
-
20
M
0
after crank: to:,
'''
-
1.5
Time (a"c)
I 20
Mean Spark (dBTDC): 2.711 d: 4.2
Lambda: O.A7
rg/Mean
i
E
std: 0.067
00
-20 L
0
5
-Spark
Lambda
L-
L
10
Is
20
Time (sac)
Figure D.3.1
In-cylinder pressure, RPM, MAP, spark timing, and lambda (?) as a function of
time after ambient startup. Data shown for -10' spark timing modification
(AOspu = -10*). Calculated Net-IMEP and COV of Net-IMEP, averaged RPM,
MAP, spark timing, and X, for 1 to 20 seconds after crank.
153
1
25
.5
D.3.2 Hydrocarbon Concentrations, Exhaust Gas and Component Temperatures
a
2-22-04b4a.xIs
10
3 -E
2.98+003
Meam FFID #2 (pmC1): 9.20+004
SUd 4.5e+003
Ski:
0
-
5
0
3
00
0L 2
00
2
5
Time (sec)
-. - -
00 ~
0
]
FFID #2
20
15
10
FFID #1
--
-
1 00
-----
0'
0
5
#1
#2
#3
#4
25
20
15
10
Cyl
Cyl
Cyl
Cyl
Time (sec)
400
V
Time
Pre-Cat
1st Brick
2nd Brick
Post-Cat
Can
300
200
(sec) afer crank: 1 U]: 20
Converter input::
Sensble Enthaepy (kJ): 42.5
HC Now input (g): 0.442
HC sow output (g): 0.469
100
00
5
15
10
20
Time (sec)
Figure D.3.2
and converter-in (FFID #2) HC
Time-resolved port exit (FFID #1)
(EGT), and exhaust component
temperature
gas
concentrations, port exhaust
startup. Data shown -10' spark
ambient
temperatures as a function of time after
enthalpy and averaged HC
sensible
Calculated
-10").
=
modification (AOspark
crank.
after
concentrations for 1 to 20 seconds
154
j
25
D.4 SPARK TIMING MODIFICATION: -150 (AOSPARK
=
-15*)
D.4.1 In-cylinder Pressure, RPM, MAP, Spark Timing, and Relative Air/Fuel Ratio
2-22-04b5a.xls
kne
8
Cyl #2 r*nep (bar): 2.361 1COV (%):16
Cyl
(sec) aftercrank:
I to: 20
#1nimep (bar):2.51 I
I Number of Cycles: 155 1 Startup cycles: 12.5
V (%):15
Cyl #3 nimep (bar): 2.32
(%): 17
Cyl #4 nimep (bar): 231 COV (%): 17
CL
2
-
-....
U
0
100
-100
-200
CA (dog)
-300
-400
-500
I
Tare (sec) after crank: I1to- 20
-
Mean RPM: 995.41
std: 1.5+0(0
Mean MAP (bar): 0.451 otd: 0.039
0.5
0
a_
cc
1--1 RPM
0
5
MAP
1
-21
10
15
20
25
Tke (sec)
20
2
Tme
5
101
CO
M-
(se)
after crank: 1 to: 20
Mean Spark (dBTDC): -5.121 sid: 2.5
Mean Lambda: 0.89 1
std: 0.055
0
1.6
1.4
0.8
Spark
Lambda
I
15
10
i
20
Time (sec)
Figure D.4.1
1.8
1.2'
-15
-10 zu I
0
-
In-cylinder pressure, RPM, MAP, spark timing, and lambda (k) as a function of
time after ambient startup. Data shown for -15' spark timing modification
(A0spark = -15*). Calculated Net-IMEP and COV of Net-IMEP, averaged RPM,
MAP, spark timing, and X, for 1 to 20 seconds after crank.
155
06
25
D.4.2 Hydrocarbon Concentrations, Exhaust Gas and Component Temperatures
x
2-22-04b5a.xis
104
,3 c
2
E
......
...
...
...
Tine sec ate rar 1to:20
Mow 7FD 1
mprCI :8.7294003
Mea- FF102 (ppmCI): 1.1e+004
Std:2.e+003
FF I1
FFD #02
-
..
0
5
10
15
5
20
25
Time (sec)
I
700
600 -
-
500 --
-
-
400300200-
-
S_----
0
0
5
15
10
Time
---
2
5
(sec) after crank: 1 to: 20
Converter input::
Sensible Enhapy (U): 79.2
HC Gow input (g): 0.492
HC flow output (g): 0.557
Tune
Pre-Cat
300
20
(sac)
400
LD
Cyl #1
Cy #2
CyI#3
Cyl #4
1st Brick
2nd Brick
Pcan
CL
E 200
ID
j__
100
n
0
10
15
20
Time (sec)
Figure D.4.2
Time-resolved port exit (FFID #1) and converter-in (FFID #2) HC
concentrations, port exhaust gas temperature (EGT), and exhaust component
temperatures as a function of time after ambient startup. Data shown -15o spark
modification (AOspark = -15o). Calculated sensible enthalpy and averaged HC
concentrations for 1 to 20 seconds after crank.
156
25
z
z
0
z
Q
z
0
COO
P42
r
cj
IIII,
Q~ I
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i
t.
~P
WI
'
-
I
inP1
tu
v
s
P1
P.
r
04,~
Wl
n-P
M r
l
r-
r1
to M11 n l.
n r
rm r
41
1 9
I-
9I
r
i
I"v
P4i
m~L
.;.
1.,
';'
1
w
-m
i
rrI
i r
ri
i
vI
1,gn MM I
mto
ir, i. inm rin
-T-n - - nririm
Li tv
r$tLL
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ri
to -4P
.)
w i
il
r-
~,qIr) 11
k
ri
a~ i"
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imi .. an
v
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m1 I
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vI
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160
APPENDIX F
EXHAUST OXIDATION MODEL
F.1 INITIAL MODEL INPUT CONDITIONS
Mass of Hydrocarbons
(F.1.1)
EVC
mHC= Evo
HCd0
Enthalpic Average Temperature
_
bulk
(F.1.2)
frhC
b VO
PTd9
Vc
fV0ih C dO
Average Bulk Velocity
Vbulk
I
(F.1.3)
EVC
ith VdO
= EVO
EVC
EVO
Exhaust Gas Mass
Mehaust
(F.1.4)
EVC
KEVO e sexhaust
dO
5
4
3
-0
2
2
Y =O.209 X+0.0302 X
1
-
0
0
2
4
6
8
10
CO (%)
Figure F.1.1
Exhaust gas hydrogen (H2) concentration as a function of CO concentration [14].
161
F.2 HEAT TRANSFER MODEL
Prandtl Number (Pr)
Pr=
(F.2. 1)
0
=0.65
kIpCp
Nusselt Number (Nu)
NuD=
(F.2.2)
hDD
k
Reynolds Number (Re)
(F.2.3)
ReD - pVD
I
where:
ReD
p
V
D
Cp
NUD
k
h
wi
V
Reynolds number
density
velocity
diameter
specific heat at constantpressure
dynamic viscosity
Nusselt number
thermal conductivity
convective heat transfer coefficient
mass reactionrate
kinematic viscosity
Type-K
1mm junction
Radiation Shielding
Exhaust Gas
Figure F.2.1
Schematic of type-k thermocouple and radiation shielding for measuring exhaust
gas temperature.
162
Energy Equation for Thermocouple Sensor
mTCC
dTrc = hA(TflUd -TTC
) + o(flfuid
(F.2.4)
-
where:
m
C
h
A
C
thermocouple mass
thermocouple specific heat
convective heat transfer coefficient
thermocouple heat transferarea
emissivity
a
Stefan-Boltzman constant (5.67e-8 W/m 2 K4)
Ts
Tf
Tw
thermocouple temperature
fluid temperature
wall temperature
Convective Heat Transfer from Gas to Inner Pipe Layer
qgp
(F.2.5)
= hrrdAx(T - T,)
where:
qgp
h
Tg
Tp
heatfluxfrom gas to inner wall
convective heat transfer coefficient
gas temperature
inner wall temperature
Heat Conduction from Inner Pipe Layer to Outer Pipe Layer
qj,
-
2A
(T -kT,)
ln(d 2 /d1 ) '
where:
qio
k
heatfluxfrom inner to outer wall
convective heat transfer coefficient
d2
outer wall diameter
di
Ti
Tp
inner wall diameter
inner wall temperature
outer wall temperature
163
(F.2.6)
F.3 CHEMKIN SOFTWARE
Reaction mechanismov
kdtC
III i
ernview
nami daabas
dic a
i
k=1
Chcnkin iterpreter
wchem.exie
Tsxco
Chekin link fvlm
hea
c het.as
tout
i
pCrChekin
senkin
kcklihbi
oki
input
I'Cet
o u1pu(1
R sef file
restnbina enltrgiyonfile
lIaroctin
iapt
Figure F.3.1
of
--
SENKIN sub-model flowchart
Tt
overview.
Energy Equation
dT
dt
dt
=0
k=
where:
ek
t0
Wk
(F.3. 1)
K
dV
c,--+p-+vYiekbWk
CV
T
t
p
v
&ctaie
specific heat at constant volume
temperature of mixture
time
pressure
specific volume
internalenergy of k-h species
molarproduction rate of khnspecies
molecular weight of ke species
164
3.0 bar Net-IMEP, 1500 RPM, X = 1.0, CMCP
1000
950
Port Exit
-U-
900
--0--Runner
-A-- Bum-up (adiabatic)
850
-
-
800
)
OL.
750
700
-
-0
E 650
--
600
550
Ca
CO
(9
500
CD
450
--
-
.0-
400
-. e--
350
1
1
*
.
*
1
-
01
10
15
20
25
30
35
40
45
50
55
60
65
70
75
Loc. 50% MFB (0 ATDC)
Figure F.3.2
Port, runner, and calculated bum-up exhaust gas temperature as a function of
combustion phasing (location of 50% MFB). Burn-up temperatures are based
upon complete oxidation of HC without the effects of heat transfer in the runner.
Data shown for 3.0 bar Net-IMEP, 1500 RPM, 200 fluids, X = 1.0 with charge
motion (CMCP).
165
3.0 bar Net-IMEP, 1500 RPM, x = 1.0, CMCP
22
20
-.OO
18
15* BTDC
BTDC
-150 BTDC
16
14
0)
.U)
LL
12
---
-
10
07
-
8
----
I
6
4
0
20
40
60
80
100
120
Distance from exhaust valve seats (cm)
Figure F.3.3
Hydrocarbon mass flow rate as a function of distance from exhaust valve seats
for three spark timings. Data shown for 3.0 bar Net-IMEP, 1500 RPM, X = 1.0,
with charge motion (CMCP).
166
10*
3200
-
T(K)
10-1
3000
10,
2800
2600
10,
2400-
-10
-.2200
10
---- -H
H2
0
OH
-4202
2000
10,
-H2M
1800
10
10,
HOO
1600
CH
10,
1400
2
6
4
17
__
8
-a
Go-0
1e
C02S
CH4
10,
----CH20
1
16
-
CH30
16-
-- C2H8
-- -C2H4
s
10-,
C2HS
14
10
a13
10
0-
12
-H
-
~H
HH
52
10,
11
10
10
90
10~
2
Figure F.3.4
4
Time (s)
0ime
3
X 10-3
4
Time (s)
6
7
8
X 10-
Super-equilibrium exhaust gas radical concentrations. Volume-time dependent
Senkin calculation from end of combustion to exhaust valve opening.
167
F.4 SINGLE-CYLINDER ENGINE
F.4.1 Spark Timing = 150 BTDC and X = 1.0
GT-Power Simultian
PFR (enthapy average)
-
1400
-
-
so
1300
GT-Power Simulation
PFR (buk average)
40
1200
30
1100
20
E
10
1000
0
900
-10
800
150
200
300
250
CA (deg)
-
350
150
200
250
CA (deg)
80--
GT-Power Simulation
300
350
GT-Power Sinulation
70-
20
6050-
15
4010
30
30
5
20
10
0-
0
-10-20150
Figure F.4.1
200
250
CA (deg)
300
150
350
200
250
CA (deg)
300
Time histories of cylinder-exit temperature, velocity, mass flow, and hydrocarbon
mass emissions as a function of crank angle. Data shown for X = 1.0 and spark
timing = 150 BTDC.
168
350
100
I-
-- - -L
T(K)|
----
---- -
--
10-,
1550
TEM
1500
83
131
10
1450
REA
10,
1400
R0 W 9
- ECC2 000M
1350
--
-2
H2
0
02
OH
H20
N2
10"
10,6
1300
HCO
N---CO
C02
CH3
10
1250
10 .8
1200
0
1
2
ime
3
10
4
(S)
10
1
0.5
100
3.6
3
2.5
Time (s)
2
1.5
X 10-
4
4.
X 10,
10
CH4
-
10 2
-
10,
10
C2H
C2H2
C2H3
CH30H
CH2OH
CH2CO
-- HCCO
C2H5OH
PC2H4OH
SC2H40H
--104
A
-
H02
H202
CH20
CH30
2H6
-2H4
C2H5
CH2
C2H
-------
/1~~~~
10
10,
0
0.5
1
Figure F.4.2
1.5
2
2.5
Time (s)
3
3.5
4
0
4.5
X 104
0.5
1
1.5
2
2.5
Time (s)
3
3.5
4
Mass element temperature and exhaust gas mole fraction histories as a function
of time for a highly diluted reactive mixture. Data shown for X = 1.0 and spark
timing = 150 BTDC.
169
4.5
x 10-
F.4.2: Spark Timing = 0* BTDC and X = 1.0
100
--0 GT-Power Simulation
PFR (enthalpy average)
E
1400
1200
_
GT-Power Simulation
PFR (bulk average)
50
0
75
E
0."
--
0
1000
800
150
200
250 300
CA (deg)
350
150
200
250
300
CA (deg)
350
100
GT-Power Simulation
30
(D
(D
20
CU
80
CF)
10
___GT-Power
Simulation
60
E
40
0
20
0
0
150
Figure F.4.3
200
250
300
CA (deg)
350
150
200
250 300
CA (deg)
350
Time histories of cylinder-exit temperature, velocity, mass flow, and hydrocarbon
mass emissions as a function of crank angle. Data shown for X = 1.0 and spark
timing = 00 BTDC.
170
10'
100
-------
10
1750
102
FO 2 7.0s3ft4
1700
10,
1650
10
. 0
.2
FF4
I
-H
010
1600
2
-
1550
---
10
1500
10
1450
1400)0
0.5
1
1.5
2
t1mO (s)
,
A
2.5
X 10,
10
-
02
OH
H120
N2
CO
HCO
002
CH3
_
S
.
0.6
-
1.5
1
2
2.5
Time (s)
X 10.
10,
10
-C21-
10
- -
---CH4
H402
H202
CH20
10,
C21H2
CH30
CH3OH
C2H6
C2H4
C2115
CH20H
10
---
10
10
CH2CO
HCCO
C2HSOH
PC2H40H
SC2H40H
CH2
CH
21
1
16
10
0
0.5
Figure F.4.4
1
1.5
Time (s)
2
2.5
0
X 10,
0.5
1
1.5
Time (s)
2
Mass element temperature and exhaust gas mole fraction histories as a function
of time for a highly diluted reactive mixture. Data shown for X = 1.0 and spark
timing = 00 BTDC.
171
2.5
X
10
F.4.3 Spark Timing = -15* BTDC and X = 1.0
-
GT-Power Simulation
PFR fbxk average)
GT-Power Simulation
PFR (enthalpy average)
2000-
1150
lw-
1800
I00
1600.2
E 1400
50
1200
0 -C1000
-50 -200
150
200
250
CA (deg)
300
150
350
2
25
300_
350
CA (deg)
300-
GT-Power Simulation
80
200
70
_
GT-Power Simulation
250 -
60
200-
50
40-
150
E)
30
100
20
10
50
00
150
Figure F.4.5
200
250
CA (deg)
300
350
150
200
250
CA (deg)
300
Time histories of cylinder-exit temperature, velocity, mass flow, and hydrocarbon
mass emissions as a function of crank angle. Data shown for A = 1.0 and spark
timing = -15 BTDC.
172
350
10
2100 J-
T(K)
10
2060
102
2000
108
ACh2
1950
EC
1900
-EAC
1860
000.0025
eO20.00130M~
VA.2 A-S
10
-
000-M
-H2
0H
02
100
10
180(
H~120
--N
!r
I a"
CO
10-7
- 002
CO
175
CH3
10-9
-
170
0
0.5
10
1
time (s)
X
0.4
0.2
0
1
0.8
0.6
1.4
X 10-3
1.2
Time (s)
1073
100
10*
---
10.2
--10-
C2H
C2H2
C2H3
0H30H
CH20H
CH2CO
H02
H202
10
-
HCCO
C2H50H
PC2H4HSC2H40H
10
104[
Figure F.4.6
0.4
0.6
0.8
Time (s)
1
1.2
CH30
-C2H6
--- C2H4
C2H5
CH2
10
100
0.2
CH20
10---
10
0
CH4
CH
10i
0
1.4
X 10-
0.2
0.4
0.6
0.8
Time (s)
1
1.2
Mass element temperature and exhaust gas mole fraction histories as a function
of time for a highly diluted reactive mixture. Data shown for X = 1.0 and spark
timing = -15' BTDC.
173
1.4
X 10,
174