Fuel Unmixedness Effects in a Gasoline HCCI Engine
IVO
(358°)
= Intake Valve Open
301°
361°
EGR
469°
25
86 mm
Stroke
94.6 mm
EVO
131 aTDC
IVO
350 aTDC
5
EVC
375 aTDC
IVC
595 aTDC
Engine Test Cell Setup
Unmixed
0
6
Optical Engine
0.0
Vaporized Fuel
f = -500 mm
Plano-Concave
Cylindrical
Lens
0.5
Peak Pressure (kPa)
Peak Pressure (kPa)
4000
3500
3000
2500
2000
To Engine
300
UG5 Schott
Glass Filter
1.0
0
1.5
2.0
Injection Timing Effects
Heated
Air + EGR
f = 1000 mm
Plano-Convex
Spherical Lens
310
320
330
Intake Charge Temperature (°C)
10
3500
8
3000
2500
Beam Stop
90° Turning
Prism
Nd:YAG Laser
Optical Setup for PLIF Experiments
Pellin-Broca
Prism
0
100
200
95
90
85
10 mg/cycle
7 mg/cycle
5 mg/cycle
Open = Port
Closed = Premixed
25
Premixed
724° bTDC
364° bTDC
256° bTDC
196° bTDC
140° bTDC
94
5
2400
2200
2000
325
350
375
Intake Charge Temperature (°C)
50
0
10
15
0
5
10
15
CA50 (° aTDC)
2400
2200
2000
1800
100
 = 0.75
 = 0.6
 = 0.5
Open = Port
Closed = Premixed
250
95
200
150
100
50
90
0
0
85
5
10
15
CA50 (° aTDC)
80
0
5
10
15
CA50 (° aTDC)
• No changes in combustion observed between premixed and port fueling.
• NOx emissions were near zero for all conditions because of high EGR rate at the 5
mg/cycle fueling condition
• Decreasing the equivalence ratio (increasing air flow, decreasing EGR at constant
fueling rate) leads to an increase in CO emissions but a decrease in the difference in CO
emissions between premixed and port fueling.
2
98
95
100
2600
4
0
30
96
5
150
2800
6
2000
99
97
2600
1800
4000
0
Dichroic
Mirror
2000
2
Effects at Varied Equivalence Ratios
2800
0
Port, Prevaporized Fuel Injector
2500
4
• No changes in combustion observed between premixed and port fueling.
• Significant NOx emissions increases only observed in 10 mg/cycle fueling. NOx
emissions were near zero for the 7 and 5 mg/cycle fueling conditions due to high EGR.
• The difference in CO emissions between premixed and port fueling increases with
decreasing fueling rate.
2
2.3
mm ID
Tube
3000
6
CA50 (° aTDC)
• For the most retarded injection timing,
regions exist in the cylinder with
equivalence ratios that differ from the
mean by +/- 50%.
724° bTDC
364° bTDC
256° bTDC
196° bTDC
140° bTDC
4
Imaging
Mirror
Intake
Valve
375
3500
0
• Fuel unmixedness increases with
retarded injection timings except for
the EoPI = 256° bTDC injection timing,
which is less unmixed than the EoPI =
364° bTDC injection timing.
10
Bore
350
0°
(TDC – Cycle of Interest)
• A significant level of unmixedness is
created with prevaporized port fueling.
Homogeneous
15
Engine Properties
10.95
325
8
Crank Angle (° bTDC)
20
CR
180°
(BDC)
Peak Pressure (kPa)
Engine
360°
(TDC Exhaust)
EINOx (g/kg)
Exhaust
1500
364°
300
Combustion Efficiency
Surge
Tank 2
2000
724°
720°
(TDC – Previous Cycle)
PDF
Port Fuel
Injection
Point
2500
Intake Charge Temperature (°C)
Bowditch
Piston
Extention
Drop-down
Liner
256°
3000
Peak Pressure (kPa)
Sapphire
Piston
Window
829°
196°
EICO (g/kg)
Premixed
Fuel Injection
Point
Quartz
Cylinder
Window
IVC
(135°)
140°
3500
Combustion Efficiency
Cylinder Head
AIR
Surge
Tank 1
245°
Peak Pressure (kPa)
Experimental Facilities
IVC
(855°)
4000
4000
EINOx (g/kg)
• Injection crank angle locations (detailed below) corresponded to those detailed
in metal engine experiments.
Peak Pressure (kPa)
• Level of fuel unmixedness created when using the port, prevaporized fuel
injection was investigated optically using fuel tracer planar laser-induced
fluorescence (PLIF).
• Quantify the effect fuel unmixedness has
on gasoline HCCI combustion.
Inline Heater
Effects at Varied Fueling Rates
EICO (g/kg)
Level of Fuel Unmixedness
EICO (g/kg)
Objective
Faculty: D.E. Foster, J.B. Ghandhi
Combustion Efficiency
Students: R.E. Herold, R.J. Iverson (MS, 2004)
20
15
Conclusions
10
5
0
10
CA50 (° aTDC)
15
0
5
10
15
CA50 (° aTDC)
• Variations with respect to intake charge temperature due to heat transfer in intake port.
• All combustion metrics investigation (i.e., peak pressure, combustion efficiency) show that
at a given combustion phasing (CA50) premixed and prevaporized port injection are
indistinguishable.
• NOx emissions increase with fuel unmixedness, resulting from regions richer than the
mean which burn hotter after autoignition.
• CO emissions show a slight increase with fuel unmixedness, possibly a result of regions
richer than stoichiometric or quenching in regions leaner than the mean.
University of Wisconsin Engine Research Center
• Fuel unmixedness in the absence of thermal and residual unmixedness had no
effect on the HCCI combustion.
• Small changes in CO and NOx emissions were observed for the port fueling,
which were attributed to the regions in the charge that were either locally richer
or leaner than the mean equivalence ratio.
• At a given operating condition the CO and NOx emissions are the lowest for a
fully homogeneous fuel distribution. Regions locally richer and leaner than the
mean equivalence ratio lead to increases in NOx and CO and therefore should
be avoiding in an HCCI engine.
• Fuel unmixedness in the absence of thermal and residual unmixedness does
not appear to be a viable method for gasoline HCCI combustion control.