FINAL TECHNICAL REPORT
IEC Grant No.: 06-05a
Title: NOx Emissions From Biodiesel Burned in Utility Generators – Modeling
Principal Investigator: Song-Charng Kong
Grantee Organization: Mechanical Engineering Department, Iowa State University
__________________________________
Signature of PI
Public Abstract
This study performed computer modeling of diesel/biodiesel combustion in large stationary
engines used for utility generation. This work is part of the IEC project awarded to Iowa
Association of Municipal Utilities on burning biodiesel in utility generators. The present
modeling study used stack test results to calibrate computer models that have been developed for
diesel combustion and emissions simulation. The purpose of this study is to use the model as a
tool to explore NOx reduction strategies when biodiesel blends are used in large diesel engines.
Two engines were modeled in this study, including a Caterpillar engine (2 MW) in Winterset
facilities and a Fairbanks Morse engine (2 MW) in Story City facilities. After model validation,
parametric studies were performed to investigate effects of fuel injection timing and exhaust gas
recirculation on NOx emissions reduction. Model results indicate that NOx can be reduced by
retarding the injection timing or increasing exhaust gas recirculation rates. On average, a 20 ~
25% reduction in NOx emissions can be achieved by retarding injection timing for 5 crank angle
degrees. On the other hand, a 25 ~ 35% reduction in NOx can also be achieved per 10% exhaust
gas recirculation rates. Model results indicate that both strategies can be effective. However,
exhaust gas recirculation requires extensive hardware modifications, in particular for large diesel
engines. Therefore, retarding injection timing appears to be a more feasible means to reduce
NOx emissions from burning biodiesel blends in large utility generators.
i
Table of Contents
1. Introduction……………………………………………………………………
1
1.1 NOx Emissions from Biodiesel Combustion ……………………
2
2. Project Objective ………………………………………………….…………
2
3. Computer Models …………………………………………….………………
3
4. Modeling Caterpillar Engine at Winterset Facilities ………………..……
5
4.1 Engine Geometry and Conditions ……………………….………
5
4.2 Model Calibration ………………….. …………………………….
6
4.3 Parametric Study …………………………………………………..
8
5. Modeling Caterpillar Engine at Winterset……………..……………………
11
5.1 Engine Geometry and Conditions ……………………….………
11
5.2 Model Calibration ………………………………………………….
11
5.3 Parametric Study …………………………………………………..
14
6. Summary ………………………………..…………..…………………………
16
7. References………………………………………………………………...……
17
ii
1. Introduction
This work is part of the IEC project awarded to Iowa Association of Municipal Utilities (IAMU)
on burning biodiesel in utility generators. The present work is a modeling study to complement
the engine test that would be carried by IAMU at both Winterset and Story City municipal
facilities.
Particulate matters (PM) and nitrogen oxides (NOx) are the two major pollutants of diesel
engines and can cause adverse effects on the environment and human health. Soot from diesel
engines can cause as much as a quarter of all global warming by reducing the ability of snow and
ice to reflect sunlight (Sato et al., 2003). On the other hand, NOx is a major pollutant of concern
as a component of smog and acid rain, contributing to the formation of ground-level ozone and
contributing to the greenhouse effect. When biodiesel is used in the engine, it is known that
biodiesel combustion produces less PM emissions but more NOx emissions. Previously
published literature has been focusing on laboratory engines or transit buses. Modeling study of
large diesel engines for utility generation is not available and is the subject of study in this work.
Biodiesel can displace petroleum-based fuels and contribute to bioeconomy. However, the
increase in NOx emissions due to biodiesel combustion can limit its application. In Iowa, NOx is
the limiting pollutant for stationary diesel generators. While generator permit types vary, a
typical Iowa Department of Natural Resources (IDNR) air permit (Iowa Administrative Code,
2005), for example, allows a generator to operate up to a certain number of hours per year, or to
burn a certain number of gallons of fuel, based on the expected emissions of NOx predicted from
emissions factors (AP-42 factors, EPA 2005) for specific fuels combined with manufacturer data
about engine performance. There are no emissions factors calculated for biodiesel blends and
there have not until recently been any emissions tests on large stationary engines used for
electricity generation. The lack of emissions data from large diesel generators has been a
significant barrier to utilities wanting to burn biodiesel.
The present modeling study is intended to help determine strategies to reduce NOx emissions
from utility generators burning biodiesel blends. The present computer code consists of various
1
physical and chemistry models to describe the in-cylinder spray combustion process. Multidimensional simulation will be performed including the simulation of flow turbulence, spray
dynamics, vaporization, mixing and chemical reactions within the engine cylinder. This work
will use stack test results to calibrate computer models that have been developed for diesel
combustion and emissions simulation.
1.1 NOx Emissions from Biodiesel Combustion
It has been suggested that the increase in NOx is due to injection timing differences caused by
the low compressibility of biodiesel. Research that used spray chamber testing showed one crank
angle degree shift in using B100, i.e., actual start of injection is earlier (Szybist and Boehman,
2003). The shift in injection timing resulted in an earlier ignition by 4 crank angle degrees that
caused a higher combustion temperature in the cylinder and produced more NOx emissions.
Other research indicates that the increase in NOx emissions is due to the lack of soot radiation
that causes a higher flame temperature in the cylinder when oxygenated fuel is used, such as
biodiesel (Mueller, 2005). In any case, various NOx reduction strategies have been proposed
including retarding the injection timing setting, intake charge cooling, fuel additive and blending,
and the use of exhaust gas recirculation (EGR) to lower the combustion temperature (Yoshimoto
and Tamaki, 2001; McCormick et al., 2002; Szybist et al., 2003). For instance, a recent study by
Minnesota Center for Diesel Research demonstrated that charge-air cooling (from 90 to 40
degree C) was very effective at reducing NOx emissions (by 25%) in a utility engine (Zarling et
al., 2004).
The updated engine performance model will be used to suggest NOx reduction methods for the
test engines. The suggested methods will be examined to consider the feasibility of the engine
hardware.
2. Project Objective
The goal of the present modeling study is to use the test data collected from the stack tests,
performed by IAMU, to calibrate the engine model. The calibrated model will be used to predict
2
effects of injection timing and related engine operating parameters on NOx reduction. Potentially
the model can also be used to predict emissions from other engine geometries in the future.
It is also hoped that the model results, together with stack test data, will provide information to
utilities and regulators to better evaluate their options for controlling NOx emissions. We
disseminate the results from this project through research papers and technical meetings.
3. Computer Models
The computer code consists of various models to describe the in-cylinder fluid dynamics and
chemical reaction processes. The models have been developed over the pasts few years and have
been validated mainly for on-high vehicle engines (Kong et al., 1995; Kong et al., 1999; Kong et
al., 2002). This study will further validate the model predictions using large diesel engines in
power plants that have different geometries and operating conditions.
The computer code was designed to simulate engine combustion that is a transient (due to piston
motion), multiphase (due to liquid spray and gas phases) and turbulent (due to high piston speed)
process with chemical reactions. The major models include the spray atomization, drop-wall
impingement, wall heat transfer, piston-ring crevice flow, combustion, and NOx and soot
formation and oxidation models (Kong et al., 1995; Kong et al., 1999). The RNG k- turbulence
model was used for in-cylinder flow simulations using the standard values for turbulence
parameters as those derived originally.
The combustion model uses multi-step chemical kinetics to describe the low-temperature
autoignition chemistry and high-temperature flame chemistry that are both important to diesel
engine. The reaction chemistry and flow solutions were coupled by using a characteristics time
approach. The turbulence also affects the combustion by property transport, wall heat flux, etc.
Details of the model can be found in the original literature (Kong et al., 1995).
The extended Zeldovich NO mechanism was used to simulate the NO emission process. The
effect of OH radical on NO formation is also considered through the reactions, as listed below.
3
By invoking the steady-state assumption for N radical and using equilibrium approach for O, H
and OH radicals, the formation rate of NO can be obtained as in the following.
O + N2
N + O2
N + OH
NO + N
NO + O
NO + H
R
|S
|T
2
1 NO / K12 O2 N 2
d
NO 2 k1 f O N 2
dt
1 k1b NO / k2 f O2 k3 f OH
d
U
|V
i|W
(1)
Soot emissions are predicted using a phenomenological soot model. Two competing processes
are considered in this model, namely soot formation and oxidation. The rate of change of soot
mass
M s within
oxidation rate
a computational cell is determined from the soot formation rate M sf and soot
M so .
dM s dM sf dM so


dt
dt
dt
(2)
The formation rate uses an Arrhenius expression and the oxidation rate is based on a carbon
oxidation model, described as
dM sf
dt
 Af M fv P 0.5 exp   E RT 
(3)
dM so 6Mwc

M s RTotal .
dt
 s Ds
(4)
Based on the current combustion model, fuel was used as the soot inception species in Eq. (3).
The pre-exponential constant Af was adjusted accordingly for the present implementation and
also to account for the fuel effects, i.e., regular diesel vs. biodiesel blends. On the other hand, the
soot oxidation rate is determined by the Nagle-Strickland-Constable model that considers carbon
oxidation by two reaction pathways whose rates depend on surface chemistry of two different
reactive sites, as in Eq. (4).
4
The combustion and emissions chemistry in the present model was calibrated based on the test
data to account for the characteristics of biodiesel blends. The calibrated was then used to
perform parametric study for NOx reduction.
4. Modeling Caterpillar Engine at Winterset Facilities
4.1 Engine Geometry and Conditions
The engine is a Caterpillar 3516B engine. The specification is listed in Table 1. The baseline
condition has a start-of-injection (SOI) timing of –10 ATDC (after top-dead-center). The
parametric study includes sweeps of EGR and SOI. The engine was run at full load conditions
with 1,825 kW output. The fuel injector has 8 nozzle holes such that the computational domain
only uses 1/8 of the entire cylinder to take advantage of symmetry, as indicated in Fig. 1. The
computational domain contains one fuel spray plume as will be seen in the following figures.
Table 1 Caterpillar 3516B engine specifications
Bore × Stroke
170 mm × 190 mm
Compression Ratio
14:1
Displacement
69 L for 16 cylinders
Connecting Rod Length
392.5 mm
Engine power and speed
185 kW at 1800 rpm
BSFC
204.7 g/kW-hr
Modeling cases:
(1) Baseline
0% EGR, SOI= –10 ATDC
(2) 0% EGR
SOI= –10, –5, 0, 5 ATDC
(3) SOI= –5 ATDC
EGR=0, 5, 10, 15%
5
Cylinder head
Computational
domain
Piston surface
Figure 1 Combustion chamber and the computational domain in this study.
4.2 Model Calibrations for Baseline Case
The present three-dimensional computational fluid dynamics (CFD) model is capable of
simulating fuel spray combustion and emissions inside the engine cylinder. Figure 2 shows the
distributions of liquid fuel spray and combustion temperature on a cross section in the cylinder.
The fuel spray experiences atomization and vaporization, and the fuel vapor mixes with air such
that combustion occurs in the cylinder. It is seen that the fuel spray is surrounded by the
combustion flame as expected in the real engine combustion process. The predicted spray and
combustion processes seem very realistic as compared with existing literature.
Figure 2 Model results of in-cylinder fuel spray and combustion temperature
distributions on a cross section inside the combustion chamber. The fuel spray is
surrounded by the high temperature combustion flame.
6
NOx
Soot
TDC
20 ATDC
50 ATDC
Figure 3 Model results of soot and NOx distributions on a cross section for a sequence
of times. The cylinder axis is located at the left boundary of each plot and only half of
the cylinder cross section is shown.
The present model also includes the chemical kinetics for NOx and soot formation. Figure 3
shows the distributions of soot and NOx on the cross section for a sequence of timing. It is seen
that the NOx forms at the region where there is high combustion temperature since NOx is
sensitive to temperature. Soot is formed in the leading edge of the spray plume where the fuel-air
mixture is rich. The soot cloud is then moved by the in-cylinder flow in a counterclockwise
direction to the squish region later in the engine cycle. Part of the in-cylinder soot will oxidize
later in the engine cycle, as will be seen in Fig. 4.
Since the experimental emissions data are available for B0, the model was further calibrated for
this baseline condition. Figure 4 shows the history of in-cylinder soot and NOx emissions in
lb/MMBTU to be consistent with the engine data. The predicted emissions at exhausts valve
7
open (approximately 120 ATDC) are compared with the engine-out stack measurements. In the
present model formulation, the kinetics rate constant for soot formation was adjusted such that
the engine-out PM emissions was matched. On the other hand, no model constants were adjusted
in the NOx model while the NOx emissions was already well predicted. More engine conditions
using biodiesel blends will be modeled once the experimental data are available.
0.06
5
0.05
Engine Data
PM (lb/MMBTU)
NOx (lb/MMBTU)
4
3
Model Prediction
2
Model Prediction
0.03
0.02
Engine Data
0.01
1
0
-100
0.04
0
-100
-50
0
50
-50
0
50
100
Crank Angle (ATDC)
100
Crank Angle (ATDC)
Figure 4 History of in-cylinder soot and NOx emissions. The predicted emissions at
exhausts valve open are compared with the engine-out stack measurements.
4.3 Parametric Study
Parametric study was performed to investigate effects of EGR and SOI on NOx and soot
emissions. Note that using EGR or retarding SOI are the most common and effective methods to
reduce NOx emissions. This is because the two methods can reduce the combustion temperature
inside the cylinder leading to lower NOx emissions.
Figure 5 shows the predicted NOx and soot emissions, cylinder pressure history and peak
cylinder pressure for various SOI conditions. It is seen that, as injection timing is retarded, the
cylinder pressure decreases resulting in lower NOx emissions but higher soot emissions due to
lower combustion temperatures. An average of 20% reduction in NOx emissions can be achieved
by retarding injection timing for 5 crank angle degrees.
8
10
200
Soot Variation (%)
NOx Variation (%)
0
-10
-20
-30
-40
150
100
50
-50
0
-60
-50
-70
-10
-5
0
5
-10
10
-5
0
Cylinder Pressure and Heat Release Rate vs. Crank Angle
CAT 3500 Full Load 1800 rpm
0% EGR
10
Peak Cylinder Pressure vs. SOI
CAT 3500 Full Load 1800 rpm
0% EGR
15.0
15
1500
1250
SOI-5 EGR 0%
SOI-10 EGR 0%
10
1000
750
5
500
250
Heat Release Rate (J/deg)
SOI 0 EGR 0%
Peak Cylinder Pressure (Mpa)
SOI 5 EGR 0%
Cylinder Pressure (Mpa)
5
SOI (ATDC)
SOI (ATDC)
10.0
5.0
0.0
0
0
-60
-40
-20
0
20
40
-10.0
-5.0
60
0.0
5.0
10.0
SOI (dATDC)
Crank Angle (dATDC)
Figure 5 Predicted NOx and soot emissions, cylinder pressure history and peak cylinder
pressure for 0% EGR with various SOI.
On the other hand, EGR is another effective means of reducing NOx emissions. The EGR rate is
defined as the ratio of re-inducted exhaust gas to the total intake charge.
EGR [%] 
mEGR
100
mintake
(5)
It is an indication of how much exhaust gas is re-inducted to the intake. If exhaust gas is not reinducted into the intake, the EGR rate will be zero. It is known that the specific heat (Cp and Cv)
of H2O and CO2 (exhaust) are higher than O2 and N2 (fresh air). If part of the exhaust gas is
directed to the intake and displacement some of the fresh air, the overall specific heat of the incylinder mixture will be higher. Since the energy release from combustion is the same, a higher
specific heat will result in lower gas temperature rise during combustion. Therefore, NOx
production can be reduced due to low combustion temperature.
9
10
50
40
Soot Variation (%)
NOx Variation (%)
0
-10
-20
-30
30
20
10
-40
0
-50
-60
-10
0
5
10
15
20
0
5
10
EGR (%)
Cylinder Pressure and Heat Release Rate vs. Crank Angle
CAT 3500 Full Load 1800 rpm
SOI -5 dATDC
SOI-5 EGR 10%
SOI-5 EGR 15%
10
1250
1000
750
5
500
250
0
Heat Release Rate (J/deg)
Cylinder Pressure (Mpa)
SOI-5 EGR 5%
Peak Cylinder Pressure (MPa)
1500
SOI-5 EGR 0%
-20
0
20
40
10.0
8.0
6.0
4.0
2.0
0.0
0
-40
20
Peak Cylinder Pressure vs. EGR
CAT 3500 Full Load 1800 rpm
SOI -5 dATDC
12.0
15
-60
15
EGR (%)
60
0.0
5.0
Crank Angle (dATDC)
10.0
15.0
EGR (%)
Figure 6 Predicted NOx and soot emissions, cylinder pressure history and peak cylinder
pressure for SOI= –5 ATDC with various EGR.
Figure 6 shows the predicted engine data of using different levels of EGR. Results are consistent
with the understanding of EGR that NOx emissions decrease with increased EGR.
Approximately a 35% reduction in NOx by increasing EGR by 10% was predicted. It is of
interest to note that NOx emissions decrease significantly while the engine cylinder pressure
does not decrease noticeably. Also note that the increase in soot emissions by using EGR is not
as significant as retarding the injection timing.
Note that the stack test data for B20 and B100 are recently available and the modeling is
currently being performed for the two biodiesel blends. Modeling results will be presented in the
final report as the parametric study data are available for B20 and B100.
10
20.0
5. Modeling Fairbanks Morse Engine at Story City Facilities
5.1 Engine Geometry and Conditions
The present computer model was also used to simulate the combustion and emission process of
the Fairbanks Morse engine in Story City facility. The engine geometry and operating conditions
are provided by Fairbanks Morse Engine. The engine is a two-stroke engine and each cylinder
has two opposed pistons compressing against each other, as shown in Fig. 7. The combustion
chamber is at the middle section of the cylinder where the fuel injectors are located. Each
cylinder has two fuel injector that produce hollow-cone sprays. The entire fuel injection process
was modeled as well as the combustion process.
Top piston
Injector #1
Injector #2
Bottom piston
Figure 7 Geometry and computational mesh of the Fairbanks Morse engine.
5.2 Model Calibrations
The model was calibrated for the baseline case ( 720 rpm, 0% EGR). A sequence of combustion
images with in-cylinder details (fuel spray distribution and combustion temperature) are shown
in Fig. 8. It is seen that the two injectors issue fuel spray from the side the cylinder wall toward
the center. Some of the liquid drops impinge on the piston surface while pistons are compressing
against each other. Auto-ignition occurs at the leading edge of the spray plumes and temperature
11
rises causing liquid fuel continuing to vaporize. Soon after ignition, the entire fuel spray is
engulfed in the flame. As time goes by, two flames merge and combustion spreads across the
majority of the combustion chamber. The model predicts that combustion is still confined in the
center of the combustion chamber with the present two-injector setup, as indicated by the high
temperature contours.
Figure 9 shows the predicted in-cylinder pressure and temperature histories. The ignition occurs
near top-dead-center and the peak cylinder pressure occurs at the early stage of piston expansion.
The predicted NOx and soot histories are also shown in Fig. 9. The model was calibrated using
the stack test results. Comparisons of measured and predicted NOx and soot emissions for B0,
B20 and B100 are shown in Fig. 10. The soot formation rate constant in Eq. (3) is adjusted for
different fuel blends.
12
(No combustion yet)
(Combustion has started)
(Combustion of two fuel spray merges and
spread over the combustion chamber.)
Figure 8 Predicted fuel spray and combustion temperature in the cylinder at different
views for a sequence of timing.
13
FM Engine
FM Engine
6
Pressure
Temp
70
35
60
5
NOx
1000
2
500
50
25
40
20
30
15
20
10
Soot
1
10
5
0
0
0
-100
-50
0
50
Soot (g/kg-f)
3
30
NOx (g/kg-f)
1500
4
Gas Temperature (K)
Cylinder Pressure (MPa)
40
2000
0
100
-40
-20
Crank Angle (TDC)
0
20
40
60
80
100
Crank Angle (TDC)
Figure 9 Histories of in-cylinder pressure, average combustion temperature, NOx and
soot emissions.
FM Engine
FM Engine
3
NOx - Test
NOx - Model
Soot - Test
Soot - Model
0.25
Emissions (lb/MMBTU)
Emissions (lb/MMBTU)
2.5
0.3
2
1.5
1
0.5
0.2
0.15
0.1
0.05
0
0
0
20
100
0
Biodiesel Blend (%)
20
100
Biodiesel Blend (%)
Figure 10 Comparisons of test data and model prediction for NOx and soot emissions
after model calibration.
5.3 Parametric Study
After model calibration for different fuel blends, parametric study was performed to investigate
effects of EGR and SOI on NOx and soot emissions for B20 and B100. Results are shown in Fig.
11.
By delaying the fuel injection timing from –5 ATDC to 0 ATDC, approximately 25% reduction
in NOx can be obtained for both B20 and B100. Further retarding injection timing can benefit
14
NOx reduction for B20 but no further NOx reduction was predicted for B100. On the other hand,
for using EGR, an average of 25% reduction in NOx per 10% EGR can be achieved. Such effects
of EGR on the reduction in NOx are similar for both B20 and B100.
Although EGR seems to be more effective and consistent in reducing NOx emissions for B20
and B100, the increase in soot emissions is more significant for EGR cases. In addition,
considering the requirement in hardware modification to implement the EGR system, retarding
the injection timing by 5 crank angle degrees seems to be a more feasible means for NOx
reduction for burning biodiesel blends without significant penalty of soot emissions.
B20
B100
20
60
10
40
Emission Variation (%)
Emission Variation (%)
Soot increase
0
-10
-20
-30
NOx reduction
-40
Soot increase
20
0
NOx reduction
-20
-50
-60
-40
-5
0
SOI (ATDC)
5
10
-5
0
B20
5
10
B100
150
150
100
100
Soot increase
Emission Variation (%)
Emission Variation (%)
SOI (ATDC)
50
0
NOx reduction
-50
Soot increase
50
0
NOx reduction
-50
-100
-100
0
5
10
15
20
25
30
35
0
EGR (%)
5
10
15
20
25
30
35
EGR (%)
Figure 11 Predicted NOx and soot emissions, cylinder pressure history and peak
cylinder pressure for SOI= –5 ATDC with various EGR.
15
6. Summary
The present computer models were validated by emissions test data for a Caterpillar engine and a
Fairbanks Morse engine used in municipal facilities. Trends of soot and NOx emissions for
different biodiesel blends are predicted by the model. Parametric studies were performed to
investigate effects of fuel injection timing and exhaust gas recirculation on NOx emissions
reduction.
Model results indicate that NOx can be reduced by retarding the injection timing or increasing
exhaust gas recirculation rates because both methods can create a lower combustion temperature
environment that can reduce NOx formation. For the Caterpillar engine studied, an average of
20% reduction in NOx emissions can be achieved by retarding injection timing for 5 crank angle
degrees. On the other hand, a 35% reduction in NOx can also be achieved per 10% exhaust gas
recirculation rates. For the Fairbanks Morse engine, by delaying the fuel injection timing from –5
ATDC to 0 ATDC, approximately 25% reduction in NOx can be obtained for both B20 and
B100. In using exhaust gas recirculation, an average of 25% reduction in NOx per 10% EGR can
be achieved but with significant penalty in soot emissions.
Model results indicate that both NOx reduction strategies can be effective. However, exhaust gas
recirculation requires extensive hardware modifications to the intake and exhaust manifolds, the
cost may be significant, in particular for large diesel engines. Therefore, it is concluded that
retarding injection timing would be a more feasible means to reduce NOx emissions from
burning biodiesel blends in large utility generators.
16
7. References
EPA, Research Triangle Park, North Carolina, Compilation of Air Pollutant Emissions Factors,
AP-42 Fifth edition, Volume 1, stationary point and and area sources, January 2005. Website:
http://www.epa.gov/ttn/chief/ap42/index.html
Iowa Administrative Code, Section 567, Chapters 20-32. Iowa Administrative Rules for Air
Quality, 2005.
Kong, S.C., Han, Z. and Reitz, R.D. “The Development and Application of a Diesel Ignition and
Combustion Model for Multidimensional Engine Simulations,” Journal of Engines, Vol. 104, pp.
502-518 (1995).
Kong, S.C. and Reitz, R.D. “Multidimensional Modeling of Diesel Ignition and Combustion
Using a Multistep Kinetics Model,” J. Engng Gas Turbines Power, Vol.101, pp.781-789 (1993).
Kong, S.C., Senecal, P.K. and Reitz, R.D. “Developments in Spray Modeling in Diesel and
Direct-Injection Gasoline Engines,” Oil & Gas Science and Technology – Rev. IFP, Vol. 54, No.
2, pp. 197-204 (1999).
McCormick, R.L., Alvarez, J.R., Graboski, M.S., Tyson, K.S. and Vertin, K. “Fuel Additive and
Blending Approaches to Reducing NOx Emissions from Biodiesel,” SAE 2002-01-1658, 2002.
Mueller, C., Private Communication, Combustion Research Facilities, Sandia National
Laboratory, Livermore, CA, 2005.
Sato, Mki., J. Hansen, D. Koch, A. Lacis, R. Ruedy, O. Dubovik, B. Holben, M. Chin, and T.
Novakov. Global atmospheric black carbon inferred from AERONET. Proc. Natl. Acad. Sci.
100, 6319-6324, doi:10.1073/pnas.0731897100, 2003.
Szybist, J.P. and A. L. Boehman “Behavior of a Diesel Injection System with Biodiesel Fuel,”
SAE 2003-01-1039, 2003.
17
Szybist, J.P., Simmons, J., Druckenmiller, M., Al-Qurashi, K., Boehman, A.L. and Scaroni, A.
“Potential Methods for NOx Reduction from Biodiesel,” SAE 2003-01-3205, 2003.
Yoshimoto, Y. and Tamaki, H. “Reduction of NOx and Smoke Emissions in a Diesel Engine
Fueled by Biodiesel Emulsion Combined with EGR,” SAE 2001-01-0649, 2001.
Zarling, D.D., Bickel, K.L., Waytulonis, R.W. and Sweeney, J.R. “Improving Air Quality by
Using Biodiesel in Generators,” SAE 2004-01-3032, 2004.
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