Effects of Biodiesel on NOx Emissions
Bob McCormickNational Renewable Energy Laboratory
Golden, Colorado
ARB Biodiesel WorkgroupJune 8, 2005
NREL/PR-540-38296
Advantages of Biodiesel
Inherent advantages of diesel engines:•Up to 40% (or even higher) improved efficiency relative to gasoline•Inherently very low hydrocarbon emissions (both tailpipe and evaporative)
B20 Blends:•Reduce life-cycle petroleum consumption by 19%•Reduce life-cycle CO2 emissions by 16%•Further reduce hydrocarbon emissions by 20%•Reductions in PM emissions
Biodiesel’s Effect on Emissions – Older Engines
EPA analysis:•data from many studies•engine models through 1997
•NOx•No change for B5•2% up for B20•10% up for B100
•PM•5% down for B5•12% down for B20•48% down for B100
Analysis from EPA420-P-02-001, October 2002
Newer Engines (2004 compliant): B20 = +4%, B100 = +30%Typical Older Engines (thru 1997): B20 = +2%, B100 = +10%
Analysis for Pre-1998 Engines from EPA420-P-02-001, October 2002
Biodiesel’s Effect on NOx Emissions-Engine Data
NOx Reduction Strategies
Injection timing retard:• Can eliminate NOx increase for pre-1998
engines• Reduces or eliminates PM benefit • Can reduce fuel economy• Requires engine certified on and
dedicated to biodieselGraboski & McCormick, Progress in Energy and Combustion Science, 24 125 (1998).
Cetane increasing additives
Use of more highly saturated biodiesel
Percent Change in PM versus No. 2 Diesel-20 -10 0 10 20
Perc
ent C
hang
e in
NO
x ve
rsus
No.
2 D
iese
l
-4
-2
0
2
4
B20
B20 + Timing Retard
1987 Cummins L101987 Cummins N14
Cetane Additives for Reducing NOx
Volume Percent DTBP or EHN0.0 0.5 1.0 1.5 2.0
NO
x Em
issi
on, g
/bhp
-h
4.5
4.6
4.7
4.8
4.9
5.0
Cert Fuel NOx
DTBP 2-EHN
For testing in older engines:•Effective for soy B20•NOx reductions significant at 95% confidence or greater•No change in PM emissions or fuel economy
Data from SAE 2002-01-1658
Cetane Additives for Reducing NOx
BP15 B20 B20+EHN
Pol
luta
nt E
mis
sion
, g/b
hp-h
0.0
0.5
1.0
1.5
2.0
2.5NOxHCx10COPMx10
BP15 B20 B20+EHN
Pollu
tant
Em
issi
on, g
/bhp
-h
0.0
0.5
1.0
1.5
2.0
2.5NOxHCx10COPMx10
2002 ISB
2003 S60
No significant effect observed for B20 in 2004 emission standard engines
Data from SAE 2005-01-2200
NOx, g/bhp-h4.0 4.5 5.0 5.5 6.0
BSF
C, l
b/bh
p-h
0.30
0.35
0.40
0.45
0.50
0.55
0.60
Cert Fuel Mean=0.390 lb/bhp-h
Biodiesel Mean=0.446 lb/bhp-h
NOx, g/bhp-h4.0 4.5 5.0 5.5 6.0
Ener
gy C
onsu
mpt
ion,
btu
/bhp
-h
5000
6000
7000
8000
9000
Cert Fuel Mean=7126 btu/bhp-h
Biodiesel Mean=7051 btu/bhp-h
Iodine Number
0 20 40 60 80 100 120 140 160 180N
Ox,
g/g
hp-h
4
5
6
Soy MECanola ME
Cert Fuel Mean
Tallow ME
Iodine# vs NOx, g/BHP-hr
Iodine Number
0 20 40 60 80 100 120 140 160 180
PM, g
/ghp
-h
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Cert Fuel Mean
Results for 1991 engine
•NOx emissions correlated with fuel unsaturation•NOx varies by 1 g/bhp-h but energy consumption varies by less than 2%•Data from Environ. Sci. & Technol. 35 1742-1747 (2001), •DDC Series 60 engine (1991)•HD FTP•B100 compared to LSD
Effect of Biodiesel Composition on NOx
Effect of Biodiesel Composition for BlendsNOx emissions for B20 blends versus biodiesel Iodine Number:
Iodine Number
60 80 100 120 140
NO
x, g
/kW
-h
5.8
6.0
6.2
6.4
6.6
Soy ME
Cert Fuel Mean
Tallow ME
•NOx neutrality at Iodine Number of roughly 95
•I.N. is typically >120 for soy
•Suggests blending of high and low I.N. fuels may be a strategy to eliminate the NOxincrease -older engines
Effect of Biodiesel Composition
B100 B20
Results for 2004 enginesMuch smaller effect of degree of unsaturation
Data from SAE 2005-01-2200
Comparison of Engine and Vehicle Emissions
Analysis from EPA420-P-02-001, October 2002
•EPA predictive model based on engine dyno data•Results compared to vehicle (chassis dyno) results•On average, NOx was reduced in vehicle test studies
Chassis Data ExamplesPlot: Weaver, report to SCAQMD, November 2004.
Data:Peterson and Reece, SAE Paper No. 961114. Taberski and Petersen, BioEnergy ’98, Expanding
Bioenergy Partnerships, available at www.biodiesel.org.
Durbin and Norbeck Environ. Sci. Technol. 2002, 36,1686. Light-duty FTP test cycle for B20 blends of three biodiesels
General observation: very high power-to-weight vehicles, such that engine operation is at light load.
Speculate: biodiesel may reduce NOx at lighter loads?
Biodiesel Bus Chassis Dynamometer Testing •B20 vs. conventional diesel fuel
•2 in-use buses tested (40,000 lb GVWR)
•City Suburban Heavy Vehicle Cycle (CSHVC) at 35,000 lb inertia
•Cummins ISM 2000 Engine – No EGR
• Expected reductions (g/mile basis)– PM ≈ 24%– HC ≈ 40%– CO ≈ 32%– Fuel Economy ≈ 3%
•Unexpected reductions in NOx– 5% reduction – statistical confidence > 99%
Biodiesel Effect on NOx Uncertainty
•Engine tests on average show NOx increasing•NOx can go up or down depending on engine and test cycle - this is not well understood fundamentally•Finding of a NOx increase is not based on testing of a representative sample of in-use engines•Finding of NOx increase is not based on a market share weighted average
•Vehicle tests on average show NOx reductions•Very limited dataset•Again, not based on representative sample or market share weighted average
Closing Remarks•There is considerable uncertainty regarding biodiesels impact on NOxemissions
•Additional research is required to fundamentally understand the cause of the NOx increase and to understand why engine and chassis tests give directionally different results
•The main benefits of biodiesel use are reductions in petroleum consumption and greenhouse gas emissions
http://www.nrel.gov/vehiclesandfuels/npbf/publications.html
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