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