Fuel Effects Issues for In-Use Diesel Applications Matthew Thornton National Renewable Energy Laboratory Center for Transportation Technologies and Systems NAMVECC Conference November 4, 2003 Chattanooga, TN
Diesel Fuel Property Effects on Emissions Well known fuel property impacts on emissions Increasing cetane number Can reduce NO x, 2-5% for an increase of 10 CN in some engines But has no effect on NO x for other engines Effect on PM is also engine dependent Can assist in cold starting and reduce white smoke Reducing aromatic content Can reduce NO x by 0-5% for a reduction from 30 to 10% Reduction in polyaromatics may account for most of this effect Magnitude of NO x reduction is engine dependent PM reductions observed in some engines Low sulfur content Reduces PM Enables exhaust catalyst and trap systems
Fuel Effects in 1991 Engine CRC VE-1 Study: 1991 DDC Series 60 (5 g/bhp-h NO x, 0.25 g/bhp-h PM) HD-FTP 5.4 5.2 NOx, g/bhp-h 5.0 4.8 4.6 4.4 4.2 35 40 45 50 55 60 0.24 Cetane Number 0 10 20 30 40 50 SFC Aromatics, wt% 12.0 12.4 12.8 13.2 13.6 14.0 Wt% Hydrogen 0.22 PM, g/bhp-h 0.20 0.18 0.16 0.14 35 40 45 50 55 60 Cetane Number 0 10 20 30 40 50 SFC Aromatics, wt% 12.0 12.4 12.8 13.2 13.6 14.0 Wt% Hydrogen Increasing CN and/or lowering aromatics lowers NO x and PM Wt% Hydrogen correlates well with NO x and PM
Fuel Effects in 1998 Engine CRC VE-10 Study: 1998 DDC Series 60 (4 g/bhp-h NO x, 0.1 g/bhp-h PM) HD-FTP, CN varied only CN correlates well with NO x but not PM 4.8 4.6 0.14 NOx, g/bhp-h 4.4 4.2 4.0 PM, g/bhp-h 0.12 0.10 0.08 3.8 0.06 3.6 40 42 44 46 48 50 52 54 56 58 60 Cetane Number 40 42 44 46 48 50 52 54 56 58 60 Cetane Number
Fuel Effects in Engines with EGR (2004) 2.5 g/bhp-h NOx+HC 0.1 g/bhp-h PM No effect of CN on NO x Lowering aromatics or increasing hydrogen content lowers NO x PM not reported SAE 2000-01-1858, Cat 3176 HD Engine, 8-mode SS tests:
Fuel CN and Aromatics Effects Conclusion Reducing aromatic content is consistently associated with emissions reductions In both old and new engines Likely this is related to reduction in adiabatic flame temperature which is higher for aromatics Poly-aromatics may have a larger effect than mono-aromatics In older engines and under cold start conditions the high CN may also be important Ryan, et al., SAE 982491
Fuel injection Technology is Advancing Rapidly and Resulting in Reduced Emissions Up to 5 independent fuel injections per cycle are now achievable at the prototype level from the major FEI suppliers Multiple injections can drop emissions significantly Ricardo 8/01
Emission Control (EC)-Diesel: Ultra Low Sulfur Fuel ECD Sulfur 4-7 ppm Cetane ~65 Aromatics 8-11 % volume Hydrogen ~14 % mass ECD-1 Sulfur ~13 ppm Cetane ~52 Aromatics 18-24 % volume Hydrogen ~14 % mass
Fleet GVW Engine Model and Chassis Type Ralphs Grocery ARCO 46,000 LA Refuse Haulers 80,000 1999 DDC Series 60, 430 hp, 58,000 tandem axle tractor 1995 Cummins M11, 330 hp, single axle tractor 1999 Cummins ISM, 305 hp, refuse truck San Diego Schools LAMTA 36,220 37,920 1998 International 530E, 275 hp, school bus 1998 DDC Series 50, 275 hp, transit bus
Fleet Ralphs Filter Types CRT DPX Miles PM Reduction Test Cycle ~100K 95% CSHVR ARCO CRT ~187K 96% CSHVR LA Refuse SD School CRT DPX ~20K 95% CBD, NYCGT DPX ~ 40K 96% CSHVR LAMTA CRT ~37K 97% CBD
PM Emissions by Fuel Sulfur Level Catalyzed filter systems will convert sulfur to sulfate, which condenses as PM. DECSE Phase I Report, 2000 PM Components, OICA Cycle Solid PM H2SO4.7H2O SOF NO3-0.25 PM Emissions (g/bhp-hr) 0.20 0.15 0.10 0.05 Engine-Out CDPF CR-DPF 0.00 3 30 150 350 30 Fuel Sulfur Level (ppm) Caterpillar 3126 Engine
FT Diesel Overview Mainly n-paraffins produced from CO/H 2 (syngas) by Fischer-Tropsch synthesis Syngas can be made from natural gas (steam/oxygen reforming) or from coal and biomass (gasification) FT-diesel from all feedstocks will have similar properties: High cetane number Low aromatic content High H/C ratio Very low (<1 ppm) sulfur content Requires lubricity additive Most likely use is as a high quality blendstock
FT Fuels: NO x and PM Summary % PM Reduction 60 40 20 0-20 Quadrant of NO x and PM Reduction Light Duty Vehicles/No. 2 Diesel Heavy Duty Engines and Vehicles/No. 2 Diesel Light Duty Vehicles/ULSD Heavy Duty Engines and Vehicles/ULSD Emissions changes relative to conventional diesel and ULSD 74 data points based on several different test cycles 24 different engines and vehicles (8 LD) -40-10 0 10 20 30 % NO x Reduction Source: SAE 2003-01-0763
Biodiesel Emissions Summary PM, HC and CO reduction NO x increase, 2-4% for B20, insignificant for B5 Soy-based biodiesel, HD engines Data from EPA420-P-02-001
Effect of Biodiesel Composition PM, g/ghp-h BSFC, lb/bhp-h 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0.60 0.55 0.50 0.45 0.40 0.35 Iodine# vs NOx, g/bhp-hr Iodine Number Biodiesel Mean=0.446 lb/bhp-h Cert Fuel Mean=0.390 lb/bhp-h 0.30 4.0 4.5 5.0 5.5 6.0 NO x, g/bhp-h Cert Fuel Mean 0 20 40 60 80 100 120 140 160 180 Energy Consumption, btu/bhp-h NO x, g/ghp-h 6 5 4 9000 8000 7000 6000 Canola ME Tallow ME Soy ME 0 20 40 60 80 100 120 140 160 180 Iodine Number Cert Fuel Mean=7126 btu/bhp-h Biodiesel Mean=7051 btu/bhp-h 5000 4.0 4.5 5.0 5.5 6.0 NO x, g/bhp-h Cert Fuel Mean Properties of biodiesel depend on fatty acid makeup-iodine Value Little effect on PM, BSFC, or efficiency NO x emissions correlated with fuel chemistry NO x varies by 1 g/bhph but energy consumption varies by less than 2% Data from Environ. Sci. & Technol. 35 1742-1747 (2001), DDC Series 60 engine (1991)
Effect of Biodiesel Composition for Blends NO x emissions for B20 blends versus biodiesel Iodine Number: 6.6 6.4 NO x neutrality at Iodine Number of roughly 95 NO x, g/kw-h 6.2 6.0 Cert Fuel Mean Soy ME I.N. is typically >120 for soy Suggests blending of high and low I.N. fuels may be a strategy to eliminate the NO x increase 5.8 Tallow ME 60 80 100 120 140 Iodine Number NOx increases can also be countered through injection timing retard or cetane additives
Natural Gas and Diesel Emissions Engine Out Emissions: CNG has a 40% reduction in NOx and an 85% reduction in PM over diesel (without EGR or DPF) NG engines can have higher toxic emissions (e.g. benzene, carbonyls), but controlled with oxidation catalysts to levels similar to diesel with DPF Little data available for comparison of NG engines with EGR equipped diesel engines
Natural Gas and Diesel Emissions Em ission rate (g/m i) 30 25 20 15 10 5 CNG Diesel Study of Washington Metropolitan area Transit Authority 40 foot transit busses. Diesel: 2000 MY DDC Series 50 with PDF operating on 17 ppm diesel fuel CNG: 2001 MY Cummins ISC with oxidation catalysts 0 CO NOx NMHC/THC x 10 PM10 x 10
Implications for Air Pollution Control Programs Know your fleet and fuels Fuel effects are engine technology dependent Emission control technology can alter fuel response Duty cycle is critical consideration (e.g. DPF retrofits with passive regeneration) Fuel composition characterized by CN, Aromatics, and Sulfur are currently important, but key fuel characterization approaches will likely be different in the future Alternative fuels (Bio-diesel, FT, CNG) display varying emissions trade-offs and proved potential for some fleets and as blending stock Understand the issues for your region Know pollutant of concern for your area (e.g. Ozone formation issues) Regional ambient conditions (e.g. temperature) and terrain (e.g. grade) can influence emission impacts and fuel effects