Life Cycle Greenhouse Gas (GHG) Emissions from Natural Gas Pathways for On-Road Vehicles 1 University of California, Davis, Oct 1, 2015 Fan Tong, Paulina Jaramillo, Inês L. Azevedo Department of Engineering and Public Policy Carnegie Mellon University Oct 1, 2015 STEPS Workshop: Technological, Economics and Environmental Potential of Natural Gas as a Sustainable Transportation Fuel in the United States
A Transition to Natural Gas Pathways? Research Gaps Previous studies do not account for recent developments in natural gas (e.g. methane leakage) extractions and current vehicle technologies. Findings from previous studies on life cycle GHG emissions of natural gas developments and heavy-duty vehicles are mixed and contradictory. Research Questions Which natural gas pathways or which vehicle segments provide GHG emissions reductions compared to petroleum fuels? How sensitive are the results to methane leakage rates and other factors? 2 University of California, Davis, Oct 1, 2015
Bottom-up Attributional Life Cycle Assessment (LCA) Emission Sources Resource extraction: natural gas and oil (baseline). Fuel production, transport, distribution. Vehicle operation (tailpipe). Vehicle manufacturing emissions (esp., battery and fuel cells). Emissions from infrastructure construction. Emissions from end-of-life disposal or treatment. GHGs CO 2, CH 4, N 2 O Global warming potential (GWP) IPCC AR5 values. Uncertainty in GWPs. Functional Unit Modified from a GREET model presentation (Argonne National Lab) Vehicle distance (kilometer) Freight distance (metric ton-km) 3 University of California, Davis, Oct 1, 2015
Modified from Tong et al. (2015a, 2015b). 4 University of California, Davis, Oct 1, 2015
Not All Transportation Fuels Can be Used to Fuel Every Vehicle Type Modified from Tong et al. (2015a, 2015b). More fuel options for light-duty vehicles; less fuel options for heavy-duty trucks. CNG is the only fuel that spans over all vehicle classes. 5 University of California, Davis, Oct 1, 2015
Sample Results - Natural Gas Pathways Are Worse. Life cycle GHG emissions (Unit: g CO -eq/km-metric-ton) 2 120 100 80 60 40 20 0 Upstream (100-yr GWP) Tailpipe (100-yr GWP) Upstream (20-yr GWP) Tailpipe (20-yr GWP) 44 44 Conv. diesel HEV 48 10 10 11 11 28 29 19 21 6 University of California, Davis, Oct 1, 2015 48 Conventional diesel 43 Class 8 Line-haul Tractor Trailer 44 45 42 CNG LNG central CI LNG distributed CI 43 47 48 41 43 48 34 32 32 25 23 20 42 48 27 45 37 LNG central SI F-T diesel w/ CCS LNG distributed SI Modified from Tong et al. (2015a). 23 48 23 48 31 48 43 Oil sand diesel F-T diesel w/o CCS
Many pathways do not achieve emissions reduction yet 4 scenarios * 9 vehicle types Baseline/Pessimistic methane emissions estimates. 100-year/20-year GWP metrics. Life Cycle fuel carbon intensity vehicle fuel efficiency tailpipe nonco 2 7 University of California, Davis, Oct 1, 2015
If natural gas vehicles have the same fuel efficiency as diesel vehicles, then it allows up to 3.1% of methane leakage rate to achieve emissions reduction. Break-even methane leakage rate 7% 6% 5% 4% 3% 2% 1% CNG, 100-year GWP 0% 80% 90% 100% 110% 120% Energy economy ratios (EERs) of natural gas vehicles 8 University of California, Davis, Oct 1, 2015 Modified from Tong et al. (2015a).
Higher or lower relative vehicle fuel efficiency allows higher or lower methane leakage. Break-even methane leakage rate 7% 6% 5% 4% 3% 2% 1% CNG, 100-year GWP 0% 80% 90% 100% 110% 120% Energy economy ratios (EERs) of natural gas vehicles 9 University of California, Davis, Oct 1, 2015 Modified from Tong et al. (2015a).
LNG/CNG vs. Diesel (MHDVs) Break-even methane leakage rate 7% 6% 5% 4% 3% 2% 1% 0% LNG, 100-year GWP LNG, 20-year GWP CNG, 100-year GWP CNG, 20-year GWP 80% 90% 100% 110% 120% Energy economy ratios (EERs) of natural gas vehicles Modified from Tong et al. (2015a). 10 University of California, Davis, Oct 1, 2015
Natural Gas Pathways vs. Gasoline (LDVs) Break-even methane leakage rate 15% 10% 5% Current CNG vehicle 2.3% CNG, 100-yr CNG, 20-yr Current FCEV 2.8% GH2 FCEV, 100-yr GH2 FCEV, 20-yr Current BEV 10.8% 4.5% BEV, 100-yr BEV, 20-yr 0% 0.9% 1.2% 100% 150% 200% 250% 300% 350% 400% Energy economy ratio (EERs) of natural gas vehicles Modified from Tong et al. (2015b). 11 University of California, Davis, Oct 1, 2015
12 University of California, Davis, Oct 1, 2015
Acknowledgement This work is financially supported by Center for Climate and Energy Decision-Making (CMU & NSF). Department of Engineering and Public Policy (EPP) at CMU. 2013-14 Northrop Grumman Fellowship. 2013-14 Steinbrenner Institute Graduate Research Fellowship. Fuels Institute. This work is intellectually benefited from Comments, suggestions, and discussions from a large and diverse group of scholars and experts. 13 University of California, Davis, Oct 1, 2015
References Tong (2015a). Tong, F.; Jaramillo, P.; Azevedo, I. Comparison of Life Cycle Greenhouse Gases from Natural Gas Pathways for Medium and Heavy-Duty Vehicles. Environ. Sci. Technol. 2015, 49, 7123 7133. Tong (2015b). Tong, F.; Jaramillo, P.; Azevedo, I. Comparison of Life Cycle Greenhouse Gases from Natural Gas Pathways for Light Duty Vehicles. Energy & Fuels 2015, 29 (9), pp 6008 6018. Please refer to Tong et al. (2015a, 2015b) for a full list of relevant literature on this topic. 14 University of California, Davis, Oct 1, 2015
Questions? Fan Tong ftong@andrew.cmu.edu Ph.D. candidate Department of Engineering and Public Policy Carnegie Mellon University 15 University of California, Davis, Oct 1, 2015