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1 University of California, Davis, Oct 1, 2015
Life Cycle Greenhouse Gas (GHG)
Emissions from Natural Gas Pathways for
On-Road Vehicles
Fan Tong, Paulina Jaramillo, Inês L. Azevedo
Department of Engineering and Public Policy
Carnegie Mellon University
Oct 1, 2015STEPS Workshop: Technological, Economics and Environmental Potential of
Natural Gas as a Sustainable Transportation Fuel in the United States
University of California, Davis, Oct 1, 2015
2 University of California, Davis, Oct 1, 2015
• 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?
A Transition to Natural Gas Pathways?
3 University of California, Davis, Oct 1, 2015
• 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.
Bottom-up Attributional Life Cycle Assessment (LCA)
• GHGs
• CO2, CH4, N2O
• Global warming potential (GWP)
• IPCC AR5 values.
• Uncertainty in GWPs.
• Functional Unit
• Vehicle distance (kilometer)
• Freight distance (metric ton-km)
Modified from a GREET
model presentation
(Argonne National Lab)
4 University of California, Davis, Oct 1, 2015
Modified from
Tong et al.
(2015a, 2015b).
5 University of California, Davis, Oct 1, 2015
Not All Transportation Fuels Can be Used to Fuel Every Vehicle Type
• 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.
Modified from Tong et al. (2015a, 2015b).
6 University of California, Davis, Oct 1, 2015
Sample Results - Natural Gas Pathways Are Worse.
0
20
40
60
80
100
120
10 1119 21
25 23 2027 23
31
4448
43 4241 43 48
42 48
48
10 11
28 2934 32 32
37
23
43
4448
44 4543 47 48
45
48
48
Conv. diesel HEV
Conventional dieselCNG
LNG central CI
LNG distributed CI
LNG central SI
F-T diesel w/ CCS
LNG distributed SI
Oil sand diesel
F-T diesel w/o CCS
Lif
e cy
cle
GH
G e
mis
sio
ns
(U
nit
: g
CO
2-e
q/k
m-m
etri
c-to
n)
Upstream (100-yr GWP)
Tailpipe (100-yr GWP)
Upstream (20-yr GWP)
Tailpipe (20-yr GWP)
Class 8 Line-haul Tractor Trailer
Modified from Tong et al. (2015a).
7 University of California, Davis, Oct 1, 2015
Many pathways do not achieve emissions reduction yet
• 4 scenarios * 9 vehicle types
• Baseline/Pessimistic methane
emissions estimates.
• 100-year/20-year GWP metrics.
2
Life Cycle
fuel carbon intensitytailpipe nonCO
vehicle fuel efficiency
8 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.
80% 90% 100% 110% 120%0%
1%
2%
3%
4%
5%
6%
7%
Bre
ak
-ev
en m
eth
an
e le
ak
ag
e ra
te
Energy economy ratios (EERs) of natural gas vehicles
CNG, 100-year GWP
Modified from Tong et al. (2015a).
9 University of California, Davis, Oct 1, 2015
Higher or lower relative vehicle fuel efficiency allows higher or lower
methane leakage.
80% 90% 100% 110% 120% 0%
1%
2%
3%
4%
5%
6%
7%
Energy economy ratios (EERs) of natural gas vehicles
Bre
ak
-ev
en m
eth
an
e le
ak
ag
e ra
te
CNG, 100-year GWP
Modified from Tong et al. (2015a).
10 University of California, Davis, Oct 1, 2015
LNG/CNG vs. Diesel (MHDVs)
80% 90% 100% 110% 120%0%
1%
2%
3%
4%
5%
6%
7%
Energy economy ratios (EERs) of natural gas vehicles
Bre
ak
-ev
en m
eth
an
e le
ak
ag
e ra
te
LNG, 100-year GWP
LNG, 20-year GWP
CNG, 100-year GWP
CNG, 20-year GWP
Modified from Tong et al. (2015a).
11 University of California, Davis, Oct 1, 2015
Natural Gas Pathways vs. Gasoline (LDVs)
100% 150% 200% 250% 300% 350% 400%0%
5%
10%
15%
Energy economy ratio (EERs) of natural gas vehicles
Bre
ak
-ev
en m
eth
an
e le
ak
ag
e ra
te
2.3%
0.9%
2.8%
1.2%
10.8%
4.5%
Current
CNG
vehicle
CNG, 100-yr
CNG, 20-yr
BEV,
100-yr
Current
BEV
Current
FCEVGH2 FCEV, 100-yr
GH2 FCEV, 20-yr
BEV, 20-yr
Modified from Tong et al. (2015b).
12 University of California, Davis, Oct 1, 2015
13 University of California, Davis, Oct 1, 2015
• 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.
Acknowledgement
14 University of California, Davis, Oct 1, 2015
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.
References
15 University of California, Davis, Oct 1, 2015
Questions?
Fan Tong
Ph.D. candidate
Department of Engineering and Public Policy
Carnegie Mellon University
