Materials Flow Analysis and Dynamic Life-cycle
Assessment of Lightweight Automotive Materials in the
US Passenger Vehicle Fleet
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Citation
Cheah, L.W. “Materials flow analysis and dynamic life-cycle
assessment of lightweight automotive materials in the U.S.
passenger vehicle fleet.” Sustainable Systems and Technology,
2009. ISSST '09. IEEE International Symposium on. 2009. 1. ©
Copyright 2009 IEEE
As Published
http://dx.doi.org/10.1109/ISSST.2009.5156692
Publisher
Institute of Electrical and Electronics Engineers
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Final published version
Accessed
Thu May 26 19:56:39 EDT 2016
Citable Link
http://hdl.handle.net/1721.1/58938
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Detailed Terms
Materials Flow Analysis and Dynamic Life-cycle
Assessment of Lightweight Automotive Materials in
the U.S. Passenger Vehicle Fleet
Lynette W. Cheah, Engineering Systems Division, Massachusetts Institute of Technology
P
ASSENGER vehicles in the U.S. are responsible for
nearly 70% of the nation’s liquid fuel use, and 18% of
greenhouse gas (GHG) emissions. These impact figures are
increasing and motivate policy efforts to curb them, such as
defining higher vehicle fuel economy standards.
To achieve better fuel economy, automakers are seriously
considering vehicle weight and size reduction. This is
achieved by using lighter-weight materials like high-strength
steel and aluminum, better vehicle design, and offering
smaller vehicle models.
To consider the effectiveness of these approaches, it is
important to take into account the dynamic life-cycle energy
and environmental impacts. For instance, primary aluminum
requires almost four times more energy to produce than steel
today. Expected efficiency improvements in material
processing would modify this ratio over time. Examining the
impact of lightweighting on the overall vehicle fleet systemlevel, as opposed to a single vehicle-level, also reveals insights
on the timing and degree of the impact reduction achieved.
RESEARCH OVERVIEW
The research applies a dynamic approach to LCA, in
combination with MFA and scenario analysis. It explores (i)
the degree of lightweighting that is likely to be employed in
order to meet the Corporate Average Fuel Economy (CAFE)
target of 35 miles per gallon (MPG) by year 2020; and (ii)
given scenarios of evolving vehicle weight, size and material
composition, the corresponding fuel use and life-cycle GHG
emission reductions that can be achieved on the vehicle fleet
level.
Spreadsheet-based models of the vehicle stock, automotive
material use, and the corresponding life-cycle energy use over
time, from 1980-2035, have been developed. Data from
Argonne National Laboratory’s GREET life-cycle inventory
database and other sources are used to derive the
corresponding life-cycle energy and GHG emissions of all
U.S. passenger vehicles over this period.
ILLUSTRATIVE RESULTS
Annual fuel use by the vehicle fleet is one of the outputs of
the model. Two scenarios are shown in Fig. 1 – one
“conservative”, and one more “optimistic”, which has new
vehicles meeting the CAFE target and then doubling their fuel
economy by 2035. The degree of lightweighting in future
vehicles necessary to meet the proposed fuel economy target,
in combination with the use of advanced powertrains, is found
to be in the order of 15-25%. Fig. 2 shows the corresponding
fuel savings achieved by the fleet. Under the “optimistic”
scenario, the cumulative fuel savings through 2035 is 3,400
billion liters.
Future work is committed to identifying factors in the
material production and vehicle design stages that are most
effective in or sensitive to reducing the overall energy and
environmental impact of U.S. passenger vehicles.
1,800
New car curb weight (kg)
1,600
1,400
1,200
Baseline
Conservative scenario
Optimistic scenario
1,000
800
600
New vehicle fuel economy (MPG)
60
50
40
30
20
10
0
1980
CAFE target
1990
2000
2010
2020
2030
2040
Fig. 1. Curb weight and fuel economy of the average new vehicle.
1000
Vehicle fleet fuel use (billion liters)
800
2,580
600
830 bil liters
400
200
0
Baseline
Conservative scenario
Optimistic scenario
Fig. 2. The corresponding impact on annual fleet fuel use in the two
scenarios.