The Impact of Vehicle Electrification and Lightweight Materials to Reduce Life Cycle Energy and Greenhouse Gas Emissions
The U.S. transportation sector consumes over one third of the nation’s energy and accounts for 27% of its greenhouse gas (GHG) emissions. Vehicle manufacturers use electrification and mass reduction to decrease vehicle use phase energy and GHG emissions. But, life cycle assessment (LCA) is required to fully understand these impacts due to electricity and lightweight material production burdens. Lightweight automotive materials, such as aluminum, high strength steel, and carbon fiber, are energy intensive to produce. This work develops a framework to simultaneously evaluate electrification and lightweighting to help guide vehicle design. This framework is applied to assess the life cycle energy and GHG emissions of a conventional vehicle (CV), hybrid electric vehicle (HEV), and plug-in hybrid electric vehicle (PHEV) constructed of baseline or lightweight materials. Baseline vehicles are designed according to powertrain configuration; powertrain mass has a significant influence on vehicle mass and powertrain design determines the functional needs from related subsystems (e.g. regenerative braking). Each vehicle is normalized for functional equivalency according to performance criteria. Lightweight vehicles are designed in an iterative process that maintains functional equivalence: 1) a conventional component is replaced with a lightweight component, 2) powertrain and secondary mass reductions iterate until vehicle performance and mass converge. Simulation results highlight the importance of simultaneously considering vehicle electrification and lightweighting in a LCA because the impact of mass reduction on fuel economy is unique to each powertrain. When an equivalent mass is reduced from each powertrain class through material substitution, the reductions in life cycle energy and GHG emissions are greatest for the CV. This occurs because HEVs and PHEVs capture energy due to regenerative braking, a function of vehicle mass. Results indicate that the lowest life cycle energy and GHG emissions are achieved with a lightweight PHEV when operated in a low carbon grid.