Lightweight materials and advanced combustion engines are being used with conventional and electrified vehicles to increase fuel economy, but such technologies may require more energy to produce and the impact of plug-in hybrid electric vehicles (PHEVs) is dependent on the electric grid. In this study, life cycle assessment (LCA) is used to evaluate the total energy and GHG emissions for baseline and lightweight internal combustion vehicles (ICVs), hybrid electric vehicles (HEVs) and PHEVs when they are operated with baseline and advanced gasoline and ethanol engines. As design harmonization techniques are developed to enable a comparison across diverse vehicle platforms, all vehicles are functionally equivalent and hybrid vehicle models account for increased structural support required for heavier, electrified powertrains. Lightweight vehicle models include primary and secondary mass reductions (including powertrain re-sizing) and are evaluated with body-in-white mass reduction scenarios with aluminum-intensive and advanced/high strength steel (A/HSS) designs. Advanced engine/fuel strategies are incorporated to the vehicle models with fuel economy maps, developed with a novel method to ensure combustion limits are not violated under boosted and dilute conditions for high compression ratio engines.
The harmonized vehicle models show that the structural mass required per kg of powertrain mass for electrified vehicles is 0.2-0.3 kg. As compared to lightweight materials, more significant life cycle improvements are achieved by using advanced gasoline and E85 engines, as fuel consumption is reduced up to 24%. As compared to A/HSS, more mass can be removed from the vehicle with aluminum, leading to greater fuel consumption and life cycle reductions. However, due to the higher energy and GHG emissions associated with aluminum production, more significant life cycle reductions occur for an equivalent decrease in vehicle mass with A/HSS. Also, life cycle impacts are reduced more for ICVs as compared to hybrid vehicles because fuel economy is most sensitive to mass for ICVs. Considering the same vehicle platform, the combination of lightweight materials and advanced engines yields the maximum life cycle energy and GHG reductions, as the technologies provide complimentary results due to engine downsizing. Minimum life cycle energy and GHG emissions occur for the lightest weight hybrid vehicles using the downsized/turbocharged gasoline or E85 engine.