Engines of Change: Comparison of Environmental Impacts Between Traditional Engines and Alternative Powertrains

Abstract

This report provides a systematic assessment of the environmental influences associated with traditional internal combustion engine (ICE) cars, specifically spark ignition (SI) and compression ignition (CI) engines, and four consultant opportunity powertrains: hybrid electric motors (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric powered cars (BEVs), and fuel cell vehicles (FCVs). As the transportation sector continues to contribute about 29% of total U.S. greenhouse gas (GHG) emissions, identifying cleaner car technologies has become a pressing issue. The analysis adopts a well-to-wheel (WTW) approach, accounting not only for direct tailpipe emissions but also upstream emissions related to fuel production, power generation, and battery or hydrogen sourcing. The results show that while SI and CI engines emit significant levels of NOx, CO, HC, and particulate matter, hybrid and electric powertrains significantly reduce those pollutants, particularly BEVs and FCVs, which have zero tailpipe emissions. However, the overall sustainability of BEVs and FCVs hinges on the cleanliness of the electric grid and hydrogen production methods, respectively. Moreover, factors such as regenerative braking, energy recovery, driving styles, infrastructure availability, and lifecycle issues (e.g., battery production and disposal) affect actual-world performance. The report concludes that the transition to low-emission transportation should be coupled with decarbonization of the power supply. BEVs and FCVs powered by renewable sources constitute the most promising pathways towards sustainable mobility, while HEVs and PHEVs function as realistic transitional solutions. This work aims to provide comprehensive insight into powertrain-specific environmental trade-offs and to inform individual and policy-level decisions for more sustainable transportation options.