As GHG and fuel economy regulations of light-duty vehicles have become more stringent, advanced emissions reduction technology has extensively penetrated the US light-duty vehicle fleet. This new technology includes not only advanced conventional engines and transmissions, but also greater adoption of electrified powertrains. In 2022, electrified vehicles – including mild hybrids, strong hybrids, plug-ins, and battery electric vehicles – made up nearly 17% of the US fleet and are on track to further increase their proportion in subsequent years.
The Environmental Protection Agency (EPA) has previously used its Advanced Light-Duty Powertrain and Hybrid Analysis (ALPHA) full vehicle simulation tool to evaluate the greenhouse gas (GHG) emissions of light-duty vehicles. ALPHA contains a library of benchmarked powertrain components that can be matched to specific vehicles to explore GHG emissions performance. Recently, EPA has updated the ALPHA model with key changes including the addition of new models for electrified vehicle architectures and a robust structure which allows batch processing of large numbers of simulations. This enables large scale characterization of current and future fleets over the EPA city, highway and US06 regulatory drive cycles.
This paper focuses on how ALPHA can be used to approximate fleetwide GHG emissions using a narrow set of engines, electric motors, transmissions, propulsion batteries, and architectures. Simulations of the 2022 model year light-duty fleet show a good overall correlation between modeled GHG emissions and certification results, with the average difference between ALPHA simulation and certification values under 0.2% when the values are production weighted.