Route-based time-dependent life-cycle carbon and NOx emissions analysis of heavy-duty trucks

Abstract

The electrification of the transportation sector is gaining traction due to the potential for greenhouse gas (GHG) emissions reductions to combat climate change. Class-8 trucks are a major contributor to emissions within this sector; therefore, battery-electric (BE) alternatives with zero tailpipe emissions are being considered as a replacement. However, a more comprehensive analysis of vehicle emissions must be conducted to cover the entire lifecycle of a vehicle. Hence, a life cycle analysis (LCA) can be used to evaluate emissions from all phases during a truck’s life. The current literature lacks studies conducted on Class-8 trucks, time-of-day impact on GHG emissions from electricity generation, and nitrogen oxide (NOx) emissions. Therefore, this thesis aims to investigate the potential carbon dioxide (CO2), and NOx emissions reductions achieved with battery electric (BE) and series-hybrid (SHE) trucks when compared to a conventional diesel internal combustion engine (ICE) Class-8 truck along a long-haul and two drayage routes. In this work, a dynamic and modular vehicle simulation tool was developed to simulate the performance and emissions of said powertrains. Additionally, the LCA accounted for emissions contributions and uncertainties from production, maintenance, fuel production, electricity generation, and distribution. The emissions from charging the BE truck are assessed under different assumptions: the US average grid, a time-dependent electricity grid based on the truck routes, and a future grid assumption applied to the same. The time-dependent route-based analysis accounts for regional and time-of-day variations in the electricity grid mix and its impact on the resultant emissions. The future grid assumption took the increase in the use of renewable sources of electricity over ten years into account. The LCA results show that BE trucks are well suited for operation on more stop-and-go routes within regions with a large share of renewable sources of electricity, emitting 23% and 6% less CO2 and NOₓ respectively than the SHE truck during drayage application in

California (CA). On the other hand, SHE trucks are best for cross-country trips on highways and operations in regions with large shares of electricity from non-renewable sources. The SHE truck emitted 36% and 46% less CO₂ and NOₓ respectively than the BE truck during long-haul transport. After considering future grid emissions reduction from 2023-2032, the BE truck’s emissions were reduced by 10-12% compared to the ICE truck. Despite this reduction, the BE truck had greater emissions during long-haul and drayage transport in a more carbon-intensive region than the SHE truck.