Alternative Fuels and Hybridization as Cost-Effective Pathways to Medium-Duty Greenhouse Gas Phase 3 Compliance

The United States Environmental Protection Agency (US EPA) Greenhouse Gas (GHG) Phase 3 regulation targets a substantial reduction in GHG emissions across model year (MY) 2027–2032 class 2b-8 vehicles. This article explores the implementation of alternative fuels, such as compressed natural gas (CNG) and liquefied petroleum gas (LPG), along with powertrain hybridization as viable pathways for achieving these stringent standards in a cost-effective manner. A detailed analysis is performed on a Class-7 medium–heavy-duty (MHD) truck configuration, featuring an inline 4-cylinder 5.2-L spark-ignited (SI) engine, modeled with both CNG and LPG fuels. The vehicle’s powertrain is simulated to evaluate GHG emissions and fuel efficiency. The study further examines the impact of low rolling resistance (LRR) tires and varying tire rolling resistance coefficients (C_rr) on vehicle performance. For further lowering the GHG emissions, a hybrid powertrain sizing study was performed. The simulation results indicate that hybrid powertrain configurations, when combined with LRR tires, can achieve significant CO₂ emission reductions, meeting and exceeding the US EPA Phase 3 GHG targets. The powertrain with the CNG engine equipped with fuel-saving technologies such as neutral-idle, engine start–stop, and automatic engine shutdown can comply with MY 2032 standards while running 7.7 N/kN C_rr tires. The hybrid powertrain with the LPG engine and 5.6 N/kN C_rr tires reaches compliance with MY 2032 fleet average standards while maintaining minimal payload penalties. This research provides critical insights into the feasibility of leveraging alternative fuels and hybrid technologies to meet upcoming GHG regulations, presenting a viable pathway for manufacturers to reduce operational costs while achieving environmental compliance.