Fuel Consumption and Emissions Reductions of Hybrid Electric Regional‐Haul Trucks Equipped with a High‐Pressure Direct Injection Natural Gas Engine in Real‐World Driving Conditions

Integrating powertrain electrification with efficient engines using low‐carbon fuels like natural gas (NG) improves energy conversion efficiency and mitigates greenhouse gas (GHG) emissions in heavy‐duty (HD) trucks. High‐pressure direct injection (HPDI) NG engines, using less than 5% diesel (energy basis) as pilot fuel, offer diesel‐like efficiency with 15–25% lower GHGs. This work evaluates integrating an HPDI NG engine with a hybrid electric powertrain to reduce net energy consumption and GHG emissions from regional‐haul trucks. The HPDI NG engine is developed and validated using experimental test‐cell data, matching the rated power of the diesel engine in the conventional baseline model. Two hybrid electric configurations: a pretransmission parallel (P) hybrid and a complex power‐split hybrid (PSH), are innovatively designed to meet the high‐torque, transient demands of HD trucks. A multistage optimal component‐sizing framework is implemented to minimize energy consumption while maintaining baseline performance. Hybridizing the HPDI NG engines improves net powertrain energy efficiency by 5.2% for the PSH and 4.0% for the P hybrid design across a real‐world highway cycle at full cargo load. Tank‐to‐wheel CO and CH emissions, along with component‐level energy losses and efficiencies, are compared between hybridized and conventional configurations across urban and highway driving under varying cargo loads.