Optimizing Fuel Economy and Reducing Emissions in Heavy- Duty Trucks: A Comparative Analysis of Different Hybrid Powertrain Layouts with an Opposed Piston Two-Stroke Engine

Hybrid powertrain architectures offer a viable pathway to reduce the carbon footprint of transportation. The degree of hybridization usually depends on the application of the vehicle and its desired performance parameters. For commercial vehicles, excessive battery and motor mass can reduce payload capacity, making freight efficiency measured in ton-miles per gallon as a more appropriate metric than traditional fuel economy alone. Hybridization also enables emission reduction during transient operations, particularly in diesel engines, where turbocharger lag can cause soot spikes. By moderating the engine's torque rise rate and allowing electric assistance during transients, both fuel consumption and emissions can be improved.This study evaluates the impact of hybrid powertrains on freight efficiency and emissions in a Class 8 heavy-duty truck, benchmarked against a Peterbilt 579. The vehicle model was developed in GT-Drive, with engine maps derived from hot steady-state data recorded on a 10.5 L Opposed-Piston Two-Stroke (OP2S) diesel engine. A custom MATLAB routine generated optimized gear shift schedules for a 12-speed PACCAR automated manual transmission. Simulations were conducted over the EPA HUDDS drive cycle, and the resulting engine speed–torque profiles were used in pseudo-Hardware in the Loop (HIL) testing to validate predicted fuel economy. The validated conventional model was hybridized into series, parallel, and series-parallel architectures, and corresponding engine profiles were tested experimentally. Results showed up to 18% improvement in freight efficiency (series) and significant emission reductions attributed to transient smoothening via hybridization; soot by 50% and NOx by 39%.