Hybrid powertrains offer a viable pathway to lower carbon footprint of transportation. In commercial vehicles, where battery and motor mass can reduce payload capacity, freight efficiency (ton-miles per gallon) is a more representative performance metric than fuel economy. By providing electric assistance to moderate torque transients, hybridization reduces fuel consumption and transient soot emissions in diesel engines. This study explores the hybridization of a Class-8 heavy duty truck powered with an Opposed-Piston Two-Stroke (OP2S) diesel engine and its impact on vehicle freight efficiency and emissions. This vehicle model was developed with experimentally recorded hot steady-state engine maps and a custom MATLAB routine to generated optimized gear shift schedules for a 12-speed PACCAR automated manual transmission. Vehicle 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 the fuel economy predicted by the model. The validated conventional model was hybridized into series, parallel, and series-parallel architectures, and the corresponding engine profiles were tested experimentally. Results showed up to 18% improvement in freight efficiency and significant emission reductions attributed to novel strategy for transient smoothening via hybridization; soot by 50% and NOx by 39%.
Bhatt et al. (Tue,) studied this question.