Retrofit of a Heavy-Duty Diesel Truck: Comparison of Parallel and Series Hybrid Architectures with Waste Heat Recovery

This paper describes and compares different powertrain configurations for the retrofit of a heavy-duty Class 8 truck, powered by a 12.6 liters diesel engine. The engine is firstly equipped with an electrification-oriented organic Rankine cycle (ORC) system and then coupled to a traction electric machine into a hybrid powertrain. An electrification-oriented ORC system can produce enough energy to cover the ancillary loads, which in long-haul applications for freight transportation are quite demanding. Nevertheless, only powertrain hybridization can achieve significant improvements in the overall system efficiency. Both systems may thus be implemented in the same vehicle, but an efficiency improvement is guaranteed only if the system is carefully managed so as to reach a trade-off between the requirements and potential benefits of the ORC system and those of the hybrid powertrain. In a previous work, the presence of the ORC system in a series hybrid retrofit has shown to allow for just a slight improvement of the powertrain performance, compared to the hybrid powertrain without the ORC system. For this reason, in the present paper an ORC and parallel hybrid electric retrofit is proposed and compared to the previously investigated ORC and series hybrid electric retrofit. To this aim, a GT-Suite model is used for the derivation of performance maps of the engine with the ORC system. Afterwards, a forward-looking simulator of the truck is realized to model both the parallel and series hybrid electric powertrains with different sizes of the electric motors, but maintaining the engine size unchanged. The powertrain performance in terms of fuel consumptions and CO₂ emissions are evaluated for different driving cycles and results are compared.