Fuel consumption assessment of an electrified powertrain with a multi-mode high-efficiency engine in various levels of hybridization

Powertrain electrification including hybridizing advanced combustion engines is a viable cost-effective solution to improve fuel economy of vehicles. This will provide opportunity for narrow-range high-efficiency combustion regimes to be able to operate and consequently improve vehicle's fuel conversion efficiency, compared to conventional hybrid electric vehicles. Low temperature combustion (LTC) engines offer the highest peak brake thermal efficiency (BTE) reported in literature, but these engines have narrow operating ranges. In addition, LTC engines have ultra-low soot and nitrogen oxides (NOx) emissions, compared to conventional compression ignition and spark ignition (SI) engines. In this study, an experimentally developed multi-mode LTC-SI engine is integrated into a parallel hybrid electric configuration, where the engine operation modes include homogeneous charge compression ignition (HCCI), reactivity controlled compression ignition (RCCI), and conventional SI. The powertrain controller is designed to enable switching among different modes, with minimum fuel penalty for transient engine operations. A pontryagin's minimum principal (PMP) methodology is used in the energy management supervisory controller to study a multi-mode LTC engine in parallel HEV architecture with various hybridization levels. The amount of torque assist by the e-motor can change the LTC mode operating time, which leads to variation in the vehicle's fuel consumption. The results for the urban dynamometer driving schedule (UDDS) driving cycle show the maximum benefit of the multi-mode LTC-SI engine is realized in the mild electrification level, where the LTC mode operating time increases dramatically from 5.0% in a plug-in hybrid electric vehicle (PHEV) to 20.5% in a mild HEV.