Optimization of the parallel and mild hybrid vehicle platforms operating under conventional and advanced combustion modes

Abstract

Abstract The stringent regulations, increased global temperature and customer demand for high fuel economy have led to rapid developments of different alternative propulsion solutions in the last decade, with special attention to the electrified vehicles. The combination of electric machines with conventional powertrains allows to diversify the powertrain architectures. In addition, alternative combustion modes as reactivity controlled compression ignition (RCCI) have been shown to provide simultaneous ultra-low NOx and soot emissions with similar or better thermal efficiency than conventional diesel combustion (CDC). Therefore, the combination of both technologies creates a promising horizon to be implemented in commercial vehicles of the near future. In this work, experimental and numerical simulations were combined to study the potential of the parallel full hybrid electric vehicle (P2-FHEV) and mild hybrid vehicle (MHEV) to obtain lower fuel consumption and NOx emissions than a conventional powertrain in the Worldwide Harmonized Light Vehicles Cycle (WLTC). The hybrid vehicles are simulated with both CDC and diesel-gasoline RCCI combustion engines as power source. Each powertrain was optimized in terms of components (battery, electric motors…) capacity, internal combustion engine operative points, energy management strategy and gear ratios. The results show a significant fuel consumption reduction as the complexity of the hybrid system increases. The parallel architecture, which represents the most complex hybrid system tested in this work, allows obtaining a fuel consumption reduction of around 20% as compared to CDC. The dual-mode CDC-RCCI concept showed improvements in NOx and soot emissions with comparable values in terms of energy consumption and CO2 emissions than CDC. Additionally, the mild hybrid technology with the functionality of start-stop, torque assist and regenerative braking showed an acceptable balance between complexity and fuel consumption gain.