Dual-Fuel Ethanol-Diesel Technology Applied in Mild and Full Hybrid Powertrains 2019-24-0115

The increasingly stringent emissions regulations together with the demand of highly efficient vehicles from the customers, lead to rapid developments of distinct powertrain solutions, especially when the electrification is present in a certain degree. The combination of electric machines with conventional powertrains diversifies the powertrain architectures and brings the opportunity to save energy in greater extents. On the other hand, alternative combustion modes as reactivity controlled compression ignition (RCCI) have shown to provide simultaneous ultra-low NO_x and soot emissions with similar or better thermal efficiency than conventional diesel combustion (CDC). In addition, it is necessary to introduce more renewable fuels as ethanol to reduce the total CO₂ emitted to the atmosphere, also called well-to-wheel (WTW) emission, in the transport sector. Therefore, the combination of these two growing technologies with the use of ethanol (E85) could be a potential way to achieve clean and efficient vehicles. In this work, numerical simulations of full hybrid electric vehicles (series, parallel and series-parallel) and mild hybrid vehicles were performed and compared versus the conventional powertrain in the WLTC driving cycle. The hybrid vehicles are simulated with both CDC and diesel-ethanol RCCI combustion engines as power source. Each powertrain was optimized in terms of electric components (battery capacity, electric motors...), internal combustion engine operating points, power management strategy and transmission/differential ratio to obtain the minimum fuel consumption and NO_x emissions. The results show a significant reduction of the total mass consumption as the complexity of the hybrid system increases (more electrical devices needed). In this sense, the series-parallel architecture, which represents the most complex hybrid system, allows reducing the energy consumption around 20% compared to the conventional powertrain operating under CDC. In addition, the combined use of CDC and RCCI in the same engine map showed improvements in NO_x, soot and CO₂ emissions versus CDC. Moreover, the series hybrid powertrain obtained the lowest NOx and soot emissions values due to using fixed operating conditions in RCCI mode for the thermal engine. Lastly, the mild hybrid technology showed an acceptable balance between complexity and fuel consumption.