A combination of electric supercharger and Miller Cycle in a gasoline engine to improve thermal efficiency without performance degradation

Miller cycle makes the expansion ratio larger than effective compression ratio by early or late closing intake valves thereby improving the thermal efficiency of gasoline engines at the risk of power degradation. Electric supercharging efficiently improves transient response and output of engines. This paper proposes an electrically supercharged non-backflow Miller cycle by combining electric supercharging and Miller cycle to improve thermal efficiency of gasoline engines without power output reduction. The results indicate that electrically supercharged non-backflow Miller cycle can effectively improve the thermal efficiency of gasoline engines. Compared to the original Otto-cycle gasoline engine, the electrically supercharged Miller-cycle engine has the highest thermal efficiency of 35.54% which is an improvement of 4.32% at 3500 rpm full load operation. The electric supercharger ensures that the power output is not reduced. Therefore, electrically supercharged non-backflow Miller cycle is an effective method to improve thermal efficiency of gasoline engines without performance degradation.