Experimental Investigations on Performance Optimization of Hybrid Diesel Engine Based on Miller Cycle

This paper takes a four-cylinder engine as the research object, analyzes the optimized operating range of this engine through the study of the hybrid power operating condition. The CAM profile with high compression ratio and late intake valve closing, combined with the optimization of supercharger, focuses on improving the operation condition of hybrid engine. The results show that based on the optimization of combustion configuration based on Miller cycle, the lowest fuel consumption is reduced under both large load and small load. Under heavy load condition 1 ($\mathrm{NOx}=12 \mathrm{~g} / \mathrm{kWh}$), the fuel consumption is reduced by about $3.07 \mathrm{~g} / \mathrm{kWh}$, and under small load condition $2(\mathrm{NOx}=8 \mathrm{~g} / \mathrm{kWh})$, the fuel consumption is reduced by $2.06 \mathrm{~g} / \mathrm{kWh}$. At large load (working condition 1), the exhaust temperature is basically flat due to the improvement of the booster pressure by the supercharger optimization, and at small load (working condition 2), the exhaust temperature is increased by about $10^{\circ} \mathrm{C}$. When the injector flow rate is increased based on Miller cycle, the fuel consumption of large load (condition 1) is slightly improved, which has little effect on the fuel consumption of small load. However, due to the reduction of the injection duration, the oil-gas mixing time is shortened, and the smoke of small load is slightly increased.The article argues that within the theoretical framework of the Miller cycle, appropriate cam profile selection and turbocharger selection in engineering applications can achieve a high expansion ratio thermal cycle. Additionally, by increasing the fuel injection rate to accelerate combustion efficiency, it is possible to effectively enhance the thermal efficiency of dedicated hybrid engines. This, in turn, improves product development efficiency and reduces development costs.