Abstract: Increasing efficiency and reducing emissions are fundamental approaches to achieving peak carbon emissions and carbon neutrality for the transportation and power industries. The Argon power cycle (APC) is a novel concept for high efficiency and zero emissions. However, APC faces the challenges of severe knock and low power density at high efficiency. To elevate efficiency and power density simultaneously of APC, the Miller cycle is applied and combined with APC. The calculation method is based on a modification of the previous thermodynamic method. The mixture of hydrogen and oxygen is controlled in the stoichiometric ratio. The results indicate that to obtain a thermal conversion efficiency of 70%, in the Otto cycle, the compression ratio and the AR (argon molar ratio in the argon-oxygen mixture) could be 9 and 95%, respectively. In comparison, for the Miller cycle, these two parameters only need to be 7 and 91%. A lower compression ratio can reduce the negative effect of knock, and a reduced AR increases the power density by 66% with the same efficiency. The improvement effect is significant when the expansion-compression ratio is 1.5. Meanwhile, increasing the expansion-compression ratio is more effective in the argon-oxygen mixture than in the nitrogen–oxygen mixture. For the next-generation Argon/Miller power cycle engine, the feasible design to achieve the indicated thermal efficiency of 58.6% should be a compression ratio of 11, an expansion-compression ratio of 1.5, and an AR of 91%.

Key words: Argon power cycle engine, , Miller cycle, , Hydrogen, , Thermal conversion efficiency, , Power density