Thermodynamic modeling of performance of a Miller cycle with engine speed and variable specific heat ratio of working fluid

The performance of an air standard Miller cycle is analyzed using finite-time thermodynamics. The results show that if the compression ratio is less than certain value, the increase of the value of the specific heat ratio will make the power output bigger. In contrast, if the compression ratio exceeds certain value, the increase of the value of the specific heat ratio will make the power output less. The results also show that if the compression ratio is less than certain value, the power output decreases with increasing engine speed, while if the compression ratio exceeds certain value, the power output first increases and then starts to decrease with increasing engine speed. With a further increase in compression ratio, the increase of engine speed results in decreasing the power output. The results are of importance to provide good guidance for the performance evaluation and improvement of practical Miller engines.