Abstract
This study analyzes the factors influencing the thermal efficiency of HCCI combustion in an over-expansion cycle engine. There are many influencing factors when combining the over-expansion cycle and HCCI combustion since 80 experimental conditions were included when varying compression ratio, expansion ratio, intake air temperature and equivalence ratio. The combustion efficiency is shown to be one of the dominant factors. Since the correlation coefficient between the combustion efficiency and ISFCg was -0.90. The over-expansion cycle is also shown to be effective to improve the thermal efficiency. The late-closing of intake valves contributes to extending the operating range of HCCI combustion.
