An Experimental and Numerical Study of a Miller Cycle for a Gas Engine Converted From a Diesel Engine

Studies on internal combustion engines have made great efforts to develop engines with high efficiency for energy saving and emission gas reduction. The thermal efficiency of an internal combustion engine can be increased by expanding the pressure energy obtained through combustion to the maximum extent to convert the supplied thermal energy into work to the maximum extent. The cycle that can realize this goal is the Miller cycle. This Miller cycle converts the supplied thermal energy into mechanical energy to the maximum extent by making the expansion ratio greater than the compression ratio by changing the intake valve close timing. It is essential that study be performed for the development of the engine with high efficiency for energy saving in this era of rising oil prices. Therefore, this study realized a low compression and high expansion ratio engine by changing the intake valve close timing in order to investigate the characteristics of the Miller cycle. Furthermore, it confirmed that both the compression pressure and maximum combustion pressure increased through thermodynamic analysis. In addition, using the engine analysis program developed by the Ricardo Company known as WAVE, this study obtained the result that the output, torque and break thermal efficiency increased by 2 PS, 1.5kg and 2%, respectively at WOT (Wide Open Throttle) position and ABDC55° through simulation by changing the intake valve close timing.