Abstract:A theoretical thermodynamic cycle model was established with the expansion ratio of constant temperature as a parameter. Based on an analysis of the thermodynamic cycle of typical the closed and open porous medium(PM) engine, a formula of the thermal efficiency and cycle net-work was derived. The relationship of thermodynamic cycle between the closed and open PM engine was defined with the compression ratio coefficient. Through calculation, six kinds of thermodynamic cycle of two types of traditional and the closed PM engine were studied, in which the variation and impact of thermal efficiency and cycle net-work with the change of other parameters were deduced. The analysis results show that the net-work of theoretical thermodynamic cycle of the closed PM engine is superior to that of the traditional engine. The high speed diesel engine cycle is found to be more suitable for PM technical scheme.