Combustion characteristics analysis of hydraulic free piston diesel engine

Compared with the conventional engine, the special characteristic of hydraulic free piston diesel engine decides its differences in the aspects of piston displacement, velocity, acceleration, etc. These differences lead to more complex fluid flow, and particular intrinsic energy distribution in-cylinder. Moreover, the mean velocity of the combustion gas is enhanced and the velocity of vortex in-cylinder is decided by the piston speed and the scavenging process. All these factors bring about the differences of heat transfer and air-fuel mixture. Fortunately all of them can be simulated and calculated by the CFD package. Therefore the rate of heat transfer in-cylinder can be obtained. Then the rate of heat release can be easily calculated. What is more, the calculated result is compared with the heat release regularity of Wiebe, and the fitted formula is used to analyze the heat release regularity of hydraulic free piston diesel engine. Further, polytropic exponent n is quoted to describe the condition of diffusion combustion. And then we analyze the working process of HFPDE based on the characteristics of the curves. Finally, the optimum proposals are presented. (C) 2015 Elsevier Ltd. All rights reserved.