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Simulation study of a two-stroke Single Piston Hydraulic Free Piston Engine

A hydraulic free piston engine combines an I.C. engine and a hydraulic pump into one compact component. The single piston hydraulic free piston engine is a kind of HFPE which has only one combustion cylinder. It is a diesel engine which is designed for an application in a hydraulic vehicle. A model in Matlab/Simulink of the proposed engine has been generated in this paper. The piston assembly dynamics, combustion process, friction characteristics and hydraulic leakage are coupled together for systematic analysis. In this model, the piston motion is controlled by Newtonpsilas second law and the combustion process is represented by a simplified model based on ignition delay integrals and Wiebe functions. The model with actual design parameters has been investigated. The simulation results indicate that the working cycle of the SPHFPE is unsymmetrical and the compression stroke time is little greater than the expansion stroke time. The maximum acceleration is about 10000 m/s2 and the maximum instantaneous flow rate reaches 300 L/min. The characteristics of the frequency control valve in the SPHFPE are offered.