Experimental Study on Hydraulic Free-Piston Diesel Engine

Free-piston engines are investigated by a number of research groups worldwide, with potential advantages of high-efficiency and low-emissions. Hydraulic free-piston diesel engine, which combines a two-stroke diesel engine and a hydraulic pump, could be an alternative to conventional technology in applications. It can fulfill the power requirements of vehicle under optimum operation conditions, only by change the operation frequency. The piston dynamics of the free-piston engine differ from those of conventional engines, and this may influence the combustion process and power output. This paper introduces the design of a single piston hydraulic free-piston diesel engine. The piston dynamics and combustion process were investigated from test data. Different from conventional engine, the main combustion phase of hydraulic free-piston diesel engine is pre-mixed combustion phase. Most of the fuel burns in the pre-mixed phase, resulting in a very high rate of heat release. Finally, the pumping process of hydraulic free-piston diesel engine has been discussed. It is seemed that the response lag between the pump chamber pressure and the piston displacement at the start of the expansion stroke is mostly determined by the close action of the suction valve. Improving response performance of the suction valve will increase the total efficiency of the hydraulic free-piston diesel engine.