Simulation of a hydraulic free piston engine : A dual piston case

A hydraulic free piston engine (HFPE) combines a diesel engine and a hydraulic pump into one compact component. In practical view there is only one linearly moving part in the HFPE, the piston assembly that contains three parts, combustion and hydraulic piston and piston rod. The piston assembly moves during operation linearly back and forth between left and right extreme by means of the fuel energy. Simultaneously hydraulic piston produces directly hydraulic energy. The paper deals with simulation study of the dual hydraulic free piston engine and the influence of design parameters on the dynamic behaviour of the engine. Interesting parameters are the mass of the piston assembly, stroke length, piston areas, hydraulic pressures and compression ratio. All the parameters have influence on the operation variables like piston acceleration and velocity, output power and operation frequency. Also the influence of the compression ratio is studied though it is not a design parameter but operational variable. Study shows that the parameters have influence on the values of the performance measures such as piston's maximum velocity and acceleration but the basic behaviour of the engine stays similar.