Parametric study on the starting of a free-piston engine alternator

Abstract

The free-piston engine alternator is a new crankless engine. The traditional starting method cannot be used to conveniently initialize the new engine. This article introduced a resonance starting method and investigated the effects of influential parameters on the free-piston engine alternator starting. An experimental free-piston engine alternator prototype was developed, and the effects of starting force, connecting rod length, and piston assembly mass on the resonance starting were experimented. Experimental results show that the piston motion is influenced by the starting force, and the final compression ratio of the engine is increased with the enlarged thrust force. A more high starting compression ratio can be obtained by either increasing or decreasing from the certain translator mass. The experiment also suggests that properly enlarging the connecting rod length can enhance the starting capacity of a linear alternator with a constant force. Moreover, an advanced simulation model was presented for the parametric study of the starting process. The effects of heat transfer, friction, and leakage on the resonance starting were investigated. Simulation indicates that the heat transfer is a significant inference on free-piston engine alternator starting, and the peak gas pressure varies in negative correlation with the piston ring closed clearance and friction load. As a result, the starting control strategy of free-piston engine alternator is required to consider these influential parameters.