Development of a coupling model and parametric analysis of an opposed free-piston engine linear generator

The opposed free-piston engine linear generator shows unique dynamic characteristics due to the elimination of the complex crankshaft and connecting rod mechanism. This paper investigated the behaviors of the design parameters and operating conditions on engine performance based on the simulation and experimental results. Considering the unique dynamic characteristics and the coupling of free-piston engine and linear generator, a numerical model was established and validated with prediction errors of 2 %. According to the experimental results, an optimal ignition position of 27 mm was obtained, and the both of indicated power and indicated work achieved their maximum value of 1.85 kW and 87.37 J improved by 17.1 % and 20.9 %, respectively. Further parametric analysis about the design parameters was carried out based on the coupling model. Simulation results showed that the brake thermal efficiency could be improved significantly from 31.95 % to 36.06 % considering the coupling effects of the piston assembly mass and the stroke length. Additionally, higher indicated power could be obtained with a shorter stroke length and lower piston assembly mass.