Modeling and Optimization of Energy Conversion Performance of a Free-Piston Linear Engine

A model-based study is carried out to optimize the energy conversion performance of a free-piston linear engine (FPLE) based on its design parameters. The FPLE is modeled by dynamic, linear alternator, and thermodynamic models. Besides, a mathematical model using particle swarm optimization (PSO) algorithm is established to optimize the FPLE energy conversion performance. To validate the FPLE models, the simulation results of in-cylinder pressure and electric power output of the engine are compared with the corresponding experimental results. Influences of design parameters, including air gap (gap) between translator and stator, number of coil turns in stator (Ncoil), and thickness of permanent magnet in translator (hm), on the FPLE dynamic, thermodynamic, power, and energy conversion characteristics are studied. The simulation results indicate that the in-cylinder pressure is increased when increasing gap and reducing Ncoil and hm; however, it also causes the electric power output and conversion efficiency of energy to reduce. By using PSO algorithm, the optimum conversion efficiency of energy is quickly found at gap = 1.9 mm, Ncoil = 252, and hm = 16 mm. This study shows a successful combination of simulation models and PSO algorithm to simulate and optimize the energy conversion performance of the FPLE.