Performance analysis of a free piston linear generator: Integrated simulation with thermodynamic and electromagnetic coupled modelling

The free piston linear generator (FPLG) features simple structure, multi-fuel applicability and high energy conversion efficiency. In this study, a real-time integrated simulation model of the FPLG system is developed and validated based on a modeling approach that considers nonlinearities. A free piston engine (FPE) and a permanent magnet linear generator (PMLG) is modeled using MATLAB/Simulink and Maxwell, respectively, and the data interaction of different models is implemented in Simulink. The results show that the external load resistance should increase synchronously when the operating stroke of the FPLG increases. The stroke and excess air ratio play a dominant role in the indicated power, and compression ratio and ignition position play a dominant role in the indicated thermal efficiency. Increasing external load resistance decreases the motor copper loss and increases the motor efficiency, while the motor efficiency saturates with a limited increase at piston speeds greater than 2 m/s. The effect of parameters on the performance of the FPLG system is investigated using response surface methodology (RSM) to develop a predictive model. A longer stroke and richer air-fuel mixture should be selected and the optimum ignition position with compression ratio should be chosen to achieve high efficiency and high-power output.