Quantitative comparison of the operating characteristics and engine performances of typical configurations of free-piston engine linear generator

Due to their unique operating characteristics and high thermal efficiencies, free-piston engine linear generator (FPELG) has attracted research interest in recent years, thanks to the crankshaft absence. The FPELG has three typical structure configurations: single-cylinder single-piston, dual-cylinder dual-piston, and opposed-piston. These structure configurations have different benefits owing to their distinctive piston operating characteristics and engine performances. This paper analysed the piston operating characteristics and engine performances of the three typical FPELG structure configurations using a quantitative comparison method. The results revealed that the output power of the dual-cylinder dual-piston FPELG was the highest, at 3.7 kW. The opposed-piston FPELG exhibited the highest indicated thermal efficiency of 34%. In addition, the indicated power of FPELG was negatively correlated with the heat transfer area. The friction loss of each FPELG was < 5% of the overall energy consumption. Our study comprehensively analysed the various FPELG structure configurations and highlighted their advantages.