Research on the implementation of free piston engine generator at various compression ratios and combustion performance of multiple fuels

The Free Piston Engine Generator (FPEG) is a novel energy conversion system that directly couples a free piston engine with a linear generator. Its ability to adjust the compression ratio over a wide range without complex auxiliary structures and its adaptability to different fuels have garnered significant attention. To improve the efficiency and cleanliness of FPEG, This study employs an FPEG prototype test bench, using ethanol and n-propanol as raw materials, mixed with aviation kerosene (RP-3) at volume ratios of 20 %, 40 %, and 60 %, respectively. It investigates the impact mechanisms and operating characteristics of different running parameters on the compression ratio of FPEG when using different fuels, and to analyze the combustion and emission characteristics of FPEG under various compression ratio conditions. The results show that compared to gasoline, the alcohol/RP-3 mixtures (with alcohol content >40 %) have higher brake thermal efficiency and significantly reduced CO emissions. As the compression ratio increases, the brake thermal efficiency of alcohol/RP-3 mixtures further improves, while CO and HC emissions decrease. At higher compression ratios, the n-propanol/kerosene blends show higher efficiency and lower CO and HC emissions. These findings provide important insights into the multi-fuel application of FPEG and the potential for cleaner energy conversion.