Effect of mover assembly mass on the performance of a dual-piston type free piston engine generator

The free piston engine generator (FPEG) is a novel energy conversion device which directly converts chemical energy of fossil fuels into electric energy by linear electric mover’s reciprocating linear motion driven by the combustion of combustible fuel-gas mixture. In this research, a validated numerical model was established to investigate the effect of the mover assembly mass on the system operation characteristics, engine performance, heat transfer loss and frictional loss. The results showed that the unique phenomenon of fast expansion and slow compression becomes more obvious as the mover assembly mass increases while the system operating frequency changes slightly. The indicated that the thermal efficiency decreases and the indicated specific fuel consumption increases as the mover assembly mass increases and the maximum indicated power is 3.37 kW when the mover assembly mass is 4.5 kg. The heat transfer loss increases and the friction loss changes slightly as the mover assembly mass increases when the input energy and the effective stroke keep constant. Lower mover assembly mass (lower than 4.0 kg) makes it difficult to achieve high operation compression ratio and higher mover assembly mass and high operation compression ratio would lead to excessive in-cylinder pressure and cause structural damage on the key components.