Research on the generation performances of a free-piston engine linear generator based on numerical models and experimental results

The free-piston engine linear generator is an advanced power device with many advantages, such as high energy conversion efficiency and power density. It directly converts the linear kinetic energy generated by a free-piston engine into electrical energy. Therefore, the generation performance metrics, such as the energy conversion efficiency and output power, are critical for evaluating its terminal output performance. This study analyzes the generation performances of the free-piston engine linear generator based on numerical models and experimental results. The results show that the linear generator generates a peak output power of 770.3 W with an efficiency of approximately 68.17 % under a load resistance of approximately 6 Ω. It is also observed that the output voltage and generation efficiency of the free-piston engine linear generator increase with the load resistance, while the output current decreases. Additionally, both the copper and mechanical losses, along with their respective ratios, decrease as the load resistance increases. Moreover, increasing the mover mass and cycle fuel injection mass increases the output power, but reduces the generation efficiency. In contrast, extending the combustion duration decreases the output power, increases the generation efficiency, and reduces the copper and mechanical losses. Finally, a multi-parameter coupling analysis of the free-piston engine linear generator shows that there exists optimal load resistance, which maximizes the output power.