Numerical study on a free-piston Stirling electric generator with a gas-spring-postpositioned displacer for high-power applications

The acquisition of spring stiffness is one of the main bottlenecks limiting the development of free-piston Stirling electric generator (FPSG) for high-power applications. To solve this issue, a high-power FPSG with a gas-spring-postpositioned displacer (GSPD) is proposed and numerically studied by using commercial software SAGE and thermoacoustic postprocessing, and its principle feasibility and performance characteristics are verified by implementing the structural refurbishment on the component test power converter (CTPC). Results show that the thermal-to-electric efficiency of the GSPD could be improved by at least 15% compared with that of the CTPC at an output electric power of 13 kW. The higher the power, the greater the performance advantage of the GSPD over the CTPC. In addition, investigation of the internal power flow distribution reveals that bounce space (BS) unexpectedly contributes a positive power flow to the piston, and this difference recedes as the volume of the BS increases. Lastly, sensitivity analysis of the structural parameters affecting the gas spring stiffness is conducted, and results demonstrate that placing the displacer gas spring into the BS is viable for simplifying the structure and improving the performance.