Operating characteristics of a 15 W free-piston Stirling generator

Abstract

Free-piston Stirling generators (FPSGs) show great potential in portable power sources for the advantages of high reliability, high efficiency, low noise, compact structure, long lifetime, etc. An FPSG aimed at 15 W electric power output is numerically and experimentally studied. By adopting the second method of Lyapunov, the onset characteristics of the FPSG are analyzed based on a thermodynamic model. The effects on the onset conditions of the interaction between the displacer and power piston are explored. It is shown that the optimal operating pressure and spring stiffness corresponding to the lowest onset heating temperature are 6.2 MPa and 5500 N/m, and the FPSG is easier to start when the damping of the displacer and power piston is smaller and the mass of the displacer and power piston is well matched. The experimental results of the effects of the pressure and spring stiffness on the onset temperature agree well with the calculated results. The FPSG can generate 15.5 W electric power with a thermal-to-electric efficiency of 16.0% in the experiment when the heating and chilling water temperatures are 820 K and 300 K, respectively. And the relative errors between the calculated and experimental PV power and their efficiencies are about 2.1%–6.8% and 24.4%–26.9%, respectively. This work can lay a good foundation for studying the onset characteristics and stable operating characteristics of FPSGs.