Study on the coupling between engine and alternator in a free-piston Stirling generator

Abstract

The free-piston Stirling generator (FPSG) is composed of a free-piston Stirling engine (FPSE) and a linear alternator. The coupling relationship between the two parts directly affects the FPSG’s performance. The published literature about simulation models mainly focuses on investigating the FPSE and the alternator separately, which could hardly show the coupling between them. From the perspective of acoustic impedance matching, this paper established a complete simulation model of the FPSG based on SAGE software. The coupling relationship between the engine and the alternator and the influence of some vital parameters on FPSG’s performance were systematically investigated. The results showed that the linear alternator parameters directly influence the acoustic impedance at the surface of the power piston facing the FPSE, thereby affecting the FPSG’s performance. The working pressure affects the linear alternator by changing the working frequency. The acoustic-to-electric efficiency is only determined by the linear alternator parameters, external load and working frequency. To verify the simulation model, a FPSG prototype was established. Its characteristics showed good agreement with the simulation. With the heating temperature of 610 ℃, it could output 1040 W electric power with a thermal-to-electric efficiency of 36.2 %.