Prediction on onset conditions of alpha, beta, and gamma type free piston Stirling generators

Abstract

The study of the onset characteristics of the free piston Stirling generator (FPSG) is essential for its development. In this study, the onset characteristics of the FPSG were discussed based on a thermodynamic model using the Routh stability criterion. First, the onset conditions of three types of FPSG, alpha, beta, and gamma, were analyzed. Then an experimental and numerical study of a 100 W beta-type FPSG prototype was conducted. The impacts on the onset temperatures of spring stiffness, charging pressure, and external load were further explored. The results demonstrate that no matter how the parameters are altered, alpha-type FPSG cannot start up. Whether beta and gamma type FPSG can start up depends on the design and operating parameters. For the prototype, as the displacer spring stiffness increases, the onset temperature rises first and then drops. When the displacer spring stiffness is 19.2 N/mm, the corresponding onset temperature is the lowest of 489 K. The FPSG is easier to start up at a higher external load and higher charging pressure. The experimental results of the impacts of the spring stiffness, charging pressure, and external load on the onset temperature agree well with the calculated results, with errors ranging from 1.7% to 9.12%. The proposed approach can play a guiding significance in studying FPSG onset conditions. K E Y W O R D Sfree piston Stirling generator, onset, Routh stability, three types | INTRODUCTIONWith the growing demand for deep space exploration, the energy system which supplies electricity for deep space exploration has emerged as a prominent topic. 1 However, due to the long distance from the sun, solar energy is sparse in deep space. 2 Nuclear energy is an ideal source for long-life-span deep space exploration. 3 An efficient, reliable, and long-life-span device is required to convert nuclear heat energy to electricity. Free piston Stirling generator (FPSG), a device that converts nuclear heat energy into electrical power, has received a lot of interest due to its high efficiency, high reliability, and long life. 4,5 The free-piston Stirling generator is one of the most typical Stirling generators, which was invented by William Beale in 1964. 6 The generator eliminates the