Transient and steady performance analysis of a free-piston Stirling generator

Free-piston Stirling generator (FPSG) is a promising distributed power generation system with compact configuration and high efficiency. In a new perspective on thermoacoustics, this paper develops a time-domain acoustic-electrical analogy method to explore the transient and steady-state performance of a highly efficient FPSG. The method captures the main characteristics of the FPSG, simplifying the calculation thus saving time, and its effectiveness has been verified by our experiments. Transient evolutions of key parameters such as volume flow rate, oscillating pressure and voltage, are first given, followed by an investigation of the acoustic field distribution. Subsequently, a performance analysis of the system is carried out. The results indicate that an increase in the damping coefficient leads to a deterioration in performance, particularly for the displacer. Operating parameters have strong influences on system performance: lower ambient temperature, higher heating temperature and larger external electric resistance contribute to higher pressure ratio and electric power, while excellent performance can be achieved at medium mean pressure. A maximum thermal-to-electric efficiency of 45.2% and a highest exergy efficiency of 68.0% are obtained at an electric resistance of 57.5 Ω and a heating temperature of 600 °C, accompanied by an electric power of 1517 W, which implies that the proposed FPSG has great promise in the field of kilowatt-scale distributed power generation. This paper provides a new viewpoint and an effective way for the rapid simulation of free-piston Stirling generator.