Study on the thermoacoustic characteristics and acoustic matching of a 15 We free-piston Stirling generator

Abstract

Free-piston Stirling generators (FPSGs) are attractive for their high reliability, high efficiency, low noise, compact structure, long lifetime, etc. An FPSG consists of a linear alternator (LA) and a free-piston Stirling engine (FPSE), which are strongly coupled and affect the generator’s performance. However, they were always studied separately in most previous studies, and their coupling relationship was ignored. In this regard, the matching between them was systematically investigated from the perspective of thermoacoustic theory. Based on a complete numerical model and a self-developed 15 We FPSG, the methodology for modulating the acoustic impedance to achieve the overall resonance of the generator was studied in detail. The results showed that the acoustic impedances of the FPSE and LA could be modulated individually and effectively by adjusting the operating parameters and external electric loads. For the output acoustic impedance of the FPSE, the absolute values of the real and imaginary parts could be increased by raising the operating pressure or hot-end temperature. The engine’s output performance could be improved as the real part increases, but the thermal-to-acoustic efficiency would deteriorate when the imaginary part deviates from zero. The maximum output electrical power and acoustic-to-electric efficiency of the LA could be achieved when the real and imaginary parts achieve the maximum value and zero, respectively. The experimental results showed that the output electrical power and thermal-to-electric efficiency could achieve 15.1 We and 15.6%, respectively. The whole FPSG could be enhanced significantly and operates with the highest efficiency when the resonant state is achieved, which always occurs with good acoustic impedance matching.