Modeling and experimental investigation of a free-piston Stirling engine based micro-combined heat and power system

In recent years, combined heat and power (CHP) systems have attracted increasing attention worldwide. Owing to their advantages of high overall thermal efficiency, fuel flexibility, low noise and vibration, and low emissions, Stirling engines, especially dynamic Stirling engines (i.e., free-piston Stirling engines, FPSEs) are promising candidates for micro-CHP systems. In this paper, recent progress in Stirling engine-based micro-CHP systems and FPSE modeling and analysis is first briefly reviewed, and then a hybrid calculation model based on thermoacoustic theory is proposed and developed to simulate the entire micro-CHP system. Finally, the construction and testing of a pilot setup is described in detail. The obtained experimental results clearly validate the numerical model and scheme, with the primary deviation within approximately 10%. CHP performance tests revealed a maximum CHP efficiency of 87.5% and an output electrical power of 2.9 kW, corresponding to a 28% thermal-to-electric efficiency, when the delivering temperature was above 60 degrees C. Furthermore, acoustic impedance analysis indicated that the CHP efficiency remains high over a large temperature lift, which was also confirmed experimentally.