A novel high-power free-piston stirling engine generator with integrated heat pipes for thermal-to-electric conversion of clean energy

The free-piston Stirling generator (FPSG) has emerged as a promising solution to meet the increasing energy demand of various small- or micro-scale application scenarios. Known for its high durability and high efficiency across various application scenarios, FPSGs can be effectively coupled with different heat sources. The success of the well-known US ‘Kilopower’ project demonstrates the feasibility of integrating FPSGs with nuclear reactors. However, the output power of a single FPSG within this project is relatively small, because of the heat transfer challenges of the current Stirling engine generators encountered when integrated with nuclear reactors. To address this issue, this paper proposes a novel high-power FPSG with integrated heat pipes. The system offers the advantage of efficient high heat transfer flux coupling to the engine through heat pipes with a simple structure, though it requires careful design of the gas passage structure for the high-temperature heat exchanger (HHX). The novel FPSG with an encouraging output power of 11.2 kW and a thermal-to-electric efficiency of 40.15 % was achieved in simulations. Analysis results indicate that the size difference between the internal gas passages (IGPs) and external gas passages (EGPs) of the HHX can lead to a maximum difference of 6 kW in the system's output electric power and a 15 % difference in thermal-to-electric efficiency. This study reveals the significant relationship between the design parameters of the HHX and the overall performance of the integrated heat pipe FPSG system, offering a straightforward and viable approach for developing high-power FPSGs.