Free piston Stirling engines: A review

This paper presents a detailed review on free piston Stirling engines (FPSEs) technology. Generally, the Stirling engines can be categorized into two broad classes comprising kinematic and dynamic converters among which FPSEs are known as the dynamic type. Other well-known dynamic Stirling converters are Fluidyne and thermosacoustic engines among which the thermosacoustic ones are the most advanced Stirling converters recently presented. In this research, the dynamic Stirling engines are first introduced and reviewed. Then, the review work is directed toward the FPSEs, one of the most reliable dynamic Stirling converters utilized in different applications such as combined heat and power systems (CHPs). Subsequently, the working principles of different types of FPSEs and their performance are summarized. Next, several manufactured FPSEs, as well as their corresponding features and applications, are discussed. Finally, the article is conducted to analysis and modeling approaches of FPSEs. Accordingly, linear and nonlinear analytical techniques of FPSEs are introduced, and some comparative data are provided to verify the modeling schemes. Then, various design parameters affecting the engine performance are introduced and studied. The outcomes of this review work demonstrate the potential of FPSEs for different applications and reveal that the perturbation-based model is likely the most comprehensive nonlinear method for modeling and design of the FPSEs.