Free-piston internal combustion engines (FPICEs) have many potential advantages, such as simple structure, high conversion efficiency, multi-fuel feasibility and multi-output power types, because their piston motion is not restricted by the crankshaft system. Therefore, FPICEs have received considerable attention worldwide for many decades. According to recent research, the typical types of FPICEs include free-piston internal combustion engine linear generator, hydraulic free-piston internal combustion engine, linear Joule engine generator, and miniature FPICEs. This paper mainly reviews recent advances in these types of FPICEs. Firstly, the early research progress of FPICEs is briefly introduced. After that, the recent advances in the typical types of FPICEs are reviewed in more detail. These included the operating principles, piston dynamic characteristics, performances and control strategies for different types of FPICEs. Finally, the research trends and future development of FPICEs are discussed. It is noted that there are numerous research prospects for each type of FPICE, including performance optimisation, development of appropriate control systems, and future application exploration.

自由活塞式内燃机（FPICE）具有许多潜在的优势，例如结构简单，转换效率高，多种燃料的可行性和多种输出功率类型，因为它们的活塞运动不受曲轴系统的限制。因此，几十年来，FPICE在全世界引起了相当大的关注。根据最新研究，FPICE的典型类型包括自由活塞式内燃机线性发电机，液压自由活塞式内燃机，线性焦耳发动机发电机和微型FPICE。本文主要回顾了这些类型的FPICE的最新进展。首先，简要介绍了FPICEs的早期研究进展。之后，将更详细地回顾典型FPICE类型的最新进展。其中包括操作原理，不同类型FPICE的活塞动态特性，性能和控制策略。最后，讨论了FPICEs的研究趋势和未来发展。值得注意的是，每种类型的FPICE都有许多研究前景，包括性能优化，适当控制系统的开发以及未来的应用程序探索。