Liquid Piston Technology for Energy Conversion and Storage: Mechanisms, Architectures, and Engineering Challenges

The increasing penetration of intermittent renewable energy has intensified the demand for efficient energy conversion, energy storage, and gas compression technologies. Liquid piston systems have attracted growing attention because of their non-contact sealing, structural simplicity, low mechanical friction, and favorable thermal management characteristics. This review establishes a unified analytical framework for understanding liquid piston technologies applied to compressed air energy storage, hydrogen compression, and Stirling energy conversion systems. The coupled interactions among liquid column dynamics, gas thermodynamics, and gas–liquid interfacial heat and mass transfer are systematically examined, with particular emphasis on how system configurations govern pressure evolution, thermal behavior, efficiency, and power density. Typical configurations and application pathways are compared to identify general design principles. Particular attention is given to approaches for achieving near-isothermal compression and expansion, including liquid spraying, porous media, internal structures, and geometric optimization. Key mechanisms limiting system performance are critically reviewed, including transient heat transfer, liquid-column inertia, gas dissolution, interfacial instability, and load interactions. A mechanism–configuration–performance framework is proposed to enable cross-system comparison and engineering design. Finally, key research priorities are identified, including standardized performance evaluation, system scale-up, control strategies, and long-term durability, providing technical guidance for the practical deployment of liquid piston systems in energy applications.