Energy and exergy analysis-based optimization of buffer parameters in ionic liquid compressor for hydrogen storage

The ionic liquid compressor is a promising hybrid system for high-pressure hydrogen storage, which combines the two-phase pressurizing subsystem and the hydraulic actuation subsystem. In this system, the free-piston motion characteristics are affected by the buffer structure inside. The piston movement significantly affects the system energy conversion efficiency, which consequently influences the cost of hydrogen compression. In this paper, the numerical simulation model of the ionic compression system is developed, which considers the main parameters of the buffer structure. The proposed model is validated by experimental data obtained in the designed test rig. Based on the validated model, the effects of design factors of the buffer structure on energy consumption and exergy efficiency at the system level are investigated. Results showed that the plunger diameter at the first buffer stage is the dominant factor for energy consumption and exergy efficiency, with 80.65 % and 79.82 % contributions, respectively. The optimal values of the main structures are identified, with which the maximum exergy efficiency can be obtained as 57.55 %. Results also show that the overflow loss is the main loss source, occupying 19.27 % of the total exergy input, which is the main optimization aspect of the hybrid compression system for further performance improvement.