Design and theoretical analysis of a liquid piston hydrogen compressor

•A liquid piston compressor is introduced to realize hydrogen ultra-high pressure compression.•A hydraulic control method is proposed to realize the motion control of compressor piston.•Dynamic characteristics are modeled and investigated.•A buffer structure is proposed and its influence on dynamic characteristics is analyzed. Hydrogen is widely considered to be the ultimate energy source and has received significant attention from research institutions. Compressors are widely used as the core device for increasing the volumetric energy density of hydrogen. However, conventional reciprocating compressors have problems, such as complex structure, frequent breakdown and large impact. This paper proposes a liquid piston compressor for hydrogen compression. Firstly, the structure and working principle of the compressor are introduced. The compressor adopts a five-stage compression structure, which is driven by a five-piston radial piston pump, and the corresponding hydraulic control system is designed. Secondly, to reduce the return shock of the compressor, the buffer structure is designed for each stage of compression, and theoretical analysis is performed to obtain the theoretical output flow rate of the compressor and the kinematic characteristics of the inlet and discharge processes. Finally, combined with the AMEsim software, the motion of the compressor piston and the characteristics of pressure change during the entire working process in the compressor are simulated. Results show that the novel multi-stage compressor can achieve stable and continuous hydrogen compression, and the buffer structure of each stage greatly reduces the piston impact on the compressor. Compared with the traditional liquid piston compressor, the proposed compressor solves the problems of unstable operation and reduced compression efficiency caused by leakage and reduces the impact and vibration of the piston and increases the stability and controllability of the compressor operation. The analysis results show that the solution is feasible.