An improved lumped parameter model for calculating piston motion of ionic compressors under pneumatic and hydraulic systems

Ionic compressors are promising as core equipment for hydrogen refueling stations. Lumped parameter models (LPMs) were extensively adopted due to their fast calculation speed in the former studies to investigate the working characteristics of ionic compressors. However, previous LPMs were incapable of calculating liquid overflow amount and pressure rise caused by liquid slugging due to their assumption of no liquid loss in gas cylinders. This paper proposes an improved LPM of pneumatic systems considering liquid slugging and overflow. A virtual piston is assumed to ensure equal pressures of the gas and liquid. The flow rates of gas and liquid are subject to their fractions at the valve aperture, which are also related to whether liquid slugging occurs. A CFD model is established to verify the feasibility of the proposed LPM. Moreover, an LPM is established incorporating both hydraulic and pneumatic systems to solve their working process during multiple cycles. Rapid drops in the piston velocity occur at the end of the discharge and suction stages, respectively. They are due to the pressure limitation of the relief valve and piston insertion into the buffer structure. The hydraulic system can avoid piston overload effectively and ensure the working stability of the compressor.