Experimental and numerical study on the decompression behavior of high-pressure hydrogen gas in a two-step valve

Pressure-reducing valve is the most vital component of the hydrogen supply system for the on-board fuel cell stack. A clear understanding of the decompression behavior can help to optimize the valve structure. In this work, a two-step pressure-reducing system is proposed, consisting of a conical throttling valve and a disc throttling valve. The decompression process of high-pressure hydrogen gas is numerically and experimentally investigated in the two-step pressure-reducing system. The flow characteristics are represented by analyzing the variations of flow variables (e.g., pressure, temperature, velocity and turbulent quantities) at different conditions. A linear relationship between the inlet pressure and the mass flow rate is achieved. Besides, the decompression performance is evaluated for the first and the second throttling part separately. The experimental results show that the two-step valve can successfully reduce the hydrogen pressure of 35 MPa to 0.14 MPa, which meets the requirement for the fuel cell stack. The gas leakage tests confirmed that the valve has a good gas tightness, eliminating the safety concern during use. This work is expected to offer in-depth insights into the hydrogen decompression behavior and provide references for the design of pressure-reducing valves.