Effects of tubes with different inlet shapes on the shock wave and self-ignition induced by accidental release of pressurized hydrogen

Spontaneous combustion caused by accidental leakage of high-pressure hydrogen affects the safe use of hydrogen energy. In this paper, the self-ignition of pressurized hydrogen discharged into tubes with different inlet shapes was studied experimentally. Inlet shapes include circles, square and triangular. The circular shapes are available in two different diameters, one is the same as the tube diameter, and the other is smaller than the tube diameter but has the same cross-sectional area as the square and triangle. Pressure transducers and photoelectric sensors are used to record pressure variations and self-ignition inside the tubes, respectively. The results show that pressure dead zone exits in the near field of the inlet as the inlet area decreases. The range of the pressure dead zone grows with increasing release pressure, which is not conducive to the occurrence of auto-ignition. In addition, under the same inlet area and release pressure, the inlet shapes play an important role in the characteristics of shock wave. It was found that the intensity and mean speed of the shock wave are greatest in tube with circular inlet, followed by the square, and least in the tube with triangle. Moreover, compared to the tube with circular inlet, the likelihood of spontaneous combustion is reduced for the tube with non-circular inlet. Among them, spontaneous ignition did not occur even though the pressure release was up to 11 MPa in the triangular inlet tube. It indicates that the better suppression of self-ignition can be achieved by changing the inlet shape of the tube.