Effects of the partially open inlet on shock waves and spontaneous ignition during the leakage of hydrogen

Unexpected spontaneous combustion and shock waves can occur when high-pressure hydrogen leaks into pipelines, whilst irregular leakage ports affect their features. In this paper, shock waves and self-ignition are experimentally and numerically studied after the pressurized hydrogen is released through the partially open inlet. And the effects of tube length and release pressure are investigated. Pressure signals, light signals, and flame images are used to characterize the shockwave, self-ignition, and flame propagation. Results show that the shock-affected region can be formed near the partially open inlet. It is accompanied by complex wave structures, shock wave interactions, and shock wave focusing. The contact surface is distorted and deformed. The flow field parameters near the inlet change dramatically and are unevenly distributed, which affect the overpressure characteristics recorded by the pressure sensors. The initial intensity of the shock wave is lower than that in tubes with the fully open inlet at the early stage of the leakage. In addition, the partially open inlet influences the critical pressure at which spontaneous ignition occurs and the flame evolution inside or outside the tube. It has an inhibition effect on spontaneous ignition, but this inhibition effect weakens with increasing tube length.