Effects of obstacles inside the tube on initial self-ignition of high-pressure hydrogen release through a tube.

• The strength of shock wave is different before and after obstacles. • Obstacles decrease the minimum burst pressure and self-ignition occurs around obstacles. • Mechanism of self-ignition is different before and after obstacles. • Obstacles before the initial ignition location significantly accelerates initial self-ignition. The safe application of hydrogen has attracted increased attention. In particular, fire and explosion disasters may be induced by self-ignition during high-pressure hydrogen leakage. This study experimentally investigates the effect of obstacles on initial self-ignition when high-pressure hydrogen is suddenly released. High-pressure hydrogen release experiments are performed at burst pressures of 2–8 MPa. The hydrogen flame inside the tube is captured by a high-speed video camera and light sensors, and shock wave variations are measured by pressure transducers. The results show that the presence of obstacles inside the tube significantly affects shock wave flow. It is found in this study that obstacles decrease the minimum burst pressure needed for self-ignition and self-ignition is prone to occur in the vicinity of obstacles. The influence of obstacles on the initial ignition process are different at different self-ignition locations. On the one hand, the reflected shock wave originating from obstacles is the main reason for the promotion of self-ignition upstream of obstacles. On the other hand, the formation of a hydrogen/air mixture under the effect of turbulent flow and multi-dimensional shock waves leads to self-ignition downstream of obstacles. Meanwhile, the presence of obstacles before the initial ignition location (L in) shortens the distance between the ignition location and the burst disk and significantly accelerates the occurrence of initial self-ignition. Obstacles participate in the self-ignition process earlier when they are placed closer to the burst disk. However, obstacles after the initial ignition location (L in) show no effect on the initial ignition process. The results can guide the safe use of high-pressure hydrogen. [ABSTRACT FROM AUTHOR]