Effects of a wall on the self-ignition patterns and flame propagation of high-pressure hydrogen release through a tube

High-pressure hydrogen gas is gaining more attention as the next-generation energy carrier, but its safe handling and storage remains an important issue. The possibility of self-ignition near an obstacle is a realistic concern in practical applications such as a hydrogen car, but only a few studies related to this issue have been conducted. In this paper, experimental investigations were carried out to understand the effects of a wall on ignition patterns by high-speed imaging. This study was conducted using extension tubes of different lengths at burst pressures up to 30 MPa. The wall height, distance of the wall from the tube exit and the burst pressure were considered as the main wall parameters affecting self-ignition. The results showed that the existence of a wall could not change the type of ignition patterns (i.e., the wall does not initiate or extinguish a flame) regardless of the wall height and burst pressure, but only when the tube was too short to generate a strong flame inside the tube. When the tube was long enough to induce a strong flame in the tube, however, the wall promoted flame stabilization, e.g., the flame stabilization time outside the tube was shortened by locating the wall near the tube. But its effect disappeared when the distance of the wall from the tube exceeded 10D.