Experimental study on shock wave propagation and spontaneous ignition induced by high-pressure hydrogen suddenly released into T-shaped tubes

To investigate the influence of bifurcation structure in tubes on the spontaneous ignition of high-pressure hydrogen, a series of experiments were conducted. The tubes including T-shaped and straight tubes with the length of 0.7/1.2/1.7 m were tested. The burst pressure ranged from 4-10 MPa. The pressure and light signals in the tube and the external flame images were recorded. The results show that the T-shaped structure has a significant influence on the occurrence of spontaneous ignition. The critical release pressure required for self-ignition in short T-shaped tube was lower than that in straight tube, because the strong reflect shock wave near the bifurcation point heated the combustible mixtures near the contact surface. However, with the extension of the tube length, the critical pressure increased, because the distance between the leading shock and contact surface increased when the leading shock reached the bifurcation point. Consequently, the reflect shock cannot heat the combustible mixture near the contact surface, but the air instead. Besides, comparing with the straight tube, the formation of jet fire was inhibited in the T-shaped long tube (1.2/1.7 m) and the shock wave attenuated rapidly after pass through the bifurcation point.