Experimental study of shock wave propagation and its influence on the spontaneous ignition during high-pressure hydrogen release through a tube

An experimental study of shock wave propagation and its influence on the spontaneous ignition during high-pressure hydrogen release through a tube are measured by pressure transducers and light sensors. Results show that the pressure behind a shock wave first increases, and subsequently remains near constant value with an increase of the propagation distance. That is, a certain propagation distance is required to form a stable shock wave in the tube. In the front of the tube, the minimum value of pressure behind the shock wave (P-shock) required for spontaneous ignition decreases with the increase in axial distance to the diaphragm. However, the minimum P-shock remains nearly a constant value in the rear part of the tube. Moreover, the critical values of shock Mach number (M-S) for spontaneous ignition decrease with the increase in tube length. And the ignition delay time decreases with the increase of the M-S. As the ignition kernel grows in size to a flame, it propagates downstream along the tube with velocity greater than the theoretical flow velocity of the hydrogen-air contact surface. The flame propagation velocity relative to tube wall increases with M-S. When the self-sustained flame exits from the tube, a rapid non-premixed turbulent combustion is observed in the chamber. The combustion-wave overpressure increases with the increase of the M-S. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.