A visualization investigation on the characteristic and mechanism of spontaneous ignition condition of high-pressure hydrogen during its sudden release into a tube

Abstract

Hydrogen is regarded as one of the promising fuels in the next decades. However, the spontaneous ignition of high-pressure hydrogen blocks its safe utilization. In this investigation, a visualization investigation is carried out to study on the characteristic and mechanism of spontaneous ignition condition of high-pressure hydrogen during its sudden release into a tube. A rectangular tube with transparent observation window is employed. The high-speed images of spontaneous ignition conditions and light signals emitted from ignition are obtained. Four spontaneous ignition conditions are observed: (1) no ignition; (2) failed ignition with one ignition spot; (3) failed ignition with two ignition spots and (4) successful ignition. The critical burst pressure for four ignition condition is determined. The jet fire (successful ignition) could be generated in the cases with a shorter distance from ignition spot to leading shock wave and contact surface due to the stronger shock wave affection and sufficient flammable mixture maintaining the chemical reaction and flame propagation. The second ignition is the precondition forming the successful ignition. The scaled ignition delay time and distance could be predicted by using the derived dimensionless shock pressure.