Study on characterization of flame propagation of spontaneous ignition caused by high-pressure hydrogen leakage

As an ideal energy source, hydrogen is highly susceptible to spontaneous ignition once leaked, which is an urgent issue that needs to be addressed. Based on the shock tube model, this paper investigates flame propagation under various pressures, tube lengths, and diameters by employing the LES approach and a detailed hydrogen/air combustion mechanism. The results indicate that within the tube, the ignition kernels gradually evolve into tulip flames when specific conditions are satisfied. As pressure and tube length increase, the likelihood of forming a complete flame rises significantly; with the increase of tube diameter, the flame front is flatter and the flame intensity is more uniformly distributed. Furthermore, this paper develops a model to predict the formation of a complete flame: $P_b/P_a=570.64{\left(L/D\right)}^{-0.6}$. Outside the tube, once the intact flame passes out of the tube and evolves into a jet flame, structures such as flame envelopes and jet vortices will appear. Higher release pressures make it more difficult for the flame to propagate steadily, whereas increasing tube length and diameter promotes combustion and sustains the flame outside the tube.