The Obstacle Effects on Spontaneous Ignition of Pres-Surized Hydrogen Jets

The Spontaneous ignition of pressurized hydrogen jets poses a major concern to the safe application of hydrogen energy. Previous studies have fo-cused on the spontaneous ignition of pressurized hydrogen released into tubes. However, in real industrial scenarios, pressurized hydrogen usually re-leases into the atmosphere or a complex hydrogen equipment environment. Therefore, the effect of obstacles on spontaneous ignition needs to be considered. In this study, the 21-step detailed chemistry was used to model the reaction of the spontaneous ignition resulting by the sudden release of pressurized hydrogen impinging on obstacles. The effects of obstacle shapes on the flow field and spontaneous ignition of pressurized hydrogen jets were analyzed. For the pressure in this study, the cylindrical obstacle did not change the ignition pattern. The highest temperature of the hydrogen jet occurs at the contact region via shock reflection and interaction, after which spontaneous ignition cannot occur due to flow divergence. The spontaneous ignition processes of pressurized hydrogen impinging on hemispherical and conical obstacles enhance the mixing of hydrogen combustible clouds and the formation of multidimensional shock waves, which significantly increases the spontaneous ignition possibility of the mixture. The obstacles confine the high-temperature region in the bottom without wide-spreading flames. The conical obstacle produces a lower flame temperature than the hemispherical obstacle but extends the flame duration. The results of this study will provide a scientific basis for hydrogen safety and can be applied in practical designs or the development of codes and standards.