Mechanism of spontaneous ignition of high-pressure hydrogen release in arc-shaped confined space

High-pressure hydrogen storage is one of the mainstream ways of hydrogen storage currently. However, its propensity for spontaneous ignition can pose challenges to the safe application of hydrogen energy. It has been recognized that the spontaneous ignition usually takes place when it is released through tubes. However, this study demonstrates that the spontaneous ignition can still take place when it is released directly into the atmosphere and impinges on an arc-shaped wall afterwards. This paper presents a numerical investigation by using LES, RNG, EDC models and detailed hydrogen/air combustion mechanisms. The evolution of the shock wave/vortex and the flame induced by the spontaneous ignition are clearly captured and interpreted. A new mechanism of spontaneous ignition is proposed: the spontaneous ignition induced by the shock wave after the reflection of under-expanded shock by the confined walls. The effect of release pressure (30–70 MPa) and wall distance (100–300 mm) are considered. It is found that higher release pressure promotes earlier ignition and larger flame areas. Shorter wall distances accelerate flame development, but excessive shortening would lead to local flame quenching. The proposed mechanism offers a new perspective for the hydrogen combustion community.