Abstract
Concerns regarding the flammability and explosiveness of hydrogen have restricted its development. Accidental release of pressurized hydrogen from a tube can result in self-ignition, and subsequently induce a catastrophic jet flame. However, the physics of transformation of a self-ignition flame into a jet flame remains unclear. Hence, this thesis focuses on the flame transition after the self-ignited flame emerges into the unconfined space. It aims to investigate the flame physics, influencing factors, critical conditions, inhibition factors, and methods to prevent jet fire formation.
Experimental and numerical studies are performed. Effects of release pressure, tube length, presence of obstacles, and partially open inlet are investigated. Different flame transitions are observed, which can be categorized into two types based on the flame morphology and shockwaves. However, all of them are controlled by the initial flow field near the exit and undergo the same four stages: initial flame, flame under the effect of shock wave, flame under the effect of vortex, and stable combustion. Furthermore, critical release conditions for jet flame formation and different transition types are identified. Understanding of flame physics has revealed inhibition factors that can induce the extinguishment during the transition. The prevention of the jet flame can be achieved through the completion of two steps: (i) changing the flow field by increasing the number of discontinuous surface (Mach disk) and reducing the vortex size, and (ii) encouraging the mixing of the flame with cold hydrogen to cool the flame and reduce its intensity at the exit. Strategic placement of an obstacle within the tube can achieve these, resulting in inside or outside extinguishment. Additionally, partial opening inlet (e.g., burst pressure safety disk) influences the critical pressure at which spontaneous ignition occurs. It has an inhibition effect on self-ignition and hence on the formation of the jet flame. Our findings can provide important insights into the prevention of jet flame and have practical implications for the safe use of hydrogen energy.