Abstract
Accidental release of high-pressure hydrogen through a tube can cause spontaneous ignition. Once the self-ignited flame enters the unconfined space, a destructive jet flame can be induced. This paper investigates the evolution of the external flame and extinguishment phenomenon, determines inhibition factors, and proposes jet flame suppression methods. Results show that external flame development can be divided into three stages, and extinguishing the flame in Stage I is the easiest to achieve because of its small size, low intensity and instability. The low intensity of the flame at the tube exit and the nature of the external shock wave are found to be detrimental for the flame stabilization, and thus act as inhibition factors for jet flame formation. Based on these, it is proposed that the jet flame prevention can be achieved through the completion of two steps. In the first step, extremely cold expanding hydrogen upstream of the flame can be used to cool the flame through enhanced mixing, with the aim of reducing the flame intensity at the exit. The second step is to change the external flow field by increasing the number of discontinuity surfaces (Mach disks) and reducing the size of the vortex. Finally, validation experiments were conducted. It has been found that after the addition of an obstacle in the tube, multiple Mach disks form and the flame intensity and vortex size are reduced. The extinguishment is more likely to occur, and the release pressure at which jet flame formation may occur increases significantly.