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High-pressure hydrogen storage is currently the mainstream way of hydrogen storage. However, the risk of spontaneous ignition and subsequent jet flame are serious obstacles to the wide application of hydrogen energy. To further reveal the interaction of shock waves, vortices and flame induced by the spontaneous ignition of high-pressure hydrogen release under the effect of release process and burst pressure, a numerical study is conducted by employing LES, RNG, EDC models and detailed hydrogen/air combustion mechanism. The qualitative and quantitative comparison of flow field and flame splitting process outside the tube between this numerical study and previous experimental results validate the numerical results. It is found that an initial vortex is formed at the edge of the jet. Then, several vortices are generated at the edge of the jet and ahead of the Mach disk. The number of vortices in the outer side of the barrel shock is larger when the opening time is shorter. After moving out of the tube, the flame front becomes hemisphere and the lateral edge has a hemispherical bulge which is induced by the initial vortex. The temperature is low and the hydrogen concentration is high in the high-speed region which is induced by the reflected shock wave, leading to the splitting of the flame into two parts: the first and the second half of the flame. However, the flame cannot be formed at the initial stage when the opening time increases to 150 μs and the flame area is larger than with smaller opening times. After splitting, under the affection of the vortices generated at the lateral side, the first half of the flame rotates backward and gradually merges with the second half of the flame, finally forming a complete hydrogen jet flame. [ABSTRACT FROM AUTHOR]

Cryogenic storage option is one of the important ways of storing hydrogen, but under-expanded ignited releases of cryogenic hydrogen could easily lead to jet fires, causing serious damage to people and properties. Barrier walls are important means to reduce the severity of cryogenic hydrogen jet flames, however, its effect on the cryogenic hydrogen jet flame and related temperature distribution are still unclear. In this work, the effect of the distance of barrier wall (0.20, 0.25, 0.30, 0.35 and 0.40 m) and release temperature (140, 180, 220, 260 and 300 K) on the hydrogen jet flame width and temperature distribution is investigated experimentally. It is found that the flame width in the horizontal and vertical direction and the temperature on the vertical barrier wall increase with the decrease of the distance to the nozzle and release temperature. The normalized flame width and inverse excess maximum temperature on the barrier wall increases linearly with the scaled distance considering nozzle diameter and release temperature. The temperature distribution is normalized as Gaussian distribution both in the horizontal and vertical direction, while the excess temperature is higher upward than that of downward. The results can provide a theoretical basis and data support for the blocking of jet fires formed by cryogenic hydrogen ignited releases. [ABSTRACT FROM AUTHOR]

Hydrogen is regard as one of the most promising primary energy vectors solving the problems of air pollution and energy shortage. However, the spontaneous ignition is a major hazard during the application of high-pressure hydrogen. In this paper, a numerical investigation is conducted to study the shock wave propagation, hydrogen/air mixing and spontaneous ignition induced by high-pressure hydrogen release into the tubes with square, pentagon and circular cross-sections (tube wall angles are 90, 108 and 180° respectively). Large Eddy Simulation, Eddy Dissipation Concept coupling with the detailed hydrogen/air reaction mechanism and 10-step like opening process of burst disk are employed. The numerical results of ignition conditions and positions agree well against the previous experimental results. In the square and pentagon tubes, the inward-reflected and outward-reflected shock wave could be generated simultaneously and interact with each other due to the radial propagation of leading shock wave. In the circular tube, however, the two types of reflected shock generate alternately and the interaction disappears. The higher viscous resistance at wall corner induces the formation of velocity shear layer on the tube wall, which promotes the mixing of hydrogen and air. The increase of the angle of wall corner reduces the flammable mixture with the chemical equilibrium equivalence ratio on the tube wall due to the low viscous resistance and short velocity shear layer. The ignition delay time/distance and combustion intensity decrease with the increase of the angle of wall corner. After the occurrence of spontaneous ignitions in the non-circular tubes, the flame propagates downstream and its length increases rapidly along the wall corner. In addition, larger combustion area could be observed with the decrease of the angle of wall corner. [ABSTRACT FROM AUTHOR]