Search

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]

• Shock wave is reflected twice inside the tubes with different angles. • Two shock reflection mechanisms for acute and non-acute tubes are proposed. • It requires a longer time and a further distance to initiate the spontaneous ignition inside the tubes with larger angle. • The flame induced by the spontaneous ignition could move upstream steadily inside the 60° angle tube. High-pressure hydrogen storage is one of the best choices of hydrogen storage at present and in the future. However, the spontaneous ignition of high-pressure hydrogen release blocks its wide application. This paper further studies the shock evolution, temperature accumulation and spontaneous ignition inside the tubes with different angles by employing LES, RNG and EDC models, 10-step like opening process of burst disk and detailed hydrogen/air combustion mechanism. Four tubes with different angles (60, 90, 120 and 150°) are employed based on the previous experimental result. It is found that the smaller the angle of the tube, the greater the maximum pressure and temperature of the first shock reflection zone. And the maximum pressure and temperature of the second shock reflection zone is the highest inside the 90° angle tube. This is due to two shock reflection mechanisms inside the tubes: in acute angle tube, only the reflected hemispherical shock hits the inner wall of the tube corner, however, for non-acute tubes, both the reflected hemispherical shock and reflected normal shock hit the inner wall of the tube corner. In addition, it requires a longer time and a further distance to initiate the spontaneous ignition inside the tubes with larger angle. And the flame induced by the spontaneous ignition could move upstream steadily inside the 60° angle tube and the flame length increases with the release time to a maximum value of 21.44 mm. [ABSTRACT FROM AUTHOR]

• The maximum hydrogen concentration increases as the distance of the vertical barrier wall decreases. • The inverse maximum hydrogen concentration increases linearly with the scaled distance. • The hydrogen concentration in the horizontal and vertical direction increases as the distance of vertical barrier wall decreases. • The hydrogen concentration in the horizontal and vertical direction follow Gaussian and exponential distribution, respectively. As a recognized clean energy source with advantages of non-pollution, high energy density and less energy loss during the cooling process, cryogenic hydrogen is widely used worldwide. The barrier wall is an effective means of preventing the backward diffusion of jets. However, the effect of distance of vertical barrier wall to the release nozzle on the hydrogen concentration profile is still unknown. In this work, cryogenic hydrogen is released with different distances of the barrier wall (0.20, 0.25, 0.30, 0.35, 0.40 m) and temperatures of cryogenic hydrogen (140, 180, 220, 260, 300 K) experimentally. 10 hydrogen concentration sensors are placed in the horizontal and vertical directions on the barrier wall, respectively, to record the hydrogen concentration. It is found that the maximum hydrogen concentration increases as the distance of the vertical barrier wall decreases. Models of the maximum hydrogen concentration in volume and mass fraction are proposed. The hydrogen concentration increases significantly in the horizontal and vertical directions as the vertical barrier wall is placed closer to the release nozzle. The hydrogen concentration in the horizontal and vertical directions of the vertical barrier wall follows the Gaussian and exponential distribution, respectively. The prediction models of hydrogen concentration in the horizontal and vertical directions are proposed as well. The research results can provide a theoretical basis and data support for the design of safety codes for cryogenic hydrogen storage and the safety distance of barrier walls in hydrogen refueling stations. [ABSTRACT FROM AUTHOR]