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Experimental investigation on shock wave propagation and spontaneous ignition of high-pressure hydrogen release through a sho (ϸ)-shaped extension tube into the atmosphere
•The influence of a sho (ϸ)-shaped tube on the spontaneous ignition is investigated.•There are complex shock wave interactions in the bend section.•Spontaneous ignition is more prone to occur in the bend section.•The flame in the bend section cannot spread to the straight section.•There are two jet fires with a long-time interval outside the sho-shaped tube.
The geometry of the extension tube has a great influence on the shock wave propagation and spontaneous ignition of high-pressure hydrogen release in this paper, piezoelectric pressure transducers, photodiodes and a high-speed camera are used to study the shock wave propagation and spontaneous ignition of high-pressure hydrogen released to the downstream sho (ϸ)-shaped extension tube. Experimental results show that the intensity of the leading shock wave is weakened due to the presence of branches when it propagates in the straight section of the sho-shaped tube, and a strong reflected shock wave is generated in the bend section. Spontaneous ignition is more prone to occur in the bend section than in the straight section, with a large optical signal value and long flame duration. However, due to the complex structure of the extension tube, there are still cases of the hydrogen flame extinguishing inside the tube even under high burst pressure. The flame detection time after the leading shock wave at the measured positions decreases with increasing burst pressure, and the time in the bend section is greater than that of the straight section. Radial flame expansion, flame separation, downstream flame extinction and upstream flame development, primary jet fire and secondary jet fire are successively observed outside the tube.