Experimental study on ignition and explosion in high-pressure hydrogen jet in open space

Abstract: The flame behaviour and overpressure evolutions at the initial stage of ignition and explosion of steady-state hydrogen jet in open space were investigated. Hydrogen with a constant pressure of 0.3-0.7 MPa was released through nozzles, whose diameters were 2 mm, 3 mm and 4 mm, respectively. A high-speed camera and an oscilloscope were employed to record the flame behaviour and the overpressure. The results show that at the initial stage of ignition and explosion, the flame spreads outwards in a spherical shape at the electrode. The flame front reaches maximum displacement and begins to quenches, finally the jet flame forms. It only takes 4-6ms to reach the maximum displacement. Flame front displacement is most affected by the nozzle diameter and increases monotonously with the nozzle diameter. The variation of flame width is different from that of flame front displacement due to the low hydrogen concentration on the edge flame. During explosion, the peak overpressure takes place only once and the positive pressure lasts nearly 1 ms. At the same ignition distance, the peak overpressure increases with flow rate. At the same flow rate, the peak overpressure decreases with the increase of ignition distance. For the same ignition distance, the position of the maximum peak overpressure shifts downstream along the direction of jet with the increase of flow rate. The maximum peak overpressure increases linearly with the flow rate and decreases linearly with ignition distance.