Ignition of Hydrogen Jet Fires from High Pressure Storage

Highly transient jets from hydrogen high pressure tanks were investigated up to 30 MPa. These hydrogen jets might self-initiate when released from small orifices of high pressure storage facilities. The related effects were observed by high speed video technics including time resolved spectroscopy. Ignition, flame head jet velocity, flame contours, pressure wave propagation, reacting species and temperatures were evaluated. The evaluation used video cross correlation method BOS, brightness subtraction and 1 dimensional image contraction to obtain traces of all movements. On burst of the rupture disc, the combustion of the jet starts close to the nozzle on the outer shell of it at the boundary layer to the surrounding air. It propagates with a deceleration approximated by a drag force of constant value which is obtained by analysing the head velocity. The burning at the outer shell develops to an explosion converting a nearly spherical volume at the jet head, the movement of the centroid is nearly unchanged and follows the jet front in parallel. The progress of the nearly spherical explosion could be evaluated on an averaged flame ball radius. An apparent flame velocity could be derived to be about 20 m/s. It seems to increase slightly on the pressure in the tank or the related initial jet momentum. Self-initiation is nearly always achieved especially induced the interaction of shock waves and their reflections from the orifice. The results are compared to thermodynamic calculations and radiation measurements. The combustion process is composed of a shell combustion of the jet cone at the bases with a superimposed explosion of the decelerating jet head volume.