Experimental Study of the Spontaneous Ignition of Partly Confined Hydrogen Jets

The current study addresses the spontaneous ignition of hydrogen jets released into a confined oxidizer environment, experimentally. The experiments are conducted in a shock tube where hydrogen gas is shock-accelerated into oxygen across a perforated plate. The operating conditions and hole dimension of the plate were varied in order to identify different flow field and ignition scenarios. Time resolved Schlieren visualization permitted to reconstruct the gasdynamic evolution of the release and different shock interactions. Time resolved self-luminosity records permitted us to record whether ignition was achieved, and also to record the dimension of the turbulent mixing layer. The ignition limits determined experimentally in good agreement with the 1D diffusion ignition model proposed by Maxwell and Radulescu. Nevertheless, the experiments demonstrated that the mixing layer is two to three orders of magnitude thicker than predicted by molecular diffusion, which can be attributed to the observed mixing layer instabilities and shock-mixing layer interactions, which provide a much more intense mixing rate than anticipated from previous and current numerical predictions. These observations further clarify why releases through partly confined geometries are more conducive to jet ignition of the jets.