Interaction of hydrogen jets with hot surfaces

The formation of hydrogen jets from pressurized sources and its ignition when hitting hot devices has been studied by many projects. The transient jets evolve with high turbulence depending on the configuration of the nozzle and especially the pressure in the hydrogen reservoir. In addition the length of the jets and the flames generated by ignition at a hot surface varies. Parameters to be varied were initial pressure of the source (2.5, 10, 20 and 40 MPa), distance between the nozzle and the hot surface (3, 5 and 7 m) and temperature of the hot surface (between 400 and 1000 K). The interaction of the hydrogen jets is visualized by high-speed cinematography techniques which allow analysing the jet characteristics. By combination of various methods of image processing, the visibility of the phenomena on the videos taken at 15 000 fps was improved. In addition, high-speed NIR spectroscopy was used to obtain temperature profiles of the expanding deflagrations. The jets ignite already above 450 K for conditions mainly from the tubular source at 40 MPa. In addition, the propagation of the flame front depends on all three varied parameters: temperature of the hot surface, pressure in the reservoir and distance between nozzle and hot surface. In most cases also upstream propagation occurs. A high turbulence seems to lead to the strong deflagrations. At high temperatures of the ignition sources, the interaction leads to fast deflagration and speeds up- and downstream of the jet. The deflagration velocity is close to velocity of sound and emission of pressure waves occurs.