Diffusion Combustion of a Round Hydrogen Microjet at Sub- and Supersonic Jet Velocity

The experimental research results on diffusion combustion of a round hydrogen microjet flowing from a slit micronozzle at subsonic and supersonic speeds are presented. For the first time, four scenarios of diffusion combustion of a round hydrogen microjet have been identified, including supersonic combustion in the presence of supersonic cells both in air and in hydrogen. It has been found that flame stabilization for a subsonic microjet velocity of hydrogen is associated with the presence of a “bottleneck flame region” leading to the nozzle choking phenomenon, and flame stabilization for a supersonic microjet flow is associated with the presence of supersonic cells. A hysteresis of the diffusion combustion process of a plane microjet of hydrogen is found depending on the method of ignition of the microjet (near or far from the nozzle exit) and the direction of change in the rate of its outflow (growth or decrease).