Combustion Modes of Hydrogen Microjets

Abstract

An experimental study of the diffusion plume during the hydrogen flow from a round and slotted micro nozzle at pre- and supersonic velocity has been carried out. Four scenarios of diffusion combustion of a planar hydrogen microjet, including combustion at supersonic hydrogen jet outflow, are found for the first time. It was found that the stabilization of the plume at subsonic hydrogen microjet velocity is associated with the presence of a plume “drag” separating the laminar and turbulent parts of the plume. At supersonic velocity of the underexpanded microjet, the plume stabilization is promoted by the wave structure of inhomogeneities formed. The hysteresis of the diffusion combustion process of a flat hydrogen microjet has been found depending on the ignition region. At ignition near the nozzle cutoff, a connected plume accompanied by nozzle heating is realized. At ignition higher up the jet, a raised flare is realized, with heating of the nozzle cutoff being much less than in the previous case. With increasing flow velocity, the development of the two types of flares proceeds according to different scenarios.