EXPERIMENTAL STUDY OF THE DIFFUSION COMBUSTION OF A HIGH-SPEED ROUND HYDROGEN MICROJET PART 1. ATTACHED FLAME, SUBSONIC FLOW
Scenario of subsonic diffusion combustion of a round hydrogen microjet is presented in this work. Stabilization of process of the laminar hydrogen microjet flow and diffusion combustion in region of the «flame bottleneck» is found. The reason of this phenomenon is connected with existence of the toroidal vortex which is promoting as intensification of mixing process of hydrogen with air and at the same time stabilizing a laminar flow of the extended microjet and its laminar diffusion combustion. It is shown that subsonic diffusion combustion of a round hydrogen microjet of is connected with availability of the «flame bottleneck» region in a wide range of a hydrogen consumption, or microjet velocity efflux close to transonic velocity. It is found that heating of a thick-walled micronozzle from «flame bottleneck» region in case of its big thermal capacity has significant effect on characteristics of development of the hydrogen microjet combustion and leads to choked nozzle. It is revealed that the spatial size of the «flame bottleneck» region with growth of a hydrogen consumption at first sharply decreases, and then gradually increases simultaneously with change of the «flame bottleneck» region shape while combustion in this region doesn't stop.