From ignition to stable combustion in a cavity flameholder studied via 3D tomographic chemiluminescence at 20 kHz

This work reports the study of the ignition processes in a Mach-2 cavity combustor based on three-dimensional (3D) measurements at 20 kHz. The 3D measurements were obtained by a combination of tomographic chemiluminescence and fiber-based endoscopes. Measurements of 3D flame and flow properties were reported under two fueling conditions of the combustor. The properties included 3D volume, surface area, shape factor, and 3D3C (three-dimensional and three-component) velocity of the ignition kernel. These results clearly distinguished the ignition stage from the stable combustion stage of the combustor and enabled the determination of a transition time to quantify both stages. The analysis of the change of the ignition kernel's shape, when combined with the 3D3C velocity measurements, also illustrated flame-flow interactions in the cavity combustor. These results demonstrated the utility of the 3D diagnostics to overcome some of the limitations of established planar diagnostics and to resolve the dynamics of high-speed combustion devices both spatially and temporally.