3D measurements of ignition processes at 20 kHz in a supersonic combustor

The ignition dynamics in a Mach 2 combustor were investigated using a three-dimensional (3D) diagnostic with 20 kHz temporal resolution. The diagnostic was based on a combination of tomographic chemiluminescence and fiber-based endoscopes (FBEs). Customized FBEs were employed to capture line-of-sight integrated chemiluminescence images (termed projections) of the combustor from eight different orientations simultaneously at 20 kHz. The measured projections were then used in a tomographic algorithm to obtain 3D reconstruction of the sparks, ignition kernel, and stable flame. Processing the reconstructions frame by frame resulted in 4D measurements. Key properties were then extracted to quantify the ignition processes, including 3D volume, surface area, sphericity, and velocity of the ignition kernel. The data collected in this work revealed detailed spatiotemporal dynamics of the ignition kernel, which are not obtainable with planar diagnostics, such as its growth, movement, and development into “stable” combustion. This work also illustrates the potential for obtaining quantitative 3D measurements using tomographic techniques and the practical utility of FBEs.