Three-dimensional chemiluminescence imaging of unforced and forced swirl-stabilized flames in a lean premixed multi-nozzle can combustor

A tomographic image reconstruction technique has been developed to measure the 3D distribution of CH* chemiluminescence of unforced and forced turbulent premixed flames. Measurements are obtained in a lean premixed, swirl-stabilized multi-nozzle can combustor. Line-of-sight images are acquired at equally spaced angle increments using a single intensified charge-coupled device camera. 3D images of the flames are reconstructed by applying a filtered back projection algorithm to the acquired line-of-sight images. Methods of viewing 3D images to characterize the structure, dynamics, interaction and spatial differences of multi-nozzle flames are presented. Accuracy of the reconstruction technique is demonstrated by comparing reconstructed line-of-sight images to measured line-of-sight downstream-view images of unforced flames. The effect of the number of acquired projection images on the quality of the reconstruction is assessed. The reconstructed 3D images of the unforced multi-nozzle flames show the structure of individual flames as well as the interaction regions between flames. Forced flame images are obtained by phase-synchronizing the camera to the forcing cycle. The resulting 3D reconstructions of forced flames reveal the spatial and temporal response of the multi-nozzle flame structure to imposed velocity fluctuations, information which is essential to identifying the underlying mechanisms responsible for this behavior.