Characterization of a Cavity Flameholding Solid-Fuel Ramjet in an Optical Combustor

Three fuel grain geometries were investigated in a two-dimensional, optically accessible solid fuel ramjet combustor to improve the understanding of the internal ballistics as it pertains to flameholding and overall performance. Two-cavity flameholding-configured fuel grains demonstrated increased flameholding and similar performance to the baseline flat fuel grain. Optical diagnostics such as high-speed CH* chemiluminescence and high-speed three-color camera pyrometry were utilized to measure and analyze the emissive species to draw conclusions about the reacting flowfield. Additionally, optical access afforded the ability to determine spatially resolved regression rates within the flameholding region of each fuel grain. The measured fuel grain regression rates demonstrated similar performance between the three configurations; however, the spatial distribution of the regression rates resulting from the high local heat flux due to the cavity corner is postulated to be the driving factor in increasing the flameholding capability of the cavity fuel grains.