OH visualization of ethylene combustion modes in the exhaust of a fundamental, supersonic combustor

This work examined combustion modes in a fundamental, axisymmetric, supersonic combustor at flight equivalent Mach numbers ranging from 7.5 to 9.0. Ethylene was injected at a variety of mass flow rates to examine both scram-mode, jet wake stabilized and dual-mode combustion. At higher flight Mach number conditions, the fuelling rate required to transition from scram-mode to dual-mode combustion increased. Distributions of the OH radical were observed using planar laser-induced fluorescence (PLIF) in a cross-sectional plane immediately downstream of the combustor exit, and analyzed according to their variation in the radial and circumferential dimensions. It was observed that radial centroids of the ring-like OH PLIF signal for the scram-mode cases approached the centerline linearly with increasing equivalence ratio, but the dual-mode cases appeared to randomly fluctuate in the observed exhaust cross-section. The distributions of scram- and dual-mode cases were clustered in specific regions on plots of circumferential variation as a function of radial centroid, with a jet wake stabilized case appearing between the two clusters. These clusters may be used to help identify scram- and dual-mode combustion in future experiments.