Fundamental Scramjet Combustion Experiments Using Hydrocarbon Fuel

Combustion of ethylene was examined experimentally via semi-freejet testing of a fundamental, axisymmetric combustor model at conditions representative of Mach 7–8 flight at 100 kPa dynamic pressure. The model consisted of diffuser, constant area isolator, cavity, and diverging combustor sections. Pressure data were measured along the wall of the model and were complemented with OH planar laser-induced fluorescence (PLIF) visualization at the exit of the diverging section. Robust combustion of ethylene was observed for two stagnation enthalpy cases for fuel-air equivalence ratios of 0.3 or greater. A low-enthalpy, low-equivalence-ratio case showed significant, but structurally different, OH PLIF signals even though there was little combustion-induced pressure rise. Edge-detection techniques were applied to the PLIF images, and the resulting circumferential distributions analyzed. Mean radii and standard deviations are presented for the inner and outer edges of the OH-rich band for four tunnel/fueling conditions. Finally, amplitude spectra of fluctuations in the edge radii are shown, indicating that low-wavenumber oscillations are dominant. These experimental results provide useful data for comparison with numerical simulation in future studies.