Flame Stability of Preheated Liquid Hydrocarbon Fuel in a Cavity-Strut Configured Scramjet Combustor

This experimental work studies the flame stability, as well as stabilization and operating modes of liquid hydrocarbon fuel combustion in a model scramjet combustor operating using vitiated air at stagnation temperature of 1300 K and stagnation pressure of 12.7 atm. Experimental results from a conventional wall-based scheme are compared against those obtained in a cavity-strut configuration. Injection temperature of n-dodecane was increased from room temperature up to 235±15 °C with the global equivalence ratio ranging from 0.12 to 0.43. Stability limits were mapped and flame zones studied with wall-pressure measurements and CH* chemiluminescence imaging. The flame stability in the wall-based configuration was poor with a rich blowout limit at ϕ=0.18 in nearly all conditions. This is presumably caused by unfavorable entrainment behavior and inability for flame propagation outside the cavity. The stable flame that was achieved with near-cavity injection of cold fuel proved inefficient. In the cavity-strut configuration, on the other hand, combustion experiments with both cold and heated fuel yielded stable and efficient combustion with different operating modes and interesting flame dynamics. Operation mode ranged from weak scram-mode at ϕ=0.27 to thermal choking at ϕ=0.43. Close to the choking limit, at ϕ=0.41, the flame oscillated between a strut-wake and cavity shear-layer stabilization mode. In this configuration the flame stabilization was not sensitive to fuel temperature.