Dual-Mode Combustion of a Jet in Cross-Flow with Cavity Flameholder

Abstract

The ignition and combustion stabilization location in a laboratory dual-mode ramjet/scramjet combustor was studied experimentally. The combustor consisted of a single hydrogen fuel jet injected normally into a supersonic cross∞ow upstream of a wall cavity pilot ∞ame. Experiments were performed with Mach 2.2 and 2.5 nozzles at stagnation temperatures (T0) of 1050K to 1400K, which correspond to ∞ight Mach numbers of 4.3 to 5.2. High speed imaging of the ∞ame luminosity resolved the ignition process which was found to begin in the wall cavity for all conditions. The lean ignition limit of the combustor was found to be a function of the cavity fueling rate. Increasing _ mcavfuel= _ mtotalfuel from 0.02 to 0.07 lowered the combustor lean ignition limit by approximately 15%. For ramjet operation, two distinct combustion stabilization modes were found for main fuel injection a su‐cient distance upstream of the cavity. At low T0, the combustion was anchored at the leading edge of the cavity by heat release in the cavity shear layer. At high T0, the combustion was stabilized a short distance downstream of the fuel injection jet in its wake. For an intermediate range of T0, the reaction zone oscillated between jet-wake and cavity stabilized positions with intermediate locations being unstable. Wall pressure measurements showed that cavity stabilized combustion is the steadiest, followed by wake stabilized, and the oscillatory case. For fuel injection close to the cavity, the reaction zone locations for the two stabilization modes overlapped, and cavity fueling became an important factor in the steadiness of the ∞ow fleld. Scramjet mode combustion was found to only exist in the cavity stabilized mode for the conditions studied.