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 crossflow upstream of a wall cavity pilot flame. Experiments were performed with Mach 2.2 and 2.5 nozzles at stagnation temperatures (T0) of 1050K to 1400K, which correspond to flight Mach numbers of 4.3 to 5.2. High speed imaging of the flame 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. Increasingṁ cavf uel /ṁ totalf uel 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 sufficient distance upstream of the cavity. At low T 0 , 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 T 0 , 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 flow field. Scramjet mode combustion was found to only exist in the cavity stabilized mode for the conditions studied.

Theoretical analysis of flamelet model for supersonic turbulent combustion

“…Traditionally, it is acknowledged that the premixed fuel gas will not be heated in circulation flow until reaching ignition point after the ignition delay. The latest experiments [24] suggested the possibility of the triple flame model [25], which assumes that there exists stable flame front and downstream diffusion flame surface induced by two factors: one is the premixed combustion velocity in the backflow region with low speed and high temperature; the other lies in the shear layer flow velocity generated by the interaction of the back flow and the main flow. Accordingly，we can assume that the flame in scramjet combustor is dominantly composed of partially premixed flame rather than pure diffusion flame.…”

Nonlinear characteristics and detection of combustion modes for a hydrocarbon fueled scramjet

“…While the mode transition occurred, Takahashi et al [14] also showed that thrust and heat-flux distribution varied considerably. Daniel et al [7] reported two distinct reaction zones corresponding to jet wake stabilization and cavity stabilization in the combustor with wall injection and a cavity, and scramjet mode combustion zone appeared only in the cavity. By increasing the total temperature of airflow to simulate a real acceleration process, Sullins [13] experimentally achieved the mode transition from a scramjet with a pre-combustion shock system to the one without pre-combustion shock system.…”

Experimental study on Dynamic Characteristics of Combustion Mode Transition

“…Sullins [8] experimentally achieved the mode transition from a scramjet with a pre-combustion shock system having a high pressure ratio, to a scramjet without pre-combustion shock system by increasing the total temperature of airflow to simulate a real acceleration process. Daniel [9] reported two distinct reaction zones in a combustor with wall injection and a cavity flameholder, corresponding to jet wake stabilization and cavity stabilization. Scramjet mode combustion zone appeared only in the cavity; in contrast, the spread of the ramjet mode combustion is significantly larger than the former.…”