Investigation of flame structure and combustion dynamics using CH<inf>2</inf>O PLIF and high-speed CH* Chemiluminescence in a premixed dual-mode scramjet combustor

Formaldehyde (CH2O) planar laser-induced fluorescence (PLIF) and high-speed CH* chemiluminescence have been performed in a premixed, ethylene-fueled dual-mode scramjet combustor in order to study the dynamic flame behavior and structure. CH2O PLIF is used as a “flame” marker to provide information on the structure and position of the lower-temperature portion of the primary reaction zone. Low-repetition-rate (10 Hz) measurements were taken at several cross-flow planes along the axial flow direction. Statistics, including the mean of the CH2O topology, indicate sparse concentrations of formaldehyde that are intermittently detected by the PLIF measurement. Comparisons between previous Large Eddy Simulations (LES) and the current experimental measurements indicate descrepancies between the expected and measured formaldehyde concentrations. Time-resolved CH* chemiluminescence was collected at 50 kHz in order to study flame motion and stabilization in the axial flow direction. From these measurements, information regarding the flame anchoring position and flame spreading angle is collected, providing insight on the effect of cavity flame-holding and flame penetration into the freestream flow. Measurements of lean blowout (LBO) events were also acquired revealing the flame dynamics at the moment of blowout