Flame Structure and Dynamics in a Premixed Dual-Mode Scramjet Combustor from Fluorescence Imaging

Formaldehyde (CH2O) planar laser- induced fluorescence (PLIF) imaging was performed in a premixed, ethylenefueled dual- mode scramjet combustor to study the flame structure and dynamic flame behavior. CH2OPLIF is used as a marker to provide information on the structure and position of the lower-temperature portion of the reaction zone. Low-repetition-rate (10 Hz) measurements were acquired at several cross-flow planes along the axial flow direction. Statistical analysis of the CH2O topology indicates sparse concentrations of formaldehyde that are intermittently detected by the PLIF measurement. Comparisons between previous large-eddy simulations, laboratory-scale flames, and the current experimental measurements indicate discrepancies between the expected and measured formaldehyde concentrations and structure. High-speed formaldehyde PLIF also was conducted at 50 kHz to further investigate the intermittency of the formaldehyde layers in the flow.