Flame Structure Characterization in a Dual-Mode Scramjet Using Hydroxyl Planar Laser-Induced Fluorescence

The flame front of a premixed ethylene-air turbulent flame in a high-speed flowfield was imaged using hydroxyl radical (OH) planar laser-induced fluorescence (PLIF). An electrically heated continuous flow facility produced inflow conditions with a total temperature of 1200 K, corresponding to a flight Mach number of about five. A statistically stationary turbulent flame stabilized over a scaled-down cavity was used to generate experimental data for future comparisons with direct numerical simulations. A laser sheet with a wavelength of 283.55 nm was used to excite the Q1(8) transition of OH. The sheet waist had a full width at half-maximum of 95 mu m. Two-dimensional OH-PLIF images were collected at high in-plane spatial resolution (approximately 40x40 mu m) with a field of view of 5.6x5.6mm. The images spanned a region of 45x15mm along the spanwise centerplane. The local OH gradient was used to isolate the flame front in all images through an automated process. Each image was processed to obtain the appropriate statistics, time-averaged flame surface density, and flame front curvature values. The distribution of local flame front curvature values was approximately constant across the domain.