High-Repetition-Rate OH Planar Laser-Induced Fluorescence of a Cavity Flameholder

OH imaging over a wide range of fuel flow rates for a directly fueled cavity were studied at a high sampling rate wherein highly transient complex flame dynamics were captured. At low fuel flow rates, flame position is determined by the primary recirculation zone, with bias toward the ramp and the shear layer. Flame convection from the main combustion region toward the upstream step occurs in periodic events, repeating approximately every 1 ms. With increasing fuel flow the shear layer thickens, and a shear-layer flame is clearly established, while the bulk of the combustion shifts downstream. Distinct flame convection from frame to frame becomes ambiguous due, presumably, to increasing out-of-plane effects. Higher fueling rates weaken the shear-layer combustion and move the flame location toward the ramp, until the region of combustion is nearly attached to the injectors. It is noted that advances in diode-pumped laser and complementary metal-oxide-semiconductor (CMOS) camera technologies will broaden the range of phenomena.