Reaction zone structure and velocity measurements in permanently blue nonpremixed jet flames

he present work addresses the question of whether the chemical reaction zone within a turbulent, high-Reynolds-number jet flame is thin--and can be modeled using strained wrinkled laminar flamelet theory--or is thick--and must be modeled using distributed reaction zone theory. The region near the wrinkled instantaneous stoichiometric contour in soot-free permanently blue jet flames (mixture fraction between 0.5-0.7) is identified using CH Planar Laser-Induced Fluorescence (PLIF) imaging and the strain on this interface is measured using simultaneous Particle Imaging Velocimetry (PIV) diagnostics. With a separate set of simultaneous images, the relative position of the CH and OH radicals is observed using PLIF. It is found that the CH reaction zone remains thin and rarely exceeds 1 mm, even near the flame tip in a high-Reynolds-number (18,600) jet flame. The mean thickness of the CH reaction layer...