RAMAN MEASUREMENT OF MIXING AND FINITE-RATE CHEMISTRY IN A SUPERSONICHYDROGEN-AIR DIFFUSION FLAME

Ultraviolet (UV) spontaneous vibrational Raman scattering and laser-in duced predissociative fluorescence (LIPF) from a KrF excimer laser are combined to simultaneously measure temperature, major species concent rations (H-2, O-2, N-2, H2O), and OH radical concentration in a supers onic lifted co-flowing hydrogen-air diffusion flame. The axisymmetric flame is formed when a sonic jet of hydrogen mixes with a Mach 2 annul ar jet of vitiated air. Mean and rms profiles of temperature, species concentrations, and mixture fraction are obtained throughout the super sonic flame. Simultaneous measurements of the chemical species and tem perature are compared with frozen chemistry and equilibrium chemistry limits to assess the local state of the mixing and chemistry. Upstream of the lifted flame base, a very small amount of reaction occurs from mixing with hot vitiated air. Downstream of the lifted flame base, st rong turbulent mixing leads to subequilibrium values of temperature an d OH concentration. Due to the interaction of velocity and temperature in supersonic compressible flames, the fluctuations of temperature an d species concentrations are found to be higher than subsonic flames. Farther downstream, slow three-body recombination reactions result in superequilibrium OH concentrations that depress temperatures below the ir equilibrium values.