Ts. Cheng et al., RAMAN MEASUREMENT OF MIXING AND FINITE-RATE CHEMISTRY IN A SUPERSONICHYDROGEN-AIR DIFFUSION FLAME, Combustion and flame, 99(1), 1994, pp. 157-173
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.