CONSERVED SCALAR MEASUREMENTS IN TURBULENT-DIFFUSION FLAMES BY A RAMAN AND RAYLEIGH RIBBON IMAGING METHOD

A new method to obtain images of conserved scalars in turbulent flames is presented and implemented with simultaneous Rayleigh and fuel Rama n measurements in a methane/air jet diffusion flame by the use of a si ngle dye laser and two intensified CCD cameras. The laser beam is focu sed to a line and retroreflected with a slight offset to form a thin r ibbon, sufficient to measure gradients in two dimensions. A robust, it erative data reduction technique is used to derive statistics of tempe rature, fuel mass fraction, mixture fraction (f), and scalar dissipati on (chi). Results for a flame of Reynolds number 20,600 show that the lower moments, pdfs, and scatter plots of the computed quantities do n ot differ markedly from published results of point measurements in sim ilar flames, strengthening confidence in this new approach. The comput ed components of chi show behavior similar to that in nonreacting flow s; there is some anisotropy, with the ratio of the radial to the axial component in the shear region around 2.0. The azimuthal component, me asured by off-axis laser beam alignment, is roughly equal to the radia l component. The correlation between f and chi is small on the flame a xis, but the correlation coefficient R(f chi) rises to around 0.4 near the edge, which is largely consistent with other recent results for c old jets and jet flames.