MEASUREMENTS OF SCALAR DISSIPATION IN THE REACTION ZONES OF TURBULENTNONPREMIXED H-2 AIR FLAMES

A new diagnostic system has been developed to obtain spatially and tem porally resolved simultaneous multiple point measurements of species c oncentrations and temperatures in turbulent flames. The diagnostic app roach is based on pulsed Raman scattering induced by a KrF excimer las er. The system has been applied in the reaction zones of turbulent non premixed H-2-air flames to obtain statistics of species concentrations , temperature, and mixture fraction (xi). Results of means, and fluctu ations of the measured quantities do not differ markedly from the publ ished point measurements in similar flames, validating the diagnostic approach. Instantaneous, one-dimensional (radial) scalar dissipation r ates (chi) are measured in the reaction zones of the nonpremixed H-2-a ir flames using the multipoint, multispecies detectivity of the diagno stic system. Radial profiles and probability density functions (pdfs) of scalar dissipation are reported. The pdfs of scalar dissipation are log-normally distributed and negatively skewed. The radial profiles o f mean scalar dissipation are similar to xi(rms)(3) consistent with th e k-epsilon models of turbulent combustion. Measurements of chi are co mpared to laminar flamelet model calculations. Laminar flame strain ra te parameters (a) estimated from the scalar dissipation measurements r ange from a = 50-1000 s(-1), much lower than the extinction strain rat es (a approximate to 12,000 s(-1)) of H-2-air flames.