The goal of this program is to understand turbulence chemistry interactions in combustion up to and including localized extinction. Experimentally, pilot stabilized non premixed turbulent jet flames of selected mixtures are being studied under conditions conducive to strain-induced local extinction. Laser based techniques such as Raman scattering and Rayleigh scattering are employed. Analytically, models based on the asymptotically thin flamelet concept and on distributed reaction zone concepts are being assessed. A significant finding is that the popular contemporary view of a turbulent flame as an ensemble of asymptotically thin flamelets seems incorrect. Alternative mechanisms based on thick flamelets are proposed. The results include: (1) A complete re evaluation of Raman data showing significant corrections due to high temperature effects. Keywords: Turbulence chemistry interactions, Extinction, Blowoff, turbulent diffusion flames, Superequilibrium, Laser diagnostics.

Turbulence chemistry interactions have been studied experimentally and theoretically in the context of turbulent diffusion flames. The goal is a quantitative understanding of these interactions under a wide range of conditions. These range from low Reynolds number conditions ('weak' interactions, affecting primarily the levels of intermediate species, pollutants and combustion efficiency) to high Reynolds number conditions, where the flame can be extinguished by intense turbulent straining. Jet flames in coflowing air have been emphasized, with a coannular pilot burner used where necessary for stabilization at the burner lip. Fuels have consisted of carbon dioxide/H2 mixtures with the fraction of hydrogen successively reduced to promote extinction. Reynolds numbers have been increased to the point of blowoff. Major species and temperature have been measured by Raman scattering, and velocity and turbulence have been measured by laser velocimetry. These experiments have provided a comprehensive set of data on CO/H2 flames, extending to conditions conducive to localized extinction. The data show significant temperature decrements due to finite-rate chemistry but no evidence of localized extinction. Keywords: Turbulence, Chemistry interactions, Extinction, Turbulent diffusion flames, Superequilibrium, Laser diagnostics. (MJM).

Development of a fundamental understanding of turbulence-chemistry interactions remains one of the most important and challenging problems in turbulent reacting flows. This program couples laser based measurements and computer modeling of well-characterized laboratory-scale jet diffusion flames to study the effects of finite-rate chemistry and localized extinction in turbulent combustion. The long-range goal is to use this fundamental understanding for control of lean and high-altitude blow out in gas-turbine engines. The results of the first year of this program include: 1) improving the data base for CO/H2/N2 turbulent jet diffusion flames by analyzing direct measurements of CO2 concentrations from Strokes vibrational Raman intensities and by comparing two independent methods of determining temperatures from the Raman data; 2) testing of the stretched laminar flamelet concept in turbulent diffusion flames by comparison of instantaneous and conditionally averaged Raman measurements in turbulent H2 and CO/H2/N2 jet diffusion flame calculations and measurements; and 3) testing of a diffusion flame pilot for stabilization of turbulent jet flames at high Reynolds number.