The structure of turbulent nonpremixed flames revealed by Raman-Rayleigh-LIF measurements

This paper reviews recent advances in our understanding of the structure of turbulent nonpremixed dames due to extensive data acquired from single-point and planar imaging experiments using the Raman, Rayleigh, and LIF diagnostic methods. These techniques, used either separately orjointly, have become standard tools in combustion research. Flames with simple streaming flows as well as complex hows with recirculating zones are discussed for a variety of fuel mixtures and a range of turbulent mixing rates. The chemistry-turbulence interaction and other related issues like local dame extinction and the bimodality of the approach toward blowoff are discussed. Additional single-point data are also presented illustrating the effects of partially premixing the fuel with air, diluting it with nitrogen or adding methane to a mixture of nonhydrocarbon fuels. The bimodality of the conditional pdfs of various reactive scalars as the dames approach blowoff, and the start of occurrence of localized extinction, are correlated with two simple parameters: (a) the stoichiometric mixture fraction, xi(s), and (b) the reaction zone width, Delta xi(R). The latter parameter may be easily determined from standard laminar dame calculations for a given fuel mixture. Copyright (C) 1996 Elsevier Science Ltd.