THE LOCAL-STRUCTURE OF TURBULENT NONPREMIXED FLAMES NEAR EXTINCTION

Using reported data collected in turbulent jet nonpremixed flames near extinction, various parameters are derived to characterize the structure of the flames as they approach blowoff. The fuels considered are CH4, H2, H2 Ar, and CO/H2/N2. The data used consist of velocity and turbulence measurements using the LDA technique and measurements of temperature, species mass fractions, and mixture fraction using the spontaneous Raman-Rayleigh scattering technique. Flames of H2 Ar and CO/H2/N2 fuels exhibit a monomodal behavior in the pdfs of their reactive scalars as they approach extinction while those of CH4 flames are bimodal. The parameters controlling this behavior are the width of the reaction zone, ΔξR and the scalar scale of turbulence Σξ. It is found that this behavior is only slightly affected by Σξ and is mainly dependent on ΔξR. Further investigations of other fuels with a range of ΔξR are recommended. © 1990.