| This work is an experimental and theoretical investigation of the structure of lean premixed (LP) methane flames under intense turbulence. Simultaneous and instantaneous, temporally and spatially resolved non-intrusive measurements of temperature, major species (CH4, O2, N2, CO2, and H2O), OH, H2, and pollutants (CO and NO) are obtained in turbulent (u′/S L = 28) LP methane flames (&phis; = 0.586) using a combination of Rayleigh scattering, Raman scattering, and laser-induced fluorescence. These multi-parameter measurements have spatial and temporal resolutions of 800 μm and 150 ns respectively.; The diagnostic system was applied to the turbulent flowfield in the LP combustor to obtain a benchmark data set of combustion scalars and pollutants. These measurements when combined with the previous velocity measurements of Pan et al. (1991a), provide a detailed map of the combustion flow field. Statistics (mean and rms measurements) of the combustion scalars across the combustor are reported and discussed in the context of LP combustion.; The scalar measurements are compared to laminar positive displacement speed flamelet models, laminar negative displacement speed flamelet models, and perfectly stirred reactor models of turbulent premixed combustion for evaluating the structure of turbulent premixed reaction zones. In the reaction zones supported by the recirculation region, the temperature, major species, OH, and CO are accurately predicted by the laminar negative displacement flamelet model. These reaction zones are weak, are at high strain rates, and are mixing dominated. In the reaction zones downstream of the recirculation zone, the temperature, major species, OH, and CO are accurately predicted by the laminar positive displacement flamelet model. Based on the results, a comprehensive modeling scheme is suggested for flame-holder stabilized turbulent premixed LP combustion.; The measurements in the LP combustor indicate that the new regime diagram of premixed turbulent combustion proposed by Peters (1999) is more appropriate for modeling than the conventional diagram (Borghi, 1995). It is proposed that the “thin reaction zones” regime (Peters, 1999) be modeled using “negative displacement speed” flamelets. |
