The structure of partially premixed methane flames in high-intensity turbulent flows

Direct numerical simulations (DNS) are conducted to study the structure of partially premixed and nonpremixed methane flames in high-intensity two-dimensional isotropic turbulent flows. The results obtained via "flame normal analysis" show local extinction and reignition for both non-premixed and partially premixed flames. Dynamical analysis of the flame with a Lagrangian method indicates that the time integrated strain characterizes the finite-rate chemistry effects and the flame extinction better than the strain rate. It is observed that the flame behavior is affected by the "pressure-dilatation" and "viscous-dissipation" in addition to strain rate. Consistent with previous studies, high vorticity values are detected Close to the reaction zone, where the vorticity generation by the "baroclinic torque" was found to be significant. The influences of (initial) Reynolds and Damkohler numbers, and various air-fuel premixing levels on flame and turbulence variables are also studied. It is observed that the flame extinction Occurs similarly in flames with different fuel-air premixing. Our simulations also indicate that the CO emission increases as the partial premixing of the fuel with air increases. Higher values of the temperature, the OH mass fraction and the CO mass fraction are observed within the flame zone at higher Reynolds numbers. (C) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved.