ON THE SCALAR STRUCTURE OF NONEQUIDIFFUSIVE PREMIXED FLAMES IN COUNTERFLOW

An experimental and computational study has been conducted for the str ucture and response to aerodynamic straining of adiabatic, planar, cou nterflow twin premixed methane/air, propane/air and hydrogen/air flame s. The temperature and major species concentration profiles were exper imentally determined as functions of the applied strain rate by using spontaneous Raman scattering. In addition, the experimental situations were computationally simulated with detailed reaction mechanisms and transport properties. The computed results were found to be in close q uantitative agreement with the experimental data. Results on the lean, stoichiometric and rich methane/air and propane/air flames demonstrat e that, except for properties related to the slow CO oxidation downstr eam of the active heat release region, the flame structure in the dire ction normal to the flame surface is mostly not sensitive to variation s in the strain rate, spanning from very low values to the state of ne ar-extinction. For the ultralean hydrogen/air and near lean-flammabili ty limit methane/air flames, the sensitivity is noticeable but still s mall as compared to the extent of the strain rate variation. Implicati ons of the present understanding on the modeling of turbulent flames t hrough the concept of laminar flamelets are discussed.