On the scalar structure of nonequidiffusive premixed flames in counterflow

An experimental and computational study has been conducted for the structure and response to aerodynamic straining of adiabatic, planar, counterflow twin premixed methane/air, propane/air and hydrogen/air flames. The temperature and major species concentration profiles were experimentally 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 quantitative agreement with the experimental data. Results on the lean, stoichiometric and rich methane/air and propane/air flames demonstrate that, except for properties related to the slow CO oxidation downstream of the active heat release region, the flame structure in the direction normal to the flame surface is mostly not sensitive to variations in the strain rate, spanning from very low values to the state of near-extinction. For the ultralean hydrogen/air and near lean- flammability limit methane/air flames, the sensitivity is noticeable but still small as compared to the extent of the strain rate variation. Implications of the present understanding on the modeling of turbulent flames through the concept of laminar flamelets are discussed.