On the structure and response of aerodynamically-strained planar premixed flames

Abstract

The effects of aerodynamic straining on the structure and response of adiabatic, unrestrained, equidiffusive, planar premixed flames were experimentally and computationally studied via the counterflow, twinflame configuration formed by oppositely-directed identical jets of nitrogendiluted, near-stoichiometric methandair mixtures. Experimentally, the doc i ty , temperature and major species concentration profiles were determined by using LDV and spontaneous Raman scattering as functions of the applied strain rate. Computationally, the experimental situation was simulated with detailed reaction mechanisms and transport properties. Both the experimental and computational results show that the flame structure remains similar in response to variations in strain rate as long as the flame is sufficiently far away from the stagnation surface so that incomplete reaction is minimal. These results substantiate the concepts that the flame structure, and thereby the f lme thickness, are invariant to strain rate variations for adiabatic, unrestrained, diffusionally-neutral premixed flames with complete reaction, and that these flames cannot be extinguished by straining alone. The computed results are further shown to agree well quantitatively with the experimental data, hence supporting the usefulness of the computational model for the simulation of strained flames. Implications of present findings on the extinction of stretched flames, the modelling of turbulent flames through the concept of laminar flamelets, and flame stabilization and blowoff, are discussed. d Introduction The structure and response of laminar premixed flames under the influence of stretch have attracted much attention because not only most practical laminar flames are stretched, but a major effort in turbulent flame modeling is also based on the concept * Graduate Student ** Professor, Fellow AIAA Copyright