Dynamics of weakly stretched flames: Quantitative description and extraction of global flame parameters

Generalized expressions for the flame response to weak stretch rate variati ons were derived based on an integral analysis. Together with values of the laminar flame speed, laminar flame thickness, and the one-step overall rea ction order and activation energy determined from the computational results of the one-dimensional planar flame, these expressions for the stretched f lames were then used to correlate the computational results of the spherica l outwardly propagating, spherical inwardly propagating, and counterflow hy drogen/air and propane/air flames. These correlations yielded the laminar f lame speeds through linear extrapolation to zero stretch rate, the Markstei n lengths representing the sensitivity of the flame response to stretch rat e, and the flame Lewis number. Furthermore, it is shown that the extracted Markstein lengths and Lewis numbers from the three flame configurations are largely the same for given equivalence ratio and system pressure, and that these Lewis numbers also agree well with those predicted from the two-reac tant flame theory of Joulin and Mitani. The feasibility of a priori quantit ative determination of stretch effects on laminar premixed flames is sugges ted. (C) 1999 by The Combustion Institute.