Stretch Effects in Counterflow and Propagating Spherical Flames

Generalized expressions for the flame response to stretch rate variations were derived based on an integral analysis. Together with values of the laminar flame speeds, laminar flame thicknesses, and the one-step overall reaction order and activation energy determined from the computational results of the one-dimensional planar flame, these expressions for the stretched flames were then used to correlate the computational results of the spherical outwardly-propagating, spherical inwardlypropagating, and counterflow hydrogen/air and propane/air flames. Such correlations yielded the laminar flame speeds through linear extrapolation to zero stretch rate, the Markstein lengths representing the sensitivity of the flame response to stretch rate, and the flame Lewis number. Furthermore, it was 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-reactant flame theory of Joulin and Mitani. The feasibility of a priori determination of stretch effects on laminar premixed flames is emphasized.