Asymptotic analysis of radiative extinction in counterflow diffusion flames of nonunity Lewis numbers

The effects of radiation heat loss and variation in near-unity Lewis numbers on the structure and extinction of counterflow diffusion flame established near the stagnation plane of two opposed free streams of fuel and oxidizer are analyzed using the asymptotic method of large activation energy. Radiation heat loss from the reaction zone is accounted for using the optically thin assumption. The main concern of this study is the thermal effects of radiation heat loss and Lewis numbers on diffusion flame extinction, particularly at small stretch rates. The existence of two extinction limits, the radiation extinction limit at a small stretch rate and the conventional quenching limit at a large stretch rate, is theoretically reproduced. This simplified analysis is able to predict the existence of inflammable limits of counterflow diffusion flames in terms of the near-unity Lewis numbers and concentrations of the fuel and oxidizer streams. Crown copyright (C) 2000. Published by Elsevier Science Inc.