Abstract
The classical diffusion flame model of Burke and Schumann is extended to include the effects of both streamwise and preferential diffusion. The study first identifies a Lewis-number-weighted coupling function as the proper one to usc in formulations involving non-unity Lewis numbers. A perturbation technique is then developed for the realistic situation of ncar-unity Lewis number flows. Results show that, depending on the effective Lewis numbers of fuel and oxidizer, the flame temperature may vary either monotonically or non-monotonically along the flame sheet, and thereby suggesting the possibilities of tip opening, and tip intensification, as well as partial and complete flame blow-off.