A numerical study on preferential diffusion effects in coflowing laminar reacting jets

Laminar diffusion-controlled jet flames are found in a wide range of applications and also used for fundamental studies on reactive flows. Diffusion flames are classically studied considering infinitely fast chemistry and equal mass and heat diffusivities. Such assumptions can be unrealistic for many practical situations. The present work evaluates the effects of preferential diffusion in an axisymmetric confined reactive flow using an extension of the classic Shvab-Zel'dovich formulation solely in terms of the Lewis numbers of the reacting species. The governing equations are solved using the finite volume method and a structured mesh. The WUDS (Weighted Upstream Differencing Scheme) is used for the discretization of the convective terms, and the SIMPLEC (Semi-Implicit Method for Pressure Linked Equations-Consistent) method is employed for pressure-velocity coupling in solving for the velocity field. Initially, results obtained for the limiting case of unity Lewis numbers are verified and validated using numerical and experimental data available in the literature. Results are then obtained for different fuel and oxidant Lewis numbers, allowing for analysis of off-adiabatic flame temperatures and of changes in flame height and width. Besides, results also show that for over-ventilated flames, the oxidant Lewis number has a more pronounced influence on the combustion processes than the fuel Lewis number.