Impinging nonpremixed coflow methane-air flames with unity Lewis number

The present work extends earlier theoretical models in order to analyze nonpremixed flames stabilized be-tween an axisymmetric coflow burner and a downstream plate that produces a stagnating flow field. This unusual configuration (i.e., it is not a coflow nor a counterflow flame but an impinging nonpremixed flame) is analyzed with two approaches previously developed as extensions to the Burke-Schumann theory: the Ex-tended Roper Model and the Stream Function as a Coordinate Model. The flow field is obtained through the solution of a stagnation point viscous flow for incompressible fluids between stationary porous plates. In order to simplify the analysis, unity Lewis number is considered. Infinitely fast conversion of the reactants into products is assumed together with the Shvab-Zel'dovich coupling function approach, which allows the solution of a reduced number of conservation equations free of source terms. The influence of the distance between the impinging plate and the burner tip on a methane-air flame is analyzed and the semi-analytical results are compared with experimental data for several vertical positions of the stagnation plate with respect to the burner port. The model is able to effectively capture general aspects of the flame such as its shape, standoff distance, and separation distance at which flame tip opening is observed. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.