COMPUTATIONAL COMPARISON BETWEEN AN ELLIPTIC AND A BOUNDARY-LAYER FORMULATION FOR METHANE AIR COMBUSTION ABOVE A HEATED NONCATALYTIC SURFACE/

A fully two-dimensional elliptic model with a detailed gas phase react ion mechanism for the combustion of premixed fuel (CH4) and air, over a non-catalytic, non-permeable plate is presented. By comparing soluti ons for ignition distances and species profiles predicted by the ellip tic and boundary layer models, a criteria, based on the equivalence ra tio and the wall temperature was obtained, which can be used to determ ine when the boundary layer approximation is valid. For low equilvalen ce ratios (phi < 0.4), no difference (except in the vicinity of the le ading edge) was observed between the predictions of the two models at downstream distances from the leading edge of the plate for wall tempe ratures up to 1580 K. For high equivalence ratios (phi greater than or equal to 0.4) and for wall temperatures above 1300 K, the predictions differed significantly. The boundary layer model always predicted a t hicker reaction zone.