Boundary layer combustion of carbon

Abstract

A theoretical investigation of the oxidation of carbon in stagnation point boundary layer flow has been performed for the case of frozen flow, equilibrium flow and the kinetically controlled flow regime. It is shown that the experimental combustion rate data of Matsui et al. could be reproduced by a frozen flow calculation, if the kinetic parameters were adequately adjusted. However, the heterogeneous reaction rates thus obtained correspond to a predominant primary combustion to CO 2 , rather than to CO in contrast to previously reported results in the literature. Also it is found that the assumption of heterogeneous equilibrium would predict higher combustion rates than those experimentally observed. Consequently, on the basis of the primary CO/CO 2 ratio given in the literature, a model was analyzed which considers predominant heterogeneous combustion to CO with subsequent homogeneous oxidation of CO to CO 2 in the nonequilibrium flow regime. These calculations reveal a very strong influence of moisture upon the homogeneous combustion rate. In dry air the conversion of CO to CO 2 is practically frozen, but at relative humidities of 10% or higher it is enhanced by a factor of about 5×10 3 compared to the dry air reaction rate. As the location of stoichiometric composition is very close to the surface, homogeneous combustion takes place under fuel lean conditions.