A Theoretical Investigation of Mixing Effects in the Selective Reduction of Nitric Oxide by Ammonia

Abstract

The macroscopic transport equations governing the axisymmetric flow, mixing, and reaction of NH₃ with high temperature combustion products containing NO and O₂ have been solved numerically and compared to published experimental data for the same geometry. The elementary chemical kinetic mechanism used was based on an earlier model developed from plug flow experimental data. The results show generally good agreement between the calculations and experimental data. Spatial distributions of the contributions of individual elementary reactions to the overall reaction and of the contribution of diffusion processes and reaction processes to the structure of the reaction zone were evaluated. Additional model calculations were used to evaluate the effect of the rate of mixing of NH₃ with combustion products on NO reduction efficiency. Finite rates of mixing were found to have little effect on the temperature dependence of the NO reduction. However, at high temperature the oxidation to form NO was found to be inhibited by finite mixing rates.