Effects of Micro- and Macroscale Turbulent Mixing on the Chemical Processes in Engine Exhaust Plumes

Abstract

Turbulent mixing and chemical reactions in the near field of an engine exhaust jet plume have been investigated using a mixing model that explicitly incorporates both large- and small-scale turbulent mixing and the molecular diffusion effects. A reduced reaction mechanism that accurately reproduces results of a detailed mechanism for the lower stratosphere was used to simulate the exhaust plume dynamics of a typical high-speed civil transport aircraft. This study shows that, compared to predictions based on models that do not include small-scale mixing and/or molecular diffusion effects, 30% less O3 and 15% less NOx are depleted in the near field of the plume. This suggests that the lack of local mixing can have an inhibiting effect on ozone depletion in the near-field plume. Inclusion of heterogeneous kinetics involving the formation of nitric and sulfuric acid due to water condensation on soot particles showed that 15% of the available NOx is converted into its inactive form but has a negligible effect on O3 concentration. This method also provides appropriate conditions for the plume?vortex interaction stage where more complex chemistry, including heterogeneous kinetics, is likely to take place.