(174c) CFD Modeling of Pollutant NOx Dispersion & Absorption From Vehicular Exhaust Pipe

The major emissions from vehicular tailpipes are ozone (O3), Particulate Matter (PM), Nitrogen Oxides (NOx), Sulfur Oxides (SOx), Carbon Monoxide (CO), and Volatile Organic Compounds (VOCs). Many methods have been implemented to reduce the NOx emissions, including the budding green technology of Photo-Catalytic Oxidation (PCO) techniques for NOx control. PCO uses a photo catalyst under UV/visible light illumination to oxidize pollutants to harmless compounds. In this control technique, NOx is oxidized to nitric acid and VOCs are oxidized to water, CO2, chlorine and other compounds.

The objective of the project is to simulate the NOx dispersion from the exhaust pipe, interaction of this plume with road surfaces, and the effects of wind speed using the help of Computational Fluid Dynamics (CFD). The gases coming out of the exhaust pipe go down to the catalyst coated road surface and get adsorbed there due to photo catalytic oxidation . But, the amount nitrogen oxides adsorbed varies with velocity, geometry, direction of tail pipe and other factors. The present study aims at modeling the NOx dispersion from the exhaust pipe of a car using the RANS approach and the k-ε turbulence model. The turbulence-chemistry interaction between the NOx and the atmospheric air, as well as, the photo catalyst surface is into consideration.

The CFD simulation package selected for this purpose is FLUENT. The NOx emitted from single vehicle source is considered and the dispersion of NOx plume in the environment is studied. The variation of concentration profile versus distance from the exit after NOx is emitted to the atmosphere having a catalytic absorbing surface is studied. With known exhaust gas velocity, reaction kinetics & exhaust pipe geometry, the simulation was done. To study further, three different cases were taken with various tail pipe directions i.e. horizontal, vertical and inclined to ground at 45 degrees. For all the three cases the dispersion from a vehicle at low idle condition (when the vehicle's engine is running but the vehicle is still, for example toll gates or at traffic signals, when the signal is ?red') and high idle condition (when the vehicle starts to move after the signal turns green or when the toll is paid) are simulated . The CFD simulations were first conducted in 2-dimensional geometries then in 3-dimensional geometry. The simulation results will facilitate the development of novel NOx reduction technologies.