The porous medium approach applied to CFD modelling of SCR in an automotive exhaust with injection of urea droplets

摘要

The automotive industry is expected to adopt SCR after-treatment to control NOx emissions from Diesel passenger cars from 2010. Ammonia promotes NOx reduction and is introduced into the exhaust as a spray of aqueous urea droplets. This is a new aspect of CFD modelling of exhaust after-treatment. When modelling sprays the mesh must be 3D and so the porous medium approach is appropriate, circumventing the need for representative single channel modelling. The porous medium technique is well established for modelling three-way catalysis and its application to SCR is demonstrated in this paper, using a kinetic scheme available in the literature. Laboratory measurements of droplet diameters have been used to specify the input of aqueous urea to the CFD model. Representative droplet parcels are modelled using a Lagrangian model within the CFD code. In this way it is possible to fully model SCR in a 3D model of an automotive catalyst system.