Modeling and simulation of the injection of urea-water-solution for automotive SCR DeNOx-systems

The evaporation of water from a single droplet of urea water solution is investigated theoretically by a Rapid Mixing model and a Diffusion Limit model, which also considers droplet motion and variable properties of the solution. The Rapid Mixing model is then implemented into the commercial CFD code Fire 8.3 from AVL Corp. Therein, the urea water droplets are treated with Lagrangian particle tracking. The evaporation model is extended for droplet boiling and thermal decomposition of urea. CFD simulations of a SCR DeNOx-system are compared to experimental data to determine the kinetic parameters of the urea decomposition. The numerical model allows to simulate SCR exhaust system configurations to predict conversion and local distribution of the reducing agent.