Analysis of the Injection of Urea-water-solution for automotive SCR DeNOx-Systems: Modeling of Two-phase Flow and Spray/Wall-Interaction

Copyright c © 2006 SAE International The selective catalytic reduction (SCR) based on urea-water-solution is an effective technique to reduce nitrogen oxides (NOx) emitted from diesel engines. A 3D numeri-cal computer model of the injection of urea-water-solution and their interaction with the exhaust gas flow and ex-haust tubing is developed to evaluate different configura-tions during the development process of such a DeNOx-system. The model accounts for all relevant processes appearing from the injection point to the entrance of the SCR-catalyst: • momentum interaction between gas phase and droplets • evaporation and thermolysis of droplets • hydrolysis of isocyanic acid in gas phase • heat transfer between wall and droplets • spray/wall-interaction • two-component wall film including interaction with gas phase and exhaust tube The single modeling steps are verified with visualizations, patternator measurements, phase-doppler-anemometer results and temperature measurements. CFD simulations of a SCR DeNOx-system are compared to experimental data to determine the decomposition parameters for urea-water-solution droplets. Numerical results for an injection including all processes addressed above are discussed