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M. Börnhorst, C. Kuntz, U. Budziankou, O. Deutschmann, J. Grunwaldt, T. Lauer, B. Geringer et al.:
"Fundamental experimental and numerical investigation on the deposit formation and decomposition from AdBlue in SCR-systems - Final report";
Report No. 1191, 2019; 127 pages.

Based on legislation for diesel engines a further minimization of emissions of nitrogen oxides (NOx) is essential. The selective catalytic reduction (SCR) is therefore an efficient and widely used method, often in combination with other emission control devices. In SCR systems, urea is injected into the tailpipe as an urea-water solution (UWS). Water evaporation and decom-position of the urea content yield to an ammonia production in front of the SCR catalyst. Due to highly transient conditions and a limited mixing length incomplete spray evaporation may lead to droplet impingement on the tailpipie, where wall film is formed on low load points. Ac-cumulated liquid film can induce solid formation due to urea crystallization and by-product formation, which impedes the SCR efficiency.
This work deals with interaction of AdBlue sprays with hot tail pipes, resulting wall film formation and accumulation of deposits from liquid film. For investigations in application scale, a lab test bench at KIT and an engine test bench at TUW are installed, which enable experiments on film- and deposit formation under realistic conditions. Generated solid deposits are sampled for detailed analysis of topology and chemical composition by thermogravimetrical analysis (TGA) and high performance liquid chromatography (HPLC).
Based on kinetic data from the experiments an existing kinetic model for urea decomposition was extended. Together with developed models for spray/wall interaction, heat transfer and an approach for substantial speed up of simulations, for the first time physical as well as chemical processes in the mixing section of SCR systems are depicted in 3D-CFD simulations. Furthermore, a new kinetic model is introduced, that is mainly based on thermodynamic data and equilibrium processes and which allows a detailed prediction on urea decomposition and de-posit formation with all upcoming experimental effects.