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Institute for Powertrains and Automotive Technology
Vienna University of Technology 
Getreidemarkt 9
1060 Vienna, Austria
Phone: +43 1 58801 31500
Mail: info[at]

Office opening hours:
Mo-Fr: 8 am - 4 pm


In order to meet future international legislative restrictions, a significant reduction of nitrogen oxide emissions of diesel engine powered vehicles is necessary. Selective Catalytic Reduction (SCR) is a promising approach to cope with the challenging limits in the sector of mid-sized and large passenger cars as well as heavy duty vehicles.

The system is based on the injection of a urea water solution, known as Diesel Exhaust Fluid (DEF) (R) or AdBlue (R). In the hot exhaust gas, the dispersed AdBlue (R) spray is converted into ammonia. The latter is then used to chemically reduce the harmful nitrogen oxides on a special SCR catalyst. In order to effectively reduce the nitrogen oxides, a fast preparation of AdBlue (R) and a good ammonia homogenisation of the reducing agent at the catalyst are a necessity.

At the Institute for Powertrains and Automotive Technology at the Technical University of Vienna, development and design of SCR systems has been investigated for more than five years. A fundamental understanding of the complicated physical and chemical processes involved in SCR technology could be developed in cooperation with partners from the automotive industry. Apart from intensive testing at the test bench, three dimensional computational fluid dynamics (CFD) is applied. Based on experiments at the test rig, a model of the preparation and mixing processes of the reducing agent upstream of the catalyst was developed. With the help of this CFD methodology the distribution and decomposition of the AdBlue (R) spray and the turbulent mixing of the ammonia vapour can be anticipated. An example is shown in figure 1. The latter depicts the simulation results as well as the good correlation with measurement data.

Based on such calculations, that are comparatively time- and cost-effective, recommendations for optimisations of the analysed SCR system can be demonstrated. Promising solutions can then be implemented and tested at the test bench. As a result of the close cooperation between engine test bench and simulation, optimum SCR systems can be developed efficiently to ensure compliance with future emission legislation.

Dipl.-Ing. Herbert Gerstl
Phone: +43 1 58801 31525
Mail: herbert.gerstl[at]