SCR Technology with Focus to Stringent Emissions Legislation

After the success of PM (Particulate Matter) reduction in exhaust gases of combustion engines due to the implementation of effective filter technology, one of the main thrusts of development concerning the future treatment of exhaust gases with respect to legislation around the world lies in the area of challenging reductions of nitrogen oxides (NO_x). In general there are at least two possible ways to reduce these limited components: NO_x Storage Catalysts (NSC) and the integration of Selective Catalytic Reduction (SCR) technology. The focus with SCR so far lies in the area of urea processing in front of the respective catalytic converter. In contrast to conventional exhaust systems with single-phase gas flow the complex processes with SCR technology call both for new developments and new components in the exhaust system. On the basis of actual developments it is obvious that the usage of mixing devices is mandatory for the majority of exhaust geometries to achieve a homogeneous urea/ammonia distribution in front of the SCR catalyst. This ensures maximized NO_x conversion rates with minimum ammonia slip at the same time.

A variety of mixers was developed which can significantly enhance the urea preparation, shorten the necessary mixing length and in some cases make possible the constructive use of SCR technology in actual platforms. Results are shown for different geometries for passenger car and commercial vehicle configurations and the respective mixer structure. Together with this the extended development process concerning durability (material choice, vibration and resonance behaviour) is highlighted.