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Current emission standards for diesel passenger cars in Europe and the US require the use of diesel particulate filters (DPF). For optimal engine performance the accumulated soot on the filter has to be removed periodically at elevated exhaust gas temperature of 600-650\,DC. Since many driving conditions do not allow such exhaust gas temperature additional measures have to be applied to increase the temperature in the exhaust. Post-injection of diesel fuel in the combustion chamber is the more common solution used to increase the exhaust temperature for particulate filter regeneration. Oil dilution is one of the drawbacks of regeneration by post-injection. The use of a fuel vaporizer is another option to increase the exhaust temperature by introducing fuel in vapor form into the exhaust system. The vaporizer can be located in front of the DOC/DPF either in a close coupled position to the engine or in an underfloor position.

The SCR after treatment system is already in production for passenger car engines with a single exhaust system. In this case, the exhaust system has to be designed very carefully to optimize the Ammonia distribution on the catalyst and therefore the DeNOx potential. The application to V8 engines with two turbochargers delivering the gas into two separated DOC & DPF units is an additional challenge. This paper describes the different optimization steps of such an exhaust system and the tools used during this work. After a design phase to integrate the SCR system in the exhaust geometry, a first CFD study was conducted to evaluate the performance of the basic system using one or two urea injectors. An optimization of the connection of the two tubes, directly in front of the SCR catalyst, has been designed using further CFD calculations as well as a marker gas SF6 on a cold flow bench.

The Selective Catalytic Reduction (SCR) is one of the most efficient technologies to reduce nitrogen oxide (NOx) emissions arising from technical combustion processes [1,2]. For compliance with future emission limits for heavy-duty Diesel engines the SCR technology might play an important role [3]. In two long-term field demonstrations heavy duty (HD) trucks were equipped with SCR emission control systems (SINOx™-System) and were operated under daily working conditions. A number of measurements of both the performance and the activity of the catalyst during the entire operation time were performed. On the engine test bench the NOx reduction at the beginning of the road test was compared to the NOx-reduction at the end of the program. The initial NOx remained unchanged within the measurement accuracy of the analyzing equipment. On-road measurements of the emissions were done using an analyzer test cell installed on the loading area of the truck.