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To comply with the upcoming emission regulations for non-road applications, especially the TIER 4 Final emission legislation, a significant reduction in particulate matters and nitrogen oxide emissions is necessary. An exhaust gas after-treatment system with a good performance helps to meet these requirements. The following paper focuses on the possibilities to reduce the nitrogen oxide emissions in exhaust gas after-treatment technology using selective catalytic reduction with AUS32. Using this technology and targeting a nitrogen oxide emission reduction of 90% the exhaust gas after-treatment system enables engine-out emissions of about 3 - 4 g/kWh nitrogen oxide. Considering an increase of only 5% reduction efficiency to 95%, a duplication of engine-out emissions could be acceptable for still meeting TIER 4 Final emission legislation.

Performance improvements, of catalytic converters, and longer service life can be achieved by improving the flow distribution of exhaust gases. Computational Fluid Dynamics (CFD) is an excellent and relatively inexpensive technique for rapid and efficient optimization of the flow. Studies indicate that a 3D representation is necessary because 2D is insufficient. The computations are confirmed by measurements of steady flow. A number of design parameters are systematically investigated and their effects on an index of flow uniformity established. The parameters include the geometry of the inlet tube and inlet cone, the geometry and placement of the monoliths, and the shape of the exit cone. The difficult flow conditions in close coupled converters are examined. The flow path is improved and the best location of the HEGO-sensor found.