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Due to the high percentage of NOX emissions generated by mobile vehicles, current and future legislation for NOX limits is of especially high importance for the automotive industry. In Europe those include not only the more stringent yearly averaged level for inner city NO2 emissions, but also a proposal of the EU parliament of a NOX limitation value for EU 6 legislation of 80 mg/km for passenger cars. In addition, a proposition of the EU commission for a NOX limitation value for Stage VI for heavy duty trucks of 400 mg/kWh is being discussed. In the US the requirements with US BIN 5 for passenger cars and US2010 for Heavy Duty Trucks are comparable. There is no doubt about the necessity of the usage of exhaust after treatment systems for NOX reduction in order to fulfil these requirements, however largely unclear are the technical details of systems capable to fulfil these requirements.

The influence of physical parameters of the catalyst's substrate such as thermal mass, hydraulic diameter and geometric surface area on catalyst's efficiency is well known as published in numerous works. This paper will show interactions of these parameters and will provide a guideline on how to design the optimum system for a specific application, taking into account system's back pressure and system costs. Based on engine test bench results that show the influence of the physical parameters, the results for the optimized design regarding emission tests and maximum conversion rate at higher loads will be demonstrated.

Fleet tests conducted on electrical vehicles around the world have very clearly shown that battery-powered cars may be regarded as zero-emission vehicles with respect to their local environments only. Emission measurements on vehicles powered by internal-combustion engines equipped with optimized exhaust-post-treatment systems have indicated the prospects the latter offer for cleaning up the environment, i.e., for yielding negative emissions, when run at their normal operating temperatures. Replacing electric cars with SULEV's is thus a matter currently under discussion. This paper will cover the functions of the various individual components of such post-treatment systems, and will show that optimizing the interactions among those components will improve their catalytic efficiencies.

The close coupled catalytic converter, together with the manifold and exhaust pipes, form a group of components that emit powerful heat energy. For temperature controle of the neighboring components, limiting the converter surface temperature in the same way as with underfloor systems will not be satisfactory for close-coupled converter systems, as the converter's surface temperature does not represent the only physical measure for assessing the thermal load on other components. Instead, it makes more sense, to control the heat output of the exhaust system and the heat transfer to the other components by choosing materials for the included surfaces which show good proporties to reduce radiative heat transfer.