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Nearly all real Diesel engine operation is leading to low exhaust temperatures. Standard catalyst technique remains therefore for significant time below light off. To improve the conversion behavior two approaches were made: placement of tailor fitted catalysts as close as possible to the engine exhaust port before turbocharger and usage of close coupled catalysts with the so-called hybrid design. Both measures are providing visible progress in reducing Diesel engine emissions. Tests were made with modern Diesel engines both for passenger cars and heavy duty vehicles.

Future catalyst systems need to be highly efficient in a limited packaging space which normally leads to a design where the flow distribution in front of the catalyst is not perfectly uniform. Measurements on the flow test bench show that the implementation of perforated foils for the corrugated and flat foils has the capability to distribute the flow within the channels in radial direction so that the maximum of the given catalyst surface is of use, even under very poor uniformity indices. Therefore a remarkable reduction in back pressure is measured. Emission results demonstrate cold start improvement due to reduced heat capacity. The use of LS-structured (Longitudinal structured) corrugated foils creates high turbulence level within the single channels. The substrate lights-up earlier and the maximum conversion efficiency is reached much quicker. It can be shown that a 300 cpsi Metalit with 50 µm foil thickness creates the same efficiency during the European Driving cycle like a 600 cpsi with ultra thin wall, even at reduced catalyst volume. The combination of LS type corrugated foil with perforated flat foils further improve catalyst efficiency.

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