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The unsteady flow effects of a Close-Coupled Converter (CCC) are investigated. The aim is to improve the catalytic efficiency by uniformly utilizing the entire converter volume. Experimental and computational methods were used to evaluate the differences between unsteady and steady-state flow. Catalytic converters placed close to the engine have individual inflow pipes from each cylinder and suffer extreme filling and emptying processes. There is severe interaction of the pulsating exhaust flows. A wide range of engine operating points were studied at different engine speeds and load conditions. Also described is the influence of the gas pulsation on the conversion characteristics.

The “Multiple Disc Converter” is an innovative concept. In comparison to conventional catalytic converters, it is significantly less expensive and more compact, at identical conversion efficiency and durability. The catalytic substrate consists of 4 to 5 cylindrical ceramic discs with 62 cells/cm2 (400 cells/inch2). These are assembled in a sheet metal casing, without gaps between the discs, and angularly offset to each other. The flow through the channels is interrupted at the contact surfaces of the individual discs. Hence, the restarted turbulent flow intensifies the transverse mass transfer. Further, the uniformity of the exhaust gas flow is improved, particularly in the first discs. Thus, the conversion of emissions is improved and the durability extended. When the conversion is maintained at the level of conventional converters, then the converter volume can be substantially reduced using the same specific catalyst loading.

Ceramic fibers, in a knitted structure, offer an elastic deep-filter medium having a very high specific surface. The robustness of this trap, and its invulnerability to thermo-shock, was demonstrated during a further year of development and tests. By using new manufacturing techniques, the filtration efficiency was further improved, pressure losses reduced, and the required volume diminished. New insight was obtained regarding the employment of the fiber medium for catalysis. The filter concept permits regeneration either electrically or by fuel-additives. The layout versatility facilitates deployment on vehicular and stationary engines, in the pre-turbo position, too.

The design of the converter has a considerable influence on exhaust emissions as well as engine performance and exhaust acoustics. Converters have an effect not just on the tailpipe noise but also on surface sound radiation of the exhaust system. The contribution of tailpipe and surface to noise emission of exhaust systems is for high performance engines in many cases approximately the same. The surface radiation affects not just the exterior noise of the vehicle but also the interior noise. The subjective noise as well as the objective noise is also influenced. Surface sound radiation therefore becomes increasingly more significant. This contribution will present results about the influence of the shape of the monoliths and the effect of different monolith mounting systems. The influence of thermal insulation and main shell design is also shown. The surface sound radiation of ceramic monoliths and metallic supports will be compared.