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EHC design and engine operation requirements for a battery powered EHC-cascade were investigated using flow rig, engine dynamometer and vehicle evaluations. Low mass and Pd-coated heater elements and light-off converters are recommended for optimum light-off performance. Raising the heating power improves light-off. However, battery powered systems are limited to 1.5 kW. Rich engine operation combined with an excess of secondary air results in high exothermic energy output. The benefit of additional heating and the impact of cascade position (close coupled or underfloor) are closely related to the test cycle. ULEV limits were achieved using a MY 91 vehicle without upgrades in engine control.

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.

This paper presents some of the innovative exhaust noise reduction techniques an exhaust system development engineer can employ, when his customer, the car manufacturer, increases the engine swept volume and engine power without allowing any change in the layout of the exhaust system, which may already be on the borderline from the acoustic point of view. The solution to this problem could be an “electronic” muffler. Here there are two possibilities: 1. A semiactive muffler, which will change the internal geometry of the muffler system or muffler in accordance with changes of engine conditions during driving. 2. An active system, which adds antinoise or modulates the pulsating exhaust gas flow in order to smooth the gas pressure pulsation and to get in this way a sound attenuation. The possibilities and limits of both solutions are shown by different measurement results.

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.