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Several different possibilities will be described and discussed on the processes of reducing NOx in lean-burn gasoline and diesel engines. In-company studies were conducted on zeolitic catalysts. With lean-burn spark-ignition engines, hydrocarbons in the exhaust gas act as a reducing agent. In stationary conditions at λ = 1.2, NOx conversion rates of approx. 45 % were achieved. With diesel engines, the only promising variant is SCR technology using urea as a reducing agent. The remaining problems are still the low space velocity and the narrow temperature window of the catalyst. The production of reaction products and secondary reactions of urea with other components in the diesel exhaust gas are still unclarified.

To meet LEV/ULEV - requirements, a considerable amount of development work was necessary to ensure suitable efficiency and durability of catalyst systems [1, 2, 3]. In addition to active emission reduction systems like the Electrically Heated Catalyst (EHC), Exhaust Gas Ignition (EGI) and the burner, passive systems like the HC-trap and Closed-Coupled Catalysts (CCC) are practical solutions to fulfill tighter emission requirements [4, 5, 6, 7]. Depending on the application, thermo-mechanical stresses, vibrations and efficiency degradation through aging increases with the reduction of the distance between the engine and the catalytic converter. Therefore, the test procedures which were suitable for converters which were to be placed in underfloor positions, needed to be modified according to the load spectra acting on close-coupled catalysts. This paper describes a new test strategy used during the development and design verification phase of catalytic converter systems.

More stringent emissions regulations, space limitations for catalytic converters in modern automotive applications, and new engine technologies constitute design challenges for today's engineers. In that context high cell density thinwall and ultrathinwall ceramic substrates have been designed into advanced catalytic converters. Whereas the majority of these substrates have a square cell geometry, a potential for further emissions improvement has been predicted for hexagonal cell structures. In order to verify these predictions, a ceramic substrate has been developed combining the features of high cell density, ultrathin cell walls, and hexagonal cell structure. Based on modeling data, the actual cell density and wall thickness of the hexagonal cell substrate will be defined. The performance of that substrate will be assessed by comparing experimental emissions results using two modern Volkswagen engines.

From SAE-Papers and several publications, the easy, effective function and management of an EHC-System is well known. The direction of the development is now to reduce the electrical energy consumption and to show the mechanical durability of the heating structure. This paper shows that it is possible to minimize the energy consumption and that the required service life can be in principle achieved with the introduction of these developments. The physical characteristics such as mass, geometrical surface area, cell density and electrical resistance of the EHC construction could be optimized to save energy. This, in conjunction with the operating parameters of the engine, the controlling of the secondary air and the catalyst configuration, will enable the goals to be met. The design of the converter, the physical characteristics and the results of the tests are shown with the Porsche 944 S2 and 968 applications.

Driven by the worldwide automotive emission regulations, ceramic substrates were developed to serve as catalyst support. Since the introduction of Standard wall substrates in 1974, substrates with thinner walls and higher cell densities have been developed to meet the tighter emission requirements; Worldwide, the amount of Thinwall and Ultrathinwall substrates in series applications is increasing continuously. The properties of the substrates determine their performance regarding pressure drop, heat-up and conversion efficiency. These properties are analyzed, as well as the packaging process for Thinwall and Ultrathinwall substrates; A new packaging technique with lower pressure load is described.

Metal supported catalysts, whose early development actually started in the sixties, are used today in a few isolated cases as starter catalysts, retrofit and underfloor catalysts of small dimensions. The new Porsche Carrera 4 is the first production car to use a large main catalytic converter with metal supports. This paper describes the design of this catalyst and the advantages of using the metal supports, especially the increase in power output due to the reduction of exhaust back pressure. Also benefits in catalytic performance could be determined. The major requirement in using large metal supports in production is mechanical sturdiness. In extensive vehicle, test bench and laboratory tests and according to the theoretical calculations, the support with S-design described here has met this requirement.