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Modern exhaust systems contain not only a piping network to transport hot gas from the engine to the atmosphere, but also functional components such as the catalytic converter and turbocharger. The turbocharger is common place in the automotive industry due to their capability to increase the specific power output of reciprocating engines. As the exhaust system is a main heat source for the under body of the vehicle and the turbocharger is located within the engine bay, it is imperative that accurate surface temperatures are achieved. A study by K. Haehndel [1] implemented a 1D fluid stream as a replacement to solving 3D fluid dynamics of the internal exhaust flow. To incorporate the 3D effects of internal fluid flow, augmented Nusselt correlations were used to produce heat transfer coefficients. It was found that the developed correlations for the exhaust system did not adequately represent the heat transfer of the turbocharger.

In order to meet the severe emission restrictions imposed by SULEV and EURO V standards the catalytic converter must reach light-off temperature during the first 20 seconds after engine cold start. Thermal losses in the exhaust manifold are driven by the heat transfer of the pulsating and turbulent exhaust flow and affect significantly the warm-up time of the catalyst. In the present paper an investigation concerning the gas-side heat transfer in the exhaust system of a spark ignited (SI) combustion engine with retarded ignition timing and secondary air injection into the exhaust port is reported. Based on this analysis, the warm-up simulation of a one-dimensional flow simulation tool is improved for an evaluation of different exhaust system configurations.

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.

The introduction of more stringent exhaust emission standards in Europe and in the USA demands substantially more effective exhaust gas treatment than previous standards have prescribed. In SI engines, the cold-start phase is responsible for contributing by far the largest proportion of total emissions. To start the chemical reaction, catalytic converters require a minimum temperature which, at present, cannot be reached quickly enough by the engine exhaust gas. The use of close-coupled main catalytic converters, accurately matched to the engine, offers the potential necessary to achieve compliance with European emission standards. A description of the design procedure and the installation of the series design is provided here followed by a discussion of the advantages and disadvantages of such systems.