The monolithic catalytic converter still is the main pollution control device for modern vehicles in order to reach the ever-increasing legislative demands for low emission standards. The catalytic converters require a large expansion from the exhaust pipe to the front face of the monolith. Unfortunately, packaging constraints often do not permit the use of long diffusers. Hence, flow separation within the diffuser leads to a non-uniform flow distribution across the monolith. A uniform flow distribution at the inlet monolith face is favorable for the conversion efficiency as well as the durability of the catalytic converter. Therefore the main problem is to optimize the flow distribution at the catalytic converter. It should be noted that due to flow maldistribution in an enlarged inlet of catalytic converter, some part of the monolith would be non effective. In this research a new design for inlet diffuser of catalytic converter has been proposed and fabricated. The new inlet diffuser is composed of some tube to tube cones that distribute the flow uniformly at the entrance face of monolith. Temperature, pressure drop and concentration of pollutants, before and after catalyst, have been measured. The results show that the new design for inlet diffuser tends in less uniform temperature field at the entrance of monolith but the flow distribution becomes more uniform and an increased conversion efficiency of catalyst will be obtained.

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