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One of the methods to reduce the engine exhaust emission is to use CCC. To obtain the maximum conversion efficiency in CCC, the exhaust gas should be uniformly distributed across the frontal area of catalytic substrate and the engine should be operated close to the stoichiometric air/fuel ratio through the use of an oxygen sensor in the exhaust system. A theoretical and computational study of three-dimensional unsteady compressible non-reacting flow in three kinds of exhaust manifold and CCC system was performed to understand the flow characteristics and to estimate the effects of the geometry change. Also, in each case, proper oxygen sensor location where the exhaust gas can be efficiently measured is proposed.

The shape of unit cell of catalytic converter has great influence on the conversion efficiency and pressure drop characteristics. Therefore, the properties of design parameters of catalyst monolith were analyzed and the parameters of various cell shapes of catalyst were compared. Also, the numerical study of a three dimensional compressible flow in a Close-coupled Catalyst Converter (CCC) system was performed to investigate the flow characteristics and the flow distribution of exhaust gases. Unsteady flow analysis shows that severe interferences of each pulsating exhaust gas flow as well as geometric factors (junction, mixing pipe, cell shape etc.) influence greatly on the flow uniformity and flow characteristic in substrate. The results can be applied for the catalytic converter design.