Modelling of a Coupled Catalyst and Particulate Filter for Gasoline Direct Injection Engines

There has been extensive research in the development of Gasoline Direct Injection ‘GDI’ engine exhaust systems with the aim of reducing engine-out emissions and meeting legislation requirements. Depending on the room available for packaging the exhaust system, the engine may be equipped with a single catalyst or two catalysts one close to the engine and another one located further downstream. With the strict particulate matter emission regulations of GDI engine, the engine has to be equipped with a Gasoline Particulate Filter ‘GPF’ in addition to the Closed Coupled Catalyst ‘CCC’. The common practice is to have the GPF further downstream the catalyst. In this paper, an assessment method is carried for a new design of a hot end exhaust system. The new design brings the GPF closer to ‘CCC’ to be packed in the same enclosure. The gas flow velocity and pressure distributions inside the exhaust system are identified using CFD for a uniform exhaust gas flow inlet conditions. The system also has been investigated considering a typical inlet exhaust gas flow conditions from a GDI engine turbocharger. Results showed that the new design offers better flow uniformity in both the catalyst and GPF. Moreover, lower pressure drop across the whole system is observed relative to the baseline design with the GPF separated from the catalyst through an intermediate exhaust pipe. The GPF enclosure end shape is found to have influence on the flow uniformity and pressure drop.