Numerical Optimization of Flow Uniformity inside an F-Oval Substrate

F-oval substrates have been widely used in automotive applications for Close Coupled Converters (CCC) of SI engines and pre-Diesel Oxidation Catalysts (DOC) of CI engines under tight packaging constraints where there is no space for other substrates with the same volume such as H-oval, a Y-oval or round substrates. Although flow uniformity in the front of a substrate is extremely important, it is very challenging to obtain excellent flow uniformity with an F-oval substrate. Current study is focused on how to optimize inlet cone design to achieve optimal flow uniformity by using 3-D Computational Fluid Dynamics (CFD) tools. First, exhaust mass flow rate and inlet cone length are investigated to understand their effects on flow uniformity and pressure loss. Then, based on a relatively short straight cone, angle cones are built. Angle cones are constructed by either rotating the flow inlet plane along the substrate's shorter or longer axis, or shifting the flow inlet plane along the longer axis. No significant improvement of flow uniformity index is found by rotation along the shorter axis. However, large improvement is observed when the flow inlet plane is shifted along the longer axis direction by 10, 20 and 30 mm away from the geometrical center. When the flow inlet plane is rotated again based on 30 mm shifted geometry, significant improvement is found at a rotation angle of 20 degrees. The optimal flow uniformity is achieved when the second shift is performed based on the second rotation. Current study shows that, for a F-oval substrate, high flow uniformity index can be achieved when the inlet cone is angled by rotating the flow inlet plane along the longer axis of substrate.