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This paper includes a numerical and experimental study of fluid flow in automotive catalytic converters. The numerical work involves using computational fluid dynamics (CFD) to perform three-dimensional calculations of turbulent flow in an inlet pipe, inlet cone, catalyst substrate (porous medium), outlet cone, and outlet pipe. The experimental work includes using hot-wire anemometry to measure the velocity profile at the outlet of the catalyst substrate, and pressure drop measurements across the system. Very often, the designer may have to resort to offset inlet and outlet cones, or angled inlet pipes due to space limitations. Hence, it is very difficult to achieve a good flow distribution at the inlet cross section of the catalyst substrate. Therefore, it is important to study the effect of the geometry of the catalytic converter on flow uniformity in the substrate.

This paper describes the experience gained during the successful development of a catalytic converter design for an in-line 4 cylinder application to meet the India 1998 cold start emissions standards. The vehicle application considered was an open loop carburetted system that met the 1997 hot start emission standards using a conventional Pt/Rh underbody mounted catalyst. The challenge was to meet the 1998 standards through catalyst changes and/or minor carburettor adjustments, thus providing the customer with the most cost-effective solution. The approach adopted was to use a mathematical computer simulation (MAESTRO™) developed by Delphi, that utilized engine out data obtained from emission testing of the vehicle to simulate proposed solutions. The biggest advantage of this approach was the ability to estimate the impact of system level changes on emissions performance thus enabling a quick optimization of the design variables.