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Evaporative emissions from automotive fuel systems have been recognized as one contributor to photochemical smog and ozone pollution, and so are subject to increasingly stringent regulation. An attractive strategy is to limit the amount of fuel vapor generated in the fuel system, thus easing the burden on the vehicle systems needed to store and eliminate vapor. High fuel tank temperature is a major contributor to vapor generation. Many efforts to reduce the temperature inside a fuel tank have been attempted such as mechanical or electrical returnless fuel systems. Even though these systems reduce vapor generation by about 80% compared to conventional return systems, further improvements may be possible. One way to identify possible improvements is to separately examine the vapor generation of fuel system components, such as fuel pumps, pressure regulators, and jet pumps. Most of these components have an orifice or a narrow flow path which generates low pressure.

The automotive industry and emission system suppliers invest considerable efforts for the improvement of the conversion efficiency of a catalytic converter, in order to lower vehicle emission. One of the methods to improve the catalyst conversion efficiency is to use a higher cell density brick with a thinner wall to increase its geometric surface area. However, there is a significant drawback for the system - higher pressure loss along the brick. Moreover, the mechanical strength and thermal degradation of the brick become major concerns. In this paper, the concept of a brick with radially variable cell density is introduced to possibly resolve several issues. A CFD study was conducted to verify benefits in both flow efficiency and pressure loss along the brick with several different flow rates.