FLOW DISTRIBUTION AND PRESSURE-DROP IN DIFFUSER-MONOLITH FLOWS

Most current automotive catalytic converters use diffusers to distribu te the pow field inside the monolithic bricks where catalysis takes pl ace. While the characteristics and performance of a simple diffuser fl ow are well documented the influence of downstream brick resistance is not clear In this paper, the trade-off between flow uniformity and pr essure drop of an axisymmetric automotive catalytic converters is stud ied numerically and experimentally for selected cases. The monolithic brick resistance is formulated from the pressure gradient of fully dev eloped laminar duct-flow and corrected for the entrance effect. The mo nolithic brick downstream stabilizes the diffuser flows both physicall y and computationally. A distribution index was formulated to quantify the degree of nonuniformity in selected test cases. The test matrix c overs a range of different diffuser angles and flow resistance (brick types). For simplicity, an axisymmetric geometry is chosen. Flow distr ibution within the monolith was found to depend strongly on diffuser p erformance, which is modified strongly by brick resistance. Pressure d rop due to the headers and brick resistance and their relative roles i s also identified The implications of these data for converter design are discussed in terms of the trade-off between pow-uniformity and pre ssure drop.