非均勻擔體的觸媒轉換器設計

IMPROVEMENT OF CATALYTIC CONVERTER PERFORMANCE BY USING NON-UNIFORM MONOLITH

本文提出非均勻阻力的擔體設計（擔體內各流道之寬度或長度不一）以改善觸媒轉換器內流場之不均勻度及壓力損失。本研究採用數值模擬的方法來探討，結果顯示非均勻擔體的設計比現有的均勻擔體將有較多的流體誘導往擔體外圍流動使得擴張壁面上迴流區域減少。所以觸媒轉換器內流場不均勻度有大幅度之改善、而總壓力損失亦有減少（以往設計無法使流場不均勻度與壓力損失同時減少），而能發揮觸媒轉換器更佳之性能，以達到充分淨化車輛排氣污染之效果。本研究針對相關之參數如雷諾數及擔體之突出厚度、位置、密度差異等亦做了一系列的探討，使觸媒轉換器之設計最佳化。

The effect of the non-uniform monolith cell resistance on the flow field and pressure drop in the catalytic converter were studied numerically. The monolith with non-uniform brick resistance resulting from either non-uniform cell length or non-uniform cell size was employed. Under steady state, axisymmetric, and incompressible flow assumptions employing the standard κ-ε turbulence model, the governing equations were discretized by the finite volume and QUICK difference schemes, while the SIMPLE algorithm was used on the non-staggered grid system. In general, flow mal-distribution and pressure loss inside the catalytic converter were improved since more flow would be guided to enter the outer region and the size of the sepration bubble around the diffuser wall would be reduced. Some related parameters including the Reynolds numbers, the protrusive thickness, the monolith position, and the cell density difference between the center and the wall were studied to optimize the design of the catalytic converter.