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Results from an experimental study of flow distribution in a close-coupled catalytic converter (CCC) are presented. The experiments were carried out with a flow measurement system specially designed for this study under steady and transient flow conditions. Flow distribution at the exit of the first monolith was measured by a pitot tube. Numerical analysis was also performed for comparison. Experimental results showed that the flow uniformity index decreases as Reynolds number for the flow increases. For steady flow conditions, the flow through each exhaust pipe concentrates on a specific region of the monolith. The transient test results showed that the flow through each exhaust pipe, in the engine firing order, interacts with each other to make the flow distribution uniform. The numerical analysis results supported the experimental results, and helped explain the flow distribution in the CCC.

Studies of driving cycles for buses have been published in a number of papers, e.g., the Central Business District (CBD) and New York Bus (NY Bus) driving cycles. Such studies, however, cannot represent the actual driving environment of Seoul because of differences in road conditions and the volume of traffic. Thus, this study presents the development of a driving cycle for the city bus system of Seoul, the capital city of Korea. A representative route is selected by means of a statistical analysis of the city bus routes in Seoul. Experiments are performed to measure velocity, road grade, engine speed, load conditions, gear-shift patterns, and vehicle acceleration in actual Seoul traffic. A simulation model is developed to evaluate a driving cycle on the basis of the measured data obtained. The coupling effect between velocity and acceleration is analyzed, as well as the coupling effect between road grade and vehicle acceleration.