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More stringent emission regulations have forced an overall systems approach to meeting standards in the most effective manner. An important part of the emissions after-treatment system is the substrate. In recent years, thin wall high cell density substrates have become available. These substrates reportedly offer lower thermal mass and better heat transfer properties for faster light-off and better mass transfer properties for increased performance under stabilized conditions. This paper examines the behavior of high cell density substrate systems under a series of test conditions. A comparison of 400/6, 600/4, 600/3 and 900/2 was carried out both on a bench engine for stabilized and light-off conversion, and also under the ECE/EUDC test procedure. Bench engine results showed significant benefits for HC, CO and NOx emissions when using the higher cell density thinwall substrates.

With the advent of stricter vehicle emission standards, the improvement of three way catalyst performance and durability remains a pressing issue. A critical consideration in catalyst design is the potential for variations in fuel sulfur levels to have a significant impact on the ability to reach TLEV, LEV, and ULEV emission levels. As a result, a better understanding of the role of PGM composition in the interplay between thermal durability and sulfur tolerance is required. Three way catalysts representative of standard Pd-only, Pd/Rh and Pt/Rh formulations were studied over a variety of aging and evaluation conditions. The parameters investigated included aging temperature, air fuel ratio and sulfur level. Evaluations were performed on a 1994 TLEV vehicle using different sulfur level fuels. The effect of PGM loading was also included within the study.