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By characterizing current three-way catalysts (TWCs) after thermal aging, it was possible to use the information obtained to develop a new generation of more thermally durable TWCs. To assess their performance, a dynamic dynamometer was used to age these new TWC formulations (Pt/Rh and Pd/Rh) at a series of different maximum catalyst operating temperature limits (960, 1010 and 1050°C) using a proprietary transient aging cycle. Each catalyst was evaluated periodically throughout the aging on a dynamic dynamometer to assess its emission performance and aging characteristics. After a representative aging time, both the Pt/Rh and the Pd/Rh formulations were capable of meeting European Stage IV emission standards on a production powertrain after prolonged 1050°C aging. The thermal resistance of the new Pt/Rh and Pd/Rh TWCs is significantly better than that of previous technologies.

The emission capability of an exhaust system tuned for improved engine performance from an in-line four-cylinder engine has been investigated. The exhaust system comprises two close-coupled catalysts; each located in separate exhaust streams and has been termed the 4-2 close-coupled catalysts (CCC) -1 system. It has been shown that, given equivalent total catalyst volume, this system configuration results in compromised high exhaust flow rate emissions performance compared with a single catalyst (4-1semi-CCC) system. This emissions performance deficit has been attributed to the effect of engine frequency flow pulsations, which result in relatively high peak space velocities in the 4-2CCC-1 system despite the mean space velocity being consistent. Engine-based AFR Bias Sweep tests suggest that hydrocarbon emissions are most strongly affected by this phenomenon. At lower exhaust flow rates, the difference in performance between the two systems is negligible.