Search Results

Within the next decade, all light-duty vehicles in the United States will be required to meet Tier 2 or LEV 2 tailpipe emission standards. As emission standards have tightened over time catalyst systems have increased in cost. The factors that have contributed to the growth in cost include increases in both precious metal content and catalyst volumes. Calibration strategy, catalyst, and substrate technology improvements have also enabled previous emission standards to be met. The recent dramatic fluctuations in precious metal price, coupled with the increasing desire to reduce system cost, have led catalyst companies to develop converter technologies containing decreasing amounts of precious metal, and still meet Tier2/LEV2 standards. In this paper the development of a novel, near base metal, catalyst technology is described. The effects of precious metal support type and catalyst preparation method are reported using model engine bench and vehicle tests.

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.

The control of emissions from mobile sources continues to play an important part in air quality improvement. Future reductions in vehicle emissions are proposed or legislated in many countries throughout the world. The most stringent of these standards under discussion are those in the Californian LEV-II proposal, a part of which is the SULEV standard which requires a large reduction in hydrocarbon emissions, together with a significant decrease in NOx, over those legislated for ULEV. This requires the engine and aftertreatment system to deliver both a substantial reduction in the emissions of hydrocarbon during engine warm-up and increased NOx conversion during high speed operation, compared to previous ULEV systems. In this paper we outline three different catalyst systems which show the potential to provide reduction in vehicle emissions below the currently legislated ULEV and European Stage IV standards.

A computer model is successfully used to predict emissions from a vehicle, fitted with a catalyst, over a standard driving cycle (the U.S. FTP cycle). Kinetic expressions to describe the catalyst's activity are derived from laboratory measurements. A study showing the effect of changing the precious metal loading of the catalyst on the activity of the catalyst is presented. The impact on model parameters is derived and the model is successfully used to predict the effect of changing precious metal loading on vehicle performance over the FTP cycle. The results indicate the model can be a useful tool in exhaust system design.