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The development of technology suitable for meeting the CARB Ultra-low- emission-vehicle (ULEV) legislation has now become a main focus for vehicle manufacturers worldwide. This proliferation of interest is mainly a result of the increasing number of eastern US-states currently considering the adoption of CARB legislation and the indication that emission legislation in Europe and Japan for the turn of the century is likely to be of the same severity as CARB ULEV legislation. Current three way catalyst (TWC) emissions control technology suffers from low catalytic conversion efficiency of HC, CO and NOx pollutants during cold operation i.e. before catalyst light off. Cold start emissions generally contribute up to 70% of HC and CO tailpipe emissions during an FTP test. However, in some cases even early light-off of the catalyst, similar to hot operation is not sufficient to achieve catalytic conversion over a test cycle to reach ULEV emissions levels.

This paper describes the use of advanced three-way catalysts to meet future European and California low emissions legislation. Firstly, it describes the performance of these catalysts tested using the European Stage II test cycle and contrasts their emissions performance over the proposed European Stage III test. The future legislation requires fast catalyst light-off for the low emissions standards to be achieved, therefore the performance of close-coupled catalysts was investigated. The close-coupled catalyst systems gave very low emissions. Space constraints often preclude the use of large volume close-coupled catalysts, and the combination of a small starter catalyst with an underfloor catalyst was tested. This gave performance levels better than the close-coupled configuration. The effect of reducing the underfloor catalyst volume is also described. The work was carried out on a 1.2 litre European Vehicle, the conclusions were verified on a 1.6 litre European vehicle.

This paper discusses the development of a new approach to achieving EURO 4 emission standards with a simplified exhaust after-treatment system in combination with an air-assisted lean stratified Direct Injection system. The results presented demonstrate the ability of the air-assist DI system to operate in highly stratified conditions at very lean A/F ratios, with excellent control of the raw HC and NOx emissions. In most cases the authors illustrate that with good stratified combustion control, the HC emissions can be lower than the baseline port injected stoichiometric engine. Further, the high tolerance to EGR and accurate A/F control at the spark plug enable the raw NOx emissions to be reduced by up to 85% over the European drive cycle in comparison to the baseline port injected engine with EGR.

Recently, significantly more demanding emissions standards for the Mercosur region were proposed, and the intention is that these will be introduced in 2004 and 2008. This paper describes the development of new high performance three-way catalyst formulations for conventional gasoline/gasohol fueled engines that enables them to meet these stringent standards without increasing the content of platinum group metals above the levels currently employed. The performance benefits of these advanced platinum and palladium-based catalysts are demonstrated on both engine bench and vehicles.

In order to meet future emission standards for gasoline vehicles, catalyst designers have developed thermally durable three-way catalysts with enhanced activity. The most effective catalysts for achieving the required hydrocarbon conversion were those containing high levels of palladium. This has led to increased levels of palladium being used. Recent palladium price fluctuations have created interest in the possibility of using advanced platinum-based technologies. The performance of a new platinum-rhodium three-way catalyst (TWC) was compared with an advanced palladium-rhodium catalyst on an engine test-bed. The results showed the new platinum-rhodium catalyst gave equivalent, or better, performance at similar total precious metal cost. The performance on selected vehicles confirmed future emissions standards can be achieved with platinum-based catalysts.

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.