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CATALYST TECHNOLOGY |
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| Fast light off catalysts allow the catalytic converter to work sooner by decreasing the exhaust temperature required for operation. Untreated exhaust emitted at the start of the legislated emissions test and on short journeys in the real world is curtailed. Changes to the thermal capacity of substrates and type and composition of the active precious metal catalyst have together affected big improvements. |
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| Thermally durable catalysts |
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| More thermally durable catalysts with increased stability at high temperature allow the catalytic converter to be mounted closer to the engine and increase the life of the catalyst, particularly during demanding driving. Precious metal catalysts with stabilised crystallites and washcoat materials that maintain high surface area at temperatures around 1000°C are needed. Improved oxygen storage components stabilise the surface area of the washcoat, maximise the air:fuel 'window' for three-way operation and indicate the 'health' of the catalyst for On Board Diagnostic (OBD) systems. |
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| Technology development of the substrates |
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| Technology of the substrates on which the active catalyst is supported has seen great progress. In 1974, ceramic substrates had a density of 200 cells per square inch of cross section (31 cells/square cm) and a wall thickness of 0.012 inch or 12 mil (0.305 mm). By the end of the 1970s, the cell density had increased from 300 to 400 cpsi and wall thickness had been reduced by 50% to 6 mil. Now 400, 600 and 900 cpsi substrates are available and wall thickness can be reduced to 2 mil - almost 0.05 mm. In the late 1970s, substrates derived from ultra-thin foils of corrosion-resistant steels came on to the market. In the beginning, the foils could be made from material only 0.05 mm thick allowing high cell densities to be achieved. Complex internal structures can now be developed; 800 and 1000 cpsi substrates are available and wall thickness is down to 0.025 mm. This progress in ceramic and metal substrate technology has major benefits. A larger catalyst surface area can be incorporated into a given converter volume and this allows better conversion efficiency and durability. The thin walls reduce thermal capacity and avoid the penalty of increased pressure losses. Alternatively, the same performance can be incorporated into a smaller converter volume, making the catalyst easier to fit close to the engine as cars are made more compact. |
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| Optimised systems incorporating these new technologies are in production. The use of additional catalytic converters close to the exhaust manifold reduces the time to light off in the cold start and, therefore, the total emissions. Light off times have been reduced from as long as one to two minutes to less than 20 seconds. Improved substrate technology, combined with highly thermally stable catalysts and oxygen storage components, allows the close-coupled catalyst approach to meet the European Union 2000 and 2005 standards as well as the California Low Emission Vehicle (LEV), Ultra Low Emission Vehicle (ULEV) and Super Ultra Low Emission Vehicle (SULEV) regulations. |
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| Diesel emissions are an important topic for European catalyst development. Sales growth of diesel cars has raised concern on the possible health effects from the ultra-fine particulates in diesel emissions. All diesel-engined cars sold in Europe are now fitted with oxidation catalysts. Some, but not many, heavy-duty vehicles also use oxidation catalysts. Oxidation catalysts lower particulate mass by up to 50%, by destruction of the organic fraction of the particulate, as well as making significant reductions in CO, HC and the characteristic diesel odour. However, the number of particles is unchanged and issues associated with the effects of ultra-fine particulates remain unresolved. |
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| Maintenance and durability |
| Maintenance and durability of emissions performance is crucial for maximum environmental benefit from the application of advanced emissions control technology. The technology used should be durable for the defined, reasonable life of the vehicle and the vehicle should be checked regularly to ensure that the installed systems are working properly and that they have not been abused or inadequately maintained. From 2000, Europe adopts OBD systems to monitor operation of the engine management and emissions control components, including the conversion efficiency of the catalytic converter. The performance and durability of the catalytic converter are very dependent on the engine and fuel management systems of which the converter is a key part. |
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