Oct 5 2004
Siemens plans to significantly reduce pollutant emissions produced by trucks. In addition to an improved fuel-injection technology and increased use of sensors for monitoring combustion in the engine, the company is turning to new catalytic converter types with integrated filters to realize this goal. At the International Commercial Vehicle Show (IAA) in Hanover, Emitec introduced a soot filter that can remove up to 80 percent of the super-fine particles from exhaust gas. Emitec, a joint venture of the automotive electronics specialist Siemens VDO and the British automotive and aerospace supplier GKN, is one of the world’s largest manufacturers of metallic substrates for catalytic converters.
The new Euro exhaust emission standard will be effective from October 2005, before becoming even more stringent from 2008. To satisfy the new limits, the developers have to combine several technologies in one exhaust system, though in part they have effects that are in direct opposition to one another. A particularly sharp reduction of nitrogen oxides in the engine, for example, results in an increased volume of particles in the exhaust. Another problem is that the filter slowly but surely becomes clogged. And as the mileage that a truck is driven increases, this leads to higher fuel consumption and additional maintenance costs.
The catalytic converter from Emitec, which the company tested and optimized with the manufacturer MAN, provides an elegant solution to both problems. It is a system that combines an oxidation catalyst and a sophisticated particle filter. In an initial stage, the platinum oxidation catalyst converts unburned hydrocarbons and carbon monoxide into carbon dioxide. At the same time, it oxidizes nitrogen oxide into nitrogen dioxide, which plays a decisive role in removing the soot particles during the second stage. The soot particles are then removed from the exhaust gas by means of specially shaped micro-channels and directed to a metallic fleece. The particles collect in the fleece’s pores. Here, beginning at about 200° Celsius, they are continuously burned off with the oxygen from the nitrogen dioxide, which is converted into nitrogen.
On average, the new filter catalyst removes about 80 percent of the super-fine particles that have diameters of from 20 to 100 nanometers (one-millionth of a millimeter). Under optimal conditions, it can even remove as much as 95 percent. Thanks to its open design, the system also can’t become clogged, even when it is in service for hundreds of thousands of kilometers. MAN is already working on engine systems in which the new filter has been integrated. In principle, the technology is also suitable for use in passenger cars.
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