Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2000-08-14
2002-09-10
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S293000, C060S297000, C060S300000, C060S303000, C422S169000, C422S170000
Reexamination Certificate
active
06446431
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a configuration for converting at least one exhaust emission component of an exhaust emission flow from an internal combustion engine and to a method for the operation of such a configuration.
Various concepts have been developed in order to reduce the environmental pollution from exhaust emissions of internal combustion engines, especially from internal combustion engines used in motor vehicles. These concepts are also aimed at meeting ever lower limits for pollutant emissions.
A problem in the conversion of at least one exhaust emission component of an exhaust emission flow is the period in which the elements of the exhaust emission control system have not yet reached their operating temperature. This is essentially the case during the so-called cold-start phase of the internal combustion engine. During the cold-start phase in internal combustion engines the exhaust emission contains increased quantities of hydrocarbons, since an internal combustion engine usually runs with an excess supply of fuel in the cold-start phase. In addition to unburned hydrocarbons the exhaust emission also contains carbon monoxide. The object during the cold-start phase is to ensure oxidation of the unburned hydrocarbons and the carbon monoxide.
Following the transition from the cold-start phase to a load range of the internal combustion engine the exhaust emissions are both oxidized and reduced, as is the case, for example, with the nitrogen oxides (No
x
).
The use of a catalytically active device for the load range, generally referred to as a three-way catalytic converter, is already known. Although the three-way catalytic converter functions excellently in the load range of the internal combustion engine, it cannot convert the unburned hydrocarbons and the carbon monoxide occurring during the cold-start phase sufficiently, so that increased emissions of hydrocarbons and carbon monoxide occur during the cold-start phase. Published, European Patent Application EP 0 485 179 A, for example, discloses an exhaust emission control system containing numerous elements, which might include, for example, a three-way catalytic converter, a hydrocarbon adsorber and a heatable honeycomb element. The configuration of individual elements may vary.
International Patent Disclosure WO 94/17290 further discloses an electrically heated catalytic converter, which at least in some partial areas has a catalytically active coating. The converter, viewed in the direction of flow, has successive electrically heatable areas. The International Patent Disclosure WO 94/17290 is based on the assumption that significant catalytic conversion of the exhaust emission only takes place at temperatures in the order of 300 to 450° C.
Both Published, Non-Prosecuted German Patent Application DE 23 33 092 A1 and U.S. Pat. No. 5,417,062 further disclose the configuration of an electrically heatable honeycomb element between two catalytically active honeycomb elements, the intention being to achieve more rapid heating of the catalytically active elements.
Proceeding from this state of the art, the object of the present invention is to specify a configuration for converting at least one exhaust emission component of an exhaust emission flow from an internal combustion engine, by which a reduction in the level of pollutant components, especially of hydrocarbons, is achieved during a cold-start phase. A further object of the invention is to specify a method for the operation of the configuration, by which the configuration achieves a high efficiency.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a configuration for converting at least one exhaust emission component of an exhaust emission flow from an internal combustion engine and a method of operating the configuration that overcome the disadvantages of the prior art devices and methods of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a configuration for converting at least one exhaust emission component of an exhaust emission from an internal combustion engine. The configuration contains a catalytically active first device and a second device disposed downstream of the first device in a direction of a flow of the exhaust emission. The second device includes at least one electrically heatable first honeycomb element, a second honeycomb element having at least one coating being hydrocarbon-adsorbent and disposed downstream of the first honeycomb element, and a electrically heatable third honeycomb element disposed downstream of the second honeycomb element in the direction of the flow of the exhaust emission. A pipe section connecting the first device to the second device is provided, and at least one secondary air line opens into the pipe section.
The first catalytically active device is, for example, a three-way catalytic converter, which forms a so-called main catalytic converter. The main catalytic converter or the first catalytically active device essentially serves for the catalytic conversion of the exhaust emission component of the exhaust emission from the internal combustion engine when the internal combustion engine is in the load range. During the cold-start phase the first catalytically active device makes only a very small, if any, contribution to the conversion of the exhaust emission component of the exhaust emission flow, since the first device has not yet reached the temperature necessary for the catalytic conversion of the exhaust emission component.
The second device, which follows the first device, has at least one electrically heatable first honeycomb element, a second honeycomb element, which has at least one coating that is at least partially at least hydrocarbon-adsorbent, and a third, electrically heatable honeycomb element disposed successively in the direction of flow of the exhaust emission.
By this configuration of the honeycomb elements with their differing functions a reduction in the emission of pollutants, especially of hydrocarbons, is achieved during the cold-start phase.
Owing to the fact that the second honeycomb element has a hydrocarbon-adsorbent coating, the hydrocarbons contained in the exhaust emission are at least partially adsorbed, thereby reducing the emission of hydrocarbons. Disposing a third, electrically heatable honeycomb element downstream of the hydrocarbon-adsorbent honeycomb element ensures that the hydrocarbons not adsorbed by the second honeycomb element and/or the already desorbed hydrocarbons are completely burned. This complete combustion is achieved, in particular, if on the third honeycomb element only the desorbed hydrocarbons pass to the third honeycomb element. This is the case, since the desorption of hydrocarbons is a relatively slow process and the third, electrically heatable honeycomb element reaches its operating temperature very rapidly.
Because a first, electrically heatable honeycomb element is disposed upstream of the second honeycomb element having the hydrocarbon-adsorbent coating, this ensures that the second honeycomb element is heated up relatively quickly. Given a very rapid temperature increase in the second honeycomb element, the hydrocarbon resorption rate is then the defining variable for the catalytic conversion of the unburned hydrocarbons, since desorption is a slower process than the catalytic conversion of the hydrocarbons.
In order to achieve the lowest possible emission of hydrocarbons during the cold-start phase it is also proposed that the first honeycomb element have a coating that adsorbs hydrocarbons. Greater hydrocarbon adsorption is thereby achieved.
According to a further advantageous development of the configuration it is proposed that the first honeycomb element have a catalytically active coating that promotes oxidation. In view of the fact that the first honeycomb element is electrically heatable and the operating temperature is attained relatively quickly, a reduction of carbon monoxide is also achi
Denion Thomas
Emitec Gesellschaft für Emissionstechnologie mbH
Greenberg Laurence A.
Locher Ralph E.
Stemer Werner H.
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