Patent Application
20050056977
The present invention relates to an apparatus for the removal of soot or carbon particles from exhaust gas of an internal combustion engine in a module by oxidation of the carbon particles, which are temporarily trapped in a catalytic converter unit, with nitrogen dioxide (NO2), whereby the nitrogen dioxide results from oxidation of the nitric oxide (NO) present in the exhaust gas at a catalytic converter as a function of the flow velocity of the exhaust gas at a temperature above about 200° C.
To reduce the carbon particle emission, measures taken only at the engine for maintaining the emission thresholds that continuously become more strict throughout the world, for example EURO IV/EURO V or ULEV/SULEV, for fuel-driven internal combustion engines can be achieved only at an expense that is not economically feasible. Thus, today, as well as in the future, so-called exhaust gas post treatment units are used.
In principle, a distinction is made between two methods for exhaust gas post treatment, which on the one hand concentrate on the mentioned, such as SCR catalytic converter systems and NOx storage catalytic converters, and on the other hand upon the minimization of the carbon particle emission.
By the use of suitable exhaust gas post treatment units for motor vehicles in combination with measures taken at the engine it is accordingly possible to maintain the strict requirements with regard to carbon particle emission and NOx emissions.
Thus, for example with classical filter units, e.g. ceramic wall-flow-filters, it is today possible to already achieve separation rates of >95% with regard to the carbon particles that are here of interest. However, due to the collection of carbon particles and ashes from the motor oil additives, with such units an undesired increase of the engine counter pressure occurs over time, which in turn leads to an increased consumption of fuel. For this reason, such filter units must be completely disassembled and cleaned at regular time intervals.
Further developed variations of such filter units take into account the aforementioned drawbacks of the filter units being used to the extent that such units are provided with a catalytic coating on the surface of the filter. By means of such a coating as an active component, the combustion temperature of the carbon particles is significantly reduced.
The reduction of the combustion temperature of the carbon particles is significant in that the exhaust gases that are discharged from newly developed combustion engines are continuously less hot. With filter units having no catalytic coating of the filter surface, the combustion temperature of the carbon particles is approximately 580 to 600° C. It should be noted that even with the variations of such filter units, there still remains a particular difficulty of removing the filtered ashes.
A further approach to the removal of the carbon accumulated in the filter is represented by thermally induced regeneration. In this connection, the filter unit is brought to the temperature necessary for the oxidation of the carbon particles by, for example, a burner or electrically. Such a method, of course, adds to the cost of the overall energy balance of the internal combustion engine.
Another possibility for the continuous removal of the filtered carbon particles is to remove the particles from the filter substrate by introducing an additive that reduces the combustion temperature of the carbon particles. However, such an approach also does not provide a particularly suitable solution because the additives that are supplied themselves contribute to the formation of ash.
Other approaches are again concerned with the oxidation of the filtered carbon particles with NO2.
EP 341832 B1 discloses a method for the exhaust gas post treatment of heavy trucks. With this method, the exhaust gas is first conveyed over a catalytic converter without filter effect in order to oxidize the nitric oxide contained in the exhaust gas to nitrogen dioxide. The exhaust gas containing nitrogen dioxide is then used to burn the carbon particles collected in a filter that is disposed downstream. In this connection, the quantity of nitrogen oxide is adequate to enable the combustion of the filtered carbon particles at below 400° C.
A method for the exhaust gas post treatment in delivery trucks and passenger vehicles is furthermore disclosed in EP 835 684 A2. In conformity with the described method, the exhaust gas is conveyed over two successively disposed catalytic converters. At the first catalytic converter, the nitric oxide contained in the exhaust gas is oxidized to nitrogen dioxide. At the second downstream catalytic converter, which acts as a filter, the collected carbon particles are then deposited and at a temperature of about 250° C. are partially oxidized to carbon dioxide CO2 in conformity with equation (1), and the nitrogen dioxide NO2 is reduced to nitrogen:
2NO2+2C→2CO2+N2 (1)
Accordingly, with the known method the filtered carbon particles are burned, i.e. oxidized, without the use of a burner or an electrical heating element. In this connection, the first catalytic converter that is used comprises a honeycomb flow-through monolith that is coated with an oxidation catalyst.
DE 3407172 C2 discloses an apparatus for the exhaust gas post treatment of diesel engines, and in a housing contains a series of filter elements having varying spacing from one another. In this connection, at least one filter element A has a coating that reduces the combustion temperature of soot or carbon. Furthermore, at least one filter element B is provided that contains a catalytic converter that enhances the combustion of harmful or noxious gaseous substances.
WO 99/09307 discloses a method for the reduction of the carbon emission from heavy trucks. With the method described, the exhaust gas, for the oxidation of nitric oxide to nitrogen dioxide, is conveyed over a catalytic converter and subsequently, as is customary, is conveyed for the oxidation of the carbon accumulated in a carbon filter. What is new with this method is that a portion of the cleaned exhaust gas is subsequently conveyed over a cooler and is mixed with the intake air of the diesel engine.
The known methods for the exhaust gas post treatment of exhaust gases produced by internal combustion engines additionally have the drawback that respective filter apparatus are utilized that despite all further auxiliary measures that are provided run the risk of eventually becoming clogged or stopped up.
It is therefore an object of the present invention to provide an apparatus, which is operated as a constantly open system, for the exhaust gas post treatment of exhaust gas produced by an internal combustion engine, which apparatus, as a unit that is itself “on-board” regenerating, is constantly open and operates essentially without the otherwise conventional filter apparatus and hence prevents a clogging of the exhaust gas post treatment unit, and simultaneously achieves an effective post treatment of the generated exhaust gas, especially with regard to the removal of the carbon particles from the exhaust gas that is to be treated and that is produced by the internal combustion engine.
This object, and other objects and advantages of the present invention, will appear more clearly from the following specification in conjunction with the accompanying schematic drawings, in which:
The apparatus of the present application for removing carbon particles from exhaust gas of an internal combustion engine comprises a module through which the exhaust gas flows, wherein the module is an open, self-regenerating module in which are disposed open-pored metallic expanded material components, including at least two first noble-metal-coated metallic expanded material components that increase nitrogen dioxide concentration in the exhaust gas for the oxidation of the carbon particles, wherein the first noble-metal-coated, open-pored metallic expanded material components are disposed by themselves in the module, or in an alternating arrangement with uncoated and/or coated second metallic expanded material components, and wherein the noble-metal-coated metallic expanded material components are configured such that nitric oxide that results thereon during the oxidation of the carbon particles again reacts to form nitrogen dioxide and is thus reused multiple times.
It has been shown to be particularly advantageous if the carbon particles that are present in the exhaust gases produced in the internal combustion engine are initially temporarily trapped with the aid of an open-pored, metallic expanded material component that is based on a FeCr alloy. The carbon particles are then oxidized, i.e. burned, via the so-called gas catalysis, in conformity with the equations (2) and (3), with the nitrogen dioxide NO2 that is intensely produced on the noble-metal-coated metallic expanded material component by recirculation of nitric oxide:
NO2+C→CO+NO (2)
2CO+O2→2CO2 (3)
The nitric oxide NO resulting pursuant to equation (2) reacts at the noble-metal-coated metallic expanded material component to again form nitrogen dioxide NO2, so that one can, to a certain extent, speak of a multiple use of the nitric oxide due to recirculation, which brings about a lasting increase of the nitrogen dioxide NO2 that is required for the reduction of carbon particles, and is produced on the noble-metal-coated metallic expanded material component.
The metallic expanded material component is characterized by high thermal resistance to oxidation, high resistance to temperature changes, high resistance to corrosion, especially relative to diluted sulfuric acid, and mechanical strength.
In this connection, the metallic expanded material component is coated at least with a noble metal of the group Ru, Rh, Pd, Os, Ir, Pt, or a mixture of these noble metals.
Furthermore, the metallic expanded material component is advantageously coated with a compound that reduces the combustion temperature of the carbon particles, whereby cerium orthovanadate (CeVO4) is preferably used.
It has been shown that in a particularly advantageous manner the coated metallic expanded material components are also not inhibited by the ashes of the motor oil additives, since such ashes can pass the metallic expanded material components and can be discharged, so that the preferred apparatus, as a self-regenerating module, remains constantly open.
The metallic expanded material component that is inventively used, and the geometry of which can be nearly freely selected, can be produced by two different processes. One process is based upon the impregnation of a PU foam precursor with a so-called slurry that contains spherical metallic particles having an exactly defined particle size distribution, and a subsequent sintering process. The other process is a conventional high quality casting process.
A particular advantage of the open-pored, metallic expanded material component that is used, in contrast to wall-flow-filters, is in particular in the random cell geometry, which within very short stretches enables a 3D intimate mixing, i.e. a turbulent intimate mixing, of the exhaust gas. This increases the degree of effectiveness of the catalytic converter, and prevents clogging.
The metallic expanded material component is preferably formed with a relative density in the range of from 2 to 20%, whereby the metallic expanded material component is electrically conductive.
Furthermore, the metallic expanded material component is preferably provided with a certain number of pores that is in a range of from 3 to 80 pores per inch (pores per (linear) inch), abbreviated (ppi).
The noble metal coating on the metallic expanded material component is preferably applied directly or by impregnation of a wash-coat with a noble metal from the group Ru, Rh, Pd, Os, Ir, Pt, or a mixture of these noble metals, in a concentration of 0.1 to 5.0 g, especially 1.0 to 2.5 g, noble metal per liter metallic expanded material. A catalytic converter embodied in this manner is an oxidation catalytic converter that as a function of the flow velocity of course also oxidizes hydrocarbons (HC), including the heavy hydrocarbons (HOF), starting at about 200° C., and carbon monoxide (CO), starting at about 150° C.
Furthermore, preferably provided with the apparatus are metallic expanded material components having a Ce(III)VO4 (cerium orthovanidate) coating, a catalytically active compound that reduces the combustion temperature of the carbon particles, a so-called oxygen storing compound. Such a catalytic converter, with direct contact, reduces the combustion temperature of the carbon particles to about 360° C., so that one refers to a so-called fixed phase catalysis.
The compound cerium orthovanadate that reduces the combustion temperature of the carbon particles is advantageously applied to the metallic expanded material component by means of a plasma process, a wash-coat process, or a sol gel process in a concentration of 0.1 to 25 g, especially 1.0 to 25 g, CeVO4 per liter metallic expanded material.
The arrangement of the coated or uncoated metallic expanded material components in the catalytic converter module is nearly freely selectable. However, the apparatus should preferably comprise at least one metallic expanded material component that is coated with a noble metal. By varying the number of pores and/or the relative density of the metallic expanded material, it is advantageously possible to achieve a continuous regeneration of the exhaust gas that is to be treated over the length of the catalytic converter module.
In this connection, the number of pores of the metallic expanded material is variable in the direction of the exhaust gas stream. However, the number of pores of the metallic expanded material preferably increases in a downstream direction. There is advantageously a spacing of 0 to 50 mm between the individual or all of the metallic expanded material components.
Furthermore, the metallic expanded material component is particularly advantageously introduced into a metallic housing in a positive manner, and in particular preferably by soldering, since, as already mentioned, the metallic expanded material that is used is a metallic compound. Consequently, by using a positive connection, it is possible to dispense with the use of toxicologically extremely hazardous material such as is conventionally used with ceramic filters.
Pursuant to a particular embodiment of the inventive apparatus, the metallic expanded material components can be introduced into the metallic module via a bearing mat.
Furthermore, a module can be built-up in an advantageous manner such that it is composed of a plurality of identical modules or of modules having differing configurations. In this connection, the modules are preferably disposed parallel to the exhaust gas stream, and in particular, depending upon the requirements, of two identical or different modules, of three identical or different modules, etc.
Further specific features of the present invention will be described in detail subsequently.
Referring now to the drawings in detail, illustrated in
Another arrangement of the metallic expanded material components 2,3, i.e. insertion of the uncoated metallic expanded material components 3 respectively upstream ahead of the coated metallic expanded material components 2 in the exhaust gas stream, is possible if required.
The embodiment of
The embodiment of
Another arrangement of the metallic expanded material components 2, 4, i.e. the disposition of the metallic expanded components 4 that are coated with a compound that reduces the combustion temperature of carbon particles, respectively upstream ahead of the metallic expanded material components 2 that are coated with noble metal in the exhaust gas stream, can also be selected depending upon need.
With the thus configured embodiment, the trapped carbon is additionally oxidized by direct contact with the coating that is disposed on the surface and that acts as a catalyst or catalytic converter. In this connection, the applied coating comprises an oxygen storing compound, such as cerium orthovanadate Ce(III)VO4.
Another arrangement of the metallic expanded material components 2,3, i.e. the disposition of the uncoated metallic expanded material components 3 respectively upstream ahead of the coated metallic expanded material components 2 in the exhaust gas stream, can also be selected if required.
Furthermore, it is possible to provide not only two parallel modules 1′ in the module 5, but to also advantageously accommodate, in conformity with requirements, a plurality of modules 1′ in the module 5 to increase the degree of effectiveness.
The parallel arrangement and the number of modules 1′ in the module 5 can be adapted in nearly any desired manner to the respective engine power. In this connection, the required degree of effectiveness with regard to the removal of carbon particles from the exhaust gas stream produced by the external combustion engine can advantageously be taken into account, and in particular by the type of the noble metal coating or noble metal charge, the geometrical surface of the metallic expanded material component, and the number of coated metallic expanded material components.
Thus, for example, emission reductions for carbon particles of about 85 to 90% can be achieved without thereby exceeding the permissible nitrogen dioxide threshold values.
Furthermore, the degree of effectiveness for the reduction of the carbon particle emission can be increased still further by means of a thermally induced regeneration, as can be achieved, for example, with a burner or an electrical energy coupling via a resistance heating.
The thermally induced regeneration can also be effected by oxidation of fuel belatedly injected into the internal combustion engine, a so-called secondary injection, by means of which the exhaust gas temperature can initially be raised from about 150 to 200° C. to about 400° C.
In addition, it is possible, by oxidation of hydrocarbons (CH) produced by the engine, at the noble-metal-coated metallic expanded material component or oxidation catalytic converter, to increase the temperature in the module by approximately a further 200° C. ultimately to the temperature, of about 600° C., required for the combustion of carbon particles.
The specification incorporates by reference the disclosure of European priority document 03020688.2 filed Sep. 11, 2003.
The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 03020688.2 | Sep 2003 | EP | regional |
