EP1515012A1 - Device for elimination of carbon black particulates from an exhaust gas stream of an internal combustion engine - Google Patents

Abstract

A modular assembly removes soot particles from automotive exhaust gases by oxidation of trapped particles with NO(2). The NO(2) is oxidized by NO exhaust gases in contact with a catalyst in relation to the gas flow speed at a temperature above about 200[deg] C. The module contains one or more layers of open-pored noble metal foam (2).

Description

The invention relates to a device for removing soot particles from an exhaust gas stream of internal combustion engines in a module (1) by oxidation of the temporarily trapped soot particles with nitrogen dioxide (NO ₂ ), wherein the nitrogen dioxide by oxidation of existing in the exhaust nitrogen monoxide (NO) to a catalyst in Depending on the flow rate of the exhaust gas at a temperature above about 200 ° C is formed.

To reduce the soot particle emission could be pure Engine-side measures to comply with the world always stricter emission limits, such as EURO IV / EURO V or ULEV / SULEV, for fuel-powered vehicles Internal combustion engines with only one economically not reasonable effort can be achieved. Therefore today come like Also in the future so-called exhaust aftertreatment systems for Commitment.

Basically, a distinction is made between two methods for exhaust aftertreatment, which focus on the one hand on the minimization of NO _x emissions, which are mentioned here only marginally, such as SCR catalyst systems and NO _x storage catalytic converters, and on the other hand to minimize the soot particle emission.

By using a suitable exhaust aftertreatment system for motor vehicles in combination with engine-side measures, it is therefore possible to comply with the strict regulations regarding soot particle emissions and NO _x emissions.

For example, today with classic filter systems, such as As ceramic wall-flow filters, in terms of here Soot particles of interest already have separation rates of> 95% be achieved. Due to the accumulation of soot particles and of Ashes from the engine oil additives, however, occur in such Investing with time to an undesirable increase in the Motor back pressure, in turn, to an increased Fuel consumption leads. That's why Filter systems at regular intervals to complete dismantle and clean.

Developed variants of such filter systems wear the mentioned disadvantages of the in use Filter systems in so far as, as such systems on the Filter surface have a catalytic coating. By such a coating as an active component is the Increase combustion temperature of the soot particles noticeably.

The reduction of the combustion temperature of the soot particles is in this respect of great importance, as the exhaust gases from new developed internal combustion engines are always ejected are less hot. For filter systems without catalytic Coating the filter surface is the Combustion temperature of soot particles at about 580 ° C to 600 ° C. However, even with the variants of such Filter systems still the particular difficulty of removal of filtered ashes.

Another solution for removing the filter accumulated soot represents the thermally induced Regeneration dar. Here, the filter system, for example with a burner or electrically to the one for oxidation the soot particles required temperature brought. Such Of course, the procedure is at the expense of Total energy balance of the internal combustion engine.

Another way to continuously remove the filtered soot particles consists in passing the particles through Injecting a the combustion temperature of the soot particles Remove degrading additive from the filter substrate. Such an approach is also not very special suitable solution, because the additives supplied to the self Contribute to ash formation.

Other approaches in turn deal with the oxidation of the filtered soot particles with NO ₂ .

From EP 341832 B1 goes a method for the Exhaust gas aftertreatment of heavy trucks. at In the process, the exhaust gas is first passed through a catalyst passed without filter action to the contained in the exhaust gas Nitric oxide to oxidize to nitrogen dioxide. The Nitrogen dioxide-containing exhaust gas is then used to burn the collected in a downstream filter Soot particles used. The amount of nitrogen oxide is sufficient off to under the combustion of the filtered soot particles at 400 ° C to allow.

Furthermore, EP 835684 A2 discloses a method for the exhaust aftertreatment of vans and passenger cars. According to the specified method, the exhaust gas is passed over two catalysts arranged one behind the other. On the first catalyst, the nitrogen monoxide contained in the exhaust gas is oxidized to nitrogen dioxide. At the second downstream catalyst, which acts as a filter, the collected soot particles are then deposited and oxidized at a temperature of about 250 ° C partly according to equation (1) to carbon dioxide CO ₂ and the nitrogen dioxide NO ₂ reduced to nitrogen: 2NO ₂ + 2C → 2CO ₂ + N ₂

Accordingly, in the known method, the filtered Soot particles without the use of a burner or electric heating element burned, i. oxidized. there the first catalyst used consists of a honeycomb flow monolith, with an oxidation catalyst is coated.

From DE 3407172 C2 is a device for Exhaust gas aftertreatment of diesel engines known in a Housing a series of filter elements with different Contains distance from each other. It has at least one Filter element A is the combustion temperature of soot degrading coating on. Next is at least one Filter element B is present, the one of the combustion of harmful gaseous substances supporting catalyst contains.

From WO 99/09307 is a method for the reduction of Soot emission from heavy trucks known. In which specified method, the exhaust gas for the oxidation of Nitric oxide to nitrogen dioxide over a catalyst and then as usual for the oxidation of the in a soot filter passed collected soot. New to the specified procedure is that a portion of the purified exhaust gas thereafter over a Radiator routed and with the intake air of the diesel engine is mixed.

The known methods for the exhaust aftertreatment of combustion engine generated exhaust gases still have the Disadvantage on that each uses filter devices despite all the other relief measures planned the danger of eventually clogging.

The object of the present invention is to be seen in a as a permanently open system operated device for Exhaust gas aftertreatment of combustion engine generated exhaust gas to create that as "on-board" self-regenerating Plant is constantly open and essentially without the otherwise usual filter devices works and thus clogging prevents the exhaust aftertreatment system and simultaneously an effective post-treatment of the evolved exhaust gas achieved, especially with regard to the removal of soot particles from the exhaust-gas engine-generated exhaust gas to be treated.

According to the invention, the object in a generic Device solved by the features of claim 1. Further advantageous embodiments of the invention are in the Subclaims specified.

It has proven to be particularly advantageous that the soot particles present in the combustion engine exhaust gases are initially captured temporarily using a FeCr alloy based open-pore metal foam. The soot particles are then oxidized via the so-called gas catalysis according to equations (2) and (3) with the nitrogen dioxide NO ₂ sustainably produced by recirculation of nitrogen monoxide on the noble metal-coated metal foam, ie burned: NO ₂ + C → CO + NO 2CO + O ₂ → 2CO ₂

The resulting according to the equation (2) nitrogen monoxide NO reacts to the noble metal coated metal foam again to nitrogen dioxide NO ₂ so that it can be said of a multiple use of nitrogen monoxide in a sense by recirculation, a sustained increase required for the reduction of soot particles and on the precious metal coated metal foam produced nitrogen dioxide NO ₂ causes.

The metal foam is characterized by high thermal Oxidation resistance, high thermal shock resistance, high corrosion resistance, especially against dilute sulfuric acid, and mechanical strength.

The metal foam is made of at least a precious metal the group Ru, Rh, Pd, Os, Ir, Pt or a mixture of these Coated precious metals.

Furthermore, the metal foam is advantageously coated with a compound which reduces the combustion temperature of the soot particles, it being preferred to use cerium orthovanadate (CeVO ₄ ).

It has proved to be particularly advantageous that the coated metal foams also not from the ashes from the Motor oil additives are inhibited, since such ashes the Metal foams can happen and be blown out, leaving the preferred device as a self-regenerating module always open.

The inventively used metal foam, whose Geometry is almost freely selectable, can with two different methods are produced. A procedure is based on the impregnation of a PU foam precursor with a so-called slurry containing spherical metal particles contains exactly defined particle size distribution, and a subsequent sintering process. In the other method it is a conventional investment casting process.

A particular advantage of the open-pore used Metal foam in contrast to wall-flow filters consists especially in the disordered cell geometry, within shortest distance a 3D mixing, i. a turbulent mixing, the exhaust gas allows. This will increases the efficiency of the catalyst device and a Clogging prevented.

Preferably, the metal foam is of relative density in the range of 2 to 20%, with the metal foam is electrically conductive.

Furthermore, the metal foam is preferably one with equipped with certain number of pores, which are in one area from 3 to 80 pores per inch (pores per (linear) inch) or in the abbreviation (ppi) is located.

The precious metal coating on the metal foam becomes preferably directly or by impregnation of a washcoat with a precious metal from the group Ru, Rh, Pd, Os, Ir, Pt or a mixture of these precious metals in a concentration from 1.0 g to 2.5 g of precious metal per liter of metal foam applied. In a thus formed catalyst is is an oxidation catalyst that depends on of course, too Hydrocarbons (HC) including the heavy ones Hydrocarbons (SOF) from about 200 ° C and carbon monoxide (CO) from oxidized about 150 ° C.

Furthermore, metal foams with a Ce (III) VO ₄ (cerium orthovanadate) coating are preferably provided in the device, a catalytically active compound which reduces the combustion temperature of the soot particles, a so-called oxygen storage compound. Such a catalyst reduces the combustion temperature of the soot particles to about 360 ° C in direct contact, so that one speaks of a so-called solid-phase catalysis.

In this case, the compound reducing the combustion temperature of the soot particles to the metal foam is advantageously cerium orthovanadate by a plasma process, a washcoat process or a sol-gel process in a concentration of 1.0 g to 25 g CeVO ₄ Applied per liter of metal foam.

The arrangement of the coated or uncoated Metal foams in the catalyst module is almost free selectable. Preferably, however, the device should at least made of a precious metal coated metal foam consist. By varying the number of pores and / or the Relative density of the metal foam succeeds in Advantageously, one over the length of the Catalyst modules continuous regeneration of the too to achieve the treatment of exhaust gas.

The number of pores of the metal foams in the direction of Exhaust flow variable design. The number of pores the However, metal foams preferably increase downstream. Between the individual or all metal foams exists advantageously a distance of 0 to 50 mm.

In addition, the metal foam can be particularly advantageous cohesively introduced into a metallic housing, and preferably by soldering, since it is in the used metal foam, as already mentioned, to a metallic compound is. This can be done when using a material connection to the insert dispensed toxicologically extremely questionable Quellmatten which are standard on ceramic filters, for example be used.

A particular embodiment of the device according to the invention is that the metal foams with a bearing mat in the metallic module are introduced.

Furthermore, a module can be constructed in an advantageous manner be that of several similarly designed modules or variously formed modules composed is. The modules are preferably parallel to the Exhaust gas flow arranged, depending on the requirement for two same or different modules or three same or different modules and the like.

Fig. 1 eine schematische Darstellung in verkleinertem Maßstab eines Ausführungsbeispiels einer Vorrichtung zur Entfernung von verbrennungsmotorisch erzeugten Rußpartikeln nach der Erfindung;

Fig. 2 eine schematische Darstellung in verkleinertem Maßstab eines weiteren Ausführungsbeispiels einer Vorrichtung zur Entfernung von verbrennungsmotorisch erzeugten Rußpartikeln nach der Erfindung;

Fig. 3 eine schematische Darstellung in verkleinertem Maßstab eines anderen Ausführungsbeispiels einer Vorrichtung zur Entfernung von verbrennungsmotorisch erzeugten Rußpartikeln nach der Erfindung;

Fig. 4 eine schematische Darstellung in verkleinertem Maßstab einer Ausführung aus zwei parallel angeordneten Modulen gemäß dem Ausführungsbeispiel nach Fig. 1 einer Vorrichtung zur Entfernung von verbrennungsmotorisch erzeugten Rußpartikeln nach der Erfindung und

Fig. 5 einen Querschnitt in verkleinertem Maßstab entlang dem Schnitt A-B entsprechend der Fig. 4.

Further advantages of the invention are explained below with reference to exemplary embodiments illustrated in the drawing. Show it:

Fig. 1 is a schematic representation on a smaller scale of an embodiment of an apparatus for removing combustion engine generated soot particles according to the invention;

Fig. 2 is a schematic representation on a smaller scale of another embodiment of an apparatus for removing combustion engine generated soot particles according to the invention;

Fig. 3 is a schematic representation on a smaller scale of another embodiment of a device for removing combustion engine generated soot particles according to the invention;

Fig. 4 is a schematic representation on a reduced scale of an embodiment of two parallel modules according to the embodiment of FIG. 1 of a device for removing combustion engine generated soot particles according to the invention and

5 shows a cross section on a reduced scale along the section AB according to FIG. 4.

FIG. 1 shows a module 1 through which exhaust gas flows. in the metal foams 2, 3 alternately one behind the other are arranged. The metal foams are alternating with a noble metal from the group Ru, Rh, Pd, Os, Ir, Pt or a mixture of these precious metals coated or uncoated. Advantageously, the coated Metal foams 2 each upstream upstream of the uncoated Metal foams 3 arranged in exhaust gas flow, respectively Temporarily trap soot particles.

Another arrangement of the metal foams 2, 3, i. the Insertion of the uncoated metal foams 3 respectively upstream of the coated metal foams 2 in Exhaust gas flow is feasible depending on the requirement.

The embodiment of FIG. 2 shows the module 1, at the only coated with precious metal foams. 2 are arranged, which capture even soot particles temporarily ..

The embodiment of FIG. 3 shows the module 1, at the metal foams coated alternately with noble metal 2 and with a combustion temperature of soot particles derating compound coated metal foams 4 are arranged. Advantageously, the respective with noble metal coated metal foams 2 upstream the one with the combustion temperature of soot particles derating compound coated metal foams 4 in Exhaust gas flow attached, each soot particles temporarily catch.

Another arrangement of the metal foams 2, 4, i. the Inserting the one with the combustion temperature of Soot particulate reducing compound coated Metal foams 4 each upstream of the noble metal coated metal foams 2 in the exhaust gas flow also selectable according to requirement.

In the embodiment thus formed, the trapped soot is additionally oxidized by direct contact with the superficially applied coating acting as a catalyst. The applied coating consists of an oxygen storage compound, such as cerium orthovanadate Ce (III) VO ₄ .

4 shows another embodiment with a module 5, which consists of two parallel modules 1 ' is constructed according to the embodiment of FIG. 1, at However, the conically tapered inlet area for the Exhaust gas and the tapered exhaust outlet area omitted in such an embodiment flows through the Exhaust respectively the parallel arranged modules 1 'as in Connection with Fig. 1 indicated. Here are the Metal foams 2, 3 alternately with a precious metal from the Group Ru, Rh, Pd, Os, Ir, Pt or a mixture of these Precious metals coated or uncoated. advantageously, the coated metal foams 2 are each upstream before the uncoated metal foams 3 in exhaust gas flow arranged.

Another arrangement of the metal foams 2, 3, i. the Insertion of the uncoated metal foams 3 respectively upstream of the coated metal foams 2 in Exhaust gas flow can also be selected as required.

Furthermore, not only two are arranged in parallel Provide modules 1 'in the module 5, but according to the Requirements are also several modules 1 'in the Module 5 to increase the efficiency in an advantageous Way to accommodate.

FIG. 5 shows a cross section through that in FIG. 4 illustrated module 5 along the section line A-B, wherein each one module 1 'arranged parallel to the exhaust gas flow and flows through the exhaust gas.

The parallel arrangement and the number of modules 1 'in the Module 5 can almost arbitrarily to the respective engine power be adjusted. It can the required efficiency regarding the removal of soot particles from the combustion engine generated exhaust stream advantageous Be taken into account by the nature of the Precious metal coating or precious metal loading, the geometric surface of the metal foam and the number of coated metal foams.

For example, emissions reductions for soot particles be achieved by about 85% to 90% without the required permissible nitrogen dioxide limits exceed.

In addition, the efficiency for the reduction of Soot particle emission by a thermally induced Regeneration can be increased even further, like this one for example, with a burner or an electric Energy coupling achieved by a resistance heater can be.

The thermally induced regeneration can also by Oxidation of late injected into the internal combustion engine Fuel, a so-called post-injection, through which the exhaust gas temperature initially from about 150 to 200 ° C. can be raised to about 400 ° C.

In addition, it succeeds by oxidation of motor sustainable produced hydrocarbons (CH) on the noble metal coated Metal foam or oxidation catalyst the temperature in the Module for another approx. 200 ° C on finally the for the Soot particle combustion temperature of about 600 ° C to increase.

Claims (22)

Device for removing soot particles from an exhaust gas stream of internal combustion engines in a module (1) by oxidation of the soot particles temporarily trapped in a catalytic converter with nitrogen dioxide (NO ₂ ), the nitrogen dioxide being oxidized by oxidation of the nitrogen monoxide (NO) present in the exhaust gas to a catalytic converter from the flow velocity of the exhaust gas at a temperature above about 200 ° C, characterized in that in the module (1) at least one nitrogen dioxide concentration in the exhaust gas for the oxidation of the soot particles increasing noble metal-coated open-pore metal foam (2) is arranged. Apparatus according to claim 1, characterized in that the precious metal-coated metal foam (2) has the property to recirculate the nitrogen monoxide (NO) and thereby use multiple times. Apparatus according to claim 1, characterized in that the metal foam (2, 3, 4) consists of a FeCr alloy for high thermal oxidation resistance, high thermal shock resistance, high corrosion resistance and high mechanical strength. Apparatus according to claim 1, characterized in that the metal foam (2) is coated at least with a noble metal from the group Ru, Rh, Pd, Os, Ir, Pt or a mixture of these noble metals. Device according to claim 3, characterized in that the metal foam (4) is coated with a compound which reduces the combustion temperature of the soot particles. Device according to claim 5, characterized in that the metal foam (4) is coated with the compound of cerium orthovanadate (CeVO ₄ ) which reduces the combustion temperature of the soot particles. Apparatus according to claim 1, characterized in that the module (1) is designed as an open, self-regenerating module. Apparatus according to claim 3, characterized in that the metal foam (2, 3, 4) is produced by a powder sintering process or a precision casting process. Apparatus according to claim 3, characterized in that the metal foam (2, 3, 4) is formed with a 3D-flow causing irregular cell geometry with a mixer function. Apparatus according to claim 3, characterized in that the metal foam (2, 3, 4) is formed with a relative density in the range of 2 to 20%. Apparatus according to claim 3, characterized in that the metal foam (2, 3, 4) is formed with a number of pores in a range of 3 to 80 ppi. Apparatus according to claim 3, characterized in that the metal foam (2, 3, 4) is formed with a freely selectable geometry. Apparatus according to claim 3, characterized in that the metal foam (2, 3, 4) is electrically conductive. Apparatus according to claim 4, characterized in that the metal foam (2) directly or by impregnation of a Wash-coats with a noble metal from the group Ru, Rh, Pd, Os, Ir, Pt or a mixture of these noble metals in a concentration of 1, 0 g - 2.5 g of precious metal per liter of metal foam is coated. Apparatus according to claim 6, characterized in that on the metal foam (4) for reducing the combustion temperature of the soot particles compound cerium orthovanadate with a plasma process, a wash-coat process or a sol-gel process in a concentration of 1 , 0 g - 25 g CeVO ₄ / liter metal foam is applied. Apparatus according to claim 3, characterized in that the number of pores of the metal foams (2, 3, 4) is designed to vary in the direction of the exhaust gas stream. Apparatus according to claim 16, characterized in that the number of pores of the metal foams (2, 3, 4) increases in the direction of the exhaust gas flow. Apparatus according to claim 3, characterized in that between individual or all metal foams (2, 3, 4) there is a distance of 0-50 mm. Apparatus according to claim 3, characterized in that the metal foams (2, 3, 4) are integrally introduced with a soldering process in the metallic module (1). Apparatus according to claim 3, characterized in that the metal foams (2, 3, 4) are embedded with a bearing mat in the metallic module (1). Apparatus according to claim 1, characterized in that a module (5) of a plurality of identically constructed modules (1) or differently constructed modules is formed. Apparatus according to claim 21, characterized in that the plurality of identically constructed modules (1) or differently constructed modules in the module (5) are arranged parallel to the exhaust gas flow.

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