Particle trap with coated fibre layer

ES 2 388 136 T3

DESCRIPTION

Coated fiber layer particle trap

The invention relates to a particle trap for the purification of exhaust gases from mobile internal combustion engines with a high temperature resistant fiber layer.

If the purification of exhaust gases is contemplated, in particular from diesel engines, then hydrocarbons (HC) as well as carbon monoxide (CO) in the exhaust gas can be oxidized in a known way, by putting them in contact, for For example, with components that optionally have a catalytically active surface. The reduction of nitrogen oxides (NOx) under oxygen-rich conditions is, however, more difficult. A three-way catalyst as used, for example, in the case of Otto engines, does not by itself provide the desired effects for Diesel engines. For this reason, for example, the selective catalytic reduction (SCR) process was developed.

In addition, accumulator catalysts were examined for their use in relation to the reduction of nitrogen oxide. The coating of an accumulator catalyst contains, apart from the usual noble metal components, also carbonate or barium oxide. With this, it is possible that in the case of an excess of oxygen the NO_xcan be accumulated. In noble metal components, nitrogen monoxide (NO) from the exhaust gas is oxidized to nitrogen dioxide (NO₂). This then accumulates, under the formation of barium nitrate, on the catalyst. In the case of this accumulation, a nitrate layer is formed on the barium grain that slows down the accumulation, since NO₂ it must penetrate through this layer for further accumulation. Since the storage capacity is therefore limited, the catalyst must be regenerated at regular intervals. This happens, for example, by a short fattening of the exhaust gas, that is, by a short period under sub-stoichiometric conditions. In a reduced atmosphere, the nitrate is transformed back into (eg) carbonate and nitrogen monoxide is released. This is immediately reduced in nitrogen. Since regeneration proceeds faster than accumulation, regeneration periods can be substantially shorter than accumulation periods.

For the reduction of particle emissions, particle traps are known which are constituted by a substrate of ceramic material. These traps have channels, so that the exhaust gas to be purified can flow into the particle trap. Adjacent channels are reciprocally closed, so that the exhaust gas enters the channel on the inlet side, passes through a wall of ceramic material and is released again through a contiguous channel on the outlet side. Filters of this type achieve an effectiveness of approx. 95% across the entire range of manifested particle sizes.

In addition to chemical interactions with additives and special coatings, the safe regeneration of the filter in the exhaust gas system of an automobile is still a problem. Regeneration of the particle trap is necessary, since the increasing accumulation of small particles on the walls of the channel to be traversed results in a constantly increasing pressure loss, which has negative effects on the performance of the engine. Regeneration essentially comprises the brief heating of the particle trap or of the particles accumulated in it, so that the carbon black particles are transformed into gaseous components. This can also be achieved, for example, because with the aid of a preceding exothermic reaction (eg. oxidation of fuel injected further into the exhaust gas line in an oxidation catalyst (“afterburning”), the exhaust gas briefly reaches temperatures that are sufficient to transform the particles that adhere to the particle trap. However, this high thermal stress on the particle trap has negative effects on the service life.

To avoid this discontinuous and thermally very wear-promoting regeneration, a system was developed for the continuous regeneration of filters (CRT: “continous regeneration trap”). In such a system, the particles are calcined at temperatures already above 200 ° C by means of oxidation with NO₂. He does not₂ required for this is often generated via an oxidation catalyst which is arranged upstream of the particle trap. However, in this case the problem arises, precisely in relation to the application in motor vehicles with Diesel fuel, that in the exhaust gas there is only an insufficient portion of nitrogen monoxide (NO) which can be transformed into the nitrogen dioxide (NO₂) wanted. As a consequence, up to now it has not been possible to ensure that a continuous regeneration of the particle trap takes place in the exhaust gas system.

It must also be taken into account that along with particles that cannot be transformed, oil or additional residues of additives also accumulate in a particle trap, which cannot be regenerated without further ado. For this reason, known filters must be exchanged and / or washed at regular intervals.

ES 2 388 136 T3

In addition to a minimum reaction temperature and a specific residence time, for the continuous regeneration of particles with NO₂, sufficient nitrogen oxide must be available. Tests related to the dynamic emission of nitrogen monoxide (NO) and particles have clearly shown that the particles are emitted precisely when carbon monoxide is not present in the exhaust gas or only in a very small quantity, and at the reverse. It follows that a filter with a real continuous regeneration must essentially function as a buffer or accumulator, so as to ensure that the two participants in the reaction are present in the filter at a given instant at the same time in the required quantities. Furthermore, the filter must be arranged as close as possible to the internal combustion engine in order to be able to acquire, immediately after cold start, the highest possible temperatures. To enable the required nitrogen dioxide, an oxidation catalyst must be placed in front of the filter, which reacts carbon monoxide (CO) and hydrocarbons (HC) and, in particular, also converts nitrogen monoxide (NO) into nitrogen dioxide. (NO2). In the case of an arrangement close to the engine of this system based on oxidation catalyst and filter, the position in front of a turbocharger is particularly suitable, which is often used in diesel vehicles to increase the charge pressure in the combustion chamber. .

Contemplating these basic reflections, the question then arises for actual use in automobile construction as to how such a filter is constituted, which, in such a position and in the presence of extremely high thermal and dynamic stresses, presents a satisfactory degree of filter effectiveness. In this case, particular account must be taken of the spatial circumstances that determine a new concept for filters. While in the case of classic filters, which were placed on the underside of a motor vehicle, a volume that was as large as possible was of particular interest in order to guarantee a long residence time in the filter of the particles that had not reacted. and, consequently, high efficiency, in the case of an arrangement close to the engine, not enough space or space is available.

For this, a new concept was developed, which has essentially been known under the term "open filter system". These open filter systems are distinguished by the fact that a constructive and reciprocal closure of the filter channels can be dispensed with. In this case, it is envisaged that the walls of the channel are made, at least in part, of a porous or highly porous material, and that the flow channels of the open filter have diverting or conductive structures. These internal structures determine that the flow or the particles contained therein are diverted towards the zones based on a porous or highly porous material. In this case, it has been found, surprisingly, that the particles are adhered by interception and / or impact next to and / or in the porous wall of the channel. For the concurrence of this effect, the pressure differences in the flow profile of the flowing exhaust gas are of importance. As a result of the deviation, local depression or overpressure ratios can additionally result, which lead to a filtration effect through the porous wall, since the above-mentioned pressure differences must be compensated for.

The particle trap is in this case open, in contrast to known closed screen or filter systems, since no flow dead ends are provided. Consequently, this property can also be used for the characterization of particle filters of this type, so that, for example, the parameter "freedom of flow" is suitable for description. Thus, a "freedom of flow" of 20% means that in a cross-sectional view, approx. 20% of the surface is penetrable. In the case of a particle filter with a channel density of approx. 600 cpsi (“cells per square inch”) with a hydraulic diameter of 0.8 mm, this freedom of flow would correspond to a surface greater than 0.1 mm². In other words, this means that a particle trap is then designated as open if it can be basically completely traversed by particles, and also by particles that are considerably larger than the particles actually to be removed from the filter (in particular, the range of characteristic particle size for diesel fuel and / or gasoline). As a result, such a filter cannot be clogged during operation, even in the event of an agglomeration of particles. A suitable procedure for measuring the openness of particle traps is, for example, to examine up to what diameter spherical particles can still flow through such a filter. In current application cases, a particle trap is particularly "open" when spheres greater than or equal to 0.1 mm in diameter can still flow through it, preferably spheres with a diameter greater than 0.2 mm. "Open" filter elements of this type can be found, for example, from DE 201 17 873 U1, DE 201 17 659 U1, WO 02/00326, WO 01/92692, WO 01/80978, the disclosure of which is This makes it entirely the object of the present description.

In connection with the general design of honeycomb bodies with internal flow-conducting surfaces, for example the German utility model DE 89 08 738 U1 provides indications. This document describes alveolar bodies, in particular catalyst support bodies for motor vehicles based on sheets arranged in the manner of layers, structured at least in partial areas, which form the walls of a plurality of channels that can be traversed by a fluid. . These documents describe that in most cases of application and in the case of the usual dimensions of alveolar bodies of this type, the flow in the channels is

ES 2 388 136 T3 essentially laminar, that is to say very small cross sections of the channel are used. Under these conditions, relatively thick boundary layers accumulate on the channel walls, which reduce contact of the core flow in the channels with the walls. In order to determine a swirling of the exhaust gas stream inside the channels and, consequently, to ensure a strong contact of the entire exhaust gas stream with a catalytically active channel surface, they are proposed in this In this case, reversions that form inflow surfaces inside the channel, so that the exhaust gas is deflected transversely to the main flow direction.

From EP 0 798 452 A a reciprocally closed particle filter is known which has a filter layer. The filtration layer comprises a filter material which can be covered on both sides by layers bearing catalyst.

Document WO 01/92692 A discloses the arrangement of an open particle trap in an exhaust gas installation. The particle trap can in this case be made with a hydrolysis coating.

Precisely in relation to the realization of an open particle trap of this type, it is now the task of the present invention to improve the effectiveness in relation to the conversion of harmful substances contained in the exhaust gas. In particular, the possibility of providing exhaust gas installations, in particular for automobiles with a diesel engine, of a particularly small construction type has to be opened up. Furthermore, the production, assembly and maintenance of exhaust gas installations of this type must be clearly simplified and thus made more economical.

These problems are solved by means of a particle trap for the purification of exhaust gases of an internal combustion engine with a fiber layer resistant to high temperatures with the characteristics of claim 1. Other advantageous embodiments are described in the dependent claims, being able the characteristics indicated there appear individually or in any arbitrary convenient combination with each other.

According to the invention, a particle trap is proposed for the purification of exhaust gases from mobile internal combustion engines, which has at least one partially structured metal foil and at least one fiber layer resistant to high temperatures according to the construction type described above, wherein preferably several structured metal foils and several fiber layers are arranged alternately with each other and, in particular, bonded to each other in a housing. In this case, an "open" particle trap is formed as described at the beginning. Accordingly, it is particularly advantageous to form an "open" filter element as described in DE 201 17 873 U1, DE 201 17 659 U1, WO 02/00326, WO 01/92692, WO 01/80978.

The particle trap forms channels that run essentially parallel to the axis, penetrating conductive surfaces of the metal foil in at least a part of the channels and causing a deflection of the gases that flow through the channels towards the fiber layer. Conductive surfaces of this type can be formed by ridges, buttons, micro-corrugations, vanes or similar structures. It is also possible that these conductive surfaces are formed by making holes in metal foils of this type. The conductive surfaces themselves can also have holes.

The metal-based, high-temperature-resistant fiber layer for the particle trap for the purification of exhaust gases of mobile internal combustion engines is distinguished by the fact that a coating is provided in at least one section that, at least in part, corresponds that of an oxidation catalyst and / or a 3-way catalyst and / or a catalyst for SCR.

The provision of such a catalytically active coating has a number of advantages which will be briefly outlined below. Thus, for example, it is possible to achieve that the components originally intended in the exhaust gas system for the oxidation or reduction and / or accumulation of harmful substances contained in the exhaust gas can be made with a small volume or even be can completely renounce them. This has the consequence that the exhaust gas system as such can be made in a significantly thinner or smaller shape, thereby enabling a simple structure, easy maintenance and economical production of the exhaust gas system. Furthermore, surprisingly, synergistic effects are also elicited. Thus, for example, directly inside a particle trap equipped with a layer of fibers of this type, components of the exhaust gas are generated which are helpful for the conversion or elimination of the accumulated particles. These components of the exhaust gas are generated and supplied directly, therefore, close to the surface of the fiber layer to which the particles adhere. Accordingly, for example, the regeneration temperature of the particle trap can also be clearly lowered, for example from more than 900 ° C to temperatures below 600 ° C.

Regarding the arrangement of the at least one section of the fiber layer, it should be noted that this section can be

ES 2 388 136 T3 also spread over the entire surface of the fiber layer. However, it is also possible to provide several sections, in which these can be coated and / or partially also uncoated, optionally also being able to choose different types of coating, section shapes or surfaces of the sections different from one another. It is also possible that the at least one section is only on one surface or outer face of the high temperature resistant fiber layer.

In relation to the properties of the coating of an oxidation catalyst, it must be taken into account that catalysts of this type serve to increase the speed of certain reactions, without thereby being themselves consumed. Using suitable catalyst substances, it is possible to ensure that the oxidation processes for CO (carbon monoxide) and HC (hydrocarbons) in the exhaust gas run at lower temperatures. With the aid of coatings of this type, which generally contain platinum group catalyst substances, gaseous hydrocarbons and carbon monoxide can be oxidized at exhaust gas temperatures already above 250 ° C in engine exhaust gas. Diesel. One particularity of oxidation coatings of this type is that in this case, under certain circumstances, an afterburning of the hydrocarbons takes place, which still accumulate to carbon black particles, with which the emission of particles can be further reduced. Up to now it has been avoided to envisage a combination of this type of oxidation-promoting coatings and filter elements in one unit, since it was feared that the catalytically active substances would be affected by virtue of an increasing coating with particles. From this prejudice of the scientific world the invention was departed and a layer of fibers resistant to high temperatures was developed that allows the production of particularly efficient particle traps.

If the three components of harmful substances CO, HC and NO are to be reduced_x (nitrogen oxides) by a subsequent reaction, then this can be achieved by coating the fiber layer with one of the 3-way catalyst The active catalyst substance in this case comprises platinum metal (Pt), palladium metal (Pd) , or rhodium metal (Rh) in a fine distribution over a large surface. In the case of a lambda value of 1, CO is oxidized to carbon dioxide (CO₂), CH in CO₂ and water (H₂O) and NO is reduced_x in nitrogen (N₂). In this case, the following coating is offered in relation to the oxidation catalyst:

Pt / Pd = 2/1 ^{0.93 - 1.2 grams of Pt / liter}catalyst support volume

0.46 - 0.6 grams of Pd / liter_v0catalyst support lumen

In relation to the multifunctional catalyst (reduction) it is proposed that the following relationships apply:

Pt / Rh = 5/1 ^{1.16 - 1.5 grams of Pt / liter}catalyst support volume ^{1.23 - 0.3 grams of Rh / liter}catalyst support volume

By volume of the catalyst support body is meant the volume comprising the support material (honeycomb structure, etc.) and the voids, channels, etc. formed by the support.

The coating of a SCR catalyst can also be multilayer or multistage. A possible urea-SCR catalyst system consists of several sub-areas of the coating arranged one after the other, which are applied on the fiber layer. In this case, the partial areas can be arranged in the direction of the exhaust gas flow as follows:

- a coating of an oxidation catalyst (optional),

- the coating of a hydrolysis catalyst,

- the coating of a catalyst for SCR and

- optionally, a downstream oxidation catalyst.

The optionally upstream oxidation catalyst serves to increase the SCR activity at low exhaust gas temperatures (in particular in the case of diesel passenger cars). By increasing the portion of NO₂ (optimum: 50% by volume) in the exhaust gas by means of partial NO oxidation, the reaction rate of the SCR reaction can be significantly increased in a temperature range below approximately 573 K. In addition, on the surface From the catalyst, the oxidation of carbon monoxide to carbon dioxide takes place, as well as the reaction of incompletely burned hydrocarbons to form carbon dioxide and water. Without the use of such a leading range with an oxidation coating, oxidation of the hydrocarbons would take place, in part, in the SCR catalyst and consequently cause a decrease in nitrogen oxide conversion.

With the aid of the coating of a hydrolysis catalyst, the complete decomposition of a

ES 2 388 136 T3 aqueous urea solution already at low temperatures, e.g. ex. around 470 K. Below approx. 470 K, the decomposition of urea is problematic since, due to incomplete decomposition, unwanted by-products can result. The SCR catalyst coating serves for the selective reduction of nitrogen oxides NOx with ammonia to give the non-troublesome products nitrogen and water.

According to another embodiment of the particle trap with the high temperature resistant fiber layer, the coating comprises a sealant coating. Coating the relatively smooth surfaces of the sealant coated fibers results in an increase in the catalytically active surface. This uneven surface guarantees, on the one hand, a sufficiently large space supply for the fixation of a catalyst (eg. platinum, rhodium, etc.) and, on the other hand, it serves to swirl the exhaust gas that flows through, determining a particularly intense contact with the catalyst.

The application of the large surface sealant coating layer that promotes catalysis takes place, in a known manner, in such a way that the fiber layer (or later the entire particle trap based on layers of fibers and metal foils) is immersed in an aqueous solution of sealer coating or is sprayed with it. The sealant coating excess dispersion is then removed, the sealant coating is dried on the fiber layer, and then calcined at temperatures most often above 450 ° C. During calcination, the volatile components of the sealer coating dispersion are expelled, so that a stable layer is generated against variations in temperature and which promotes catalysis with a high specific surface area. Eventually this process would be repeated several times in order to achieve a desired layer thickness. The average layer thickness is in this case preferably in a range of 0.001 to 0.02 mm, in particular between 0.005 and 0.012 mm.

The sealant coating is usually composed of a mixture of an aluminum oxide and at least one promoter oxide such as, for example, rare earth dioxides, zirconium oxide, nickel oxide, iron oxide, germanium oxide and oxide of barium. In this case, the sealant coating dispersion must have the best possible flow property during application to the honeycomb body, in order to achieve a desired and uniform layer thickness over the entire length of the channel.

In order to achieve such a flow property, known sealant coating dispersions have a certain pH value, only a limited proportion of solids being allowed. However, tests have shown that such a sealant coating dispersion exhibits a time-dependent viscosity. This has the consequence that the sealant coating dispersion gels very quickly and prevents the generation of a uniform layer thickness. This gelation can be retarded by keeping the sealant coating dispersion in motion, that is, by moving the dispersion or the filter layer moistened therewith, in particular by exciting it for vibration.

According to yet another embodiment of the particle trap with the fiber layer, the fiber layer consists of a porous sinter and / or fiber material (eg steel). In particular, high temperature resistant and corrosion stable steels with relatively high amounts of chromium, nickel, aluminum and / or molybdenum are offered here. In this case, it is particularly advantageous that the fiber layer has fibers with a mean diameter that is less than 0.082 mm, which is in particular in a range of 0.01 to 0.05 mm. In order to prevent such a fiber layer from generating a high dynamic pressure in the exhaust gas stream, it is proposed that the fiber layer has a porosity of at least 50%, in particular at least 75%. %, preferably at least 85%, and preferably even at least 95%. In this connection it should be noted that fiber layers of this type could be produced relatively well with fibers of an average length of 0.4 mm to 0.05 mm, with shorter fiber lengths preferably being chosen in the case of thicker fibers.

Furthermore, it is proposed that the fiber layer has, in a longitudinal section, holes essentially parallel to the larger external surface, which have on average a dimension of 0.01 mm to 0.5 mm, in particular 0.05 mm. to 0.25 mm. Basically, at this point it should be noted that the fiber layer can have fibers in an almost arbitrary arrangement, in this case it is to be understood in particular also disordered layers, loom fabric or similar structures. In this case, the regular structures can also be present only by region, while in the remaining regions a rather chaotic arrangement of the fibers occurs.

In order to ensure that sufficiently large cavities are provided for the particles or their agglomerates, it is proposed in this case, precisely for the application in exhaust gas systems of Diesel engines, that a certain size of the pores is enabled. For the calculation of the pore size, a longitudinal cut through the material is used here, indicating small cross sections of the pores or cavities, which in this case are called holes. All these holes have on average one dimension in the range mentioned above. In this case, here we want to imply a mean value of all the

ES 2 388 136 T3 maximum dimensions of recognizable holes in longitudinal section. Since the dimension of the hole refers to the already coated fiber layer, it is also possible to resort to a corresponding averaged distance of the fibers, which should preferably be chosen less than 0.6 mm, in particular between 0.05 mm and 0. , 35 mm.

Furthermore, it is proposed that the fiber layer has a thickness that is less than 3 mm, in particular less than 1.5 mm, preferably less than 0.5 mm, and preferably less than 0.1 mm. The thicknesses mentioned here are chosen precisely in relation to the use of the fiber layer for particle traps for the purification of exhaust gases from mobile internal combustion engines.

According to another embodiment, the particle trap has a volume, and the amount of coating of the particle trap in relation to this volume is in the range of 20 to 300 g / l (grams per liter), preferably even between 50 and 120 g / l. In this connection, volume is understood to mean the volume that is made up of the metal foils, the fiber layers as well as the channels formed. Usually such a volume is in the range of 0.01 to 1.51, preferably between 0.31 and 0.81.

Furthermore, it is proposed that the at least one metal foil, at least partly structured, has holes extending along at least one width of the structure, preferably even along 2, in particular 3 widths of the structure. . This means that, for example, such a hole connects several contiguous channels formed by the structure together. In this way, a particularly efficient thorough mixing of the partial exhaust gas streams is ensured without an undesirably high dynamic pressure being generated in front of the particle trap. In this case, it is further noted that the holes extend essentially in the plane of the metal foil.

The invention is now explained in more detail with the aid of the figures. In this case it should be noted that the figures show particularly preferred embodiments of the invention, but the invention is not limited thereto. They show:

Fig. 1, schematically and an exploded representation, a detail of a particle trap according to the invention, Fig. 2, another detail of an embodiment of the particle trap according to the invention, Fig. 3, schematically, an embodiment of an exhaust gas system of a mobile internal combustion engine, Fig. 4, schematically and in perspective, another embodiment of the particle trap according to the invention, Fig. 5, schematically a longitudinal section through an embodiment of the fiber layer, and FIG. 6, another longitudinal section through a fiber layer in the coated state.

Fig. 1 shows schematically and in an exploded representation a detail of a particle trap as used, for example, for the treatment of exhaust gases from mobile internal combustion engines. Two fiber layers 1 are shown, between which a metal foil 14 is arranged. The fiber layers 1 each have a section 3 in which a coating 4 is arranged. This coating 4 can be an oxidation catalyst, a three-way catalyst and / or a catalyst for SCR. Preferably, the metal foils 14 (at least in partial areas) also have a catalytically active and / or accumulative coating. Adjoining layers are usually arranged next to each other and are preferably joined to each other by an assembly technique, in particular they are welded to each other. For this, it is necessary, for example, not to coat a partial area, in particular the edge of the fiber layer 1, in order to guarantee here the possibility for the execution of technical assembly connections.

The structuring of the metal sheet 14 has the consequence that this "sandwich" based on smooth layers (fiber layer 1) and corrugated layer (metal sheet 14) can be traversed for an exhaust gas in a flow direction 21. In In this case, conductive surfaces 18 are incorporated into the channels 17, which result in swirling of the partial gas streams, so that these are conducted, in particular, against the coated fiber layer 1. The structure of the metal foil 14 is in this case a corrugated structure with a predetermined width of the structure 36. Preferably, the conductive surfaces 18 or the holes 19 located below are made larger than the width of the structure 36, so that the holes 19 can connect several adjacent channels 17 to each other.

ES 2 388 136 T3

Fig. 2 shows an arrangement of metal sheets 14 and a layer of fibers 1 in detail. Again, the metal sheets 14 and the fiber layer 1 are arranged alternately, forming the structure of the metal sheets 14, in conjunction with the fiber layer 1, channels 17 that can be traversed by the exhaust gas in a flow direction 21. Conductive surfaces 18 which were produced from the metal foil 14 itself by punching, pressing or otherwise penetrate the channels 17. In this way, holes 19 are created at the same time, so that a partial stream of the edge 17 can be "cut off" from the gas flowing through a channel 17 and can be directed towards the fiber layer 1. In this way, also the particles 22 are entrained and are led to the fiber layer 1. There they remain on the external surface 9, for example glued, or accumulate in cavities, pores or similar holes in the fiber layer 1. The fiber layer 1 represented here has a plurality of fibers 6 arranged in a chaotic manner, which are provided of a coating 4. As a whole, the fiber layer 1 has a thickness 12 that is less than 3 mm.

Fig. 3 schematically shows the structure of an exhaust gas installation of an automobile internal combustion engine 13. The exhaust gas generated in the internal combustion engine 13 is supplied through an exhaust gas pipe 23 to the most diverse components for the treatment of the exhaust gas until it is ultimately emitted to the environment. The exhaust gas system that is represented in Fig. 3 has 21 components arranged one after the other in the flow direction: a starter catalyst 24, a turbocharger 25, an oxidation catalyst 26, a reducing agent feed 27, a mixer 28, a particle trap 2 according to the invention , as well as a main catalyst 29.

The starter catalytic converter 24 is distinguished by its particularly small volume (for example less than 0.1 liter) and, by virtue of its low thermal capacity and its immediate proximity to the engine, it warms up even after a short time after the start of the engine. engine to such an extent that a catalytic reaction of harmful substances contained in the exhaust gas is possible (eg temperatures above 230 ° C after a few seconds). The function of the oxidation catalyst 26 in front of a particle trap 2 for regeneration was already explained in detail above. The reducing agent supply line 27 and the mixer 28 serve, for example, for the supply of solid or liquid urea, so that a reaction of harmful substances is also possible with the SCR process. The mixer 28 can be designed as a conductive surface, screen, honeycomb body, or the like. However, it is also possible to omit the mixer 28 in front of the particle trap 2, since the particle filter 2 itself also determines a swirling of the exhaust gas streams or a fine distribution of the introduced reducing agent. The main catalyst 29 arranged downstream usually has a relatively large volume, in particular greater than 1.5 liters.

Fig. 4 shows in perspective and schematically the structure of a particle trap 2. The particle trap 2 for the purification of exhaust gases from mobile internal combustion engines comprises a structured metal foil 14 and a layer of fibers 1 resistant to high temperatures, which is arranged in a spiral around an axis 16 of the particle trap 2 (alternatively, simple stacked arrangements, S-braided or other twisting of the metal foils and / or fiber layers are also possible). The metal foil 14 and the fiber layer 1 form channels 17 which extend essentially parallel to the axis 16 through the particle trap 2. The combination of metal foil 14 and fiber layer 1 is incorporated in a housing 15 and, advantageously, it is also connected to it by means of assembly technique. In the illustrated embodiment of the particle trap 2, the housing 15 protrudes from the front surfaces 34 of the particle trap 2 or from the metal foil 14 and from the fiber layer 1. The thickness 30 of the material of the Corrugated metal foil 14 is preferably in a range below 0.05 mm, preferably even below 0.02 mm. In this case, in particular, the possibility is offered that the thickness 30 of the material or the coating 4 (not shown) or other parameters of the particle trap 2 are not constant over the total length 31 of the particle trap 2. This means, for example, that the particle trap 2 has in a first longitudinal section 32 a lower thermal capacity, a higher porosity, a higher load in relation to the catalytically active coating, an increased number / size of holes 19, conductive surfaces 18 or fibers than in a second longitudinal section 33. Basically, it is also possible to subdivide the particle trap 2 into more than two longitudinal sections.

The represented particle trap 2 has a volume 20 that is characterized by the volume occupied by the fiber layer 1 and the metal sheet 14 inside the casing 15, the volume of the channels 17 being also comprised. coating 4, the particle trap according to the invention is provided with an amount ranging from 20 to 300 g / l. In this case it is possible that this quantity is uniformly arranged over the entire length 31 on the outer surfaces 9 of the fiber layer 1 and / or the envelope sheets 14, however, it is also possible that only the fiber layer 1 or only partial areas of the metal foil 14 are provided with a catalytically active coating 4. It is also possible that different types or quantities of coating 4 are provided in different longitudinal sections.

Fig. 5 schematically shows a longitudinal section 8 through the fiber layer 1. In this case, it is possible to

It is recognized by ES 2 388 136 T3 that the fiber layer 1 is formed by a plurality of fibers 6 which in this case are joined together partly in an orderly way, partly in a chaotic way. The fibers 6 preferably have a diameter 7 in the range of 0.012 and 0.035 mm. By arranging the fibers 6 in the longitudinal section 8, holes 10 are formed. These practically represent a cross section of the cavities that are formed inside the fiber layer 1.

Fig. 6 also shows schematically a longitudinal section 8 of the fiber layer 1, the fibers 6 now being made with a coating 4. The coating 4 comprises a sealing coating 5 which, by virtue of its rough surface, forms a sufficient possibility for the accumulation of the catalytically active substances. Despite the coating 4, the longitudinal section 8 still has holes 10 with an extension 11. This extension 11 of all the holes 10 ranges, on average, between 0.05 and 0.4 mm. In this case, it is preferred to maintain a porosity of approx. 87%.

The present invention is the result of a plurality of complex technical tests in order to improve the effectiveness of particle traps in exhaust gas systems of automobile internal combustion engines.

Reference symbols list

Fiber layer

Particle trap

Stretch

Coating

Sealant coating

Fiber

Diameter

Longitudinal cut

External surface

Orifice

Extension

Thickness

Internal combustion engine

Metal foil

Case

Axis

Channel

Conductive surface

Hole

Volume

Flow direction

Particle

Exhaust gas piping

Starter catalyst

Turbocharger

Oxidation catalyst

Reducing agent feed line

Mixer

Main catalyst

Material thickness

Total length

First longitudinal section

Second longitudinal section

Front surface

Substance

Structured width