WO2004099578A1 - Regeneration of a particle trap - Google Patents

Abstract

The invention relates to an exhaust system (1) for purifying a gas flow (2) of harmful substances (3), said exhaust system comprising at least means for supplying a reducing agent, a first catalytic converter (5), and a particle trap (8), in the direction of flow (4) of the gas flow (2) through the exhaust system (1). According to the invention, at least one other exhaust purification component is provided and/or there is a distance of at least 0.5 metres between the first catalytic converter (5) and the particle trap (8), and a mixer (6) and a second catalytic converter (7) are positioned directly upstream of the particle trap (8). The invention also relates to a method for regenerating a particle trap (8) arranged in the exhaust system (1), whereby a reducing agent (23) is introduced into the exhaust gas system (1), (only) upstream of the turbocharger (6), for carrying out a regeneration process of the particle trap (8).

Description

 Regeneration of a particle trap

The present invention relates to an exhaust system for cleaning a gas flow from pollutants, which comprises a particle trap which is regenerated discontinuously using a reducing agent. A method for regenerating a particle trap is also described.

Due to legal regulations, which place increasing demands on the exhaust systems in the automotive industry, the exhaust systems have been continuously developed in the past. A large number of components are used, each of which has different functions within the exhaust system. For example, starting catalytic converters or pre-turbo catalytic converters are known which have a particularly small volume and thus quickly reach their starting temperature required for catalytic conversion after a cold start of the internal combustion engine. Furthermore, electrically heatable catalysts are known which also enable improved cold start behavior of the exhaust system. So-called adsorbers in the exhaust system of an internal combustion engine have the task of adsorbing certain pollutants contained in the exhaust gas for a certain period of time, these being preferably stored until a downstream catalytic converter has reached its operating temperature. In particular in the exhaust system of diesel engines, particle traps or particle filters are also used, which collect soot particles and / or other solid contaminants contained in the exhaust gas. The collected particle collections can in principle be implemented continuously or discontinuously, for example by supplying high thermal energy.

To reduce the particle emissions in the exhaust gas, in particular in the case of diesel engines, particle traps are known which are constructed from a ceramic substrate. These have channels so that the exhaust gas to be cleaned enters the particulate trap. le can flow in. The adjacent channels are alternately closed, so that the exhaust gas flows into the channel on the inlet side, passes through at least one ceramic wall and escapes again through the adjacent channel on the outlet side. Such particle traps are known as "closed" particle filters. They achieve an effectiveness of approximately 95% across the entire range of the particle sizes that occur.

Another type of particle trap that can withstand high thermal loads and has a significantly lower pressure drop is evident from the unpublished German patent application DE 101 53 283. In this document, a particle trap is described, which is referred to as an “open” filter system. In such an open system, the filter channels are not structurally and mutually closed. The channel walls consist at least partially of porous or highly porous material. The flow channels of the open filter point Deflecting or guiding structures that direct the exhaust gas with the particles contained therein to the areas made of porous or highly porous material A particle filter is said to be open if it can basically be completely traversed by particles, including particles that Such a filter cannot clog up even during agglomeration of particles during operation. A suitable method for measuring the openness of a particle filter is, for example, checking up to which diameter spheres shaped particles can still trickle through such a filter. In the present application cases, a filter is particularly open when balls with a diameter greater than or equal to 0.1 mm can still trickle through, preferably balls with a diameter above 0.2 mm.

Regardless of the type of particle trap used, safe and, if possible, complete regeneration of the particle filter in the exhaust system of an automobile must be guaranteed. Such a regeneration of the particle trap is necessary because the increasing accumulation of particle particles in the flowing channel wall has a steadily increasing pressure loss, which has a negative impact on engine performance. The regeneration essentially comprises the short-term heating of the particle trap or the particles accumulated therein, so that the soot particles are converted into gaseous components.

In the past, such particle traps were heated directly, for example by ohmic resistance heating. It was also known to convert the deposited soot particles with a separate burner. The following devices for regeneration of the particle filter are characterized in that a reducing agent is added upstream of such a particle trap, which ultimately causes a chemical conversion of the soot particles deposited in the particle trap. Essentially two different systems have emerged: discontinuous and continuous regeneration.

The system for continuous regeneration of filters is called CRT (Continuous Regeneration Trap) and is described, for example, in US 4,902,487. In such a system, the particles are converted at temperatures above 200 ° C by means of oxidation by contacting them with nitrogen dioxide (NO ₂ ). The nitrogen dioxide required for this is often generated by an oxidation catalytic converter which is arranged upstream of the filter. However, with regard to use in motor vehicles with diesel fuel, the problem arises that there is only an insufficient proportion of nitrogen monoxide (NO) in the exhaust gas which can be converted into the desired nitrogen dioxide. As a result, it has not yet been possible to ensure that the particle trap in the exhaust system is continuously regenerated. For this reason, it is also common to feed urea or similar reducing agents into the exhaust system, which enable the filters to be continuously regenerated. A disadvantage of such systems is the high level of technical complexity and the fact that separate consumables or operating resources must be carried in the motor vehicle. In the discontinuous regeneration of particle traps, it is known to precede the particle trap with an oxidation catalyst to which unsaturated or unburned hydrocarbons (HC) are fed. When the unsaturated hydrocarbons come into contact with the oxidation catalytic converter, a particularly exothermic reaction arises, which results in a significant increase in the temperature of the exhaust gas. Temperatures are reached that are in a range that enables the particle agglomerations stored in the particle traps to be converted. Temperatures above 600 ° C often have to be reached. The reducing agent clock can be carried out separately, but it is also known to introduce unburned fuel components from the internal combustion engine directly into the exhaust pipe, so that they hit the oxidation catalytic converter.

The desire described at the outset to effect catalytic conversion of the exhaust gas immediately after the cold start of the internal combustion engine can be realized by using starting catalysts which are characterized by a small volume (e.g. less than 20% of the displacement of the internal combustion engine) and their proximity to the engine. The technical problem arises that it is no longer possible to supply unsaturated hydrocarbons which are intended to bring about regeneration in a particle trap located downstream and clearly removed from the starting catalyst. The fuel acting as a reducing agent would hit the catalytic converter and lead to an exothermic reaction. Due to the fact that the particle trap is arranged very far from the starting catalytic converter or additional components for exhaust gas purification are arranged between the starting catalytic converters and the particle trap, the required temperature increase is not brought about in the particle trap.

It is therefore an object of the present invention to eliminate the technical problems outlined, in particular an exhaust system and a method for Specify regeneration of a particle trap, so that discontinuous regeneration of the particle trap can also be guaranteed if large distances are covered between the starting catalyst and the particle trap for the exhaust gas or temperature-sensitive components for converting certain exhaust gas components are arranged between the starting catalyst and the particle trap. The exhaust system should also be simple and the regeneration should be easy to carry out.

These objects are achieved by an exhaust system with the features of claim 1 and a method for regenerating a particle trap with the features of claim 11. Further advantageous configurations are described in the respective dependent claims. The further developments shown there can also be combined with one another in any meaningful manner.

The exhaust system for cleaning a gas stream with pollutants comprises at least means for supplying the reducing agent, a first catalytic converter and a particle trap in the flow direction of the gas stream through the exhaust system, with at least one further exhaust gas cleaning component and / or a distance of at least 0.5 m is provided between the first catalytic converter and the particle trap. According to the invention, a mixer and a second catalytic converter precede the particle trap.

To clarify the terms used here, the meaning is explained in more detail below. The "direction of flow of the gas stream" is to be understood as the direction of the gas stream which the flow takes from an internal combustion engine to the exhaust or outlet into the atmosphere. This means a main flow direction, so local flow turbulence or the like is particularly disregarded Arrangement of the individual means in the direction of flow through the exhaust system means that the gas stream first comes into contact with the means for supplying a reducing agent, then with the first catalytic converter and finally with the particle trap. This is without prejudice to the fact that the gas flow between these individual components comes into contact with other components of the exhaust system, such as, for example, further adsorbers, exhaust pipes, etc. Furthermore, with reference to the fact that “at least” the facilities listed are provided, that the devices can be arranged several times, directly or indirectly, one behind the other.

A “catalytic converter” is to be understood as meaning a multiplicity of known support bodies for catalytically active material. The support bodies can be composed predominantly of metal and / or ceramic. In the case of metallic catalyst support bodies, it is known that at least partially structured sheet metal foils are wound together, that channels for which fluid can flow are formed. It is also known to produce metallic carrier bodies by extrusion. Furthermore, ceramic carrier bodies are known which also obtain their honeycomb shape through an extrusion and sintering process. Such a honeycomb shape has therefore become special proven to be advantageous because in this way a particularly large surface area is made available which results in intimate contact with the gas stream.

The term “particle trap” means both classic filter systems with mutually closed channels and the “open” filter systems described above.

The term “exhaust gas cleaning component” represents a generic term for a large number of different components for exhaust gas treatment, in particular honeycomb bodies, water traps, heating elements, mufflers, adsorbers, storage devices, etc. A “distance” between the first catalytic converter and the particle trap is to be understood to mean, in particular, their distance along the flow path of the gas stream. This means that the distance along the exhaust pipe, which the first catalytic converter and the particle trap on the shortest route, connects.

A "mixer" in the sense of this disclosure describes a device which causes a swirling or a significant flow deflection of partial gas flows, in particular the proportion of redirected partial gas flows is above 50%, in particular 80%, preferably above 95%. It is particularly advantageous here that the partial exhaust gas streams are not deflected essentially parallel to one another, but rather move at least partially towards one another so that mixing takes place. As an example, a mixing element of the type described in DE 199 38 840 may be mentioned here. Of course, all others can also be used , known mixers can be used as long as they meet the above criteria.

Regarding the second catalytic converter, it should be pointed out that this is again an exhaust gas treatment component of the type described with reference to the first catalytic converter. However, this second catalytic converter is not designed as a starting catalyst, i. H. it is not in the vicinity of the engine.

With the exhaust system according to the invention, it is possible, as will be explained in more detail below with reference to the method, to use fuel as a reducing agent for the regeneration of the particle trap, the fuel passing the first catalytic converter essentially without a complete exothermic reaction. This fuel-gas mixture is then processed by the mixer so that the desired exothermic reaction takes place in the second catalytic converter, which causes the temperature increase required for the regeneration of the particle trap. An essential aspect of the invention is that the fuel required for regeneration is passed through the first catalytic converter in a concentrated manner in a section or partial volume flow of the exhaust gas stream, so that there is insufficient oxygen available for a significant proportion of the fuel carried, which is required for the catalytic conversion. Thus, catalytically motivated reactions occur only in the edge areas of the high-fuel partial gas stream, but a large part of the additionally injected fuel quantity passes through the first catalytic converter without conversion.

The mixer now causes this fuel-enriched partial gas flow to mix with the remaining exhaust gas, which is particularly lean, particularly in diesel engines, i.e. H. is oxygen-rich. This mixing process dissolves the high-gas partial gas flow, so that the fuel flows finely dispersed with the exhaust gas flow towards the downstream particle trap. In this context, it does not matter whether or not the mixed exhaust gas stream flows through further (non-oxidizing) exhaust gas cleaning components on the way to the second catalytic converter. Ultimately, the mixed exhaust gas flow meets the second catalytic converter, which in turn has a catalytically active surface and now brings about a conversion of the exhaust gas fuel dispersion.

Since this second catalytic converter is connected directly (or immediately, that is, without further exhaust gas purification components being arranged in between) upstream of the particle trap, the temperature increase due to the exothermic reaction is passed on directly to the particle trap. This now ensures complete regeneration of the particle trap. It is particularly advantageous that the second catalytic converter and the particle trap are arranged with respect to one another in such a way that the exhaust gas can deliver the greatest possible amount of energy to the particle trap. This can be ensured, for example, that the catalytic converter and the particle trap are only a short distance from one another, in particular this distance is less than 10 cm, in particular less than 5 cm and preferably less than 2 cm. The distance describes the distance that the exhaust gas travels after exiting the second catalytic converter until it enters the particle trap. In particular, it is advantageous if the exhaust pipe between the second catalytic converter and the particle trap is thermally insulated or has no additional components such as flaps, baffles, probes or the like, or also curved sections.

According to a further embodiment of the invention, the mixer is a turbocharger. Especially in the newer diesel engines, which work on the principle of direct injection, the use of an exhaust gas turbocharger for compressing the intake air has proven itself. Such a compressor for the intake air is operated by the exhaust gas flowing through the turbocharger. When flowing through the turbocharger, the exhaust gas is swirled so that the turbocharger fully meets the criteria described above with regard to the mixer. I.e. For example, that now only the first catalytic converter can be followed by a turbocharger, which in turn is followed by a second catalytic converter and the particle trap. Especially with such an arrangement of the exhaust gas cleaning components or the turbocharger, the method described below is advantageous because it prevents the first catalytic converter, which is preferably designed as a starting catalyst, from generating such high temperatures in the exhaust gas that the directly connected turbocharger is damaged becomes. It is thus possible to pass the exhaust gas at temperatures which are tolerable for the turbocharger, and then to heat it up to such a temperature by means of the second catalytic converter that regeneration of the particle trap is ensured.

According to a further embodiment of the exhaust system, the means for

Supply of the reducing agent at least one injection nozzle for providing fuel in the combustion chamber of a mobile combustion engine. This means in particular that only one or more injection nozzles are used for Supply of the combustion engine with fuel are intended to be used to provide reducing agents for the regeneration of the particle trap. I.e. in other words, the at least one injection nozzle injects fuel into the cylinders of the internal combustion engine, which essentially leaves the cylinder unburned, passes the first catalytic converter (and possibly also the turbocharger) and finally only through contact with the second catalytic converter Converter an exothermic reaction to convert the fuel takes place. In this way, a particularly simple construction of the exhaust system is possible. Finally, additional lines or nozzles can be used. The like. For the introduction of the reducing agent.

It is further proposed that the injection nozzle be arranged so that the fuel can be introduced into an outlet channel of the internal combustion engine. It is clear to the person skilled in the art that further means may be required for this. It should be taken into account that the injection nozzle is usually oriented in such a way that a particularly good compression or combustion behavior of the fuel-air mixture in the cylinder of the internal combustion engine is guaranteed. To ensure that the fuel reaches the outlet channel, predetermined positions of the piston or the valve may be required.

In order to obtain, for example, an easily retrofittable embodiment of the exhaust system that does not require a modification of the cylinder or the combustion chamber, it is proposed that at least one separate feed line be provided in or on an outlet duct of the internal combustion engine and / or the exhaust system. This means that, for example, an additional line is provided from the fuel supply to the engine, and the fuel is supplied to the exhaust gas flow between the combustion chamber or the engine cylinder and the first catalytic converter. It should be noted that this is done in such a way that a relatively narrowly limited partial gas flow is generated which has a particularly high concentration of fuel. This ensures that the oxygen required to carry out an exothermic reaction is displaced, and the high-fuel partial gas stream flows through both the first catalytic converter and possibly downstream components without experiencing any significant chemical conversion.

According to a further embodiment, it is proposed that the means for supplying a reducing agent are connected to a reducing agent reservoir and a control unit, so that an intermittent supply of reducing agent can be carried out. With regard to the reducing agent reservoir, separate containers or storage spaces can be provided, but it is also possible that this is directly the fuel tank. The control unit takes over the tasks of regulating or controlling the opening times or the pressures at the injection nozzle or other nozzles as required. This has to be done in particular as a function of the piston or exhaust valve position of the cylinder of the internal combustion engine.

It is also advantageous that the first catalytic converter has a first contact surface which promotes the oxidation of at least one pollutant contained in the gas stream. I.e. in particular, that the first catalytic converter converts unsaturated hydrocarbons into less harmful components. Precisely because there is always a particular interest of the public in this context, it is proposed that the second catalytic converter also have a second contact surface which requires the oxidation of at least one pollutant contained in the gas stream. It is u. It is possible that both the first catalytic converter and the second catalytic converter have the same catalytically active material on or in the contact area. This is surprising in that the device proposed here and the method explained below ensure that the reducing agent on the one hand passes through the same coating, but on the other hand is reacted with an exothermic reaction with a considerable increase in the temperature of the exhaust gas. According to yet another embodiment of the exhaust system, the second catalytic converter and the particle trap form a structural unit. This means in particular that the second catalytic converter and the particle trap are not only connected via the exhaust pipe surrounding them. For example, it is possible for the second catalytic converter and the particle trap to be arranged in a common casing tube which is in contact with the exhaust pipe. However, it is also possible for the second catalytic converter and the particle trap not only to be connected to one another over the circumference, but also for contact to be made via the end faces, for example via pins, sheet metal foils or the like. Furthermore, it is also possible, for example, to provide thermal insulation with respect to the structural unit, so that the exothermic energy generated in the second catalytic converter is almost completely released to the particle trap.

According to a further advantageous embodiment of the exhaust system, the second catalytic converter and the particle trap together form a body through which a fluid can flow, which in the direction of flow initially has a catalytically active coating and subsequently means for the attachment of particles. I.e. for example, that the second catalytic converter and the particle trap are designed with the same carrier body. I.e. in other words that, for example, the channel walls, which are generally formed by ceramic material or metal sheets, extend together over an entire length in the direction of flow of the second catalytic converter and the particle trap. A subdivision of the carrier body itself then does not have to exist. However, recesses, deformations, material accumulations or the like can be made in partial sections of the body or the channel walls, so that the section of the body is adapted to the respective function, catalyst on the one hand and particle trap on the other. In principle, however, it is possible that these sections of the carrier body or body (only or additionally) differ by different coatings. An overlap tion area of the section that represents the second catalytic converter and the section that forms the particle trap.

According to a further aspect of the invention, a method for regenerating a particle trap is proposed which is arranged in an exhaust gas system, the exhaust gas system (viewed in the direction of flow of a gas stream) at least a first catalytic converter, a turbocharger, a second catalytic converter and the particle trap having. A reducing agent is introduced into the exhaust system upstream of the turbocharger in order to carry out a regeneration process for the particle trap. For this purpose, the reducing agent is fed to the exhaust system in a concentrated manner in a partial gas stream that no or only a very slight exothermic reaction takes place when flowing through the first catalytic converter. This partial gas stream, which is still high in fuel, is now led through the turbocharger, with a particularly intensive mixing with the partial exhaust gas streams from other cylinders of the internal combustion engine. Since these partial exhaust gas flows from the other cylinders essentially represent a particularly lean (oxygen-rich) mixture, the partial gas flow, which still has a high fuel content, is now enriched with oxygen. The result of this is that the desired exothermic reaction takes place when the partial gas stream subsequently hits an oxidation catalyst. The thermal energy released is used to burn off the soot particles that have accumulated in the downstream particle trap. This prevents flow paths (which the exhaust gas takes through the particle trap) from clogging, which leads to an increase in the flow resistance of the particle trap. The resulting drop in pressure of the exhaust gas flow over the particle trap has negative effects on the engine performance, which are reliably avoided with the method described here.

It is particularly advantageous that the reducing agent is supplied intermittently. This applies in particular when the reducing agent is supplied by means of at least one injection nozzle, fuel being injected into a combustion chamber mobile internal combustion engine is initiated. The main focus here is on diesel engines.

According to a further advantageous embodiment of the method, the fuel is subsequently injected into the combustion chamber, so that unburned partial volume flows of the fuel reach an outlet channel of the internal combustion engine. In this sense, retrospectively means that the injector injects fuel at two different times in the cylinder during a working cycle of the piston. At the first point in time, the amount of fuel required for self-ignition or combustion is injected into the combustion chamber of the cylinder, compressed and burned. During the upward movement of the piston, the exhaust gas produced during combustion is expelled through an open exhaust valve into the exhaust duct and further to the exhaust pipe. At this point in time, in particular after the combustion in the combustion chamber has ended, a predeterminable or calculable quantity of fuel (or another reducing agent) is introduced into the combustion chamber via the injection nozzle and which, with or after the exhaust gas partial flow is pushed out, through the exhaust duct the exhaust pipe flows.

In internal combustion engines with a plurality of cylinders, each with a combustion chamber, it is particularly advantageous that the reducing agent is injected into the cylinders alternately. This includes, on the one hand, that the individual cylinders take over one injection of the reducing agent one after the other, but it is also possible that individual cylinders are skipped, individual injection nozzles take over the injection of the reducing agent several times in succession and / or no rigidly specified change is made with regard to the cylinders. The latter is the case in particular when the injection into the respective cylinders takes place as a function of measured values which reflect the operating state of the internal combustion engine or the exhaust system. This ensures, on the one hand, that in a single cylinder after the reducing agent injection, remaining amounts of fuel are burned again and again. So there is even combustion in all cylinders.

According to a further embodiment of the method, the triggering time schedule for an injection of the reducing agent is determined as a function of a detected and / or calculated parameter which characterizes the functionality of the particle trap. This means that means (sensors, probes, etc.) are provided that monitor the functionality of the particle trap. Suitable measured values are the pressure drop across the particle trap, the temperature in the particle trap, the concentration of at least one pollutant in the exhaust gas after the particle trap has emerged, etc. If the pressure drop reaches a predetermined limit value, for example, this can be an indication of the triggering of a Regeneration cycle. Here u. U. also take into account the length of time that the amount of fuel injected close to the engine needs to reach the particle trap. This must be done in such a way that the temperature of the particle trap is increased before it has a noticeable negative effect, for example on engine performance.

According to yet another embodiment of the method, the location of the injection of the reducing agent is selected as a function of a detected and / or calculated parameter which characterizes the temperature of the gas flow in a partial area of the exhaust system. This means, for example, that the choice of the injection nozzle of the plurality of cylinders is determined by certain temperatures of the gas flow or the exhaust system and / or the internal combustion engine. If, for example, a remaining amount of fuel in the cylinder subsequently leads to an increased thermal load during the next combustion, it may be advantageous to inject the reducing agent only via the other injection nozzles when a predetermined limit temperature is reached. Under certain circumstances, it is also possible that the flow paths in the exhaust line, depending on the injection location, have different areas on the exhaust gas cleaning system. The flow of components is increased, so that the temperature of the exhaust gas stream is a thermal load in these areas. An adaptation to ensure the functionality of the exhaust gas treatment components can also be provided here.

The invention is explained in more detail below with reference to the figures. It should be clarified that the figures show schematically illustrated, particularly preferred exemplary embodiments, to which the invention cannot, however, be limited.

Show it:

Fig. 1: Schematic of the structure of an exhaust system; Fig. 2: schematically the structure of a direct injection diesel

Verbrennungskxaftmaschine;

3 schematically shows a subsequent injection of reducing agent; 4 shows an exemplary embodiment of a first catalytic converter; 5: shows an exemplary embodiment relating to a structural unit consisting of a second catalytic converter and a particle trap; and FIG. 6: schematically and in perspective a detail of a

Particle trap as shown in Fig. 5.

1 shows schematically and in perspective an exhaust system 1 for cleaning a gas stream 2 from pollutants 3. This exhaust system 1 comprises in the flow direction 4 of the gas stream 2 through the exhaust system 1 at least a first catalytic converter 5, a mixer 6 and a second catalytic converter Converter 7 and a particle trap 8. Furthermore, means for supplying a reducing agent are provided, which are arranged only upstream of the mixer 6. In this way, fuel 10 is injected into the combustion chambers 11 of the various cylinders 24 in the squeezing machine 12, which is preferably a diesel engine for a passenger car. This fuel 10 is compressed with high ter intake air burned and then expelled through the exhaust pipe 26 to the environment.

A plurality of first catalytic converters 5 are provided directly in the vicinity of the internal combustion engine 12, in particular at a distance of less than 70 cm, a first catalytic converter 5 being integrated in each case in a pipe of the exhaust manifold. In the embodiment shown, a reducing agent 23 is fed to the exhaust gas flow via a separate feed line 14 upstream of a mixer 6, which is designed here as a turbocharger. The reducing agent 23 flows through the mixer 6 or the turbocharger and then meets a second catalytic converter 7. This second catalytic converter 7 is designed in a conical shape and is arranged in an expansion of the exhaust gas line 26. Directly after the second catalytic converter, the particle trap 8 is positioned at a distance 44, which is preferably less than 5 cm. Downstream of the particle trap is a three-way catalytic converter 27 of the known type. There is a distance 43 between the first catalytic converter 5 and the particle trap 8, which is at least 0.5 m, preferably even more than 1 m. The arrow marked 43 is only to be understood schematically; the actual distance 43 is determined by the flow path of the gas stream 2 from the outlet of the first catalytic converter 5 to the entry into the particle trap 8.

Fig. 2 shows schematically and obviously not to scale a combustion chamber 11, as can be found, for example, in a direct-injection diesel internal combustion engine. The cylinder 24 comprises a piston 32, the cylinder 24 and the piston 32 at least partially delimiting a combustion chamber 11, also called displacement. An injection nozzle 9 is also arranged in the engine block of the internal combustion engine 12 and is connected on the one hand to a fuel reservoir 15 and to a control unit 16. The task of the injector 9 is to supply a predefined or predetermined amount of fuel 10 to the combustion chamber 11 as required inject, which then ignites with highly compressed intake air. The ignition of the fuel-air mixture results in an expansion of the gas mixture, by means of which the piston 32 is pressed downwards. After the combustion, the valve 33 is moved upward and the exhaust gas located in the combustion chamber 11 is expelled through an outlet duct 13 in the flow direction 4. In the form shown, the outlet valve 33 is closed, the injector 9 therefore finely disperses the required amount of fuel 10, which is required for the actual combustion or power development.

Fig. 3 shows schematically and with a partial section the subsequent injection of fuel as a reducing agent. Again, the cylinder 24 and the piston 32 are schematically indicated, which delimit the combustion chamber 11. In the snapshot shown here, the valve 33 is in a position such that the exhaust gas flow can flow from the combustion chamber 11 into the exhaust duct 13. This is caused by the piston 32 moving upwards. Now the desired amount of fuel, which is required to reduce the particle trap, is injected into the combustion chamber through the injection nozzle 9. If possible, this fuel 10 is introduced into the exhaust gas duct 13 in such a way that a type of “rich disk” is created. This preferably means a partial volume flow 25 which has a particularly high concentration of hydrocarbons. This partial volume flow is low in oxygen, a condition which is usually the case 3 is schematically indicated that the gas stream 2 or the exhaust gas stream comprises pollutants 3 as well as particles 22 that propagate in the flow direction 4 through the outlet duct 13. While a relatively high concentration of oxygen is provided for a catalytic reaction in the indicated partial area, in which pollutants 3 and particles 22 have accumulated, in the partial volume flow 25 there are almost no oxygen molecules or a proportion clearly below 50%, preferably less than 30 %. This ensures that This partial volume flow 25 flows through the first catalytic converter 5 without there already being a strongly exo- to cause thermal reactions that could damage the downstream turbocharger.

FIG. 4 shows schematically and in a perspective view an embodiment of a first catalytic converter 5, as can be found, for example, for use in a pipe of an exhaust manifold. The first catalytic converter 5 comprises a housing 31, in which a plurality of sheet metal foils 28 are arranged such that channels 29 through which the gas stream 2 can flow are formed. Thus, despite the small volume, a relatively large first contact area 17 is formed. The sheet metal foils 28 are partially structured and arranged in such a way that channels running essentially parallel to one another are formed. A kind of honeycomb body is formed in the interior of the housing 31 by first stacking smooth and corrugated sheet metal foils 28 and then winding them in an S-shape (or involute shape) and inserting them into the housing 31. Soldering technology is predominantly used to fix the metal foils 28 to the housing 31 or to fasten the metal foils 28 together.

5 shows schematically and in a perspective view an exemplary embodiment of a second catalytic converter 7 and a particle trap 8, which together form a structural unit 19. The unit 19 is also characterized in that the second catalytic converter 7 and the particle trap 8 are arranged in a common casing tube 34. In the variant shown, the second catalytic converter 7 and the particle trap 8 are formed by a body 20 which comprises a plurality of sheet metal foils 28 which are at least partially structured such that channels 29 through which a fluid can flow are formed. This also means, for example, that metallic honeycomb bodies of a special design, whose general design is already known, can be used as such a unit 19.

A distinction is made primarily between two typical designs for metallic honeycomb bodies. An earlier design, for which the DE 29 02 776 AI typical examples shows, is the spiral design, in which essentially a smooth and a corrugated sheet metal layer are superimposed and wound spirally, as is also shown in Fig. 5. In another design, the honeycomb body is built up from a multiplicity of alternatingly arranged smooth and corrugated or differently corrugated sheet metal layers, the sheet metal layers initially forming one or more stacks which are intertwined with one another. The ends of all sheet metal layers come to the outside and can be connected to a housing or casing tube, which creates numerous connections that increase the durability of the honeycomb body. Typical examples of these designs are described in EP 0 245 737 B1 or WO 90/03220. It has also been known for a long time to provide the sheet metal layers with additional structures in order to influence the flow and / or to achieve cross-mixing between the individual flow channels. Typical examples of such configurations are WO 91/01178 and WO 91/01807. and WO 90/08249. Finally, there are also honeycomb bodies in a conical design, possibly also with additional structures for influencing the flow. Such a honeycomb body is described, for example, in WO 97/49905. In addition, it is also known to leave a recess in a honeycomb body for a sensor, in particular for accommodating a lambda probe. An example of this is described in DE 88 16 154 Ul.

The body 20 has a catalytically active coating 21 on the gas inlet side, which is shown on the left in FIG. 5. This catalytically active coating 21 in conjunction with the second contact surface 18, which is partly formed by the catalytic coating 21, ensure an effective conversion of the amounts of reducing agent, generating thermal energy that the entire body 20 or the exhaust gas contained therein significantly increased, for example to temperatures above 600 ° C. The sheet metal foils 28 shown here are provided with a thickness 35 which is in the range from 0.02 to 0.11 mm. FIG. 6 shows an embodiment of a particle trap 8, such as may be present in the assembly 19 shown in FIG. 5. The sheet metal foil is referred to here as corrugated sheet 36, since this corrugated sheet 36 has additional structures for collecting solid components in the exhaust gas flow. In principle, however, the sheet metal foil 29 can also be the corrugated layer 36 at the same time. The arrows represent the flow direction 4 in FIG. 6 and illustrate which flow paths the exhaust gas, in which particles 22 are contained, can take. At least in the partial area of the body 20, which represents the particle trap 8, a fiber layer 37 is arranged in the direct vicinity of the corrugated layer 36, the pores 38 have for receiving the particles 22. The corrugated layer 36 forms a plurality of channels 29 which enables the exhaust gas to flow freely through the particle trap 20 (the principle: “open filter”). In order to influence the flow, the corrugated layer 36 has guide surfaces 40 which are at least partially delimited by openings 39. Through the openings 39, adjacent channels 29 are connected to one another , so that an exchange of partial gas flows is made possible in adjacent channels 29. The guide surfaces 40 form calming points 41 and swirling points 42, which ensure that the particles 22 are directed on the one hand towards the fiber layer 37 and on the other hand can collect in partial areas until the Regeneration takes place.

The device described here or the method explained here allows simple regeneration of a particle filter with fuel, even if further components or exhaust gas cleaning components are positioned in the flow path of the fuel to the particle trap or the oxidation catalytic converter positioned directly in front of it. The proposed method is particularly effective in connection with exhaust systems that have an exhaust gas turbocharger. LIST OF REFERENCE NUMBERS

exhaust system

gas flow

pollutant

flow direction

First catalytic converter

mixer

Second catalytic converter

particulate trap

injection

fuel

combustion chamber

Internal combustion engine

exhaust port

supply

Reducing agent reservoir

Control unit

First contact area

Second contact area

unit

body

coating

particle

reducing agent

cylinder

Partial volume flow

exhaust pipe

3-way catalytic converter

metal sheets channel

collar

casing

piston

Valve

casing pipe

thickness

Well location

fiber layer

pore

opening

baffle

calming place

Verwirbelungsstelle

distance

distance

Claims

claims 1. Exhaust system (1) for cleaning a gas stream (2) with pollutants (3) in the flow direction (4) of the gas stream (2) through the exhaust system (1) at least means for supplying a reducing agent, a first catalytic converter ( 5) and a particle trap (8), wherein at least one further exhaust gas cleaning component and / or a distance of at least 0.5 meters is provided between the first catalytic converter (5) and the particle trap (8), characterized in that a mixer (6 ) and a second catalytic converter (7) of the particle trap (8) are placed directly in front. 2. Exhaust system (1) according to claim 1, characterized in that the mixer (6) is a turbocharger. 3. Exhaust system (1) according to claim 1 or 2, characterized in that the means. for supplying the reducing agent is at least one injection nozzle (9) for providing fuel (10) in the combustion chamber (11) of a mobile internal combustion engine (12). 4. Exhaust system (1) according to claim 3, characterized in that the injection nozzle (9) is arranged so that the fuel (10) in an outlet channel (13) of the internal combustion engine (12) can be introduced. 5. Exhaust system (1) according to one of the preceding claims, characterized in that at least one separate feed line (14) is provided in an outlet channel (13) of the internal combustion engine (12) and / or the exhaust system (1). 6. Exhaust system (1) according to one of the preceding claims, characterized in that the means for supplying a reducing agent with a reducing agent reservoir (15) and a control unit (16) are connected so that an intermittent supply of reducing agent can be carried out. 7. Exhaust system (1) according to one of the preceding claims, characterized in that the first catalytic converter (5) has a first contact surface (17) promoting the oxidation of at least one pollutant (3) contained in the gas stream (2). 8. Exhaust system (1) according to one of the preceding claims, characterized in that the second catalytic converter (7) has a second contact surface (18) promoting the oxidation of at least one pollutant (3) contained in the gas stream (2). 9. Exhaust system (1) according to one of the preceding claims, characterized in that the second catalytic converter (7) and the particle trap (8) constitute a structural unit (9). 10. Exhaust system (1) according to claim 9, characterized in that the second catalytic converter (7) and the particle trap (8) are formed with a body (20) through which a fluid can flow, which in the direction of flow (4) is initially a catalytically active one Coating (21) and subsequently means for attaching particles (22). 11. A method for regenerating a particle trap (8) which is arranged in the exhaust system (1), the exhaust system (1) in the flow direction (4) of a gas stream (2) at least a first catalytic converter (5), a turbocharger, and a second Catalytic converter (7) and the particle trap (8), in which a reducing agent (23) upstream of the turbocharger Carrying out a regeneration process of the particle trap (8) into the exhaust system (1). 12. The method according to claim 11, wherein the ReduMonsrittel supply is intermittent. 13. The method according to claim 11 or 12, in which the reducing agent is supplied by means of at least one injection nozzle (9), fuel (10) being introduced into a combustion chamber (11) of a mobile internal combustion engine (12). 14. The method according to claim 13, wherein a subsequent injection of the fuel (10) into the combustion chamber (11) takes place, so that unburned partial volume flows (25) of the fuel (10) get into an outlet channel (13) of the internal combustion engine (12) , 15. The method according to claim 13 or 14, wherein the internal combustion engine (12) has a plurality of cylinders (24) me each with a combustion chamber (23), in which the injection of the reducing agent into the cylinders (24) takes place alternately. 16. The method as claimed in one of claims 11 to 15, in which the triggering time for an injection of the reducing agent is dependent on a detected and / or calculated parameter which characterizes the functionality of the particle trap (8). 17. The method according to any one of claims 11 to 16, wherein the location of the injection of the reducing agent is selected depending on a detected and / or calculated parameter which characterizes the temperature of the gas stream (2) in a partial area of the exhaust system (1).