Exhaust gas purification device for an internal combustion engine and method for operating an exhaust gas purification device

Abstract

Exhaust gas purification device (1) for an internal combustion engine (2), comprising an exhaust gas line (3) for guiding an exhaust gas flow, a first exhaust gas catalyst (5) arranged in the exhaust gas line (3), and a second exhaust gas catalyst (6) arranged downstream of the first exhaust gas catalyst (5) in the exhaust gas line (3) with respect to the direction of the exhaust gas flow, wherein a reducing agent can be introduced into the exhaust gas line (3) at an injection point (9) between the first exhaust gas catalyst (5) and the second exhaust gas catalyst (6), wherein a secondary line (11) branches off from the exhaust gas line (3) at a withdrawal point (12) spaced apart from the injection point (9) and opens into the exhaust gas line (3) at the injection point (9), wherein the reducing agent can be introduced into the secondary line (11), characterized in that the secondary line (11) is at least partially enclosed by a catalyst body (7) of the first exhaust gas catalyst. (5) proceeds.

Description

The invention relates to an exhaust gas purification device for an internal combustion engine, having an exhaust line for guiding an exhaust gas flow, a first exhaust gas catalytic converter arranged in the exhaust line and a second exhaust gas catalytic converter arranged in the exhaust line downstream of the first exhaust gas catalytic converter with respect to a flow direction of the exhaust gas flow, wherein a reducing agent can be introduced into the exhaust line at an introduction point in terms of flow between the first exhaust gas catalytic converter and the second exhaust gas catalytic converter, wherein a bypass line branches off from the exhaust line at an extraction point spaced apart from the introduction point and opens into the exhaust line at the introduction point, wherein the reducing agent can be introduced into the bypass line. The invention further relates to a method for operating an exhaust gas purification device.The prior art discloses, for example, the publication DE 102 06 028 A1. This relates to a method and an apparatus for generating ammonia and then feeding it as reducing agent into a nitrogen oxides contained therein, resulting from an exhaust gas stream resulting from a combustion process of an engine, a gas turbine or a burner, for the selective catalytic reduction. The device according to the invention is designed such that the method according to the invention can proceed as follows. Dry urea from a stock is fed in controlled quantity to a reactor and split therein by flash thermolysis into ammonia and isocyanic acid. The resulting gas mixture is then immediately after-treated catalytically in the presence of water in such a way that the isocyanic acid resulting from the flash hydrolysis is also converted into ammonia and carbon dioxide by quantitative hydrolysis.Furthermore, the prior art shows the publication DE 10 2005 029 835 A1. This relates to an exhaust gas treatment device having an SCR catalyst through which the exhaust gas of an internal combustion engine flows and having a feed device for feeding a gaseous reducing agent into the exhaust gas, which opens upstream of the SCR catalyst into an exhaust gas duct through which the exhaust gas flows. It is provided that the exhaust gas duct has a cross-sectional constriction at the opening of the feed device.Furthermore, the documents DE 10 2007 061 005 A1, DE 10 2004 036 036 A1 and DE 10 2008 038 720 A1 are known from the prior art.It is the object of the invention to propose an exhaust gas purification device for an internal combustion engine, which has advantages over known exhaust gas purification devices, in particular realizes an effective treatment of the reducing agent and an effective mixing of the reducing agent with the exhaust gas stream.This is achieved according to the invention with an exhaust gas purification device for an internal combustion engine having the features of claim 1. It is provided here that the bypass line runs at least in regions through a catalytic converter body of the first exhaust gas catalytic converter.The exhaust gas purification device serves for purifying exhaust gas which is generated by the internal combustion engine during operation of the internal combustion engine. The exhaust gas flows in this respect in the form of the exhaust gas flow through the exhaust gas purification device or the exhaust gas line. For the purification of the exhaust gas, the exhaust gas purification device has the first exhaust gas catalytic converter and the second exhaust gas catalytic converter, which are arranged one behind the other in terms of flow in the exhaust line or are connected to one another in terms of flow via the exhaust line.Finally, the exhaust gas generated by the internal combustion engine or the exhaust gas flow therefore initially flows through the first exhaust gas catalytic converter and subsequently through the second exhaust gas catalytic converter. Downstream of the second exhaust catalytic converter, the exhaust gas flow can be discharged from the exhaust gas purification device, in particular in the direction of an external environment. Both the first exhaust gas catalytic converter and the second exhaust gas catalytic converter each serve to catalytically promote a chemical reaction, within the scope of which at least one pollutant contained in the exhaust gas stream is degraded, for example reduced or oxidized.The first exhaust gas catalytic converter can in principle be configured as desired, but is preferably present in the form of an oxidation catalytic converter. The oxidation catalyst oxidizes carbon monoxide and unburned hydrocarbons. The second exhaust gas catalytic converter is in the form of an SCR catalytic converter, which serves for carrying out a selective catalytic reduction. In particular, nitrogen oxides contained in the exhaust gas flow are reduced in the second exhaust gas catalytic converter.A reducing agent is required for carrying out the selective catalytic reduction. This is therefore introduced into the exhaust gas stream or into the exhaust gas line during operation of the exhaust gas purification device or of the internal combustion engine downstream of the second exhaust gas catalytic converter. The introduction takes place at the introduction point. Ammonia or a solution serving for the provision of ammonia are used as reducing agents, for example. This solution is, for example, a urea solution, wherein the urea contained therein is converted into ammonia and carbon dioxide in the exhaust gas purification device by photolysis and subsequent hydrolysis. Isocyanic acid can be obtained as intermediate product. The hemolysis and / or hydrolysis of the solution are carried out in the course of a treatment of the reducing agent.In summary, it can be provided in this respect that the ammonia is introduced directly in the form of the reducing agent or alternatively in the form of the solution, in particular the urea solution. By introducing the reducing agent upstream into the exhaust line, the reducing agent is entrained by the exhaust gas flow in the direction of the second exhaust gas flow catalytic converter, wherein mixing with the exhaust gas flow takes place. The better the mixing of the reducing agent with the exhaust gas flow, the more efficiently the second exhaust gas catalytic converter operates.The efficiency of the mixing of the reducing agent with the exhaust gas flow depends in particular on the length of the flow path between the introduction point and the second exhaust gas catalytic converter. For this reason, it is expedient to choose the available route, which can also be referred to as a mixing route, as large as possible. However, this is counteracted by a limited installation space and / or the exhaust gas temperature in the second exhaust gas catalytic converter necessary for carrying out the selective catalytic reduction.For this reason, the secondary line is provided, which branches off at the extraction point of the exhaust line and opens back into it at the introduction point. The exhaust gas flow is thus divided at the extraction point into two partial exhaust gas flows, namely into a main exhaust gas flow in the exhaust gas line and a secondary exhaust gas flow in the secondary line. At the introduction point, the two partial exhaust gas streams are merged again by the secondary exhaust gas stream being fed to the main exhaust gas stream.It is now provided that the reducing agent can be introduced into the bypass line or the exhaust gas bypass flow. In other words, the reducing agent is introduced at least temporarily into the bypass line or into the exhaust gas bypass flow, namely directly. The reducing agent is entrained by the exhaust gas bypass flow as far as the introduction point and fed to the main exhaust gas flow together with the exhaust gas bypass flow.The introduction of the reducing agent into the bypass line has the advantage that, on the one hand, the mixing section available for mixing the reducing agent with the exhaust gas flow between the introduction point or an injection device for injecting the reducing agent into the bypass line, on the one hand, and the second exhaust gas catalytic converter, on the other hand, is greater at a given fluidic distance between the two exhaust gas catalytic converters than when injecting the reducing agent downstream of the first exhaust gas catalytic converter, and that, on the other hand, the processing of the reducing agent in the bypass line can be carried out more easily. The latter is due to a lower heating expenditure.A further development of the invention provides that the exhaust gas purification device is designed to branch off an exhaust gas bypass from the exhaust gas stream by means of the bypass line and to introduce the reducing agent together with the exhaust gas bypass into the exhaust gas line at the introduction point. This has already been pointed out above. At the extraction point, the exhaust gas flow is divided into the main exhaust gas flow and the secondary exhaust gas flow. The main exhaust gas flow flows through the exhaust line starting from the extraction point, and the secondary exhaust gas flow flows through the secondary line. In other words, the main exhaust gas stream and the secondary exhaust gas stream are carried in parallel to one another in terms of flow, for which purpose the exhaust gas line and the secondary line are arranged in parallel to one another in terms of flow.The reducing agent is now introduced or injected at least temporarily into the bypass line. It is entrained by the secondary exhaust gas flow flowing through the bypass line in the direction of the introduction point and enters the exhaust line or exits the bypass line together with the secondary exhaust gas flow at the introduction point. The processing of the reducing agent can now already take place at least partially in the auxiliary line, so that at the introduction point at least partially or already completely processed reducing agent is introduced into the exhaust line. In this respect, a comparatively large mixing section up to the second exhaust gas catalytic converter is available for the already processed reducing agent, whereby the efficiency of the exhaust gas purification device is significantly increased.Within the scope of a preferred further embodiment of the invention, it can be provided that the withdrawal point is arranged downstream of the first exhaust gas catalytic converter. The secondary line in this respect only branches off from the exhaust line downstream of the first exhaust gas catalytic converter in terms of flow. The exhaust gas supplied to the bypass line or the exhaust gas bypass flow supplied to the bypass line has already flowed through the first exhaust gas catalytic converter in this respect, so that a portion of the pollutants contained in the exhaust gas is already oxidized or reduced. In other words, the waste gas bypass is removed from the exhaust gas line there, wherein the reducing agent is introduced into exhaust gas purification devices known from the prior art. In contrast to these, the reducing agent introduced into the bypass initially flows through the bypass line together with the secondary exhaust gas flow before it enters the exhaust gas line from the latter, so that-as already explained-a particularly effective treatment of the reducing agent and / or an efficient mixing takes place.A preferred further embodiment of the invention provides that the withdrawal point is arranged fluidically between the first exhaust gas catalytic converter and the second exhaust gas catalytic converter. In principle, the extraction point can be present at any desired point on the exhaust line, that is to say also upstream of the first exhaust gas catalytic converter. However, it is preferably situated at least downstream of the first exhaust gas catalytic converter and upstream of the second exhaust gas catalytic converter, so that the secondary exhaust gas flow has already flowed through the first exhaust gas catalytic converter, but not through the second exhaust gas catalytic converter. This achieves a particularly effective treatment and mixing of the reducing agent.A further embodiment of the invention provides that the auxiliary line is heatable. To process the reducing agent, i.e. to carry out the photolysis and / or the hydrolysis, the reducing agent must have a specific temperature. At least temporarily, it may happen that the exhaust gas temperature of the exhaust gas at the extraction point has an exhaust gas temperature which is not sufficient for processing the reducing agent. For this reason, additional heat is supplied to the bypass line and therefore to the secondary exhaust gas flow, namely by means of a heating device.The heating device is present, for example, in the form of an electrical heating device, so that in other words the auxiliary line can be electrically heated. The at least temporary heating of the bypass line enables a particularly efficient treatment of the reducing agent with a comparatively low energy input, because only the secondary exhaust gas flow and not approximately the entire exhaust gas flow has to be brought to the temperature required for treatment.A preferred further embodiment of the invention provides that an injection device for injecting the reducing agent opens into the auxiliary line, wherein the auxiliary line has a first part line and a second part line, and wherein the extraction point is fluidically connected to the injection device via the first part line and the injection device is fluidically connected to the introduction point via the second part line. The secondary line is thus at least notionally divided into the first sub-line and the second sub-line. Preferably, the two partial lines adjoin one another directly or merge directly into one another.The injection device opens into the secondary line at that point at which the two partial lines merge into one another. Accordingly, the injection device is arranged on the end of the first sub-line facing the second sub-line and on the end of the second sub-line facing the first sub-line. The first partial line extends from the extraction point to the injection device and the second partial line extends from the injection device to the introduction point. In other words, the extraction point and the introduction point are connected to one another in terms of flow via the two partial lines.For example, it is provided that the first sub-line is heatable, preferably electrically heatable. The first partial line particularly preferably runs at least partially outside the exhaust line. Starting from the extraction point which is present within the exhaust line, the first partial line therefore runs out of the exhaust line. The injection device is also preferably arranged outside the exhaust line. The second partial line is, for example, likewise partially present outside the exhaust line. Starting from the injection device, it enters the exhaust line and extends therein as far as the introduction point.Preferably, the part of the second partial line present in the exhaust line is larger than the part of the first partial line present in the exhaust line. This means that at least 50%, at least 60%, at least 70%, at least 75%, at least 90% of the first partial line is present outside the exhaust line. In contrast, at least 50%, at least 60%, at least 70%, at least 75%, at least 80% or at least 90% of the second partial line are present in the exhaust line. Such a configuration enables the injection device to be arranged at a distance from the exhaust line and, on the other hand, ensures that the heat taken from the exhaust gas stream acts on the second partial line, so that the secondary exhaust gas stream is kept at a temperature which is sufficient for preparing the reducing agent.A further embodiment of the invention provides that the auxiliary line branches off from the exhaust line in a manner offset in the radial direction with respect to a longitudinal central axis of the exhaust line and opens into the exhaust line. The auxiliary line protrudes with its opposite ends into the exhaust line. However, the two ends are offset from each other in the radial direction. For example, the introduction point is located further inward in the radial direction than the removal point. Particularly preferably, the introduction point is arranged centrally with respect to the longitudinal central axis of the exhaust line, whereas the removal point is located further outwards in the radial direction.For example, the exhaust line reaches through a wall of the exhaust line at the extraction point and terminates flush with the latter. However, it is preferably provided that the exhaust line also engages into the exhaust line on the side of the extraction point, so that the extraction point is located at a distance from the wall of the exhaust line in the radial direction and therefore preferably between the wall and the introduction point in the radial direction.It is particularly preferred that the bypass line is formed on the side of the extraction point in such a way that the secondary exhaust gas flow is forced into it due to its flow speed. On the side of the introduction point, on the other hand, the bypass line is oriented in such a way that a main flow direction of the main exhaust gas flow and a main flow direction of the bypass exhaust gas flow are identical, so that the bypass exhaust gas flow can emerge unimpeded from the bypass lines into the exhaust line.It can be the case that the extraction point and the introduction point are arranged identically in the axial direction with respect to the longitudinal central axis of the exhaust line. However, it can also be provided that the introduction point is arranged downstream of the removal point in order to prevent reducing agent from entering the auxiliary line from the exhaust line. The described arrangement of the bypass line enables good treatment and mixing of the reducing agent.A further refinement of the invention provides that the bypass line runs at least in regions through a catalytic converter body of the first exhaust-gas catalytic converter. The bypass line thus enters the catalyst body at a first point, for example, and exits the catalyst body at a second point. Particularly preferably, the secondary line passes completely through the first exhaust gas catalytic converter or its catalytic converter body in one direction, in particular in the direction of its longitudinal central axis or the longitudinal central axis of the exhaust gas line. For example, the bypass line runs completely straight in the first exhaust gas catalytic converter or its catalytic converter body.The catalyst body is preferably understood to mean an element of the first exhaust gas catalyst which is itself catalytically active or has a catalytically active coating. The catalyst body is present, for example, in the form of a ceramic body, in particular a ceramic honeycomb body. The arrangement of the bypass line in the catalyst body of the first exhaust gas catalyst has the advantage that a heat input from the catalyst body into the bypass line takes place, so that a sufficient temperature for preparing the reducing agent is ensured.Finally, in the context of a further embodiment of the invention, it may be provided that the first partial line runs at least in regions outside and the second partial line runs at least in regions inside the catalytic converter body of the first exhaust catalytic converter. Particularly preferably, the first partial line is present completely outside the catalyst body, whereas the second partial line is preferably predominantly arranged in the catalyst body. This is understood to mean that at least 50%, at least 60%, at least 70%, or at least 75% of the second branch line are present within the catalyst body. Particularly preferably, the first partial line ends together with the catalytic converter body or the first exhaust gas catalytic converter. This means that the already at least partially processed reducing agent is introduced into the exhaust line directly downstream of the catalyst body, so that a very long mixing section is achieved.The invention further relates to a method for operating an exhaust gas purification device for an internal combustion engine, in particular an exhaust gas purification device according to the statements within the scope of this description, wherein the exhaust gas purification device has an exhaust line for guiding an exhaust gas flow, a first exhaust gas catalytic converter arranged in the exhaust line and a second exhaust gas catalytic converter arranged downstream of the first exhaust gas catalytic converter in the exhaust line with respect to a flow direction of the exhaust gas flow, wherein a reducing agent can be introduced into the exhaust line at an introduction point in terms of flow between the first exhaust gas catalytic converter and the second exhaust gas catalytic converter.In this case, it is provided that a bypass line branches off from the exhaust line at a removal point spaced apart from the introduction point and opens into the exhaust line at the introduction point, wherein the reducing agent can be introduced into the bypass line, such that an exhaust gas substream is removed at least temporarily from the exhaust gas stream, the reducing agent is injected into the exhaust gas substream and the reducing agent is introduced into the exhaust line together with the exhaust gas substream formed by part of the exhaust gas stream at the introduction point. Furthermore, it is provided that the bypass line runs at least in regions through a catalytic converter body of the first exhaust catalytic converter.The advantages of such a procedure or such a configuration of the exhaust gas purification device have already been discussed. Both the exhaust gas purification device and the method for operating it can be further developed according to the statements in the context of this slurry description, so that reference is made to this in this respect.The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without any restriction of the invention being effected. The only one is shown hereFIG. is a schematic illustration of an exhaust gas purification device for an internal combustion engine.The FIGURE shows a schematic illustration of an exhaust gas purification device 1 for an internal combustion engine 2 which is merely indicated here. the exhaust gas which arises during operation of the internal combustion engine 2 is fed to the exhaust gas purification device 1 in the form of an exhaust gas stream. The exhaust gas purification device 1 has an exhaust gas line 3 through which the exhaust gas can flow in the direction of the arrows 4 or through which the exhaust gas flows during operation of the internal combustion engine 2.A first exhaust gas catalytic converter 5 and a second exhaust gas catalytic converter 6, each having a catalytic converter body 7 or 8, are arranged in the exhaust line 3. The exhaust gas catalytic converter 6 is arranged downstream of the first exhaust gas catalytic converter 5 with respect to a main flow direction of the exhaust gas, which is indicated by the arrows 4. The first exhaust gas catalytic converter 5 is present, for example, in the form of an oxidation catalytic converter, whereas the second exhaust gas catalytic converter 6 is in each case designed as an SCR catalytic converter for carrying out a selective catalytic reduction.In order to carry out the selective catalytic reduction with the aid of the second exhaust gas catalytic converter 6, a reducing agent is introduced into the exhaust line 3 at an introduction point 9. This is indicated by the arrows 10. In order to improve a treatment of the reducing agent and to enlarge the mixing section present between the introduction point 9 and the second exhaust gas catalytic converter 6, a secondary line 11 is realized, which branches off from the exhaust gas line 3 at a removal point 12 and opens into it at the introduction point 9. In other words, a part of the exhaust gas flow is removed from the exhaust line 3 by means of the secondary line 11 at the removal point 12, flows through the secondary line 11 in the form of an exhaust gas secondary flow and exits again into the exhaust line 3 at the introduction point 9.For this purpose, the auxiliary line 11 is designed and / or arranged in such a way that the exhaust gas flow flowing through the exhaust line 3 brings about a flow of exhaust gas or in the exhaust gas bypass through the auxiliary line 11. For this purpose, the bypass line 11 is oriented on the side of the extraction point 12 in such a way that a dynamic pressure caused by the bypass line 11 causes the secondary flow of exhaust gas through the bypass line 11. For this purpose, the secondary line 11 is open at the extraction point 12 counter to the main flow direction of the exhaust gas flow in the exhaust gas line 3. At the introduction point 9, on the other hand, the secondary line 11 is opened in the direction of the main flow direction of the exhaust gas flow through the exhaust line 3, so that the exhaust gas secondary flow can emerge unimpeded from the secondary line 11 into the exhaust line 3.An injection device 13 opens into the auxiliary line 11, which is provided and designed for injecting reducing agent into the auxiliary line 11. The reducing agent is indicated by sprays 14. The reducing agent introduced into the auxiliary line 11 is processed in the auxiliary line 11 at a sufficiently high exhaust gas temperature and is thus present in the auxiliary line 11 in the form of processed reducing agent 15, which exits from the auxiliary line 11 together with the exhaust gas bypass into the exhaust line 3 at the introduction point 9.The secondary line 11 has a first partial line 16 and a second partial line 17. The first partial line 16 extends in the flow direction of the secondary exhaust gas flow from the extraction point 12 as far as the injection device 13, the second partial line 17 extends from the injection device 13 as far as the introduction point 9. Particularly preferably, the second partial line 17 extends completely through the first exhaust gas catalytic converter 5 or its catalytic converter body 7, particularly preferably in the direction of a longitudinal central axis of the first exhaust gas catalytic converter 5. For example, for this purpose, the second partial line 17 is arranged continuously straight and / or centrally within the catalytic converter body 7. The auxiliary line 11 is preferably assigned a heating device 18, by means of which the secondary exhaust gas flow in the auxiliary line 11, in particular in the first partial line 16, can be heated. The heating device 18 is preferably in the form of an electrical heating device.The exhaust gas purification device 1 described makes it possible to realize a long mixing path between the introduction point 9 and the second exhaust gas catalytic converter 6. The secondary line 11 is arranged fluidically parallel to the exhaust line 3. Because only a part of the exhaust gas flow is guided through the bypass 11, namely the exhaust gas bypass flow, a smaller amount of heat is required to achieve the exhaust gas temperature necessary for preparing the reducing agent.In addition, due to the effective treatment and / or mixing, an additional mixer between the introduction point 9 and the second exhaust gas catalytic converter 6 can be dispensed with, as a result of which the pressure loss across the exhaust gas purification device 1 falls.

Claims

Exhaust gas purification device (1) for an internal combustion engine (2), having an exhaust line (3) for guiding an exhaust gas flow, a first exhaust gas catalytic converter (5) arranged in the exhaust line (3) and a second exhaust gas catalytic converter (6) arranged in the exhaust line (3) downstream of the first exhaust gas catalytic converter (5) with respect to a flow direction of the exhaust gas flow, wherein a reducing agent can be introduced into the exhaust line (3) at an introduction point (9) in terms of flow between the first exhaust gas catalytic converter (5) and the second exhaust gas catalytic converter (6), wherein a secondary line (11) branches off from the exhaust line (3) at an extraction point (12) spaced apart from the introduction point (9) and opens into the exhaust line (3) at the introduction point (9), wherein the reducing agent can be introduced into the secondary line (11), characterized in that, the auxiliary line (11) runs at least in regions through a catalytic converter body (7) of the first exhaust catalytic converter (5).Exhaust gas purification device according to Claim 1, characterized in that the exhaust gas purification device (1) is designed to branch off an exhaust gas bypass from the exhaust gas stream by means of the bypass line (11) and to introduce the reducing agent into the exhaust gas line (3) together with the exhaust gas bypass at the introduction point (9).Exhaust gas purification device according to one of the preceding claims, characterized in that the extraction point (12) is arranged downstream of the first exhaust gas catalytic converter (5).Exhaust gas purification device according to one of the preceding claims, characterized in that the extraction point (12) is arranged fluidically between the first exhaust gas catalytic converter (5) and the second exhaust gas catalytic converter (6).Exhaust gas purification device according to one of the preceding claims, characterized in that the auxiliary line (11) can be heated.Exhaust gas purification device according to one of the preceding claims, characterized in that an injection device (13) for injecting the reducing agent opens into the secondary line (11), wherein the secondary line (11) has a first partial line (16) and a second partial line (17), and wherein the extraction point (12) is fluidically connected to the injection device (13) via the first partial line (16), and the injection device (13) is fluidically connected to the introduction point (9) via the second partial line (17).Exhaust gas purification device according to one of the preceding claims, characterized in that the secondary line (11) branches off from the exhaust line (3) offset in the radial direction with respect to a longitudinal central axis of the exhaust line (3) and opens into the exhaust line.Exhaust gas purification device according to Claim 6, characterized in that the first part line (16) runs at least in regions outside and the second part line (17) runs at least in regions inside the catalytic converter body (7) of the first exhaust gas catalytic converter (5).Method for operating an exhaust gas device (1) for an internal combustion engine (2), in particular an exhaust gas purification device (1) according to one or more of the preceding claims, wherein the exhaust gas purification device (1) has an exhaust line (3) for guiding an exhaust gas stream, a first exhaust gas catalytic converter (5) arranged in the exhaust line (3) and a second exhaust gas catalytic converter (6) arranged in the exhaust line (3) downstream of the first exhaust gas catalytic converter (5) with respect to a flow direction of the exhaust gas stream, wherein a reducing agent can be introduced into the exhaust line (3) in terms of flow between the first exhaust gas catalytic converter (5) and the second exhaust gas catalytic converter (6), wherein a secondary line (11) branches off from the exhaust line (3) at a removal point (12) spaced apart from the introduction point (9) and opens into the exhaust line (3) at the introduction point (9), wherein the reducing agent can be introduced into the auxiliary line (11), so that at least temporarily a partial exhaust gas stream is taken from the exhaust gas stream, the reducing agent is injected into the partial exhaust gas stream and the reducing agent is introduced together with the partial exhaust gas stream formed by a part of the exhaust gas stream into the exhaust gas line (3) at the introduction point (9), characterized in that the auxiliary line (11) runs at least in regions through a catalyst body (7) of the first exhaust gas catalyst (5).

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