Exhaust aftertreatment system

Abstract

Method for operating an arrangement (1) of an internal combustion engine (2) with an exhaust tract (4) from which at least one exhaust gas recirculation line of a low-pressure exhaust gas recirculation system (9) branches off, and in which an exhaust gas aftertreatment system is arranged, wherein the exhaust gas aftertreatment system comprises at least one first nitrogen oxide storage catalyst (7), at least one second catalytic device (10) arranged downstream of the first nitrogen oxide storage catalyst (7), and at least one particulate filter (8) arranged downstream of the first nitrogen oxide storage catalyst (7), wherein the exhaust gas recirculation line of the low-pressure exhaust gas recirculation system (9) branches off downstream from the first nitrogen oxide storage catalyst (7) and upstream from the second catalytic device (10) and comprises at least one valve (9a) for controlling a mass of recirculated exhaust gas,and comprising at least one temperature sensor in the area of ​​the first nitrogen oxide storage catalyst (7), comprising the steps: , - Operating the internal combustion engine (2) at low or medium load, - Switching to a high-load operating state of the internal combustion engine (2), - Starting a substoichiometric combustion mode of the internal combustion engine (2), - Returning exhaust gas through the exhaust gas recirculation line of the low-pressure exhaust gas recirculation system (9), - Ending the substoichiometric combustion mode and switching to an operating state of the internal combustion engine (2) with low or medium load.

Description

[0001] The invention relates to a method for operating an arrangement of an internal combustion engine with an exhaust gas tract, an exhaust gas recirculation system and at least one first and one second nitrogen oxide storage catalyst, wherein the first nitrogen oxide storage catalyst is arranged within the exhaust gas recirculation circuit.

[0002] Lean NOx storage catalysts (also called NOx storage catalysts, or in English lean NOx traps, LNTs) are used for the temporary adsorption of nitrogen oxides from the exhaust gas of internal combustion engines. They also perform oxidative aftertreatment of carbon monoxide (CO) and hydrocarbons (HC). Nitrogen oxides produced during lean-burn operation of an internal combustion engine can be stored in an LNT; to do this, the LNT oxidizes the nitric oxide (NO) contained in the lean exhaust gas to nitrogen dioxide (NO2) and then stores it in the form of nitrates. Adsorbents used in the coating of the LNT include, for example, barium and / or other oxides.

[0003] Once the storage capacity of the LNT (Low Nitrogen Nitrogen Storage) is exhausted, it must be regenerated. During a regeneration event (purge), rich, substoichiometric exhaust gas conditions are created, for example, by operating the internal combustion engine with a corresponding fuel-air mixture. During this process, the stored nitrogen oxides are desorbed and reduced to nitrogen at catalytically active components of the LNT using the components in the rich exhaust gas (CO, HC). In addition to purges solely for regeneration purposes, the LNT is also regenerated when the exhaust gas becomes substoichiometric, for example, due to a power demand from the internal combustion engine.

[0004] The stored nitrates continue to react in the LNT (Low Nitrogen Transfer Valve) with molecular hydrogen, which is produced under rich exhaust gas conditions by incomplete combustion of the fuel and also by reactions within the LNT, thus also generating ammonia during regeneration. This ammonia can be utilized by storing it downstream in a catalyst for selective catalytic reduction (SCR). The stored ammonia is used in the SCR to reduce nitrogen oxides to nitrogen under lean exhaust gas conditions. To ensure the SCR catalyst has a high storage capacity, it is advantageously installed far enough downstream to achieve optimal operating temperatures. The corresponding temperature range is a function of the specific SCR coating and is known to those skilled in the art. An arrangement of SCR and other exhaust aftertreatment devices with temperature sensors is known from DE 20 2014 103 378 U1.

[0005] The storage capacity of a liquid nitrogen storage (LNT) unit is limited, among other things, by the exhaust gas temperature. Modern LNT units can store nitrogen oxides (NOx) within a temperature range of approximately 250–550°C with varying degrees of efficiency. Furthermore, the storage capacity can be limited by the exhaust gas velocity. When the combustion engine is operated under high load, for example, during acceleration, high exhaust gas temperatures and mass flows are reached, which can exceed the technological limits of the LNT unit. Consequently, the NOx storage efficiency of the LNT unit is significantly reduced due to the gas temperature and velocity. Under these conditions, NOx cannot be stored in the LNT unit.It is possible to counteract the escape of nitrogen oxides under high loads by switching between different combustion modes depending on the engine load, the catalyst fill level, and the exhaust gas temperature. These modes include lean exhaust gas conditions and a rich, substoichiometric exhaust gas condition. Particularly under high load conditions and the resulting high exhaust gas temperatures, the internal combustion engine operates in a rich mixture. Under these conditions, the LNT (Low Nitrogen Nitrogen) no longer acts as a storage catalyst but immediately converts the nitrogen oxides in the exhaust gas to nitrogen with the help of the reducing agents (carbon monoxide and hydrocarbons) also present in the exhaust gas. In this way, nitrogen oxides are advantageously removed from the exhaust gas exiting the internal combustion engine under high load conditions.Furthermore, the fat content in the exhaust gas can be adjusted so that, under these conditions, ammonia is produced at the catalytically active components of the LNT through the reaction of hydrogen with nitrogen oxides, once previously stored oxygen has been removed from the LNT. In an advantageous embodiment, this ammonia can be used downstream for further reduction of the nitrogen oxides with the aid of a second LNT or SCR catalyst. An arrangement with two sequentially arranged LNTs, in which the second LNT is located downstream of a branch of a low-pressure exhaust gas recirculation line, is disclosed by way of example in German patent application DE 10 2011 101 079 A1. An arrangement of the second LNT with an SCR is also possible (DE 10 2015 206 838 A1, GB 2 511 537 A). In DE 10 2014 200 092 A1 it is disclosed that a corresponding LNT can be combined with an SCR.

[0006] The task is to optimize exhaust aftertreatment.

[0007] This problem is solved by a method having the features of the main claim. Further advantageous embodiments and configurations of the invention will become apparent from the dependent and subclaims, the figures, and the exemplary embodiments.

[0008] The method is carried out with an arrangement of an internal combustion engine with an exhaust tract from which at least one exhaust gas recirculation line of a low-pressure exhaust gas recirculation system (LP-EGR) branches off, and in which an exhaust gas aftertreatment system is arranged, wherein the exhaust gas aftertreatment system comprises: - at least one first nitrogen oxide storage catalyst, - at least one second catalytic device located downstream of the first nitrogen oxide storage catalyst, - at least one particulate filter located downstream of the first nitrogen oxide storage catalyst, wherein the exhaust gas recirculation line branches off downstream from the first nitrogen oxide storage catalyst and upstream from the second catalytic device and includes at least one valve for controlling the mass of the recirculated exhaust gas, and which includes at least one temperature sensor in the area of ​​the first nitrogen oxide storage catalyst.

[0009] This arrangement advantageously enables the control of nitrogen oxide emissions under all operating conditions of the internal combustion engine. The high exhaust gas temperature generated under high load can be detected by the temperature sensor, which is advantageously located in the area of ​​the low-temperature exhaust gas recirculation (LNT), and transmitted to the control unit, or determined by a stored temperature model. Furthermore, a high torque demand can also be detected and transmitted to the control unit in a manner known to those skilled in the art. In addition, the low-pressure exhaust gas recirculation (LP-EGR) system enables advantageous control of nitrogen oxide emissions according to the current operating conditions by recirculating exhaust gas.

[0010] By arranging the particulate filter within the low-pressure EGR circuit, the recirculated exhaust gas is cleaned of soot, which has a positive effect on the compressor's service life. Furthermore, fouling (deposits from exhaust particles) of a cooler located in the low-pressure EGR line is prevented, as fouling would impair heat transfer. The cooler thus maintains a high efficiency.

[0011] The design of the second catalytic device of the arrangement as a second nitrogen oxide storage catalyst is particularly preferred. By arranging the second LNT downstream of the exhaust gas recirculation line branch, the storage capacity of the second LNT is utilized more effectively because the exhaust gas volume flow and the space velocity are reduced at this position compared to the first LNT. Furthermore, the amount of reducing agent required during a purge is also reduced.

[0012] Preferably, in this arrangement, the first nitrogen oxide storage catalyst is positioned in close proximity to the internal combustion engine such that it heats up quickly to its operating temperature during cold starts, while the second nitrogen oxide storage catalyst is positioned further away from the internal combustion engine such that even exhaust gas temperatures occurring under high load enable effective storage of nitrogen oxides. This arrangement thus fully utilizes the advantages of the first LNT being located close to the engine and the second LNT being located further away, downstream of the low-pressure EGR circuit.

[0013] Preferably, the second nitrogen oxide storage catalyst in the arrangement has a catalytically active coating that differs from the catalytically active coating of the first nitrogen oxide storage catalyst. Particularly preferably, the catalytically active coating of the second nitrogen oxide storage catalyst is optimized for nitrogen oxide conversion at high temperatures relative to the catalytically active coating of the first nitrogen oxide storage catalyst.

[0014] In an alternative, also preferred embodiment of the arrangement, the second catalytic device is a catalyst for selective catalytic reduction (SCR catalyst).

[0015] A second LNT and an SCR catalyst are also preferably arranged downstream of the branch of the low-pressure exhaust gas recirculation line in the exhaust tract. The SCR catalyst allows ammonia, which can be generated in the LNT under certain circumstances during a purge, to be used for the reduction of nitrogen oxides, thereby advantageously and more efficiently controlling nitrogen oxide reduction.

[0016] Furthermore, it is preferred if the arrangement additionally includes a throttle valve located downstream of the second catalytic unit. The throttle valve can advantageously be used to control the exhaust gas flow, particularly with regard to low-pressure exhaust gas recirculation (LPEG).

[0017] Furthermore, the arrangement advantageously includes an exhaust gas recirculation line of a high-pressure exhaust gas recirculation (HP-EGR) system, which branches off from the exhaust tract upstream of the first nitrogen oxide storage catalyst. Under certain operating conditions, the use of HP-EGR can be advantageous as an alternative or in addition to low-pressure EGR.

[0018] During substoichiometric operation or a purge, ammonia can be produced in the low-temperature exhaust gas recirculation (LNT) unit. If this is undesirable, for example, for use in a catalyst for selective catalytic reduction (SCR), recirculation into the combustion chamber would lead to oxidation of the ammonia and thus to the undesired production of additional nitrogen oxides (NOx). In this case, low-temperature exhaust gas recirculation (LTCR) operation can be stopped and high-temperature exhaust gas recirculation (HPGR) can be used. Ideally, however, the amount of reducing agent supplied is adjusted so that no undesired ammonia production occurs.

[0019] Preferably, the particle filter assembly has a catalytically active coating. Particularly preferably, the catalytically active coating is designed for selective catalytic reduction.

[0020] The invention relates to a method for operating an arrangement of an internal combustion engine with an exhaust tract from which at least one exhaust gas recirculation line of a low-pressure exhaust gas recirculation system branches off, and in which at least one first nitrogen oxide storage catalyst and a particulate filter are arranged upstream of the branch of the exhaust gas recirculation line, at least one temperature sensor is arranged in the spatial area of ​​the first nitrogen oxide storage catalyst, and at least one second catalytic device is arranged downstream of the branch of the exhaust gas recirculation line, comprising the steps: - Operating the internal combustion engine at low or medium load, - Switching to a high-load operating state of the internal combustion engine, - Starting a rich combustion mode of the internal combustion engine, - Returning exhaust gas through the exhaust gas recirculation line of the low-pressure exhaust gas recirculation system, - Ending the rich operating mode and switching to a low or medium load operating state of the internal combustion engine.

[0021] The method according to the invention is advantageous because the emission of nitrogen oxides can be controlled under all operating conditions of the internal combustion engine. The high exhaust gas temperature generated under high load is detected by the temperature sensor, which is advantageously located in the area of ​​the LNT (low-temperature regulator), and transmitted to a control unit or determined by a stored temperature model. Furthermore, a high torque demand is also detected and transmitted to the control unit in a manner known to those skilled in the art. The control unit can then initiate substoichiometric operation of the internal combustion engine, if it is not already occurring, thereby generating a slightly substoichiometric "rich" exhaust gas mixture with a lambda value of < 1.

[0022] Furthermore, fouling of the cooler in the low-pressure exhaust gas recirculation (EGR) line and the intake manifold is prevented by the fact that the first nitrogen oxide storage catalyst almost completely converts the hydrocarbons contained in the exhaust gas. In particular, the substoichiometric operation of the internal combustion engine provides a nearly inert gas downstream of the first LNT (low-pressure EGR), which is therefore ideally suited for recirculation into the combustion chamber. This allows a larger volume of exhaust gas to be recirculated compared to a high-pressure EGR, thereby reducing the oxygen content of the exhaust gas downstream of the internal combustion engine and thus requiring less fuel to reach the substoichiometric state. Consequently, a low-pressure EGR reduces the fuel consumption disadvantage of achieving the substoichiometric state compared to a high-pressure EGR.Furthermore, the required substoichiometric conditions can be achieved quickly and effectively by using the ND-EGR, since in substoichiometric operation or during a purge there is no recirculation of fuel added by post-injection into the internal combustion engine without an intermediate LNT.

[0023] Furthermore, the recirculation of exhaust gas enables advantageous control of nitrogen oxide emissions according to the current operating conditions. A particularly preferred embodiment of the inventive method is therefore one in which the amount of recirculated exhaust gas is regulated to control the regeneration of the first nitrogen oxide storage catalyst.

[0024] The invention is explained in more detail using the figures. They show: Fig. 1 A schematic representation of one embodiment of the arrangement. Fig. 2 a schematic representation of another embodiment of the arrangement. Fig. 3 a schematic representation of another embodiment of the arrangement. Fig. 4 a flowchart of an embodiment of the method according to the invention. Fig. 5 a diagram showing the reduction of nitrogen oxides over time during substoichiometric operation.

[0025] An arrangement 1 has, in one embodiment according to the illustration of Fig. Figure 1 shows an internal combustion engine 2. The internal combustion engine 2 can be a compression-ignition or spark-ignition engine. The internal combustion engine has at least one cylinder (not shown), but can also have a different number of cylinders, e.g., two, three, four, or more.

[0026] The internal combustion engine 2 is connected to an intake manifold 3 and an exhaust manifold 4. A turbine 5 of a turbocharger is located in the exhaust manifold 4. The turbine 5 is connected via a shaft to a compressor 6, which is located in the intake manifold 3. A cooling device 6a is located downstream of the compressor in the intake manifold 4. Alternatively, there may be no turbocharger, and therefore no turbine or compressor.

[0027] Downstream of turbine 5, a first nitrogen oxide storage catalyst (NOC) 7 is arranged in the exhaust tract 4. Downstream of the first NOC 7, a particulate filter 8 is arranged. If the internal combustion engine 2 is a compression-ignition engine, the particulate filter 8 is a diesel particulate filter. Ideally, the particulate filter 8 has at least a partially catalytically active coating. Preferably, the catalytically active coating is designed for selective catalytic reduction. This allows ammonia, which is produced in the first NOC 7 during a substoichiometric operating mode, to be stored in the particulate filter 8 and used for the reduction of nitrogen oxides in the exhaust gas.

[0028] Downstream of the particulate filter 8, a low-pressure exhaust gas recirculation line 9 of a low-pressure exhaust gas recirculation (LP-EGR) system branches off from the exhaust tract 4. This exhaust gas recirculation line 9 connects the exhaust tract 4 fluid to the intake tract 3. A first exhaust gas recirculation valve 9a is arranged in the exhaust gas recirculation line 9, which allows control of the exhaust gas mass flow from the exhaust tract 4 into the intake tract 3. Furthermore, a first exhaust gas recirculation cooler 9b is arranged in the exhaust gas recirculation line 9. The exhaust gas recirculation cooler 9b may have a bypass.

[0029] A second LNT 10 is arranged downstream of the exhaust gas recirculation line branch 9. The second LNT 10 preferably has a different catalytically active coating than the first LNT 7. The catalytically active coating of the first LNT 7 is that of a conventional LNT. This means that the coating is optimized for the absorption and conversion of nitrogen oxides during cold starts and at medium temperatures, using, according to the prior art, precious metals (typically Pt, Pd, or Rd), oxygen-storing materials such as cerium, and barium compounds for the coating. The catalytically active coating of the second LNT 10 is preferably optimized differently. Since the first LNT 7 performs the cold-start emission control tasks, the second LNT 10 can be optimized for NOx conversion at high temperatures in a manner known to those skilled in the art.This also makes it possible to reduce the amount of oxygen-storing components, meaning that less stored oxygen needs to be reduced during regeneration, which in turn means less fuel is required. Optionally, the second LNT 10 can also be designed with a zone coating, in which a zone with oxygen storage capacity is applied only at the end to prevent breakthrough of reducing agents.

[0030] A throttle valve 11 is arranged downstream of the second LNT 10. The throttle valve 11 serves to regulate the exhaust gas flow. In some embodiments of the arrangement 1, a throttle valve may not be present.

[0031] Upstream of the turbine 5, an exhaust gas recirculation line 12 of a high-pressure exhaust gas recirculation system branches off from the exhaust tract 4, connecting the exhaust tract 4 fluid to the intake tract 3. A second exhaust gas recirculation valve 12a and a second exhaust gas recirculation cooler 12b are arranged in the exhaust gas recirculation line 12. The exhaust gas recirculation cooler 12b may have a bypass.

[0032] The arrangement 1 further comprises sensors (not shown), e.g., nitrogen oxide, ammonia, lambda, and / or temperature sensors, which can be arranged at any location within the arrangement 1. The sensors are connected to a control unit (not shown). Furthermore, the arrangement 1 can, for example, also include at least one device for introducing a reducing agent, in particular an aqueous urea solution, into the exhaust tract 4. A throttle valve can also be arranged in the downstream end region of the exhaust tract 4. The control unit regulates the operating modes, the quantities of fuel introduced into the internal combustion engine and aqueous urea solution introduced into the exhaust tract, as well as the settings of valves and cooling devices.The control unit remains connected to the internal combustion engine 2 in order to issue control commands regarding rich or lean operation based on an evaluation of the measured values.

[0033] In one embodiment according to the illustration of Fig. 2 The arrangement 1 includes a catalyst for selective catalytic reduction (SCR catalyst) 13, which is arranged downstream of the branch of the low-pressure exhaust gas recirculation line 9 in the exhaust tract 4. In an embodiment according to the illustration of Fig. In 3, arrangement 1 includes both a second LNT 10 and an SCR catalyst 13.

[0034] In one embodiment of the method according to the illustration of Fig. In step 4, the internal combustion engine 2 is operated in a first step S1, so that exhaust gas is routed through the exhaust system. The internal combustion engine 2 is operated with a lean air-fuel mixture, resulting in lean exhaust gas. The load is low to medium.

[0035] In a second step, S2 switches the internal combustion engine 2 to a high-load operating state. This occurs, for example, during acceleration, when the accelerator pedal is fully depressed or depressed to a significantly greater extent than during steady driving. In this state, exhaust gas is produced at a temperature so elevated compared to normal operation that the first LNT 5 can no longer effectively store nitrogen oxides. For example, under high load, temperatures in the area of ​​the first LNT 7 can quickly rise above 550°C, which does not allow for efficient storage.

[0036] In a third step, S3, a rich combustion mode is initiated for the internal combustion engine 2. This is preferably achieved by post-injection of fuel into the internal combustion engine, but can also be accomplished by measures in the air path, e.g., by reducing the amount of air supplied. In a fourth step, S4, exhaust gas is routed through the exhaust gas recirculation line 9. The amount of recirculated exhaust gas is regulated by adjusting the exhaust gas recirculation valve 9a. Step S4 can also be performed simultaneously with steps S1, S2, and S3.

[0037] Ideally, rich-fuel operation is maintained for the duration of the high load. In a fifth step, S5, the internal combustion engine 2 is operated again at a low load, and a lean-burn combustion mode is initiated. However, rich-fuel operation can also be interrupted if, for example, a larger quantity of ammonia is produced during rich-fuel operation than can be stored. In this case, lean-burn operation is carried out for a specific period, during which the previously stored ammonia is used to reduce nitrogen oxides. The two operating modes can be used alternately as long as high temperatures and space velocities require it.

[0038] In Fig.Figure 5 shows the effective reduction of nitrogen oxide emissions via the first LNT 7 by enriching the exhaust gas during high-load operation. The nitrogen oxide concentration is plotted against time. The period of high load (step S3) is indicated by vertical dashed lines. The nitrogen oxide concentration in the exhaust gas is elevated, as shown by the thick solid line, which represents the concentration upstream of the first LNT 7. The applied enrichment is also shown as a thin solid line based on the lambda curve.

[0039] It can be seen that the nitrogen oxide concentration downstream of the first LNT 7 (dotted line) decreases during rich operation, with the nitrogen oxides being primarily captured by the first LNT 7 during rich operation under high load. This can lead to the desorption of previously stored nitrogen oxides by the first LNT, as seen by the peak of the dotted line between times 5275 and 5280. These can then be stored or converted downstream, for example, by the second LNT 10. However, some of these nitrogen oxides are recirculated into the combustion chamber when the low-pressure EGR is used and can again be treated by the first LNT 7, for example, as part of an immediate nitrogen oxide conversion according to step S3.The ND-EGR also increases the overall capacity for nitrogen oxide reduction, which can also be used to make the nitrogen oxide storage components smaller and therefore more cost-effective with the same performance. Reference symbol list 1. Arrangement 2 Internal combustion engine 3 Intake tract 4 Exhaust system 5 Turbine 6 Compressor 6a Cooling device in the intake tract 7 first LNT 8 particulate filters 9 Low-pressure exhaust gas recirculation line 9a first exhaust gas recirculation valve 9b first exhaust gas recirculation cooler 10 second LNT 11 Throttle valve 12 High-pressure exhaust gas recirculation line 12a second exhaust gas recirculation valve 12b second exhaust gas recirculation cooler 13 SCR catalyst

Claims

[1] Method for operating an arrangement (1) of an internal combustion engine (2) with an exhaust tract (4) from which at least one exhaust gas recirculation line of a low-pressure exhaust gas recirculation system (9) branches off, and in which an exhaust gas aftertreatment system is arranged, wherein the exhaust gas aftertreatment system comprises at least a first nitrogen oxide storage catalyst (7), at least a second catalytic device (10) arranged downstream of the first nitrogen oxide storage catalyst (7), and at least one particulate filter (8) arranged downstream of the first nitrogen oxide storage catalyst (7), wherein the exhaust gas recirculation line of the low-pressure exhaust gas recirculation system (9) branches off downstream from the first nitrogen oxide storage catalyst (7) and upstream from the second catalytic device (10) and comprises at least one valve (9a) for controlling a mass of recirculated exhaust gas,and comprising at least one temperature sensor in the area of ​​the first nitrogen oxide storage catalyst (7), comprising the steps: - Operating the internal combustion engine (2) at low or medium load, - Switching to a high-load operating state of the internal combustion engine (2), - Starting a substoichiometric combustion mode of the internal combustion engine (2), - Returning exhaust gas through the exhaust gas recirculation line of the low-pressure exhaust gas recirculation system (9), - Ending the substoichiometric combustion mode and switching to an operating state of the internal combustion engine (2) with low or medium load. [2] Method according to claim 1, wherein an amount of the recirculated exhaust gas is regulated to control a regeneration of the first nitrogen oxide storage catalyst (7). [3] Method according to claim 1 or 2, wherein the second catalytic device (10) of the arrangement (1) is a second nitrogen oxide storage catalyst (10). [4] Method according to claim 3, wherein the first nitrogen oxide storage catalyst (7) of the arrangement (1) is arranged in such a spatial proximity to the internal combustion engine (2) that effective storage of nitrogen oxides is prevented at exhaust gas temperatures occurring under high load, and the second nitrogen oxide storage catalyst (10) is arranged in such a spatial distance from the internal combustion engine (2) that effective storage of nitrogen oxides is enabled even at exhaust gas temperatures occurring under high load. [5] Method according to claim 3 or 4, wherein the second nitrogen oxide storage catalyst (10) has a catalytically active coating which is different from a catalytically active coating of the first nitrogen oxide storage catalyst (7). [6] Method according to claim 5, wherein the catalytically active coating of the second nitrogen oxide storage catalyst (10) is optimized relative to the catalytically active coating of the first nitrogen oxide storage catalyst (7) for nitrogen oxide conversion at high temperatures. [7] Method according to claim 1, wherein the second catalytic device is a catalyst for selective catalytic reduction (13). [8] Method according to one of the preceding claims, wherein both a second nitrogen oxide storage catalyst (10) and a catalyst for selective catalytic reduction (13) are arranged downstream of the branch of the exhaust gas recirculation line of the low-pressure exhaust gas recirculation system (9) in the exhaust tract (4). [9] Method according to one of the preceding claims, wherein a throttle valve (11) is arranged downstream of the second catalytic device. [10] Method according to one of the preceding claims, wherein upstream of the first nitrogen oxide storage catalyst (7) an exhaust gas recirculation line of a high-pressure exhaust gas recirculation system (12) branches off from the exhaust tract (4). [11] Method according to any of the preceding claims, wherein the particle filter (8) has a catalytically active coating. [12] Method according to claim 11, wherein the catalytically active coating is designed for selective catalytic reduction.

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