DE102020128786A1 - Process for reducing nitrous oxide emissions from an internal combustion engine and exhaust gas aftertreatment system - Google Patents

Abstract

The invention relates to a method for reducing nitrous oxide emissions in an exhaust system (20) of an internal combustion engine (10). The outlet (18) of the internal combustion engine (10) is connected to the exhaust system (20). In the exhaust system (20), in the direction of flow of an exhaust gas stream of the internal combustion engine (10), there is a nitrogen oxide storage component (28, 30, 32), downstream of the nitrogen oxide storage component (28, 30, 32) an electrical heating device (34) and downstream of the electrical heating device (34) an oxidation catalyst (38) arranged. It is provided that the temperatures (TNS, TOX) of the nitrogen oxide storage component (28, 30, 32) and of the oxidation catalytic converter (38) are determined, an operating state of the internal combustion engine (10) is determined and the electric heating device (34) is activated when the temperatures (TNS, TOX) and the determined operating state of the internal combustion engine (10) indicate the formation of nitrous oxide in at least one of the exhaust gas aftertreatment components (28, 30, 32, 38). The invention also relates to an exhaust gas aftertreatment system for carrying out such a method.

Description

The invention relates to a method for reducing the nitrous oxide emissions of an internal combustion engine and an exhaust gas aftertreatment system for carrying out such a method according to the preamble of the independent patent claims.

The Kyoto Protocol is a joint result of international climate policy. In it, the member states of the international community commit themselves to an absolute and legally binding limitation of the emission of greenhouse gases in an international treaty. With the ratification of the Kyoto Protocol, it is obligatory and binding for industrialized countries to reduce emissions of the most important greenhouse gases - including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O).

Nitrous oxide is a greenhouse gas that is around 300 times more harmful to the climate than carbon dioxide. The main sources of nitrous oxide emissions are nitrogenous fertilizers in agriculture and animal husbandry. Other sources are the industrial processes in the chemical industry as well as stationary and mobile combustion processes.

In the course of a further tightening of future emissions legislation for motor vehicles with internal combustion engines, a limit value for nitrous oxide emissions is also to be expected. The demands for a further reduction in consumption and the further tightening of the exhaust gas standards with regard to the permissible nitrogen oxide and nitrous oxide emissions pose a challenge for the engine developers -Catalyst upstream and downstream further catalysts. Exhaust gas aftertreatment systems are currently used in diesel engines, which have an oxidation catalytic converter, a catalytic converter for the selective catalytic reduction of nitrogen oxides (SCR catalytic converter) and a particle filter for separating soot particles and optionally further catalytic converters. Ammonia is preferably used as the reducing agent. Because handling pure ammonia is complicated, vehicles usually use a synthetic, aqueous urea solution, which is mixed with the hot exhaust gas flow in a mixing device upstream of the SCR catalytic converter. This mixing heats up the aqueous urea solution, with the aqueous urea solution releasing ammonia in the exhaust gas duct. A commercially available, aqueous urea solution is generally made up of 32.5% urea and 67.5% water.

In internal combustion engines, nitrous oxide is not primarily produced during engine combustion, but is formed under certain unfavorable temperature conditions on the catalytic converters for exhaust gas aftertreatment.

From the DE 102 42 303 A1 an exhaust gas cleaning system and a method for cleaning exhaust gases are known. In this case, an oxidation catalytic converter, a NOx storage catalytic converter, a particle filter and an SCR catalytic converter are arranged in the exhaust system of the internal combustion engine in the flow direction of an exhaust gas flow through this exhaust system. A metering valve is provided downstream of the particle filter and upstream of the SCR catalytic converter in order to introduce a reducing agent into the exhaust system. It is provided that the NOx storage catalytic converter can be heated by means of an electric heating element in order to control the storage behavior of nitrogen oxides.

The object of the invention is now to minimize the nitrous oxide emissions in addition to the already limited exhaust gas components (NOx, CO, HC) and thus to further improve the exhaust gas purification or to avoid negative secondary effects.

This object is achieved by a method for reducing nitrous oxide emissions in an exhaust system of an internal combustion engine. The outlet of the combustion engine is connected to the exhaust system. In the exhaust system, a nitrogen oxide storage component is arranged in the flow direction of an exhaust gas stream of the internal combustion engine, an electric heating device, in particular an electrically heatable catalytic converter, is arranged downstream of the nitrogen oxide storage component, and an oxidation catalytic converter is arranged downstream of the electric heating device. Provision is made for the temperatures of the nitrogen oxide storage component and the oxidation catalytic converter to be determined, an operating state of the internal combustion engine to be determined and the electric heating device to be activated if the temperatures and the determined operating state of the internal combustion engine indicate nitrous oxide formation on at least one of the exhaust gas aftertreatment components, in particular on the oxidation catalytic converter can be expected.

Nitrous oxide emissions occur in the exhaust system in particular when nitrogen oxides are released, unburned hydrocarbons are present in the exhaust gas at the same time and the temperature of a catalytic converter is in the range of 200 - 240°C. Under these conditions, a increased nitrous oxide formation, so it is important to avoid such conditions in order to minimize the formation of nitrous oxide. As long as the nitrogen oxide storage component absorbs the nitrogen oxides in the exhaust gas of the internal combustion engine, an essential reactant for the formation of nitrous oxide is missing. If an operating situation of the internal combustion engine is detected in which nitrogen oxides are released or can no longer be absorbed by the nitrogen oxide storage component, while unburned hydrocarbons are present in the exhaust gas and the temperature of the oxidation catalytic converter is in the critical range of 200° - 240°C, the electrical Heating device activated to heat the oxidation catalytic converter to such an extent that nitrous oxide formation is minimized.

Targeted temperature control of the oxidation catalytic converter via the electrically heatable catalytic converter can minimize the formation of nitrous oxide on the catalytic converters in the exhaust system. High combustion and exhaust gas temperatures lead to rapid decomposition of nitrous oxide and thus further minimization of nitrous oxide emissions.

Advantageous further developments and improvements of the method specified in the independent claim are possible as a result of the features listed in the dependent claims.

In a preferred embodiment of the invention, it is provided that a loading state of the nitrogen oxide storage component, in particular a passive NOx adsorber or a NOx storage catalytic converter, is determined. By determining the loading status, it is possible to estimate whether an operating status is to be expected in which nitrogen oxides are released and there is a risk of the formation of nitrous oxide.

In an advantageous further development of the method, it is provided that a first nitrogen oxide concentration is measured upstream of the nitrogen oxide storage component and a second nitrogen oxide concentration downstream of the nitrogen oxide storage component, with a charge state of the storage component or a nitrogen oxide discharge from the nitrogen oxide storage component being determined from the measured nitrogen oxide concentrations. By measuring the nitrogen oxide concentration, the charge state of the nitrogen oxide storage component can be calculated and/or a discharge of nitrogen oxides from the nitrogen oxide storage component can be detected.

Alternatively or additionally, it is advantageously provided that a loading state of the nitrogen oxide storage component or a nitrogen oxide discharge from the nitrogen oxide storage component is calculated using a loading model. Alternatively or additionally, a corresponding calculation model can be used to calculate whether nitrogen oxide discharge from the nitrogen oxide storage component is to be expected and the risk of nitrous oxide formation is increased.

In an advantageous embodiment of the method, it is provided that a concentration of unburned hydrocarbons is determined in the exhaust system upstream of the oxidation catalytic converter. Since the formation of nitrous oxide is favored by the simultaneous presence of unburned hydrocarbons, the control of the electrically heatable catalytic converter can be improved by additionally determining the concentration of unburned hydrocarbons upstream of the oxidation catalytic converter.

A further improvement of the method provides that the electrically heatable catalytic converter is activated when a threshold value for the nitrogen oxide loading of the nitrogen oxide storage component is exceeded. Since the risk of the release of nitrogen oxides increases from a threshold value, in particular from a loading of the nitrogen oxide storage component of more than 75% of the storage capacity of the nitrogen oxide storage component, it is advantageous to activate the electrically heatable catalytic converter when the threshold value is exceeded. Due to the timely activation of the electrical heating device, the oxidation catalytic converter is heated to such an extent that the oxidation catalytic converter reaches a temperature of at least 250° C., preferably at least 350° C., particularly preferably at least 450° C., before the nitrogen oxides are released from the nitrogen oxide storage component and thus the formation of nitrous oxide is minimized.

Another aspect of the invention relates to an exhaust gas aftertreatment system for an internal combustion engine, which is connected to an exhaust system at its outlet, wherein in the exhaust system in the flow direction of an exhaust gas stream of the internal combustion engine a nitrogen oxide storage component, downstream of the nitrogen oxide storage component an electrical heating device, in particular an electrically heatable catalyst, and downstream an oxidation catalytic converter is arranged in the electrical heating device, and with a control unit which is set up to carry out such a method when a machine-readable program code is executed by the control unit. Such an exhaust gas after-treatment system can prevent the oxidation catalyst from being operated in a temperature range which is critical for the formation of nitrous oxide when the internal combustion engine is in an operating state in which such a formation of nitrous oxide occurs favored. This means that nitrous oxide emissions can be minimized.

In a preferred embodiment of the exhaust gas aftertreatment system, it is provided that the nitrogen oxide storage component is a NOx storage catalytic converter or comprises a NOx storage catalytic converter. Nitrogen oxides can be stored using a NOx storage catalytic converter. In order to regenerate the NOx storage catalytic converter, however, rich phases in the engine or metering of fuel into the exhaust system are necessary in order to convert the stored nitrogen oxides with the unburned hydrocarbons. However, since the simultaneous presence of unburned hydrocarbons and nitrogen oxides promotes the formation of nitrous oxide, it is helpful to heat up the oxidation catalytic converter with the electrical heating device to such an extent that the temperature of the oxidation catalytic converter is above the critical temperature range of 200°C - 250°C for the formation of nitrous oxide.

It is particularly preferred if the NOx storage catalytic converter is designed as a low-temperature NOx storage catalytic converter. In this context, a low-temperature NOx storage catalytic converter is to be understood as meaning a NOx storage catalytic converter which can store nitrogen oxides from a temperature of 140°C, preferably from 120°C, particularly preferably from 100°C. Such a low-temperature NOx storage catalytic converter can in particular minimize the nitrogen oxide emissions in a cold start phase of the internal combustion engine, in which other exhaust gas aftertreatment components for reducing nitrogen oxides, in particular one or more catalytic converters for the selective, catalytic reduction of nitrogen oxides, have not yet reached their operating temperature.

Alternatively or additionally, it is advantageously provided that the nitrogen oxide storage component is a passive NOx adsorber or includes a passive NOx adsorber. With a passive NOx adsorber, nitrogen oxides can be adsorbed and temporarily stored at exhaust gas temperatures of around 80°C. If the exhaust gas temperature and the temperature of the passive NOx adsorber exceed a threshold value of around 200 - 250°C, the stored nitrogen oxides are released again and the passive NOx adsorber is regenerated. The passive NOx adsorber is therefore particularly suitable for minimizing nitrogen oxide emissions in a cold-start phase of the internal combustion engine. Since the nitrogen oxides are released at a temperature level which is critical with regard to the formation of nitrous oxide, it is advantageous to heat the oxidation catalytic converter using the electric heating device so that the oxidation catalytic converter is hot enough when the nitrogen oxides are released to avoid or minimize the formation of nitrous oxide .

Unless stated otherwise in the individual case, the various embodiments of the invention mentioned in this application can advantageously be combined with one another.

• 1 einen Verbrennungsmotor mit einem Abgasnachbehandlungssystem in einer schematischen Darstellung;
• 2 eine Katalysatoranordnung das Abgasnachbehandlungssystems in einer schematischen Darstellung;
• 3 einen zeitlichen Temperaturverlauf des Oxidationskatalysators sowie die Ansteuerung der elektrischen Heizeinrichtung bei einem Kaltstart des Verbrennungsmotors; und
• 4 ein Ablaufdiagramm zur Durchführung eines erfindungsgemäßen Verfahrens zur Verminderung der Lachgasemissionen.

The invention is explained below in exemplary embodiments with reference to the associated drawings. Identical components or components with the same function are identified in the different figures with the same reference numbers. Show it:

• 1 an internal combustion engine with an exhaust aftertreatment system in a schematic representation;
• 2 a catalytic converter arrangement of the exhaust gas aftertreatment system in a schematic representation;
• 3 a time course of the temperature of the oxidation catalytic converter and the actuation of the electric heating device when the internal combustion engine is started cold; and
• 4 a flowchart for carrying out a method according to the invention for reducing nitrous oxide emissions.

1 shows a schematic representation of an internal combustion engine 10, which is connected to an exhaust system 20 with its outlet 18. The internal combustion engine 10 is designed as a direct-injection diesel engine. Internal combustion engine 10 has multiple combustion chambers 12 . A fuel injector 14 for injecting a fuel into the respective combustion chamber 12 is arranged on each of the combustion chambers 12 . The combustion chambers are each delimited by a piston 16 which is arranged displaceably in a cylinder bore of the internal combustion engine 10 . The internal combustion engine 10 is connected to an air supply system (not shown) at its inlet and to an exhaust system 20 at its outlet 18 . The internal combustion engine 10 can have a high-pressure exhaust gas recirculation with an exhaust gas recirculation line and a high-pressure exhaust gas recirculation valve, via which an exhaust gas of the internal combustion engine 10 can be recirculated from the outlet 18 to the inlet. Inlet valves and outlet valves are arranged on the combustion chambers 12, with which a fluidic connection from the air supply system to the combustion chambers 12 or from the combustion chambers 12 to the exhaust system 20 can be opened or closed.

In the exhaust system 20 is in the flow direction of an exhaust gas flow through the combustion engine 10 through an exhaust duct 22 of the exhaust system 20 downstream of a turbine 26 of an exhaust gas turbocharger 24 as the first component of the exhaust gas aftertreatment, a nitrogen oxide storage component 28, in particular a passive NOx adsorber 32 is arranged. The passive NOx adsorber 32 is preferably designed as a passive NOx adsorber 32 without an oxidation component and is only used for the temporary storage of nitrogen oxides in the cold start phase of the internal combustion engine. An electrical heating device 34 with an electrical heating element 36 is arranged downstream of the nitrogen oxide storage component 28 and can be used to heat the exhaust gas flow of the internal combustion engine 10 essentially independently of the mode of operation of the internal combustion engine 10 . An oxidation catalytic converter 38, in particular a diesel oxidation catalytic converter, is arranged further downstream. Alternatively, the nitrogen oxide storage component 28 can also be designed as a NOx storage catalytic converter 30, in particular as a low-temperature NOx storage catalytic converter.

Further exhaust gas aftertreatment components 40, 42, 44, 46, in particular at least one exhaust gas aftertreatment component 40 for the selective, catalytic reduction of nitrogen oxides, preferably an SCR catalytic converter 42 or a particle filter 44 with an SCR coating 46, can be arranged in exhaust system 20 downstream of oxidation catalytic converter 38 , with which a reducing agent can be metered into the exhaust gas channel 22. A dosing element 58 is arranged downstream of oxidation catalytic converter 38 and upstream of exhaust gas aftertreatment component 40 for the selective, catalytic reduction of nitrogen oxides, with which a reducing agent, in particular an aqueous urea solution, can be metered into exhaust system 20 of internal combustion engine 10 .

An exhaust gas mixer can be arranged downstream of metering element 58 and upstream of exhaust gas aftertreatment component 40 for the selective, catalytic reduction of nitrogen oxides in order to improve mixing of the reducing agent with the exhaust gas flow of internal combustion engine 10 before it enters exhaust gas aftertreatment component 40 for selective catalytic reduction.

Furthermore, several exhaust gas sensors 48, in particular NOx sensor(s) 54, 56, or a sensor for detecting unburned hydrocarbons, as well as temperature sensors 50, 52 can be provided in the exhaust system 20. Internal combustion engine 10 and sensors 48, 50, 52, 54, 56 are connected to a control unit 60, which controls, among other things, the injection quantity and the injection time of the fuel into combustion chambers 12 of internal combustion engine 10 and the activation or heating output of electric heating device 34 . The control unit 60 includes a processing unit 62 and a memory unit 64 in which a machine-readable program code 66 is stored, which can be executed by the processing unit 62 to carry out a method according to the invention.

2 shows a catalytic converter arrangement of the exhaust gas aftertreatment system in a schematic representation. A partial segment of an exhaust gas duct 22 of an exhaust system 20 is shown. The catalytic converter arrangement includes a nitrogen oxide storage component 28 and an electric heating device 34 in the form of an electrically heatable catalytic converter which includes an electric heating element 36 . An oxidation catalytic converter 38 is connected downstream of the electrical heating device 34 . The nitrogen oxide storage component 28 is preferably designed as a passive NOx adsorber 32, but can alternatively also be designed as a NOx storage catalytic converter 30.

A first NOx sensor 54 is arranged in the exhaust gas duct 22 upstream of the nitrogen oxide storage component 28 . A second NOx sensor 56 is arranged downstream of the nitrogen oxide storage component 28, so that a loading of the nitrogen oxide storage component 28 or a release of nitrogen oxides can be determined via the difference measured between the NOx sensors 54, 56. A first temperature sensor 50 is arranged on the nitrogen oxide storage component 28, with which the temperature T _NS of the nitrogen oxide storage component 28 can be measured. A second temperature sensor 52 is arranged on the oxidation catalytic converter 38, with which the temperature T _ox of the oxidation catalytic converter 38 can be measured.

In 3 a diagram is shown which shows the temperature curve T _ox of the oxidation catalytic converter 38 during a cold start of the internal combustion engine 10 . The temperature T _ox is raised from a first, cold temperature zone I, which is uncritical from the point of view of nitrous oxide formation, into a non-critical, hot, third temperature zone III, with the critical temperature zone II being passed through as quickly as possible by activation A of the electrical heating device 34 and the passing through of the Critical temperature zone II takes place when either all nitrogen oxides can be stored in the nitrogen oxide storage device 28 and/or there are no unburned hydrocarbons in the exhaust gas flow in order to minimize the formation of nitrous oxide. In internal combustion engines 10, nitrous oxide is not primarily produced by engine combustion in combustion chambers 12, but essentially as secondary emissions during exhaust gas aftertreatment. A nitrous oxide formation on the oxidation Catalyst 38 or an oxidation stage of the NOx storage catalytic converter 30 only takes place if the reactants required for the formation of nitrous oxide, nitrogen oxides and unburned hydrocarbons, are present and at the catalytic converter 30, 38 there is a critical temperature range of around 200° C. to 250° C. for the formation of nitrous oxide prevails.

As long as the nitrogen oxide storage component 28 adsorbs the nitrogen oxides, an essential reactant for the formation of nitrous oxide at the oxidation catalytic converter 38 is missing. The current storage loading of nitrogen oxide storage component 28 is determined using a calculation model in control unit 60 or by measuring the nitrogen oxide concentration in exhaust gas duct 22 at one NOx sensor 54, 56 upstream and one downstream of nitrogen oxide storage component 28, or using a combination of both methods. The maximum storage capacity of the nitrogen oxide storage component is stored in control unit 60 in an application-specific manner. The temperature T _ox of the oxidation catalytic converter 38 and the temperature T _NS of the nitrogen oxide storage component 28 are determined using a calculation model, temperature sensors 50, 52 or a combination of both methods.

1. 1.) Die Stickoxidspeicherkomponente 28, insbesondere der passive NOx-Adsorber 32, wird über das motorische Abgas bis in den Bereich der Desorptionstemperatur erwärmt und die eingelagerten Stickoxide durch thermische Desorption freigesetzt. Dies kann sowohl passiv im Normalbetrieb des Verbrennungsmotors 10 als auch durch gezielte innermotorische Heizmaßnahmen, beispielsweise zur Regeneration eines Partikelfilters, erfolgen.
2. 2.) Der Schwellenwert der Stickoxidbeladung der Stickoxidspeicherkomponente 28 wird überschritten, sodass die eintretenden Stickoxide nicht mehr vollständig in der Stickoxidspeicherkomponente 28 eingelagert werden können und Stickoxide in die Abgasanlage 20 stromabwärts der Stickoxidspeicherkomponente 28 gelangen.
3. 3.) Die Abgastemperatur T_EG beziehungsweise die Temperatur T_NS der Stickoxidspeicherkomponente 28 liegt so hoch, dass eintretende Stickoxide nicht in der Stickoxidspeicherkomponente 28 eingelagert werden und die Stickoxidspeicherkomponente 28 durchströmen.

There are three operating situations of internal combustion engine 10 in which nitrogen oxides can occur downstream of nitrogen oxide storage component 28 .

1. 1.) The nitrogen oxide storage component 28, in particular the passive NOx adsorber 32, is heated by the exhaust gas from the engine up to the desorption temperature range and the stored nitrogen oxides are released by thermal desorption. This can take place both passively during normal operation of the internal combustion engine 10 and through specific heating measures within the engine, for example to regenerate a particle filter.
2. 2.) The threshold value of the nitrogen oxide loading of the nitrogen oxide storage component 28 is exceeded, so that the entering nitrogen oxides can no longer be completely stored in the nitrogen oxide storage component 28 and nitrogen oxides reach the exhaust system 20 downstream of the nitrogen oxide storage component 28 .
3. 3.) The exhaust gas temperature T _EG or the temperature T _NS of the nitrogen oxide storage component 28 is so high that entering nitrogen oxides are not stored in the nitrogen oxide storage component 28 and flow through the nitrogen oxide storage component 28 .

If nitrogen oxides are detected downstream of the nitrogen oxide storage component 28 via one of the three mechanisms or a combination of several of these mechanisms and at the same time the temperature T _ox of the oxidation catalytic converter 38 is in the critical range for the formation of nitrous oxide, the electric heating element 36 of the electric heating device 34 is activated in order to Heat oxidation catalyst 38 in the non-critical with respect to the formation of nitrous oxide temperature zone III.

4 shows a flowchart for carrying out a method according to the invention for reducing nitrous oxide emissions. In a method step <100>, the temperature T _NS of the nitrogen oxide storage component 28 is determined. This can be done using a temperature sensor 50 or using a calculation model stored in control unit 60 . In a method step <110>, the temperature T _OX of the oxidation catalytic converter 38 is determined. This can be done using a temperature sensor 52 or using a calculation model stored in control unit 60 . In a method step <120>, the current operating situation of internal combustion engine 10 is determined. In a method step <130>, the concentration of the nitrogen oxides in the exhaust system 20 upstream of the nitrogen oxide storage component 28 is determined. This can be done by a nitrogen oxide sensor 54 or by one in control unit 60 of internal combustion engine 10 . In addition, the nitrogen oxide concentration downstream of the nitrogen oxide storage component 28 is determined in a method step <140>. In a method step <150>, it is calculated whether the prerequisites for the formation of nitrous oxide as a secondary emission at the oxidation catalytic converter 38 are met. If this is the case, the oxidation catalytic converter 38 is heated in a method step <160> by means of the electrical heating device 34 to a temperature above the critical temperature zone II in order to minimize the formation of nitrous oxide.

Reference List

10

combustion engine

12

combustion chamber

14

Pistons

16

fuel injector

18

outlet

20

exhaust system

22

exhaust duct

24

exhaust gas turbocharger

26

turbine

28

nitric oxide storage component

30

NOx storage catalyst

32

passive NOx adsorber

34

electric heating device

36

electric heating element

38

oxidation catalyst

40

Exhaust aftertreatment component for selective, catalytic reduction

42

SCR catalytic converter

44

particle filter

46

SCR coating

48

exhaust gas sensor

50

first temperature sensor

52

second temperature sensor

54

first NOx sensor

56

second NOx sensor

60

control unit

62

unit of account

64

storage unit

66

program code

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 10242303 A1 [0006]

Claims (10)

A method for reducing nitrous oxide emissions in an exhaust system (20) of an internal combustion engine (10) whose outlet (18) is connected to the exhaust system (20), wherein a nitrogen oxide storage component ( 28, 30, 32), an electric heating device (34) downstream of the nitrogen oxide storage component (28, 30, 32) and an oxidation catalytic converter (38) downstream of the electric heating device (34), comprising the following steps: • determining the temperature (T _NS ) of the nitrogen oxide storage component (28, 30, 32) • determining the temperature (T _OX ) of the oxidation catalytic converter (38) • determining an operating state of the internal combustion engine (10) • activating the electric heating device (34) when the temperatures (T _NS , T _OX ) and the determined operating state of the internal combustion engine (10) expect a formation of nitrous oxide on at least one of the exhaust gas aftertreatment components (28, 30, 32, 38). leaves. procedure after claim 1 , characterized in that a loading condition of the nitrogen oxide storage component (28, 30, 32) is determined. procedure after claim 1 or 2 , characterized in that upstream of the nitrogen oxide storage component (28, 30, 32) a first nitrogen oxide concentration (K _NOX1 ) and downstream of the nitrogen oxide storage component (28, 30, 32) a second nitrogen oxide concentration (K _NOX2 ) is measured, with the measured nitrogen oxide concentrations (K _NOX1 , K _NOX2 ) a loading condition of the nitrogen oxide storage component (28, 30, 32) or a nitrogen oxide discharge from the nitrogen oxide storage component (28, 30, 32) is determined. Procedure according to one of Claims 1 until 3 , characterized in that a loading state of the nitrogen oxide storage component (28, 30, 32) or a nitrogen oxide discharge from the nitrogen oxide storage component (28, 30, 32) is calculated by means of a loading model. Procedure according to one of Claims 1 until 4 , characterized in that in the exhaust system (20) upstream of the oxidation catalytic converter (38), a concentration of unburned hydrocarbons is determined. Procedure according to one of Claims 1 until 5 , characterized in that the electrical heating device (34) is activated when a threshold value (T _BNOX ) for the nitrogen oxide loading of the nitrogen oxide storage component (28, 30, 32) is exceeded. Exhaust aftertreatment system for an internal combustion engine (10), which is connected with its outlet (18) to an exhaust system (20), wherein in the exhaust system (20) in the flow direction of an exhaust gas flow of the internal combustion engine (10) a nitrogen oxide storage component (28, 30, 32), downstream of the nitrogen oxide storage component (28, 30, 32) an electric heating device (34) and downstream of the electric heating device (34) an oxidation catalytic converter (38) are arranged, and with a control unit (60) which is set up to carry out a method according to one of the Claims 1 until 6 to be carried out when a machine-readable program code is executed by the control unit (60). exhaust aftertreatment system claim 7 , characterized in that the nitrogen oxide storage component (28) is a NOx storage catalyst (30) or comprises a NOx storage catalyst (30). exhaust aftertreatment system claim 8 , characterized in that the NOx storage catalyst (30) is a low-temperature NOx storage catalyst. Exhaust aftertreatment system according to one of Claims 7 until 9 , characterized in that the nitrogen oxide storage component (28) is a passive NOx adsorber (32) or comprises a passive NOx adsorber (32).

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