DE102017101610A1 - Method for reducing cold-start emissions in a spark-ignited internal combustion engine - Google Patents

Abstract

The invention relates to a method for reducing the cold-start emissions, in particular the particle emissions, of a spark-ignited internal combustion engine. For this purpose, after a cold start, the internal combustion engine is operated with a lean or stoichiometric combustion air ratio until a light-off temperature of a three-way catalytic converter arranged in the exhaust duct of the internal combustion engine is established instead of a richly stoichiometric combustion mixture which otherwise would otherwise be used during cold starting. In order to avoid misfiring during lean operation in the cold start phase, a multiple ignition is provided in the cold start phase to stabilize the engine combustion.

Description

The invention relates to a method for reducing the cold-start emissions in a spark-ignited internal combustion engine and to a control device for carrying out such a method.

The continuous tightening of the exhaust emission legislation places high demands on the vehicle manufacturers, which are solved by appropriate measures for the reduction of the engine raw emissions and by a corresponding exhaust aftertreatment. With the introduction of the legislative level EU6, a limit value for gasoline engines is prescribed for a number of particles, which in many cases necessitates the use of an Otto particle filter. Such soot particles are formed especially after a cold start of the internal combustion engine due to incomplete combustion in combination with a superstoichiometric combustion air ratio after the cold start, cold cylinder walls and the heterogeneous mixture distribution in the combustion chambers of the internal combustion engine. The cold start phase is thus decisive for compliance with the legally prescribed particle limit values, both with regard to the particle mass and with regard to the number of particles. In addition, a cold start with a stoichiometric, rich combustion air ratio leads to higher emissions of carbon monoxide (CO) and unburned hydrocarbons (HC), since a conversion into carbon dioxide and water vapor due to the cold catalyst is not yet possible. When driving, this Ottopartikelfilter is then further loaded with soot in motor vehicles with a Ottopartikelfilter. So that the exhaust gas backpressure does not increase too much, this Otto particle filter must be regenerated continuously or periodically. The increase in the exhaust back pressure can lead to an increase in consumption of the internal combustion engine, loss of power and impairment of smoothness to misfires. In order to carry out a thermal oxidation of the soot retained in the Otto particle filter with oxygen, a sufficiently high temperature level in conjunction with simultaneously existing oxygen in the exhaust system of the gasoline engine is necessary. Since modern gasoline engines are normally operated without oxygen surplus with a stoichiometric combustion air ratio (λ = 1), additional measures are required. These come as measures, for example, a temperature increase by a Zündwinkelverstellung, a temporary lean adjustment of the gasoline engine, the injection of secondary air into the exhaust system or a combination of these measures in question. An ignition angle adjustment in the direction of late in combination with a lean adjustment of the gasoline engine is preferably used so far, since this method requires no additional components and can deliver a sufficient amount of oxygen in most operating points of the gasoline engine.

From the DE 101 31 937 A1 A vehicle emission reduction apparatus and a method of reducing cold start emissions of an internal combustion engine are known in which the valve timing, the ignition angle and the combustion air ratio are adjusted to improve the combustion temperature and the combustion efficiency in the cold start phase and to reduce the cold start emissions.

• - Ermitteln der Startkonditionen des Verbrennungsmotors, wobei
• - bei Erkennen eines Kaltstarts des Verbrennungsmotors der Verbrennungsmotor mit einem mageren Verbrennungsluftverhältnis (λ > 1) oder einem stöchiometrischen Verbrennungsluftverhältnis (λ = 1) betrieben wird, und wobei
• - während des Kaltstarts des Verbrennungsmotors eine Mehrfachzündung in den Brennräumen des Verbrennungsmotors erfolgt, um die Zündfähigkeit des mageren Verbrennungsgemischs zu erhöhen.

The invention is based on the object to reduce the emissions of a spark-ignition internal combustion engine according to the Otto principle in a cold start phase of the internal combustion engine and thus to improve the exhaust gas performance of the internal combustion engine. According to the invention, this object is achieved by a method for reducing the cold-start emissions of a spark-ignition internal combustion engine in whose exhaust system a three-way catalytic converter is arranged, comprising the following steps:

• - Determining the starting conditions of the internal combustion engine, wherein
• - When a cold start of the internal combustion engine is detected, the internal combustion engine is operated with a lean combustion air ratio (λ> 1) or a stoichiometric combustion air ratio (λ = 1), and wherein
• - During the cold start of the internal combustion engine, a multiple ignition takes place in the combustion chambers of the internal combustion engine in order to increase the ignitability of the lean combustion mixture.

Additionally or alternatively, it is possible to stabilize the combustion by maintaining the spark. Likewise, it is alternatively or additionally possible to introduce more ignition energy into the combustion chambers as a result of the longer closing time of the ignition distributor.

In a cold-start process known from the prior art, the internal combustion engine is operated in the cold start phase with a substoichiometric, rich combustion mixture in order to improve the ignitability of the mixture in the cold start phase. By a cold start of the internal combustion engine according to the invention with a lean, superstoichiometric combustion air ratio or a stoichiometric air ratio, both the gaseous emissions and the organic solid emissions can be significantly reduced. The primary aim of the proposed method is to reduce the raw emissions occurring during engine combustion in the cold start phase. Through a Stoichiometric operation of the internal combustion engine, on the one hand reduces the number of soot particles and, on the other hand, reduces the size of the resulting soot particles. In this case, the residual oxygen present in the combustion chambers can be used for the oxidation of the soot particles occurring during combustion due to the cold combustion chamber walls and a heterogeneous mixture distribution, so that the raw emissions of the internal combustion engine are reduced. In addition, the super-stoichiometric combustion air mixture prevents local formation of droplets of unburned fuel, which contribute particularly strongly to the formation of particulate emissions. As a further advantage of the proposed method, the three-way catalyst heats up faster in a superstoichiometric cold start operation than in a substoichiometric cold start operation, since no excess fuel evaporates and thus no additional heat is removed by the evaporation of the fuel combustion air or the exhaust gas. In order to avoid misfiring during a cold start of the internal combustion engine with a superstoichiometric combustion air mixture, a multiple ignition of the combustion air mixture is performed in the combustion chambers of the internal combustion engine during the cold start phase to increase the ignitability of the lean combustion air mixture and to avoid misfiring. A stoichiometric combustion air ratio after the cold start has the advantage that the raw emissions, in particular the particle emissions are also lowered, but no additional oxidizing agent for the oxidation of the resulting soot particles is present. Thus, the primary emissions at a stoichiometric combustion air ratio are slightly higher than at a lean combustion air ratio, but the ignitability of the combustion mixture is higher and the nitrogen oxide emissions and the risk of misfires lower. In order to reduce the risk of misfires after a cold start with stoichiometric or lean combustion air ratio, at least two sparks are generated per combustion cycle in each combustion chamber so that at least one of the sparks meets an ignitable combustion air mixture and thus ensures the combustion even in the cold start phase despite the lean combustion air ratio is. As a result, stricter emission standards without an additional particulate filter may also be adhered to in vehicles with spark-ignited internal combustion engines, or the number of regeneration cycles for the particulate filter may be reduced. In this way, not only the emissions can be reduced, but also the consumption of the internal combustion engine, since a consumption-increasing regeneration of the particulate filter is required less often.

By the features listed in the dependent claims, further improvements of the method specified in the independent claim for reducing the cold-start emissions are possible.

In a preferred embodiment of the method, it is provided that the multiple ignition takes place by means of a spark band ignition. By spark ignition, two or more sparks can be generated in a combustion cycle of the respective combustion chamber of the internal combustion engine in a relatively simple manner with a spark plug. By a spark-band ignition, a plurality of sparks can be emitted in a short period of time, that is, within a combustion cycle per combustion chamber. The number of sparks is dependent on the speed of the internal combustion engine, since with increasing speed, the number of possible sparks per combustion cycle decreases. By spark ignition the smoothness of the engine is stabilized and prevents misfiring in the cold start phase. Alternatively, a multiple ignition can also be realized by a corona ignition or a laser ignition, however, the spark-band ignition offers by far the most cost-effective solution for multiple ignition. Furthermore, it is possible to generally stabilize the combustion by spark ignition and thus to reduce the enrichment of the combustion air mixture at cold starting temperatures.

According to a preferred embodiment of the method is provided that the internal combustion engine is operated after reaching a light-off temperature of the three-way catalyst with a stoichiometric combustion air ratio. In order to keep the load on the spark plugs in the cold start phase low and to keep the secondary emissions during the cold start phase, in particular the emissions of nitrogen oxides (NOx) low, it makes sense from the time when the three-way catalyst its Reached light-off temperature and thus has reached 50% of its maximum conversion capacity for harmful exhaust gas components to operate the internal combustion engine with a stoichiometric combustion air ratio. As a result, a very effective conversion of the raw emissions occurring during the combustion of the fuel in the combustion chambers of the internal combustion engine by the three-way catalyst is possible. In addition, from the achievement of the light-off temperature of the catalyst can be dispensed with a multiple ignition, which keeps the phases of high load for the spark plugs low and thus reduces the life of the spark plug only slightly.

In a further preferred embodiment of the invention, it is provided that the Internal combustion engine during the cold start phase with a combustion air ratio λ of 1.02 - 1.05 is operated. Tests have shown that even a slight increase in the combustion air ratio beyond a stoichiometric combustion air ratio leads to a significant decrease in the raw emissions in the cold start phase of the internal combustion engine. In this case, the risk of misfiring is limited with a low excess air, whereby a high degree of smoothness of the engine is ensured even in the starting phase.

In an alternative embodiment of the method it is provided that the internal combustion engine during the cold start phase with a combustion air ratio λ> 1.05 is operated. A higher excess air again leads to an improvement in the raw emissions, in particular the particle emissions of the internal combustion engine. However, the excess air also increases the risk of misfiring and NOx emissions. Therefore, it is particularly advantageous if the air ratio is set in a cold start of the internal combustion engine as a function of the temperature of the three-way catalyst to reduce the raw emissions during the cold start phase until reaching the light-off temperature of the internal combustion engine.

In a preferred embodiment of the method it is provided that the internal combustion engine is operated for a period of 30 seconds to 240 seconds, particularly preferably for a period of 30 seconds to 180 seconds, with a lean of lean, lean combustion air ratio. In general, a three-way catalyst has reached its light-off temperature no later than 240 seconds after a cold start of the internal combustion engine and can ensure efficient conversion of the limited exhaust gas constituents. Depending on the size of the three-way catalyst and the arrangement within the exhaust system, a heating time of the three-way catalyst, for example, in a small, close to the engine arranged pre-catalyst can be significantly shortened, so that the inventive method only necessary for a very short period is. As a result, the additional wear of the spark plugs can be kept low and at the same time an emission-optimized cold start of the internal combustion engine can be ensured.

According to a further improvement of the method, it is provided that the maximum possible number of sparks is generated during the cold start phase. In order to improve the ignitability of the lean combustion mixture in the cold start phase, it is provided that the spark plugs emit in the cold start phase a maximum possible number of sparks per combustion cycle in order to improve the smoothness of the engine and to avoid misfires. In this case, the first spark is preferably emitted at the same time as in a stoichiometric combustion in normal operation of the internal combustion engine in the combustion chamber and the subsequent spark corresponding time offset. As a result, an efficient fuel utilization is ensured even during the cold start, whereby the consumption of the internal combustion engine compared to a conventional, known from the prior art cold start with a rich combustion air mixture, can be reduced.

In a further, preferred embodiment of the method, it is provided that the ignition point provided in a stoichiometric normal operation of the internal combustion engine is maintained. By dispensing with a retardation of the ignition, the efficiency of the internal combustion engine can be increased in the cold start phase, also such adjustment of the ignition angle is not necessary because in the cold start phase no unburned hydrocarbons evaporate in the exhaust gas and thus extract additional heat from the exhaust gas, which Delay heating of the three-way catalyst.

In a further improvement of the method for reducing the cold-start emissions is provided that the exhaust gas of the internal combustion engine is passed through a particulate filter or a four-way catalyst. By means of a particle filter or a four-way catalytic converter, in addition to the gaseous emissions such as carbon monoxide (CO), unburned hydrocarbons (HC) and nitrogen oxides (NOx), soot particles can also be removed from the exhaust gas and thus the efficiency of the exhaust gas aftertreatment can be further increased.

According to the invention, a control unit for a spark-ignition internal combustion engine is proposed, which has a machine-readable program code with which a method according to the invention is carried out when the program code is executed on the control unit. By a machine-readable program code, the inventive method can be applied in a simple and cost-effective manner in a control unit of the internal combustion engine, so that the inventive method for reducing emissions in a cold start of the internal combustion engine requires no additional components.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The various embodiments of the invention mentioned in this application are unless otherwise stated in the individual case, can be combined with each other with advantage.

• 1 einen Verbrennungsmotor mit einer Luftversorgung, einem KraftstoffEinspritzsystem, einem Zündsystem und einer Abgasanlage, an dem ein erfindungsgemäßes Verfahren zur Reduzierung der Kaltstart-Emissionen durchgeführt werden kann;
• 2 ein Ablaufdiagramm zur Durchführung eines erfindungsgemäßen Verfahrens zur Reduzierung der Kaltstart-Emissionen eines fremdgezündeten Verbrennungsmotors;
• 3 einen Verlauf der Partikelkonzentration / Partikelmasse bei einem erfindungsgemäßen Verfahren zur Reduzierung der Kaltstart-Emissionen im Vergleich zu den Kaltstartemissionen bei einem konventionellen, aus dem Stand der Technik bekannten Kaltstart; und
• 4 einen Verlauf der Partikelanzahl bei einem erfindungsgemäßen Verfahren zur Reduzierung der Kaltstart-Emissionen im Vergleich zu den Partikelemissionen bei einem konventionellen, aus dem Stand der Technik bekannten Kaltstart.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

• 1 an internal combustion engine with an air supply, a fuel injection system, an ignition system and an exhaust system, on which a method according to the invention for reducing the cold start emissions can be performed;
• 2 a flowchart for performing a method according to the invention for reducing the cold start emissions of a spark-ignited internal combustion engine;
• 3 a profile of the particle concentration / particle mass in a method according to the invention for reducing the cold start emissions compared to the cold start emissions in a conventional, known from the prior art cold start; and
• 4 a profile of the number of particles in a method according to the invention for reducing the cold-start emissions compared to the particle emissions in a conventional, known from the prior art cold start.

1 shows a spark-ignition internal combustion engine 10 for a motor vehicle, with an exhaust system 12 in which a three-way catalyst 14 is arranged. In addition to the three-way catalyst 14 can be arranged in the exhaust system further catalysts and exhaust aftertreatment devices, in particular a NOx storage catalyst 46 and / or a particulate filter 16 , The particle filter 16 may have a three-way catalytically active coating, and as a so-called four-way catalyst 18 be formed, wherein the particulate filter 16 in this case, the functions of the three-way catalyst 14 and the particulate filter 16 united in one component. The internal combustion engine 10 is via an air supply system 30 supplied with fresh air. In this case, in an intake tract 40 of the internal combustion engine 10 an air filter 32 and an air mass meter 34 arranged. The fresh air can by means of a turbocharger 48 be compacted, taking in the exhaust system 12 a turbine 50 is arranged, which is a compressor 36 in the intake tract 40 of the internal combustion engine 10 drives and in this way the combustion chambers 52 . 54 . 56 , 58 of the internal combustion engine 10 supplied fresh air compressed. To control the combustion chambers 52 . 54 . 56 . 58 supplied fresh air amount is in the intake 40 a throttle 38 arranged. The internal combustion engine 10 also has a fuel supply, in which fuel from a fuel tank 22 by means of a fuel pump 26 through a fuel line 24 a fuel injection system 28 supplied and as needed in the intake system 40 or in the combustion chambers 52 . 54 . 56 . 58 of the internal combustion engine 10 is injected. The internal combustion engine 10 also has an ignition distributor 42 on, over which spark plugs 44 at the combustion chambers 52 . 54 . 56 . 58 can be controlled and each one or more sparks in the combustion chamber 52 , 54, 56, 58 emitted. Thus, the combustion air mixture in the combustion chambers 52 . 54 . 56 , 58 are detonated. In the exhaust system 12 of the internal combustion engine 10 are in the flow direction of an exhaust gas of the internal combustion engine 10 through the exhaust system 12 upstream of the three-way catalyst 14 and downstream of the three-way catalyst 14 lambda probes 60 . 62 arranged, with which the combustion air ratio λ of the internal combustion engine 10 can be regulated. These are the lambda probes 60 . 62 , the fuel injection system 28 and the ignition distributor via signal lines to a control unit 20 of the internal combustion engine 10 connected, via which the combustion air ratio λ , the amount of fuel and the spark timing at which the spark plugs 44 each emit an ignition pulse to be controlled.

In 2 is an inventive method for reducing the cold start emissions of a spark plugs 44 spark ignited internal combustion engine 10 shown. These are the internal combustion engine 10 and / or in the intake tract 40 and the exhaust system 12 further sensors, in particular temperature sensors are provided, with which a cold start of the internal combustion engine 10 can be detected. If the presence of cold start conditions is detected in a first method step <100>, the internal combustion engine becomes 10 in a second process step <110> in a cold start phase for a period of 30 seconds to 240 seconds with a lean of stoichiometric, lean combustion air ratio λ > 1 operated. Due to the cold start of the internal combustion engine 10 with a lean combustion air ratio λ > 1 will be in the combustion chambers 52 . 54 . 56 . 58 additional oxygen molecules for the oxidation of the combustion in the cold zones of the combustion chambers 52 . 54 . 56 . 58 provided primary particles as reactants. Further, for the cold start phase <120>, the ignition through the ignition distributor becomes 42 changed so much that the spark plugs 44 provide multiple sparks, preferably spark-band firing, per combustion cycle to during lean start of the internal combustion engine 10 to improve the ignition conditions and misfiring and associated uneven engine running of the engine 10 to avoid. In addition, due to the lean operation of the internal combustion engine 10 local, fat hotspots with fat Combustion air mixture can be avoided, whereby the number and mass of primary particles formed during combustion can be reduced. Due to the lean cold start, the three-way catalyst 14 faster than a conventional cold start with a stoichiometric combustion air ratio λ <1 are heated to a light-off temperature, whereby an efficient and effective conversion of the exhaust gas components such as carbon monoxide CO, unburned hydrocarbons HC and nitrogen oxides NOx time faster after the cold start is possible. To the lean start of the engine 10 No or only small secondary emissions, in particular of nitrogen oxides NOx, to emit, the lean combustion air ratio λ <1 depending on the temperature of the three-way catalyst 14 set. After the three-way catalyst 14 in a process step <130> has reached its light-off temperature and can contribute to the efficient conversion of the pollutants contained in the exhaust gas, the combustion air ratio λ of the internal combustion engine 10 in a process step <140> to a stoichiometric combustion air ratio λ = 1 controlled for efficient exhaust aftertreatment by the three-way catalyst 14 to enable. Due to the temperature-dependent adjustment of the combustion air ratio λ of the internal combustion engine 10 During the cold start phase, secondary emissions are avoided and at the same time the number of particles, the particulate mass and the emissions of unburned hydrocarbons HC and carbon monoxide CO are significantly reduced. The proposed spark band ignition stabilizes the combustion in the cold start phase and misfires during the lean start of the internal combustion engine 10 are avoided. In this case, the maximum possible number of sparks per spark plug in the cold start phase 44 and combustion cycle in the respective combustion chamber 52 . 54 . 56 . 58 emitted, this maximum number of sparks depending on the speed of the internal combustion engine 10 is. In this case, the ignition is compared to a normal operation of the internal combustion engine 10 not shifted, so that the first spark at the time of ignition of the spark plug 44 in normal operation in the respective combustion chamber 52 , 54, 56, 58 is emitted.

In 3 are the particle concentration P _K in a conventional cold start of an internal combustion engine 10 with a substoichiometric combustion air ratio λ <1 and in a lean start of an internal combustion engine according to the invention 10 in a NEDC driving cycle as well as the vehicle speed v of the vehicle passing through the test over a test cycle of 1200 seconds. In this case, the drive cycle with a dashed line, the output measurement according to the prior art with thin lines and the emissions are shown in a method according to the invention with a thick line. It can be seen that the particle concentration P _K and thus the particle mass of soot particles with otherwise unchanged test conditions in all test ranges below the particle concentration P _K in a conventional cold start. Thus, the particulate mass can be significantly reduced in a cold start, resulting in a rarer regeneration of a particulate filter 16 or four-way catalyst 18 in the exhaust system 12 of the internal combustion engine 10 allows or even can cause the particle limits without a particulate filter 16 can be achieved. In addition, the lower particle concentration P _K results when using a particulate filter 16 or four-way catalyst 18 to a slower increase in exhaust back pressure in the exhaust system 12 so that the consumption of the internal combustion engine 10 can be further reduced.

In 4 are the particle number P _N in a conventional cold start of an internal combustion engine 10 with a substoichiometric, rich combustion air ratio λ <1 compared to the particle number P _N in a cold start according to the invention with a superstoichiometric, lean combustion air ratio λ > 1 in a NEDC drive cycle and the vehicle speed of a motor vehicle passing this drive cycle over a test cycle of 1200 seconds. In this case, the drive cycle with a dashed line, the output measurement according to the prior art with thin lines and the emissions are shown in a method according to the invention with a thick line. It can be seen that the number of particles P _N by a cold start according to the invention with a lean combustion process by about 30%, in the example shown by 31%, can be lowered. As already to the particle concentration P _K executed, can be reduced by an inventive method for several reasons, the fuel consumption of the motor vehicle. On the one hand, less fuel is consumed in a lean start than in a cold start with a rich fuel mixture. On the other hand, less soot particles with a smaller particle mass than primary emissions of the internal combustion engine 10 are produced, as a result of which fewer particles are present in a particle filter 16 or a four-way catalyst 18 must be retained and the exhaust back pressure rises more slowly. In addition, less consumption-increasing regeneration cycles for the oxidation of the particulate filter 16 or four-way catalyst 18 retained soot necessary so that again fuel can be saved compared to a conventional cold start with a higher particle emission.

LIST OF REFERENCE NUMBERS

10

internal combustion engine

12

exhaust system

14

Three-way catalytic converter

16

particulate Filter

18

Four-way catalyst

20

control unit

22

Fuel tank

24

Fuel line

26

Fuel pump

28

Fuel injection system

30

Air supply system

32

air filter

34

Air flow sensor

36

compressor

38

throttle

40

intake system

42

distributor

44

spark plug

46

NOx Storage

48

turbocharger

50

turbine

52

first combustion chamber

54

second combustion chamber

56

third combustion chamber

58

fourth combustion chamber

60

lambda probe

62

lambda probe

P _K

particle concentration

P _N

particle number

v

speed

t

Time

s

seconds

λ

Combustion air ratio of the internal combustion engine

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• DE 10131937 A1 [0003]

Claims (10)

Method for reducing the cold-start emissions of a spark-ignition internal combustion engine (10), in whose exhaust system (12) a three-way catalytic converter (14) is arranged, comprising the following steps: - Determining the starting conditions of the internal combustion engine (10), wherein at - detecting a cold start of the internal combustion engine (10) of the internal combustion engine with a lean combustion air ratio (λ> 1) or with a stoichiometric combustion air ratio (λ = 1) is operated, and wherein - During the cold start of the internal combustion engine (10) is a multiple ignition in the combustion chambers (52, 54, 56, 58) of the internal combustion engine (10) to increase the ignitability of the lean or stoichiometric combustion mixture. Method according to Claim 1 , characterized in that the multiple ignition takes place by means of a spark band ignition. Method according to Claim 1 or 2 , characterized in that the internal combustion engine (10) after reaching a light-off temperature of the three-way catalytic converter (14) is operated with a stoichiometric combustion air ratio and the multiple ignition is replaced by a single ignition. Method according to one of Claims 1 to 3 , characterized in that the internal combustion engine (10) during the cold start phase with a combustion air ratio λ of 1.02 - 1.05 is operated. Method according to one of Claims 1 to 3 , characterized in that the internal combustion engine (10) during the cold start phase with a combustion air ratio λ> 1.05 is operated. Method according to one of Claims 1 to 5 , characterized in that the internal combustion engine for a period of 30 s to 240 s with a lean combustion air ratio (λ> 1) is operated. Method according to one of Claims 1 to 6 in that during the cold start phase the maximum possible number of sparks is generated. Method according to one of Claims 1 to 7 , characterized in that in a stoichiometric normal operation of the internal combustion engine (10) provided ignition is maintained. Method according to one of Claims 1 to 8th , characterized in that the exhaust gas of the internal combustion engine (10) through a particulate filter (16) or a four-way catalytic converter (18) is passed. Control unit (20) for a spark-ignition internal combustion engine (10), wherein the control unit (20) has a machine-readable program code with which a method according to the invention is carried out when the program code is executed on the control unit (20).

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