DE102020210640A1 - Method for reducing gaseous emissions from an internal combustion engine - Google Patents

Abstract

The present invention relates to a method for reducing emissions from an internal combustion engine (1) having at least one combustion chamber (3) and an exhaust gas aftertreatment device (2) after the internal combustion engine (1) has restarted, which has at least the following steps: a) detecting a restart of the internal combustion engine (3);b) operating the engine (3) lean of stoichiometry for a first time period (10) after restart;c) operating the engine (1) rich of stoichiometry for a second time period (11) after restart, the following the first period;d) performing a stoichiometric operation of the internal combustion engine (3) after the end of the second period after the restart.

Description

The present invention relates to a method for reducing emissions from an internal combustion engine having at least one combustion chamber and an exhaust gas aftertreatment device after the internal combustion engine has been restarted.

During the operation of internal combustion engines, ever more stringent emission limits must be observed. Here, the manufacturers of internal combustion engines are confronted with increasingly strict exhaust gas legislation. Among other things, special attention is paid to the emission of nitrogen oxides. Basically, it is desirable to reduce the emission of nitrogen oxides as much as possible.

In particular, it should be avoided that untreated exhaust gas is emitted, which still contains nitrogen oxides to a significant extent. This can occur, for example, in the case of a so-called emissions slip during a restart of an internal combustion engine.

In order to reduce such raw nitrogen oxide emissions, it is known to operate the internal combustion engine in a substoichiometric operating state as quickly as possible after a restart.

The sub-stoichiometric operation of the internal combustion engine after a restart currently represents a compromise that meets the applicable legal regulations.

However, this sub-stoichiometric operating state has the disadvantage that it causes increased emissions of hydrocarbons and carbon monoxide.

A stoichiometric combustion air ratio of 1 (lambda = 1.0) means that there is exactly the amount of air that is required for the complete combustion of a fuel. If the value is greater than 1, there is excess air, which can also be referred to as lean operation. If the value is less than 1, on the other hand, there is a lack of air and the fuel is not completely burned.

Another known solution consists in injecting water into the combustion process in order to lower the combustion temperature and thus achieve the reduction of raw nitrogen oxide emissions. In order to implement an injection of water into an internal combustion engine, however, a great deal of effort is required, which is reflected, among other things, in high component costs.

It is therefore the object of the present invention to at least partially solve the problems arising from the prior art. In particular, a solution is to be specified with which, after a frequently occurring restart of the internal combustion engine, emission slippage of nitrogen oxides is avoided and exhaust gas aftertreatment that is as complete as possible is achieved.

A method with the features according to patent claim 1 contributes to the solution of these tasks. Advantageous developments are the subject matter of the dependent patent claims. The features listed individually in the patent claims can be combined with one another in a technologically meaningful manner and can be supplemented by explanatory facts from the description and/or details from the figures, with further embodiment variants of the invention being shown.

1. a) Erkennen eines Wiederanlaufs der Brennkraftmaschine;
2. b) Ausführen einer überstöchiometrischen Betriebsweise der Brennkraftmaschine während eines ersten Zeitraums nach dem Wiederanlauf;
3. c) Ausführen einer unterstöchiometrischen Betriebsweise der Brennkraftmaschine während eines zweiten Zeitraums nach dem Wiederanlauf, der auf den ersten Zeitraum folgt;
4. d) Ausführen einer stöchiometrischen Betriebsweise der Brennkraftmaschine nach dem Ende des zweiten Zeitraums nach dem Wiederanlauf.

The proposed method for reducing emissions from an internal combustion engine with at least one combustion chamber and an exhaust gas aftertreatment device after restarting the internal combustion engine has at least the following steps:

1. a) detecting a restart of the internal combustion engine;
2. b) operating the engine lean of stoichiometry for a first period after restart;
3. c) operating the engine rich of stoichiometry for a second time period after the restart following the first time period;
4. d) performing a stoichiometric engine operation after the end of the second post-restart period.

The restart can take place, for example, in the form of a restart or a reinstatement. A restart occurs when an internal combustion engine is first shut down in order to then be put back into operation after a period that can last from a few seconds to a few minutes. Such a restart occurs, for example, in internal combustion engines with a so-called automatic start-stop system, which can mechanically shut down an internal combustion engine for a short time if no drive power is called up from the internal combustion engine. This can be the case, for example, with a motor vehicle that is waiting at a red traffic light. The restart thus includes restarting the internal combustion engine within seconds or minutes after the internal combustion engine was previously stopped.

Another form of restarting can be a restart of combustion within the internal combustion engine after a previous overrun fuel cut-off. In contrast to restarting, the internal combustion engine is not shut down here, but only an overrun cut-off is implemented, in that at least the supply of fuel to the combustion chambers of the internal combustion engine is prevented. Upon restart, combustion of fuel is then resumed in the continuously moving internal combustion engine. In this case, too, the duration of the fuel cutoff before the restart can be from a very short duration of less than 1 second to a few minutes.

If such a state of restarting is now detected, for example by a control device of the internal combustion engine, this can initiate over-stoichiometric operation of the internal combustion engine in a first period of time after the restart.

During the period immediately before the internal combustion engine restarts, an oxygen storage catalytic converter provided in the exhaust gas aftertreatment device is initially filled. Here, unburned oxygen gets into the exhaust aftertreatment device and is initially stored in it. As a result of this introduction and storage of oxygen, the exhaust aftertreatment device is briefly unable to convert nitrogen oxides. In order to avoid a breakthrough, for example of nitrogen oxides and their untreated emissions, the present invention provides that, immediately after restarting the internal combustion engine, superstoichiometric operation with combustion of the fuel with excess air is initially set. For this purpose, the internal combustion engine is operated in lean operation.
In this case, the strategy of the present invention is to dispense entirely with the hitherto customary sub-stoichiometric combustion and instead carry out a super-stoichiometric combustion of fuel in the first period after the restart. Here, an excess of nitrogen oxides is generated for a short time, which is briefly stored in a nitrogen oxide storage catalytic converter. For this purpose, the exhaust gas aftertreatment device has at least two reservoirs. One for oxygen and another for nitrous oxide. This makes it possible to condition the combustion chamber of the internal combustion engine and the exhaust gas aftertreatment device in the manner required for the further process in a very short time.

If the combustion chamber and the exhaust gas aftertreatment device are conditioned in a corresponding manner, the internal combustion engine is then operated in a substoichiometric mode of operation, with the previously filled oxygen storage catalytic converter being regenerated by oxidizing the oxygen stored therein and the nitrogen oxide storage catalytic converter downstream in the direction of flow being regenerated by oxidizing the nitrogen oxide stored therein.

The invention involves a procedure which requires a two-catalyst system with an oxygen storage catalytic converter in the first position and a nitrogen oxide storage catalytic converter in the second position. The nitrogen oxide storage catalytic converter can be designed as a NOx storage catalytic converter, for example.
The aim of the invention is to avoid the raw nitrogen oxide emissions during the frequent restarts. The emission-heavy operating states when restarting with the resumption or the restart are optimized with the procedure described here with regard to their gaseous emissions.

In particular in connection with an Otto engine, this method can be used in order to significantly reduce the untreated emissions of nitrogen oxides after a restart.

The invention has recognized that after a restart there is the possibility of storing nitrogen oxides within the exhaust gas aftertreatment device. This takes place in the phase in which the exhaust gas aftertreatment device is not yet able to convert the nitrogen oxide due to the oxygen that is also still stored. This first period of time is dimensioned so short that there is no breakthrough of nitrogen oxides through the exhaust gas aftertreatment device by the nitrogen oxide being stored in the nitrogen oxide storage catalytic converter. For this purpose, the first time period is selected in such a way that the nitrogen oxide storage catalytic converter provided in the exhaust gas aftertreatment device is only filled up with nitrogen oxides to a part of its storage capacity.

This first period of time can therefore be chosen to be very short and last for example only a few seconds or even less than 1 second. The lean phase brought about in this way should be kept short in order to avoid unnecessary nitrogen oxide slippage.

After that, the internal combustion engine was operated substoichiometrically in order to regenerate the storable components of the exhaust gas aftertreatment device that are capable of storing oxygen and nitrogen oxides. Regeneration then occurs during a second Period of sub-stoichiometric operation of the internal combustion engine. The components of the exhaust gas aftertreatment device are (partially) freed from enriched oxygen and nitrogen oxides as part of the regeneration by substoichiometric operation of the internal combustion engine.

After regeneration of the exhaust gas aftertreatment device has taken place, the internal combustion engine can then be operated again in an approximately substoichiometric operating mode.

Steps a) to d) can be carried out at least once in the order given here. It is possible for these steps to be carried out with different frequency and/or at least partially in a temporally overlapping manner.

Step a) can be carried out by a control unit of the internal combustion engine in order to detect a restart and then carry out steps b) and c) before step d) then resets the usually stoichiometric or substoichiometric operating state.

If a restart follows a previous restart at a very short time interval, it is possible to shorten step d) or even to omit it entirely.

In particular, it can be provided that the method is carried out in such a way that the over-stoichiometric mode of operation is carried out with a lambda value of greater than 1.0 and in particular from 1.05 to 1.3 and very particularly from 1.05 to 1.15. As a result, the storage of nitrogen oxides can take place in a particularly quick and efficient manner. Here, for example, a particularly high raw nitrogen oxide emission could be determined, particularly with lambda values in the range from 1.05 to 1.15.

The combustion temperature drops with increasing lambda, which also reduces the raw nitrogen oxide emissions at the same time. The storage capacity of the nitrogen oxide store required for the concept described here can be reduced in this way.

In particular, it can also be provided that in the subsequent second period of regeneration, a strongly substoichiometric mode of operation with a lambda value of less than 0.8 is carried out in order to carry out the regeneration in a particularly effective manner and in a short time.

An upper limit for highly over-stoichiometric combustion is reached when poor combustion progresses or even misfires occur.
It is important to avoid these operating states, since the lack of engine torque would have to be compensated for by the resulting loss of efficiency, which would result in reduced drivability of the internal combustion engine and a vehicle driven by it. Accordingly, it is also important to avoid highly sub-stoichiometric operating states.

In particular, the method can be carried out in such a way that a two-catalytic converter system with a first storage catalytic converter and a second storage catalytic converter is used as the exhaust gas aftertreatment device. The first storage catalyst is different from the second storage catalyst. In particular, the first storage catalytic converter can comprise an oxygen storage catalytic converter and the second storage catalytic converter can comprise a nitrogen oxide storage catalytic converter. Both storage catalysts are seen in the flow direction of the outflowing exhaust gas downstream of the internal combustion engine. In this case, the first storage catalytic converter is arranged upstream of the second storage catalytic converter.

If, before a restart, the combustion is stopped due to the internal combustion engine being stopped or due to an overrun cut-off, oxygen can accumulate in the first storage catalytic converter and be stored there. After restarting the internal combustion engine, the nitrogen oxide generated during the first period in substoichiometric operation can first be stored in the second storage catalytic converter before it is then released from there again during the second period and as part of the regeneration.

In particular, it can be provided that the method is carried out in such a way that an oxygen storage catalytic converter is used as the first catalytic converter and a nitrogen oxide storage catalytic converter is used as the second catalytic converter. It is possible here, for example, to use an oxygen storage catalytic converter which is designed as a 3-way catalytic converter or as an exclusive oxygen storage catalytic converter.

It is also particularly advantageous if the method is implemented in such a way that a storage capacity of the second storage catalytic converter is only partially used.

The present method is therefore not used for complete regeneration of the first or second catalyst, but to avoid Nitrogen oxide emissions after a common restart. In contrast to the known regeneration processes, in the case of the present invention, storage and regeneration are carried out much more quickly and much more frequently, since the aim is not to regenerate the catalytic converter, but rather to avoid unwanted emissions after a restart. This is reflected in the fact that the storage capacity of the second catalytic converter is used only partially, ie at most 90%, preferably less than 75%, in particular less than 50% to 10%, for storing nitrogen oxides.

In particular, the second period of time can be selected in the method such that it begins when the combustion chamber, the first storage catalytic converter and the second storage catalytic converter are conditioned after the restart.

This ensures that all components are optimally conditioned when regeneration begins.

It is particularly advantageous if the first time period is selected in such a way that it lasts less than two seconds (2 s) and in particular less than one second (1 s). A first time period of less than two seconds (1 s) ensures that the storage capacity of the second catalytic converter for nitrogen oxides is not exceeded and that nitrogen oxides do not break through at this nitrogen oxide storage catalytic converter. For a large number of applications, it is even sufficient if the first time period is chosen to be no longer than one second (1 s).

It is possible that the battery management system is provided with at least one measuring device and means that are suitable or set up to carry out steps a) to d) of the proposed method described here, in particular according to steps a) to c) of the method claims.

Furthermore, the invention can be implemented with an internal combustion engine having at least one combustion chamber, an exhaust gas aftertreatment device and a control device for controlling the combustion process, which is characterized in that the at least one control device has a data memory and for carrying out the method according to one of steps a) to d ) is set up.

Furthermore, a computer program is proposed, comprising commands that
cause this evaluation device to carry out these method steps. Finally, a computer-readable medium is also proposed, on which the computer program is stored.

As a precaution, it should be noted that the numerals used here (“first”, “second”, ...) primarily (only) serve to distinguish between several similar objects, sizes or processes, i.e. in particular no dependency and/or sequence of these objects, sizes or make processes mandatory for each other. Should a dependency and/or order be necessary, this is explicitly stated here or it is obvious to the person skilled in the art when studying the specifically described embodiment.

• 1: eine mögliche Ausführungsform einer erfindungsgemäßen Brennkraftmaschine mit Abgasnachbehandlungsvorrichtung;
• 2: einen bekannten stöchiometrischen Verlauf nach einem Wiederanlauf einer Brennkraftmaschine; und
• 3: einen möglichen stöchiometrischen Verlauf nach einem Wiederanlauf einer Brennkraftmaschine gemäß der vorliegenden Erfindung.

The invention and the technical environment are explained in more detail below with reference to the accompanying figures. It should be pointed out that the invention should not be limited by the exemplary embodiments given. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and to combine them with other components and findings from the present description. In particular, it should be pointed out that the figures and in particular the proportions shown are only schematic. Show it:

• 1 1: a possible embodiment of an internal combustion engine according to the invention with an exhaust gas aftertreatment device;
• 2 : a known stoichiometric profile after restarting an internal combustion engine; and
• 3 : a possible stoichiometric profile after a restart of an internal combustion engine according to the present invention.

In 1 a possible embodiment of an internal combustion engine 1 according to the invention with an exhaust gas aftertreatment device 2 is shown in a schematic side view. The internal combustion engine 1 has four combustion chambers 3 . The exhaust gas aftertreatment device 2 , which is designed as a two-catalyst system, is arranged downstream of the internal combustion engine 1 . The exhaust gas aftertreatment device 2 includes line means 4 and a first storage catalytic converter 5 and a second storage catalytic converter 6. The first catalytic converter 5 includes an oxygen storage catalytic converter 7 and the second catalytic converter includes a nitrogen oxide storage device 8.

Furthermore, a control device 9 is provided, which is designed to control the combustion taking place within the internal combustion engine 1 at least with regard to the combustion stoichiometry and to detect a restart of the internal combustion engine 1 .

the 2 shows a known stoichiometric course of the combustion of fuel and oxygen contained in air after a restart of an internal combustion engine 1. The lambda value present in the combustion chamber 3 is plotted on the Y-axis in the diagram shown. The course of this lambda value over time is plotted on the X-axis. After a restart [WA], the known method switches over from an over-stoichiometric operating state to an under-stoichiometric operating state as quickly as possible. This change takes place so quickly that no storage of nitrogen oxides takes place. In the further course of time, according to the known method, a stoichiometric operating state with a lambda value of approx. 1 is then set very quickly again. In these known methods, breakthroughs of hydrocarbons and/or nitrogen oxides usually occur after a restart.

This disadvantage is overcome by the in 3 illustrated embodiment. The diagram shown there depicts a possible stoichiometric curve after restarting an internal combustion engine according to the present invention.

According to the invention, after a restart, the over-stoichiometric operating state is initially maintained for a first period of time 10 in order to be able to store the nitrogen oxide present at this moment after the restart in the second storage catalytic converter 6 . A first surface 12 shown characterizes the storage of the nitrogen oxides. A second area 13 indicates the regeneration of exhaust gas aftertreatment device 2 during second time period 11.

While the reduction in emissions when restarting or restarting always represents a compromise with regard to different gaseous emissions, the present invention creates the prerequisites for significantly reducing the emissions of nitrogen oxides, hydrocarbons and carbon monoxide after restarting an internal combustion engine. This is particularly advantageous because a restart in modern internal combustion engines occurs regularly and at very short intervals, while the regeneration processes that have been customary in the prior art have only been carried out very rarely and at long time intervals.

This can be achieved by carrying out the method with a two-catalyst arrangement, which has an oxygen storage catalytic converter 7 in the first position and a nitrogen oxide storage catalytic converter 8, specifically a nitrogen oxide storage catalytic converter, in the second position. In this case, after a stop phase of the internal combustion engine 1 or after an overrun cut-off, the oxygen storage catalytic converter is initially filled with oxygen from the air and is therefore unable to convert the nitrogen oxides that occur. In order to minimize gaseous emissions, particularly in the driving situations of restart or resumption, the first combustions after the restart or resumption are initially over-stoichiometric, with the resulting excess of nitrogen oxides being stored in the second storage catalytic converter 6, which is designed, for example, as a nitrogen oxide storage catalytic converter . Are the combustion chamber 3 and the catalysts 5.6 sufficiently conditioned, is then switched to a sub-stoichiometric mode of operation in order to regenerate both the nitrogen oxide and oxygen storage catalyst of the two catalysts 5.6.

reference list

1

internal combustion engine

2

exhaust aftertreatment device

3

combustion chamber

4

line means

5

first storage catalyst

6

second storage catalyst

7

oxygen storage catalyst

8th

nitrogen oxide storage catalyst

9

control device

10

First period

11

second period

12

First face

13

second face

Claims (10)

Method for reducing emissions from an internal combustion engine (1) having at least one combustion chamber (3) and an exhaust gas aftertreatment device (2) after restarting the internal combustion engine (1), which has at least the following steps: a) detecting a restart of the internal combustion engine (3); b) running the engine (3) lean of stoichiometry for a first period (10) after restart; c) operating the engine (1) rich of stoichiometry for a second period (11) after restart following the first period; d) performing a stoichiometric mode of operation the internal combustion engine (3) after the end of the second period after the restart. Method according to the preceding claim, in which the over-stoichiometric mode of operation is carried out with a lambda value of greater than 1.0 and in particular from 1.05 to 1.3 and very particularly from 1.05 to 1.15. Method according to one of the preceding claims, wherein a two-catalytic converter system with a first storage catalytic converter (5) and a second storage catalytic converter (6) is used as the exhaust gas after-treatment device (2). Method according to one of the preceding claims, in which an oxygen storage catalytic converter (7) is used as the first storage catalytic converter (5) and a nitrogen oxide storage catalytic converter (8) is used as the second storage catalytic converter (6). Method according to one of the preceding claims, wherein a storage capacity of the second storage catalyst (6) is only partially used. Method according to one of the preceding claims, wherein the second time period (11) is selected such that it begins when the combustion chamber (3), the first storage catalyst (5) and the second storage catalyst (6) are conditioned after the restart are. Method according to one of the preceding claims, wherein the second period of time (11) is selected in such a way that it has a duration of less than two seconds and in particular of less than one second. Internal combustion engine (1) with at least one combustion chamber (3), an exhaust gas aftertreatment device (2) and a control device (9) for controlling the combustion process, characterized in that the at least one control device (9) has a data memory and for carrying out a method according to one of the previous Claims 1 until 7 is set up. Computer program comprising instructions that cause the device according to claim 8 the procedural steps according to claim 1 executes Computer-readable medium on which the computer program claim 9 is saved.

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