DE102007032734A1 - Process for the regeneration of at least one particle agglomerator and motor vehicle comprising an exhaust aftertreatment system - Google Patents

Abstract

A method for regenerating at least one particle agglomerator of an exhaust gas after-treatment system of an internal combustion engine of a motor vehicle, includes operating the internal combustion engine in at least one operating phase in such a way that a sufficient portion of nitrogen dioxides is directly produced in the exhaust gas in order to ensure a conversion of particles containing carbon in the at least one particle agglomerator. A motor vehicle suitable for carrying out the method is also provided.

Description

The The present invention relates to a regeneration process at least a particle agglomerator of an exhaust aftertreatment plant a Internal combustion engine of a motor vehicle. About that In addition, the invention also relates to a motor vehicle, comprising an internal combustion engine and an exhaust aftertreatment system, which with at least one continuously regenerable particle agglomerator is executed. In that regard, the invention relates in particular the removal of soot particles from mobile internal combustion engines, such as diesel engines.

It is known that the particles entrained in the exhaust gas stream, which essentially contain carbon, can be thermally incinerated or reacted with the aid of nitrogen dioxide (NO ₂ ) formed in the exhaust gas aftertreatment system. For this purpose, it is known to provide particle agglomerators, for example filters, particle separators and the like, in which the entrained particles are at least temporarily collected and deposited. In the case of a thermal regeneration, the particle agglomerator is heated so high (for example, to above 800 ° C.) that reaction of the carbon with oxygen carried in the exhaust gas begins. For this purpose, for example, burners, heating elements, electrically heatable filters or an exothermic conversion of hydrocarbons can be used as a source of heat energy. In contrast, the so-called continuous regenerative conversion of particles (so-called CRT process) relies on conversion of the carbonaceous particles at lower temperatures, for example below 400 ° C., using nitrogen dioxide. For this purpose, it is known to lead the exhaust gas generated by the engine via an oxidation catalyst and thus to oxidize nitrogen oxides already contained in the exhaust gas in order to provide sufficient nitrogen dioxide for the implementation of the soot particles can. The nitrogen dioxide has a high affinity for the carbon, so that forms carbon dioxide and nitrogen on contacts of the nitrogen dioxide with the soot particles regularly.

at the known methods and devices with respect to the passive regenerable particle agglomerator (CRT process) becomes upstream of the particle agglomerator or directly in the particle agglomerator Oxidation coating provided. This, regular Platinum-containing, however, coating is expensive and may require additional exhaust treatment facilities, the more complex Exhaust aftertreatment systems result.

Of these, It is an object of the present invention, with reference At least partially attributed to the prior art problems to solve. In particular, a practicable and cost-effective Process for the regeneration of at least one particle agglomerator be specified, in particular a needs-based passive Regeneration allowed. In addition, should also be a for Such a method may be given suitable apparatus which by a low pressure drop and a particularly high Effectiveness of small particles (for example with a average diameter of at most 500 nanometers).

These Tasks are solved with a method according to the Features of claim 1 and a motor vehicle according to the features of claim 10. Further advantageous embodiments of Invention are in the dependent formulated claims specified. It should be noted that the in the claims individually listed features in any, technological more meaningful, way can be combined with each other and show further embodiments of the invention. The description, in particular in connection with the figures, further illustrates Embodiments of the invention.

In the method according to the invention for the regeneration of at least one particle agglomerator in an exhaust aftertreatment system of an internal combustion engine of a motor vehicle, the internal combustion engine is operated at least in an operating phase that directly a sufficient proportion of nitrogen dioxide (NO ₂ ) is generated in the exhaust gas to a conversion of carbonaceous particles with the to ensure at least one particle agglomerator.

This means, in particular, that the first particle agglomerator subsequently arranged in the internal combustion engine is regenerated in the manner proposed here. It is dispensed with a thermal regeneration, so that the reaction of carbonaceous particles takes place at temperatures below 400 ° C or even below 300 ° C. In principle, the particle agglomerator may be designed in the manner of a filter, a particle separator or similar simple devices for temporarily stopping the particles. In the internal combustion engine, it is preferably a lean-burn engine, in which predominantly a combustion with excess air takes place, such as the diesel engine or a so-called lean-burn engine. In other words, it is therefore proposed here to operate the internal combustion engine, at least in a specific operating phase (regeneration phase), such as in a low-load situation, for example, so that a sufficiently high proportion of nitrogen dioxide is generated directly by the internal combustion engine becomes. Regarding the individual mechanisms, how the internal combustion engine can be regulated accordingly, reference will be made in detail below. In this context, therefore, it is first proposed to use the internal combustion engine itself as a nitrogen dioxide source for the regeneration of the particle agglomerator, so that it is possible to dispense with additional sources of nitrogen dioxide, such as, for example, upstream oxidation catalysts.

Preference is given to a method in which the internal combustion engine is a proportion of nitrogen dioxide (NO ₂ ) in the range of 25 vol .-% to 60 vol .-% of all existing nitrogen oxides (NO _x ). In particular, therefore, the conditions in the combustion chamber of the internal combustion engine are adjusted so that the proportion of nitrogen oxides based on all generated nitrogen oxides reaches a significant range, in particular of more than 30 vol .-% or even 45 vol .-% (these ratios may possibly equally in mol .-% are used for regulation). This concerns just the proportion of nitrogen dioxide during the operating phase, in which the regeneration of the particle agglomerator takes place. The 25% by volume can be used as the lower limit and / or as the mean value during the operating phase. It is also preferably proposed that the proportion of nitrogen dioxide does not substantially exceed 60% by volume, in order to still be able to generate sufficient power via the internal combustion engine.

According to a development of the method, it is also proposed that the internal combustion engine actively generates nitrogen dioxide (NO ₂ ) up to at least one particle agglomerator alone. In other words, this means in particular that the exhaust aftertreatment system between the internal combustion engine and the particle agglomerator concerned has no means or measures for targeted enrichment of the exhaust gas with nitrogen dioxide. Thus, the method, or the device, can be carried out particularly easily and controlled targeted regeneration of the particle agglomerator by the corresponding operation of the internal combustion engine who the. Of course, redox processes can not be prevented in the exhaust gas itself, but these are generally not suitable for effecting a corresponding active, significant generation of nitrogen dioxide.

About that In addition, the method can be formed so far that in the operating phase an increase in the proportion of one in the internal combustion engine returned exhaust gas flow is effected. To For this purpose, the exhaust aftertreatment system is for example with a so-called exhaust gas recirculation (EGR = Exhaust Gas recirculation), so that by the internal combustion engine produced exhaust (partially) back to the internal combustion engine is fed, in particular before this at least reached a particle agglomerator. A targeted increase in the exhaust gas recirculation rate can lead to a significant increase in nitrogen dioxide content lead in the exhaust and thus the proposed here regeneration favor. Preferably, the rate of recirculation is Current in the range up to 60 vol .-%, especially in a range from 20% to 50% by volume.

According to one Further development of the method becomes a reduction in the operating phase the combustion chamber temperature made in the internal combustion engine. It was found that during combustion processes, which are carried out at a lower temperature, usually a high proportion of nitrogen dioxide is produced in the exhaust gas. Especially For example, the combustion chamber temperature will become a peak temperature controlled combustion in a range below 450 ° C.

About that It is also considered advantageous that in the operational phase, alternatively or cumulatively to the abovementioned possibilities, a Increase of the boost pressure in the internal combustion engine is made. In this case, the exhaust aftertreatment system for example, with an exhaust gas turbine of the running, the a compression of the sucked air flow has the consequence. The boost pressure, So the pressure in the combustion chamber of the internal combustion engine, the fuel-air mixture is usually in the range of 30 to 50 bar. For the regeneration phase is now proposed in particular that an increase in the boost pressure, for example, at least 15%, possibly even 25% of the previously regulated boost pressure made becomes. As the boost increases, so does the peak temperature the combustion in the combustion chamber and thus the formation of nitrogen monoxide affected.

In addition, it is also possible to make an increase in the oxygen content in the internal combustion engine in the operating phase. Accordingly, the combustion is carried out, for example, with an even higher excess air. For example, the oxygen content in the fuel-air mixture can be raised to a value of at least 1% and, in particular, regulated in a range from lambda 1.05 to 1.1 (about 1% oxygen or 2% oxygen). The so-called combustion air ratio (lambda) sets the actual air mass m _{(AIR, actually)} available for combustion in relation to the minimum necessary stoichiometric air mass m _{(AIR, stoichiometric)} required for complete combustion. Also, this effect can, in particular for a short time, to the desired generation of nitrogen lead dioxides.

For an equally effective implementation of the carbonaceous Particles at the same time low volume of the intended particle agglomerator It is also suggested that the internal combustion engine operated this way is that in the exhaust carbonaceous particles with majority a mean diameter of at most 200 nanometers [nm] are generated. The internal combustion engine is very particularly preferred operated so that the mean diameter at most 100 nanometers. Basically, this is true preferably also in an operating state of the internal combustion engine, not with the operating phase for regeneration of the particle agglomerator (Regeneration phase) matches. The very small particles can be particularly cheap with the provided Nitrogen dioxide converted to carbon dioxide and elemental nitrogen become. For providing the particles of this size, in particular, the outlet of the combustion chamber and the exhaust pipe should be adjusted, so that excessive agglomeration from particles to a size above the here mentioned limit value is avoided.

Further It is also proposed that at least in the operational phase a active temperature increase of the exhaust gas carried out becomes. This means in particular that the exhaust gas in the exhaust aftertreatment system with additional means for increasing the temperature be contacted at the latest at the Contacting with the particles to be reacted a setpoint temperature for significant implementation of the CRT method. The means for increasing the temperature include in particular (uncoated) (electrically operated) radiators, heat exchangers and the same. The idea of targeted or regulated (non-catalytic and / or catalytic) temperature increase of the exhaust gas to improve the oxidation of nitrogen monoxide in the exhaust aftertreatment plant can generally have significant benefits in implementation of the CRT procedure - is therefore possibly independent from the method described herein according to the invention desirable..

According to a further aspect of the invention, a motor vehicle comprising an internal combustion engine and an exhaust aftertreatment system is proposed, which is designed with at least one continuously regenerable particle agglomerator, wherein the internal combustion engine sole active nitrogen dioxide (NO ₂ ) source up to at least one particle agglomerator and the at least one particle agglomerator a bypass filter is.

The here proposed motor vehicle can in particular according to the here operated according to the invention described method so that a non-thermal regeneration of at least a particle agglomerator to desired operating phases is possible. The proposed motor vehicle draws characterized by its particularly simple exhaust aftertreatment system, wherein a corresponding control of the internal combustion engine results in a safe regeneration of the particle agglomerator, so that clogging of the particle agglomerator and thus a pressure increase over the particle agglomerator is avoided.

In essence, reference is made to the above explanations with respect to the design of the internal combustion engine as the sole (single), active nitrogen dioxide source. With regard to the particle agglomerator proposed here, it is specified that this comprises a bypass filter. Such a bypass filter is characterized in that it provides a plurality of flow paths for the exhaust gas, wherein the exhaust gas (theoretically) has the ability to flow the particle agglomerator, without coming in contact with a filter material, or to flow through this. For this purpose, the bypass filter can be formed in the manner of a honeycomb body, which is designed for example with channel walls which are at least partially formed with a gas-impermeable material and optionally may additionally comprise a filter medium. The gas-impermeable material (preferably a metal foil) is mm with projections, vane executed, which at least partially close the channel (or redirect) and thus cause a deflection of at least a portion of the exhaust stream towards the channel wall (or the filter medium). In this case, the elevations are formed so that they do not completely close the channel at any point, thus allowing a bypass flow past the survey. A possible structure of such a bypass filter is for example from the WO 01/80978 A1 or the WO 02/00326 A1 so that reference may be made in particular to these documents for explanation.

According to a preferred embodiment variant of the motor vehicle, the at least one particle agglomerator has at least a first zone and a second zone in the flow direction of the exhaust gas, wherein the second zone extends as far as a downstream end side and the second zone comprises an oxidation catalytic converter. This means in particular that the particle agglomerator can be subdivided into at least two zones extending in the axial direction and over the entire cross section of the particle agglomerator, wherein the downstream zone extending to the downstream end of the particle agglomerator comprises an oxidation catalyst hen is. In this case, the first zone is preferably catalytically inactive - that is, for example, free of a coating. The oxidation catalyst can be designed, for example, in the manner of a conventional waxcoat coating with a noble metal doping.

The Invention and the technical environment will now be based on the figures explained in more detail. It should be noted that the figures particularly preferred embodiments of the Invention, but not limited thereto is. They show schematically:

1 A first variant of an exhaust aftertreatment system of a motor vehicle

2 a possible course of the nitrogen dioxide concentration during the operation of the internal combustion engine,

3 the construction of a favorable particle agglomerator in detail and

4 : A cross section through a further embodiment of a particle agglomerator.

1 is intended schematically a possible structure for an exhaust aftertreatment system 2 an internal combustion engine 3 of a motor vehicle 4 illustrate, which is in principle suitable for carrying out the method described here. The car 4 thus initially has an internal combustion engine 3 , in particular a diesel engine, having a plurality of combustion chambers 21 has burned in which the supplied fuel-air mixture and from which the exhaust gas through the exhaust pipe 19 is discharged into the environment.

This is an exhaust aftertreatment system 2 shown in the flow direction 7 after the internal combustion engine 3 a branch for exhaust gas recirculation 12 has, so that regulated a part of the exhaust gas flow back to the combustion chambers 21 the internal combustion engine 3 can be supplied. Further downstream in the direction of flow 7 is a particle agglomerator 1 shown. This is followed further downstream by a turbocharger 13 , wherein when flowing through the exhaust gas 13 at the same time a turbine is driven, which controls the amount of air flowing through the intake tract 20 the internal combustion engine 3 is fed, compressed.

After now the exhaust gas in the flow direction 7 continue the exhaust pipe 19 , for example, into an underbody area of the motor vehicle 4 , has flowed, it is with other exhaust aftertreatment units 24 further freed of pollutants. In the case illustrated here, the exhaust gas flows in Strö flow direction 7 an oxidation catalyst 11 , a filter 22 and an SCR catalyst 23 (for selective catalytic reaction of nitrogen oxide), wherein the exhaust gas upstream of the SCR catalyst 23 is mixed with a reducing agent that only a corresponding reducing agent addition 25 is initiated. The cleaned and reacted exhaust gas then flows through the exhaust pipe 19 in the nearby areas.

The illustrated here construction of the exhaust aftertreatment system 2 allows in particular a discontinuous, targeted regeneration of the particle agglomerator 1 with nitrogen dioxide, which specifically with the internal combustion engine 3 to be provided.

In 2 are schematically and exemplified different courses of the nitrogen dioxide concentration of the exhaust gas produced by the internal combustion engine for a regeneration of the particle agglomerator. The abscissa 30 indicates the time, while the ordinate 31 essentially illustrates the nitrogen dioxide concentration.

Regarding a first course 26 It should be noted that the nitrogen dioxide concentration is usually below a given regeneration field 28 during operation of the internal combustion engine 3 is arranged. If now a regeneration of the particle agglomerator take place, then the nitrogen dioxide concentration in the exhaust gas over a regeneration phase 29 or an operating phase of the internal combustion engine adjusted so that these in regeneration field 28 lies. If the requirements for the internal combustion engine change (eg performance query, load range, ...) or the regeneration of the particle agglomerator is finished, the internal combustion engine can 3 be operated again with a lower proportion of nitrogen dioxide in the exhaust gas. Thus, a non-thermal regeneration of the particle agglomerator can be carried out discontinuously and at predetermined and / or calculated times.

In addition, it is also possible that the proportion of nitrogen dioxide in the exhaust gas is basically controlled so that this at regular intervals and / or permanently in the field of regeneration field 28 lies, as in particular by the dashed lines shown second course 27 is illustrated.

3 illustrates a detail of a variant embodiment of a particle agglomerator 1 , This is with substantially smooth Feinstdrahtlagen 15 executed in the manner of a metallic fleece, between which structured metal foils 14 provided see, so in the direction of flow 7 or a corresponding axis of the particle agglomerator 1 along extending channels 16 form. Inside these channels 16 are through fins 32 in the metal foil 14 Kanalengstellen 17 formed, which is a (partial) discharge of the exhaust stream towards the Feinstdrahtlage 15 cause. Here are the channel narrows 17 or the fins 32 so formed that the channel 16 not completely closed, but a side stream 33 remains possible. As a result of the evasion of the guide surface 32 from the metal foil 14 becomes a passage opening 18 formed, the passage of exhaust gas to adjacent channels 16 allows.

In addition, in the 3 illustrates that the exhaust gas containing nitrogen (NO ₂ ), carbon (C) and oxygen (O ₂ ) in the particle agglomerator 1 occurs and there is an implementation of the contained carbonaceous particles 5 using the nitrogen dioxide, so that nitrogen monoxide (NO), nitrogen (N ₂ ), carbon dioxide (CO ₂ ) and oxygen (O ₂ ) finally the particle agglomerator 1 leave again. With the help of the particle agglomerator, the probability of the reaction of nitrogen oxide and soot particles is significantly increased, so that relatively high conversion rates can be realized with low pressure loss of the exhaust gas and clogging of the particle agglomerator is reliably avoided.

In 4 is a particle agglomerator 1 shown in the flow direction 7 first a first zone 8th and then a second zone 9 has, extending to a rear end 10 extends. Basically, the particle agglomerator 1 over its entire length with smooth Feinstdrahtlagen 15 and structured metal foils 14 executed, wherein the metal foils 14 in neighboring channels 16 mutually (oppositely arranged) tapered canal narrowing 17 have at the same time a side stream 33 allow and a portion of the exhaust gas towards Feinstdrahtlage 15 cause. That way, the particles become 5 , preferably with a diameter 6 less than 200 nm, in or on the walls (or the fine wire layer) of the particle agglomerator 1 attached and reacted with the nitrogen dioxide provided. The first zone 8th has no oxidatively effective coating, while the second zone 9 by a suitably provided oxidation catalyst 11 again generated new nitrogen dioxide for regeneration of the particle agglomerator in the back in situ.

Of course, various modifications of the system proposed herein may readily be made without departing from the spirit of the invention as described herein. For example, other particle agglomerators can be used, but it is also possible to use the particle agglomerator 1 for example, after a turbocharger 13 to position. The following exhaust aftertreatment units 24 can be combined and supplemented as desired. In addition, the invention can also be operated with another internal combustion engine - such. B. a direct-injection gasoline engine.

1

particle agglomerator

2

aftertreatment system

3

Internal combustion engine

4

motor vehicle

5

particle

6

diameter

7

flow direction

8th

first Zone

9

second Zone

10

front

11

oxidation catalyst

12

Exhaust gas recirculation

13

turbocharger

14

metal foil

15

Feinstdrahtlage

16

channel

17

Kanalengstelle

18

Through opening

19

exhaust pipe

20

intake system

21

combustion chamber

22

filter

23

SCR catalyst

24

exhaust gas treatment unit

25

Reducing agent addition

26

first course

27

second course

28

regeneration field

29

regeneration phase

30

abscissa

31

ordinate

32

baffle

33

sidestream

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 01/80978 A1 [0018]
• WO 02/00326 A1 [0018]

Claims (11)

Process for the regeneration of at least one particle agglomerator ( 1 ) an exhaust aftertreatment system ( 2 ) an internal combustion engine ( 3 ) of a motor vehicle ( 4 ), in which the internal combustion engine ( 3 ) is operated at least in an operating phase, that directly a sufficient proportion of nitrogen dioxide (NO ₂ ) is generated in the exhaust gas to a conversion of carbonaceous particles ( 5 ) in the at least one particle agglomerator ( 1 ) to ensure. Method according to claim 1, in which the internal combustion engine ( 3 ) a proportion of nitrogen dioxide (NO ₂ ) in the range of 25 vol .-% to 60 vol .-% of all existing nitrogen oxides (NO _x ) is. Method according to claim 1 or 2, in which the internal combustion engine ( 3 ) to at least one particle agglomerator ( 1 ) alone nitrogen dioxide (NO ₂ ) actively generated. Method according to one of the preceding claims, wherein in the operating phase an increase in the proportion of a in the internal combustion engine ( 3 ) guided back exhaust stream is made. Method according to one of the preceding claims, wherein in the operating phase, a reduction of the combustion chamber temperature in the internal combustion engine ( 3 ) is made. Method according to one of the preceding claims, wherein in the operating phase an increase of the boost pressure in the internal combustion engine ( 3 ) is made. Method according to one of the preceding claims, wherein in the operating phase an increase in the oxygen content in the internal combustion engine ( 3 ) is made. Method according to one of the preceding claims, in which the internal combustion engine ( 3 ) is operated so that in the exhaust carbonaceous particles ( 5 ) with a majority of average diameter ( 6 ) of at most 200 nanometers. Method according to one of the preceding claims, at least during the operating phase, an active temperature increase the exhaust gas is carried out. Motor vehicle ( 4 ) comprising an internal combustion engine ( 3 ) and an exhaust aftertreatment system ( 2 ), which with at least one continuously regenerable particle agglomerator ( 1 ) is executed, wherein the internal combustion engine ( 3 ) sole active nitrogen dioxide (NO ₂ ) source up to at least one particle agglomerator ( 1 ) and the at least one particle agglomerator ( 1 ) is a bypass filter. Motor vehicle ( 4 ) according to claim 10, wherein the at least one particle agglomerator ( 1 ) in the flow direction ( 7 ) of the exhaust gas at least a first zone ( 8th ) and a second zone ( 9 ), the second zone ( 9 ) to a downstream end face ( 10 ) and the second zone ( 9 ) an oxidation catalyst ( 11 ).