EP2171228B1 - Method for the regeneration of at least one particle agglomerator and motor vehicle comprising an exhaust gas after-treatment 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 present invention relates to a method for the regeneration of at least one particle agglomerator of an exhaust aftertreatment system of an internal combustion engine of a motor vehicle. In addition, the invention also relates to a motor vehicle, comprising an internal combustion engine and an exhaust aftertreatment system, which is designed with at least one continuously regenerable particle agglomerator. In that regard, the invention relates in particular to the removal of soot particles of 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 to such a high level (eg, above 800 ° C.) that reaction of the carbon with the oxygen introduced 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 carbon, so that contacts of the Nitrogen dioxide with the soot particles regularly forms carbon dioxide and nitrogen.

In the known methods and apparatuses with respect to the passively regenerable particle agglomerator (CRT method), an oxidation coating is provided upstream of the particle agglomerator or directly in the particle agglomerator. However, this regular platinum-containing coating is expensive and may require additional exhaust treatment facilities that result in more complex exhaust aftertreatment systems.

From the DE 10 2004 045 178 A1 An exhaust system is known in which a particulate receiving reservoir is regenerated by NO ₂ contained in the exhaust gas, so that a downstream particle trap can be relieved with regard to the particle volume. The positioning of the particulate receiving accumulator takes place so close to the engine that it is at least partially regenerated during operation due to the NO ₂ -Oxidationseffekts. Thus, a relief of the particulate filter unit is to be achieved, which is located further downstream. For the removal of the entire particles in both particle traps, NO ₂ produced by an oxidation catalyst is also used.

On this basis, it is an object of the present invention, at least partially solve the problems described with reference to the prior art. In particular, a practicable and cost-effective method for the regeneration of at least one particle agglomerator is to be specified, which in particular allows an on-demand passive regeneration. In addition, a suitable device for such a method is to be specified, which is characterized by a low pressure drop and a particularly high efficiency with small particles (for example, with a mean diameter of at most 500 nanometers).

These objects are achieved by a method according to the features of claim 1. Further advantageous embodiments of the invention are specified in the dependent formulated claims. It should be noted that the features listed individually in the claims in any technologically meaningful way, can be combined with each other and show other embodiments of the invention. The description, in particular in conjunction with the figures, illustrates further embodiments of the invention.

In the inventive method for regeneration of at least one particle agglomerator in an exhaust aftertreatment system of an internal combustion engine a motor vehicle, the internal combustion engine is operated at least in an operating phase so that a sufficient proportion of nitrogen dioxide (NO ₂ ) is generated directly in the exhaust gas to ensure a targeted implementation of carbonaceous particles with the 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 here proposed to operate the internal combustion engine, at least in a specific operating phase (regeneration phase), such as in a low-load situation, so that a sufficiently high proportion of nitrogen dioxide is generated directly by the internal combustion engine. A "regeneration phase" is understood as meaning a time interval in which the particle quantity in the particle agglomerator is reduced, in particular by at least 20% by weight, if appropriate by at least 40% by weight or even by at least 80% by weight. For the individual mechanisms, as the internal combustion engine can be regulated accordingly, reference will be made below in detail. 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.

The method operates the internal combustion engine so that a proportion of the nitrogen dioxide (NO ₂ ) is in the range of 25% by volume to 60% by volume of all nitrogen oxides present (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 essentially does not exceed 60% by volume in order to still be able to generate sufficient power via the internal combustion engine.

According to the invention, it is proposed that the internal combustion engine actively generate 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, are particularly easy to perform and a targeted regeneration of the particle agglomerator can be controlled by the corresponding operation of the internal combustion engine. 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.

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

According to a development of the method, a lowering of the combustion chamber temperature in the internal combustion engine is carried out in the operating phase. It has been found that combustion processes that are carried out at a lower temperature usually produce a high proportion of nitrogen dioxide in the exhaust gas. In particular, the combustion chamber temperature for this purpose is controlled according to a peak combustion temperature in a range below 450 ° C.

In addition, it is also considered advantageous that in the operating phase, alternatively or cumulatively to the aforementioned possibilities, an increase in the boost pressure in the internal combustion engine is made. In this case, the exhaust aftertreatment system is designed for example with an exhaust gas turbocharger, which has a compression of the intake air flow result. 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, it is now proposed, in particular, that an increase in the charge pressure be made, for example, by at least 15%, possibly even 25%, of the previously regulated charge pressure. With the increase of the boost pressure, the peak temperature of the combustion in the combustion chamber and thus the formation of nitrogen monoxide is also influenced.

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 increased by 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 available for combustion m _{(AIR, in fact)} . in relation to the minimum necessary stoichiometric air mass m _(AIR , _{stoichiometric)} , which is needed for complete combustion. This effect can, in particular for a short time, lead to the desired generation of nitrogen dioxides.

For an equally effective conversion of the carbonaceous particles with simultaneously low volume of the intended particle agglomerator, it is also proposed that the internal combustion engine be operated in such a way that carbonaceous particles having a mean diameter of at most 200 nanometers [nm] are produced in the exhaust gas. Most preferably, the internal combustion engine is operated so that the average diameter is at most 100 nanometers. In principle, this also preferably applies in an operating state of the internal combustion engine that does not coincide with the operating phase for regeneration of the particle agglomerator (regeneration phase). The very small particles can be converted particularly favorably with the provided nitrogen dioxide to carbon dioxide and elemental nitrogen. For the provision of the particles of this size, in particular the outlet of the combustion chamber and the exhaust pipe are to be adjusted so that an excessive agglomeration of particles towards a size above the limit value mentioned here is avoided.

Furthermore, it is also proposed that at least in the operating phase an active temperature increase of the exhaust gas is carried out. This means, in particular, that the exhaust gas in the exhaust aftertreatment system is brought into contact with additional means for increasing the temperature, so that this has a target temperature for the significant implementation of the CRT method at the latest when contacting with the particles to be reacted. The means of increasing the temperature include in particular (uncoated) (electrically operated) radiators, heat exchangers and the like. The idea of targeted or controlled (non-catalytic and / or catalytic) temperature increase of the exhaust gas to improve the oxidation of nitrogen monoxide in the exhaust aftertreatment system can generally bring significant benefits in the implementation of the CRT process - is thus possibly also independent of the here Desirable according to the invention described method.

Furthermore, a motor vehicle comprising an internal combustion engine and an exhaust aftertreatment system is proposed, which is embodied with at least one continuously regenerable particle agglomerator, 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 (also " Semi-filter "is called).

The motor vehicle proposed here is operated according to the method described here according to the invention, so that a non-thermal regeneration of the at least one particle agglomerator to desired operating phases is possible. The proposed motor vehicle here is characterized by its particularly simple exhaust aftertreatment system, with a corresponding control of the internal combustion engine has a safe regeneration of the particle agglomerate result, so that clogging of the particle agglomerator and thus a pressure increase across 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, the exhaust gas (theoretically) the possibility has to flow the particle agglomerator, without coming into 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 now executed with elevations, guide vanes, which at least partially close (or deflect) the channel and thus cause a deflection of at least part of the exhaust gas flow toward 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 is provided with an oxidation catalytic converter. 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 customary washcoat coating with a noble metal doping.

Fig. 1:

eine erste Ausführungsvariante einer Abgasnachbehandlungsanlage eines Kraftfahrzeugs,

Fig. 2:

einen möglichen Verlauf der Stickstoffdioxid-Konzentration wäh- rend des Betriebs der Verbrennungskraftmaschine,

Fig. 3:

den Aufbau eines vorteilhaften Partikelagglomerators im Detail und

Fig. 4:

einen Querschnitt durch eine weitere Ausgestaltung eines Partike- lagglomerators.

The invention and the technical environment will now be explained in more detail with reference to FIGS. It should be noted that the figures were particularly preferred Embodiment variants of the invention, but this is not limited thereto. They show schematically:

Fig. 1:

a first embodiment of an exhaust aftertreatment system of a motor vehicle,

Fig. 2:

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

3:

the structure of an advantageous particle agglomerator in detail and

4:

a cross section through a further embodiment of a particle lagglomerators.

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

Here, an exhaust aftertreatment system 2 is shown, which has a branch for an exhaust gas recirculation 12 in the flow direction 7 after the internal combustion engine 3, so that regulated part of the exhaust gas stream can be fed back to the combustion chambers 21 of the internal combustion engine 3. Further downstream in the direction of the flow direction 7, a particle agglomerator 1 is shown. This is followed downstream of a turbocharger 13, wherein the passage of the exhaust gas 13 at the same time a turbine is driven, the Air quantity, which is supplied via the intake manifold 20 of the internal combustion engine 3, compressed.

Now that the exhaust gas has flowed further in the direction of flow 7, the exhaust pipe 19, for example all the way into an underbody area of the motor vehicle 4, it is further freed from pollutants with further exhaust aftertreatment units 24. In the case illustrated here, the exhaust gas flows in the flow direction 7 an oxidation catalyst 11, a filter 22 and an SCR catalyst 23 (for the selective catalytic reaction of nitrogen oxide), wherein the exhaust gas is mixed before the SCR catalyst 23 with a reducing agent that only one corresponding reducing agent addition 25 is initiated. The thus purified and reacted exhaust gas then flows finally through the exhaust pipe 19 into the environment.

The structure of the exhaust gas aftertreatment system 2 illustrated here permits, in particular, a discontinuous, targeted regeneration of the particle agglomerator 1 with nitrogen dioxides, which are provided specifically with the internal combustion engine 3.

In Fig. 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 substantially illustrates the nitrogen dioxide concentration.

With regard to a first course 26, it should be noted that the nitrogen dioxide concentration is usually arranged below a predetermined regeneration field 28 during operation of the internal combustion engine 3. If a regeneration of the particle agglomerator now takes place, then the nitrogen dioxide concentration in the exhaust gas is adjusted via a regeneration phase 29 or an operating phase of the internal combustion engine such that it lies in regeneration field 28. Should the requirements of the internal combustion engine Change (eg, performance query, load range, ...) or be completed, the regeneration of the particle agglomerator, the internal combustion engine 3 can be operated again with a smaller 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, however, it is also possible that the proportion of nitrogen dioxide in the exhaust gas is in principle regulated so that it is at regular intervals and / or permanently in the region of the regeneration field 28, as illustrated in particular by the second curve 27 shown in dashed lines.

Fig. 3 FIG. 1 illustrates a detail of a variant embodiment of a particle agglomerator 1. It is designed with substantially smooth ultrafine wire layers 15 in the manner of a metallic nonwoven, between which structured metal foils 14 are provided, so that channels 16 extend along flow direction 7 or a corresponding axis of particle agglomerator 1 form. Inside these channels 16 channel fences 17 are formed by guide surfaces 32 in the metal foil 14, which cause a (partial) discharge of the exhaust gas flow to Feinstdrahtlage 15. Here, the channel galleries 17 and the guide surfaces 32 are formed so that the channel 16 is not completely closed, but a side stream 33 remains possible. As a result of the protuberance of the guide surface 32 of the metal foil 14, a passage opening 18 is formed, which allows the passage of exhaust gas to adjacent channels 16.

In addition, in the Fig. 3 illustrates that the exhaust gas containing nitrogen dioxide (NO ₂ ), carbon (C) and oxygen (O ₂ ) enters the particle agglomerator 1 and uses a reaction of the carbonaceous particles 5 contained therein with the nitrogen dioxide, so that nitrogen monoxide (NO), nitrogen (N ₂ ), carbon dioxide (CO ₂ ) and oxygen (O ₂ ) finally leave the particle agglomerator 1 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 Fig. 4 a particle agglomerator 1 is shown, which first in the flow direction 7 has a first zone 8 and then a second zone 9, which extends to a rear end face 10. In principle, the particle agglomerator 1 is designed over its entire length with smooth ultrafine wire layers 15 and structured metal foils 14, the metal foils 14 in adjacent channels 16 having mutually (oppositely disposed) tapered channel channels 17 which simultaneously allow a bypass 33 and a portion of the exhaust gas cause the fine wire layer 15. In this way, the particles 5, preferably with a diameter 6 less than 200 nm, are deposited in or on the walls (or the fine wire layer) of the particle agglomerator 1 and reacted with the nitrogen dioxide provided. In this case, the first zone 8 has no oxidatively effective coating, while the second zone 9 again generates in situ by means of a correspondingly provided oxidation catalytic converter 11 new nitrogen dioxide for regeneration of the particle agglomerator in the rear part.

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 position the particle agglomerator 1, for example, after a turbocharger 13. The subsequent 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 Otto engine.

LIST OF REFERENCE NUMBERS

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

Claims (9)

1. A method for regenerating at least one particle agglomerator (1) of an exhaust gas after treatment system (2) of an internal combustion engine (3) of a motor vehicle (4), in which the combustion engine (3) is operated at least in one operating phase to cause a proportion of nitrogen dioxides (NO₂) being sufficient to ensure a targeted conversion of carbon-containing particles (5) in the at least particle agglomerator (1) to be directly generated in the exhaust gas, wherein the internal combustion engine (3) is correspondingly operated to targetly produce exhaust gas in which the proportion of the nitrogen dioxides (NO₂) is in a range of from 25 % by volume to 60 % by volume of all nitrogen oxides (NO_x) present, wherein the internal combustion engine (3) up to the at least one particle agglomerator (1) solely actively generates nitrogen dioxide (NO₂).
2. The method according to claim 1 in which a proportion of an exhaust gas flow being recirculated into the internal combustion engine (3) is increased in the operating phase.
3. The method according to any of the preceding claims, wherein a combustion chamber temperature in the internal combustion engine (3) is reduced in the operating phase.
4. The method according to one of the preceding claims, wherein a charge pressure in the internal combustion engine (3) is increased in the operating phase.
5. The method according to one of the preceding claims, wherein an oxygen content in the internal combustion engine (3) is increased in the operating phase.
6. The method according to one of the preceding claims, wherein the internal combustion engine (3) is operated so that carbon-containing particles (5) in the exhaust gas are generated with a majority of the carbon-containing particles (5) having a mean diameter (6) of at most 200 Nanometers.
7. The method according to one of the preceding claims, wherein a temperature of the exhaust gas is actively increased at least in the operating phase.
8. A motor vehicle (4) comprising an internal combustion engine (3) and an exhaust gas after treatment system (2) having at least one continuously regenerable particle agglomerator (1), wherein the internal combustion engine (3) is being the sole active nitrogen dioxide (NO₂) source up to the at least one particle agglomerator (1), wherein a control for the internal combustion engine is arranged for carrying out the method according to one of the preceding claims, and wherein the at least one particle agglomerator (1) is a bypass flow filter.
9. The motor vehicle (4) according to claim 8, in which the at least one particle agglomerator (1) includes, in a flow direction (7) of the exhaust gas, at least one first zone (8) and a second zone (9), wherein the second zone (9) extends to a downstream positioned end side (10) and the second zone (9) includes an oxidation catalytic converter (11).

Images