WO2000008310A1

WO2000008310A1 - Method and device for post-treatment of exhaust gases of an internal combustion engine

Info

Publication number: WO2000008310A1
Application number: PCT/EP1999/004187
Authority: WO
Inventors: Axel König
Original assignee: Volkswagen Aktiengesellschaft
Priority date: 1998-07-31
Filing date: 1999-06-17
Publication date: 2000-02-17
Also published as: JP2002522684A; CN1311844A; EP1101019A1; US20010004831A1

Abstract

The invention relates to a method and device for post-treating the exhaust gases of an internal combustion engine. The inventive device comprises a body (4) through which exhaust gases flow and which is rotatably placed in the flow of said exhaust gases, as well as a filter (6) which can rotate with said body (4). The rotation speed of the body (4) is selected so that a major part of the temperature front which forms in the body remains in said body. Preferably, said body is in the form of a cylinder with an axial cavity (7) which houses the filter (6) and through which channels (3) extend in the radial direction (3). The rotation axis of said cylinder is perpendicular to the direction of flow of the exhaust gases. When the body is in the form of a NOx accumulating catalyst, removal of nitric oxide can be achieved by cyclic enrichment of the exhaust gases or by introduction of extra fuel in the inventive device. Thus, desulfurization of the catalyst is triggered by a corresponding command of rotation of said catalyst.

Description

Device and method for the aftertreatment of the engine exhaust gases

Internal combustion engine

The invention relates to a device and a method for the aftertreatment of the engine exhaust gases of an internal combustion engine, and in particular relates to a device and a method for the aftertreatment of soot particles and / or nitrogen oxides in the exhaust gas stream.

Known NOx catalysts absorb the nitrogen oxides generated during the lean operation of an engine and reduce the stored NOx during rich operation of the engine, the known processes being discontinuous and the storage and reduction of the nitrogen oxides taking place in different phases. In order to be able to carry out such a method, the memory must be emptied after a certain time due to its finite absorption capacity. This either happens after a fixed predetermined time or the degree of filling of the catalyst must be determined. If the memory is regenerated after a predefined time has elapsed, this has the disadvantage that the storage capacity of the catalytic converter is not fully utilized for safety reasons, so that optimum engine operation with regard to consumption and exhaust gas behavior is not possible. If the storage is regenerated when a certain filling level of the storage is reached, this has the disadvantage that an additional device is required which determines the filling level of the NOx storage catalytic converter. The exact determination of the degree of filling of the memory is difficult, so that here too the switch is made to regenerative operation when the memory is not yet completely filled. Ultimately, this also leads to less than optimal operation of the engine. Furthermore, it applies to both methods that optimal exhaust gas behavior is not achieved during rich engine operation and complicated engine control is required for cyclic engine operation.

Furthermore, a minimum temperature of approximately 250 ° C. is required for a NOx storage catalytic converter to function adequately. If the exhaust gas coming from the engine is too cold, the process can only work if the catalytic converter is on it Minimum temperature is heated. This causes heat losses, which greatly increases the energy requirement.

In addition, soot particles occur in the exhaust gas of diesel engines that cannot be released into the environment. For the aftertreatment of such gases containing soot particles, the soot particles are retained in a known device and are cyclically replaced when the soot filter reaches a certain filling level, or the retained soot particles are ignited and burned with an appropriate heating device. Both approaches are unsatisfactory for continuous use.

The invention is therefore based on the object of developing a device and a method for treating the exhaust gas flow of an internal combustion engine, which enable optimal engine operation.

The invention is solved by the features of claims 1, 24 and 27. Preferred embodiments of the invention are the subject of the dependent claims.

The device according to the invention for the aftertreatment of the engine exhaust gases of an internal combustion engine has a body or monolith with channels through which the exhaust gas flows and which is rotatably arranged in the exhaust gas flow. Monolith is understood here to mean a body which can be made in one piece from ceramic, from metallic carrier materials or from ceramic or metallic segments which are arranged in a receiving structure.

Furthermore, the device has an inflow channel which is in flow connection with a part (B1) of the channels of the body. Furthermore, a flow connection is provided, which is connected on the output side to the part B1 of the ducts flowed against by the inflow duct and connects this in terms of flow to a part B2 of the ducts which is not in flow connection to the inflow duct.

The body or monolith is preferably divided into two areas B1, B2, the exhaust gas entering the first area B1 on the front face of the body, exiting on the rear face of the first area B1, passing through the filter attached there, into one End face of the second area B2 enters and leaves the second area B2 on the other end face 2, the body 4 during the Flow around an axis essentially perpendicular to the flow direction of the exhaust gas stream.

The body preferably has a cylindrical shape, the channels extending in the radial direction. The body has a cylindrical recess in the axial direction, in other words the cylinder is hollow in the axial direction. The body can consist of metal or ceramic, whereby it can be formed in one piece or assembled from segments. If the body consists of segments, these are traversed by channels so that the channels extend in radial direction with respect to the axis of symmetry of the cylinder after the segments have been assembled.

Preferably, the device comprises a filter which can be rotatably arranged, the filter in particular being able to rotate with the monolith, in the case of the cylindrical body with the axial cavity the filter being arranged therein. The filter can be stationary or rotate with the body, the speed of rotation not having to be identical to the speed of rotation of the body.

Furthermore, the internal combustion engine has a direct fuel injection into the combustion chamber and / or is a diesel fuel engine.

The filter preferably has a heating element which serves to bring the filter to operating temperature after a cold start. After reaching the required temperature, the heating element can be switched off. In principle, additional heating is only provided if the engine conditions (exhaust gas temperature) do not lead to soot burn-off. In particular, the temperature required for the conversion of pollutants can alternatively or in a supportive manner also be quickly achieved by suitably selected engine parameters (injection quantity, injection course, post-injection); here, too, the engine parameters are returned to their normal conditions when the desired temperature has been reached.

Furthermore, the body can be at least partially catalytically coated to reduce pollutants, in particular to reduce NOx, HC and / or CO. The device also has a fixed housing (12) in which the body rotating about its longitudinal axis is arranged. The housing is preferably made of a non-metallic material.

The body is preferably rotated by a drive unit. The drive unit can be formed by an electric motor. It is also possible for the drive unit to be formed by an external magnetic field and magnets arranged inside the housing. Furthermore, the body can also be rotated through the exhaust gas flow in the manner of a turbine. The speed of rotation of the body (4) is preferably approximately 0.3 to 10 rpm, the speed of rotation being selected so that the maximum of the temperature distribution which arises remains inside the body, preferably at the location of the filter.

Furthermore, the device can have a means for introducing additional fuel in order to bring about a reduction in the NOx exhaust gas component when the engine can be operated lean. The means for introducing additional fuel is preferably arranged in the axis of rotation of the body.

The method according to the invention for the aftertreatment of the exhaust gas of an internal combustion engine, a body being arranged in the exhaust gas flow and having channels in the exhaust gas flow direction and being divided into two areas, has the following steps:

Directing the exhaust gas flow into the front end face of a first area,

Directing the exhaust gas flow at the rear end face of the first area into an end face of a second area and releasing the exhaust gas flow at the other end face of the second area, and

Rotating the body around an axis during operation so that the channels change from the first area to the second area.

Furthermore, the body is rotated about its axis at such a speed that heating of the second region by the exhaust gas flow leads to heating of the exhaust gas flow by the first region. A retention of the soot particles of the exhaust gas flow is preferably effected on a filter which is arranged between the exhaust gas outlet side face of the first region and the exhaust gas inlet side end face of the second region, and the speed of rotation is selected such that the maximum of the temperature front approximately approaches the filter located.

The body used in the method is preferably at least partially catalytically coated, so that NOx storage of the exhaust gas is effected during the lean phases of the internal combustion engine. A continuous NOx storage regeneration process can be brought about by adding reducing agents to the body.

The method according to the invention for desulfating the device according to the invention for aftertreatment of the exhaust gases of an internal combustion engine, the device being designed as a NOx storage device, has the following steps:

Slowing or stopping the rotation of the body while simultaneously increasing the amount of pollutants in the exhaust gas at the beginning of the desulfation until a temperature maximum has migrated into or through the second region, in particular near the end face of the second region on the exhaust outlet side,

Rotating the body until the second area at least predominantly takes the place of the first area, so that the temperature maximum is predominantly in the first area, and suspending the rotation until the temperature maximum has reached at least the second area,

Decrease post-injection and re-rotate the body.

It may be necessary to repeat the slowdown of the rotation or the stop several times until essentially all areas have been desulfurized. The continuous rotation of the body is resumed when the temperature maximum is approximately at the interface of the two areas. A preferred embodiment of the invention is explained in more detail below with reference to the drawings.

1a shows a horizontal cross-sectional view through a first embodiment of the device according to the invention for the aftertreatment of the exhaust gas of an internal combustion engine,

Fig. 1b shows a vertical cross section through the device of Fig. 1a, and

2 shows a horizontal cross-sectional view through a second embodiment of the device according to the invention for the aftertreatment of the exhaust gas of an internal combustion engine

1a shows a horizontal cross section through a first preferred embodiment of a device according to the invention for the aftertreatment of the exhaust gas of an internal combustion engine. Raw exhaust gas from an engine (not shown) flows through an exhaust gas supply 1 into an outer end face 2, a first region B1 of a cylindrical body 4, which is traversed by channels 3. The channels 3 run in the radial direction with respect to the axis of rotation 9 formed by the axis of symmetry of the cylinder. The channels 3 arranged perpendicular to the axis of rotation 9 are at least partially catalytically coated, as has already been mentioned above. After the exhaust gas emerges from the inner end face 5 of the body 4, which is formed by an axial cavity 7 formed centrally in the body, the exhaust gas passes through a particle filter 6 arranged in the cavity 7 and passes through the outer end face 5 into an opposite second one Area B2 and enters an outflow channel 8 on the outer end face 2 of the second area B2. 1 a shows that the first area and the second area are limited to three channels 3 by the inflow channel 1 and the outflow channel 8. This is not absolutely necessary. Another construction of the housing 10 enclosing the body 4 can ensure that the inflowing and outflowing exhaust gas each reach a first and second region B1, B2 of a maximum of 180 °. In other words, the first and the second region can comprise at most half of the body 4. 1b shows a vertical section through the device according to the invention. The filter 6, which generally rotates synchronously with the body 4, is arranged in the interior of the body 4 through which the channels 3 pass. The body 4 and the filter 6 are arranged in a corresponding housing 10. The rotation takes place about an axis of rotation 9, which can serve as the supply of additional fuel for combustion in a catalytically active filter or in the rotor matrix, ie the body 4.

As a result of the filter 6 flowing through the body 4, the temperature rises on the inlet side due to the catalytic conversion of CO and HC present in the exhaust gas during the passage through the catalytically coated channels 3. At the same time, nitrogen oxides can be chemically absorbed if the channels 3 are coated with a NOx-absorbing catalyst. The temperature maximum is reached in the middle of the device, in the particle filter 6. Upon further passage through the body 4 or rotor, the exhaust gas releases its heat again and leaves the rotor 4 at approximately the same temperature as on the inlet side. Without rotation, the temperature front, i.e. the maximum temperature driven out of the device. By turning the rotor 4, the temperature font is driven back into the system again and again. On average, a periodically stationary profile is created, the maximum of which lies in the area of the filter 6.

2 shows a horizontal cross-sectional view through a second embodiment of the device according to the invention for the aftertreatment of the exhaust gas of an internal combustion engine, in which the device is operated as a pure NOx storage catalytic converter.

Fig. 2 shows a body 4 rotating about its longitudinal axis, which is coated as a NOx storage catalytic converter, which is used as a regenerative heat exchanger. The body 4 has a large number of fine channels 3 in the radial direction and the exhaust gas flows radially through it, namely the exhaust gas is supplied to it via an inflow channel 1 and is discharged via an outflow channel 8, as a result of which first and second regions B1, B2, as in the case of the first Embodiment are formed. Furthermore, the body has an axial cavity 7 which is delimited by the inner end face 5 of the body 4. The axial cavity serves for the fluidic connection of the channels 3 of the first and the second region B1, B2. Advantageously, there is no flow deflection, which keeps the pressure loss low. The inner part, represented as a circular ring T1, of the channels 3 is equipped with a NOx-storing Coated catalyst. The outer part of the channels, represented by a circular ring T2, is not coated and does not participate in the catalysis, it only functions as a heat exchanger. Due to the radial flow with simultaneous rotation, a temperature profile can be set in the body 4, which is located on the inlet and outlet sides of the outer end face 2 of the body approximately at the exhaust gas temperature and rises steeply towards approximately 350 to 400 ° C. towards the center . This means that part of the catalytic converter is always in an optimal temperature range for NOx storage. The rotating arrangement of the catalyst, ie the body 4, ensures the best possible heat recovery according to the regenerator principle. With ideal thermal insulation and correct dimensioning and rotation speed, the heat once entered will no longer leave the system. The heat losses actually occurring are compensated for by the heat of reaction which is released in the T1 area during the pollutant oxidation.

To start the cold system, the ignition temperature of approx. 200 ° C must be reached in the catalytically active area T2. For this purpose, an electrical heating element 11 can be provided in the middle of the body 4. As an alternative and / or as a support, the temperature required for the conversion of pollutants can also be achieved by suitably selected engine parameters (in particular in the case of common rail injection, for example by varying the injection timing, the injection process, the injection quantity, and / or post-injection). The measures are ended after the ignition temperature has been reached. The further temperature increase only takes place by a brief increase in the pollutant concentrations, which raises the catalyst temperature through the heat of reaction released in the area T1 during the conversion of the pollutants. This increase in the pollutant concentration can either be done by a separate fuel metering in the middle of the body 4, or can also be brought about by motor parameters.

The rotation of the body 4 is realized by a suitable electrical or mechanical drive (not shown). For this purpose, the body 4 is mounted on a rotatably mounted shaft or axis of rotation 9, which is set in rotation by the above-mentioned drive. The additional fuel can also be introduced through this shaft 9. When using an electric motor, the speed of rotation can be determined with the help of suitable information Engine control unit to be adapted to the operating state of the vehicle engine. Furthermore, the body 4 is arranged in a suitable fixed housing 10.

The regeneration of the NOx storage catalytic converter takes place in the known manner by engine enrichment of the exhaust gas.

If sulfur-containing fuel is used, the catalyst must be desulfated from time to time, as has already been described above. This is done thermally at temperatures above 600 ° C. As already mentioned above, in the system described an almost arbitrary temperature increase can be achieved by increasing the pollutant concentration or its oxidation. By appropriately controlling the speed of rotation and the concentration of pollutants, the catalyst can be kept at the required high temperatures for the required time of several minutes. As already described above, the energy consumption is significantly lower compared to conventional systems.

The following embodiments of the device described above using two examples are therefore possible:

Device with a body 4 rotatable in the exhaust gas flow without catalytic coating and without filter for generating a temperature maximum in the device;

Device with a body 4 rotatable in the exhaust gas flow and a filter 6 arranged in the body 4 for burning off the soot particles;

Device with a body 4 rotatable in the exhaust gas flow and an at least partial catalytic coating of the body 4;

Device with a body 4 rotatable in the exhaust gas flow, as well as a filter 6 arranged in the body 4 and an at least partial catalytic coating of the body. LIST OF REFERENCE NUMBERS

1 inflow channel

2 outer face

3 channels

4 bodies or rotor

5 inner face

6 filters

7 axial cavity

8 outlet channel

9 axis of rotation

10 housing

11 electric heating element

B1 first area

B2 second area

T1 inner ring

T2 outer ring

Claims

PATENTAN PRINTING

1. Device for the aftertreatment of the engine exhaust gases of an internal combustion engine, characterized in that the device has a body (4) with channels (3) through which the exhaust gas flows, which is rotatably arranged in the exhaust gas flow.

2. Device according to claim 1, characterized in that an inflow channel is provided which is in flow connection with a part (B1) of the channels (3) of the body (4).

3. Apparatus according to claim 2, characterized in that a flow connection is provided which is connected on the outlet side to the part (B1) of the ducts (3) which is flown against by the inflow duct and which is in flow terms with a part (B2) of the ducts (3). connects that is not in flow connection with the inflow channel.

4. Device according to one of the preceding claims, characterized in that the body (4) is divided into two areas (B1, B2), the exhaust gas on the front end face (2) of the body (4) in the first area (B1 ) occurs, exits at the rear end face (5) of the first area (B1), enters an end face (5) of the second area (B2) and leaves the second area (B2) at the other end face (2), the body (4) rotates about an axis substantially perpendicular to the direction of flow of the exhaust gas stream during the flow.

5. Device according to one of the preceding claims, characterized in that the device has a filter (6).

6. The device according to claim 5, characterized in that the filter is rotatably arranged, in particular together with the body (4).

7. Apparatus claim 4 and according to one of claims 5 or 6, characterized in that the filter (6) between the rear end face (4) of the first region (B1) and the end face (5) of the second region (B2) is arranged .

8. Device according to one of the preceding claims, characterized in that the body (4) for pollutant reduction, in particular for the reduction of NOx, HC and / or CO, is at least partially (T1) catalytically coated.

7. Device according to one of the preceding claims, characterized in that the body (4) has a cylindrical shape, the channels (3) extending in the radial direction.

8. The device according to claim 7, characterized in that the body (4) has a cylindrical recess (7) in the axial direction,

9. The device according to claim 8, characterized in that the filter (6) is arranged in the cylindrical recess (7).

10. Device according to one of the preceding claims, characterized in that the internal combustion engine has a direct fuel injection into the combustion chamber and / or is a diesel fuel machine.

11. Device according to one of the preceding claims, characterized in that the device has a heating element (11).

12. Device according to one of the preceding claims, characterized in that the device has a fixed housing (12) in which the body (4) rotating about its longitudinal axis is arranged.

13. The apparatus according to claim 11, characterized in that the housing is made of a non-metallic material.

15. Device according to one of the preceding claims, characterized in that the body (4) is rotated by a drive unit (9).

16. The apparatus according to claim 15, characterized in that the drive unit (9) is formed by an electric motor.

17. The apparatus according to claim 15, characterized in that the drive unit is formed by an external magnetic field and magnets arranged within the housing.

18. Device according to one of the preceding claims, characterized in that the rotational speed of the body (4) is approximately 0.3 to 10 U / min.

19. Device according to one of the preceding claims, characterized in that the body (4) is made of metal or ceramic.

20. Device according to one of the preceding claims, characterized in that the body (4) is a monolith.

21. Device according to one of the preceding claims, characterized in that the body (4) consists of segments which are traversed by channels (3).

22. Device according to one of the preceding claims, characterized in that the device has a means for introducing additional fuel.

23. The device according to claim 19, characterized in that the means for introducing additional fuel is arranged in the axis of rotation (9) of the body (4).

24. The method for aftertreatment of the exhaust gas flow of an internal combustion engine, characterized in that a body (4) is arranged in the exhaust gas flow in the exhaust gas flow direction with channels (3) and in two areas (B1,

B2) is divided, the exhaust gas flow is directed into the front end face (2) of the first area (B1), the exhaust gas flow at the rear end face (5) of the first area (B1) into one

End face (5) of the second area (B2) is passed and on the other

End face (2) of the second region (B2) emerges, and the body (4) is rotated about an axis during operation, so that the

Change channels (3) from the first area (B1) to the second area (B2).

25. The method according to claim 24, characterized in that the body (4) is rotated about its axis at such a speed that heating of the second region (B2) by the exhaust gas flow leads to heating of the exhaust gas flow through the first region.

26. The method according to any one of claims 24 or 25, characterized in that a retention of the soot particles of the exhaust gas flow is effected on a filter (6) which between the rear end face (5) of the first region (B1) and the exhaust gas inlet end face (5th ) of the second region (B2) is arranged, and the speed of rotation is selected so that the maximum of the temperature front is approximately at the filter (6).

27. The method according to any one of claims 24 to 26, characterized in that NOx storage is carried out on correspondingly catalytically coated parts (T1) of the body.

28. The method according to claim 27, characterized in that a continuous reduction of the stored NOx is carried out by additional supply of reducing agent.

29. A method for desulfating a device designed as a NOx storage catalyst for aftertreatment of the exhaust gases of an internal combustion engine according to one of the preceding claims, characterized in that at the beginning of the desulfation, the rotation of the body (4) is slowed down or suspended while increasing the amount of pollutants in the exhaust gas , to an emerging temperature maximum in or through the second area (B2), in particular near the exhaust gas outlet-side end face (2) of the second area

(B2) has migrated, the body (4) is rotated until the second area (B2) takes the place of the first

Range occupies at least predominantly, so that the temperature maximum is predominantly in the first range, and the rotation is suspended until the

Temperature maximum has reached at least in the second area (B2), the post-injection is reduced and the body (4) is rotated again.

30. The method according to claim 29, characterized in that the slowdown of the rotation or the stop is repeated several times until substantially the body (4) are desulfurized.

31. The method according to claim 29 or 30, characterized in that the continuous rotation of the body (4) is resumed when the temperature maximum is approximately at the interface of the two areas (B1, B2).