Device and method for post-treatment of exhaust gases of an internal combustion engine

Abstract

An exhaust gas treatment device has a cylindrical body with axial passages having a catalyst and a central cavity. A filter is provided in the cavity and the cylindrical body is mounted for rotation in a housing through which the exhaust gas flows.

Description

BACKGROUND OF THE INVENTION

[0001] The invention relates to a device and method for post-treatment of exhaust gases of an internal combustion engine, and in particular relates to a device and method for post-treatment of soot particles and/or nitrogen oxides in the exhaust gas stream.

[0002] Known NOx catalysts absorb nitrogen oxides produced during lean operation of an engine and reduce accumulated NOx during rich operation of the engine, where the known methods are discontinuous and accumulation and reduction of nitrogen oxides takes place at different times. In order to be able to carry out such a method, the accumulator must be emptied after a certain period of time because of its finite absorption capacity. This is done after a fixed predetermined time has elapsed or else the degree of fill of the catalyst must be determined. If the accumulator is regenerated after a fixed predetermined time, this has the disadvantage that for safety reasons the accumulating capacity of the catalyst is not fully utilized, so that optimal engine operation with regard to fuel consumption and exhaust gas behavior is not possible. If the accumulator is regenerated when a given degree of fill of the accumulator has been reached, this has the disadvantage that an additional device is required, to determine the degree of fill of the NOx-accumulating catalyst. There, exact determination of the degree of fill of the accumulator is difficult, so that here too a switch to regenerative operation is made when the accumulator is not yet completely full. In the end, this likewise leads to less than optimal operation of the engine. In addition, in both these methods optimal exhaust gas behavior is not obtained during rich operation of the engine and a complicated engine control system is required for cyclical engine operation.

[0003] In addition, a minimum temperature of about 250° C. is required for effective function of a NOx-accumulating catalyst. If the exhaust gas coming from the engine is too cold, the method can only function when the catalyst is heated to this minimum temperature. Then heat losses occur, as a result of which the energy requirement is greatly increased.

[0004] In addition, soot particles that should not be allowed to escape into the environment are present in the exhaust gas of diesel engines. For post-treatment of such exhaust gases carrying soot particles, in one well known device the soot particles are retained and cyclically, as a given degree of fill of the soot filter is reached, they are either removed or the retained soot particles are ignited with a suitable heating device and burned. Both of these procedures are unsatisfactory for continuous use.

[0005] The object of the invention therefore is to develop a device and method for treatment of the exhaust gas stream of an internal combustion engine that permit optimal engine operation.

SUMMARY OF THE INVENTION

[0006] The device according to the invention for post-treatment of exhaust gases of an internal combustion engine has a body or monolith with channels through which the exhaust gas flows and which is arranged to rotate in the exhaust gas stream. Here, a monolith is understood to mean a body that may consist of one piece that is made of ceramic, of metallic carrier materials or of ceramic or metallic segments, which are arranged in an accommodating support structure.

[0007] The device has an inflow channel that is in flow communication with a part (B1) of the channels of the body. Additionally provided is a flow connection that is in communication on the output side with the part B1 of the channels approached by the inflow channel and connects said part with a part B2 of the channels that is not in flow communication with the inflow channel.

[0008] The body or monolith preferably is divided into two regions B1, B2, where the exhaust gas enters the first region B1 at the front face of the body, exits at the rear face of the first region B1, flows through the filter mounted there, enters a face of the second region B2 and leaves the second region B2 at the other face, while during flow the body rotates about an axis substantially perpendicular to the direction of flow of the exhaust gas stream.

[0009] The body preferably has a cylindrical shape, and the channels extend 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 may consist of metal or ceramic, and may be built in one piece or of segments fitted together. If the body consists of segments, the latter are traversed by channels in such a way that after the segments are assembled the channels extend in the radial direction with respect to the axis of symmetry of the cylinder.

[0010] The device preferably comprises a filter, which may be arranged for rotation, and the filter may in particular rotate with the monolith, while in the case of the cylindrical body with the axial recess the filter is arranged in the latter. There, the filter may be stationary or may rotate along with the body, where its speed of rotation need not be identical to the speed of rotation of the body.

[0011] In addition, the internal combustion engine preferably has direct fuel injection into the combustion chamber and/or is a diesel engine.

[0012] The filter preferably has a heating element that serves to bring the filter to operating temperature after a cold start. When the required temperature has been reached, the heating element may be shut off. In principle, extra heating is provided only when engine conditions (exhaust gas temperature) do not lead to soot burnup.

[0013] In particular, the required temperature for pollutant conversion may alternatively or secondarily also be rapidly obtained by suitably selected engine parameters (injection quantity, injection course, reinjection), and here too the engine parameters are restored to their normal conditions when the desired temperature has been reached.

[0014] In addition, for pollutant reduction, in particular for the reduction of NOx, HC and/or CO, the body may be at least partially catalytically coated.

[0015] In addition, the device may have a stationary housing (10), having a chamber in which is arranged the body rotating about its longitudinal axis. The housing preferably is made of a nonmetallic material.

[0016] Rotation of the body preferably is effected by a drive unit. The drive unit may be an electric motor. It is alternatively possibly for the drive unit to be formed by an outer magnetic field source and magnets arranged within the housing. In addition, the body may alternatively be rotated in the manner of a turbine by the exhaust gas stream. The speed of rotation of the body (4) preferably is about 0.3 to 10 rpm, and the speed of rotation is selected so that the maximum of the temperature distribution obtained remains within the body, preferably at the site of the filter.

[0017] In addition, the device may have a means for the introduction of additional fuel in order to produce a reduction of the NOx exhaust gas component when the engine can be operated lean. The means for introducing additional fuel is arranged in the axis of rotation of the body.

[0018] The method according to the invention provides for post-treatment of exhaust gases of an internal combustion engine, wherein a body is arranged in the exhaust gas stream, which body is traversed by channels in the direction of flow of the exhaust gas and is divided into two regions, has the following steps:

[0019] Passing of the exhaust gas stream into the front face of the first region,

[0020] Passing of the exhaust gas stream at the rear face of the first region into a face of a second region and discharge of the exhaust gas stream at the other face of the second region, and

[0021] Rotation of the body during operation about an axis, so that the channels shift from the first region into the second region.

[0022] Preferably, the body is rotated about its axis at a speed such that heating of the second region by the exhaust gas stream leads to heating of the exhaust gas stream through the first region.

[0023] Soot particles in the exhaust gas stream preferably are retained in a filter, which is arranged between the exhaust gas outlet-side face of the first region and the exhaust gas inlet-side face of the second region, and the speed of rotation is selected so that the maximum of the temperature region is located approximately at the filter.

[0024] The body used in the method preferably is at least partially catalytically coated, so that NOx accumulation of the exhaust gas is effected during the lean phases of internal combustion engine operation. A continuous NOx-accumulating regeneration method can be effected by addition of reducing agents into the body.

[0025] The method according to the invention for desulfurization of the device according to the invention for post-treatment of exhaust gases of an internal combustion engine, where the device is designed as a NOx accumulator, has the following steps:

[0026] at the start of desulfurization retardation or interruption of rotation of the body, with simultaneous increase of pollutant quantity in the exhaust gas, until a resulting temperature maximum has migrated into or through the second region, in particular near the exhaust gas exit-side face of the second region,

[0027] rotation of the body until the second region at least predominantly assumes the place of the first region, so that the temperature maximum lies predominantly in the first region, and interruption of rotation until the temperature maximum has moved into at least the relocated first region,

[0028] reduction of reinjection and restored rotation of the body.

[0029] At the same time it may be necessary for retardation or interruption of rotation to be repeated a number of times, until all regions have been substantially desulfurized. Continuous rotation of the body is resumed when the temperature maximum is located at approximately the interface of the two regions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1a shows a horizontal cross-sectional view through a first embodiment of the device according to the invention for post-treatment of the exhaust gas of an internal combustion engine.

[0031] FIG. 1b shows a vertical cross section through the device of FIG. 1a.

[0032] FIG. 2a shows horizontal cross-sectional view through a second embodiment of the device according to the invention for post-treatment of the exhaust gas of an internal combustion engine.

DESCRIPTION OF THE INVENTION

[0033] FIG. 1a shows a horizontal cross section through a first preferred embodiment of a device according to the invention for post-treatment of the exhaust gas of an internal combustion engine. A cylindrical body is arranged in a chamber within a housing 10. Untreated exhaust gas of an engine (not illustrated) flows through an exhaust gas inlet 1 in to an outer face 2 of a first region B1 of a cylindrical body 4 that is traversed by channels 3. 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 described above. After exit of the exhaust gas from the inner face 5 of the body 4, which forms an axial cavity 7 located centrally in the body, the exhaust gas goes through a particle filter 6 arranged in the cavity 7, through the inner face 5, enters an opposite second region B2, leaves region B2 through outer face 2 and enters a discharge channel 8. In FIG. 1a, it is shown that the first region and the second region are each limited to 3 channels by the inflow channel 1 and the discharge channel 8. This is not mandatory. In another design of the housing 10 surrounding the body 4, the waste gas flowing in and out in each instance reaches a first and second region B1, B2 of at most 180°. In other words, the first and second region may comprise at most one-half of the body 4.

[0034] FIG. 1b shows a vertical section through the device according to the invention. The filter 6, which in general rotates synchronously with the body 4, is arranged in the interior cavity of the body 4 which is traversed by channels 3. The body 4 and the filter 6 are arranged in a chamber formed by a suitable housing 10. Rotation takes place about an axis of rotation 9, which may serve as inlet for additional fuel for combustion in a catalytically active filter or in the rotor matrix, i.e., the body 4.

[0035] Owing to flow through the body 4 with the filter 6, the temperature rises at the inlet side due to catalytic conversion of CO and HC present in the exhaust gas during passage through the catalytically coated channels 3. At the same time, nitrogen oxides can be absorbed chemically if the channels 3 are coated with a NOx-absorbing catalyst. The temperature maximum is reached in the center of the device, in the particle filter 6. Upon continued passage through the body 4 or rotor the exhaust gas again gives off its heat and leaves the rotor 4 at about the same temperature as on the inlet side. Without rotation the temperature front, i.e., the maximum temperature, would be driven out of the device. Owing to rotation of the rotor 4 the temperature front is always driven back into the system. A periodically stationary temperature profile, whose maximum lies in the region of the filter 6, is produced in the body.

[0036] FIG. 2 shows a horizontal cross-sectional view through a second embodiment of the device according to the invention for post-treatment of exhaust gases of an internal combustion engine, in which the device is operated as a pure NOx-accumulating catalyst.

[0037] FIG. 2 shows a body 4, rotating about its longitudinal axis, which is coated as a NOx-accumulating catalyst and which is used as a regenerative heat exchanger. The body 4 has a great plurality of fine channels 3 in the radial direction and exhaust gases flow through it radically, specifically, exhaust gases are supplied to it through an inflow channel 1 and are carried away through a discharge channel 8, whereby first and second regions B1, B2 are formed as in the case of the first embodiment. In addition, the body has an axial cavity 7, which is bounded by the inner face 5 of the body 4. The axial cavity serves for flow communication of the channels 3 of the first and of the second region B1, B2. Advantageously, no flow deflection takes place, whereby pressure loss is kept low. The inner part of the channels 3, represented as a ring-shaped area T1, is coated with a NOx-accumulating catalyst. The outer part of the channels, represented by a ring-shaped area T2, is not coated and does not participate in catalysis, having the function only of heat exchange. The radial flow with simultaneous rotation allows a temperature profile to be established in the body 4, which at the inlet and outlet sides of the outer face 2 of the body is at about exhaust gas temperature and toward the center rises steeply to about 350 to 400° C. As a result, part of the catalyst is always in an optimal temperature region for NOx accumulation. The rotating arrangement of the catalyst, i.e., the body 4, provides for best possible heat recovery by the regeneration principle. With ideal heat insulation and correct dimensioning and rotational speed, the heat once brought in will not leave the system. The heat losses actually occurring are offset by the heat of reaction that is released upon pollutant oxidation in the region T1.

[0038] For starting up the cold system, the ignition temperature of about 200° C. must be reached in the catalytically active region T2. For this purpose, an electric heating element 11 may be provided in the center of the body 4. Alternatively and/or secondarily, the temperature required for pollutant conversion may also be obtained by suitably selected engine parameters (particularly in the case of common-rail injection, for example, by variation of injection timing, injection course, injection quantity, and/or reinjection). After the ignition temperature has been reached, such measures are ended. Additional temperature increase takes place only through a brief increase in pollutant concentrations, which raises the catalyst temperature through the heat of reaction released upon conversion of pollutants in the region T1. This increase in pollutant concentration may take place either through separate fuel introduction in the center of the body 4, or may also be brought about through modifications of engine parameters.

[0039] Rotation of the body 4 is realized by a suitable electric or mechanical drive (not represented). For this purpose, the body 4 is mounted on a shaft rotatable about its axis of rotation 9, which is put into rotation by the abovementioned drive. The additional introduction of fuel may also be effected through this shaft 9. When an electric motor is used, the speed of rotation may be adapted to the operating condition of the vehicle engine by means of suitable information from the engine-control device. In addition, the body 4 is arranged in a suitable stationary housing 10.

[0040] Regeneration of the NOx-accumulating catalyst is effected in known fashion by engine enrichment of the exhaust gas.

[0041] When sulfurous fuel is used, desulfurization of the catalyst must be carried out 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 a temperature rise of almost any degree may be obtained by increasing the concentration of pollutant or by its oxidation. By appropriate control of the speed of rotation and pollutant concentration, the catalyst can be kept at the necessary high temperatures for the required time of several minutes. As already described above, the consumption of energy is distinctly lower than in conventional systems.

[0042] Therefore, the following embodiments of the device described above by means of two examples are possible:

[0043] Device with a body 4, capable of rotation in the exhaust gas stream, without catalytic coating and without filter, for producing a temperature maximum in the device;

[0044] Device with a body 4, capable of rotation in the exhaust gas stream and a filter 6 arranged in the body 4, for burnup of soot particles;

[0045] Device with a body 4, capable of rotation in the exhaust gas stream and having an at least partial catalytic coating of the body 4;

[0046] Device with a body 4, capable of rotation in the exhaust gas stream, as well as a filter 6 arranged in the body 4, and having an at least partial catalytic coating of the body.

[0047] While there has been described what are believed to be the preferred embodiment of the present invention, those skilled in the art will recognize that other and further changes and modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the true scope of the invention.

LIST OF REFERENCE NUMERALS

[0048] 1 Inflow channel

[0049] 2 Outer face

[0050] 3 Channels

[0051] 4 Body or rotor

[0052] 5 Inner face

[0053] 6 Filter

[0054] 7 Axial cavity

[0055] 8 Discharge channel

[0056] 9 Axis of rotation

[0057] 10 Housing

[0058] 11 Electric heating element

[0059] B1 First region

[0060] B2 Second region

[0061] T1 Inner ring-shaped area

[0062] T2 Outer ring-shaped area

Claims

1. Apparatus for treatment of exhaust gases of an internal combustion engine comprising a housing having a gas inlet and a gas outlet and a chamber arranged between said inlet and said outlet, a gas permeable body at least partially coated with a catalyst for reduction of pollutant gases, and arranged for rotation in said chamber about an axis transverse to a direction corresponding to flow of gas between said inlet and said outlet, said gas permiable body having a central cavity having a filter arranged therein, said gas permeable body being arranged in said chamber such that gases entering said gas inlet flow through a first region of said body, through said filter in said central cavity and through a second region of said body to said gas outlet.

2. Apparatus as specified in

claim 1 wherein said gas inlet of said housing is in flow communication with channels in said first region of said body.

3. Apparatus as specified in

claim 1 wherein said filter is arranged to rotate with said body.

4. Apparatus as specified in

claim 1 wherein said body has a cylindrical shape and includes radially extending gas flow channels.

5. Apparatus as specified in

claim 4 wherein said cavity comprises a cylindrical recess extending along the axis of said cylindrical body.

6. Apparatus as specified in

claim 1 further including a heating element.

7. Apparatus as specified in

claim 1 wherein said body is arranged to rotate about a cylindrical axis within said housing.

8. Apparatus as specified in

claim 7, wherein said housing is made of a nonmetallic material.

9. Apparatus as specified in

claim 1 wherein said body is rotated by a drive unit.

10. Apparatus as specified in

claim 9, wherein said drive unit is an electric motor.

11. Apparatus as specified in

claim 9, wherein said drive unit is formed by providing an magnetic field and magnets arranged within the housing.

12. Apparatus as specified in

claim 1 wherein said body is arranged to rotate a speed of about 0.3 to 10 rpm.

13. Apparatus as specified in

claim 1 wherein said body comprises ceramic.

14. Apparatus as specified in

claim 1 wherein said body is fabricated using metal.

15. Apparatus as specified in

claim 1 wherein said body is a monolith.

16. Apparatus as specified in

claim 1 wherein said body comprises segments that are traversed by channels.

17. Apparatus as specified in

claim 1 further including an inlet for the introduction of additional fuel.

18. Apparatus as specified in

claim 17 wherein said inlet apparatus for the introduction of additional fuel is arranged at the axis of rotation of the body.

19. A method for post-treatment of an exhaust gust gas stream of an internal combustion engine comprising:

providing a body having a catalyst in portions thereof and having a cavity with a filter; passing said exhaust gas through channels in a first region of said body, through said filter and through channels a second region of said body whereby soot particles are retained in said filter; and

rotating said body to interchange said first and second regions of said body.

20. A method as specified in

claim 19 wherein said body is rotated at a speed which causes a maximum temperature region of said body to be located at said filter thereby to cause combustion of said soot particles.

21. A method as specified in

claim 19 wherein reducing agents are added to cause continuous reduction of Nox accumulation in said body.

22. A method as specified in

claim 19 further providing desulfurigation of said body, comprising periodically increasing the pollutant quantity of supplied exhaust gas and retarding or interrupting rotation of said body until a maximum temperature region is in said second region, and wherein said body is thereafter rotated so that second region assumes the original position of said first region and said maximum temperature region is predominantly in said repositioned first region and thereafter reducing the pollutant quantity.

23. Method according to

claim 22, wherein said retardation or interruption of rotation is repeated a number of times, until said body is substantially desulfurized.

24. Method according to

claim 22, wherein that continuous rotation of said body is resumed when the temperature maximum is located at approximately the interface of the first and second regions.