Exhaust-gas treatment arrangement

Abstract

An exhaust-gas treatment arrangement for an exhaust system of an internal-combustion engine includes a diesel internal-combustion engine. The arrangement includes a first exhaust-gas treatment unit and, downstream of the first exhaust-gas treatment unit, an exhaust-gas treatment assembly. The first exhaust-gas treatment unit and the exhaust-gas treatment assembly are arranged axially succeeding one another in the direction of a longitudinal axis of a flow path encompassing the first exhaust-gas treatment unit and the exhaust-gas treatment assembly. A hydrocarbon-feeding assembly is provided for feeding hydrocarbon into exhaust gas flowing in the flow path. The hydrocarbon-feeding assembly includes a hydrocarbon-dispensing unit dispensing hydrocarbon into the flow path downstream of the first exhaust-gas treatment unit and upstream of the exhaust-gas treatment assembly. A swirl-flow-generating unit is provided in the flow path upstream of the hydrocarbon-dispensing unit.

Claims

1. An exhaust-gas treatment arrangement for an exhaust gas system of an internal combustion engine including a diesel internal combustion engine, the exhaust-gas treatment arrangement defining a flow path and comprising: a first exhaust-gas treatment unit; an exhaust-gas treatment assembly downstream of said first exhaust-gas treatment unit; said first exhaust-gas treatment unit and said exhaust-gas treatment assembly being arranged axially one after the other in a direction of a longitudinal axis (L.sub.2) of said flow path with said flow path including said first exhaust-gas treatment unit and said exhaust-gas treatment assembly; a hydrocarbon feeding assembly for introducing hydrocarbon into exhaust gas flowing in said flow path; said hydrocarbon feeding assembly including a hydrocarbon-dispensing unit for dispensing hydrocarbon into said flow path downstream of said first exhaust-gas treatment unit and upstream of said exhaust-gas treatment assembly; a swirl-flow-generating unit arranged in said flow path upstream of said hydrocarbon-dispensing unit; a second exhaust-gas treatment unit arranged downstream of said exhaust-gas treatment assembly; and, an exhaust-gas/reagent mixing section defining a longitudinal axis (L.sub.3) and having a mixing duct elongated substantially in a direction of said longitudinal axis (L.sub.3) of the mixing section; said exhaust-gas/reagent mixing section further having a reagent-dispensing unit for dispensing reagent into said mixing duct and being disposed downstream of said exhaust-gas treatment assembly and upstream of said second exhaust-gas treatment unit.

2. The exhaust-gas treatment arrangement of claim 1, further comprising a flow-path housing accommodating said flow path therein; and, said hydrocarbon-dispensing unit being supported on said flow-path housing axially between an outlet region of said first exhaust-gas treatment unit and an inlet region of said exhaust-gas treatment assembly.

3. The exhaust-gas treatment arrangement of claim 2, wherein said hydrocarbon-dispensing unit is arranged with a main dispensing direction (H.sub.2) which is substantially orthogonal to said longitudinal axis (L.sub.2) of said flow path or oriented substantially tangentially with respect to said longitudinal axis (L.sub.2) of said flow path.

4. The exhaust-gas treatment arrangement of claim 1, wherein said swirl-flow-generating unit includes a plurality of current-deflecting elements.

5. The exhaust-gas treatment arrangement of claim 4, wherein at least one of the following applies: i) said current-deflecting elements are arranged succeeding one another in a peripheral direction about said longitudinal axis (L.sub.2) of said flow path; and, ii) said current-deflecting elements are arranged extending substantially radially with respect to said longitudinal axis (L.sub.2) of said flow path; and, iii) said current-deflecting elements are arranged in a star-like configuration.

6. The exhaust-gas treatment arrangement of claim 4, wherein said swirl-flow-generating unit includes a ring-like body supported on said flow path; and, wherein at least one of the following applies: i) said current-deflecting elements adjoin said ring-like body in a radial outer end region thereof; and, ii) said current-deflecting elements adjoin one another in a radial inner end region thereof; and, iii) said swirl-flow-generating unit assumes the form of a sheet-metal formed part.

7. The exhaust-gas treatment arrangement of claim 1, wherein said swirl-flow-generating unit is arranged on an outlet region of said first exhaust-gas treatment unit.

8. The exhaust-gas treatment arrangement of claim 1, wherein at least one of the following applies: i) said longitudinal axis (L.sub.3) of said mixing section is substantially parallel to said longitudinal axis (L.sub.2) of said flow path; and, ii) said flow path and said exhaust-gas/reagent mixing section overlap one another substantially completely in axial direction, so that an inlet region of the exhaust-gas/reagent mixing section in said direction of said longitudinal axis (L.sub.3) of said mixing section is positioned substantially in a same axial region as an outlet region of said exhaust-gas treatment assembly; and, iii) an outlet region of said exhaust-gas/reagent mixing section in said direction of said longitudinal axis (L.sub.3) of said mixing section is positioned substantially in a same axial region as an inlet region of said first exhaust-gas treatment unit.

9. The exhaust-gas treatment arrangement of claim 1, wherein a main flow direction (H.sub.4) of exhaust gas in said mixing duct is directed substantially opposite to a main flow direction (H.sub.1) of exhaust gas in the flow path.

10. The exhaust-gas treatment arrangement of claim 1, wherein said second exhaust-gas treatment unit is elongated in a direction of a longitudinal axis (L.sub.4, L.sub.5) of said exhaust-gas treatment unit which is substantially parallel to said longitudinal axis (L.sub.2) of said flow path and is configured to be flowed through substantially in the direction of the longitudinal axis (L.sub.4, L.sub.5) of said second exhaust-gas treatment unit; and, said second exhaust-gas treatment unit and said exhaust-gas/reagent mixing section overlap one another substantially completely in an axial direction, so that an inlet region of said exhaust-gas/reagent mixing section is positioned in said direction of the longitudinal axis (L.sub.3) of said mixing section substantially in a same axial region as an outlet region of said second exhaust-gas treatment unit, and an outlet region of said exhaust-gas/reagent mixing section is positioned in a direction of said longitudinal axis (L.sub.3) of said mixing section substantially in the same axial region as an inlet region of said second exhaust-gas treatment unit.

11. The exhaust-gas treatment arrangement of claim 10, wherein said inlet region of said exhaust-gas/reagent mixing section is connected to the outlet region of said exhaust-gas treatment assembly via a first current-deflecting housing, and the outlet region of the exhaust-gas/reagent mixing section is connected to the inlet region of said second exhaust-gas treatment unit via a second current-deflecting housing.

12. The exhaust-gas treatment arrangement of claim 10, further comprising an additional second exhaust gas treatment unit to provide two second exhaust-gas treatment units, which are configured to be flowed through parallel to one another, and are provided transverse to the longitudinal axis (L.sub.4, L.sub.5) of the second exhaust-gas treatment units, alongside one another and overlapping one another substantially completely in the direction of the longitudinal axis (L.sub.4, L.sub.5) of the second exhaust-gas treatment units.

13. The exhaust-gas treatment arrangement of claim 1, wherein at least one of said exhaust-gas treatment units includes at least one SCR catalytic-converter unit and/or at least one ammonia-blocking catalytic-converter unit and/or wherein said exhaust-gas treatment assembly includes an oxidation catalytic-converter unit and/or a particle-filter unit.

14. The exhaust-gas treatment arrangement of claim 1, further comprising a flow-distribution element arranged in said flow path downstream of the hydrocarbon-dispensing unit and upstream of said exhaust-gas treatment assembly.

15. The exhaust-gas treatment arrangement of claim 14, wherein said flow-distribution element is formed in the manner of a plate and covers an inlet region of said exhaust-gas treatment assembly substantially completely, wherein a plurality of flow-through openings are formed with substantially the same cross-section and substantially uniformly distributed over the flow-distribution element, are provided in the flow-distribution element.

16. The exhaust-gas treatment arrangement of claim 15, wherein said flow-through openings are formed with substantially the same cross-section and substantially uniformly distributed over the flow-distribution element.

17. An exhaust system for an internal-combustion engine including a diesel internal-combustion engine, the exhaust system comprising: an exhaust-gas conduit conducting exhaust gas away from the combustion engine; and, an exhaust-gas treatment arrangement communicating with said exhaust-gas conduit and defining a flow path and said exhaust-gas treatment arrangement including: a first exhaust-gas treatment unit; an exhaust-gas treatment assembly downstream of said first exhaust-gas treatment unit; said first exhaust-gas treatment unit and said exhaust-gas treatment assembly being arranged axially one after the other in a direction of a longitudinal axis (L.sub.2) of said flow path with said flow path including said first exhaust-gas treatment unit and said exhaust-gas treatment assembly; a hydrocarbon feeding assembly for introducing hydrocarbon into exhaust gas flowing in said flow path; said hydrocarbon feeding assembly including a hydrocarbon-dispensing unit for dispensing hydrocarbon into said flow path downstream of said first exhaust-gas treatment unit and upstream of said exhaust-gas treatment assembly; a swirl-flow-generating unit arranged in said flow path upstream of said hydrocarbon-dispensing unit; a second exhaust-gas treatment unit arranged downstream of said exhaust-gas treatment assembly; and an exhaust-gas/reagent mixing section defining a longitudinal axis (L.sub.3) and having a mixing duct elongated substantially in a direction of said longitudinal axis (L.sub.3) of the mixing section; said exhaust-gas/reagent mixing section further having a reagent-dispensing unit for dispensing reagent into said mixing duct and being disposed downstream of said exhaust-gas treatment assembly and upstream of said second exhaust-gas treatment unit.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The invention will now be described with reference to the drawings wherein:

(2) FIG. 1 shows a side view, represented partially open, of an exhaust-gas treatment unit for an internal-combustion engine;

(3) FIG. 2 shows, in schematic and developed representation, the system regions of the exhaust-gas treatment arrangement shown in FIG. 1, succeeding one another in the direction of flow and overlapping one another substantially axially;

(4) FIG. 3 shows a schematic cross-sectional view of the exhaust-gas treatment arrangement shown in FIG. 1, cut along a line III-III in FIG. 1; and,

(5) FIG. 4 shows a perspective cross-sectional view of the exhaust-gas treatment arrangement shown in FIG. 1, cut along a line IV-IV in FIG. 1.

DETAILED DESCRIPTION

(6) In FIG. 1 an exhaust-gas treatment arrangement 10 for an exhaust system 12, in particular for a diesel internal-combustion engine, can be discerned in side view. An exhaust-gas treatment arrangement 10 of such a type may, for instance, have been provided in an exhaust system 12 of a utiiity motor vehicle or of a truck. In FIGS. 2 and 3 the exhaust-gas treatment arrangement 10 is represented in schematic view, FIG. 2 representing a peripheral embodiment of the exhaust-gas treatment arrangement 10, basically elongated in the direction of a longitudinal axis L.sub.1 of the exhaust-gas treatment arrangement.

(7) The exhaust-gas treatment arrangement 10 includes a flow path, denoted generally by 14 and elongated in the direction of a longitudinal axis L.sub.2 of the flow path, with a substantially tubular flow-path housing 16 which is in one piece or composed of several parts. At an upstream end region 18 of the flow path 14 a feed housing 20 adjoins the flow-path housing 16. Exhaust gas A emitted by an internal-combustion engine is fed into the exhaust-gas treatment arrangement 10, or into the flow path 14, via the feed housing 20. In a downstream end region 22 of the flow path 14 a first deflecting housing 24 adjoins the flow-path housing 16. In the first deflecting housing 24 the exhaust gas A flowing through, or emerging from, the flow path 14 is deflected by approximately 180 and fed into an exhaust-gas/reagent mixing section 26. The exhaust-gas/reagent mixing section 26 includes, in a tubular mixing-section housing 28, a mixing duct 30 elongated in the direction of a longitudinal axis L.sub.3 of the mixing section. At an upstream end region 32 of the exhaust-gas/reagent mixing section 26 a reagent-dispensing unit 34, also generally designated as an injector, has been provided, supported, for instance, on the first deflecting housing 24, through which a reagent R, for instance a urea/water solution, is injected into the mixing duct 30. For the purpose of assisting the intermixing of exhaust gas A and reagent R, a mixer 36, including, for instance, a plurality of deflecting blades or such like, may have been arranged in the mixing-section housing 28.

(8) In a downstream end region 37 of the exhaust-gas/reagent mixing section 26 the mixing-section housing 28 adjoins a second deflecting housing 38. In the second deflecting housing 38 a deflection of the stream of exhaust gas by approximately 180 again takes place. In the embodiment represented, the exhaust gas is fed via the second deflecting housing 38 into two second exhaust-gas treatment units 40, 42 which are capable of being flowed through parallel to one another. Each of the second exhaust-gas treatment units 40, 42 includes a tubular exhaust-gas treatment-unit housing 44, 46 elongated in the direction of a respective longitudinal axis L.sub.4, L.sub.5 of the exhaust-gas treatment unit. A respective upstream end region of the exhaust-gas treatment-unit housings 44, 46 provides a respective inlet region 48, 50 of the second exhaust-gas treatment units 40, 42, and a respective downstream end region of the exhaust-gas treatment-unit housings 44, 46 provides a respective outlet region 52, 54 of the second exhaust-gas treatment units 40, 42. These are open to a drainage housing 56 via which the exhaust gas A treated in the exhaust-gas treatment arrangement 10 leaves the exhaust-gas treatment arrangement 10 to reach further system regions of the exhaust system 12, for instance one or more mufflers or such like.

(9) FIGS. 1 and 3 show that in the exhaust-gas treatment arrangement 10 the flow path 14, the exhaust-gas/reagent mixing section 26 and the second exhaust-gas treatment units 40, 42 are positioned in such a manner that longitudinal axes L.sub.2, L.sub.3, L.sub.4, L.sub.5 thereof are substantially parallel to one another and to the longitudinal axis L.sub.1 of the exhaust-gas treatment arrangement, and that they overlap one another substantially completely in the axial direction. This means that an inlet region 58 of the exhaust-gas/reagent mixing section 26 is situated substantially in the same axial region as an outlet region 60 of an exhaust-gas treatment assembly 62 arranged in the flow path 14, and that an outlet region 64 of the exhaust-gas/reagent mixing section 26 is situated substantially in the same axial region as an inlet region 66 of a first exhaust-gas treatment unit 68 arranged in the flow path 14. Equally, the outlet region 64 of the exhaust-gas/reagent mixing section 26 is situated substantially in the same axial region as the inlet regions 48, 50 of the second exhaust-gas treatment units 40, 42, whereas the inlet region 58 of the exhaust-gas/reagent mixing section 26 is situated substantially in the same axial region as the outlet regions 52, 54 of the second exhaust-gas treatment units 40, 42.

(10) In the embodiment represented, the first exhaust-gas treatment unit 68 arranged in the flow path 14, or in the flow-path housing 16, includes an SCR catalytic-converter unit 70 and an ammonia-blocking catalytic-converter unit 72, succeeding one another in the direction of flow or axially in the direction of the longitudinal axis L.sub.2 of the flow path. The exhaust gas A, fed into the flow path 14 via the feed housing 20, flows through the two catalytic-converter units 70, 72 of the first exhaust-gas treatment unit 68 substantially in a main flow direction H.sub.1 of exhaust gas in the flow path 14, the main flow direction H.sub.1 of exhaust gas in the flow path 14 being oriented substantially parallel to the longitudinal axis L.sub.2 of the flow path. Of course, flow-direction components deviating from this main flow direction H.sub.1 of exhaust gas may be present, for instance in regions in which occurrences of swirling or turbulence arise. In the exhaust system 12 a further reagent-dispensing unit may have been arranged upstream of the exhaust-gas treatment arrangement 10 or of the SCR catalytic-converter unit 70, in order to feed a reagent, for instance a urea/water solution, into the stream of exhaust gas upstream of the SCR catalytic-converter unit 70.

(11) Downstream of the two catalytic-converter units 70, 72 of the first exhaust-gas treatment unit 68 an oxidation catalytic-converter unit 74, in particular a diesel oxidation catalytic-converter unit, and a particle-filter unit 76 of the exhaust-gas treatment assembly 62 are arranged, succeeding one another in the direction of flow. The exhaust gas A flowing through the flow path 14 flows substantially in the main flow direction H.sub.1 of exhaust gas, firstly through the oxidation catalytic-converter unit 74 and then through the particle-filter unit 76, before it is deflected by the first deflecting housing 24 in the direction toward the exhaust-gas/reagent mixing section 26.

(12) Attention is drawn to the fact that in the case of the exhaust-gas treatment arrangement 10 both the first exhaust-gas treatment unit 68 and the exhaust-gas treatment assembly 62 may have been constructed differently than in the embodiment represented. For instance, the first exhaust-gas treatment unit 68 might include only the SCR catalytic-converter unit 70. The exhaust-gas treatment assembly 62 might, for instance, include only the oxidation catalytic-converter unit 74.

(13) The exhaust-gas treatment arrangement 10 includes, assigned to the flow path, a hydrocarbon-feeding assembly denoted generally by 78. This assembly includes a hydrocarbon-dispensing unit 80, also generally designated as an injector, which is positioned on the flow-path housing 16 axially between the at least one first exhaust-gas treatment unit 68 and the exhaust-gas treatment assembly 62.

(14) The hydrogen-dispensing unit 80 inputs hydrocarbon Kfor instance, the fuel also used in an internal-combustion enginein the form of a spray mist or in droplet form into the flow path 14 in a region downstream of the at least one first exhaust-gas treatment unit 68 and upstream of the exhaust-gas treatment assembly 62. In this process, the hydrocarbon K can be fed into the flow path 14 with a main dispensing direction H.sub.2, discernible in FIG. 2, which is oriented substantially orthogonally or tangentially to the longitudinal axis L.sub.2 of the flow paththat is, it may have a peripheral-orientation component.

(15) The hydrocarbon-feeding assembly 78 further includes a swirl-flow-generating unit 82 downstream of the first exhaust-gas treatment unit 68, in particular covering an outlet region 84 thereof. This swirl-flow-generating unit 82, discernible in FIG. 4, may take the form, for instance, of a sheet-metal formed part and may include a plurality of current-deflecting elements 86 extending substantially radially with respect to the longitudinal axis L.sub.2 of the flow path. The current-deflecting elements 86 may have been formed in the swirl-flow-generating unit 82 as axial moldings, between which openings 96 extending substantially radially, for instance slit-like openings, have been formed. In the region of these openings 96 the exhaust gas flowing through the first exhaust-gas treatment unit 68 is able to flow into the region of the flow path 14 into which the hydrocarbon K is fed. In a radially outer region, the current-deflecting elements 86 adjoin a ring-like body 88 of the swirl-flow-generating unit 82, with which the latter can be supported, for instance on the inner periphery of the flow-path housing 16 or at the downstream end of the at least one first exhaust-gas treatment unit 68. The current-deflecting elements 86 adjoin one another radially on the inside, so that a basically very stable structure of the swirl-flow-generating unit 82, taking the form, for instance, of a sheet-metal formed part, is obtained.

(16) The current-deflecting elements 86 provide deflecting surfaces positioned with respect to the longitudinal axis L.sub.2 of the flow path, which deflect the exhaust gas emerging from the first exhaust-gas treatment unit 68 substantially in the main flow direction H.sub.1 of exhaust gas in the peripheral direction, so that this exhaust gas has a peripheral-flow-direction component superimposed on the main flow direction H.sub.1 of exhaust gas. The hydrocarbon K is injected into this swirl current of the exhaust gas A by the hydrocarbon-dispensing unit 80 and is consequently carried along by the swirl current to the current in the peripheral direction or even in the axial direction. As a result, an efficient intermixing of hydrocarbon K and exhaust gas A is obtained in the flow path in the volume region between the outlet region 84 of the first exhaust-gas treatment unit 68 and an inlet region 90 of the exhaust-gas treatment assembly 62.

(17) In order to obtain a feeding that is as uniform as possible of the exhaust gas A permeated with hydrocarbon K into the exhaust-gas treatment assembly 62, in particular into the oxidation catalytic-converter unit 74, a plate-like flow-distribution element 92 is arranged upstream of the exhaust-gas treatment assembly 62, covering an inlet region 90 of the same substantially completely. This flow-distribution element 92, taking the form, for instance, of a sheet-metal formed part, is perforatedthat is, it exhibits a large number of flow-through openings 94 through which the mixture including exhaust gas A and hydrocarbon K enters the exhaust-gas treatment assembly 62, in particular the oxidation catalytic-converter unit 74. The flow-through openings 94 are distributed substantially uniformly over the surface of the flow-distribution element 92 and have substantially identical opening cross-sections relative to one another.

(18) By oxidation of the hydrocarbon K transported in the exhaust gas A in the oxidation catalytic-converter unit 74, heat is released which, on the one hand, contributes to a heating of the oxidation catalytic-converter unit 74 and consequently ensures that the latter is quickly brought to an operating temperature required for the catalytic reaction, or is efficiently maintained at this temperature. On the other hand, some of this heat can be carried by the exhaust gas flowing through the oxidation catalytic-converter unit 74 to the following system regions, in particular to the exhaust-gas/reagent mixing section 26 and to the second exhaust-gas treatment units 40, 42. In the exhaust-gas/reagent mixing section 26 this can contribute to an intensified evaporation of the reagent R injected in liquid form. In the second exhaust-gas treatment units 40, 42, respective SCR catalytic-converter units 98, 100 of the same can be efficiently heated and brought to the temperature required for the SCR reaction more quickly, or can be maintained at this temperature.

(19) With the structure, according to the disclosure, of an exhaust-gas treatment assembly, it is ensured, on the one hand by the admixture of hydrocarbon into the stream of exhaust gas, and on the other hand by an efficient intermixing of the hydrocarbon with the exhaust gas flowing in the exhaust-gas treatment assembly, that as a result of oxidation of the hydrocarbon, distributed over a large area, heat that is capable of being utilized for heating various system regions of the exhaust-gas treatment arrangement 10 provided for the purpose of carrying out catalytic reactions can be released substantially uniformly. By virtue of the integration of the hydrocarbon-feeding assembly into the flow path in the manner described in the foregoing, a compact configuration of the exhaust-gas treatment arrangement is obtained or retained, in which the flow principle is guaranteed, namely that the main flow direction H.sub.1 of exhaust gas in the flow path, also encompassing the hydrocarbon-feeding assembly, is directed substantially contrary to a main flow direction H.sub.4 of exhaust gas in the exhaust-gas/reagent mixing section, whereas a main flow direction H.sub.5 of exhaust gas in the second exhaust-gas treatment units is directed to be identical to the main flow direction H.sub.1 of exhaust gas in the flow path but is directed contrary to the main flow direction H.sub.4 of exhaust gas in the exhaust-gas/reagent mixing section. Hence it can be guaranteed that, with an axially very compact style of construction, by reason of the feeding of hydrocarbon and by reason of the efficient intermixing of the hydrocarbon with the exhaust gas the statutory limiting values for pollutant contents in the exhaust gas can be attained or maintained under highly diverse operating circumstances of an internal-combustion engine or of the exhaust system.

(20) It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.