EXHAUST GAS / REACTANT MIXING ASSEMBLY

Description

[0001] The present invention relates to an exhaust gas / reactant mixing assembly which is used to create a mixing of exhaust gas and reactant injected into the exhaust gas in an exhaust system of an internal combustion engine, in particular in a vehicle.

[0002] When introducing a reactant, such as a urea / water solution, into the exhaust gas emitted by an internal combustion engine, it is important that thorough mixing of the exhaust gas and reactant is achieved before the mixture of exhaust gas and reactant is introduced into a catalyst arrangement, such as an SCR catalyst arrangement. For this purpose, mixing elements are generally inserted into the exhaust gas stream downstream of a reactant delivery unit in order to generate turbulence in the exhaust gas stream, which supports the mixing of the exhaust gas and the reactant injected into it. The insertion of such mixing elements, which are constructed, for example, with turbulence-generating guide vanes or the like, into the exhaust gas stream leads, on the one hand, to increased flow resistance, and, on the other hand, entails the risk of reactant deposits forming, particularly in flow dead spaces.

[0003] From DE 10 2017 124 541 A1, an exhaust gas / reactant mixing assembly for an exhaust system of an internal combustion engine according to the preamble of claim 1 is known. In this mixing assembly, two inlet channel sections of an inlet channel region in the region of a mixing channel housing peripheral wall of a mixing channel housing open into a channel formed in the mixing channel housing upstream of a region in which reactant is introduced, and thus upstream of a mixing channel formed in the mixing channel housing, in which the reactant is mixed with exhaust gas introduced via the inlet channel sections.

[0004] It is the object of the present invention to provide an exhaust gas / reactant mixing assembly which, while being structurally simple, reduces the risk of deposits forming.

[0005] According to the invention, this object is achieved by an exhaust gas / reactant mixing assembly for an exhaust system of an internal combustion engine according to claim 1. This comprises: a mixing channel extending in the direction of a mixing channel longitudinal axis, a reactant discharge unit for discharging reactant into the mixing channel, an exhaust gas supply channel upstream of the mixing channel, wherein the exhaust gas supply channel opens into the mixing channel in an inlet channel region, wherein the inlet channel area has two inlet channel sections flowing into the combined channel.

[0006] By introducing separate or parallel exhaust gas streams into the mixing channel via at least two junction channel sections, turbulence is generated when the portions of the exhaust gas emitted by an internal combustion engine flowing through these junction channel sections merge in the mixing channel, without the need for additional mixing elements installed in the mixing channel. The formation of dead flow spaces in the mixing channel, which are prone to deposit formation, can thus be avoided.

[0007] In order to generate turbulence in the mixing channel as efficiently as possible when merging the exhaust gas flows supplied via different inlet channel sections, the mixing channel is formed in a mixing channel housing with a mixing channel housing base and a mixing channel housing peripheral wall, and the two inlet channel sections are open to the mixing channel in the region of the mixing channel housing peripheral wall, optionally also in the region of the mixing channel housing base. In particular, it is provided that the two inlet channel sections are open to the mixing channel at circumferential regions of the mixing channel housing peripheral wall that are substantially opposite one another with respect to the mixing channel longitudinal axis. A configuration of this type, in which the two inlet channel sections are open to the mixing channel in the same axial region with respect to the mixing channel longitudinal axis, also supports the creation of strong turbulence in the mixing channel.

[0008] In order to be able to use the entire length of the mixing channel efficiently for the mixing of exhaust gas and reactant, the reactant discharge unit can be provided on the mixing channel housing base and / or a reactant main discharge direction of the reactant discharge unit can be oriented substantially in the direction of the mixing channel longitudinal axis.

[0009] Intensive turbulence in the mixing channel can be further promoted by ensuring that, in at least one, preferably each, junction channel section, a main exhaust gas outflow direction of exhaust gas flowing from the junction channel section into the mixing channel has a flow direction component that is substantially tangential to the mixing channel longitudinal axis. In the two junction channel sections, a respective main exhaust gas outflow direction of exhaust gas flowing from the junction channel sections into the mixing channel lies substantially in a plane orthogonal to the mixing channel longitudinal axis. It should be noted in this context that such a main outflow direction can, for example, correspond to the main flow direction in the region of a central flow filament of a respective junction channel section.

[0010] The main exhaust gas flow direction in the exhaust gas supply duct can be essentially orthogonal to the mixing duct's longitudinal axis. This results in a substantially angled structure, which can support integration into other system areas of a vehicle.

[0011] In an alternative embodiment, the main exhaust gas inflow direction in the exhaust gas supply duct can be substantially parallel to the mixing duct's longitudinal axis. This results in a slender structure that is elongated in the direction of the mixing duct's longitudinal axis.

[0012] The exhaust gas supply duct can be formed substantially in an exhaust gas supply duct housing having an exhaust gas supply duct housing base and an exhaust gas supply duct housing peripheral wall and a plurality of inlet line regions extending from the exhaust gas supply duct housing base and / or the exhaust gas supply duct housing peripheral wall, wherein an inlet channel section is formed in each inlet line region.

[0013] Since, in the exhaust gas / reactant mixing assembly constructed according to the invention, the efficient mixing of exhaust gas and reactant is achieved by generating turbulence in the exhaust gas by means of the flow guidance, the arrangement of one or more mixing elements in the mixing channel can be dispensed with.

[0014] The invention further relates to an exhaust system for an internal combustion engine, comprising an exhaust gas / reactant mixing assembly constructed according to the invention.

[0015] To convert the reactant in a catalytic reaction, an SCR catalyst arrangement can be provided downstream of the mixing channel.

[0016] To further reduce the pollutant content in the exhaust gas, at least one exhaust gas treatment unit can be provided upstream of the exhaust gas supply duct and / or in the exhaust gas supply duct. The at least one exhaust gas treatment unit can comprise a catalyst arrangement and / or a particulate filter arrangement.

[0017] The present invention is described in detail below with reference to the accompanying figures. It shows: Fig. 1 is a perspective view of an exhaust gas / reactant mixing assembly; Fig. 2 is another perspective view of the exhaust gas / reactant mixing assembly of the Fig. 1 ; Fig. 3 a view of the exhaust gas / reactant mixing assembly of the Fig. 1 , viewed in the direction of a mixing channel longitudinal axis; Fig. 4 one of the Fig. 1corresponding representation with partially open exhaust gas supply duct housing or mixing duct housing; Fig. 5 a perspective view of another design type of exhaust gas / reactant mixing assembly; Fig. 6 another perspective representation of the exhaust gas / reactant mixing assembly of the Fig. 5 ; Fig. 7 a side view of the exhaust gas / reactant mixing assembly of the Fig. 5 ; Fig. 8 a view of the exhaust gas / reactant mixing assembly of the Fig. 5 , viewed in the direction of a mixing channel longitudinal axis.

[0018] The Fig. 1 to 4 show a first embodiment of an exhaust gas / reactant mixing assembly 10 in which the exhaust gas emitted by an internal combustion engine is mixed with reactant R injected into it.

[0019] The Fig. 1 to 4The exhaust gas / reactant mixing assembly 10 shown comprises an exhaust gas supply duct housing, generally designated 12, and an adjoining mixing duct housing, generally designated 14. The exhaust gas supply duct housing 12 comprises, for example, a substantially cylindrical exhaust gas supply duct housing peripheral wall 16 and an exhaust gas supply duct housing base 18 adjoining the exhaust gas supply duct housing peripheral wall 16. In an exhaust gas supply duct formed in the exhaust gas supply duct housing 12 and generally designated 20, exhaust gas emitted by an internal combustion engine flows in the direction of a main exhaust gas inflow direction Z on the exhaust gas supply duct housing base 18, particularly in the area enclosed by the exhaust gas supply duct housing peripheral wall 16.

[0020] Two inlet line regions 22, 24 extend from the exhaust gas supply duct housing base 18. In each of the inlet line regions 22, 24, an inlet channel section 26, 28 of an inlet channel region of the exhaust gas supply duct 20, generally designated 30, is formed.

[0021] The mixing channel housing 14 comprises a mixing channel housing peripheral wall 32, which is for example substantially cylindrical and extends in the direction of a mixing channel longitudinal axis L, and a mixing channel housing base 34 adjoining said peripheral wall in an axial end region. A mixing channel 36 extending substantially linearly is formed in the mixing channel housing 14.

[0022] The two inlet line regions 22, 24 of the exhaust gas supply duct housing 12 adjoin the mixing duct housing 14 in the region of the mixing duct housing peripheral wall 32, for example, directly adjacent to the mixing duct housing base 34. Thus, each of the two inlet duct sections 26, 28 provided in the inlet line regions 22, 24 opens into the mixing duct 36 defined by the mixing duct housing, essentially in the region of the mixing duct housing peripheral wall 32. Fig. 3It can be clearly seen that the two inlet line regions 22, 24 run or adjoin the mixing channel housing peripheral wall 32 in such a way that they are offset from one another transversely to the mixing channel longitudinal axis L. This results in exhaust gas flows emerging from the two inlet channel sections 26, 28 each having a main exhaust gas outflow direction A 1 or A 2, which are equally offset transversely to the mixing channel longitudinal axis L or run essentially tangentially thereto or have a significant flow direction component oriented tangentially with respect to the mixing channel longitudinal axis L.

[0023] It should be noted that such a main exhaust gas outflow direction A 1 or A 2 can approximately correspond to the main flow direction or can be defined by a main outflow direction which an exhaust gas flow flowing through a respective inlet channel section 26 or 28 has in the region of the central flow path of a respective inlet channel section 26 or 28. This means that such a main exhaust gas outflow direction A 1 or A 2 can essentially also correspond to the course of a respective central flow path in the region of the confluence of a respective inlet channel section 26, 28 into the mixing channel 36. Since, in the axial direction of the mixing channel longitudinal axis L, the inlet channel sections 26, 28 adjoin the mixing channel housing peripheral wall 32 essentially in the same area, the two main exhaust gas outflow directions A 1 , A 2 andwhich, for example, predetermine the middle flow threads with their course, also in a plane defined, for example, by the plane of the drawing. Fig. 3 defined plane which is essentially orthogonal to the mixing channel longitudinal axis L.

[0024] A reactant delivery unit 38, also generally referred to as an injector, is provided on the mixing channel housing base 34, for example, centrally to the mixing channel longitudinal axis L. This delivers the reactant R, for example, in the form of a spray cone in a main reactant delivery direction H along the mixing channel longitudinal axis L into the mixing channel 36. Due to the exhaust gas flows introduced into the mixing channel 36 via the two inlet channel sections 26, 28 in the area where the reactant R is fed in, the exhaust gas flows are open to the mixing channel 36 at areas of the mixing channel housing peripheral wall 32 which are essentially diametrically opposite one another with respect to the mixing channel longitudinal axis L, and the main exhaust gas outflow directions A 1 and A 2 areA 2 with their tangentially oriented flow direction components are offset from one another transversely to the mixing channel longitudinal axis L, generates a vortex flow in the mixing channel 36, which collects the reactant R injected into the mixing channel 36 and, in accordance with the direction of the vortex flow, leads it along the inside of the mixing channel housing peripheral wall 32 and in the direction of the mixing channel longitudinal axis L away from the mixing channel housing base 34 to a discharge opening 40 of the mixing channel 36.

[0025] Due to this turbulence generated in the mixing channel 36, an efficient mixing of exhaust gas and reactant R and thus also an efficient evaporation of the reactant R is generated, which is particularly contributed to by the fact that, due to this swirling flow, the reactant R covers a significantly greater flow path in the mixing channel 36 than would be the case if the exhaust gas and with it the reactant R were to flow essentially in the direction of the mixing channel's longitudinal axis L. Thus, the residence time of the reactant R in the mixing channel 36 and thus also the time in which it can evaporate and mix with the exhaust gas is also increased.

[0026] Since with the in the Fig. 1 to 4Since, in the structure of an exhaust gas / reactant mixing assembly shown, efficient mixing of exhaust gas and reactant R is achieved solely by the flow guidance of the exhaust gas supplied to the mixing channel 36, it is not necessary to provide any mixing elements in the mixing channel 36 downstream of the inlet of reactant R, which generate turbulence by flow deflection. The risk that the incorporation of such mixing elements would create flow dead spaces in which deposits of the reactant R preferentially form, is therefore completely eliminated with such a structure of an exhaust gas / reactant mixing assembly 10. This is also a significant advantage when using, for example, a urea / water solution as such a reactant, in which urea in particular has a strong tendency to form crystalline deposits.Furthermore, by omitting such mixing elements in the mixing channel 36, an increased flow resistance introduced by them is avoided, which already fundamentally contributes to a reduced pollutant emission of an internal combustion engine and, of course, also supports a simply structured overall design.

[0027] The Fig. 1 to 4 show that at the transition from the exhaust gas supply channel 20 to the mixing channel 36, a basic flow deflection of approximately 90° occurs, since the main exhaust gas inflow direction Z in the exhaust gas supply channel 20 is oriented approximately orthogonally to the mixing channel longitudinal axis L. The exhaust gas / reactant mixing assembly 10 thus has a substantially angled structure.

[0028] An alternative design, particularly with regard to this aspect, is described in the Fig. 5 to 8 Components or system areas, which were previously described with reference to the Fig. 1 to 4described components or system areas are designated by the same reference symbols.

[0029] In the Fig. 5 to 8In the illustrated structure of an exhaust gas / reactant mixing assembly 10, the exhaust gas supply duct housing 12 is arranged essentially in the axial extension of the mixing duct housing 14, so that, for example, the exhaust gas supply duct housing peripheral wall 16 is positioned essentially coaxially with the mixing duct peripheral wall 32. The inlet line regions 22, 24, which essentially originate from the exhaust gas supply duct housing base 18, extend essentially in the direction of the mixing duct longitudinal axis L away from the exhaust gas supply duct housing base 18 towards the mixing duct housing 14 and adjoin the mixing duct housing peripheral wall 32 in regions that are essentially diametrically opposite one another with respect to the mixing duct longitudinal axis L in radially inwardly directed end regions.In this embodiment, too, the exhaust gas guided through the inlet channel sections 26, 28 formed in the inlet line regions 22, 24 flows in the respective main exhaust gas outflow directions A 1 , A 2 toward the mixing channel 36, which are laterally offset with respect to the mixing channel longitudinal axis L or are directed essentially tangentially and oppositely to each other. In this embodiment, too, the exhaust gas flows flowing through the two inlet channel sections are introduced into the mixing channel 36 essentially in the same axial region, so that a vortex flow is also efficiently generated, which also entrains the reactant introduced into the mixing channel 36 in the main reactant discharge direction H and leads to the mixing effect described above.

[0030] The Fig. 7illustrates in principle the integration of such an exhaust gas / reactant mixing assembly 10 into an exhaust system, generally designated 42. This comprises, downstream of the mixing channel 36 or the mixing channel housing 14, an SCR catalyst arrangement 44, in which the nitrogen oxide content in the exhaust gas is reduced by converting the reactant. The exhaust system 42 can further comprise one or more discharge treatment units 46 upstream of the exhaust gas / reactant mixing assembly 10. Such an exhaust gas treatment unit 46 can, for example, be designed as a catalyst arrangement, in particular a diesel oxidation catalyst arrangement. The integration of an exhaust gas treatment unit 46 designed as a particulate filter arrangement into such an exhaust system 42 upstream of the exhaust gas / reactant mixing assembly 10 is also possible.In principle, such an exhaust gas treatment unit 46 can also be inserted into the exhaust gas supply duct housing 12, in particular the volume area surrounded by the exhaust gas supply duct housing peripheral wall 16, or positioned in an engaging manner.

[0031] Although the introduction of the inlet channel sections 26, 28 into the mixing channel 36 in the region of the mixing channel housing circumferential wall 32, as shown in the figures, is particularly advantageous due to the comparatively large radial distance from the mixing channel longitudinal axis L and the particularly efficient generation of a vortex flow, it may be advantageous for a radially slim design to alternatively or additionally connect the inlet line regions 22, 24 providing the inlet channel sections 26, 28 to the mixing channel housing 14 in the region of the mixing channel housing base 34. The exhaust gas or a portion of it emerging from the respective inlet channel sections 26, 28 then enters the mixing channel 36 in the region of the mixing channel housing base 34, i.e. closer to the mixing channel longitudinal axis L.

Claims

1. An exhaust gas / reactant mixing assembly for an exhaust gas system of an internal combustion engine, comprising: - a mixing channel (36) formed in a mixing channel housing (14) having a mixing channel housing floor (34) and a mixing channel housing peripheral wall (32) and extending in the direction of a mixing channel longitudinal axis (L), - a reactant delivery unit (38) for delivering reactant (R) into the mixing channel (36), - an exhaust gas supply channel (20) upstream of the mixing channel (36), wherein the exhaust gas supply channel (20) opens into the mixing channel (36) at an opening channel region (30), wherein the opening channel region (30) comprises two opening channel portions (26, 28), characterized in that the two opening channel portions (26, 28) discharge into the and are open to the mixing channel (36) at peripheral regions of the mixing channel housing peripheral wall (32) which lie substantially opposite one another relative to the mixing channel longitudinal axis (L), so that exhaust gas is introduced into the mixing channel (36) via the two opening channel portions (26, 28) in the region of delivery of the reactant (R) into the mixing channel (36) and so that main exhaust gas outflow directions (A1, A2) of exhaust gas flowing out of the two opening channel portions (26, 28) into the mixing channel (36) are in a plane which is orthogonal to the mixing channel longitudinal axis (L).

2. The exhaust gas / reactant mixing assembly as claimed in claim 1, characterized in that the two opening channel portions (26, 28) are open to the mixing channel (36) in the region of the mixing channel housing floor (34).

3. The exhaust gas / reactant mixing assembly as claimed in claim 1 or 2, characterized in that at least the two opening channel portions (26, 28) are open to the mixing channel (36) in the same axial region relative to the mixing channel longitudinal axis (L).

4. The exhaust gas / reactant mixing assembly as claimed in any of claims 1 - 3, characterized in that the reactant delivery unit (38) is provided at the mixing channel housing floor (34), and / or in that a main reactant delivery direction (H) of the reactant delivery unit (38) is oriented substantially in the direction of the mixing channel longitudinal axis (L).

5. The exhaust gas / reactant mixing assembly as claimed in any of the preceding claims, characterized in that for the two opening channel portions (26, 28), a respective main exhaust gas outflow direction (A1, A2) for exhaust gas flowing out of the opening channel portion (26, 28) into the mixing channel (36) has a flow direction component which is substantially tangential relative to the mixing channel longitudinal axis (L).

6. The exhaust gas / reactant mixing assembly as claimed in any of the preceding claims, characterized in that a main exhaust gas inflow direction (Z) in the exhaust gas supply channel (20) is substantially orthogonal to the mixing channel longitudinal axis (L).

7. The exhaust gas / reactant mixing assembly as claimed in any of claims 1 - 5, characterized in that a main exhaust gas inflow direction (Z) in the exhaust gas supply channel (20) is substantially parallel to the mixing channel longitudinal axis (L).

8. The exhaust gas / reactant mixing assembly as claimed in any of the preceding claims, characterized in that the exhaust gas supply channel (20) is formed substantially in an exhaust gas supply channel housing (12) having an exhaust gas supply channel housing floor (18) and an exhaust gas supply channel housing peripheral wall (16) and a plurality of opening line regions (24, 26) starting from the exhaust gas supply channel housing floor (18) and / or from the exhaust gas supply channel housing peripheral wall (16), wherein an opening channel portion (26, 28) is formed in each opening line region (22, 24).

9. The exhaust gas / reactant mixing assembly as claimed in any of the preceding claims, characterized in that no mixer element is arranged in the mixing channel (36).

10. An exhaust gas system for an internal combustion engine, comprising an exhaust gas / reactant mixing assembly (10) as claimed in any of the preceding claims.

11. The exhaust gas system as claimed in claim 10, characterized in that an SCR catalyst arrangement (44) is provided downstream of the mixing channel (36).

12. The exhaust gas system as claimed in claim 10 or 11, characterized in that at least one exhaust gas treatment unit (46) is arranged upstream of the exhaust gas supply channel (20) and / or in the exhaust gas supply channel (20).

13. The exhaust gas system as claimed in claim 12, characterized in that the at least one exhaust gas treatment unit (46) comprises a catalyst arrangement and / or a particle filter arrangement.