EP2687286A2 - Mixing device for the aftertreatment of exhaust gases - Google Patents

Abstract

The mixing device (1) has an inner tube (7) with a premixing area (10) formed inside the inner tube, which is arranged inside a housing (4) and is extended parallel to a main injection device (5) of a metering device (6) for feeding a liquid or a liquid-gas mixture. A main exhaust gas stream (12) is guided between the housing and the outer lateral surface (14) of the inner tube. The partial exhaust gas stream (17) flows through the premixing area in the main mixing area (16). The main exhaust gas stream comprises a larger exhaust gas volume proportion than the partial exhaust gas stream.

Description

The invention relates to a mixing device for the aftertreatment of exhaust gases in an exhaust system of an internal combustion engine having a housing having an inlet cross-section and disposed within the housing, substantially parallel to a main injection direction of a metering device for supplying a liquid and / or a liquid-gas mixture extending inner tube, with a formed in the interior of the inner tube mixing region comprises.

The publication DE 10 2009 053 950 A1 teaches a mixing device in which an exhaust gas is mixed with a, applied via a metering liquid reducing agent, the exhaust passes through dosing device remote openings of an inner tube radially into the interior and passes through a frontally arranged, metering device near opening into the interior of the inner tube. In this case, a substantial partial flow of the exhaust gas flows directly into the injection area of the metering device and influences the introduction of reducing agent.

The invention has the object of developing a mixing device with the features of claim 1 such that the mixing of the liquid with the exhaust gas is independent or only with little effect of the exhaust gas flow reliably and as homogeneous as possible. It is another object of the invention to realize the mixing while passing through a short mixing section and to keep the volume of the mixing device low.

This object is solved by the features of claim 1. Advantageous developments of the invention will become apparent from the dependent claims 2 to 15.

As the core of the invention, it is considered that the housing has a spiral-shaped housing section and on an end face of the housing A metering device is arranged, wherein a main exhaust stream between the housing and the outer surface of the inner tube out and fed to a main mixing area and a partial exhaust stream is fed through an inner tube passage in a dosing nearer Vormischbereich, wherein the partial exhaust gas flows through the Vormischbereich in the main mixing region and the main exhaust stream a larger Volume fraction as the exhaust gas partial stream comprises. Characterized in that the exhaust gas stream is divided into a low-volume exhaust gas partial stream and a higher-volume exhaust main stream and both exhaust streams are combined within a main mixing area, both a lying under slight influence of the exhaust gas volume flow liquid introduction, as well as simultaneously taking place by still taking place in the main mixing area merging of the exhaust main and exhaust gas partial stream reliably achieved homogeneous mixing of the liquid within the entire exhaust gas stream. The function of the spiral-shaped housing can be seen in that at least the exhaust main flow is imparted a swirling motion. This swirling movement has an advantageous effect on the mixing of liquid and offgas and their homogenization in the pre-mixing and / or main mixing region. The inner tube passage allows a pressure equalization between the exhaust main flow and the nozzle-near interior of the inner tube and a smaller partial exhaust gas mass flow to support the spray discharge from the interior of the inner tube to achieve. Without the provision of the bypass channel and the supply of the exhaust gas partial stream in the premixing the temporarily introduced liquid behave like a spring-mass system and at least temporary pressure fluctuations in the mixing areas - and thus unfavorable conditions for a homogeneous mixing lead, this is with prevents the execution of the invention.

If the introduction of a liquid is described by the metering device, then this may also comprise a liquid-gas mixture, for example in the form of a spray, below it is simplified and assumed as an example of a liquid. Basically, the metering device brings a reducing agent such as a urea solution or a hydrocarbon-containing substance in the mixing device and mixed as homogeneously as possible with the exhaust gas. In the case of the urea solution, this becomes for example, fed to a downstream arranged hydrolysis and reacted there.

In an advantageous embodiment, the main injection direction of the metering device is arranged substantially parallel and / or coaxially to the longitudinal axis of the housing and / or to the longitudinal axis of the inner tube. This makes it possible to achieve a compact and effective construction of the mixing device, since the partial exhaust gas streams are aligned with the walls of the housing and / or the inner tube and are directed thereto. Thus, a rectified Abgasteil- and / or exhaust main flow and liquid introduction is achieved in a simple constructive manner.

It has proved to be advantageous if the exhaust gas flow is divided into two or at most three partial flows. In particular, when an exhaust main stream introduced last into the mixing area comprises at least 70% by volume of the exhaust gas stream, preferably at least 80% by volume of the exhaust gas stream, more preferably at least 90% by volume of the exhaust gas stream, the effect described above becomes reliable Homogenization and the slight influence of liquid introduction achieved by the exhaust gas supply. Because only a small part (at least less than 30% by volume) undergoes mixing with the supplied liquid as one or, if appropriate, as a plurality of partial streams over the longitudinal axis of the inner tube upstream of the main exhaust gas flow, a homogeneous introduction is produced that is only slightly dependent on the exhaust gas volume flow the liquid reaches the exhaust gas. In particular, for the injected liquid droplets with low mass, the partial exhaust gas flow with its low volume flow is advantageous because these drops are then not deflected excessively by the exhaust gas volume flow. These droplets have a low momentum and would be so strongly deflected when exposed to a larger volume flow (see main exhaust stream) that they could be deposited excessively on the inner wall of the inner tube. This is with the inventive device - in particular by the low-volume, earlier acting on the liquid exhaust partial stream - avoided or kept at least in a small, not significantly affecting the mixing process frame. The exhaust gas flow is the supplied exhaust gas in the inlet cross-section area.

Further, it has proved to be advantageous to provide the inner tube with a cylindrical portion and with a tapered portion, wherein the tapered portion is upstream of the cylindrical portion in the flow direction of the main exhaust gas stream. The tapered portion acts as a deflection region and directs the supplied exhaust mainstream "low pressure loss" -. with a minimum resistance - parallel to the main injection direction of the metering device. In this case, the tapering section preferably comprises a continuously and / or continuously changing radius, which is designed, for example, as a radius which increases continuously on the outside of the inner tube and / or continuously in the flow direction of the exhaust main flow. The continuous change or enlargement of the radius means an uninterrupted change and / or a change that is always progressing in a (magnifying) direction. This measure leads to a deflection of the exhaust gas under a small, acting on the exhaust gas flow resistance. Alternatively, the deflection region may also include a constant and continuous radius, this design is less expensive and easier to manufacture.

Through the tube width of the inner tube, which is to be understood as the area between the maximum tube outer diameter and the minimum tube inner diameter, the partial exhaust gas flow to the premix area is substantially (i.e., +/- 10%) perpendicular to the main injection direction. Since only a small proportion of the exhaust gas passes through this bypass to the mixing region, its movement taking place at right angles to the main injection direction, at least in regions, is not or only insignificantly disadvantageous for the introduction of the liquid into the mixing region.

Alternatively and / or in addition to the above-described, at least partially extending perpendicular to the main injection direction supply of the exhaust gas partial stream in the premixing, it is advantageous if within the inner tube and / or in the premixing area guide elements are arranged, which deflect the exhaust gas partial flow toward the main injection direction To run. Thus, for example, a "protective collar" can be arranged around the vicinity of the metering device, so that initially the liquid introduction experiences no disturbance as a result of being exposed to the partial exhaust gas flow. Also can by the guide elements, an advantageous deflection of the exhaust gas partial stream in the main injection direction. Thus, three areas are formed for fluid mixing, a first area within the guide element, in which only a liquid introduction takes place without exposure to exhaust gas. A second area - the premix area - in which the partial exhaust gas stream is "premixed" with the liquid leaving the first area. In the third area - the main mixing area - the supply of the main exhaust stream to the premixed liquid-waste gas partial stream mixture takes place. In this case, the guide element is preferably designed like a ring and formed on its inside circular cylindrical and tapering in its cross section to its free end.

In a particularly preferred embodiment, the guide elements and / or a further deflection element can induce the exhaust gas partial flow to have a movement component running at right angles to the main injection direction and / or a spiral-like course of movement. Thus, a swirling movement is impressed on the exhaust gas partial flow. For example, it is thus possible for a swirl of the exhaust gas partial stream, which may have already been generated by the spiral shape of the housing, to be taken over into the premixing area and / or reinforced.

In an advantageous structural embodiment, the length of the guide element (in the direction of the longitudinal axis of the inner tube) is shorter than the length of the inner tube. In particular, the length of the guide element may be shorter than half or shorter than a quarter of the inner tube. This embodiment enables a compact and effective mixing device. The guide element serves primarily to protect the area near the metering device in front of the exhaust gas part flow and to divert the exhaust gas partial flow radially directed to the guide element or the main injection axis into the main injection direction. So that in particular the low-mass drops of the liquid in the inlet region do not experience any deflection by the partial exhaust gas flow.

Also, alternatively or additionally, the main exhaust gas flow may have a positive effect even with regard to the flow conditions in the premixing area, by a suction effect generated by the main exhaust gas flow (negative pressure generation) in the premixing area a further directional influence of the liquid and / or the partial exhaust gas stream, out or parallel to the main injection direction is executable.

Preferably, the spray angle α is selected such that the spray (the liquid) does not substantially touch the inner wall of the inner tube in the non-exhaust gas flowed through state. This should only touch a small proportion by mass of the liquid to the inner wall of the inner tube and possibly attach there. If this is fulfilled in the non-exhaust gas flow condition, then a slight (smaller 15%, preferably less than 8%) and existing at least in defined load scenarios of the engine wetting of the inside of the inner tube is achieved in the exhaust gas flowed through state (operating state). This contact or this wetting takes place on the inner tube inside on the end region facing away from the metering device, preferably in the last eighth of the inner tube and thus close to the transition to the main mixing region A slight and / or temporary wetting of the inner wall of the inner tube end is tolerable and also in particular in the exhaust gas flowed through state advantageous. Due to the fact that a small part of the liquid attaches at least temporarily to the inner wall of the inner tube, a certain liquid reservoir is realized in this way. The metering device usually works temporarily. This can be achieved during the non-injection periods, a "degradation" of the liquid located on the inner wall of the inner tube. This effect is favored by the fact that the inner tube is thin-walled and / or is heated on the outside by the exhaust main flow, so that the liquid located on the wall portions of the inner wall is heated. This heat facilitates the separation effect and splitting effect (secondary rupture) of the liquid droplets laying on the inner tube on the inside. In other words, the mixing function of the mixing device is further promoted by the targeted slight temporary wall contact of the liquid. In particular, the fact that this "liquid reservoir" is arranged at the inner tube end and thus close to the main mixing region, can also prove the suction and negative pressure effects of over the preferably formed as an annular gap crossing into the main mixing area, as a conveyor of the mixing properties of the mixing device.

About the design of the length of the inner tube can be adjusted in a structurally simple and effective way, the degree of temporary adhesion of the liquid. In general, the metering device and thus the spray angle and the density of the liquid is specified. These parameters affect the propagation characteristics of the spray depending on the exhaust gas volume flow. If now a liquid with a different density and / or a metering device with a different spray angle to be installed, it is sufficient if the mixing device is adjusted by changing the length of the inner tube to adjust the effect described above (secondary rupture). This also allows a modular design and / or a retrofit system by appropriate selection of an inner tube of the preferred length.

A further advantageous measure is to make the inlet cross section (i.e., diameter or inside diameter of the inlet cross section) of the exhaust gas at the housing smaller or equal than the length of the inner tube. In particular, a ratio of inlet cross section of the exhaust gas to the length of the inner tube in the range of 1: 1 to 1: 1.5 has proven. Thus, a compact and effective mixing device is achieved.

According to an advantageous embodiment of the mixing device is provided that the inner tube passage is formed by a plurality of passage openings, wherein the passage openings are preferably arranged lying on a circular ring or on a circular ring segment, wherein particularly preferably the circular ring or the circular ring segment in the first, the metering device facing third or longitudinal quarter of the inner tube is arranged. This metering device near arrangement of the passage openings allows the homogeneous mixing and the only slight influence of the liquid introduction by the exhaust gas partial stream. The passage openings may be formed, for example, as slots, elongated holes or the like.

Also, the passage opening may be formed as a completely circumferential annular gap. Here, the inner tube is connected via at least one web to the housing supporting and / or supporting. This at least one web is preferably arranged on the front side and within the bypass channel. Of the Bypass passage is the area in which the partial exhaust gas flow passes from the passage opening into the radially inward premix area. The web can furthermore have a geometry which allows a defined influencing of the exhaust gas part stream passing past it (eg its direction), for example the exhaust gas partial stream is deflected by the web and / or put into a twisting motion. In a specific embodiment, the partial exhaust gas flow undergoes a deflection by at least 10 °, preferably by at least 25 °. In general, it is advantageous if the webs are equidistantly spaced lying on a circular line and whose geometry is at least designed similar, so that a partial exhaust gas flow deflection over the circumference is similar executable.

Additionally or alternatively, it may further be provided that the exhaust gas partial stream, starting from the inlet cross-section to the passage openings, performs a movement counter to the main injection direction, before it enters the premixing area. The passage openings of the inner tube can also be arranged closer to the dosing device in the longitudinal direction than the region of the entry cross-section facing the dosing device. These two individual or combinable embodiments require a greater distance for the partial exhaust gas flow than the path for the exhaust main flow. This allows and / or promotes the formation and / or the setting of a negative pressure or a suction effect in the premixing chamber, starting from the main exhaust stream. Due to the shorter distance of the exhaust main flow compared to the partial exhaust gas flow to the main mixing area, the suction effect (and thus a negative pressure) is generated in a simple and effective manner in the premixing area.

The passage of the exhaust main flow into the main mixing area is preferably carried out by passing through an annular gap at the end of the inner tube. The easy-to-define dimensioning and design of the geometry of the annular gap allows to easily and effectively set the negative pressure conditions of the premixing.

In a further advantageous embodiment, the inner tube, the guide element and / or the at least one web over the inner tube cross-section point-symmetrical to the main injection direction / axis and / or the inner tube, the guide element and / or the webs rotationally symmetrical / arranged, preferably around the main injection direction / axis. For example, the inner tube and the guide element are formed as a rotationally symmetrical body which is aligned coaxially with one another and coaxially with the main injection direction / axis. Further, in this case, the webs may be formed similar, so that they are rotationally symmetrical (eg with a 120 ° twist at three bars or 90 ° twist at four bars, etc.) are arranged. This symmetrical design enables an easy-to-manufacture mixing device and positive flow conditions with a high degree of homogenization of liquid and exhaust gas.

A simple and cost-effective production of the mixing device can be achieved, for example, in that the housing, the inner tube, the guide element and / or the deflecting element are integrally formed in one piece, preferably a one-piece molded or in a melting process (eg laser sintering or laser melting) manufactured component ,

Fig. 1

eine schematische Längsschnittdarstellung einer ersten Ausführungsform der Mischvorrichtung;

Fig. 2

eine schematische Längsschnittdarstellung einer zweiten Ausführungsform der Mischvorrichtung;

Fig. 3

eine schematische Vollschnittdarstellung einer weiteren Ausführungsform der Mischvorrichtung;

Fig. 4

eine Vollschnittdarstellung gemäß Detail C aus Figur 3;

Fig. 5

eine Vollschnittdarstellung gemäß Schnittlinie A-A aus Figur 3;

Fig. 6

eine Vollschnittdarstellung einer alternativen Ausgestaltung zu Fig. 4.

The invention is explained with reference to exemplary embodiments in the drawing figures. These show:

Fig. 1

a schematic longitudinal sectional view of a first embodiment of the mixing device;

Fig. 2

a schematic longitudinal sectional view of a second embodiment of the mixing device;

Fig. 3

a schematic full sectional view of another embodiment of the mixing device;

Fig. 4

a full sectional view according to detail C from FIG. 3 ;

Fig. 5

a full sectional view according to section line AA FIG. 3 ;

Fig. 6

a full sectional view of an alternative embodiment Fig. 4 ,

Exhaust gases 2 of an internal combustion engine (not shown) are fed into the mixing device 1 through the inlet cross-section 3 of a housing 4 of the mixing device 1 and, after passing through the mixing device 1, are fed to a catalytic converter (not shown). Within the housing 4 is a substantially parallel to a main injection direction 5 (shown as an arrow) of a metering device 6 extending inner tube 7 is arranged. By the metering device 6, a liquid 9, for example in the form of a spray - represented by the two beams 29, 30 - introduced into the interior 8 of the inner tube 7. The interior 8 is thus defined as Vormischbereich 10. The spray is introduced conically or in the form of several spray cones, wherein the axis of symmetry of the cone or the axis of symmetry of the plurality of cones essentially form the main axis of reflection. Also, the main injection axis can be generally regarded as an imaginary line, around which the main amount of the liquid 9 is introduced in a straight line in the inner space 8 of the inner tube 7. In this case, the exhaust gases 2 are mixed with the liquid 9. The main injection direction 5 and thus in FIG. 1 The main injection axis coincide and are aligned coaxially to the longitudinal axis of the housing 4, wherein the longitudinal axis of the housing 4 refers to the rotationally symmetric region of the housing 4, that is, the spiral portion 13 subsequent housing portion 26. Alternatively or - as in FIG. 1 In addition, the main injection direction 5 may extend coaxially to the longitudinal axis of the inner tube 7.

The housing 4 has a spiral-shaped housing section A, which extends at least partially around the inner tube 7. Due to the spiral shape, the exhaust gas 2 is supplied evenly around the circumference of the inner tube 7. At the end face 11 of the housing 4, the metering device 6 is arranged.

The exhaust main flow 12 is deflected on the outer surface (lateral surface 14) of the inner tube 7 to the main injection direction 5 and guided between the inner wall of the housing 4 and the outer surface of the inner tube 7 and directed to the arranged at the end 15 of the inner tube 7 main mixing region 16. By the at least spiral-shaped first region 13 of the housing 4, a uniform, radially inwardly acting force component of the exhaust gas 2 is achieved on the inner tube 7. Thus, a symmetrical, radially inwardly acting pressurization is achieved by the exhaust gas 2. A lower partial exhaust gas flow 17, which is smaller than the mass and / or volume of the exhaust main flow 12, is transported through an inner tube passage 18 via a bypass channel 19 to the premixing region 10 and from there comes to the Main mixing region 16 and thus to the main exhaust stream 12. The premixing region 10 is arranged closer to the metering device 6 than the main mixing region 16.

The inner tube 7 has a cylindrical portion 20 and a tapered portion 21, wherein the tapered portion 21 of the metering device 6 is disposed closer and / or upstream in the flow direction S of the exhaust main flow 12. The tapered portion 21 relates at least to the outer circumferential surface 14 of the inner tube 7. The inner surface may have a corresponding curvature - as in FIG. 1 shown - comprise or according to FIG. 2 in the interior 8 of the inner tube 7 have a constant cross-section.

A guide element 22 is arranged inside the inner tube 7 and prevents the fluid 9 from being exposed to the exhaust gas flow 17 passing through the bypass passage 19 in the introduction area near the metering device and the premixing area 10. The guide element 22 also directs the exhaust gas flow 17 in the main injection direction 5 to the premixing area 10 out to, um. For this purpose, the guide element 22 is annular and preferably rotationally symmetrical. On the inner side 24 of the guide element 22, this is circular-cylindrical and, in its cross section, at least on its outer surface, it tapers towards the free end 25.

The length 27 of the guide element 22 is shorter than the length 28 of the inner tube 7. Thus, the cross section in the premixing area 10 extends. The length 27 of the guide element 22 is shorter than a quarter of the length 28 of the inner tube. 7th

As in the FIGS. 1 and 2 by the number of arrows showing the exhaust gas 2, the exhaust main flow 12 and the exhaust gas partial flow 17, the exhaust main flow 12 corresponds essentially to 75% by volume and the exhaust gas partial flow 17 corresponds to essentially 25% by volume of the incoming exhaust gas 2.

The spray angle α is the angle which results between the beams 29, 30 extending linearly from the center of the metering device 6, the beams 29, 30 forming the substantially outer beam region of the liquid introduction represent. The main injection direction 5 and / or the main injection axis here is the bisector of the two beams 29, 30, cf. FIG. 1 ,

The inlet cross section 3 and thus the maximum transverse extent of the inlet region of the exhaust gas 2 are dimensioned such that it is less than or equal to the length 28 of the inner tube 7, preferably the ratio of the inlet cross section 3 to the length 28 of the inner tube 1: 1.3 to 1: 5.0. Wherein it is advantageous if the inlet cross section substantially (i.e., +/- 10%) corresponds to the length 31 of the tapered portion 21 of the inner tube 7. As a result of this adaptation, the exhaust gas 2 supplied in part radially, partly by the spiral shape of the housing 4, can be deflected with little loss through the tapered section 21 of the inner tube 7.

The inner tube passage 18 is according to the embodiment of FIGS. 4 and 5 formed with a plurality of equidistantly arranged on a circular line passages 32, wherein this circular line along the longitudinal axis of the inner tube 7 viewed in the metering device 6 facing quarter is arranged. Also, the inner tube 7 and the guide element 22 in cross-section - see. FIG. 5 - Arranged point-symmetrically to the main injection 5 direction. Also, both the inner tube 7 and the guide element 22 has a rotationally symmetrical geometry and is coaxial with the main injection direction 5 (center in FIG. 5 ).

Via the passage openings 32, the partial exhaust gas flow 17 passes through the bypass channel 19 into the premixing area 10, in which case the partial exhaust gas flow 17 undergoes a movement in the direction B, which runs opposite to the main injection direction 5. Through this "detour" a compact mixing device 1 is made possible. This embodiment provides that the passage openings 32 of the inner tube 7 and / or the bypass channel 19 are arranged closer to the metering device 6 in the longitudinal direction than the region of the inlet cross section 3 facing the metering device 6. The facing region (delimiting surface 33) of the inlet cross section 3 is as the nearest (here linear) boundary surface 33 of the inlet cross-section 3 to understand. As in the FIGS. 4 and 5 shown in each case the bypass channel 19 extends in the longitudinal direction closer to the metering device 6 as the boundary surface 33 of the inlet cross-section 3. A Another advantage of this embodiment is that is removed by the "detour" or by the return movement of the exhaust gas flow 17 in direction B from the volute casing the exhaust gas imparted swirl component, so that the penetrating into the premixing 10 exhaust partial flow 17 has no or at least a lesser twist as the main exhaust stream 12.

According to the execution FIG. 2 the bypass channel 19 has a widened space. The volume of the bypass channel 19 expands at least temporarily before the partial exhaust gas flow 17 reaches the premixing area, preferably the exit to the premixing area is provided with a diameter-reduced opening section directed in the direction of the main injection direction 5. The widened section of the bypass channel 19 can act for further swirl component removal at the exhaust gas partial flow 17. Furthermore, this also means - as in FIG. 2 represented impetus in the bypass channel supplied exhaust gas partial stream 17, the pulse component are degraded, so that the extended portion acts as a "comfort chamber" for the exhaust gas partial stream 17. LIST OF REFERENCE NUMBERS 1 mixing device A housing section 2 exhaust B direction 3 Inlet cross-section S flow direction 4 casing 5 Main injection direction 6 metering 7 inner tube 8th Interior v. 7 9 liquid 10 premix 11 front 12 Exhaust gas main stream 13 first area v. 4 (spiral shape) 14 Lateral surface v. 7 15 End of v. 7 16 Main mixing area 17 Partial exhaust gas stream 18 Inner tube passage 19 bypass channel 20 cylindrical section v. 7 21 Rejuvenated section v. 7 22 vane 23 inserting section 24 Inside v. 22 25 End of v. 22 26 second area v. 4 27 Length v. 22 28 Length v. 7 29 beam 30 beam 31 Length v. 21 32 Through opening 33 Boundary surface v. 3

Claims (14)

1. A mixing device (1) for the aftertreatment of exhaust gases (2) in an exhaust system of an internal combustion engine having a housing (4) having an inlet cross-section (3) and a housing arranged inside the housing (4) substantially parallel to a main injection direction (5 ) a metering device (6) for supplying a liquid and / or a liquid-gas mixture extending inner tube (7) with a in the interior (8) of the inner tube (7) formed Vormischbereichs (10), wherein the housing (4) has a spiral housing portion (13) and on a front side (11) of the housing (4) the metering device (6) is arranged, wherein a main exhaust stream (12) between the housing (4) and the outer lateral surface (14) of the inner tube (7) is guided and a main mixing area (16) can be supplied and an exhaust partial flow (17) through an inner tube passage (18) in the metering device nearer Vormischbereich (10) can be fed, wherein the exhaust ilstrom (17) via the Vormischbereich (10) in the main mixing region (16) opens and the exhaust main stream (12) comprises a larger exhaust gas volume fraction than the exhaust gas partial stream (17). 2. Mixing device (1) according to claim 1, wherein the main injection direction (5) of the metering device (6) is substantially parallel and / or coaxial with the longitudinal axis of the housing (4) and / or to the longitudinal axis of the inner tube (7). 3. Mixing device (1) according to claim 1 or 2, wherein the exhaust main flow (12) at least 70% by volume of the inlet cross-section (3) supplied exhaust gas (2), preferably at least 80 vol .-% of the exhaust gas (2), especially preferably at least 90% by volume of the exhaust gas (2). A mixing apparatus (1) according to any one of the preceding claims, wherein the inner pipe (7) comprises a cylindrical portion (20) and a tapered portion (21), the tapered portion (21) facing the cylindrical portion (20) in the flow direction (S) of the exhaust main stream (12) is upstream. 6. mixing device (1) according to any one of the preceding claims, wherein within the inner tube (7) and / or immediately before the premixing region (10) and / or at the front end of the premixing region (10) by a guide element (22), a deflection of the exhaust gas partial stream (17) towards the main injection direction (5). 7. mixing device (1) according to claim 6, wherein the guide element (22) is annular and / or rotationally symmetrical and preferably on its inner side (24) is circular cylindrical and / or tapered in its cross section to its free end (25). 8. Mixing device (1) according to claim 6 or 7, wherein the length (27) of the guide element (22) is shorter than the length (28) of the inner tube (7), preferably that the length (27) of the guide element (22). shorter than half the length (28) of the inner tube (7), particularly preferred that the length (27) of the guide element (22) is shorter than a quarter of the length (28) of the inner tube (7). 9. mixing device (1) according to any one of the preceding claims, wherein the spray angle □ is selected such that the spray, the inner wall of the inner tube (7) in the non-exhaust gas flow state substantially does not touch. 10. Mixing device (1) according to one of the preceding claims, wherein, the inlet cross-section (3) of the exhaust gas is less than or equal to, as the length (28) of the inner tube (7), preferably, that the ratio of inlet cross-section (3) of the exhaust gas (2) to the length (28) of the inner tube (7) is 1: 1 to 1: 1.5. 11. Mixing device (1) according to one of the preceding claims, wherein the inner tube passage (18) is formed by a plurality of passage openings (32), wherein the passage openings (32) are preferably arranged lying on a circular ring or a circular ring segment, wherein particularly preferably Circular ring or the circular ring segment in the first, the metering device (6) facing the longitudinal thirds or quarter of the inner tube (7) is arranged. 12. Mixing device (1) according to one of the preceding claims, wherein the inner tube (7) via webs within the mixing device (1) and the Webs are preferably arranged exclusively in the bypass duct (17) leading from the inlet region into the premixing region (10). 13. Mixing device (1) according to claim 12, wherein at least one web is shaped such that the exhaust gas partial stream (17) guided past the web undergoes a defined change in direction, preferably undergoes a deflection of at least 10 °, the geometry of the webs particularly preferably is similar, so that the deflection is at least similarly executable. 14. Mixing device according to one of the preceding claims, wherein the exhaust partial stream (17) starting from the inlet cross section to the passage openings a movement (B) against the main injection direction (5) must perform and / or that the passage openings and / or the bypass channel (19) of Inner tube (7) in the longitudinal direction closer to the metering device (6) are arranged as the metering device (6) facing the region of the inlet cross-section. 15. Mixing device according to one of the preceding claims, wherein the inner tube (7), the guide element (22) and / or the webs in cross-section point symmetrical to the main injection direction (5) / - axis and / or that the inner tube (7), the Guide element (22) and / or the webs has a rotationally symmetrical geometry, preferably around the main injection direction (5) / - axis.

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