DE102008044170A1 - Arrangement for dosing additive i.e. diesel emissions fluid urea solution, into exhaust system of diesel engine, has dosing element and ramp area arranged to each other such that additive escapes from element in direction to ramp area - Google Patents

Abstract

The arrangement has a dosing element (18) for dosing additive into exhaust gas (22), which flows through an exhaust duct segment (16). The exhaust duct segment includes a ramp area (20) that is attached to the dosing element. A flow cross section of the exhaust duct is changed in relation to an upstream lying end of the exhaust duct segment and direction of exhaust gas flow changes in the ramp area. The dosing element and the ramp area are arranged to each other such that the additive escapes from the dosing element in a direction to the ramp area.

Description

State of the art

The The present invention relates to an arrangement for dosing Additive in an exhaust system of an internal combustion engine.

to Exhaust aftertreatment of internal combustion engines, it is often necessary usually liquid Add auxiliary substances, so-called additives, into the exhaust gas. Examples therefor are the addition of urea solution (eg one known as "AdBlue" solution of 32.5% urea in demineralized water) into the exhaust of diesel engines for the regeneration of SCR-NOx catalysts for the conversion of NOx, or / and the addition of liquid Fuel (eg diesel fuel) for the regeneration of particulate filters. In all cases it is necessary to distribute the additive as evenly as possible and in particular with one possible metered into the exhaust gas high degree of evaporation, since the catalysts or filter sensitive the impact of still liquid Additive, and are too low evaporation of the metered Additive's damages the catalyst or filter are to be feared.

In order to achieve a satisfactory mixture preparation, so far in the usually additional, the actual metering elements (spray valves o. Ä.) Downstream mechanical mixing elements, eg. As flap mixer, belt wave mixer or swirl mixer required. A schematic representation of such a conventional arrangement with a directly acted upon by the dosed additive mixing element shows 1 ,

Of the Use of additional Mixing elements leads to additional costs for the additional component and because of the more complex installation. In addition, such must be Mixing element for specially adapted to the corresponding pipe cross-section of the exhaust duct be so for different exhaust systems usually specially adapted mixing elements must be used. Also, the required durability of the mixing elements to thermal and mechanical stress can only be achieved with great effort. A particular disadvantage of so far used combinations of metering and mixing element lies in that the use of mixing elements invariably a high Pressure loss of the exhaust system entails, due to the increased flow resistance of the Is due to mixing element.

Disclosure of the invention

The present invention solves the task of metering additive into the exhaust flow of a Improve combustion engine. In particular, this metering should Additive with reduced pressure loss of the exhaust system at the same good or even improved degree of evaporation of the additive are made possible.

These The object is achieved by an arrangement for dosing additive in an exhaust system of a An internal combustion engine comprising an exhaust passage segment with an upstream one End and one downstream lying end, and a the exhaust duct segment associated metering for metering additive into exhaust gas flowing through the exhaust passage segment, wherein the exhaust gas channel segment at least one associated with the metering element Ramp area, in which the flow cross-section of the exhaust passage across from the upstream lying end of the exhaust duct segment is changed and / or in which the direction of the exhaust flow changes, where the dosing element and the ramp area arranged in such a way to each other are that additive from the dosing element towards the ramp area going out.

Changes in the ramp area, the shape of the exhaust gas channel segment in cross-sectional view, does this to a changed one Flow cross section of the Exhaust duct. This is accompanied by a change in the position of the flow lines the gas flow to each other in the ramp area with respect to the areas downstream or / and upstream. Preferably move the streamlines in the ramp area closer together. This change is utilized according to the invention, to improve the mixing of exhaust gas and additive.

One corresponding effect leaves achieve when in the ramp area, alternatively or in addition to the above change the shape of the exhaust duct in the cross-sectional direction, the direction the streamlines of the exhaust gas changes in the longitudinal direction, and in particular the direction of a mean flow line or flow axis of the flowing through the exhaust passage Exhaust gas over the Direction of the flow axis at the upstream End of the exhaust duct segment changes or the exhaust duct forms a deflection.

The invention enables targeted guidance of exhaust gas flow and metered additive relative to each other. In particular, by appropriately designing the cross section of the exhaust gas channel segment in the ramp region, the metered additive can be guided even better into regions in which the exhaust gas flow has a high velocity and / or a strong velocity gradient, which promotes the mixing of exhaust gas and additive. The change of the cross section of the Exhaust gas ducts in the ramp area can take place in such a way that the ramp area protrudes locally into the exhaust gas duct to the flow axis of the exhaust gas. The additive can then be selectively guided into the core region of the exhaust gas flow and mix there effectively with the exhaust gas. If exhaust strands with a high concentration of additive still occur in the ramp region or downstream thereof, these are restricted to the core region of the exhaust gas flow and do not occur in the vicinity of the exhaust gas duct wall.

Preferably Dosing element and ramp area are located opposite each other walls arranged the exhaust duct segment. The direction of the dosing outgoing additive metering jet relative to the exhaust gas passage segment to be chosen appropriately depending on the circumstances. For example it has to be cheap proved to direct the dosing jet such that an axis of the Metering jet orthogonal to the flow axis the exhaust duct is.

The guide of exhaust gas flow and metered additive relative to each other can in particular such happen that the ramp area at least partially dosed with the Additive is applied and an immediate contact of additive and wall surface the ramp area takes place. When hitting (liquid) Additive drops on the wall of the exhaust duct segment in the ramp area occur Drop / wall interactions that can be exploited to to reduce the drop size. In general, the wall can be used in the impact area of the additive be to increase the spray angle of the rebounding from the wall additive and / or to better guide the metered additive into areas, in which the exhaust flow a high speed and / or a strong speed gradient having.

One very particular advantage of the arrangement according to the invention is that the ramp area designed aerodynamic can be and thus only low flow losses occur. Of the Ramp area needs in particular only one coherent Form area in which the wall of the wall of the exhaust duct segment is deformed. The ramp area may be substantially longitudinal of the exhaust duct segment and needs little in the cross-sectional direction protrude into the exhaust duct. It's compared to conventional ones Over mixing elements the entire length the exhaust duct segment and in particular also over the cross section of the exhaust duct segment at the point of the ramp area only very moderate deflections the exhaust flow relative to the direction of the flow axis required. Furthermore needs the with the exhaust flow contacting wall surface the exhaust duct segment in the ramp area not to be greater than in the other areas the exhaust duct. This results in comparison to conventional ones Mixing elements only low flow losses.

This creates the opportunity the cross-sectional area of the exhaust duct in the ramp area to reduce locally. With the reduction the cross-sectional area is a locally in the ramp area higher flow rate at reduced pressure accompanied by the mixing of exhaust gas with additive promotes. One due to the reduced cross-sectional area of the exhaust passage in the ramp area effected local lowering of the exhaust pressure can in this arrangement almost completely recovered as soon as the cross-section of the exhaust duct downstream of the Ramp area, z. B. at the downstream end of the exhaust duct segment, back to the original value extended.

Especially the exhaust duct segment in the ramp area one opposite the Cross sectional area the exhaust duct segment at the upstream end by up to 50%, preferably up to 30%, and most preferably up to 20% reduced cross-sectional area exhibit.

Of the Ramp area can be adapted to the shape and the course of the exhaust duct be, for example, so that the occurrence of turbulence is amplified and / or that secondary flows occurring anyway (eg in areas with crooked Course of the exhaust duct) and thus be used to improve the mixing. In a particularly simple example, the exhaust duct segment form a deflection of the exhaust passage in the ramp area, which seen in the radial direction of the deflection of an inner wall and one of these across from lying outer wall and wherein the metering element on the outer wall of the deflection in such a way is arranged that an outgoing from the metering dosing directed towards the inner wall. The dosing jet can, for example a Dosierstrahlachse have the approximately parallel or in a small Angle to the flow axis the exhaust gas at the downstream lying end of the exhaust duct segment runs and in the direction of inner wall of the deflection is directed towards. Similar effects, though generally in somewhat less pronounced form, can be obtained be when the metering on the inner wall of a deflection and he dosing jet on the outer wall in the area of the deflection is addressed to.

In a preferred embodiment the ramp area, with respect to the exhaust duct, comprises a concave Shape.

A concave shape can, compared to the rest of the exhaust duct, to the flow axis projecting area, figuratively speaking one to the flow axis out into the exhaust duct projecting into "dent" form. The concave shape can be formed by corresponding concave curvature of the metering facing wall of the exhaust duct segment, z. B. in the form of a uniform concave curved Dent of the exhaust passage wall to the flow axis of the exhaust gas out. A concave shape can also be formed by Stringing together several sections concave or even areas each with a different inclination to each other. In some cases the concave shape may even include convex shaped portions.

The concave shape can in the cross-sectional direction of the exhaust passage, d. H. in a section orthogonal to the direction of the flow axis, be formed, which in particular to a better distribution of the additive the exhaust duct cross section after rebounding from the wall of Abgaskanalsegements leads. The concave shape ensures one opposite the opening angle of the Dosing jet enlarged "spray angle" of the additive after contact with the exhaust gas facing wall of the concave shape and thereby improves the mixing of additive and exhaust gas.

The Concave shape can also be formed in the direction of the flow of the exhaust gas be. Even then, with regard to the distribution of additive relative to the exhaust gas flow conditions achieve those already mentioned. As an example pointed to a deflection in the exhaust duct segment, in which the direction of the flow axis of the exhaust gas changes. The radially inner wall of the exhaust gas channel segment has in the region of Deflecting a strong concave curvature in longitudinal direction the exhaust gas flow on. Spraying the additive in the vicinity of such a deflection, preferably a bit upstream of it, from the radially outer wall the exhaust duct with only small opening angle of the metering jet in a direction in which the metering jet to those in the area the deflection relatively strong concave inner wall of the exhaust duct deflection impinges, so that one reaches the additive from the inner wall in bounces off a relatively wide spray angle to the flow axis. Also an initially sharply focused Dosing jet with small opening angle spreads over so effectively a wide range along the flow direction of the exhaust gas. For example, the Dosierstrahlachse substantially parallel to Direction of the flow axis downstream be the deflection or a small angle to the flow axis downstream to make the diversion.

The concave shape may be an expansion in both the cross-sectional direction as well as in the direction of the exhaust flow. She is often the Have a dent or "dent" shape and in the ramp area to a reduced cross-sectional area of the Exhaust duct segment via a predetermined length lead the exhaust duct segment.

A extending in the direction of the flow axis concave shaping can be a compression of the flow lines of the exhaust gas flow in the ramp area cause and thus improve the mixing of additive and exhaust gas. The denser streamlines to lead Furthermore to a reduction in the thickness of a on the wall of the exhaust duct segment forming boundary layer. This results in an improved Heat transfer between exhaust and pipe wall, which is positive in a fast warming of the ramp area. In the case of conditions under which a movie of liquid Forms additive on the acted upon by additive wall of the exhaust passage, results in a reduced thickness of the wall film of additive. Provided through the ramp area additional Turbulence is induced, the thickness of the boundary layer decreases and possibly the wall film even further. In general, it is cheap when one possible thinner and as possible wide expansive wall film sets.

The concave shape can be over extend the entire ramp area. Alternatively, it is conceivable that only part of the ramp area, z. B. its center, is formed concave.

Of the Ramp section can be one in the vertical direction highest Central area and starting from the central area, preferably with increasing tendency to fall off. In this embodiment the central area forms one towards the flow axis of the exhaust gas protruding area, preferably on the dosed additive incident. Forms a wall film from undamped and therefore liquid Additive, so leads This shaping of the ramp area to a divergence of the liquid Wall film under the action of gravity. The wall film is with it thinner and has a larger surface area that is in contact with the exhaust gas flowing in the exhaust gas passage. The wall film can thus evaporate much more effectively than if only in the Area around the point of impact of the metered additive Wall film (with then correspondingly greater thickness) could train. Of the thinner Wall film also has the advantage that the residence time of additive decreases in a wall film, and thus a lower risk of coking and other deposits.

In an embodiment the exhaust duct segment has a local deformation in the ramp area on. Such local deformation is easy to produce by one piece Deformation of the exhaust gas channel segment by means of suitable forming processes, for example, by bending, pressing or drawing process. For example, can be a "dent" or "ramp" in one Exhaust duct segment of any cross section and size in a simple manner, wherein the exhaust duct segment may be a metal pipe, however Plastic and / or ceramic materials may be provided.

Especially in double-walled design of the exhaust duct segment, it is advantageous if the ramp region has a backwashed from the exhaust gas region. This takes care of rapid warming of the ramp area by the exhaust gas flow.

Furthermore can, in the direction of the exhaust gas flow and / or over the cross section of the exhaust duct segment, a plurality of Ramp areas may be provided. It is conceivable, for example, in a plurality of deflections having exhaust passage segment more Ramp areas in the flow direction to provide the exhaust gas sequentially in such a way that on the inner wall of a respective deflection of the exhaust gas channel segment a ramp area immediately follows. Another possible design provides a plurality of ramp areas in the flow direction the exhaust gas at the same level, but to disperse the circumference of the exhaust duct, with the angular distances between the ramp areas that between the injection holes of a multi-hole valve correspond to those emanating from the respective injection holes Dosing directed into the core region of the exhaust gas flow downstream of the To steer ramp area.

In the rule allows the described arrangement of the exhaust system, that liquid Additive without the aid of additional mixing elements in the exhaust gas can be metered. Should still an additional Mixing desired it can be, of course also in the described arrangement, an additional mixing element downstream of the Ramp area be arranged, this mixing element are chosen so may cause the resulting pressure loss in reasonable Keeps borders.

The Invention will be described below with reference to the drawings embodiments explained in more detail. It shows:

1 a schematic and simplified representation of a conventional arrangement for dosing additive in the exhaust passage of an internal combustion engine, comprising a metering element and a downstream mixing element,

2 a schematic and simplified representation of an arrangement for metering additive into the exhaust gas passage segment of an internal combustion engine according to an embodiment of the present invention, comprising a metering element and a concave ramp portion,

3 a schematic and simplified representation of two cross-sectional views of a conventional convex wall of the exhaust passage (a) and a ramp area in the cross-sectional direction concave shaped wall of an exhaust duct segment according to an embodiment of the present invention, according to one in 2 indicated section line AA (b)

4 2 shows, in a schematic and simplified representation, two cross-sectional views of a wall film on a conventional convexly shaped wall of the exhaust gas duct (a) and a wall of an exhaust gas duct segment concave in the ramp area in the cross-sectional direction according to an exemplary embodiment of the present invention (b),

5a ), b), c) each in a schematic and simplified representation of a cross-sectional view of a possible embodiment of a Rampenbe rich in the cross-sectional direction concave shaped wall of the exhaust duct segment according to embodiments of the present invention,

6a ), b), c) in each case in a schematic and simplified representation, a longitudinal sectional view of a possible embodiment of a ramp region in the flow direction concave shaped wall of an exhaust duct segment according to embodiments of the present invention,

7a ), b) and c) in each case in a schematic and simplified representation a longitudinal sectional view of a possible arrangement of dosing element and ramp region according to embodiments of the present invention,

8th a schematic and simplified representation of a longitudinal sectional view of a backlashed from the exhaust ramp area according to an embodiment of the present invention,

9 a schematic and simplified representation of a longitudinal sectional view of a plurality of successively arranged in the flow direction ramp areas according to an embodiment of the present invention,

10 in schematic and simplified 9 is a cross-sectional view of a plurality of circumferentially successive ramp portions according to an embodiment of the present invention;

11 in a schematic and simplified representation of a longitudinal sectional view of a metering element with associated ramp area and downstream mixing element according to an embodiment of the present invention,

1 shows a schematic and simplified representation of an arrangement for metering additive into the exhaust gas duct 10 an internal combustion engine, consisting of a metering element 12 and a downstream mixing element 14 according to the prior art.

2 on the other hand shows in a likewise schematic and simplified representation an arrangement for dosing additive in an exhaust gas duct segment 16 an internal combustion engine according to an embodiment of the present invention. The arrangement comprises a metering element 18 and a concave shaped ramp area 20 , Through solid arrows 22 is the flow of exhaust gas through the exhaust duct segment 16 indicated as a bunch of streamlines. The metering jet of additive which propagates in the exhaust gas is denoted by the reference numeral 24 indicated. The additive may be, for example, a urea solution ("adblue") for the regeneration of an SCR (= "selective catalytic reduction") NOx catalyst or additionally injected fuel for the regeneration of a particulate filter. One recognizes that the ramp area 20 forms a concave shape which extends into the exhaust passage to the flow axis B and, so to speak, a "dent" of the exhaust duct segment 16 forms. In the ramp area 20 is the cross-sectional area of the exhaust duct segment 16 is significantly reduced in relation to its cross-sectional area Q1 at the upstream end: in the present example, the ratio of the cross-sectional area Q2 is at the center of the ramp area projecting farthest towards the flow axis B. 20 to the cross-sectional area Q2 of the exhaust duct segment 16 at the upstream end about 80%, ie the ramp area reduces the cross-sectional area of the exhaust duct segment 16 by up to 20%. Accordingly, the flow lines of the exhaust gas in the ramp area close together. Associated with this is a corresponding increase in the flow velocity and reduction of the pressure of the exhaust gas.

3a ) shows, also in a schematic and simplified representation, a cross-sectional view of a convexly shaped in the cross-sectional direction wall 26 the exhaust duct, as in the embodiment according to 2 at the upstream end and at the downstream end of the exhaust duct segment 16 is provided, and as described in the prior art 1 also in the metering element 12 acted upon area of the exhaust passage 10 is provided. 3b ) shows in contrast one in the ramp area 20 the exhaust duct segment 16 , more precisely at its central location according to the in 2 indicated section line AA in the cross-sectional direction, concave shaped wall 28 the exhaust duct segment 16 according to an embodiment of the present invention. From the comparison of 3a ) and 3b ) is immediately apparent that the concave shape of the wall 28 in 3b ) to a widening of a Dosierkegel forming metering jet 24 leads as soon as additive from the concave-shaped wall 28 gets back into the exhaust duct. This provides efficient and uniform mixing of the additive and the exhaust gas over much of the cross section of the exhaust duct segment 16 time.

4 shows a schematic and simplified representation of two cross-sectional views of under certain conditions, especially at relatively low exhaust gas temperatures, forming wall film 30 respectively. 32 from metered additive. 4a shows the proportions of the wall film 30 on a convexly shaped wall in the cross-sectional direction 26 the exhaust duct according to the prior art and 4b ) shows the proportions of the wall film 32 at a ramp area located on the ground 20 in the cross-sectional direction concave shaped wall 28 the exhaust duct segment 16 according to an embodiment of the present invention. It can be seen that at the concave shaped wall 28 under the action of the downward gravity G, the wall film 32 more and more pulling apart, so compared to the convex shaped wall 26 according to 4a ) a much thinner wall film 32 results, which extends over a larger area. This promotes the evaporation of the liquid additive from the wall film 32 and promotes its even distribution in the exhaust gas. As the wall film 32 evaporates much faster than the wall film 30 , significantly lower risks of coking of liquid additive in the exhaust duct.

The 5a ), b), c) show in a schematic and simplified representation in cross-sectional view a number of possible embodiments of a ramp in the area 20 in the cross-sectional direction concave shaped wall 28 the exhaust duct segment 16 according to embodiments of the present invention. In 5a ) is the ramp area 20 from an orthogonal to the flow axis B concave shaped wall 28 which project in a circular cross-section to the flow axis B out The dent forms. In contrast, the ramp area 20 in the 5b ) and 5c ) from several wall parts 28a . 28b and 28c formed, each adjacent to each other and a total of the flow axis B protruding wall 28 form. The individual wall parts 28a . 28b . 28c may be flat, or concave and even convex, such as the central part 28b in 5c ).

The 6a ), b), c) show in a schematic and simplified representation in longitudinal section view of a number of other possible embodiments of a ramp in the area 20 in the flow direction concave shaped wall 28 the exhaust duct segment 16 according to embodiments of the present invention. In 5a ) is the ramp area 20 from a in the direction of the flow axis B concave shaped wall 28 , which forms an indentation, which curves uniformly in section to the flow axis B. In contrast, the ramp area 20 in the 6b ) and 6c ) from several wall parts 28a . 28b and 28c formed, each adjacent to each other and a total of the flow axis B protruding wall 28 form. Also the individual wall parts 28a . 28b . 28c may be flat, or concave and even convex.

It is understood that an exhaust duct segment 16 a ramp area 20 with concave shape, which can be in both the cross-sectional direction, as in 5a ) 5b ) 5c ) extends as well as in the flow direction, as in 6a ) 6b ) 6c ) extends.

7 shows in 7a ) 7b ) and 7c ) in a schematic and simplified representation of a longitudinal sectional view of a possible arrangement of dosing 18 and ramp area 20 according to embodiments of the present invention. In all embodiments according to 7a ) 7b ) and 7c ) forms the exhaust gas channel segment 16 one diversion each 34 in that the direction of the flow axis B of the exhaust gas changes from a direction B1 in the upstream part to a direction B2 in the downstream part.

The dosing element 18 according to 7a ) is arranged such that a Dosierstrahl 24 , whose beam axis C with the flow axis B2 of the exhaust gas in the downstream part of the exhaust duct segment 16 coincides. Immediately downstream of the diversion 34 is a ramp region extending in both the flow direction and the cross-sectional direction 20 on the radially inner wall of the exhaust duct segment 16 educated. The dosing jet 24 is directed such that its lower part on the ramp area 20 impinges and is directed from there in the direction of the flow axis B2.

The dosing element 18 according to 7b ) is arranged such that a Dosierstrahl 24 results whose beam axis C at an acute angle with the flow axis 62 the exhaust gas in the downstream part of the exhaust duct segment 16 forms. A ramp region extending in the flow direction 20 is directly at the diversion 34 through the radially inner wall of the exhaust duct segment 16 , educated. The dosing jet 24 is directed such that its lower part on the ramp area 20 impinges and is directed from there in the direction of the flow axis B2.

The dosing element 18 according to 7c ) is arranged such that a Dosierstrahl 24 results whose beam axis C at an acute angle with the flow axis 62 the exhaust gas in the downstream part of the exhaust duct segment 16 forms. Immediately downstream of the diversion 34 is a ramp region extending in both the flow direction and the cross-sectional direction 20 on the radially outer wall of the exhaust duct segment 16 educated. The dosing jet 24 is directed such that its upper part on the ramp area 20 impinges and from there in the direction of the flow axis 62 is steered.

8th shows in a schematic and simplified representation of a longitudinal sectional view of a back-flushed from the exhaust ramp area 20 according to another embodiment of the present invention. In this embodiment, the exhaust duct segment 16 double-walled, allowing the inner wall to form the concave ramp area 20 can be shaped. The inner wall is at the foot of the ramp area 20 Openings through which the exhaust gas behind the ramp area 20 can flow. The outer wall forms the boundary for the exhaust gas flow. The advantage of this embodiment is that the temperature of the ramp area 20 can be quickly brought to exhaust gas temperature by the backwash with hot exhaust gas, which suppresses the formation of wall films and generally promotes the mixing of exhaust gas and additive.

9 time in a schematic and simplified representation of a longitudinal sectional view of an exhaust duct segment 16 according to an embodiment of the present invention, wherein in the flow direction a plurality of ramp areas 20a . 20b arranged consecutively. The ramp areas 20a . 20b are located on opposite sides of the exhaust duct segment 16 , so that through the ramp areas of the flow of exhaust gas 22 and dosing jet injected into the exhaust gas 24 a meandering movement is impressed, which in turn promotes mixing. Also be there is the upstream ramp area 20a immediately after a diversion 34 the exhaust duct segment 16 on the radially inner side of the deflection 34 , This allows the targeted utilization of deflection in the area 34 generated secondary flows and turbulence of the exhaust gas for mixing with additive.

10 shows a schematic and simplified representation of a cross-sectional view in the direction of the flow axis B of another embodiment of the present invention with a plurality of circumferentially successive ramp areas 20 . 20b . 20c , The arrangement of the ramp areas 20 is distributed in the circumferential direction, that the conical metering jets (indicated by arrows 24a . 24b . 24c representing the projection of the respective beam axis on the cutting plane) of a three-hole valve located in the extension of the flow axis B, in each case to an associated one of the ramp areas 20a . 20b . 20c incident.

Finally shows 11 in a schematic and simplified representation of a longitudinal sectional view of a metering element 18 with assigned ramp area 20 and downstream mixing element 36 according to another embodiment of the present invention.

Claims (11)

Arrangement for dosing additive in an exhaust system of an internal combustion engine, comprising an exhaust gas channel segment ( 16 ) having an upstream end and a downstream end, and an exhaust passage segment (FIG. 16 ) associated dosing element ( 18 ) for dosing additive in through the exhaust gas channel segment ( 16 ) flowing exhaust gas ( 22 ), wherein the exhaust gas channel segment ( 16 ) at least one dosing element ( 18 ) associated ramp area ( 20 ), in which the flow cross section of the exhaust gas passage with respect to the upstream end of the exhaust gas channel segment (FIG. 16 ) is changed and / or in which the direction of the exhaust gas flow changes, wherein the metering element ( 18 ) and the ramp area ( 20 ) are arranged to each other such that additive from the metering element ( 18 ) towards the ramp area ( 20 ) out. Arrangement according to claim 1, wherein the exhaust gas channel segment ( 16 ) in the ramp area ( 20 ) has a reduced cross-sectional area (Q2) opposite to the cross-sectional area (Q1) of the exhaust passage segment at the upstream end. Arrangement according to claim 2, wherein the exhaust gas channel segment ( 16 ) in the ramp area ( 20 ) one opposite the cross-sectional area (Q1) of the exhaust gas channel segment ( 16 ) at the upstream end by up to 50%, preferably up to 30% and most preferably up to 20% reduced cross-sectional area (Q2). Arrangement according to one of claims 1 to 3, wherein the exhaust gas channel segment ( 16 ) in the ramp area ( 20 ) a diversion ( 34 ) of the exhaust duct, which seen in the radial direction of the deflection ( 34 ) has an inner wall and an outer wall opposite thereto, and wherein the dosing element ( 18 ) on the outer wall of the deflection ( 34 ) is arranged such that one of the dosing ( 18 ) outgoing dosing jet ( 24 ) is directed towards the inner wall. Arrangement according to one of claims 1 to 4, wherein the ramp area ( 20 ), based on the exhaust duct, a concave shape ( 28 ). Arrangement according to one of claims 1 to 5, wherein the ramp area ( 20 ) has a highest vertical central portion and sloping away from the central portion. Arrangement according to one of claims 1 to 6, wherein the exhaust gas channel segment ( 16 ) in the ramp area ( 20 ) has a local deformation. Arrangement according to claim 6, wherein the local deformation by one piece Forming is formed. Arrangement according to one of claims 1 to 8, wherein the ramp area ( 20 ) one of the exhaust gas ( 22 ) has backwashed area. Arrangement according to one of claims 1 to 9, wherein a plurality of ramp areas ( 20a . 20b . 20c ) are provided. Arrangement according to one of claims 1 to 10, wherein a mixing element ( 36 ) downstream of the ramp area ( 20 ) is arranged.