Mixing arrangement

Abstract

A mixing arrangement for an exhaust system of an internal combustion engine, comprising a mixing section (18) with a mixing section inlet region (20) to be positioned downstream with respect to a reactant delivery arrangement (12) and a mixing section outlet region (22) to be positioned upstream with respect to a catalyst arrangement (16), wherein the mixing section (18) comprises an inner wall (26) surrounding an inner volume (28) through which exhaust gas (A) and / or reactant (R) can flow, and an outer wall (24) surrounding the inner wall (26), wherein an outer volume (30) surrounding the inner volume (28) in a ring-like manner is formed between the inner wall (26) and the outer wall (24), wherein an electrically excitable heating device (34) is provided on the inner wall (26), wherein the electrically excitable heating device (34) comprises at least one heating element (38) that can be heated by electrical excitation, characterized in thatthat at least one heating element (38) is provided on an inner side (32) of the inner wall (26).

Description

[0001] The present invention relates to a mixing arrangement for an exhaust system of an internal combustion engine, comprising a mixing section with a mixing section inlet region to be positioned downstream with respect to a reactant discharge arrangement and a mixing section outlet region to be positioned upstream with respect to a catalyst arrangement.

[0002] DE 102 01 044 A1 discloses an exhaust system for an internal combustion engine in which, along a longitudinal section of the exhaust system, a tubular inner wall is surrounded by a tubular outer wall. The inner wall surrounds an inner volume through which exhaust gas can flow. An outer volume through which exhaust gas can also flow is formed between the inner wall and the outer wall. A swirl generator is provided upstream of the inner wall or the outer volume formed between the inner wall and the outer warning device. The swirl generator imparts a circumferential flow direction component to the exhaust gas, which flows essentially straight from upstream.Depending on the flow velocity of the exhaust gas flowing toward the swirl generator, the exhaust gas flow is directed such that at a comparatively low flow velocity, it flows essentially completely through the inner volume, at a very high flow velocity, it flows essentially completely through the outer volume, and in a central flow region, the exhaust gas flow is distributed between the inner and outer volumes. To achieve this, the swirl generator has guide vanes that are angled relative to the flow direction of the exhaust gas flowing toward it and arranged in a ring-like formation.

[0003] In order to reduce pollutant emissions from internal combustion engines, particularly diesel engines, it is known to add a reactant, such as a urea / water solution, to the exhaust gas. In a mixing section, the reactant mixes with the exhaust gas, evaporating or thermally decomposing it, essentially producing ammonia, which reacts in a downstream SCR (selective catalytic reduction) catalyst arrangement in a catalytic reaction to reduce the proportion of harmful nitrogen oxide. Particularly at comparatively low operating or ambient temperatures or high dosing rates of the reactant, there is a risk that the reactant is not efficiently mixed with the exhaust gas or decomposed, thus preventing the efficient provision of the ammonia required for selective catalytic reduction.

[0004] A mixing arrangement according to the preamble of claim 1 is known from DE 10 2014 205 156 A1. In this known mixing arrangement, an exhaust pipe of an exhaust system forms an inner wall of a mixing section in a region in which reactant is injected by means of a reactant inlet arrangement. An outer wall surrounding the inner wall is provided on an outer side of the inner wall. Furthermore, a heating element spirally surrounding the inner wall is provided on the outer side of the inner wall. This heating element is embedded in insulating material filling the volume between the inner and outer walls.

[0005] It is the object of the present invention to provide a mixing arrangement for an exhaust system of an internal combustion engine, which ensures efficient mixing of reactant and exhaust gas as well as efficient decomposition of the reactant.

[0006] According to the invention, this object is achieved by a mixing arrangement for an exhaust system of an internal combustion engine according to claim 1. This comprises a mixing section with a mixing section inlet region to be positioned downstream with respect to a reactant input arrangement and a mixing section outlet region to be positioned upstream with respect to a catalyst arrangement, wherein the mixing section comprises an inner wall surrounding an inner volume through which exhaust gas and / or reactant can flow, and an outer wall surrounding the inner wall, wherein an outer volume surrounding the inner volume in a ring-like manner is formed between the inner wall and the outer wall, wherein an electrically excitable heating device is provided on the inner wall.

[0007] The present invention provides measures which ensure that improved thermal conditions can be provided for the evaporation or decomposition of the reactant added to the exhaust gas. On the one hand, an electrically excitable heating device can be used for this purpose. This heating device is operated primarily when the exhaust gas and / or exhaust gas-carrying components of an exhaust system have comparatively low temperatures in order to provide sufficient thermal energy for the evaporation or thermal decomposition of the reactant, particularly in such an operating state. If the exhaust gas transports sufficient heat or the exhaust gas-carrying components are sufficiently heated by the exhaust gas flow, the provision of a heat transfer fin formation and the enlarged interaction surface thus provided for heating the reactant can also lead to an improved heat input into the exhaust gas orthe reactant.

[0008] In order to be able to actively introduce heat into the mixing arrangement in a simple manner, the electrically excitable heating device comprises at least one heating element that can be heated by electrical excitation. Such a heating element can be provided, for example, as a heating coil, heating conductor, heating band, or heating sleeve and can be primarily constructed of metal, ceramic, or semiconductor material.

[0009] The provision of at least one heating element on an inner side of the inner wall ensures that heat is introduced into the inner wall, particularly where primary thermal interaction with the reactant will occur. Furthermore, heat loss to the outside via the outer wall is largely avoided in this way.

[0010] In a structurally simple embodiment, it can be provided that at least one heating element comprises a heating conductor that surrounds a longitudinal center axis of the inner wall in a winding manner.

[0011] If the heat requirement is approximately constant over substantially the entire length of the mixing section, it is proposed that a pitch of the windings of the heating conductor in the direction of the longitudinal center axis of the inner wall is substantially constant at least in some areas.

[0012] If the heat demand varies over the length of the mixing section, the pitch of the heating conductor's windings can vary in the direction of the longitudinal center axis. For example, with such a configuration, the pitch of the heating conductor's windings can preferably increase substantially continuously in a main flow direction in at least one longitudinal region of the inner wall.

[0013] In another embodiment, at least one heating element may comprise a meandering heating conductor.

[0014] For a very uniform heat input into the inner wall, it is proposed according to the invention that at least one heating element comprises a surface heating element covering at least 50%, preferably at least 80%, of an outer surface of the inner wall, and / or that at least one heating element comprises a surface heating element covering at least 50%, preferably at least 80%, of the inner surface of the inner wall.

[0015] At least one heating element can be a PTC heating element. The resistance characteristic of such a PTC heating element is particularly advantageously utilized, as it exhibits a significantly progressive increase over a certain temperature range, thus leading to self-limitation of the electrical current flowing through such a heating element. This can, for example, ensure that the temperature of the actively heated inner wall is maintained within a temperature range of approximately 300°C without the need for temperature control. For this purpose, barium titanate, for example, can be used as the construction material for such a PTC heating element.

[0016] If the outer volume is sealed against flow of exhaust gas and / or reactant, this outer volume essentially forms an insulating gap, which is intended to keep heat losses to the outside as low as possible.

[0017] If the outer volume of the exhaust gas and / or reactant can flow through, this volume can also be used to transfer heat to the exhaust gas or reactant flowing around the inner wall on its outer side.

[0018] According to a further aspect, a heat transfer fin formation may be provided on the inner wall.

[0019] It is particularly advantageous if the heat transfer fin formation comprises a plurality of heat transfer fins arranged successively in the circumferential direction on the outside of the inner wall.

[0020] The heat transfer fins can, for example, be plate-like and / or can be arranged extending radially outwards substantially from the outside of the inner wall with respect to the longitudinal center axis of the inner wall.

[0021] In an alternative embodiment, a comparatively large heat transfer surface can be provided by arranging the heat transfer fins in a wave-like manner surrounding the inner wall on its outer side.

[0022] A particularly efficient thermal interaction of the exhaust gas or the reactant with the heat transfer fin formation can be achieved by providing a plurality of groups of heat transfer fins arranged successively in the direction of the longitudinal center axis of the inner wall, wherein the heat transfer fins of immediately successive groups are offset from one another in the circumferential direction and / or the heat transfer fins in immediately successive groups have a different circumferential spacing from one another. This ensures that, at the transition between the groups following one another in the flow direction, a continuous renewal of the boundary layer that thermally interacts with the surface of the heat transfer fins occurs.

[0023] In order to be able to provide a large surface area on the one hand and to hinder the exhaust gas flow in the mixing section as little as possible on the other, it is proposed that the heat transfer fins have heat transfer surfaces running essentially in the direction of the longitudinal center axis of the inner wall.

[0024] The heat transfer fin formation can simultaneously be used to support the inner wall in the outer warning device if the heat transfer fins abut radially on the outside against an inner side of the outer wall. Preferably, at least some of the heat transfer fins have axially limited support areas radially outward in the direction of the longitudinal center axis of the inner wall for support with respect to the outer wall, thus preventing excessive heat transfer to the outer wall.

[0025] The outer wall and / or the inner wall can be tubular.

[0026] The present invention further relates to an exhaust system for an internal combustion engine, comprising a reactant delivery arrangement, an SCR catalyst arrangement downstream of the reactant delivery arrangement and a mixing arrangement constructed according to the invention between the reactant delivery arrangement and the SCR catalyst arrangement.

[0027] The present invention is described in detail below with reference to the accompanying figures. They show: Fig. 1 shows a schematic representation of part of an exhaust system with a mixing section of a mixing arrangement not constructed according to the principles of the present invention; Fig. 2 is a schematic representation of an alternatively constructed mixing section of a mixing arrangement not constructed according to the principles of the present invention; Fig. 3 an inner wall of a mixing section with a heating element of a heating device provided on an inner side thereof; Fig. 4 an inner wall of a mixing section with a heating element of a heating device provided thereon; Fig. 5 an inner wall of a mixing section with a heating element of a heating device provided thereon; Fig. 6 shows an inner wall of a mixing section of a mixing arrangement not constructed according to the principles of the present invention, with a heating element of a heating device provided thereon; Fig. 7 shows an inner wall of a mixing section of a mixing arrangement not constructed according to the principles of the present invention, with a heating element of a heating device provided thereon; Fig. 8 a mixing section with a heat transfer fin formation provided on an inner wall; Fig. 9 two different designs of heat transfer fin formations provided on an inner wall; Fig. 10 is a perspective view of an inner wall of a mixing section with groups of heat transfer fins of a heat transfer fin formation provided on an outer side thereof.

[0028] The Fig. 1 shows a schematic representation of part of an exhaust system, generally designated 10, of an internal combustion engine, for example in a vehicle. The exhaust system 10 comprises a reactant delivery arrangement 12, through which a reactant, for example a urea / water solution, is added to the exhaust gas A flowing further upstream. Downstream of the reactant delivery arrangement 12, which is also generally referred to as an injector, a mixing arrangement 14 is provided, in which the reactant R is mixed with the exhaust gas A. In this process, the water contained in the reactant R is to be evaporated, and the urea is to be thermally decomposed, so that ammonia and generally also isocyanic acid are produced, which can be catalytically reacted with the evaporated water in a thermolysis reaction to form further ammonia.The ammonia generated from the reactant is catalytically converted in an SCR catalyst arrangement 16 positioned further downstream in order to reduce the proportion of harmful nitrogen oxides in the exhaust gas stream.

[0029] The Fig. Figure 1 illustrates that the reactant delivery arrangement 12 can be positioned in various ways. It can be arranged, as shown by a solid line, such that the reactant R is injected as a spray cone substantially in a longitudinal direction of the mixing arrangement 14 or a mixing section 18 thereof. Alternatively, an oblique injection can be performed, as illustrated, for example, by the dashed arrangements 12' and 12".

[0030] The mixing section 18, located in the flow direction between the reactant delivery arrangement 12 and the SCR catalyst arrangement 16, has a mixing section inlet region 20 following the reactant delivery arrangement 12 and a mixing section outlet region 22 substantially preceding the SCR catalyst arrangement in the flow direction. Between the mixing section inlet region 20 and the mixing section outlet region 22, the mixing arrangement 14 constructed according to the invention, or the mixing section 18 thereof, has a double-walled construction. In this region, the mixing section 18 comprises an outer wall 24, designed, for example, as a tube or tubular, and an inner wall 26, likewise designed as a tube or tubular. The outer wall 24 and the inner wall 26 can, for example, be substantially cylindrical and, for example, have a substantially circular cross-section.

[0031] The inner wall 26 surrounds an inner volume 28. Between the inner wall 26 and the outer wall 24, an outer volume 30 is formed which surrounds the inner volume 28 in a ring-like manner. Fig. 1, the mixing section 18 is constructed such that both the inner volume 28 and the outer volume 30 can be flowed through by exhaust gas A or reactant R. However, it is preferably provided that the reactant dispensing arrangement 12 is positioned such that it dispenses the reactant R in such a way that it essentially wets an inner side 32 of the inner wall 26, i.e. essentially impinges on the inner side 32 of the inner wall 26 when dispensed in the form of a spray cone.

[0032] The mixing arrangement 14 further comprises an electrically excitable heating device 34. In the Fig. 1, the electrically excitable heating device 34 comprises a heating element 38, for example in the form of a heating conductor, positioned on an outer side 36 of the inner wall 26 and surrounding the inner wall 26 in a helical manner with a substantially constant winding pitch. In particular, the heating element 38 can be designed as a sheathed heating conductor having a metallic outer sheath, which can be attached to the inner wall 26, for example by soldering, and an insulated heating wire arranged therein. When electrically excited, the heating element 38 heats the inner wall 26 so that the reactant R impinging on the inner wall 26 can absorb heat. Since a portion of the exhaust gas A entering the mixing section 18 at the mixing section inlet region 30 flows along the outer side 36 of the inner wall 26, i.e., through the outer volume 30, this portion of the exhaust gas A can also transfer heat to the inner wall 26.

[0033] By assigning the heating device 34 to the inner wall 26, it is ensured that essentially all of the thermal energy provided by the heating device 34 is introduced into the inner wall 26 and via this into the exhaust gas A or the reactant R. Heat loss via the outer wall 24 can be largely avoided. Furthermore, the flow around the inner wall 26 on both sides significantly increases the surface area available for absorbing heat from the exhaust gas A, so that, particularly in an operating phase in which the exhaust gas A already transports sufficient heat and excitation of the heating device 34 is therefore not necessary, sufficient transfer of thermal energy to the reactant R wetting the inner wall 26 is also ensured.For this purpose, it can be provided, for example, that the proportion of exhaust gas A flowing through the outer volume 30 is in the range of 20% to 30% of the total flow, so that the predominant part of the exhaust gas A, i.e., approximately 70% to 80%, flows through the inner volume 28. Since the inner wall is arranged essentially parallel to the outer wall 24, a significant impairment of the exhaust gas flow is avoided.

[0034] In the mixing section inlet region 20, a swirl generator, as previously explained with reference to the prior art, could be provided, which ensures that the proportion of the exhaust gas flowing through the outer volume 30 varies, in particular increases, depending on the flow velocity and thus also depending on the load state of an internal combustion engine emitting the exhaust gas A.

[0035] An alternative design is in Fig. 2. In this embodiment too, the inner wall 26 is surrounded in a spiral manner on its outer side 36 by the heating element 38 of the heating device 34. However, the outer volume 30 formed between the inner wall 26 and the outer wall 24 is designed such that exhaust gas cannot flow through it. Thus, the outer volume 30 essentially forms an insulating gap which is intended to prevent heat losses to the outside as far as possible. In this embodiment too, the heating device 34 can be used to ensure sufficient evaporation or decomposition of the reactant R by active heating, i.e. the introduction of thermal energy via the heating device 34, particularly in operating states in which the exhaust gas-carrying components, such as the inner wall 26 or the outer wall, are comparatively cold or in which high dosing rates of the reactant R are used.

[0036] With reference to the Fig. 3 to 7, various configurations of the heating device 34 are described below.

[0037] The Fig. 3 shows an embodiment in which the heating element 38 of the heating device 34, again provided as a helical heating conductor, is provided on the inner side 32 of the inner wall 26 and is fixed thereto, for example, in a materially bonded manner, such as by soldering. Thus, the heating element 38 is also significantly more exposed to the flow of exhaust gas A or reactant R, which can lead to increased heat transfer. Arranging the helically wound heating element 38 on the inner side 32 of the inner wall 26 has the further advantage that the reactant R, which primarily impinges on the inner side 32, is conveyed along a correspondingly helical path predetermined by the individual turns of the heating element 38 during its movement along the inner side 32 of the inner wall 26, brought about by the exhaust gas flow, so that the interaction distance with the inner side 32 of the inner wall 26 is significantly increased.

[0038] It can be seen in Fig. 3 also shows that the pitch of the windings of the heating element 38 can vary. While in the left part of the inner wall 26 the pitch is constant over a length range, it increases towards the right, so that the distance between the individual windings increases accordingly. In this way, it is possible, where, for example, due to the impact of a comparatively large amount of reactant R, a stronger heat input is advantageous, this is also ensured by a greater winding density. In the part lying further downstream in a main flow direction H, which can essentially correspond to an extension direction of a longitudinal center axis L of the inner wall 26, only a reduced heat input into the inner wall 26 occurs due to the lower winding density or the greater pitch.In this way, it is possible to adjust the heat input in such a way that in those areas where a greater heat input is advantageous, a greater heat input actually occurs due to a correspondingly smaller pitch and thus higher winding density.

[0039] It should be noted that this can of course also be realized if the heating element 38, as in the Fig. 1 and Fig. 2, is arranged on the outer side 36 of the inner wall 26, regardless of whether the outer volume 30 can be flowed through by exhaust gas or reactant or not.

[0040] An alternative design is in Fig. 4. This shows a heating element 38, again designed, for example, as a jacket heating element, which is formed on the inner wall 26 with a meandering structure that runs back and forth essentially in a circumferential direction. In this embodiment, the heating element 38 can be arranged on the inner side 32, but preferably on the outer side 36 of the inner wall.

[0041] A corresponding configuration is in Fig. 5. Here, the heating element 38 arranged with a meandering structure is positioned such that it is designed to run back and forth in a meandering manner essentially in the direction of the longitudinal center axis L of the inner wall 26.

[0042] Even in the Fig. 4 and Fig. 5, it is possible in a simple manner to vary the input of heat energy into the inner wall 26 accordingly by the mutual spacing of the meander sections 39 of the respective heating element 38 or a varying spacing, i.e. to provide a greater density of meander sections 39 in areas where a large heat input is advantageous than in other areas.

[0043] A further alternative embodiment of a heating device 34 is shown in Fig. 6. In this embodiment of the heating device 34, the inner wall 26 itself forms a heating element 38 of the heating device 34. The inner wall 26 is generally constructed from electrically conductive material, for example sheet metal. Contacting regions 44, 46, in which the inner wall 26 is electrically contacted, are formed at the two longitudinal end regions 40, 42 of the inner wall 26. In order to ensure uniform current conduction or heating over the circumference of the inner wall 26, the contacting regions 44, 46 can be provided, for example, by material thickenings, so that preferential current conduction in these contacting regions 44, 46 occurs in the circumferential direction and then between the contacting regions 44, 46. The thickening can be provided, for example, by applying additional material to the contacting regions 44, 46.

[0044] At the Fig. 7, the essentially tubular inner wall 26 is interrupted in a circumferential region 48 and has, in this region, opposite longitudinal edge regions 50, 52. At these longitudinal edge regions 50, 52, which extend, for example, essentially in the direction of the longitudinal center axis L of the inner wall 26, the contacting regions 44, 46 are provided, for example, by a material thickening, so that a substantially uniform current conduction over the entire length of the inner wall 26 and thus a correspondingly substantially uniform heating can be ensured. Fig. The embodiment of the inner wall 26 providing a heating element 38 shown in Figure 7 can be used in a particularly advantageous manner in conjunction with the Fig. 1 with the reference numeral 12". The reactant dispensing arrangement 12" and the inner wall 26 can be positioned relative to one another such that the reactant R can be injected from the reactant dispensing arrangement 12" in the peripheral region 48 through the gap formed there into the inner volume 28.

[0045] The design of the heating device 40 with a substantially planar heating element, provided, for example, by the inner wall 26, is therefore particularly advantageous because in those surface regions in which greater cooling occurs due to increased interaction with the reactant R impinging thereon, the electrical resistance will also decrease accordingly, and thus preferential current conduction will occur in these regions, with the result that correspondingly greater heating will occur in these regions subject to greater thermal stress. A corresponding effect can also be achieved, for example, by applying a planar heating element to the surface of the inner wall 26, which itself does not fundamentally function as a heating element, preferably with an electrically insulating layer interposed therebetween.Such a surface coating with electrically conductive material, for example PTC material, which thus provides a heating element, can cover, for example, at least 50%, preferably at least 80% of the surface of the inner wall 26 on the inside thereof and / or also on the outside thereof.

[0046] With reference to the Fig. 8 to 10, configurations of the mixing arrangement 14 are explained below, in which an increased heat transfer to the inner wall 26 or an increased thermal interaction of the inner wall 26 with the reactant R occurs by enlarging the surface area of ​​the inner wall 26. It should be noted that the aspects explained below can be realized in combination with the aspects described above and relating to the provision of an electrically excitable heating device.

[0047] The Fig. The mixing arrangement 14 shown in Figure 8 is constructed with the inner wall 26 and the outer wall 24 surrounding it. On the outer side 36 of the inner wall 26, a heat transfer fin formation 54 is provided with a plurality of heat transfer fins 56 that project essentially radially outward from the inner wall 26 on the outer side 36 and run in the direction of the longitudinal center axis L of the inner wall 26. The heat transfer fins 56 thus extend essentially into the outer volume 30 through which exhaust gas can flow. The exhaust gas A flowing in the outer volume 30 transfers heat to the heat transfer fins 56 around which it flows. The heat transported in the exhaust gas A flowing in the outer volume 30 can thus also be used to support improved evaporation or thermal decomposition of the reactant R that essentially impinges on the inner side 32 of the inner wall 26.Since the heat transfer fins 56 with the heat transfer surfaces 58 formed on both sides thereof extend substantially in the direction of the longitudinal center axis L of the inner wall 26, they substantially do not impair the exhaust gas flow.

[0048] The Fig. 9 illustrates in its upper and lower parts two different configurations of the heat transfer fin formation 54. In the upper part of the Fig. 9 are also in Fig. 8, with the heat transfer surfaces 58 formed on both sides thereof. These extend essentially radially outward from the outer side 36 of the inner wall 26 and can, for example, be dimensioned such that they essentially do not touch the outer wall 24 in order to largely avoid heat transfer to the outer wall 24.

[0049] In the Fig. In the configuration shown below in Figure 9, the heat transfer fin formation 54 is designed such that it surrounds the inner wall 26 with its heat transfer fins 58 in a substantially wave-like manner. For example, the heat transfer fin formation 54 can be provided by a heat transfer sheet bent into such a wave or meander structure, which is secured to the outer side 36 of the inner wall 26, for example by soldering. Thus, channels 60 are formed in the wave-like structure, through which exhaust gas A can flow equally, so that the heat transfer fin formation 54 provided with the wave-like structure provides respective heat transfer surfaces 58 on both its inner and outer sides.

[0050] You can see in the lower part of the Fig. 9 further shows that on the or at least some of the heat transfer fins 56 provided with a wave-like structure, in respective apex regions 62 in which adjacent heat transfer fins 56 merge into one another, support regions 64 are provided, formed for example by knob-like formations, with which the heat transfer fin formation 54 and, via this, the inner wall 26 can be supported on the outer wall 24. For example, a material-locking connection, for example by soldering, can be made in these regions. The support regions 64 are limited not only in the circumferential direction but also in the axial direction, i.e., they are significantly shorter than the heat transfer fins 54, so that heat transfer contact between the heat transfer fin formation 54 and the outer wall 24 is minimized.

[0051] The Fig. Figure 10 shows an embodiment in which several groups 66, 68, 70 of circumferentially successive heat transfer fins 56 are provided in the direction of the longitudinal center axis L of the inner wall 26. In the individual groups 66, 68, 70, the heat transfer fins 56 provided therein preferably have a uniform circumferential spacing from immediately adjacent heat transfer fins 56, wherein, unlike in Fig. 10, the heat transfer fins 56 are naturally distributed over the entire circumference of each group 66, 68, 70. The heat transfer fins 56 of immediately adjacent groups 66, 68, 70 are offset from one another in the circumferential direction. The heat transfer fins 56 of immediately adjacent groups 66, 68, 70 can also each have different circumferential spacings from one another.

[0052] By providing such groups 66, 68, 70 of heat transfer fins 56, it is achieved that in the transition region of each group to an immediately adjacent group, a previously existing interface flow along a respective heat transfer surface 58 is dissolved and a new interface flow is formed in the next group, so that a more efficient heat transfer can be achieved. For example, the successive groups 66, 68, 70 in the direction of the longitudinal center axis L can be arranged such that their respective heat transfer fins 56 do not overlap in the direction of the longitudinal center axis L, as in Fig. 10. Alternatively, the groups 66, 68, 70 could also mesh with each other in the direction of the longitudinal center axis L, i.e., be interlocked with each other, whereby a greater density of the heat transfer fins 56 provided on the outer side 36 of the inner wall 26 can be achieved. Furthermore, in the embodiment according to Fig. 10, the heat transfer fins 56 have the illustrated plate-like configuration or may have a wave-like structure, such as that shown in the lower part of the Fig. 9 is shown.

Claims

[1] Mixing arrangement for an exhaust system of an internal combustion engine, comprising a mixing section (18) with a mixing section inlet region (20) to be positioned downstream with respect to a reactant delivery arrangement (12) and a mixing section outlet region (22) to be positioned upstream with respect to a catalyst arrangement (16), wherein the mixing section (18) comprises an inner wall (26) surrounding an inner volume (28) through which exhaust gas (A) and / or reactant (R) can flow, and an outer wall (24) surrounding the inner wall (26), wherein an outer volume (30) surrounding the inner volume (28) in a ring-like manner is formed between the inner wall (26) and the outer wall (24), wherein an electrically excitable heating device (34) is provided on the inner wall (26), wherein the electrically excitable heating device (34) comprises at least one heating element (38) that can be heated by electrical excitation, characterized bythat at least one heating element (38) is provided on an inner side (32) of the inner wall (26). [2] Mixing arrangement according to claim 1, characterized by that at least one heating element (38) comprises a heating conductor which surrounds a longitudinal center axis (L) of the inner wall (26) in a winding manner. [3] Mixing arrangement according to claim 2, characterized by that a pitch of the windings of the heating conductor in the direction of the longitudinal center axis (L) of the inner wall (26) is at least partially substantially constant. [4] Mixing arrangement according to claim 2 or 3, characterized by that a pitch of the turns of the heating conductor varies in the direction of the longitudinal center axis (L), preferably wherein in at least one length region of the inner wall (26) the pitch of the turns of the heating conductor preferably increases substantially continuously in a main flow direction (H). [5] Mixing arrangement according to one of the preceding claims, characterized bythat at least one heating element (38) comprises a meandering heating conductor. [6] Mixing arrangement according to one of the preceding claims, characterized by that at least one heating element comprises a surface heating element covering at least 50%, preferably at least 80%, of an outer side (36) of the inner wall (26), and / or that at least one heating element comprises a surface heating element covering at least 50%, preferably at least 80%, of the inner side (32) of the inner wall (26). [7] Mixing arrangement according to one of the preceding claims, characterized by that at least one heating element (38) is a PTC heating element. [8] Mixing arrangement according to one of the preceding claims, characterized by that the outer volume (30) is closed off against flow of exhaust gas (A) and / or reactant (R). [9] Mixing arrangement according to one of claims 1-7, characterized bythat the external volume (30) can be flowed through by exhaust gas (A) and / or reactant (R). [10] Mixing arrangement according to one of the preceding claims, characterized by that a heat transfer rib formation (54) is provided on the inner wall (26). [11] Mixing arrangement according to claim 9 and claim 10, characterized by that the heat transfer fin formation (54) comprises a plurality of heat transfer fins (56) arranged successively in the circumferential direction on the outer side (36) of the inner wall (26). [12] Mixing arrangement according to claim 11, characterized by that the heat transfer ribs (56) are plate-like and / or are arranged to extend radially outwards substantially from the outer side (36) of the inner wall (26) with respect to the longitudinal center axis (L) of the inner wall (26). [13] Mixing arrangement according to claim 11, characterized bythat the heat transfer fins (56) are arranged in a wave-like manner surrounding the inner wall (26) on its outer side (36). [14] Mixing arrangement according to one of claims 11-13, characterized by that a plurality of groups (66, 68, 70) of heat transfer fins (56) are provided, which are arranged one after the other in the direction of the longitudinal center axis (L) of the inner wall (26), wherein the heat transfer fins (56) of immediately successive groups (66, 68, 70) are offset from one another in the circumferential direction and / or in immediately successive groups (66, 68, 70) the heat transfer fins (56) have a different circumferential distance from one another. [15] Mixing arrangement according to one of claims 11-14, characterized by that the heat transfer ribs (56) have heat transfer surfaces (58) extending substantially in the direction of the longitudinal center axis (L) of the inner wall (26). [16] Mixing arrangement according to one of claims 11-15, characterized by that the heat transfer ribs (56) rest radially outwardly against an inner side of the outer wall (24), preferably wherein at least some of the heat transfer ribs (56) have axially limited support regions (64) radially outwardly in the direction of the longitudinal center axis (L) of the inner wall for support with respect to the outer wall (24). [17] Mixing arrangement according to one of the preceding claims, characterized by that the outer wall (24) and / or the inner wall (26) is tubular. [18] Exhaust system for an internal combustion engine, comprising a reactant delivery arrangement (12), downstream of the reactant delivery arrangement (12) an SCR catalyst arrangement (16) and between the reactant delivery arrangement (12) and the SCR catalyst arrangement (16) a mixing arrangement (14) according to one of the preceding claims.

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