MIXER ASSEMBLY FOR MIXING AN ADDITIVE WITH AN EXHAUST GAS FLOW

Abstract

A mixer arrangement for mixing an additive with an exhaust-gas flow, having an exhaust-gas line, an exhaust gas flowing through the exhaust-gas line in a main flow direction, and having at least one exhaust-gas purification element which is arranged in the exhaust-gas line and which has a casing and, arranged within the casing, a flow-over surface for the exhaust gas. Here, the casing of the at least one exhaust-gas purification element has a guide structure.

Description

FIELD OF THE INVENTION

The invention relates to a mixer arrangement for mixing an additive with an exhaust-gas flow, having an exhaust-gas line, an exhaust gas flowing through the exhaust-gas line in a main flow direction, and having at least one exhaust-gas purification element which is arranged in the exhaust-gas line and which has a casing and, arranged within the casing, a flow-over surface for the exhaust gas.

BACKGROUND OF THE INVENTION

In internal combustion engines, in particular diesel engines or lean-burn engines, undesirably high quantities of nitrogen oxides are formed. A suitable approach for the elimination of these is in particular the addition of the additive ammonia, whereby, in the presence of an excess of oxygen, the nitrogen oxides can be reduced to form nitrogen, and the hydrogen fraction of the ammonia bonds to form water.

It is known for additive to be introduced into the exhaust-gas line. With the exhaust-gas flow, the additive is transported to a selective reduction catalytic converter (SCR catalytic converter). With the injection of the additive counter to the main flow direction of the exhaust-gas flow, it is sought to achieve uniform mixing of the additive with the exhaust gas. From DE 10 2011 117 139 A1, it is known to provide a depression in the exhaust-gas line. By means of the depression, it is sought to realize swirling of the exhaust gas in the exhaust-gas line in order to further improve the mixing with the additive. It has however been found that even such depressions, despite the swirling that is generated, generate an uneven droplet load of the additive in relation to the cross-sectional area of the exhaust-gas line. To achieve high nitrogen oxide reduction rates, a highly uniform concentration distribution of the additive and a uniform temperature distribution, in particular with regard to the relatively cold edge region, are necessary over the cross section of the exhaust-gas line upstream of the SCR catalytic converter. A further disadvantage consists in that such depressions are associated with an enlargement of the cross section of the exhaust-gas line, whereby the exhaust-gas line requires a larger structural space.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of providing an apparatus with which high nitrogen oxide reduction rates are achieved.

The object is achieved according to the invention in that the casing of the at least one exhaust-gas purification element has a guide structure.

The guide structure is in this case not a functional element of the exhaust-gas purification element, in particular of the flow-over surface arranged within the casing. The guide structure is arranged as an additional functional unit on the at least one exhaust-gas purification element. With the arrangement of the guide structure on the casing, it is possible for influencing of the exhaust-gas flow and thus swirling of the exhaust-gas flow to be achieved in a particularly simple and effective manner. The swirling is significantly conducive to achieving that the additive supplied in droplet form to the exhaust-gas flow is distributed more uniformly over the entire cross section of the exhaust-gas line, and thus the exhaust-gas aftertreatment takes place in a manner distributed more uniformly over the entire cross section. Likewise, as a result of the mixing, the temperature in the end region is increased, whereby a more uniform temperature distribution is realized. Owing to the improved utilization of the cross section, the aftertreatment rate of the exhaust gas increases, or the length of the exhaust-gas treatment path is shortened while achieving the same aftertreatment rate. The arrangement on the casing furthermore has the advantage that, in this way, an inexpensive fastening of the guide structure to an exhaust-gas purification element is realized. An additional carrier structure for the fastening of the guide structure is therefore not necessary. Furthermore, by means of the design of the guide structure, an adaptation of the swirling to the respective exhaust-gas line is achieved.

The adaptation of the swirling of the exhaust-gas flow by means of the design of the guide structure is achieved in a particularly simple manner by virtue of the guide structure having multiple guide elements.

In a further advantageous embodiment, the guide structure is generated in a particularly simple manner by virtue of the guide structure being formed in one piece with the casing. In particular in the case of a casing produced from sheet metal, the guide structure is generated by means of corresponding cutting-out of the sheet-metal casing in the same working step. The fastening of the guide structure to the casing is thereby eliminated.

In a further advantageous embodiment, the guide structure is connected to the casing. This refinement has the advantage that the handling of the casing and guide structure during the production and assembly processes is easier. The fastening of the guide structure to the casing may advantageously be realized by means of welding or stapling, for example by induction welding. It is likewise conceivable for the guide structure to be fastened to the casing by means of rivets or screw connections. A further advantage consists in that, by means of the solution according to the invention, existing exhaust-gas purification elements are enhanced to include the guide structure.

A fastening of the guide structure to the casing of the exhaust-gas purification element without additional fastening means is achieved if the guide structure is pressed together with the casing. Here, the guide structure may either be pressed into the casing or pressed onto the casing. The pressing of the guide structure into the casing has the advantage that the guide structure does not increase the outer diameter of the exhaust-gas purification apparatus, such that no additional structural space is required with regard to the outer diameter.

In a particularly simple embodiment, the guide structure is a cylindrical component, the casing surface of which has at least one radially inward indentation. It is preferable for 2 to 10, particularly preferably 3 to 8, indentations to be provided. Since the indentations are intended to generate swirling, the demands on the dimensional accuracy of the indentations are low, whereby the guide structure according to the invention is manufactured at relatively low cost.

A particularly good adaptation of the swirling of the exhaust-gas flow to the respective exhaust-gas line is achieved, in a further advantageous embodiment, in that the guide structure has at least two guide elements, preferably 3 to 20 guide elements, in particular 4 to 10 guide elements.

The swirling in the exhaust-gas flow is improved if the guide elements are at least partially bent radially inward in the direction of the axis of symmetry of the exhaust-gas line. Here, “at least partially bent” is to be understood to mean that the entire guide element or only a part of the guide element is bent inward. Here, in the context of the invention, a bend refers both to a discontinuous profile of the guide element, such as arises in the case of a kink, and a continuous profile of the guide element, if the bend is described with a radius.

Improved swirling may also be achieved by virtue of the guide element being multiply bent. Here, it is conceivable that, in the flow direction, the guide element may be initially bent initially inward and subsequently also bent outward again in the direction of the wall of the exhaust-gas line.

Further setting of the swirling of the exhaust-gas flow is easily achieved by virtue of the individual guide elements having different sizes and/or bends. In this way, swirling patterns in the exhaust-gas flow that repeat in relation to the circumferential direction is minimized. These would otherwise result in swirling being generated over a particular sector, but swirling over the entire circumference of the exhaust-gas flow being impeded.

In order that the guide elements project as far as possible into the exhaust-gas flow, they must have a certain length. If the guide elements are oriented parallel to the casing axis in the case of an unwound casing, the required length of the metal sheet for the production thereof is defined by the axial length of the casing and the length of the guide elements. In a further advantageous embodiment, the length of the metal casing sheet required for production purposes are considerably reduced if the guide elements are oriented at an angle with respect to the casing. By means of this orientation, the guide elements have a considerably smaller axial extent. In this way, the production costs are reduced.

In a simple embodiment, all of the guide elements are formed with the same shape. This has the advantage that a punching tool for the production of the guide elements may be designed to be inexpensive.

Improved swirling of the gas flow is achieved with asymmetrically designed guide elements. Asymmetrical means that the guide elements have for example an area which deviates from a rectangular shape.

In another embodiment, it is likewise possible for in each case two adjacent guide elements to have different areas through variation of the respective lengths and widths.

By means of these different shapes of the guide elements, it is sought to prevent partially identical swirling patterns from arising, which collectively permit little swirling over the entire cross section of the exhaust-gas flow.

In a further advantageous embodiment, to further intensify the swirling, the guide elements have substructures. Such substructures may be embossments, perforations or incisions in the end regions, wherein, in the case of the incisions in the end regions, the individual regions may be additionally bent.

Different arrangements of the guide structure may be advantageous depending on the field of use, that is to say specifically the geometrical form of the exhaust-gas line, the exhaust-gas flow with regard to throughflow rate and temperature, the exhaust-gas purification elements used and the arrangement thereof.

The flow-over surfaces used in exhaust-gas purification elements generally give rise to a certain laminarization of the exhaust-gas flow within the exhaust-gas purification element and when the exhaust gas exits the exhaust-gas purification element. The laminar flows not only have the disadvantage that they give rise to and maintain non-uniformities that arise during the injection of the additive. They also have the effect that they maintain the temperature gradients that arise in the exhaust-gas flow. Such temperature gradients arise as a result of exhaust-gas purification elements having a relatively low temperature radially at the outside. The exhaust-gas aftertreatment is therefore less intensive in the regions. In one advantageous embodiment, the formation of such temperature gradients in the adjoining section of the exhaust-gas line is avoided by virtue of the guide structure according to the invention being arranged on the downstream-facing side of the casing of the exhaust-gas purification element. The swirling thus generated of the emerging flow counteracts the formation of such temperature gradients in the adjoining section of the exhaust-gas line. The exhaust gas mixes over the entire cross section of the exhaust-gas line, and the exhaust-gas aftertreatment is thus improved.

This embodiment is furthermore also advantageous if the exhaust-gas aftertreatment is performed using multiple exhaust-gas purification elements and the guide structure is arranged on at least one of those exhaust-gas purification elements which is positioned upstream of the final exhaust-gas purification element as viewed in the flow direction.

In another advantageous embodiment, the guide structure is arranged on the casing on the upstream-facing side of the exhaust-gas purification element. This is advantageous in particular if the exhaust-gas flow fed to the exhaust-gas purification element is laminar and thus has temperature gradients in relation to the cross section of the exhaust-gas line. For these situations, the laminar flow is changed into a turbulent flow by means of the guide structure arranged upstream. In this way, the exhaust-gas purification element is impinged on by a flow without temperature gradients, which results in an improved temperature distribution in the exhaust-gas purification element and thus improved exhaust-gas aftertreatment. This is advantageous in particular in the case of catalytic converters in which the temperature distribution has a particularly great influence on the effectiveness, such as for example catalytic converters for methane oxidation. Likewise, with the change from a laminar to a turbulent flow, the droplet distribution of a supplied additive in relation to the cross section is more uniform.

The arrangement according to the invention of a guide structure is furthermore not restricted to particular structural forms of exhaust-gas purification elements. Aside from exhaust-gas purification elements with cylindrical honeycomb bodies, the guide structure may also be provided in the case of so-called ring-shaped catalytic converters. Ring-shaped catalytic converters are exhaust-gas purification elements which have a cylindrical recess in their center, in the manner of a hollow cylinder, and the honeycomb body extends around the cylindrical recess. The exhaust-gas purification element requires no additional structural space in an axial direction if the guide structure does not extend beyond the axial extent of the honeycomb body. Furthermore, the guide structure with the above-described embodiments are applied to hollow cylindrical honeycomb bodies.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be discussed in more detail on the basis of multiple exemplary embodiments. In the figures:

FIG. 1 is a schematic illustration of a mixer arrangement;

FIG. 2-4 show further arrangements of a mixer arrangement as per FIG. 1,

FIG. 5 shows an exhaust-gas purification element with a flow-over surface,

FIG. 6 shows the casing of an exhaust-gas purification element,

FIG. 7-9 show guide elements of the guide structure,

FIG. 10 shows a further embodiment of a mixer arrangement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

FIG. 1 shows a mixer arrangement having an exhaust-gas line 1 in a motor vehicle (not illustrated in any more detail). The arrow indicates the main flow direction of the exhaust gas flowing through the exhaust-gas line 1. By means of an injector 2 arranged on the exhaust-gas line 1, urea solution is injected into the exhaust-gas flow at an angle with respect to the main flow direction, such that the jet 3 strikes an exhaust-gas purification element 4 approximately centrally. The exhaust-gas purification element is an SCR catalytic converter 4. The SCR catalytic converter 4 is composed of a schematically illustrated honeycomb body 5, which forms a flow-over surface for the exhaust gas, and a casing 6, which fully encloses the honeycomb body 5. On the downstream-facing side 7 of the casing 6, a guide structure 8 is fastened to the casing 6. The construction of the guide structure 8 is described in the following figures. During the operation of the mixer arrangement, the injected urea solution is sprayed onto the honeycomb body 5 and is transported through the honeycomb body 5 by the exhaust gas. Owing to the structure of the flow-over surface, the exhaust gas and the droplets of urea solution still contained therein emerge from the honeycomb body 5 on the side 7 substantially as a laminar flow. The guide structure 8 disrupts the laminar flow, such that, downstream of the guide structure 8 in the flow direction, the laminar flow is caused to swirl and thus changes into a turbulent flow. As a result of this swirling, more exhaust gas comes into contact with the droplets of the urea solution, whereby the efficiency of the exhaust-gas after treatment is increased.

The mixer arrangement in FIG. 2 is composed of the exhaust-gas line 1 and two SCR catalytic converters 4, 4′ as exhaust-gas purification elements. Both SCR catalytic converters 4, 4′ have in each case one honeycomb body 5 and one casing 6 surrounding the honeycomb body. The SCR catalytic converter 4 arranged upstream of the final SCR catalytic converter 4′ as viewed in the flow direction has a guide structure 8 on its downstream-facing side 7. By means of the guide structure 8, the flow emerging from the SCR catalytic converter 4 is caused to swirl, such that a thoroughly mixed exhaust-gas flow enters the downstream SCR catalytic converter 4′. As a result of this swirling, hot exhaust gas from the center of the SCR catalytic converter 4 is mixed with the less hot exhaust gas from the regions in the vicinity of the casing 6, such that exhaust gas entering the SCR catalytic converter 4′ exhibits greater temperature homogeneity in relation to the cross section, which increases the efficiency of the second SCR catalytic converter 4′.

The mixer arrangement as per FIG. 3 may be regarded as a combination of the mixing arrangements from FIGS. 1 and 2. The guide structure 8 causes swirling of the exhaust-gas flow emerging from the SCR catalytic converter 4, whereby the exhaust-gas flow entering the SCR catalytic converter 4′ exhibits a more uniform distribution both with regard to the temperature distribution but also with regard to the droplet distribution of the injected urea solution. In particular in the case of the distribution of the urea solution, the guide structure 8 assists the jet 3 in order to distribute the urea solution more uniformly over the entire cross section.

The mixer arrangement shown in FIG. 4 differs with regard to the exhaust-gas purification element 4. The latter has a guide structure 8 on the upstream-facing side 9 of the casing 6. Thus, the impinging exhaust-gas flow is influenced with a swirling action by the exhaust-gas purification element 4 to which the exhaust-gas flow is supplied.

FIG. 5 shows a plan view of an exhaust-gas purification element 4, in particular an SCR catalytic converter. The exhaust-gas purification element is composed of a casing 6 in which a honeycomb body 5 is arranged. The honeycomb body 5 is composed of a multiplicity of interconnected foil layers, which form the flow-over surface for the exhaust gas. The casing 6 has a greater length than the honeycomb body 5. The guide structure 8 is fastened to the inner side of the free casing surface by means of induction welding. The guide structure 8 is composed of an encircling ring 10 which bears against the inner side of the casing 6. Guide elements 11 extend in an axial direction from the ring 10. The guide elements 11 all have the same area and shape and are bent radially inward by virtue of the guide elements 11 being kinked in discontinuous fashion along an edge, such that they project at an angle of between 0° and 90° into the exhaust-gas flow.

In FIG. 6, the guide structure 8 with the guide elements 11 is formed in one piece with the casing 6 of the SCR catalytic converter 4. The casing tube 6 is illustrated in unwound form. For the production of the casing 6, the casing tube is rolled up, such that the two outer edges 13, 14 abut against one another. The casing 6 may subsequently be welded. Along the edges 12, the guide elements 11 are bent at the desired angle. To intensify the mixing and to avoid partial swirling patterns, adjacent guide elements 11 have different shapes. This is achieved through variation of the lengths and widths of the guide elements 11 but also by means of bends at different angles.

The following figures show different guide elements 11. The guide element in FIG. 7 has a multiplicity of apertures 15, such that, as a result of the passage from one side of the guide element 11 to the other side, the exhaust gas intensifies the thorough mixing of the exhaust-gas flow. Thorough mixing is also realized even if, in this arrangement, depressions 15 are arranged in place of the apertures, which depressions project as protuberances on the opposite side of the guide element 11. These substructures effect additional swirling and thus improve the thorough mixing.

FIG. 8 shows a guide element 11 that has not yet been bent in a side view, which guide element has incisions on the circumference as a substructure, and individual regions 16 are bent in the manner of tongues out of the plane of the guide element 11.

The guide element 11 in FIG. 9 has a first region 17, in which the guide element 11 has been bent radially inward. In a second region 18, the guide element has been bent in the opposite direction thereto. By means of both regions 17, 18, the guide element 11 has a twist about its longitudinal axis 19.

FIG. 10 shows a further embodiment of a mixer arrangement, which is directed substantially to the embodiment of the honeycomb body 5 of the exhaust-gas purification element 4. The honeycomb body 5 is formed as a hollow cylinder with a cylindrical recess 20 situated in the center. The guide structure 8 is arranged in the cylindrical recess 20, preferably on the wall, which delimits the honeycomb body 5 in a radially inward direction, of the casing 6. In the illustration shown, the guide structure 8 is arranged at the downstream-facing end of the exhaust-gas purification element 4. It is however also conceivable for the exemplary embodiments described in the above figures to be applied to a honeycomb body 5 as per FIG. 10.

The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

Claims

1. A mixer arrangement for mixing an additive with an exhaust-gas flow, comprising: an exhaust-gas line;at least one exhaust-gas purification element which is arranged in the exhaust-gas line;a casing;a flow-over surface for the exhaust gas, the flow-over surface arranged within the casing;a guide structure connected to the casing of the at least one exhaust-gas purification element;wherein an exhaust gas flows through the exhaust-gas line in a main flow direction.

2. The mixer arrangement of claim 1, the guide structure further comprising multiple guide elements.

3. The mixer apparatus of claim 2, wherein the multiple guide elements are at least partially bent radially inward.

4. The mixer apparatus of claim 2, further comprising an unwound casing, wherein the multiple guide elements are, in the unwound casing, arranged at an angle with respect to the axial extent of the casing.

5. The mixer apparatus of claim 2, wherein each of the multiple guide elements further comprising the same shape.

6. The mixer apparatus of claim 2, wherein the multiple guide elements are of asymmetrical design.

7. The mixer apparatus of claim 2, wherein two adjacent multiple guide elements have different areas.

8. The mixer apparatus of claim 2, the multiple guide elements further comprising substructures.

9. The mixer apparatus of claim 8, the substructures in the guide elements further comprising embossments.

10. The mixer apparatus of claim 8, the substructures in the guide elements further comprising perforations.

11. The mixer apparatus of claim 8, the substructures further comprising incisions in the end regions of the respective guide element.

12. The mixer apparatus of claim 11, wherein, in the case of the incisions in the end regions, the individual regions may be additionally bent.

13. The mixer arrangement of claim 1, wherein the guide structure is formed in one piece with the casing.

14. The mixer arrangement of claim 1, wherein the guide structure is connected to the casing.

15. The mixer arrangement of claim 1, wherein the guide structure is connected to the casing using inductive welding.

16. The mixer apparatus of claim 1, wherein the guide structure is arranged on the downstream-facing side of the casing of the exhaust-gas purification element.

17. The mixer apparatus of claim 1, wherein the guide structure is arranged on the upstream-facing side of the casing of the exhaust-gas purification element.

18. The mixer apparatus of claim 1, the at least one exhaust-gas purification element further comprising multiple exhaust-gas purification elements, wherein the multiple exhaust-gas purification elements are arranged in the exhaust-gas line.

19. The mixer apparatus of claim 18, wherein the guide structure is arranged on at least one of the multiple exhaust-gas purification elements which is positioned upstream of another of the multiple exhaust-gas purification elements as viewed in the flow direction.

20. The mixer arrangement of claim 1, the honeycomb body further comprising a hollow cylinder with a radially internally situated cylindrical recess.