MIXING PATH FOR AN EXHAUST GAS SYSTEM OF AN INTERNAL COMBUSTION ENGINE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application claims priority of German patent application no. 10 2024 119 108.2, filed Jul. 5, 2024, the entire content of which is incorporated herein by reference.

JOINT RESEARCH AGREEMENT

[0002]This disclosure was created pursuant to a joint development agreement between Purem GmbH, a German corporation, and Volvo Truck Corporation, a Swedish corporation, that was in effect on or before the date the claimed invention was made, and the claimed invention was made as a result of activities undertaken within the scope of the joint development agreement.

TECHNICAL FIELD

[0003]The present disclosure relates to a mixing path for an exhaust gas system of an internal combustion engine.

BACKGROUND

[0004]In order to reduce the emission of nitrogen oxides in exhaust gas systems of diesel internal combustion engines, it is known to lower the nitrogen oxide content in the exhaust gas via selective catalytic reduction. For this purpose, a reactant generally including a liquid mixture of urea and water is injected into the exhaust gas in order thereby to generate ammonia upstream of an SCR catalytic converter when this mixture mixes with the exhaust gas, the ammonia contributing in the SCR catalytic converter to the catalytic conversion of the nitrogen oxides contained in the exhaust gas.

SUMMARY

[0005]It is an object of the present disclosure to provide a mixing path which is intended for an exhaust gas system of an internal combustion engine and which, with a structurally simple configuration, ensures efficient mixing of exhaust gas and reactant injected into it.

[0006]According to the disclosure, this object is achieved by a mixing path for an exhaust gas system of an internal combustion engine, including a mixing path housing, through which exhaust gas can flow in a main direction of flow of the exhaust gas, and a tubular mixing body, which is arranged in the mixing path housing and extends in the direction of a mixing body longitudinal axis, wherein the mixing body radially outwardly delimits a first flow volume, through which exhaust gas can flow, and radially inwardly delimits a second flow volume, through which exhaust gas can flow, wherein the mixing body includes a tubular first mixing body part, extending in the direction of the mixing body longitudinal axis, and, on an outer side of the first mixing body part, the outer side facing the second flow volume, or an inner side of the first mixing body part, the inner side facing the first flow volume, it includes at least one tubular second mixing body part, extending in the direction of the mixing body longitudinal axis, wherein the second mixing body part has a plurality of first shaped formations, which are arranged adjacent to each other in the direction of the mixing body longitudinal axis and in the circumferential direction about the mixing body longitudinal axis and are directed toward the first mixing body part, and wherein the second mixing body part abuts the first mixing body part in the region of at least some of the first shaped formations, preferably all of the first shaped formations.

[0007]The second mixing body part, which abuts the first mixing body part in principle via the first shaped formations and is at a distance from the first mixing body part in regions outside the first shaped formations, forms a heat exchanger, which absorbs heat when comparatively hot exhaust gas flows around it and transfers this heat to the first mixing body part. This structure uses the effect that, in the region of the second mixing body part, the multiplicity of first shaped formations creates turbulence, which prevents a laminar surface flow, which is less efficient for heat transfer, from occurring along the surface of the first mixing body part and thus ensures a considerably more efficient input of heat into the first mixing body part than would be the case if exhaust gas were to flow around a comparatively smooth surface.

[0008]In order to maintain a substantially regular shaped formation pattern, it is proposed that the first shaped formations are arranged in a plurality of rows of first shaped formations, the rows being arranged so as to follow one after another in the circumferential direction about the mixing body longitudinal axis and extending preferably substantially in the direction of the mixing body longitudinal axis, or/and that the first shaped formations are arranged in a plurality of rings of first shaped formations, the rings being arranged so as to follow one after another in the direction of the mixing body longitudinal axis and extending preferably substantially in the circumferential direction about the mixing body longitudinal axis.

[0009]In at least some of the rows, preferably all of the rows, of first shaped formations, the first shaped formations can be arranged at a substantially constant distance from each other, or/and, in the case of at least two, preferably all, of the rows of first shaped formations, the rows being directly adjacent to each other in the circumferential direction about the mixing body longitudinal axis, the first shaped formations can be offset from each other in the direction of the mixing body longitudinal axis.

[0010]Furthermore, providing a substantially regular shaped formation pattern and thus also a uniform input of heat over the entire length and the entire circumference of the first mixing body part can be aided in that, in at least some of the rings, preferably all of the rings, of first shaped formations, the first shaped formations are arranged at a substantially constant distance from each other, or/and in that, in the case of at least two, preferably all, of the rings of first shaped formations, the rings being directly adjacent to each other in the direction of the mixing body longitudinal axis, the first shaped formations are offset from each other in the circumferential direction about the mixing body longitudinal axis.

[0011]For particularly efficient heat transfer between the second mixing body part and the first mixing body part, it is proposed that at least some of the first shaped formations, preferably each first shaped formation, are/is configured in the form of a closed shaped formation, or/and that at least some of the first shaped formations, preferably each first shaped formation, are/is configured with a circumferential wall and a floor, which abuts the first mixing body part and is preferably substantially planar or curved so as to be substantially adapted to a curvature of the first mixing body part, or/and that at least some of the first shaped formations, preferably each first shaped formation, are/is in the form of a circle.

[0012]A heat-transfer-aiding, stable connection of the two mixing body parts can be achieved for example in that, in the region of at least some of the first shaped formations, preferably all of the first shaped formations, the second mixing body part is connected to the first mixing body part via a material bond, preferably welding or soldering.

[0013]A further-intensified thermal interaction with the exhaust gas can be achieved in that the second mixing body part has a plurality of second shaped formations, which are arranged adjacent to each other in the direction of the mixing body longitudinal axis and in the circumferential direction about the mixing body longitudinal axis and are directed away from the first mixing body part.

[0014]If it is further provided here that, adjoining at least some of the second shaped formations, preferably each second shaped formation, at least one opening is provided in the second mixing body part, preferably wherein, in the case of each pair made up of a mutually associated second shaped formation and opening, the second shaped formation and the opening overlap with each other in some regions, it is possible that exhaust gas that has flowed into the interspace between the two mixing body parts flows out of this interspace again and in its place even warmer exhaust gas enters this interspace and transfers heat to the mixing body parts.

[0015]The outflow and inflow of exhaust gas out of and into the interspace formed between the two mixing body parts can be further aided in that, in the case of some of the pairs made up of a mutually associated second shaped formation and opening, the opening is arranged on a first side, preferably a first axial side, of the associated second shaped formation and, in the case of some other pairs made up of a mutually associated second shaped formation and opening, the opening is arranged on a second side, preferably a second axial side, of the associated second shaped formation, the second side being substantially opposite the first side.

[0016]In conjunction with the second shaped formations, too, a regular shaped formation pattern aiding uniform heat transfer is provided in that the second shaped formations are arranged in a plurality of rows of second shaped formations, the rows being arranged so as to follow one after another in the circumferential direction about the mixing body longitudinal axis and extending preferably substantially in the direction of the mixing body longitudinal axis, or/and in that the second shaped formations are arranged in a plurality of rings of second shaped formations, the rings being arranged so as to follow one after another in the direction of the mixing body longitudinal axis and extending preferably substantially in the circumferential direction about the mixing body longitudinal axis.

[0017]In at least some of the rows, preferably all of the rows, of second shaped formations, the second shaped formations can be arranged at a substantially constant distance from each other, or/and, in the case of at least two, preferably all, of the rows of second shaped formations, the rows being directly adjacent to each other in the circumferential direction about the mixing body longitudinal axis, the second shaped formations can be offset from each other in the direction of the mixing body longitudinal axis.

[0018]It is also advantageous for a regular shaped formation pattern if, in at least some of the rings, preferably all, of the rings, of second shaped formations, the second shaped formations are arranged at a substantially constant distance from each other, or/and, in the case of at least two, preferably all of the rings of second shaped formations, the rings being directly adjacent to each other in the direction of the mixing body longitudinal axis, the second shaped formations are offset from each other in the circumferential direction about the mixing body longitudinal axis.

[0019]The inflow and outflow of exhaust gas into and out of the interspace formed between the two mixing body parts can be further improved in that, in the case of at least two, preferably all, of the rows of second shaped formations, the rows being directly adjacent to each other in the circumferential direction, the openings in one of the rows are arranged on the first side of the associated second shaped formations and the openings in the other of the two rows are arranged on the second side of the associated second shaped formations, or/and in that, in the case of at least two, preferably all, of the rings of second shaped formations, the rings being directly adjacent to each other in the direction of the mixing body longitudinal axis, the openings in one of the rings are arranged on the first side of the associated second shaped formations and the openings in the other ring are arranged on the second side of the associated second shaped formations.

[0020]In order to be able to use the effects introduced by the different types of shaped formations particularly efficiently and uniformly, at least some of the rows, preferably all of the rows, of first shaped formations can correspond to at least some of the rows, preferably all of the rows, of second shaped formations, so that, in at least some of the rows, preferably all of the rows, first shaped formations and second shaped formations are arranged so as to alternate, or/and at least some of the rings, preferably all of the rings, of first shaped formations can correspond to some of the rings, preferably all of the rings, of second shaped formations, so that, in at least some of the rings, preferably all of the rings, first shaped formations and second shaped formations are arranged so as to alternate.

[0021]If the first mixing body part includes a completely closed circumferential wall surrounding the mixing body longitudinal axis, that is, that in the substantially tubular first mixing body part there are no openings establishing a flow connection between the first flow volume and the second flow volume, it is ensured that the second mixing body part substantially does not come into contact with the reactant injected into the exhaust gas and thus the development of deposits in the region of the second mixing body part or in the interspace formed between the two mixing body parts is substantially avoided.

[0022]To aid this effect, in the case of the mixing path according to the disclosure, a reactant discharge arrangement for discharging reactant substantially only into one flow volume of the first flow volume and the second flow volume can be arranged upstream of the mixing body, as seen in the main direction of flow of the exhaust gas, and the second mixing body part can be arranged on that side of the first mixing body part which faces away from the flow volume.

[0023]In order for the entire volume available to be utilized particularly efficiently, it is advantageous if the one flow volume is the first flow volume, and if the second mixing body part is arranged on the outer side of the first mixing body part.

[0024]The present disclosure also relates to an exhaust gas system for an internal combustion engine, including a mixing path configured according to the disclosure and, downstream of the mixing path, an exhaust gas treatment unit, preferably an SCR catalytic converter.

BRIEF DESCRIPTION OF DRAWINGS

[0025]The invention will now be described with reference to the drawings wherein:

[0026]FIG. 1 shows a basic illustration of an exhaust gas system for an internal combustion engine having a mixing path configured according to the disclosure;

[0027]FIG. 2 shows a perspective view of a mixing body, configured with two tubular mixing body parts, of the exhaust gas system from FIG. 1;

[0028]FIG. 3 shows a cross-sectional view of the mixing body from FIG. 2, sectioned along a line III-III in FIG. 2;

[0029]FIG. 4 shows a cross-sectional view of the mixing body from FIG. 2, sectioned along a line IV-IV in FIG. 2; and,

[0030]FIG. 5 shows a longitudinal sectional view of a detail of the mixing body from FIG. 2.

DETAILED DESCRIPTION

[0031]FIG. 1 is a basic illustration of a portion of an exhaust gas system, generally denoted by 10, for an internal combustion engine. The exhaust gas system 10 includes a mixing path, generally denoted by 12, and, downstream of the mixing path 12, an exhaust gas treatment unit 14. In the example illustrated, the exhaust gas treatment unit 14 includes an SCR catalytic converter.

[0032]The mixing path 12 includes a mixing path housing 16, in which a substantially tubular mixing body 18, which is elongated in the direction of a mixing body longitudinal axis L, is arranged. Exhaust gas A emitted by an internal combustion engine, in particular a diesel internal combustion engine, flows into the mixing path housing 16, or rather toward the mixing body 18, in a main direction of flow H of the exhaust gas, which corresponds substantially to the orientation of the mixing body longitudinal axis L.

[0033]The mixing body 18 includes a tubular first mixing body part 20 having a closed circumferential wall 22 which is for example substantially cylindrical and is configured for example with a circular cross section. Due to the first mixing body 20, or the circumferential wall 22 thereof, the inner volume of the mixing path housing 16 is divided in the region of axial extent of the mixing body 18 into a first flow volume 24, which is formed inside the first mixing body part 20, or the circumferential wall 22 thereof, and is surrounded by the circumferential wall 22, or is delimited by it radially outwardly, and a second flow volume 26, which is formed between the mixing path housing 16 and the first mixing body part 20, or is delimited by it radially inwardly.

[0034]The exhaust gas system 10, or the mixing path 12, also includes a reactant discharge arrangement 28, generally also referred to as an injector, which injects a reactant R, for example a urea/water solution, in the form of a spray mist, that is, in the form of fine droplets, into the exhaust gas A flowing in the mixing path housing 16. The reactant discharge arrangement 28 is configured such that it discharges the reactant R into the first flow volume 24 and consequently into a partial flow T₁, which flows in the first flow volume 24, of the exhaust gas A. Thus, substantially no reactant R is injected into the second flow volume 26 and into a second partial flow T₂, which flows in the second flow volume 26, of the exhaust gas A. Thus, only the exhaust gas A, that is, the second partial flow T₂, flows through the second flow volume 26, which serves, as explained in detail below, primarily to transfer heat transported in the exhaust gas A to the mixing body 18, or the first mixing body part 20. The intensified heating of the first mixing body part 20 results in the evaporation of reactant R which comes into contact with an inner side 30 of the circumferential wall 22 and thus in improved mixing of reactant R and exhaust gas A, without there being any need for system regions, such as a mixer or the like, which lead to increased flow resistance.

[0035]A tubular second mixing body part 34 is arranged on an outer side 32 of the circumferential wall 22 of the first mixing body part 20, the outer side facing the second flow volume 26,. This second mixing body part surrounds the first mixing body part 20 preferably substantially in its entire region of axial extent and fully in the circumferential direction and substantially fulfills the function of a heat exchanger, via which more heat transported in the second partial flow T₂ of the exhaust gas A can be input into the mixing body 18.

[0036]The structure of the mixing body 18 with the tubular first mixing body part 20 and its circumferential wall 22, which is closed in the circumferential direction, and the tubular second mixing body part 34 or its circumferential wall 22, the second mixing body part surrounding the first mixing body part 20, is described in detail below with reference to FIGS. 2 to 5.

[0037]The second mixing body part 34, which, just like the first mixing body part 20, is configured for example as a shaped sheet metal part, has a multiplicity of for example substantially cup-like first shaped formations 36, which are distributed over the axial length of the second mixing body part 34 and in the circumferential direction about the mixing body longitudinal axis L. The cup-like first shaped formations 36 are formed on the second mixing body part 34 such that they extend from a base level N of the second mixing body part 34, the base level being at a substantially constant distance from the outer side 32 of the first mixing body part 20, toward the outer side 32 of the first mixing body part 20 and abut this outer side. Advantageously, the shaped formations 36 are configured with a circumferential wall 38 and a floor 40, which abuts the outer side 32 of the first mixing body part 20, and they are circular when viewed from above. The shaped formation floor 40 is substantially planar or is adapted to the curvature of the outer side 32 of the first mixing body part 20, so that, in the region of the shaped formation floor 40, there is surface-area contact between the second mixing body part 34 and the first mixing body part 20. Preferably in the region of all of the first shaped formations 36, there is a materially bonded connection between the two mixing body parts 20, 34, for example via welding or soldering, in order to generate good heat transfer contact.

[0038]It can be seen in FIG. 2 that a multiplicity of rows RE of first shaped formations 36 is formed on the second mixing body part 34, the rows extending substantially in the direction of the mixing body longitudinal axis L. In the case of rows RE of first shaped formations 36, the rows being directly adjacent to each other in the circumferential direction, the first shaped formations 36 are offset from each other in the direction of the mixing body longitudinal axis L, so that, in the direction of the mixing body longitudinal axis L, a first shaped formation 36 of one of the rows RE is positioned between two first shaped formations 36 of the respectively other row RE. For uniform heat transfer contact, preferably in the rows RE of first shaped formations 36, the first shaped formations 36 following one after another in the direction of the mixing body longitudinal axis L are arranged at a substantially uniform distance from each other.

[0039]Likewise, rings RI of first shaped formations 36 are formed on the second mixing body part 34, the rings running in the circumferential direction about the mixing body longitudinal axis L. In these rings RI of first shaped formations 36, too, the first shaped formations 36 are at a substantially uniform distance from each other and, in the case of rings RI of first shaped formations 36, the rings being directly adjacent to each other in the direction of the mixing body longitudinal axis L, the first shaped formations 36 are offset from each other in the circumferential direction, so that a first shaped formation 36 of one of the two rings RI is positioned between two first shaped formations 36 of the respectively other ring RI.

[0040]Via such a substantially uniform pattern of first shaped formations 36 over the entire axial expanse of the second mixing body part 34 and over the entire circumference thereof, substantially uniform heat transfer contact is generated between the two mixing body parts 34, 20. Exhaust gas A of the second partial flow T₂ flowing in the second flow volume 26 along the second mixing body part 34 can thus flow around the second mixing body part 34 on its outer side 42, which faces away from the first mixing body part 20, and on its inner side 44, which faces the first mixing body part 20, and in doing so transfer heat to the first mixing body part. The heat absorbed in the second mixing body part 34 is transferred to the first mixing body part 20 via the contact between the two mixing body parts 34, 20 in the region of the first shaped formations 36. It is particularly advantageous that, due to the multiplicity of first shaped formations 36 being provided in the region of the inner side 44 and the outer side 42 of the second mixing body part 34, turbulence is created and this improves the thermal interaction of the exhaust gas A in the second partial flow T₂ with the second mixing body part 34.

[0041]For even further improved thermal interaction and intensified heat input into the first mixing body part 20, the second mixing body part 34 has a multiplicity of second shaped formations 46. An opening 48 is associated to each second shaped formation 46, so that respective pairs of second shaped formations 46 and openings 48 are formed. The second shaped formations 46 are oriented radially outwardly with respect to the mixing body longitudinal axis L, that is, in the direction away from the first mixing body part 20, and positioned with respect to the respectively associated opening 48 so that, in the case of each pair made up of a second shaped formation 46 and an opening 48, they overlap with each other, that is, the opening 48 extends into the region of the shaped formation 46. This results in the structure visible in FIG. 5, in which each such second shaped formation 46 is formed in the manner of a portion of a spherical dome or similarly shaped dome and is open in the direction toward the respectively associated opening 48.

[0042]It can also be seen in FIGS. 2 and 5 that, in the case of each pair made up of a second shaped formation 46 and an opening 48, these are arranged so as to follow one after another axially in the direction of the mixing body longitudinal axis L. The second shaped formations 46 or openings 48, or pairs of second shaped formations 46 and openings 48, are also arranged in rows RE running substantially in the direction of the mixing body longitudinal axis L, wherein here too the arrangement is such that the second shaped formations 46 or openings 48, or pairs of second shaped formations 46 and openings 48, of rows RE of second shaped formations 46, the rows being directly adjacent to each other in the circumferential direction, are offset from each other in the direction of the mixing body longitudinal axis L. Likewise, the second shaped formations 46 or the associated openings 48, or pairs of second shaped formations 46 and openings 48, form respective rings RI running in the circumferential direction, wherein, also in the case of rings RI directly adjacent to each other in the direction of the mixing body longitudinal axis L, the second shaped formations 46 positioned at a uniform distance from each other both in the circumferential direction and in the direction of the mixing body longitudinal axis L are offset from each other. In particular, this provides a structure in which the second shaped formations 46 or openings 48 are each integrated both in the axial direction and in the circumferential direction between two first shaped formations 36, so that, both in the axial direction and in the circumferential direction, an alternating sequence of first shaped formations 36 and second shaped formations 46 with respectively associated openings 48 results and consequently the rows RE and rings RI of first shaped formations 36 correspond respectively to the rows RE and rings RI of second shaped formations 46.

[0043]It can also be seen in FIG. 2 that, in the case of respectively two rows RE of second shaped formations 46, the rows being directly adjacent to each other in the circumferential direction, the openings 48 are positioned on different sides of the second shaped formations 46. In one of two rows RE of second shaped formations 46, the rows being directly adjacent to each other in the circumferential direction, the associated openings 48 are arranged on a first side, in particular a first axial side, of the second shaped formations 46, while in the other row RE of two rows RE of second shaped formations 46, the rows being directly adjacent to each other in the circumferential direction, the associated openings 48 are positioned on the other side, that is, in particular the other axial side, of the second shaped formations 46. Thus, in the case of directly adjacent rings RI of second shaped formations, this results in an alternating pattern of the axial opening direction of the second shaped formations 46 both in the circumferential direction and in the axial direction, and this aids the inflow of exhaust gas A into an interspace 50 formed between the two mixing body parts 20, 34 and the outflow of exhaust gas A from this interspace 50. The second shaped formations 46 thus not only contribute to intensifying the turbulence in the near-surface region of the second mixing body part 34, but also aid the exhaust gas exchange in the interspace 50, as a result of which the heat transfer between the two mixing body parts 34, 20 and also the thermal contact of the first mixing body part 20 with the second partial flow T₂ flowing in the second flow volume 26 are improved.

[0044]By providing the mixing body part 34 in the flow volume through which substantially only exhaust gas A flows, while the reactant R is introduced into the flow volume in which a substantially smooth surface is provided for contact with the reactant, the development of deposits from the reactant R is largely prevented. Since it is nevertheless the case that, due to the presence of the second mixing body part 34, the first mixing body part 20, which provides this smooth surface, can absorb more heat from the exhaust gas A emitted by an internal combustion engine, the evaporation of reactant R is aided, which is advantageous in particular in a cold starting state, that is, in a phase of the beginning of operation of an internal combustion engine, or at low load of the internal combustion engine.

[0045]A wide variety of different variations can be realized on the structure of the mixing body 18 illustrated in the figures. For example, the rows RE of first and second shaped formations 36, 46 can have an orientation that deviates from the parallel orientation in relation to the mixing body longitudinal axis L, that is, they can have a circumferential extent component, this resulting in a helical-winding-like pattern of the rows RE of first and second shaped formations 36, 46, the rows being adjacent to each other in the circumferential direction. In another embodiment, the second mixing body part 34 could be arranged on the inner side 30 of the first mixing body part 20, while the reactant discharge arrangement 28 can then be configured to introduce the reactant R into the second flow volume 26, so that substantially only exhaust gas A flows through the first flow volume 24. It is also possible to arrange multiple such second mixing body parts 34 so as to follow one after another in the direction of the mixing body longitudinal axis L, for example at an axial distance from each other, in which case for example the rows of the first and second shaped formations 36, 46 can be offset from each other in the circumferential direction in the case of second mixing body parts 34 following one after another in the axial direction.

[0046]The number of first shaped formations 36 and/or second shaped formations 46 can also be changed. Thus, two second shaped formations 46, each with an associated opening 48, could be positioned for example in the axial direction or/and in the circumferential direction between respectively two first shaped formations 36, or two or more first shaped formations 36 could be provided between two second shaped formations 46 with associated openings 48.

[0047]In another alternative embodiment, in the case of at least some of the second shaped formations 46, two openings 48 associated with a respective second shaped formation 46 can be provided on opposite sides of the second shaped formation 46. Each of these openings 48 can then extend into the associated second shaped formation 46, or overlap with it for example axially, so that the second shaped formation 46 forms a bridge, which is directed away from the first mixing body part 20, between the two of these associated openings 48.

[0048]Finally, it can be provided that, at least in a subregion of the mixing body 18, at least some of the first shaped formations 36 or/and some of the second shaped formations 46 with the respectively associated openings 48 are not arranged in the symmetrical or orderly structure illustrated in the figures, but rather that a statistical or non-orderly distribution of these shaped formations 36, 46 is provided, with non-uniform distances between them in the circumferential direction and in the axial direction and with no defined orientation in relation to each other in the circumferential direction and in the axial direction.

[0049]It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.