Patent Application
20180142597
The present invention relates to an arrangement for introducing a fluid into a gas flow, in particular for introducing a reductant into an exhaust gas flow of an internal combustion engine.
The problem of distributing a liquid additive reliably in a suitable form in a gas flow in order, for example, to enable a chemical reaction of components of the gas flow with components of the introduced fluid is one which arises in a number of application areas. This problem arises in exhaust gas engineering, for example, in connection with the SCR process in which an aqueous urea solution is introduced into the exhaust train of a motor vehicle, for example by means of a metering apparatus. Ammonia and CO2 are produced from the urea solution by thermolysis and hydrolysis. The ammonia produced in this manner can react in a suitable catalytic converter with the nitrogen oxides contained in the exhaust gas which are thus efficiently removed from the exhaust gas.
It is of particular relevance in this process that the urea solution is introduced into the exhaust gas flow in a well-defined form. It is moreover of great importance that the urea solution introduced into the exhaust gas flow is evaporated as completely as possible and is uniformly distributed in the exhaust gas flow.
In many cases, the urea solution is injected or sprayed into the exhaust train by a metering apparatus that the exhaust gas flow flows onto obliquely or laterally. This can have the result that the reductant sprayed in is scattered. The additive introduced frequently forms a spray cone. The latter is deformed by the exhaust gas flow and under certain circumstances is even urged toward the walls of the exhaust train. This has the consequence that the injected fluid is distributed less well, which results in a reduction of the efficiency of the catalysis. In addition, unwanted deposits of the fluid can form in the interior of the apparatus, in particular also in the region around the metering apparatus, which can likewise result in a reduction of the efficiency or even in a failure of the apparatus or of the exhaust gas cleaning system.
It is therefore an object of the present invention to provide an apparatus of the initially named kind having an improved introduction and distribution efficiency of the fluid.
This object is satisfied by an apparatus having the features of claim 1.
In accordance with the invention, the apparatus has a mixing chamber and a metering apparatus. The fluid can be introduced by means of a metering tip by the metering apparatus into an injection space defined by a protective sleeve. The injection space is arranged in the interior of the chamber and is in fluid communication therewith. The protective sleeve has an intermediate chamber that extends in the peripheral direction and that is bounded at the radial inner side by an inner wall and at the radial outer side by an outer wall. The intermediate chamber is in fluid communication with the injection space via a gap, in particular an annular gap, formed by or configured at the inner wall. On the other hand, the intermediate chamber is in fluid communication with the mixing chamber via at least one opening—in particular a plurality of openings—in the outer wall.
In other words, the fluid is introduced into the injection space defined by the protective sleeve by means of the metering tip of the metering apparatus. The injection space is open toward the mixing chamber. The protective sleeve thus forms a kind of screen that prevents the gas from flowing directly onto the metering tip. The protective sleeve—at least initially—also protects the spray cone, which results in a better distribution of the fluid in the gas flow.
In addition, the protective sleeve acts as a kind of “flushing apparatus” to protect the metering tip from the formation of deposits by being flowed around by gas. Some of the gas flowing onto the protective sleeve can namely penetrate into the intermediate chamber through the openings in the outer wall of the protective sleeve. The gas flows from said intermediate chamber into the injection space through the gap forming a constricted opening. The exhaust gas flowing through the gap into the injection space can be guided in this respect such that it at least largely prevents the formation of deposits in the region of the injection space and in particular of the metering tip.
Further embodiments of the invention are set forth in the description, in the dependent claims and in the enclosed drawings.
In accordance with an embodiment, the gap surrounds the metering tip at least partly, preferably completely, in the peripheral direction. The gap is in particular arranged such that at least some of the gas flow flowing therethrough flushes behind the metering tip. For this purpose, the gap can be arranged—viewed in the axial direction, i.e. in the direction of introduction of the fluid—approximately at the level of the metering tip or even in front of it.
At least one guide element can be arranged in the gap and a swirl component can be imparted through said gap to at least some of the gas flow flowing therethrough. Such a flow eddy can contribute to preventing the formation of deposits even more efficiently. In addition, the swirl provides that the flow follows a contour of the inner wall defining the injection space better so that flow separations are minimized.
In accordance with a further embodiment of the apparatus in accordance with the invention, a part of a wall of the mixing chamber at least sectionally bounds the intermediate chamber. It in particular bounds it in the region around the metering tip. The protective sleeve can, for example, be fastened to the wall of the mixing chamber, in particular via its outer wall, so that the wall of the mixing chamber and the inner and outer walls of the protective sleeve together define the intermediate chamber. It is, however, also possible to at least sectionally bound an end of the intermediate chamber facing the metering tip by a base section of the protective sleeve. The base section of the protective sleeve is in particular connected to the outer wall or is formed in one piece therewith. The base section can be arranged spaced apart from the wall of the mixing chamber. A flow path is thereby established between the protective sleeve and the mixing chamber wall and contributes to an (additional) flowing behind of the metering tip to further reduce the formation of deposits.
The gap can be bounded by an end section of the inner wall facing the metering tip, by a part of a wall of the mixing chamber sectionally bounding the intermediate chamber and/or—if provided—by the base section of the protective sleeve. The inner wall is in particular provided with a collar at its end facing the metering tip, said collar projecting into the intermediate chamber to efficiently guide the gas flow through the gap. I.e. in an embodiment of the apparatus in accordance with the invention, the end section of the inner wall of the sleeve—with or without a collar—is spaced apart from the wall of the mixing chamber or from the base section to form the gap.
The at least one opening in the outer wall can be a bore, an elongate hole and/or a slit. A plurality of openings are in particular provided that are preferably evenly distributed in the peripheral direction. Provision can, however, also be made for specific applications to provide larger, differently shaped and/or more openings in specific regions of the outer wall, for example to compensate an uneven onflow onto the protective sleeve by the gas flow. Openings having different shapes can also be combined.
In accordance with an embodiment, the inner wall has a funnel-like or conical section that opens in a direction away from the metering tip. I.e. the named section diverges in the direction of introduction of the fluid to take account of its “development”. The inner wall is in particular configured without interruption so that the gas can only enter into the injection space from the intermediate chamber through the gap.
Alternatively or additionally, the outer wall can also have a funnel-like or conical section that opens in a direction toward the metering tip. I.e. in this embodiment, the named section converges in the direction of introduction of the fluid.
In accordance with an embodiment of the protective sleeve, it is formed in one piece. Alternatively, the inner wall and the outer wall of the protective sleeve can be separately manufactured elements that are connected to one another, in particular welded or soldered to one another. The connection between the inner wall and the outer wall can be provided at their ends remote form the metering tip, for example.
In accordance with an inexpensive embodiment of the protective sleeve that is also suitable for many application cases, the protective sleeve is substantially rotationally symmetrical. To take account of special flow conditions, however, an asymmetrical design can also be provided.
The mixing chamber can have at least one inlet opening that is arranged and configured such that the protective sleeve, in particular its outer wall, is flowed onto by at least some of the gas flow flowing into the mixing chamber. An at least partly radial, oblique and/or lateral onflow of the protective sleeve can in particular be present.
A plurality of inlet openings can, however, also be provided that are arranged around the protective sleeve. At least one opening, in particular exactly one opening, in the outer wall of the protective sleeve can be associated with each of the inlet openings.
A gas guidance element that guides at least some of the gas flow toward the protective sleeve can be arranged in the mixing chamber. The gas guidance element can be connected to the protective sleeve and can project into the gas flow flowing onto the protective sleeve. An upstream end of the gas guidance element is in particular arranged substantially in parallel with the gas flow to prevent the generation of unnecessary eddies.
The gas conductance element can generally be a separate component that—as mentioned above—is connected, or is also not connected, to the protective sleeve. The gas conductance element can, however, also be formed by a section of the outer wall of the protective sleeve. In accordance with an embodiment, the gas conductance element is associated with at least one opening in the outer wall of the protective sleeve to guide some of the gas flow into or through the opening so that it enters into the intermediate chamber. The gas conductance element is in particular arranged in the region of the opening. The gas conductance element is, for example, formed at least in part by a section of the outer wall of the protective sleeve that was bent out, for example, to form the at least one opening in the outer wall.
The gas conductance element can have a section that is formed in U shape or that has the form of an incomplete U. It is e.g. conceivable that the gas conductance element is bent out of the outer wall so that it merges into the outer wall in a bend. In the further course, the gas conductance element can be correspondingly shaped to guide a desired part proportion of the gas flow into the intermediate chamber.
The gas conductance element can comprise openings, e.g. holes. The openings are in particular arranged in a region that is arranged adjacent to the protective sleeve.
The gas conductance element can project into an inlet opening of the mixing chamber or can even project through it to optimize the gas flow.
In accordance with a further embodiment of the present invention, the mixing chamber has a bypass flow path through which the at least some of the gas flow flows into or through the mixing chamber without flowing onto the protective sleeve or even flowing through the protective sleeve, in particular its intermediate chamber. The bypass flow path is, for example, at least sectionally defined by a wall of the mixing chamber and by an end of the protective sleeve remote from the metering tip.
The wall of the mixing chamber can have an inwardly directed bead that is arranged approximately at the level of the protective sleeve in the axial direction of the mixing chamber to optimize the onflow of the protective sleeve.
A gas guidance pipe whose outer periphery is arranged spaced apart from the wall of the mixing chamber can be arranged in the mixing chamber for the additional protection of the spray cone—spray-in geometries differing from a conical shape are also conceivable. The wall of the mixer chamber and the outer periphery of the gas guidance pipe thus sectionally define a gap through which gas can flow. The gas guidance pipe is in particular arranged downstream of the metering apparatus.
At least one flow conductance element can be arranged in the gap between the wall of the mixer chamber and the gas conductance pipe to impart a well-defined flow pattern on the gas flowing through the gap. A swirl is in particular imparted on the gas flow by a flow conductance element or preferably by a plurality of flow conductance elements arranged distributed in the peripheral direction of the gap. The flow conductance element or elements is/are in particular arranged at the inlet side of the gap.
In accordance with an embodiment, at least one flow conductance element is arranged in the gas conductance pipe. This means that, in an embodiment, at least one flow conductance element at least partly projects into the gas conductance pipe or is completely arranged therein. A flow conductance element that at least sectionally projects into the gas conductance pipe and/or is connected to the inner periphery of the gas conductance pipe is in particular provided at the inlet-side end of the gas conductance pipe. A plurality of flow conductance elements are preferably provided.
The at least one flow conductance element can be arranged between the protective sleeve and the gas conductance pipe. In other words, the at least one flow conductance element is arranged at least sectionally in an intermediate space or gap between the protective sleeve and the gas conductance pipe. A plurality of flow conductance elements are preferably provided that impart a swirl on the gas flow that flows into the gas conductance pipe through the intermediate space or gap between the protective sleeve and the gas conductance pipe. The at least one flow conductance element is in particular arranged between a downstream section of the protective sleeve and an upstream section of the gas conductance pipe. The flow conductance element can be in contact with or even connected to the gas conductance pipe and/or to the protective sleeve.
The protective sleeve can project at least sectionally into the gas conductance pipe in the axial direction. Laterally onflowing gas can therefore not flow directly onto the injected fluid.
The gas conductance pipe can have a section that flares in the flow direction of the gas flow. In accordance with an embodiment, the gas conductance pipe has a funnel-like inlet region and/or a constriction having a reduced cross-section. The gas flowing into the gas conductance pipe and the injected fluid are efficiently “captured” by the funnel-like inlet region. The optionally provided constriction generates an advantageous nozzle effect that increases the efficiency of the apparatus in accordance with the invention. To take account of the construction space circumstances, the gas conductance pipe can also have a curved section.
The gas conductance pipe can in particular be arranged coaxially to the mixing chamber and/or protective sleeve.
The mixing chamber is in particular a tubular section of an exhaust gas system.
The invention will be explained in the following purely by way of example with reference to advantageous embodiments and to the enclosed drawings. There are shown:
a a sectional view and a side view respectively of a further embodiment of the apparatus in accordance with the invention;
The protective sleeve 22 comprises an outer wall 26 that is connected, in particular welded or soldered, to the base section 18 (e.g. deflection shell) of the mixer pipe 16. The outer wall 26 has openings 28 through which some of the exhaust gas flowing onto the protective sleeve 22 can enter into an intermediate chamber 30 that is bounded by the outer wall 26 and by an inner wall 32 opening conically in a direction away from the metering tip 20. The inner wall 32 and the outer wall 26 are indirectly connected to one another via an end face section 34. A direction connection of the walls 26, 32 is likewise conceivable. The inner wall 32 and the outer wall 26 as well as the end face section 34—if present—are in particular formed in one piece. Provision can, however, also be made to manufacture the inner wall 32 and the outer wall separately from one another and then to connect them to one another, in particular at their ends remote from the metering tip 20.
The substantially funnel-like inner wall 32 defines an injection space 36 which is open toward the interior of the mixer pipe 16 and in which the spray cone 24 which is generated by the metering tip 20 is protected from a direct onflow by the exhaust gas.
To prevent the formation of reductant deposits in the region of the metering tip 20, provision is made to flush behind it in a well-defined form. The flushing behind has to be sufficiently efficient, on the one hand, and, on the other hand, an impairment of the development of the spray cone 24 should be avoided as much as possible.
The exhaust gas flowing into the intermediate chamber 30 is used for this purpose. An annular gap 38 that represents a constricted opening for exhaust gas flowing out of the intermediate chamber 30 into the injection space 36 is formed between the base section 18 and the end of the inner wall 32 facing the metering tip 20.
As is indicated by flow paths 40, at least some of the exhaust gas flowing laterally onto the protective sleeve 22 flows through the openings 28 into the intermediate chamber 30. Some of the exhaust gas also flows around the protective sleeve 22 and enters into the intermediate chamber 30 at sides of the protective sleeve 22 not facing the inlet opening 14. Substantially homogeneous pressure conditions are present in the intermediate chamber 30 in an operation of the exhaust gas system. The exhaust gas moves out of the intermediate chamber 30 through the gap 38 into the injection space 36. A flow through the gap 38 that is also substantially homogeneous in the peripheral direction is formed due to the homogeneous pressure conditions in the chamber 30. The positioning of the gap 38 ensures that the metering tip 20 is flowed around by exhaust gas so that no deposits of the reductant can be formed here.
The protective sleeve 22 acts—in functional terms—approximately as a two-stage restriction apparatus. The first restriction takes place on the flowing of the exhaust gas through the openings 28 into the intermediate chamber 30. The second restriction is achieved by the gap 38. It is thereby ensured that well-defined flow conditions and pressure conditions that reliably prevent the formation of deposits are present in the region around the metering tip 20. Since the inner wall 32 is formed without interruption, the spray cone 24 is also not disturbed by gas inflowing in the radial direction—apart from the region around the gap 38. The exhaust gas passing through the gap 38 follows the geometry of the inner wall 32 in the injection space 36 and therefore has mainly axial flow components.
To design the inflow of the exhaust gas out of the intermediate chamber 30 into the injection space 36 as free of eddies as possible, the end of the inner wall 32 facing the metering tip 20 is provided with a curved collar 42 that extends into the intermediate chamber 30.
However, the total exhaust gas that enters into the mixer pipe 16 through the inlet opening 14 does not flow around or even through the protective sleeve 22. Some of the exhaust gas—marked by flow paths 40′—flows between the end of the protective sleeve 22 remote from the metering tip 20 and the right hand lower outer wall of the mixer pipe 16 directly into said mixer pipe. The flow paths 40′ thus symbolize a bypass flow. It is understood that the bypass flow depends inter alia on the dimensioning of the protective sleeve 22 and of the mixer pipe 16. It is by all means conceivable that the protective sleeve 22 has a smaller axial extent than shown in
The inner wall 32 of the protective sleeve 22a is formed in funnel shape (see in particular
a show a further embodiment 10′ of the apparatus in accordance with the invention. The apparatus 10′ is connected in one piece to an inlet stub 48 and to an outlet stub 50 that make the connection to the further components of the exhaust gas system possible.
To guide the exhaust gas entering into the mixer pipe 16 through the inlet opening 14 toward the protective sleeve, that is here formed as a further embodiment 22b, in a well-defined manner, it comprises a gas conductance element 52. The gas conductance element 52 is also shown in different views in
The gas flow flowing onto the apparatus 10′ is split into two part flows by the gas conductance element 52. A first part flow flows beneath the gas conductance element 52 onto the protective sleeve 22b. The outer wall 26 of the protective sleeve 22b is provided with circular holes 44′ in the region flowed onto by the first part flow so that this portion of the gas flow can enter into the intermediate chamber 30. The exhaust gas flows from there through the gap 38 into the injection space 36 and in so doing flushes behind the metering tip 20 of the metering apparatus (not shown) that is fastened via a fastening flange 55 to the base section 18 in a gas tight manner.
The second part flow flows above the gas conductance element 52 toward a section of the protective sleeve 22b that is free of interruption. I.e. this portion of the exhaust gas cannot enter into the intermediate chamber 30, but rather flows into the pipe 58 through an annular gap 56 between a gas conductance pipe 58 arranged in the mixer pipe 16 and the end of the protective sleeve 22b remote from the metering tip. Since the protective sleeve 22b projects in the axial direction into the end of the gas conductance pipe 58 facing the metering tip 20, no exhaust gas can flow directly into the gas conductance pipe 58, but it must rather “force” itself through the gap 56. It is thereby effected that the exhaust gas originally onflowing obliquely or laterally has a substantially axial flow direction in the interior of the gas conductance pipe 58, which contributes to a further protection of the spray cone 24 and thus assists the uniform distribution of the reductant in the exhaust gas flow.
The portion of the second part flow not flowing onto the protective sleeve 22b impacts the outer wall of the end of the gas conductance pipe 58 facing the protective sleeve 22′ and flows through a bypass gap 60 that is formed by the outer wall of the gas conductance pipe 58 and by the inner wall of the mixer pipe 16 spaced apart therefrom. This portion of the exhaust gas flow thus does not come into contact with the protective sleeve 22b.
The protective sleeve 22b and the gas conductance pipe 58 are aligned coaxially to the mixer pipe 16.
The flow conductance elements 59 are arranged in the bypass gap 60, more precisely in its inlet region. The flow conductance elements 59 that in particular have surface sections that are angled, curved and/or planar with respect to the main flow direction impart a swirl-like flow pattern onto the gas flow flowing into the bypass gap 60 in the embodiment 10′″. It is thereby achieved that the gas conductance pipe 58 is—in simplified terms—spirally flowed around. It is understood that the number, arrangement and/or design of the flow conductance elements 59 is/are freely selectable to generate the flow pattern (with or without a swirl component) suitable for the respective application.
The flow conductance elements 59′ span the annular gap 56 between the gas conductance pipe 58 and the end of the protective sleeve 22b remote from the metering tip. The flow conductance elements 59′ are also provided in the apparatus 10′″ to generate a swirl-like flow pattern. I.e. the exhaust gas flowing into the gas conductance pipe 58 through the annular gap 56 has a flow pattern acted on by swirl. It also applies here that the number, design and/or arrangement of the flow conductance elements 59′ can be adapted to the respective circumstances present to generate the respective desired flow pattern. In the apparatus 10′″ shown by way of example, the flow conductance elements 59′ extend over the total annular gap 56. However, they only project partly into the pipe 58. The flow conductance elements 59′ are in contact with the upstream end section of the gas conductance pipe 58, on the one hand, and with a downstream section of the protective sleeve 22b, on the other hand. The flow conductance elements 59′ can be fixedly connected to the components 58, 22b. It is, however, also possible that the flow conductance elements 59′ only extend over a part of the annular gap 56. The same naturally applies analogously to the flow conductance elements 59.
It becomes clear from a joint review of
To optimize the flow conditions, the wall of the mixer pipe 16 is provided in the region of the protective sleeve 22d with a bead 70 whose design varies in the peripheral direction. Depending on the axial position—in particular when the bead 70 is above the inlet opening 14 in the axial direction—it can also have a constant design in the peripheral direction.
The fastening flange 55 shown in
A further difference between the apparatus 10′ and 10″ is that a gas conductance pipe 58′ of the apparatus 10 has a somewhat different design than the gas conductance pipe 58. The gas conductance pipe 58′ has a funnel-like inlet region 74 into which the end (end face section 34) of the protective sleeve 26f remote from the metering tip 20 projects. An opening plane of the funnel-like inlet region 74 is in this respect not in parallel with a plane defined by the margin of the protective sleeve 26f remote from the metering tip 20.
A constriction 76 that develops a nozzle effect adjoins the funnel-like inlet region 74 by which the efficiency of the apparatus 10″ is increased.
The gas conductance pipe 58′ additionally extends further into the mixer pipe 16 than the mixer pipe 58. In this respect, it substantially follows a downstream geometry of the mixer pipe 16 so that it has a curved section 78.
A gas conductance element 52′ of the apparatus 10″ is likewise of a somewhat different design than the gas conductance element 52 of the apparatus 10′. It not only projects into the inlet stub 48, but even extends into a pipe 80 connected to the inlet stub 48. The gas conductance element 52′ in this respect follows the geometry of the pipe 80 so that the upstream end 54 of the gas conductance element 52′ is arranged in parallel with the main flow direction of the exhaust gas in the pipe 80. The gas conductance element 52, 52′ can also be formed as multi-piece e.g. can comprise components plugged into one another or connected to one another with material continuity.
Unlike the gas conductance element 52, the gas conductance element 52′ additionally has holes 44″. They are arranged in a region adjacent to the protective sleeve 22f and allow a passage of exhaust gas in this region.
The design of the gas conductance element 52′ provides an early separation of the exhaust gas flow into a portion that is guided toward a lower section of the protective sleeve 22f and into a portion that is guided toward the upper part of the protective sleeve 22f or to the bypass gap 60. Due to the constriction 76 and due to the geometry of the funnel-like inlet region 74, the bypass gap 60 has a fluid mechanically more favorable design of the entry region than the gap 60 of the apparatus.
To guide exhaust gas flowing through the respective inlet opening 14 of the stubs 48 at least partly toward the gap openings 84, the tabs 82 are correspondingly curved or bent.
It is understood that individual features that have been described in connection with specific embodiments of the protective sleeve can be freely combined to obtain a design of the protective sleeve that is optimum for the respective conditions present. It is generally also possible to provide openings at the end face of the protective sleeve remote from the metering tip so that exhaust gas can also flow out of the intermediate chamber in the axial direction. The constriction sleeve can be actively heated to evaporate reductant impacting it even faster, in particular when the exhaust flow has not yet led to the heating of the components of the apparatus in accordance with the invention (e.g. briefly after starting the engine). The surface of the protective sleeve can also be catalytically coated.
The gap forming a constricted opening to establish a fluid communication between the intermediate chamber and the injection space can have a design varying in the peripheral direction (e.g. a varying gap width). It is, however, preferred to configure the gap in as constant a manner as possible in the peripheral direction to enable a flow of the gas into the injection space that is homogeneous in the peripheral direction.
The concept in accordance with the invention of first enabling an entry of the exhaust gas into an intermediate chamber through openings in the outer wall of the protective sleeve and only subsequently to utilize the exhaust gas to flow behind the metering tip leads to much smaller deposits than with previously known concepts. A substantially even pressure level is namely formed in the intermediate chamber so that the throughflow of the gap and thus the flowing behind of the metering tip are likewise comparatively homogeneous. The exhaust gas flowing through the gap additionally flushes the reductant out of the injection space. A more homogeneous distribution of the reductant in the exhaust gas results overall.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 106 078.7 | Apr 2015 | DE | national |
| 10 2015 110 319.2 | Jun 2015 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/056161 | 3/21/2016 | WO | 00 |
