US20180142596A1

US20180142596A1 - Injection module and exhaust system having an injection module

Info

Publication number: US20180142596A1
Application number: US15/315,564
Authority: US
Inventors: Markus Buerglin
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2014-06-04
Filing date: 2015-04-29
Publication date: 2018-05-24
Also published as: CN106536882A; KR20170015480A; DE102014210638A1; WO2015185297A1; EP3152420B1; EP3152420A1

Abstract

An injection module (10) for injecting a reducing agent, urea (AdBlue), into the exhaust system (22) of an internal combustion engine (2) has at least two outlet openings (12) for discharging at least one reducing agent la primary stream (13), the outlet openings (12) being angled and spaced apart in such a way that the reducing agent primary streams (13) being discharged from the outlet openings (12) meet each other so that they largely, but not entirely overlap and thereby achieve a uniform distribution in the spray mist (11).

Description

The invention relates to an injection module, in particular an injection module for injecting a reducing agent into the exhaust system of an internal combustion engine, and to an exhaust system fitted with an injection module of this kind.

PRIOR ART

SCR technology (“selective catalytic reduction”) using a urea-containing liquid reducing agent (“AdBlue®”) has proven its worth in removing nitrogen oxides from the exhaust gases of diesel engines. In this process, the liquid reducing agent, an aqueous urea solution, is sprayed into the exhaust gas stream upstream of a reducing agent catalyst and, at the same time, finely atomized before the exhaust gas/reducing agent mixture is fed to the SCR catalyst.
In order to achieve a high nitrogen oxide conversion rate with the minimum reducing agent slip, the reducing agent must be distributed as uniformly as possible over the inlet area of the catalyst. Hitherto, this has been achieved either by means of a mixer mounted in the exhaust pipe or by means of a long mixing section between the point at which the reducing agent is metered in and the catalyst.
DE 44 17 238 A1 discloses a device for reducing nitrogen oxides in the exhaust gases of an internal combustion engine, having an inlet chamber, a hydrolysis catalyst, a deNOx catalyst and an oxidation catalyst, in which the inlet chamber, the hydrolysis catalyst, the deNOx catalyst and the oxidation catalyst form a substantially cylindrical unit through which the exhaust gas stream can flow in the sequence stated and the diameter of the inlet chamber exceeds the diameter of the hydrolysis catalyst. This ensures that the exhaust gas mixed with a reducing agent in the inlet chamber enters the catalyst with a uniform distribution of the reducing agent and an exhaust gas flow density which is as uniform as possible over the cross section of the exhaust system.
DE 10 2010 039 079 A1 describes an injection device for injecting a fluid into an exhaust system of an internal combustion engine, having a first flow region, which is designed in such a way that the fluid flows substantially in a first direction of flow, which is parallel to a valve axis, in the first flow region during operation; a valve plate, which delimits the first flow region downstream, wherein a valve opening which has a smaller cross section than the first flow region in a plane orthogonal to the valve axis is formed in the valve plate; and at least one spray hole plate, which is formed downstream of the valve opening and has at least one injection hole, which is designed in such a way that the fluid flows out of the injection hole in a second direction of flow during operation. Here, the second direction of flow has a component aligned in the direction of the valve axis.
In order to achieve the desired homogenization of the reducing agent with the exhaust gas, a reducing agent spray mist (“reducing agent spray”) which is as flat as possible but as far as possible covers the full area is required. In order to avoid unwanted deposits of the reducing agent in the exhaust system, only a limited quantity of the reducing agent must strike the walls of the exhaust system.
DE 10 2013 223 296 discloses an injection module for injecting a reducing agent into the exhaust system of an internal combustion engine, having at least two outlet openings for dispensing a reducing agent primary jet in each case. In this case, the outlet openings are designed in such a way that the reducing agent primary jets emerging through the outlet openings meet in the exhaust system in order to produce a spray mist.

DISCLOSURE OF THE INVENTION

One object of the invention is to optimize the spray mist produced by a jet collision in the exhaust system and, in particular, to produce a spray mist (“spray”) which as far as possible covers the full area and has a mass distribution which is as uniform as possible.
An injection module according to the invention for injecting a reducing agent into the exhaust system of an internal combustion engine has at least two outlet openings for dispensing at least one reducing agent primary jet in each case.
In this case, the outlet openings are formed in such a way that the reducing agent primary jets emerging through the at least two outlet openings do not meet over their full area but with only a partial overlap in order to produce a spray mist in the exhaust system by means of the collision.
The invention also comprises a method of injecting a reducing agent into the exhaust system of an internal combustion engine, wherein the method includes injecting at least two reducing agent primary jets into the exhaust system in such a way that they do not meet over their full area but with only a partial overlap in order to produce a suitable spray mist in the exhaust system.
In this way, a flat reducing agent spray mist covering the full area and having a very uniform mass distribution is produced through jet collision in the exhaust system, said mist mixing in an optimum manner with the exhaust gases flowing through the exhaust system and thus allowing an effective reduction in pollutants with a low consumption of reducing agent.
In order to implement the partially overlapping collision of the reducing agent primary jets in accordance with the invention, it is possible, in particular, for the outlet openings to be arranged offset and/or tilted relative to one another. By arranging the outlet openings in a manner offset and/or tilted relative to one another, partially overlapping collision of the reducing agent primary jets can be achieved in an effective manner and by simple means.
In one embodiment, the overlap is in a range of from 30% to 70%, in particular in a range of from 40% to 60%, of the area of the primary jets. An overlap in this range has proven particularly advantageous for the production of a spray mist which is as uniform as possible.
In one embodiment, the outlet openings are less than 5 mm apart, in particular less than 2 mm apart, ensuring that, from their respective outlet opening to the point of collision, the primary jets are compact jets that have not yet broken down into individual droplets. If the primary jets have already broken down into individual droplets, individual droplets repeatedly lack collision partners; collision is therefore optimized by compact jets.
In one embodiment, the outlet openings are formed in such a way that the reducing agent primary jets meet at an angle of more than 30° in order to optimize the collision between the two primary jets and bring about optimum atomization of the primary jets.
In one embodiment, the outlet openings are formed in such a way that the reducing agent primary jets meet after a free path length of less than 10 mm, in particular of less than 5 mm, in order to avoid the primary jets splitting into individual droplets before the point of collision.
The outlet openings preferably have a circular cross section since the jet diameter and the outlet angle of the jet are precisely defined in the case of a circular cross section. However, the outlet openings can also be formed with an oval cross section.
The invention also comprises a section of an exhaust system of an internal combustion engine in which an injection module according to the invention is provided.
In one embodiment, the section of the exhaust system has, in addition to the injection module, a shielding plate, which is designed and arranged in such a way that it prevents the spray mist from striking a wall of the exhaust system. Unwanted deposits of the reducing agent, which could negatively affect the flow properties in the exhaust system, are in this way reliably prevented.
The shielding plate can have one or more openings, which allow a defined flow of the exhaust gases through the shielding plate in order to selectively influence the flow behavior of the exhaust gases in the exhaust system.
In one embodiment, the shielding plate is arranged in such a way that a buildup chamber is formed between the shielding plate and at least one wall of the exhaust system. During operation, an exhaust gas excess pressure arises in the buildup chamber, causing exhaust gases to flow through holes formed in the shielding plate, which results in particularly effective mixing of the exhaust gases with the reducing agent atomized in accordance with the invention.
In one embodiment, an additional plate is arranged upstream of the injection module to prevent the reducing agent spray mist from being dispersed by the exhaust flow at the point of collision of the primary jets and thus to ensure reliable production of a spray mist by the primary jets.
In one embodiment, an oxidation catalyst is arranged upstream of the injection module, and a reduction catalyst is arranged downstream of the injection module, in order to ensure optimum exhaust gas purification. In particular, the injection module is arranged in a connecting duct which connects the outlet of the oxidation catalyst with the inlet of the reduction catalyst in terms of flow in order to feed the reducing agent to the exhaust gases directly ahead of the reduction catalyst.
In one embodiment, the direction of flow of the exhaust gases is changed by the connecting duct. This allows a particularly compact structural shape of the exhaust system and brings about swirling of the exhaust gas flow. Such swirling of the exhaust gas flow results in particularly effective mixing of the exhaust gases with the reducing agent spray mist.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic sectional view of an exhaust system according to the invention.

FIG. 2 shows a schematic partially sectioned view of an injection module according to the invention.

FIG. 3a shows the collision of two primary jets which meet over their full area.

FIG. 3b shows a graphical representation of a spray mist of the kind produced by the collision shown in FIG. 3 a.

FIG. 4a shows the collision of two primary jets which meet with a slight overlap.

FIG. 4b shows a graphical representation of a spray mist of the kind produced by the collision shown in FIG. 4 a.

FIG. 5a shows the collision of two primary jets 13 which meet with a considerable but not full overlap.

FIG. 5b shows a graphical representation of a spray mist of the kind produced by the collision shown in FIG. 5 a.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic view of an internal combustion engine 2 having an exhaust system 22.
Fresh air 7 a is fed into the cylinders 2 a-2 d of the engine 2 via a compressor 1 of a turbocharger 1, 3. The exhaust gases formed during operation in the cylinders 2 a-2 d pass through a turbine 3 of the turbocharger 1, 3, which drives the compressor 1, into an oxidation catalyst 4 arranged downstream of the internal combustion engine 2.
In addition to the oxidation catalyst 4, there is a reducing agent catalyst 6. This can be designed as an SCR catalyst 6 or as a particulate filter with an SCR catalyst coating. The outlet of the oxidation catalyst 4 and the inlet of the reducing agent catalyst 6 are connected to one another in terms of flow by a connecting duct 5, with the result that the exhaust gases from the oxidation catalyst 4 flow through the connecting duct 5 into the reducing agent catalyst 6. The exhaust gases 7 b purified by the catalysts 4, 5 emerge from the reducing agent catalyst 6 into the environment.
Mounted on the connecting duct 5 is an injection module 10 according to the invention, which is supplied with a liquid reducing agent, in particular an aqueous urea solution (“AdBlue®”), by a reducing agent metering system, which is conventional and is therefore not shown in detail.
During operation, the injection module 10 produces a reducing agent spray mist 11 in the connecting duct 5 between the oxidation catalyst 4 and the reducing agent catalyst 6.
To prevent the reducing agent spray mist 11 being forced against the wall 24 of the connecting duct 5 situated opposite the oxidation catalyst 4 by the exhaust gas flow emerging from the oxidation catalyst 4 (said wall being shown on the right in FIG. 1) and to prevent unwanted reducing agent deposits forming there, a shielding plate 20 is arranged in front of the wall 24, in particular between the injection module 10 and the wall 24. The shielding plate 20 is narrower than the connecting duct 5, with the result that some of the exhaust gas flow emerging from the oxidation catalyst 4 flows to the side of the shielding plate 20 (at the top in the illustration in FIG. 1) into a buildup chamber 15 formed between the wall 24 of the connecting duct 5 and the shielding plate 20 and produces an excess pressure (“backpressure”) there.
The exhaust gases flow out of the buildup chamber 15 through openings 16 formed in the shielding plate 20 into a region on the side of the shielding plate 20 facing the oxidation catalyst 4, where they mix with the reducing agent spray mist 11. The exhaust gas flow from the buildup chamber 15 into the region of the spray mist 11 through the openings 16 is symbolized by exhaust gas flow arrows 7 c. In particular, the shielding plate 20 can be embodied as a low-cost perforated plate.
An additional baffle plate 17 can be mounted upstream, adjacent to the injection module 10, in order to prevent dispersal of the reducing agent spray mist 11 at the collision point P of the primary jets and thus to guarantee reliable spray mist production.
FIG. 2 shows the end of the injection module 10 facing the connecting duct 5 in an enlarged partially sectioned representation. The injection module 10 shown in FIG. 2 has two outlet openings 12 for the reducing agent, through each of which a reducing agent primary jet 13 emerges during operation. Further illustrative embodiments of injection modules 10 according to the invention, which are not shown in the figures, can have additional outlet openings 12.
The primary jets 13 emerging from the outlet openings 12 collide within the connecting duct 5 (not shown in FIG. 2) in the region in front of the injection module 10. Owing to the respective momentum of the primary jets 13, a finely atomized reducing agent spray mist 11 is produced in the connecting duct by the collision in accordance with the “collision beam principle”. The reducing agent spray mist 11 produced in this way covers the full area and is flat.
The distance d between the outlet openings 12 is less than 5 mm, in particular less than 2 mm. Owing to the short distance d between the outlet openings 12, the primary jets 13 in the region between the outlet openings 12 and the collision point P of the two primary jets 13 are compact jets, which have not yet separated into individual droplets; the meeting of compact primary jets 13 optimizes the collision since each part of a first primary jet 13 meets a corresponding part of a second primary jet 13 and there are no gaps in the primary jets 13 in which no collision occurs.
The outlet openings 12 preferably have a circular cross section since the jet diameter and the outlet angle of the primary jet 13 are precisely defined in the case of a circular cross section. However, the outlet openings 12 can also be formed with an oval cross section.
There can also be further outlet openings 12 (not shown in FIG. 2) in order to produce additional primary jets 13, which are preferably aligned with the same collision point P. As an alternative, there can also be a plurality of collision points P, with which in each case two primary jets 13 are aligned, with the result that there is one spray mist source in the connecting duct 5 for each collision point P.
In one embodiment, the outlet openings 12 are formed in such a way that the primary jets 13 meet at an angle a of more than 30° in order to optimize the collision between the two primary jets 13 and, in this way, to bring about optimum atomization of the primary jets 13, thereby ensuring that a particularly fine spray mist 11 is produced in the connecting duct 5 and the reducing agent mixes in a particularly effective manner with the exhaust gases in the exhaust system 22.
In one embodiment, the outlet openings 12 are formed in such a way that the primary jets 13 meet after a free path length L, i.e. after emerging from their respective outlet opening 12, of less than 10 mm, in particular of less than 5 mm. This is a reliable way of avoiding a situation where the primary jets 13 break down into individual droplets before the collision point P, which would reduce the effectiveness of spray mist production.
The collision of two primary jets 13 which meet over their full area is illustrated schematically in FIG. 3a . The spray mist 11 produced in the case of such a full-area collision of the primary jets 13 has a nonuniform mass distribution, wherein the largest proportion of the mass of the reducing agent is present in the center of the spray mist 11.
The arrows 14 show the preferential directions of flow of the droplets produced in the collision, wherein the length and thickness of the arrows 14 are proportional to the mass density in the respective directions. The mass distribution δ of the spray mist 11 is illustrated in FIG. 3a in a graphical diagram below the spray mist 11 as a function of the position x along the width of the spray mist 11.
FIG. 3b shows a schematic graphical representation of a spray mist 11 of this kind, as produced with a full-area collision of the primary jets 13. In the illustration in FIG. 3b , the density of the points is proportional to the mass density δ. Both in the graphical diagram in FIG. 3a and in the illustration in FIG. 3b , the increased mass concentration at the center of the spray mist 11 is clearly visible.
FIG. 4a shows the collision of two primary jets 13, which meet with an overlap which is considerably smaller than the respective areas of the two primary jets 13.
A spray mist 11 produced in this way also has a nonuniform mass distribution.
In the case of a slight overlap between the primary jets, the largest proportion of the mass of the reducing agent is present at the boundaries of the spray mist 11. The arrows 14 once again show the preferential directions of flow of the droplets produced in the collision, wherein the length and thickness of the arrows 14 are proportional to the mass density in the respective directions. Once again, the mass density δ of the spray mist 11 is shown below the spray mist 11 as a diagram across the width of the spray mist 11.
FIG. 4b shows a graphical representation of such a spray mist 11, wherein the density of the points is once again proportional to the mass density δ.
Both in the graphical diagram in FIG. 4a and in the illustration in FIG. 4b , the higher mass density δ at the boundaries of the spray mist 11 is clearly visible.
FIG. 5a shows the collision of two primary jets 13 which meet with a considerably greater overlap than in FIGS. 4a and 4b but not with a full overlap as shown in FIGS. 3a and 3 b.
By virtue of the greater but not complete overlap of the two primary jets 13, the mass of the reducing agent is carried uniformly both into the center of the spray mist 11 and into the boundary regions thereof. The arrows 14 show the preferential directions of flow of the droplets produced in the collision, wherein the length and thickness of the arrows 14 are proportional to the mass density δ in the respective directions of flow. The arrows 14 have substantially the same thickness and length for all directions.
Once again, the mass density δ of the spray mist 11 is shown graphically below the spray mist 11 across the width of the spray mist 11. FIG. 5b shows a graphical representation of such a spray mist 11, wherein the density of the points is proportional to the mass density δ.
The very uniform mass distribution in the spray mist 11 is clearly visible both in the graphical diagram in FIG. 5a and in the illustration in FIG. 5b , especially in a direct comparison with FIGS. 3a, 3b, 4a and 4 c.
An overlap of the primary jets 13 in a range of from 30% to 70%, in particular of from 40% to 60%, of the area of the primary jets 13 has proven particularly suitable. With overlaps in this range, a spray mist 11 with a particularly uniform mass distribution can be produced.

Claims

1-10. (canceled)

11. An injection module (10) for injecting a reducing agent into the exhaust system (22) of an internal combustion engine (2), the injection module comprising at least two outlet openings (12) for discharging at least one reducing agent primary jet (13) in each case, wherein the outlet openings (12) are formed in such a way that the reducing agent primary jets (13) emerging through the outlet openings (12) meet and produce a spray mist (11) in the exhaust system (22), wherein the outlet openings (12) are formed in such a way that the reducing agent primary jets (13) emerging through the outlet openings (12) meet with only a partial overlap, wherein the outlet openings (12) are formed in such a way that the reducing agent primary jets (13) meet after a free path length (L) of less than 10 mm.

12. The injection module (10) as claimed in claim 11, wherein the outlet openings (12) are formed in a manner offset and/or tilted relative to one another.

13. The injection module (10) as claimed in claim 11, wherein the overlap is in a range of from 30% to 70% of an area of the primary jets (13).

14. The injection module (10) as claimed in claim 13, wherein the overlap is in a range of from 40% to 60% of the area of the primary jets (13).

15. The injection module (10) as claimed in claim 11, wherein the outlet openings (12) are formed in such a way that the reducing agent primary jets (13) meet at an angle (α) of more than 30°.

16. The injection module (10) as claimed in claim 11, wherein the free path length (L) is less than 5 mm.

17. A section of an exhaust system (22) of an internal combustion engine (2) having an injection module (10) for injecting a reducing agent into the exhaust system (22) of an internal combustion engine (2), the injection module comprising at least two outlet openings (12) for discharging at least one reducing agent primary jet (13) in each case, wherein the outlet openings (12) are formed in such a way that the reducing agent primary jets (13) emerging through the outlet openings (12) meet and produce a spray mist (11) in the exhaust system (22), wherein the outlet openings (12) are formed in such a way that the reducing agent primary jets (13) emerging through the outlet openings (12) meet with only a partial overlap, wherein the outlet openings (12) are formed in such a way that the reducing agent primary jets (13) meet after a free path length (L) of less than 10 mm.

18. The section of an exhaust system (22) as claimed in claim 17, having a shielding plate (20), which is configured and arranged to prevent the spray mist (11) from striking a wall (24) of the exhaust system (22.

19. The section of an exhaust system (22) as claimed in claim 17, wherein an oxidation catalyst (4) is arranged upstream of the injection module (10), and a reduction catalyst (6) is arranged downstream of the injection module (10).

20. The section of an exhaust system (22) as claimed in claim 17, having a shielding plate (20), which is configured and arranged to prevent the spray mist (11) from striking a wall (24) of the exhaust system (22), wherein the shielding plate (20) has one or more openings (16).

21. The section of an exhaust system (22) as claimed in claim 17, wherein an oxidation catalyst (4) is arranged upstream of the injection module (10), and a reduction catalyst (6) is arranged downstream of the injection module (10), wherein the injection module (10) is arranged in a connecting duct (5) between the oxidation catalyst (4) and the reduction catalyst (6), and wherein the direction of flow of the exhaust gases is deflected by the connecting duct (5).

22. The section of an exhaust system (22) as claimed in claim 17, wherein the outlet openings (12) are formed in a manner offset and/or tilted relative to one another.

23. The section of an exhaust system (22) as claimed in claim 17, wherein the overlap is in a range of from 30% to 70% of an area of the primary jets (13).

24. The section of an exhaust system (22) as claimed in claim 23, wherein the overlap is in a range of from 40% to 60% of the area of the primary jets (13).

25. The section of an exhaust system (22) as claimed in claim 17, wherein the outlet openings (12) are formed in such a way that the reducing agent primary jets (13) meet at an angle (α) of more than 30°.

26. The section of an exhaust system (22) as claimed in claim 17, wherein the free path length (L) is less than 5 mm.

27. A method of injecting a reducing agent into the exhaust system (22) of an internal combustion engine (2), characterized in that the method comprises injecting at least two reducing agent primary jets (13) into the exhaust system (22) in such a way that the reducing agent primary jets meet with only a partial overlap in order to produce a reducing agent spray mist (11) in a region of the exhaust system (22), wherein the reducing agent primary jets (13) meet after a free path length (L) of less than 10 mm.

28. The method as claimed in claim 27, wherein the free path length (L) is less than 5 mm.