EP3752721B1 - Exhaust aftertreatment device for dosing a liquid exhaust aftertreatment agent - Google Patents

Description

The invention relates to an exhaust gas after-treatment device for metering a liquid exhaust gas after-treatment agent into an exhaust gas stream of an internal combustion engine, with a mixing chamber in which the exhaust gas after-treatment agent is mixed with the exhaust gas stream, the mixing chamber having a circular-cylindrical mixing tube which has a funnel-shaped circumference extending towards a free end has an enlarging end section, with a funnel element that opens conically at least in sections in the direction of the mixing tube, which funnel element has a plurality of flow openings in its jacket wall, and with an injection valve that is arranged on the end of the funnel element that faces away from the mixing tube, in order to inject the exhaust gas aftertreatment agent into the funnel element .

Furthermore, the invention relates to an exhaust gas aftertreatment system with the exhaust gas aftertreatment device mentioned above.

State of the art

Exhaust gas aftertreatment devices of the type mentioned are known from the prior art. In order to comply with the increasingly strict legislation with regard to permissible emissions of pollutants in the exhaust gas of internal combustion engines in motor vehicles, it is known to use exhaust gas aftertreatment devices that ensure pollutant reduction by using an additional exhaust gas aftertreatment agent. So it is known, for example, by the so-called SCR method (SCR = Selective Catalytic Reduction) to first mix an exhaust gas with an exhaust aftertreatment agent and then to supply it to an SCR catalytic converter, in which the exhaust gas reacts together with the exhaust aftertreatment agent and pollutant emissions are reduced. An aqueous urea solution, which is injected into the exhaust gas or the exhaust pipe by means of suitable metering systems, in particular injection valves, is suitable as an exhaust aftertreatment agent. The reducing agent ammonia is obtained from the aqueous urea solution, which is fed to the exhaust gas during operation of the internal combustion engine, by means of thermolysis and hydrolysis. When processing the urea solution in the exhaust gas, there is the difficulty that, in addition to the desired chemical reaction of thermolysis, in which the ammonia is released, crystalline by-products can also arise.

From the disclosure document WO 2015/197145 A1 For example, an exhaust gas aftertreatment device of the type mentioned is known. In order to improve the mixing of exhaust gas aftertreatment agent and exhaust gas, the exhaust gas is introduced radially into a mixing chamber so that a swirl is created even before the exhaust gas and exhaust gas aftertreatment agent are mixed with one another. This improves mixture preparation. A funnel-shaped element ensures that the injected exhaust gas aftertreatment agent can initially expand over a predetermined length essentially undisturbed by the exhaust gas flow before it is mixed with the exhaust gas flow. The exhaust gas can flow into the mixing tube independently of the exhaust gas aftertreatment agent.

Other exhaust aftertreatment devices are available, for example EP 2 956 233 A1 , DE 10 2010 032 576 A1 , DE 10 2014 211 260 A1 , EP 2 884 069 A1 , DE 11 2015 001 958 T5 or EP 2 171 229 B1 already known. From the disclosure document EP 3 067 529 A1 a generic exhaust gas aftertreatment device is already known.

Disclosure of Invention

The exhaust gas aftertreatment device according to the invention with the features of claim 1 has the advantage that, despite a small installation volume, the exhaust gas and exhaust gas aftertreatment agent are optimally mixed, and crystalline by-products are avoided during operation. According to the invention, this is achieved in that the funnel element lies at least substantially within the end section coaxially to the end section, and that at least some of the through-flow openings are each assigned a flow guide element that rises from the casing wall, in particular outwards, for generating a swirl flow in the mixing tube. The funnel element lies essentially freely in the mixing chamber, but ends in a funnel-shaped, widened end section of the mixing tube, which also protrudes into the mixing chamber. The fact that the funnel element lies at least essentially inside the end section ensures that the exhaust gas flowing into the mixing tube acts on the funnel element. The exhaust gas flows at least partially through the through-flow openings through the casing wall of the funnel element in order to be mixed with the exhaust gas after-treatment agent inside the funnel element. The flow guide elements assigned to the respective through-flow openings ensure that the exhaust gas flowing in or flowing through the jacket is directed into a swirling movement, which additionally improves the mixing of the exhaust gas aftertreatment agent with the exhaust gas. Because the swirl flow is achieved by the funnel element, the swirl flow takes place independently of how the exhaust gas is fed to the exhaust gas aftertreatment device. The mixing chamber is therefore completely in the mixing tube. This makes it possible to design the exhaust gas aftertreatment device to be significantly more space-saving than was previously possible and at the same time to avoid the aforementioned disadvantages.

According to the invention, it is provided that the through-flow openings are free of flow guide elements in a region close to the injector. This means that the through-flow openings in the area close to the injector represent simple openings that do not have a swirling effect on the exhaust gas and/or the exhaust gas aftertreatment agent. Rather, the simple through openings allow that

Exhaust gas can flow into the funnel element without serious recirculation areas.

All flow openings, with the exception of the flow openings in the area close to the injector, are preferably each assigned a flow guide element. In the area away from the injection valve, the flow guide elements are thus present in order to prevent the swirl flow through the

Shell wall of the funnel element to generate flowing exhaust gas. The late generation of swirl also means that the exhaust gas aftertreatment agent spray can initially expand and atomize more or less undisturbed before it is mixed with the exhaust gas, as a result of which optimized mixing is achieved. The fact that all through-flow openings remote from the injection valve are provided with flow guide elements ensures that swirl is generated with a high degree of efficiency.

According to a preferred development of the invention, the funnel element is arranged on a cup-shaped flow element, with the flow element lying in an exhaust gas supply channel into which the free end of the mixing tube opens. The funnel element is thus held by a separate flow element, with the flow element being located in an exhaust gas supply duct and, in particular, being fastened to it. The cup-shaped element directs the air flow from the feed channel in the direction of the mixing tube. The cup-shaped configuration ensures that the injection valve is arranged particularly close to the tip of the funnel element in a simple manner. In particular, the central axes of the cup-shaped flow element and the mixing tube are aligned with one another in order to achieve an advantageous flow effect.

Provision is furthermore preferably made for the flow element to have a closed cone wall which tapers in the direction of the mixing tube. The conical design of the cup-shaped flow element optimizes the routing of the exhaust gas from the exhaust gas feed channel into the mixing tube, in that turbulence in particular is avoided at the transition from the feed channel into the mixing tube. In addition, the flow element defines an annular gap to the mixing tube or its orifice, through which the exhaust gas flowing into the mixing tube is compressed and/or accelerated, thereby further improving mixing with the exhaust gas aftertreatment agent.

According to a preferred embodiment of the invention, the flow element protrudes in some areas into the end section of the mixing tube. As a result, the formation of the annular gap and a defined guidance of the Exhaust flow guaranteed in the mixing tube. In addition, this results in a compact embodiment of the exhaust gas aftertreatment device.

Furthermore, the injection valve is preferably fastened or arranged on the flow element and/or on the funnel element in such a way that a central axis of the exhaust gas aftertreatment agent sprayed out conically and a swirl axis generated by the flow guide elements are at least essentially aligned with one another. As a result, the exhaust gas aftertreatment agent is injected into the exhaust gas particularly close to the eye of the swirl flow, resulting in advantageous mixing.

Furthermore, it is preferably provided that the flow guide elements are designed or aligned in such a way that at least part of the injected exhaust gas aftertreatment agent impinges on an inner wall of the mixing tube. The result of this is that the exhaust gas aftertreatment agent is distributed uniformly on the inside of the mixing tube wall and at least largely evaporates there during further operation of the internal combustion engine. The swirl flow increases the thermal energy input into the wall, which is used to vaporize the exhaust aftertreatment agent. The swirling flow prevents larger amounts of the exhaust aftertreatment agent from passing through the mixing tube without coming into contact with the inner wall.

According to a preferred development, the funnel element rests radially on the mixing tube. At its free end, at which the funnel element has its largest outer circumference, the funnel element thus bears radially against the inner wall of the mixing tube, which means that all of the exhaust gas has to flow through through-flow openings in the funnel element in order to get into the mixing tube. As a result, the swirl flow is adjusted in a particularly reliable manner and the advantageous mixing is ensured.

According to an alternative embodiment of the invention, it is preferably provided that an in particular annular bypass gap for the exhaust gas is present radially between the funnel element and the mixing tube. In this case, a radial distance remains between the funnel element and the mixing tube or its inner wall. This leaves the distance also at the largest outer circumference of the funnel element. Through the bypass gap, the exhaust gas can pass past the funnel element into the mixing tube without being transferred into the swirl flow. Here, for example, one advantage is that the dynamic pressure of the exhaust gas aftertreatment device on the exhaust gas is reduced. The bypass channel can extend in the form of a ring or a ring segment over the circumference of the funnel element. This leaves the possibility that the funnel element is positioned radially in the mixing tube by means of one or more webs or spacers which are arranged on its outer circumference and bear against the inner wall of the mixing tube.

Advantageously, the funnel element opens in the shape of a funnel along its entire length. The funnel element is thus configured in a funnel shape overall, so that it can be optimally adapted to the shape of the exhaust gas aftertreatment agent spray of the injection valve.

Alternatively, the funnel element is funnel-shaped only in one end area and cylindrical in an area in particular close to the injection valve, with the through-flow openings preferably being formed only in this area. In this case, too, a flow guide element, as described above, is preferably assigned to the or at least most of the through-flow openings in order to generate the hydraulic flow. The funnel-shaped end area means that the exhaust gas aftertreatment agent spray can expand to the end of the funnel section and that advantageous mixing also occurs downstream of the funnel element in the mixing tube.

Furthermore, it is preferably provided that the exhaust gas supply channel extends transversely, in particular perpendicularly, to the central axis of the mixing tube. This results in a deflection of the exhaust gas into the mixing tube, which is, for example, 90°. This ensures a compact design, with the deflection having no adverse effect on the flow behavior due to the advantageous design of the exhaust gas aftertreatment device. In particular, the exhaust gas feed channel causes an exhaust gas deflection of the exhaust gas into the mixing tube by 180° or less. As a result, particularly compact designs of the exhaust aftertreatment device can be achieved.

The flow guide elements preferably have a straight cross section and/or longitudinal section, or alternatively have a curvature in cross section and/or longitudinal section, through which the preferred swirl flow is achieved.

The exhaust gas aftertreatment system according to the invention with the features of claim 14 is characterized by the exhaust gas aftertreatment device according to the invention. This results in the advantages already mentioned.

Further advantages and preferred features and feature combinations result from what has been described above and from the claims.

The invention will be explained in more detail below with reference to the drawing.

Figur 1

ein Abgasnachbehandlungssystem in einer vereinfachten Längsschnittdarstellung,

Figur 2

eine Abgasnachbehandlungseinrichtung des Abgasnachbehandlungssystems in einer vergrößerten Schnittdarstellung,

Figuren 3A und 3B

ein erstes nicht von den Ansprüchen gedecktes Beispiel eines Trichterelements der Abgasnachbehandlungseinrichtung,

Figuren 4A und 4B

ein Ausführungsbeispiel des Trichterelements,

Figuren 5A und 5B

ein weiteres Ausführungsbeispiel des vorteilhaften Trichterelements und

Figuren 6A und 6B

ein nicht von den Ansprüchen gedecktes Beispiel des Trichterelements, jeweils in einer Seitenansicht und in einer Draufsicht.

to show

figure 1

an exhaust aftertreatment system in a simplified longitudinal sectional view,

figure 2

an exhaust aftertreatment device of the exhaust aftertreatment system in an enlarged sectional view,

Figures 3A and 3B

a first example of a funnel element of the exhaust aftertreatment device not covered by the claims,

Figures 4A and 4B

an embodiment of the funnel element,

Figures 5A and 5B

a further embodiment of the advantageous funnel element and

Figures 6A and 6B

an example of the funnel element not covered by the claims, each in a side view and in a plan view.

figure 1 shows an exhaust gas aftertreatment system 1 for an internal combustion engine of a motor vehicle in a simplified sectional view. The exhaust aftertreatment system 1 has an exhaust pipe 2 which is connected to the internal combustion engine and has an exhaust gas inlet 3 . In the exhaust pipe 2, for example, a first catalytic converter 4 and a particle filter 5 are arranged downstream of the catalytic converter 4, which treat the exhaust gas flowing into the exhaust pipe 2 in a known manner. The exhaust gas pipe 2 merges into an exhaust gas supply channel 6 for an exhaust gas aftertreatment device 7, which is described in more detail below.

figure 2 shows an enlarged sectional view of the exhaust gas aftertreatment device 7 . This has a mixing tube 8 opening into the exhaust gas supply channel 6 . An end section 9 of the mixing tube facing the exhaust gas supply channel 6 widens conically in the direction of the exhaust gas supply channel 6 . The end section 9 ends on a first side wall 10 of the exhaust gas supply duct 6. A cup-shaped flow element 12 is fastened to a side wall 11 of the exhaust gas supply duct 6, which is arranged opposite the side wall 10 in the present case penetrates completely from the side wall 11 to the side wall 10 . On the side wall 10 the flow element 12 protrudes into an orifice of the end section 9 in the side wall 10 .

The flow element 12 has an end section 13 which faces the mixing tube 8 and tapers in the direction of the mixing tube 8 . The end section 13 extends, as seen in the longitudinal extension of the flow element 12, or in the axial extension, over more than half of the entire longitudinal extension of the flow element 12 a mixing tube 8 facing bottom portion 15, which is substantially extends parallel to the side walls 10 and 11 of the exhaust gas supply channel 6. In the bottom portion 15, an opening 16 is formed centrally. A funnel element 17 is assigned to this opening 16 . According to the present exemplary embodiment, the funnel element 17 is funnel-shaped overall in such a way that, starting from the flow element 12, it widens in the direction of the mixing tube 8, with a central axis of the funnel element 17 and the mixing tube 8 being aligned with one another, at least in the end section 9. The funnel element 17 or its casing wall 19 protrudes from the flow element 12 through the entire conical end section 9 and into the mixing tube 8 . The funnel element 17 is thus located overall in the end section 9. At its free end, its maximum outer circumference corresponds essentially or almost to the inner circumference of the mixing tube 8.

The funnel element 17 has a multiplicity of flow openings 18 which are distributed uniformly in a casing wall 19 of the funnel element 17 . For reasons of clarity, only some of the flow openings 18 are provided with a reference number in the present case.

According to the present example, each through-flow opening is assigned a flow-guiding element 20, which extends radially in sections over the respective through-flow opening, so that the flow-guiding elements 20 specify a flow direction for exhaust gas flowing through the flow opening 18, which is in the circumferential direction or at least essentially in the circumferential direction of the funnel element 17 , so that a swirling flow through the funnel element 17 for the exhaust gas, which flows axially into the mixing tube 8, is generated. Because the funnel element 17 extends almost to the inner wall of the mixing tube 8 , the exhaust gas is forced to pass through the flow openings 18 or the funnel element 17 . The flow guide elements 20 ensure that the exhaust gas entering the mixing tube 8 is guided through the mixing tube 8 in a swirling flow. For this purpose, the flow guide elements 20 are all aligned in the same direction.

In addition, an injection valve 21 is arranged in the flow element 12, which is connected by a delivery device, not shown here, to a tank that provides liquid exhaust gas aftertreatment agent. By actuating the injection valve 21, the liquid exhaust gas after-treatment agent is mixed with the exhaust gas flow which penetrates into the mixing tube 8. The mixing tube 8 thus represents a mixing chamber 22. The injection valve 21 is arranged centrally on the flow element 12 in such a way that a central axis of a spray cone of the injection valve 21 is aligned with the central axis of the funnel element 17 (dash-dot line in figure 2 ). The funnel element 17 is preferably designed in such a way that the funnel opening axially facing the mixing tube is larger than the spray cone of the injection valve 21, so that wetting of the funnel element 17 with the exhaust gas aftertreatment agent is prevented.

In normal operation, the exhaust gas flows through the exhaust gas feed duct 6 in the direction of the exhaust gas aftertreatment device 7 and is conducted through the advantageous flow part 12 into the end section 9 of the mixing tube 8 . Because the flow part 12 partially projects into the mixing tube 8, an annular gap is formed through which the exhaust gas flow flows, as a result of which it is compressed and accelerated. When passing through the throughflow openings 18 of the funnel element 17, the exhaust gas flow is forced into a swirling movement and mixed with the injected exhaust gas aftertreatment agent.

The flow part 12 can be designed symmetrically or asymmetrically in order to ensure an optimal flow of exhaust gas. The external inner area of the flow part 12 is preferably designed in such a way that the injection valve 21, including the necessary insulation elements, is accommodated in the depression. In particular, the flow part 12 is formed from sheet metal.

Due to the advantageous flow element 12, the exhaust gas is supplied to the funnel element 17 particularly evenly. Optionally, a flow-evening geometry fitted upstream of the funnel element 17 can be supplemented in order to ensure that the exhaust gas is supplied to the funnel element 17 as homogeneously as possible.

The funnel element 17 is expediently fastened to the flow part 12 and optionally supported laterally or radially on the mixing tube 8 . For this purpose, radial spacer elements or spacers can be present at the end of the funnel element 17 , which bear against the inside of the mixing tube 8 . The advantageous swirl flow ensures that the introduced exhaust gas after-treatment agent is distributed evenly over the inner wall of the mixing tube 8 and from there it is largely evaporated. The swirling flow increases the thermal energy input into the mixing tube 8, which can be further used for evaporating the exhaust gas aftertreatment agent. Depending on the design of the funnel element 17 , it can also be designed in such a way that part of the exhaust gas is guided past the transition or radially between the funnel element 17 and the mixing tube 8 through an annular gap as a bypass channel 23 .

Also in the example of figure 2 Such a bypass channel 23 is formed radially between the free end of the funnel element 17 and the mixing tube 8 . As a result, for example, a dynamic pressure acting on the exhaust system is reduced.

While in the present example the exhaust gas is deflected by the exhaust system 1 by 180°, other exhaust gas feeds can also be conceivable which, for example, have a deflection of only 90° or less.

Figures 3A and 3B show the funnel element 17 according to the first example of FIG figure 2 in a side view ( Figure 3A ) and in a plan view ( Figure 3B ). It can be seen here that the flow guide elements 20 have an arched contour in order to generate an optimal swirl flow. The openings of the flow guide elements 20 are always aligned in the same direction in order to ensure a clear swirl flow.

Figures 4A and 4B show an embodiment of the funnel element 17, in a side view and in a plan view, the funnel element 17 according to this embodiment differing from the preceding one Example differs in that in an end region close to the injector, that is to say at the end with the smaller diameter, a plurality of through-flow openings 18 are formed without flow-guiding elements. As a result, the penetration of the spray from the injection valve 21 into the mixing tube 8 is initially unaffected by the exhaust gas, at least without a swirl being generated. Only after the spray has already fanned out sufficiently in the funnel element 17 is the swirl flow generated by the flow guide elements 20 in the subsequent section of the funnel element 17 remote from the injection valve and the mixing of the exhaust gas aftertreatment agent with the exhaust gas is brought about. The advantageous design also ensures that no serious recirculation areas arise in the area close to the metering point, which could act to promote deposits with regard to crystalline by-products.

Figures 5A and 5B show another embodiment of the funnel element 17, which differs from the embodiment of FIG Figures 4A and 4B differs in that the flow guide elements 20 are not formed in the shape of an archway, but each have a straight contour in cross section and longitudinal section, that is to say are formed in the shape of a plate. This enables the funnel element 17 to be realized in a particularly cost-effective manner. Also in the embodiment of Figure 3A and 3B the flow guide elements 20 can be plate-shaped. The flow guiding elements 20 are preferably designed as outwardly bent air guiding tongues of the jacket wall 19 .

The example of the funnel element 17 shown in FIGS Figures 6A and 6B shown in a side view and a top view, differs from the previous exemplary embodiment and the examples not covered by the claims in that the funnel-shaped section of the funnel element 17 is axially particularly short. Otherwise, the funnel element 17 is designed in the shape of a circular cylinder. The through-flow openings 18 with the flow-guiding elements 20 are arranged/designed in the circular-cylindrical section. In this way, too, an advantageous mixing of exhaust gas and exhaust gas after-treatment agent and the avoidance of crystal formation is achieved.

Claims (14)

1. Exhaust-gas aftertreatment device (7) for the dosed injection of a liquid exhaust-gas aftertreatment agent into an exhaust-gas stream of an internal combustion engine, having a mixing chamber (22) in which the exhaust-gas aftertreatment agent is mixed with the exhaust-gas stream, wherein the mixing chamber (22) has a circular cylindrical mixing pipe (8) which has a funnel-shaped end section (9) which increases in circumference toward a free end, with a funnel element (17) which opens conically at least in certain sections in the direction of the mixing pipe (8) and which has multiple throughflow openings (18) in its shell wall (19), and wherein, on that end of the funnel element (17) which is averted from the mixing pipe (8), there is arranged an injection valve (21) for the exhaust-gas aftertreatment agent for the purposes of injecting the exhaust-gas aftertreatment agent into the funnel element (17), wherein the funnel element (17) is situated at least substantially within the end section (9) and coaxially with respect to the end section, and that at least some of the throughflow openings (18) are assigned a respective flow-guiding element (20), which is elevated from the shell wall (19), for generating a swirling flow in the mixing pipe (8), characterized in that the throughflow openings (18) in a region close to the injection valve have no flow-guiding element.
2. Exhaust-gas aftertreatment device according to Claim 1, characterized in that all throughflow openings (18) with the exception of the throughflow openings (18) in the region close to the injection valve, or all throughflow openings (18), are assigned a respective flow-guiding element (20).
3. Exhaust-gas aftertreatment device according to any one of the preceding claims, characterized in that the funnel element (17) is arranged on a cup-shaped flow element (12) which is situated in an exhaust-gas feed channel (6) in which the free end of the mixing pipe (8) opens out.
4. Exhaust-gas aftertreatment device according to Claim 3, characterized in that the flow element (12) has a conical wall (14) which narrows in the direction of the mixing pipe (8) and which is of closed form.
5. Exhaust-gas aftertreatment device according to either of Claims 3 and 4, characterized in that the flow element (12) projects in certain regions into the end section (9) of the mixing pipe (8).
6. Exhaust-gas aftertreatment device according to any one of Claims 3 to 5, characterized in that the injection valve (21) is fastened or arranged on the flow element (12) and/or on the funnel element (17) such that a central axis of the conically discharged exhaust-gas aftertreatment agent and a swirl axis generated by the flow-guiding elements (20) are at least substantially aligned with one another.
7. Exhaust-gas aftertreatment device according to any one of the preceding claims, characterized in that the flow-guiding elements (20) are configured or oriented such that at least a proportion of the injected exhaust-gas aftertreatment agent impinges on an inner wall of the mixing pipe (8).
8. Exhaust-gas aftertreatment device according to any one of the preceding claims, characterized in that the funnel element (17) lies radially against the mixing pipe (8) .
9. Exhaust-gas aftertreatment device according to any one of the preceding claims, characterized in that an in particular ring-shaped bypass channel (23) for the exhaust gas is present radially between the funnel element (17) and the mixing pipe (8).
10. Exhaust-gas aftertreatment device according to any one of the preceding claims, characterized in that the funnel element (17) opens in a funnel shape along its entire longitudinal extent.
11. Exhaust-gas aftertreatment device according to any one of Claims 1 to 9, characterized in that the funnel element (17) opens in a funnel-shaped only in an end region, and in that the throughflow openings (18) are formed only in a cylindrical region of the funnel element (17) .
12. Exhaust-gas aftertreatment device according to any one of the preceding claims, characterized in that the exhaust-gas feed channel (6) extends transversely, in particular perpendicularly, with respect to the central axis of the mixing pipe (8).
13. Exhaust-gas aftertreatment device according to any one of the preceding claims, characterized in that the exhaust-gas feed channel (6) causes a diversion of exhaust gas into the mixing pipe (8) through 180° or less.
14. Exhaust-gas aftertreatment system (1) for reducing pollutant emissions in the exhaust gas of an internal combustion engine of a motor vehicle, having an exhaust-gas treatment device (7) according to any one of Claims 1 to 13.

Images