EP2687697B1 - Mixing device for the aftertreatment of exhaust gases - Google Patents

Description

The invention relates to a mixing device for the aftertreatment of exhaust gases in an exhaust system of an internal combustion engine, which comprises a housing with an inlet opening having an inlet cross section and an inner tube arranged inside the housing with a mixing area formed inside the inner tube, with a metering device for Supply of a liquid and / or a liquid-gas mixture is arranged. The inner pipe has access openings on its outer surface, through which the exhaust gases can be introduced into the mixing area. The invention further relates to a method for mixing an exhaust gas with a liquid and/or a liquid-gas mixture using such a mixing device.

The use of a hydrolysis catalytic converter to reduce nitrogen oxides in an exhaust gas stream, in particular in a motor vehicle, is generally known. As part of the selective catalytic reduction (SCR) carried out, for example, with an SCR catalytic converter, a substance with a direct reducing effect, such as ammonia or a precursor, such as an aqueous urea solution, which only releases reducing substances in the exhaust gas, is fed to the exhaust gas stream. Usually, the precursor is sprayed into the exhaust gas stream before the SCR catalytic converter.

In addition, a so-called particle filter is regularly used to minimize the emission of fine particles in a motor vehicle. The exhaust gas usually flows through the filter medium. This can lead to a "clogging" of the particle filter and consequently to an increase in the exhaust back pressure. This in turn has a negative effect on engine performance and fuel consumption of the internal combustion engine. Therefore, as a rule, a particle filter regeneration is carried out, which is carried out in particular by an active increase in the exhaust gas temperature of an exhaust gas flow, which then the particle filter is supplied, is realized. In this case, hydrocarbons are usually added to the exhaust gas flow upstream of the particle filter in order to heat the exhaust gas flow. This mixture is then fed to an HC oxidation catalytic converter, the active component of which generates a heated exhaust gas stream with the hydrocarbons through an exothermic reaction. This hot flow of exhaust gas flows to the particle filter, where the carbonaceous soot particles stored in the particle filter are converted into CO, CO2, N2 and NO, which regenerates the particle filter.

In this case, the substance to be introduced into the exhaust gas, which is usually in liquid form, is usually sprayed into the exhaust gas flow via a nozzle of a metering device. In order to achieve the highest possible degree of efficiency, a uniform distribution of the liquid introduced into the exhaust gas is of particular importance.

A mixing device of the type mentioned is for example in DE 42 03 807 A1 disclosed. Therein, an arrangement designed as a mixing device for after-treatment of exhaust gases in an exhaust system of an internal combustion engine is presented, which enables thorough mixing of exhaust gases with a urea solution before they enter a hydrolysis catalytic converter. For this purpose, a conical guide plate designed as an inner tube is arranged in a housing. The baffle has a multiplicity of bores as access openings into a mixing region formed within the baffle. A dosing device designed as a pressure atomizer nozzle is arranged on the front side of the housing, via which a urea solution is supplied as a spray into the mixing area. The exhaust gas is introduced into the housing via an inlet opening and flows through the holes in the baffle into the mixing area, where the exhaust gas is mixed with the spray. The disadvantage here, however, is that, seen in the circumferential direction, forces of different strengths act on the introduced spray as a result of the exhaust gas introduced via the bores, which leads to a deflection and thus to an asymmetrical spread of the spray. As a result, the spray is not mixed homogeneously with the urea.

the WO 2011/163395 A1 which discloses a mixing device according to the preamble of claim 1, discloses an exhaust aftertreatment device having a mixing tube and a swirling structure that swirls exhaust gas into the mixing tube. The swirling structure may have a cross section that gradually decreases along an exhaust gas flow path.

the FR 1 323 501 A discloses an apparatus for atomizing or mixing solid particles or a liquid in a gaseous carrier. The device has a vortex chamber which has a tangential inlet and an axial outlet but, apart from its outer walls, has no inner guide walls for the carrier medium. The device has a feed line, which runs axially through the vortex chamber, for the substances to be mixed with the carrier medium. The cross-section of the vortex chamber has the outline of a logarithmic spiral and the feed line ends approximately in the cross-sectional plane of the outlet opening. The device can be used as a carburetor, spray gun, burner, aerosol generator or nebulizer.

the DE 40 12 411 A1 discloses a burner that can be operated with exhaust gas from an internal combustion engine for regenerating a particle filter device in the exhaust system of an internal combustion engine. An exhaust gas supply device of the burner divides the exhaust gas into partial exhaust gas streams that are essentially the same in terms of quantity and direction, symmetrically around the circumference at least before entering a precombustion chamber of the burner. An inflow casing is helical. As a result, the exhaust gas introduced into an intermediate space via the inflow housing can be reliably divided into exhaust gas partial flows which are essentially equal in terms of quantity and direction and which are high-energy before they reach a precombustion chamber via inlet openings.

the U.S. 2003/079467 A1 and U.S. 2011/167810 A1 disclose further exhaust gas aftertreatment devices.

The invention is based on the first object of providing a mixing device which is as homogeneous as possible mixing a liquid and / or a liquid-gas mixture with the exhaust gas is ensured independently or only under the slight influence of an inflowing inflowing exhaust gas volume flow. Furthermore, the invention is based on the second object of providing a method for mixing a liquid and/or a liquid-gas mixture with the exhaust gas as homogeneously as possible.

This first object is achieved by a mixing device for the after-treatment of exhaust gases in an exhaust system of an internal combustion engine, which comprises a housing with an inlet opening having an inlet cross section and an inner tube arranged inside the housing with a mixing area formed inside the inner tube, wherein on a front side of the housing a dosing device for supplying a liquid and/or a liquid-gas mixture is arranged, and wherein the inner tube has access openings on its outer surface, through which the exhaust gases can be introduced into the mixing area. The housing has a spiral-shaped housing section, with the spiral-shaped housing section extending at least along all access openings of the inner tube.

In a first step, the invention is based on the consideration that homogeneous spreading of the spray in the mixing area is necessary for homogeneous mixing of the liquid introduced in particular in the form of a spray and/or the liquid-gas mixture introduced with the exhaust gas. In a second step, the invention is based on the consideration that for a homogeneous spread of the spray onto it, uniform flow forces must prevail in the circumferential direction around the central main flow axis of the spray. In other words, there must be uniform flow and pressure conditions in the circumferential direction. The invention therefore provides that the housing has a spiral-shaped housing section which extends at least along all of the access openings of the inner tube. The spiral shape ensures that approximately the same flow and pressure conditions prevail on the outer lateral surface along the section of the inner tube provided with access openings, so that, especially seen in the circumferential direction, a uniform supply of the exhaust gas via the Access openings takes place in the mixing area and rotationally symmetrical flow conditions can form in the mixing area.

The inlet opening of the housing serves in particular to feed exhaust gas into the housing. The main body of the inner tube is, in particular, an elongate hollow body with a circular, oval, rectangular or polygonal cross section. The mixing area is formed inside the inner tube, in which the exhaust gas is mixed with a liquid and/or a liquid-gas mixture supplied via the metering device. In particular, the liquid contains urea and/or hydrocarbons.

In particular, the spiral-shaped housing section guides the exhaust gas flowing in via the inlet opening to the inner tube and in the circumferential direction along the inner tube. The spiral shape causes a volume reduction in the circumferential direction in this housing section between the outer surface of the inner tube and the housing wall, and the spiral shape imparts a certain twist to an exhaust gas flow flowing through the spiral housing section. This spiral-shaped housing section extends at least along all access openings, that is, all access openings of the inner tube are arranged within this housing section.

The invention has the advantage that a mixing device is thereby provided which ensures the most homogeneous possible mixing of a liquid and/or a liquid-gas mixture with the exhaust gas independently of or only under the slight influence of the inflowing exhaust gas volume flow. Due to the spiral-shaped housing section running along the access openings, approximately the same flow and pressure conditions occur on the outer lateral surface, so that, particularly viewed in the circumferential direction, the exhaust gas is fed evenly via the access openings into the mixing area and rotationally symmetrical flow conditions can develop in the mixing area.

An exhaust gas flowing into the housing from the axial direction, which flows axially within the housing to the axial end facing away from the metering device, can accumulate at least temporarily in this end area of the housing, as a result of which the exhaust gas volume flow through the access openings located in this area would be greater than the exhaust gas volume flow which flows through the access openings of an area closer to the dosing device. In order to nevertheless obtain exhaust gas volume flows that are as large as possible, a passage cross section formed by the access openings advantageously decreases towards the axial end of the inner tube facing away from the metering device. The passage cross-section is the cross-sectional area that is available for the exhaust gas to enter the mixing area due to the access openings. This passage cross section can, for example, steadily decrease towards the end facing away from the dosing device. However, the passage cross-section can also decrease, in particular in certain areas, towards the end facing away from the dosing device. In other words, the passage cross section in an area close to the metering device is larger than the passage cross section in an area further away from the metering device. The individual areas are essentially the same size as one another. One area is formed by a defined peripheral area of the inner tube, this peripheral area resulting from the sum of the area of the solid material and the cross-sectional area of the access openings. This means that the ratio of the area of the solid material to the cross-sectional area of the access openings in an area close to the dosing device is smaller than the ratio of the area of the solid material to the cross-sectional area of the access openings in an area further away from the dosing device.

In order to achieve a decrease in the passage cross-section, the number of access openings expediently decreases, at least in regions, toward the axial end of the inner tube facing away from the dosing device. As a result, the decrease in the passage cross section formed by the access openings towards the axial end of the inner tube facing away from the dosing device can be implemented in a relatively simple manner. This ensures that the exhaust gas flowing into the inner tube is as homogeneous as possible along the entire section of the inner tube provided with access openings in the mixing area, particularly with exhaust gas flowing into the housing from the axial direction flows. For this purpose, the distance between two adjacent access openings increases in the axial direction and/or in the circumferential direction toward the axial end of the inner tube facing away from the dosing device. The number of access openings can steadily decrease towards the end facing away from the dosing device. However, the number of access openings can also decrease in areas towards the end facing away from the dosing device. In other words, the number of access openings in an area remote from the metering device is smaller than the number of access openings in an area closer to the metering device.

In order to realize a decrease in the passage cross-section, the cross-sectional area of the access openings advantageously decreases at least in regions towards the axial end facing away from the dosing device. The cross-sectional area of the individual access openings can decrease steadily towards the end facing away from the dosing device. However, the cross-sectional area of the individual access openings can also decrease in some areas towards the end facing away from the dosing device. This means that the cross-sectional area of the individual access openings in an area remote from the dosing device is smaller than the cross-sectional area of the individual access openings in an area closer to the dosing device.

In an advantageous embodiment, an exhaust gas inlet pipe extends at least partially into the housing, with the longitudinal center axis of the exhaust gas inlet pipe and the longitudinal center axis of the inner pipe being aligned essentially parallel to one another. The exhaust gas can be supplied in a targeted manner to a specific area within the housing via such an exhaust gas inlet pipe. In this case, the exhaust gas inlet pipe extends over the inlet opening into the housing, which means that the exhaust gas inlet pipe is led through the inlet opening into the housing. In this case, the exhaust gas inlet pipe is designed in particular in the form of a circular cylinder or a cone. In the case of a circular inlet opening, the outside diameter of the exhaust gas inlet pipe in the area of the inlet opening essentially corresponds to the diameter of the inlet opening.

Advantageously, the exhaust gas inlet pipe extends within the housing at least along the spiral housing section, the Exhaust gas inlet pipe has outlet openings on the circumferential surface extending along the spiral-shaped housing section. An exhaust gas flow supplied to the exhaust gas inlet pipe can flow through these outlet openings, in particular into the spiral-shaped housing section. The outlet openings are in particular arranged over the entire circumference on the peripheral surface of the exhaust gas inlet pipe and have, for example, a circular or slit-shaped geometry. As a result, an exhaust gas flow fed in particular from an axial direction to the exhaust gas inlet pipe can be “deflected” into a radial direction when exiting the exhaust gas inlet pipe through the outlet openings, or it can be given at least a radial velocity component. Furthermore, this contributes to the fact that the exhaust gas flows as homogeneously as possible into the spiral-shaped housing section along the entire section of the exhaust gas inlet pipe provided with outlet openings.

Since the exhaust gas flowing into the exhaust gas inlet pipe can accumulate at least temporarily at the axial end of the exhaust gas inlet pipe facing away from the inlet opening, and the exhaust gas volume flow from the outlet openings located in this area can therefore be greater than the exhaust gas volume flow from the outlet openings in an area closer to the inlet opening, the number of outlet openings preferably decreases at least in regions towards the axial end of the exhaust gas inlet pipe facing away from the inlet opening. What is thereby achieved is that the exhaust gas flowing into the exhaust gas inlet pipe flows as homogeneously as possible into the spiral-shaped housing section along the entire section of the exhaust gas inlet pipe provided with outlet openings. For this purpose, the distance between two adjacent outlet openings increases in the axial direction and/or in the circumferential direction towards the axial end of the exhaust gas inlet pipe facing away from the inlet opening. The number of outlet openings can steadily decrease towards the end facing away from the inlet opening. However, the number of outlet openings can also decrease in some areas towards the end facing away from the inlet opening. In other words, the number of outlet openings in an area remote from the metering device is smaller than the number of inlet openings in an area closer to the metering device. The individual areas are essentially the same size as each other. An area is formed by a defined peripheral surface of the exhaust gas inlet pipe, wherein this peripheral area results from the sum of the area of the solid material and the cross-sectional area of the outlet openings. This means that the ratio of the area of the solid material to the cross-sectional area of the outlet openings in an area close to the metering device is smaller than the ratio of the area of the solid material to the cross-sectional area of the outlet openings in an area further away from the metering device.

Alternatively or cumulatively to the decrease in the number of outlet openings, the cross-sectional area of the individual outlet openings preferably decreases steadily towards the end remote from the dosing device. However, the cross-sectional area of the individual outlet openings can also decrease in some areas towards the end facing away from the dosing device. This means that the cross-sectional area of the individual outlet openings in an area remote from the metering device is smaller than the cross-sectional area of the individual outlet openings in an area closer to the metering device.

The inner tube is expediently designed in the shape of a circular cylinder or cone. Depending on the dosing device used and the spread of the liquid and/or the liquid-gas mixture associated therewith, these shapes also have a positive effect on a homogeneous spread of the liquid and/or the liquid-gas mixture in the mixing area. In the case of a cone-shaped inner tube, the diameter of the inner tube widens towards the end facing away from the dosing device.

The access openings are advantageously provided with exhaust gas guide elements which protrude from the main extension of the lateral surface. These exhaust-gas guide elements are used in particular to guide the flow of the exhaust gas and also to prevent the liquid and/or the liquid-gas mixture from escaping from the mixing area. Furthermore, the exhaust gas streams flowing through the access openings are imparted with a swirl by the exhaust gas guiding elements and/or the swirl movement generated by the spiral-shaped housing section is reinforced. The geometry of the exhaust gas guiding elements must be selected in accordance with the respective individual case and in particular depends on the propagation characteristics of the liquid introduced and/or the introduced liquid-gas mixture in the mixing area and the occurring exhaust gas volume flows.

In this case, the exhaust gas guide elements expediently extend at least into the mixing area. In addition, an exhaust gas guide element can also be provided at an access opening, which extends into the intermediate space between the lateral surface of the inner pipe and the housing wall. Preferably, the exhaust gas guide element or both exhaust gas guide elements are shaped in such a way that, seen from the longitudinal center axis of the inner pipe radially outwards, they opaquely "close" the access opening, i.e. that an (imaginary) jet going radially outwards from the longitudinal center axis and perpendicular to it can penetrate the access opening as much as possible.

Advantageously, the exhaust gas guide elements are formed in one piece on the lateral surface of the inner pipe. This enables simple and inexpensive production.

In an advantageous embodiment, the projection of an opening axis of the exhaust gas guide element onto a central longitudinal plane of the inner pipe running through the access opening of the exhaust gas guide element closes an angle of inclination of 5° to 90°, preferably from 30° to 50°, particularly preferably from 35° to the longitudinal central axis of the inner pipe 40° in. When the exhaust gas guide elements are inclined at such an angle, the liquid and/or the liquid-gas mixture can be particularly effectively prevented from escaping from the mixing area. In this case, the central longitudinal plane runs on the one hand through the center point of the respective access opening and on the other hand through the longitudinal central axis of the inner tube and extends along this longitudinal central axis. In other words, the angle of inclination is the angle by which the exhaust gas guide element protrudes from the base lateral surface of the inner pipe, ie from the lateral surface without taking the exhaust gas guide elements into account.

Expediently, an opening axis of the exhaust gas guide element encloses an orientation angle of 0° to 90°, preferably 10° to 90°, particularly preferably 20° to 90°, with a central longitudinal plane of the inner pipe running through the access opening of the exhaust gas guide element. Here, the median longitudinal plane runs to one through the center of the respective access opening and the other through the longitudinal center axis of the inner tube and extends along this longitudinal center axis. In other words, the orientation angle indicates that angle by which the access opening is "twisted out" from a course aligned in the direction of the longitudinal central axis of the inner tube. If the exhaust-gas guide elements are aligned at an angle of less than 90°, the exhaust-gas guide elements cause a partial deflection of the partial exhaust-gas flow toward the main injection direction. This ensures in particular that the exhaust gas flowing in from the spiral-shaped housing section is deflected through the access openings and the exhaust gas guide elements arranged thereon into partial exhaust gas flows, which have a certain velocity component running in the main injection direction of the metering device, which in turn leads to a homogeneous mixing of the liquid and/or the liquid Gas mixture with the exhaust gas contributes.

In an expedient embodiment, the dosing device is arranged coaxially to the longitudinal central axis of the inner tube. This enables dosing in the middle into the mixing area, which has a further positive effect on the even spread of the liquid and/or the liquid-gas mixture and thus on the homogeneous mixing with the exhaust gas.

The passage cross section formed by the access openings advantageously corresponds to 80% to 300% of the entry cross section of the entry opening, preferably 90% to 250%. Such a ratio of inlet cross section to passage cross section also has a positive effect on the homogeneous inflow of the exhaust gas into the mixing area.

In addition to the access openings, the lateral surface of the inner tube preferably has an at least partially circumferential annular gap, particularly in the area of an axial end of the spiral-shaped housing section, which serves as a kind of "bypass" for the exhaust gas. In this case, a guide element can optionally be arranged in the region of the annular gap, which guide element causes a partial flow of exhaust gas flowing through the annular gap to be deflected at least partially in the main injection direction of the metering device.

The inner tube is preferably arranged in the spiral-shaped housing section in such a way that in the circumferential direction between the inner tube and the housing wall there is always a distance dependent on the progression of the spiral shape. As a result, there is always an intermediate space between the inner tube and the housing wall, seen in the circumferential direction, and no “dead end” is formed at which the inflowing exhaust gas would accumulate. This further contributes positively to a homogeneous flow pattern through the spiral-shaped housing section.

The second object is achieved by a method for mixing an exhaust gas with a liquid and/or a liquid-gas mixture using a mixing device as described above.

This method enables a liquid and/or a liquid-gas mixture to be mixed with the exhaust gas as homogeneously as possible independently or only with a slight influence of the inflowing exhaust gas volume flow. Because the exhaust gas flows in via a spiral-shaped housing section running along the access openings of the inner pipe, approximately the same flow and pressure conditions occur on the outer lateral surface of the inner pipe, so that, especially viewed in the circumferential direction, the exhaust gas is fed evenly via the access openings into the Mixing area takes place and rotationally symmetrical flow conditions can form in the mixing area.

• Fig. 1 in einer schematischen Darstellung eine Mischvorrichtung,
• Fig. 2 in einer schematischen Längsschnittdarstellung gemäß Schnittlinie A-A die Mischvorrichtung aus Fig. 1,
• Fig. 3 in einer schematischen Querschnittdarstellung gemäß Schnittlinie B-B die Mischvorrichtung aus Fig. 2,
• Fig. 4 in einer schematischen Darstellung einen spiralförmigen Gehäuseabschnitt einer alternativen Ausführungsform,
• Fig. 5 in einer schematischen Darstellung ein Innenrohr in einer weiteren Ausführungsform,
• Fig. 6 in einer schematischen Längsschnittdarstellung gemäß Schnittlinie E-E einen vergrößerten Ausschnitt des Innenrohrs aus Fig. 5,
• Fig. 7 in einer schematischen Längsschnittdarstellung verschiedene Ausführungsformen eines Abgasleitelements,
• Fig. 8 in einer schematischen Längsschnittdarstellung eine Mischvorrichtung in einer alternativen Ausführungsform,
• Fig. 9a - 9c in schematischen Längsschnittdarstellungen eines vergrößerten Ausschnitts C verschiedene Ausführungsformen eines Leitelements und eines Innenrohrs aus Fig. 8.

Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. Show in it:

• 1 a schematic representation of a mixing device,
• 2 the mixing device in a schematic longitudinal sectional view according to section line AA 1 ,
• 3 the mixing device in a schematic cross-sectional representation according to section line BB 2 ,
• 4 in a schematic representation, a spiral housing section of an alternative embodiment,
• figure 5 in a schematic representation of an inner tube in a further embodiment,
• 6 shows an enlarged detail of the inner tube in a schematic longitudinal sectional representation according to section line EE figure 5 ,
• 7 in a schematic longitudinal sectional view, various embodiments of an exhaust gas guiding element,
• 8 in a schematic longitudinal sectional view, a mixing device in an alternative embodiment,
• Figures 9a - 9c in schematic longitudinal sectional representations of an enlarged section C, various embodiments of a guide element and an inner tube 8 .

In 1 is shown in a schematic representation of a mixing device 2 for after-treatment of exhaust gases in an exhaust system of an internal combustion engine. In this case, the mixing device 2 is upstream of an SCR catalytic converter in terms of flow technology. The mixing device 2 comprises a housing 4 and a circular-cylindrical inner tube 6 arranged inside the housing 4. Inside the inner tube 6, a mixing region 8 is formed.

2 shows the mixing device 2 in a schematic longitudinal sectional view according to section line AA 1 . Here again the inner tube 6 arranged in the housing 4 with the mixing area 8 formed in its interior can be seen. A dosing device 10 is attached to an end face of the housing 4 coaxially to the longitudinal center axis of the inner tube 6 . The metering device 10 serves to feed a liquid-gas mixture into the mixing area 8 via a nozzle 12 in the form of a spray 14. The liquid is a urea solution.

The inner tube 6 has access openings 18 on its outer surface 16 through which exhaust gases can be introduced into the mixing area 8 . The access openings 18 are provided with exhaust gas guide elements 20 which protrude from the main extent of the lateral surface 16 . These exhaust gas guide elements 20 are used in particular to guide the flow of the exhaust gas and also to prevent the spray 14 from escaping from the mixing area 8. The exhaust gas guide elements 20 integrally formed on the lateral surface 16 of the inner tube 6, which enables simple and inexpensive production.

The number of access openings 18 decreases steadily towards the axial end of the inner tube 6 facing away from the dosing device 10 . For this purpose, the distance between two adjacent access openings 18 increases in the axial direction and in the circumferential direction towards the axial end of the inner tube 6 facing away from the dosing device 10 . As a result, the passage cross section formed by the access openings 18 decreases towards the axial end of the inner tube 6 facing away from the dosing device 10 . Next is in 2 to see that the access openings 18 are "twisted out" about a course aligned in the direction of the longitudinal central axis of the inner tube 6 .

Furthermore, the housing 4 includes a spiral housing section 20 which extends along all access openings 18 of the inner tube 6, that is, all access openings 18 of the inner tube 6 are arranged within this spiral housing section 20.

An exhaust gas inlet pipe 26 embodied in the shape of a circular cylinder extends into the housing 4 via an inlet opening 24 . For this purpose, the outer diameter of the exhaust gas inlet pipe 26 essentially corresponds to the diameter of the inlet opening 24. The central longitudinal axis of the exhaust gas inlet pipe 26 and the central longitudinal axis of the inner pipe 6 are aligned parallel to one another and the exhaust gas inlet pipe 26 extends axially along the entire spiral-shaped housing section 22. Along the spiral-shaped housing section 22 points the exhaust gas inlet pipe 26 also has outlet openings 28 . The outlet openings 28 are arranged all around on the peripheral surface 30 of the exhaust gas inlet pipe 26 and have a circular geometry.

During operation, an inflow of exhaust gas 32 supplied to the mixing device 2 first flows via the exhaust gas inlet pipe 26 in the direction of the housing 4 and, in the process, flows through the outlet openings 28 into the spiral-shaped housing section 22. The inflow of exhaust gas 32 therefore flows through the outlet openings as it exits the exhaust gas inlet pipe 26 28 is "deflected" from an axial direction into a radial direction or at least one radial velocity component is imparted to it. Furthermore, the exhaust gas inflow 32 is fed relatively homogeneously to the spiral-shaped housing section 22 along the entire section of the exhaust gas inlet pipe 26 provided with outlet openings 28 .

The fact that the spiral-shaped housing section 22 extends along all outlet openings 28 and in particular along all access openings 18 ensures that approximately the same flow and pressure conditions prevail on the lateral surface 16 of the inner pipe 6 along the section provided with access openings 18. This results in a uniform supply of partial exhaust gas flows via the access openings 18 into the mixing area 8 , particularly viewed in the circumferential direction, and rotationally symmetrical flow conditions can develop in the mixing area 8 . This allows the spray 14 to spread homogeneously in the mixing region 8, since there are approximately uniform flow and pressure conditions, particularly in the circumferential direction around the central main flow axis of the spray 14, which essentially corresponds to the longitudinal center axis of the inner tube 6 in such an arrangement. This ensures homogeneous mixing of the spray 14 with the exhaust gas supplied via the access openings 18 in the form of partial exhaust gas streams.

Since the exhaust gas inflow 32 flowing from the axial direction into the exhaust gas inlet pipe 26, which flows axially to the axial end facing away from the metering device 10, can accumulate at least temporarily in this end region of the exhaust gas inlet pipe 26, the exhaust gas volume flow that flows through the outlet openings 28, which are located in this area, at least at times greater than the exhaust gas volume flow which flows through the outlet openings 28 of an area closer to the metering device.

The steady decrease in the number of access openings 18 towards the axial end of the inner pipe 6 facing away from the metering device 10 nevertheless ensures that the exhaust gas flowing into the inner pipe 6, also axially along the entire section provided with access openings 18, is extremely homogeneous in the mixing area 8 flows. This has a further positive effect on even flow and pressure conditions in the mixing area 8 and thus on the homogeneous mixing of the spray 14 with the exhaust gas.

Furthermore, the illustrated alignment of the access openings 18 and thus in particular of the respective exhaust gas guiding elements 20 causes a partial deflection of the partial exhaust gas streams flowing through the access openings 18 towards the main injection direction of the spray 14 . The partial exhaust gas streams that are deflected in particular in the area close to the metering device thus receive a certain velocity component running in the main injection direction of the metering device 10 . This also contributes to homogeneous mixing of the spray 14 with the exhaust gas, since there is little or no deflection of the spray 14, particularly in the area close to the dosing device.

A homogeneously mixed spray/exhaust gas mixture thus flows in the axial direction from the inner pipe 6 and finally from the housing 4 to the SCR catalytic converter.

3 shows the mixing device in a schematic cross-sectional representation according to section line BB 2 . The arrangement of the inner tube 6 in the spiral-shaped housing section 22 can be seen here in particular. Due to the reduction in volume of the intermediate space between the inner pipe 6 and the housing wall caused by the spiral shape in the circumferential direction, this contributes to the pressure and flow conditions being approximately the same along the circumference on the outer lateral surface 8 of the inner pipe 6, which means that the exhaust gas is fed as evenly as possible into the mixing area 8 can take place.

In 4 a spiral housing section 22 of an alternative embodiment is shown in a schematic representation. It can be seen here that the inner tube 6 is arranged in the spiral-shaped housing section 22 such that in the circumferential direction between the inner tube 6 and the housing wall there is always a distance s dependent on the progression of the spiral shape. As a result, there is always an intermediate space between the inner tube 6 and the housing wall, seen in the circumferential direction, and no “dead end” is formed at which inflowing exhaust gas could accumulate. This further contributes positively to a homogeneous flow pattern by the helical housing section 22. The radius of curvature of the spiral housing section 22 behaves according to the following spiral equation: $$\mathrm{right}\left(\square \right)=\left(\mathrm{D}+\mathrm{s}\right)/2+\mathrm{A}-\square /360*\mathrm{A}$$

In this equation, r is the radius of curvature, D is the diameter of the inner tube 6, s is the distance between the outer surface 8 of the inner tube 6 and the housing wall of the spiral housing 22 and A is the cross section of the inflow opening of the spiral housing.

figure 5 shows a schematic representation of an inner tube 6 in a further embodiment. Here, the access openings 18 arranged on the lateral surface 16 of the inner pipe 6 and the exhaust gas guide elements 20 formed in one piece on the access openings 18 are shown. The access openings 18 and the exhaust-gas guiding elements 20 are "twisted" out of a course aligned in the direction of the longitudinal central axis of the inner tube 6 by an alignment angle α. The orientation angle α is enclosed between an opening axis 36 of an exhaust gas guiding element 20 and a central longitudinal plane 38 of the inner pipe 6 running through the access opening 18 of the exhaust gas guiding element 20 . Here, the central longitudinal plane 38 runs on the one hand through the center point of the respective access opening 18 and on the other hand through the longitudinal central axis of the inner tube 6 and extends along this longitudinal central axis. When the exhaust gas guide elements 20 are aligned according to an orientation angle α of less than 90°, the access openings 18 and in particular the exhaust gas guide elements 20 bring about a certain deflection of the partial exhaust gas flow flowing through the access openings 18 towards the main injection direction of a metering device 10. The orientation angle α increases axially to the right , that is, axially facing away from a dosing device 10 end to. The size of the alignment angle α and in particular the increase axially to the right is particularly dependent on the metering device 10 and nozzle 12 used in the individual case, as well as on the exhaust gas volume flows that flow through the access openings 18 into the mixing area 8 of the inner tube 6.

6 shows an enlarged section of the inner tube in a schematic longitudinal sectional view along section line EE figure 5 . Here, the access openings 18 arranged on the lateral surface 16 of the inner pipe 6 and in particular the exhaust gas guide elements 20 formed in one piece on the access openings 18 can be seen. At each access opening 18, an exhaust gas guide element 20 extends into a mixing area 8 and another exhaust gas guide element 20 extends into an intermediate space between the lateral surface 16 of the inner pipe 6 and a housing wall of a housing 4 in which the inner pipe 6 is arranged. The two exhaust gas guide elements 20 of an access opening 18 are shaped in such a way that, viewed from a longitudinal center axis of the inner tube 6 , they “close” the access opening radially outwards as opaquely as possible. In this way, a discharge of a metering device 10 into a mixing area 8 formed inside the inner tube 6 is particularly effectively prevented. The exhaust gas guide elements 20 shown protrude from the base lateral surface of the inner pipe 6 at an angle of inclination β, ie from the lateral surface 8 without taking the exhaust gas guide elements 20 into account.

In 7 various embodiments of an exhaust gas guide element 20 are shown in a schematic longitudinal sectional representation, which are arranged on access openings 18 of a lateral surface 16 of an inner tube 6, which is installed in a housing 4. In V1 only one exhaust gas guide element 20 is arranged at an access opening 18 which extends into an intermediate space between the lateral surface 16 and a housing wall of the housing 4 . V2 shows an access opening 18 on which an exhaust gas guiding element 20 is arranged, which extends into a mixing area 8 formed inside an inner pipe 6 . V3 corresponds to the in 6 illustrated embodiment.

8 shows a mixing device 2 in an alternative embodiment in a schematic longitudinal section. Here, the mixing device 2 essentially corresponds to that in Figures 1 to 3 shown mixing device. In contrast to this, the distance between two axially adjacent outlet openings 28 of the exhaust gas inlet pipe 26 increases in the axial direction toward the axial end of the exhaust gas inlet pipe 26 facing away from the inlet opening 24 . Consequently, the number of outlet openings 28 increases towards the end remote from the inlet opening 24 down This ensures that the exhaust gas inflow 32 flowing into the exhaust gas inlet pipe 26 flows as homogeneously as possible into the spiral-shaped housing section 22 along the entire section of the exhaust gas inlet pipe 26 provided with outlet openings 28 .

In addition, the lateral surface 16 of the inner tube 6 has a circumferential annular gap in the area close to the metering device, which serves as a bypass channel 40 for the exhaust gas. A guide element 42 is arranged on and coaxially with the dosing device 10 and protrudes axially into the mixing area 8 of the inner tube 6 . The guide element 42 prevents the spray 14 from being acted upon by the exhaust gas partial flow passing through the bypass channel 40 in the area close to the dosing device. The guide element 42 also deflects this partial flow of exhaust gas into the axial main injection direction. For this purpose, the guide element 42 has a ring-like and preferably rotationally symmetrical design and is designed to taper in its cross section on its outer surface towards the end facing away from the dosing device 10 .

Figures 9a - 9c 12 show various embodiments of a guide element 42 and an inner tube 6 of an enlarged section C in schematic longitudinal sectional representations 8 . Here, on the one hand, the differently designed access openings 18 can be seen. On the other hand, the guide elements 42 are designed differently, in particular with regard to their axial and/or radial extent.

The axial extent of the end region 44 of the in Figure 9b shown guide element 42 selected relatively large. As a result, contact or wetting of the radially inner end region 44 of the guide element 42 facing away from the dosing device 10 can be realized with the spray 14 . Slight and/or temporary wetting of the inner wall 46 of the guide element 42 is particularly advantageous when the exhaust gas is flowing through it. Due to the fact that a small part of the spray 14 attaches itself at least temporarily to the inner wall 46 of the guide element 42, a certain liquid reservoir is realized. The dosing device 10 usually works intermittently. A “breakdown” of the liquid located on the inner wall 46 of the guide element 42 can thus be achieved during the non-injection periods. This The effect is promoted by the fact that guide element 42 has thin walls and/or is heated on the outside by the partial flow of exhaust gas flowing through bypass channel 40, so that the liquid located on the wall sections of inner wall 46 is also heated. This heat facilitates the separating effect and splitting effect (secondary break-up) of the liquid droplets lying against the guide element 42 on the inside. In other words, the mixing function of the mixing device 2 is further promoted by the targeted slight temporary wall contact of the spray 14 .

The degree of temporary adhesion of the liquid can be adjusted in a constructively simple and effective manner by the design of the axial extension of the guide element 42 and in particular its end region 44 facing away from the dosing device 10 . As a rule, the dosing device 10 and thus the spray angle and the density of the liquid are predetermined. These parameters affect the propagation properties of the spray 14 depending on the exhaust gas volume flow. If a liquid with a different density and/or a metering device 10 with a different spray angle is to be installed, it is sufficient if the mixing device 2 is adapted by changing the axial extension of the guide element 42 and in particular its end region 44 facing away from the metering device 10 in order to set the effect described above (secondary break-up). This enables a modular design and/or a retrofit system by appropriate selection of a guide element 42 of the preferred axial extent.

Reference List

2

mixing device

4

Housing

6

inner tube

8th

mixing area

10

dosing device

12

jet

14

spray

16

lateral surface

18

access opening

20

exhaust guide element

22

spiral casing section

24

entry opening

26

exhaust gas inlet pipe

28

exit port

30

peripheral surface

32

exhaust flow

34

spray gas mixture

36

opening axis

38

median longitudinal plane

40

bypass channel

42

guiding element

44

end area

46

inner wall

V1

version 1

v2

Variant 2

V3

Variant 3

a

orientation angle

β

tilt angle

s

Distance

Claims (15)

1. A mixing device (2) for the aftertreatment of exhaust gases in an exhaust system of an internal combustion engine, said mixing device comprising a housing (4) with an inlet opening (24) which has an inlet cross section, and comprising an inner pipe (6) which is arranged within the housing (4) and which has a mixing region (8) formed in the interior of the inner pipe (6), wherein on a face side of the housing (4) there is arranged a dosing device (10) for the supply of a liquid and/or of a liquid-gas mixture (14), and wherein the inner pipe (6) has, on its lateral surface (16), access openings (18) through which the exhaust gases can be introduced into the mixing region (8), characterized in that the housing (4) has a spiral-shaped housing portion (22), wherein the spiral-shaped housing portion (22) extends at least along all of the access openings (18) of the inner pipe (6).
2. The mixing device (2) according to Claim 1, characterized in that a passage cross section formed by the access openings (18) decreases in the direction of that axial end of the inner pipe (6) which faces away from the dosing device (10).
3. The mixing device (2) according to Claim 2, characterized in that the number of access openings (18) decreases at least in regions in the direction of that axial end of the inner pipe (6) which faces away from the dosing device (10).
4. The mixing device (2) according to one of the preceding claims, characterized in that the cross-sectional area of the access openings (18) decreases at least in regions in the direction of that axial end which faces away from the dosing device (10).
5. The mixing device (2) according to one of the preceding claims, characterized in that an exhaust-gas inlet pipe (26) extends at least partially into the housing (4), wherein the longitudinal central axis of the exhaust-gas inlet pipe (26) and the longitudinal central axis of the inner pipe (6) are oriented substantially parallel to one another.
6. The mixing device (2) according to Claim 5, characterized in that the exhaust-gas inlet pipe (26) extends within the housing (4) at least along the spiral-shaped housing portion (22), wherein the exhaust-gas inlet pipe (26) has outlet openings (28) on its circumferential surface (30) extending along the spiral-shaped housing portion (22).
7. The mixing device (2) according to one of the preceding claims, characterized in that the inner pipe (6) is of circular cylindrical form or conical form.
8. The mixing device (2) according to one of the preceding claims, characterized in that the access openings (18) are provided with exhaust-gas guiding elements (20) which project out of the main extent of the lateral surface (16).
9. The mixing device (2) according to Claim 8, characterized in that the exhaust-gas guiding elements (20) extend at least into the mixing region (8).
10. The mixing device (2) according to Claim 8 or 9, characterized in that the exhaust-gas guiding elements (20) are formed integrally on the lateral surface (16) of the inner pipe (6).
11. The mixing device (2) according to one of Claims 8 to 10, characterized in that the projection of an opening axis (36) of the exhaust-gas guiding element (20) onto a central longitudinal plane (38), which runs through the access opening (18) of the exhaust-gas guiding element (20), of the inner pipe (6) encloses an inclination angle (β) of 5° to 90°, preferably of 30° to 50°, particularly preferably of 35° to 40°, with the longitudinal central axis of the inner pipe (6).
12. The mixing device (2) according to one of Claims 8 to 11, characterized in that an opening axis (36) of the exhaust-gas guiding element (20) encloses an orientation angle (α) of 0° to 90°, preferably of 10° to 90°, particularly preferably of 20° to 90°, with a central longitudinal plane (38), which runs through the access opening (18) of the exhaust-gas guiding element (20), of the inner pipe (6).
13. The mixing device (2) according to one of the preceding claims, characterized in that the dosing device (10) is arranged coaxially with respect to the longitudinal central axis of the inner pipe (6).
14. The mixing device (2) according to one of the preceding claims, characterized in that the passage cross section formed by the access openings (18) amounts to 80% to 300% of the inlet cross section of the inlet opening (24), preferably 90% to 250%.
15. A method for mixing an exhaust gas with a liquid and/or with a liquid-gas mixture, using a mixing device (2) according to one of Claims 1 to 14.

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