DE102014223382A1 - Method for operating a device for aftertreatment of the exhaust gases of an internal combustion engine and corresponding device - Google Patents

Abstract

The invention relates to a method for operating a device for the aftertreatment of the exhaust gases of an internal combustion engine, comprising a mixing tube 7 leading an exhaust gas stream and a reducing agent upstream of a post-treatment device into the mixing tube 7, a metering injector 11, and wherein the device comprises an exhaust gas mixing device. According to the invention, a method for operating a device for the aftertreatment of the exhaust gas of an internal combustion engine is specified, which operates more effectively than known methods in a simple construction of the device. This is achieved in that the exhaust gas mixing device causes a twisting of the exhaust stream 10, and that the reducing agent from the injector 11 is metered into the mixing tube 7 in an injector jet axis so that an exhaust gas flow is adjusted around the injector jet axis and into the mixing tube 7, and , This combination of method steps according to the invention enables effective operation of the exhaust gas aftertreatment device in a robust operation of the overall system.

Description

The invention relates to a method for operating a device for the aftertreatment of the exhaust gases of an internal combustion engine, comprising a mixing tube leading an exhaust gas stream and an injector metering a reducing agent upstream of an aftertreatment device into the mixing tube, and wherein the device comprises an exhaust gas mixing device. Furthermore, the invention relates to a corresponding device for the aftertreatment of the exhaust gases of an internal combustion engine.

The invention relates to the technical field of aftertreatment of the exhaust gases of an internal combustion engine. When burning fuel while supplying combustion air in an internal combustion engine, exhaust gas is produced which must be cleaned before leaving the exhaust gas line in order to comply with the environmental compatibility requirements of the internal combustion engine, for example designed as a self-igniting internal combustion engine and powered by diesel fuel. In this segment, a system is known in which a reducing agent is introduced into the exhaust gas, which causes desired chemical reactions in a subsequent catalyst.

State of the art

Such a device is known from DE 100 60 808 A1 known. This device has an SCR catalyst for selective catalytic reduction, which is installed in an exhaust pipe of an internal combustion engine. In order to perform this selective catalytic reduction, a reducing agent is introduced into the exhaust gas upstream of the SCR catalyst. In order to achieve a thorough mixing of the reducing agent with the exhaust gas flow, an exhaust gas mixing device is installed further upstream of the injector for introducing the reducing agent into the exhaust gas line, which is installed in a separate housing. The exhaust gas mixing device has guide vanes, which deflect the exhaust gas from the main flow direction and cause a mixing of a flowing gas with the introduced behind the exhaust gas mixing device in the exhaust pipe reducing agent.

Another device and another method for operating such a device is known from WO 2011/073240 A1 known. In this device, the exhaust pipe has a front end into which the injector is installed. At the side of the injector supply pipes for the exhaust gas open into the exhaust pipe.

The invention has for its object to provide a method for operating a device for the aftertreatment of exhaust gas of an internal combustion engine, which is more effective than known methods with a simple construction of the device. Furthermore, a corresponding device should be specified.

Disclosure of the invention

This object is achieved in that the exhaust gas mixing device causes a twisting of the exhaust gas flow, and that the reducing agent is metered by the injector in an injection beam axis into the mixing tube so that a homogeneous exhaust gas flow is adjusted around the injector jet axis and into the mixing tube. Homogeneous in this context means that the exhaust gas enters uniformly in the mixing tube and not, as is customary in classical arch dosing, operating point dependent pressed against the wall of the mixing tube. This homogeneity prevents the area load of reducing agent when striking the wall of the mixing tube is significantly minimized. As a result, this combination of method steps according to the invention enables effective operation of the exhaust gas aftertreatment device in a robust operation of the overall system. With the corresponding method and the corresponding device, moreover, a system which is robust compared to a possible deposit formation is created, which furthermore is distinguished by a high uniform distribution over a wide characteristic field range.

In a development of the invention, the injector jet axis coincides with the swirl center axis. Here, the term "coincide" means that the injector beam axis at least largely follows the swirl center axis. For concrete embodiment, further features are mentioned in subsequent dependent claims, as can be advantageously achieved in detail with possibly different conditions. In the implementation of this feature of the method, therefore, tolerable small deviations between the injector jet axis and the swirl center axis can occur, but even with small deviations the area load of reducing agent upon impact with the wall of the mixing tube is significantly minimized. As a result, the reducing agent spreads centrically in the mixing tube. This ensures a safer operation in a wide map range. In addition, a formation of deposits of the reducing agent on the walls of the mixing tube is thereby at least largely prevented.

In a further embodiment of the invention, the injector is completely surrounded by the exhaust gas stream and the exhaust gas stream, together with the metered reducing agent, enters the mixing tube. This represents a basic requirement for robust operation.

In a further embodiment of the invention, the twisting of the exhaust gas flow takes place before the metering of the reducing agent. Such a twisting of the exhaust gas flow before the metering of the reducing agent is preferably effected by turbine blades. Alternatively, however, a twisting of the exhaust gas stream can take place after the metering of the reducing agent. This twisting of the exhaust gas stream is preferably effected by a mixer.

The apparatus configured according to the method provides that the exhaust gas mixing device is a swirl generating device for swirling the exhaust gas flow about a swirl center axis, that the injector is arranged on the input side of the mixing tube, and that the device comprises means for generating an exhaust gas flow around an injector jet axis and into the mixing tube has in it. The exhaust gas flow is preferably a homogeneous exhaust gas flow in accordance with the previously defined definition of "homogeneous". This combination of features describes an exhaust system that is robust relative to a deposit formation and that includes a device that is characterized by a high degree of uniform distribution over a wide map range.

In a further development of the invention, the injector is arranged and fastened to an end wall of a cup-shaped deflection device. This represents a simple mounting option for the injector, with which in addition the following described different orientations of the injector with respect to a mixing tube center axis and a swirl center axis is easy to implement.

In a further embodiment, the injector jet axis, the swirl center axis and the mixing tube center axis are arranged coincidentally. In this case, the injector projects centrally into the swirl generating device with the turbine blades and the mixing tube center axis z of the mixing tube is at the same time the swirl center axis of the swirl generated by the swirl device. The injector sprays the reducing agent in the injector jet axis exactly in the direction of the mixing tube center axis z and thus also of the swirl center axis. This is the ideal embodiment in which the exhaust gas enters the mixing tube homogeneously and in which the injector jet of the injector propagates through the mixing tube along the swirl center axis located in the mixing tube center. Incidentally, the injector jet can also be divided into a number of partial beams, which are arranged distributed around the central axis of the injector jet.

In a further embodiment, the swirl center axis is inclined by an angle γ to the mixing tube center axis z and the injector beam axis is inclined by an inclination angle α to the mixing tube central axis and 0 <α <γ. At the same time, the mixing tube center axis z 'coincides with an axis z which lies parallel to a center axis of a particle filter and an SCR catalytic converter and is arranged perpendicular to the end wall of the cup-shaped deflection device. Here, the injector is arranged eccentrically or centrally on the end wall, but in particular by an angle α inclined to the mixing tube center axis z arranged. In this embodiment, the fact is taken into account that the swirl center axis is not equal to the mixing tube center axis z when the injector is unequally flowed around by the exhaust gas flow. The amount of exhaust gas flowing around the injector and entering from above into the mixing tube is often lower compared to the amount that enters the mixing tube from below, that is to say directly from the upstream particle filter. As a result, the swirl center axis shifts or pivots slightly upward by an angle γ. As a result, the swirl center axis and the mixing tube central axis z are unequal. To compensate for this angle γ, the injector is inclined at an angle of incidence α, where 0 <α <γ. Typical values for both angles are 0.5 ° to 15 °, preferably 0.5 ° to 5 °. If appropriate, these angles can also be negative, namely if the exhaust gas stream is deflected in front of the mixing tube in some way before entering the deflection space or the cup-shaped deflection device.

In a further embodiment, the swirl center axis is displaced relative to the mixing tube center axis and the injector jet axis is displaced toward the mixing tube center axis. This refinement takes into account the circumstance that, for structural reasons, for example, the mixing tube central axis z is displaced or pivoted relative to the z axis, which is parallel to a center axis of the particle filter and the SCR catalytic converter and is arranged perpendicular to the end wall of the deflection head , In this embodiment, therefore, the alignment of the z-axis is not equal to the Michrohrmittelachse z`. Typical angles are in the range of 0.5 ° to 20 °. Since, in this case too, the exhaust gas flow preferably flows from below into the mixing tube, ie, directly from the particle filter, analogously to the previous embodiment, the swirl center axis is also displaced upwards here. Spherical axis and mixing tube center axis z` can, but need not be aligned the same. This means that the injector is arranged off-center with an offset V and with an inclination angle α 'inclined to the z-axis on the end wall of the Umlenktopfes.

Finally, it is provided in a further embodiment that the swirl generating device is formed by turbine blades or by a mixer. In particular through the use of Turbine blades ensure a clean twisting of the exhaust gas flow.

In summary, the inventive method for operating the device for aftertreatment of the exhaust gases and the corresponding device ensures that a central Reduktionsmittelindindosierung takes place, an exhaust gas flow around the injector around and in the mixing tube is ensured in and a twisting of the exhaust gas stream, be it by a mixer in the mixing tube after the metering of the reducing agent or by turbine blades before the metering of the reducing agent or possibly also by a combination thereof and that possible inhomogeneities in the exhaust gas mass distribution are compensated by previously described countermeasures. This provides a system that allows for robust operation with airless metering of reductant. This system is ideal for meeting current and future emissions legislation.

Further advantageous embodiments of the invention are described in the drawings, are described in more detail in the embodiments illustrated in the figures.

Show it:

1 a schematic longitudinal section through an inventively designed device for the aftertreatment of the exhaust gases of an internal combustion engine,

2 a detailed view too 1 in a first embodiment,

3 a detailed view too 1 in a second embodiment,

4 a detailed view too 1 in a third embodiment,

5 a cross section through a arranged on a pot-shaped deflection swirl device,

6 a schematic longitudinal section through a second partially illustrated embodiment of an apparatus for post-treatment of the exhaust gases of an internal combustion engine,

7 a detailed perspective view of a mixer of the device according to 6 and

8th a plan view of the mixer according to 5 ,

1 shows a system layout of a device for post-treatment of the exhaust gases of an internal combustion engine. The internal combustion engine, which is, for example, a self-igniting internal combustion engine operated with diesel fuel, is supplied with fuel from a tank via an injection system, which is designed, for example, as a common-rail injection system, which is injected into a combustion chamber of the internal combustion engine. At the same time, combustion air is supplied and compressed into the combustion chamber via a charge air duct. In the operation of the internal combustion engine, the fuel burns with the combustion air to generate work, and the burned exhaust gas becomes an exhaust passage 2 derived from an exhaust tract. The exhaust pipe 2 flows into a housing 1 , where the case 1 essential components of a device for aftertreatment of the exhaust gases receives and is made for example of a metallic material, such as sheet metal. The housing 1 with the components for the aftertreatment of the exhaust gases or the exhaust gas flow is explained in detail below.

One from the engine through the exhaust pipe 2 guided exhaust gas flow 10 reaches the input side of the housing 1 into a diesel oxidation catalyst (DOC) 12 and subsequently flows through a particle filter 5 , After that, the exhaust gas flow arrives 10 to a diversion 6 in the embodiment, a cup-shaped deflection 4 and a swirl generating device 8th having. In this embodiment, the swirl generating device 8th of turbine blades 9 formed in the deflection device 4 can be integrated or the deflection 4 can form. In the swirling device 8th becomes the exhaust gas flow 10 twisted and an injector 11 guided, preferably downstream of the swirl generating device 8th is arranged and wherein essentially only one Reduktionsmittelzuführleitung for the injector 11 by the swirl generating device 8th protrudes through. The injector 11 but can also at least partially by the swirl generating device 8th protrude through. It is important that the injector 11 entirely from the exhaust stream 10 flows around. In a subsequent mixing tube 7 an intimate mixing of the exhaust gas flow takes place 10 with one through the injector 11 metered reducing agent. It is further ensured by the inventive design beyond that no deposit formation of reducing agent on the walls of the mixing tube 7 takes place. On the output side of the mixing tube 7 the exhaust gas flow arrives 10 with the metered-in and mixed reducing agent optionally via a further deflection into a catalyst, in particular an SCR catalyst 3 , In the SCR catalyst 3 a selective catalytic reduction takes place before the exhaust gas flow 10 in the Environment or other facilities for the aftertreatment of the exhaust gas is removed.

The pot-shaped deflection 4 may be a deep-drawn part preferably made of sheet metal, which at the deflection 6 is attached. The pot-shaped deflection 4 carries or includes the swirl generating device 8th , The mixing tube 7 is preferably with the deflecting device 4 and / or the redirection before the SCR catalyst 3 connected. The injector 11 is preferably on an end wall 22 the cup-shaped deflection 4 attached.

The swirl generating device 8th has a number of turbine blades 9 (see also 5 ) on. The example, twelve turbine blades 9 ( 5 ) are aligned at an angle of, for example, 45 ° to the flow direction of the exhaust gas and cause the twisting of the through the mixing tube 7 passing through the exhaust stream 10 ,

Centrally protrudes through the swirl generating device 8th the injector 11 or is optionally completely or partially downstream of the swirl generating device 8th arranged. Through the injector 11 For example, the reducing agent, which is, for example, an aqueous urea solution, enters the spin-loaded exhaust gas stream 10 injected. The injector 11 works - as shown - without air support and is therefore opposite an air-assisted injector 11 particularly simple. The injector 11 However, in principle it can also be air-assisted, in which case the reducing agent is supplied to the injector via a first inlet and, in particular, compressed air via a second inlet. It is essential that the swirl generation of the exhaust gas flow 10 takes place before the metering of the reducing agent.

2 shows an enlarged detail 1 in a first embodiment with a center on an end wall 22 the cup-shaped deflection 4 in the entrance to the mixing tube 7 arranged injector 11 , The injector 11 protrudes centrally into the swirl generating device 8th with the turbine blades 9 into and the mixing tube center axis z of the mixing tube 7 is at the same time the swirl central axis of the swirl device 8th generated swirls. The injector 11 the reducing agent sprays in an injector jet axis exactly in the direction of the mixing tube center axis z and thus also of the mixing tube center axis. This is the ideal design where the injector jet of the injector 11 along the twisted exhaust gas flow 10 through the mixing tube 7 spreads. The injector jet may also be split into a number of sub-beams distributed around the central injector beam axis.

3 shows an enlarged detail 1 in a second embodiment, in which case the injector 11 off-center or centered on the front wall 22 is arranged, but in particular by an angle α inclined to the mixing tube central axis z, which at the same time parallel to a central axis of the particulate filter 5 and the SCR catalyst 3 lies and perpendicular to the front wall 22 the Umlenktopfes is arranged, is arranged. In this embodiment, the fact is taken into account that the swirl center axis is not equal to the mixing tube center axis z when the injector 11 unlike the exhaust stream 10 is flowed around. The amount of exhaust gas flow 10 around the injector 11 flows around and, so to speak, from above into the mixing tube 7 that is, compared to the amount that enters the mixing tube from below, so to speak 7 entry, often less. As a result, the swirl center axis shifts or pivots slightly upward by an angle γ. As a result, the swirl center axis and the mixing tube central axis z are unequal. To compensate for this angle γ, the injector 11 and hence also the injector beam axis is tilted by an angle of incidence α to the mixing tube central axis z, where 0 <α <γ.

Typical values for both angles are 0.5 ° to 15 °, preferably 0.5 ° to 5 °. If necessary, these angles can also be negative, that is to say the exhaust gas flow 10 before entering the deflection space 6 or the cup-shaped deflection 4 in front of the mixing tube 7 is diverted in any way.

4 shows an enlarged detail 1 in a third embodiment and takes into account the fact that, for structural reasons, it may happen, for example, that the mixing tube center axis z is displaced or, in particular, pivoted relative to the z axis, which is parallel to a center axis of the particle filter 5 and the SCR catalyst 3 lies and perpendicular to the front wall 22 the Umlenktopfes is arranged. In this embodiment, therefore, the alignment of the z-axis is not equal to the Michrohrmittelachse z`. Typical angles are in the range of 0.5 ° to 20 °. Because here too analogous to 3 the exhaust gas flow 10 preferably from below into the mixing tube 7 flows in, the swirl center axis can be shifted upwards here as well. Spherical axis and mixing tube center axis z` can, but need not be aligned the same. In the illustration after 4 the swirl center axis and the mixing tube center axis z are aligned identically. This means that the injector 11 Off-center with an offset V and thus the injector beam axis with an inclination angle α` inclined to the z-axis on the end wall 22 the Umlenktopfes is arranged.

5 shows a cross section through the at the deflection 4 arranged and in this embodiment twelve turbine blades 9 having swirl generating device 8th with the center of the swirl generating device arranged injector 11 ,

6 shows in a simplified representation of another embodiment of a device for exhaust aftertreatment. Basically, the device has the same system components already in the 1 to 5 are described. Based on this, particular attention is given below to the design differences.

The exhaust gas flow 10 also gets here to a diversion 6 in which an injector 11 is arranged and secured in a suitable manner. The diversion 6 is with the mixing tube 7 connected, wherein in this embodiment, the swirl generating device 8th downstream of the injector 11 on the input side of the mixing tube 7 is arranged. Also in this embodiment, the injector 11 arranged so that a centric metering of the reducing agent in the mixing tube 7 takes place, an exhaust gas flow around the injector 11 into the mixing tube 7 forms and a twisting of the exhaust stream 10 by the swirl generating device 8th in the mixing tube 7 given is. The swirl generating device 8th is in this embodiment by a mixer described in detail in the following figures 13 educated. The swirl generating device 8th is suitably fixed in the device, the device being a fastening device 14 may have, at which the swirl generating device 8th is attached. In the embodiment shown, the fastening device 14 from a pipe socket 15 formed, the input side of the mixing tube 7 to the mixing tube 7 can be cultivated. For this purpose, the mixing tube 7 for example, be shared and the pipe socket 15 on the corresponding ends of the mixing tube 7 attachable and by means of a pipe clamp 16 be determinable. The fastening device 14 but can also be a holder, for example, at the deflection 6 is arranged or fixed, and an optional or combined attachment of the swirl generating device 8th in the form of turbine blades 9 or the mixer 13 allows.

7 shows the swirl generating device 8th in the form of the mixer 13 in a perspective view. The swirl generating device 8th has a pipe element 17 on which the mixer 13 wearing. The mixer 13 is by nine integral with the pipe element 17 trained and radially inwardly pointing air guide elements 18 formed evenly over the circumference of the tubular element 17 are arranged distributed. The air guiding elements 18 are wing-like and each have two opposite side edges 19a . 19b on, at the free end of the respective air guide element 18 through an end edge 20 connected to each other. The two side edges 19a . 19b of each air guide element 18 have a course deviating from a mutually parallel course, so that the air guide elements 18 each are twisted in themselves. In this case, it is provided that along its longitudinal axis, at least substantially radially with respect to the tubular element 17 is aligned, wounded.

For this purpose, a radially outer longitudinal section 21a of the air guide element 18 opposite a radially inner longitudinal section 21b less strong with respect to the tube longitudinal axis of the tubular element 17 tilted. In particular, it is provided that the outer longitudinal section 21a the respective air guide element 18 is formed at an angle of for example 45 ° to the tube longitudinal axis, while the radially inner longitudinal section 21b is aligned for example 55 ° inclined to the tube longitudinal axis. Furthermore, it is provided that the side edges 19a . 19b the respective air guide element 18 are formed differently long, so that the air guide elements 18 pointed to the middle of the tubular element 17 run. Here are the side edges 19b shorter than the side edges 19a so that the end edges 20 essentially wedge-shaped with respect to the longer side edge 19a extend, in particular in the in 8th shown top view is visible. The end edges 20 can be as shown here, have a straight course, or else be provided with a curvature or a kink.

The longer side edges 19a the air guide elements 18 are designed such that the inwardly directed air guide elements 18 at its end edges 20 spaced from each other, so that there is a free diameter D _f between the air guide elements 18 results, which is for example 32.5mm in the present embodiment, and thus about one third of the example 97.6mm wide inner diameter of the tubular element 17 having. The air guiding elements 18 each have an area of about 210mm ² in the present embodiment. As a result, a free area of about 75% of the total cross section of the tubular element 17 commanded by the exhaust stream 10 can be flowed through, so that a large part of the reducing agent without direct contact with the air guide elements 18 the mixing tube 7 can flow through.

By this configuration it is achieved that the surface of the mixing tube 7 , which could wet the reducing agent and could cause deposits, is significantly minimized, without the equal distribution or the mixing of the exhaust gas stream 10 suffer from. This advantage is incidentally also by the embodiment, which under 1 described reached. By the distortion of the air guide elements 18 becomes a twist in the exhaust stream 10 which also causes mixing of the reducing agent with the exhaust stream 10 downstream of the swirl generating device 8th in the mixing tube 7 ensures, so that in the diesel oxidation catalyst, not shown here 12 an advantageous mixture for the preparation of chemical reactions is ready. This embodiment allows as well as the previously under 1 described embodiment thus a robust, deposition-minimized operation of an apparatus for exhaust aftertreatment with a high uniform distribution of the reducing agent in the exhaust stream 10 , In addition, this is achieved in that in addition to an air-assisted injector system and a shown airless injector 11 can be used because of the advantageous embodiment of the swirl generating device 8th Deposits in the mixing tube 7 be avoided.

Finally, it is pointed out that in the context of the invention, any details of the device shown in the figures can be combined with each other and with each other.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10060808 A1 [0003]
• WO 2011/073240 A1 [0004]

Claims (12)

Method for operating a device for after-treatment of the exhaust gases of an internal combustion engine, comprising a mixing tube leading to an exhaust gas flow ( 7 ) and a reducing agent upstream of a treatment device in the mixing tube ( 7 ) metering injector ( 11 ), and wherein the device comprises an exhaust gas mixing device, characterized in that the exhaust gas mixing device causes a twisting of the exhaust gas flow around a swirl center axis, and that the reducing agent from the injector ( 11 ) in an injector jet axis so into the mixing tube ( 7 ) is metered that a homogeneous exhaust gas flow around the injector jet axis and into the mixing tube ( 7 ). A method according to claim 1, characterized in that the injector jet axis coincides with the swirl center axis. Method according to one of claims 1 or 2, characterized in that the injector ( 11 ) is completely flowed around by the exhaust stream. Method according to one of the preceding claims, characterized in that the twisting of the exhaust gas stream takes place before the metering of the reducing agent, and that the twisting of turbine blades ( 9 ) is effected. Method according to one of claims 1 to 3, characterized in that the twisting of the exhaust gas stream takes place after the metering of the reducing agent, and that the twisting of a mixer ( 13 ) is effected. Device for the aftertreatment of the exhaust gases of an internal combustion engine, comprising a mixing tube leading to an exhaust gas flow ( 7 ), and an injector injecting a reducing agent into the mixing tube upstream of an aftertreatment device ( 11 ), and wherein the device comprises an exhaust gas mixing device, characterized in that the exhaust gas mixing device comprises a swirl generating device ( 8th ) for a twisting of the exhaust gas flow around a swirl center axis is that the injector ( 11 ) on the input side of the mixing tube ( 7 ), and in that the device has means for generating an exhaust gas flow around an injector jet axis of the injector ( 11 ) and into the mixing tube ( 7 ) into it. Apparatus according to claim 6, characterized in that the injector on an end wall ( 22 ) a pot-shaped deflection device ( 4 ) is arranged. Apparatus according to claim 6 or 7, characterized in that the injector jet axis, the swirl center axis and a mixing tube center axis of the mixing tube ( 7 ) are arranged coincidentally. Apparatus according to claim 6 or 7, characterized in that the swirl center axis is inclined by an angle γ to the mixing tube central axis and that the injector jet axis is inclined by an inclination angle α to the mixing tube central axis and that 0 <α <γ. Device according to one of claims 6 to 9, characterized in that the swirl center axis to the mixing tube center axis and the injector jet axis are shifted to the mixing tube center axis. Device according to one of claims 6 to 10, characterized in that the swirl generating device ( 8th ) of turbine blades ( 9 ) is formed. Device according to one of claims 6 to 10, characterized in that the swirl generating device ( 8th ) from a mixer ( 13 ) is formed.

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