DE102017213954A1 - Mixture preparation device, exhaust aftertreatment system - Google Patents

Abstract

The invention relates to a device (1) for mixture preparation for an exhaust aftertreatment system, comprising an injection device (2) for injecting a liquid reducing agent (3) into an exhaust gas stream and a mixing tube (4) leading to the exhaust gas stream with static flow guide elements (10) for vaporizing and mixing of the reducing agent (3) with the exhaust gas. According to the invention, the mixing tube (4) opens into a cylindrical vortex chamber (5) in the flow direction of the exhaust gas, wherein the mixing tube (4) is oriented substantially tangentially with respect to the cross section of the vortex chamber (5), at least in the region of the mouth an exhaust aftertreatment system with an SCR catalyst (7) and a device according to the invention (1).

Description

The invention relates to a device for mixture preparation with the features of the preamble of claim 1. Furthermore, the invention relates to an exhaust aftertreatment system with a device for mixture preparation, in particular for the evaporation and mixing of a reducing agent with exhaust gas.

State of the art

In order to reduce nitrogen oxide emissions, exhaust gases from internal combustion engines, in particular from diesel engines, are subjected to exhaust gas aftertreatment. Here, SCR catalysts are used (SCR = Selective Catalytic Reduction), in which nitrogen oxide molecules with the aid of ammonia (NH ₃ ), which serves as a reducing agent, are reduced to elemental nitrogen. To provide the reducing agent, a urea-water solution (HWL) is introduced into the exhaust gas flow upstream of the SCR catalytic converter by means of an injection device.

In order to achieve a sufficient mixing of the urea-water solution with the exhaust gas, static mixers are usually used. The liquid jets of urea-water solution are aligned directly on the static mixer, so that it comes in contact of the drops with the mixer to break up the drops into smaller drops. Smaller drops have the advantage that the urea-water solution evaporates faster and mixes with the exhaust gas

From the publication DE 10 2014 208 743 A1 is an example of an exhaust aftertreatment system with an exhaust pipe and an exhaust pipe associated with the injection device for an exhaust aftertreatment agent forth. Downstream of the injector means are provided which serve to mix the exhaust aftertreatment agent with the exhaust gas to achieve optimum mixture treatment upstream of a catalyst. The device comprises for this purpose a mixing device with a plurality of wing-like air guide elements which are static and extend from radially outside to radially inside a mixing tube. About the air guide elements, the exhaust stream is set in a swirling motion, which promotes mixing with the exhaust aftertreatment agent in the mixing tube.

Known devices for mixture preparation in an exhaust aftertreatment system usually have a mixing tube with a length between 400 mm and 1000 mm. The length of the mixing tube also increases the degree of mixing. However, the available space is usually limited, so that no optimal mixing is achieved.

The present invention is therefore based on the object of specifying a device for mixture preparation for an exhaust aftertreatment system, which is particularly compact and at the same time allows optimal mixing in order to increase the efficiency of the exhaust gas purification.

To solve the problem, the device for mixture preparation with the features of claim 1 and the exhaust aftertreatment system with the features of claim 6 are proposed. Advantageous developments of the invention can be found in the respective subclaims.

Disclosure of the invention

The device proposed for mixture preparation comprises an injection device for injecting a liquid reducing agent into an exhaust gas stream and a mixing tube leading the exhaust gas flow with static flow guide elements for vaporising and mixing the reducing agent with the exhaust gas. According to the invention, the mixing tube opens into a cylindrical vortex chamber in the flow direction of the exhaust gas, wherein the mixing tube is oriented substantially tangentially with respect to the cross section of the vortex chamber, at least in the region of the mouth.

In the device according to the invention accordingly includes in the flow direction of the exhaust gas, a swirl chamber to the mixing tube. The vortex chamber lengthens the mixing section, since the gas mixture undergoes further mixing in the vortex chamber. Accordingly, the mixing and thus the mixture preparation is optimized, which leads to an efficient exhaust gas purification in a downstream SCR catalytic converter.

The further mixing in the vortex chamber is based on an additional turbulence of the gas mixture, which is due to further mixing and / or Strömungsleitelemente in the vortex chamber, the geometry of the vortex chamber and / or on the substantially tangential connection of the mixing tube to the vortex chamber.

In the context of the application, substantially tangential means that the pipe section of the mixing tube which opens into the vortex chamber is arranged radially eccentrically or parallel offset relative to a radial with respect to the cross section of the vortex chamber.

About the substantially tangential orientation of the mixing tube with respect to the vortex chamber, the mixture flow when flowing into the Whirl chamber added to a swirl, which further increases the degree of mixing. Upstream of the vortex chamber, the static flow guide elements are preferably used to set the mixture flow into a twist, so that an angular momentum promoting the mixing is already generated in the mixing tube. This means that preferably a first turbulence of the gas mixture in the mixing tube and a further turbulence takes place in the vortex chamber, whereby the mixture preparation is further optimized.

To reduce the space requirement of the device, it is proposed that the mixing tube has a bent pipe section and a straight pipe section, wherein the straight pipe section has a longitudinal axis A, which is employed with respect to a longitudinal axis B of the vortex chamber at an angle α <90 ° , This means that the longitudinal axes of the mixing tube and the vortex chamber intersect at an angle α <90 °. In this way, a compact arrangement can be achieved at the same time extended mixing distance. To further reduce the space requirement, an angle α <60 °, preferably an angle α = 45 ° can be selected.

Furthermore, the mixing tube preferably has a curved pipe section for connection to an exhaust pipe. In this case, the exhaust gas flows via the curved tube section into the mixing tube, so that the static flow guidance elements provided in the mixing tube are optimally flown. The exhaust pipe has a longitudinal axis C, which is preferably set against the longitudinal axis A of the straight pipe section of the mixing tube at an angle β, which is also smaller than 90 °. Preferably, an angle β <60 °, further preferably an angle β = 45 ° is selected. In this way, the space requirement of the device can be further reduced.

Preferably, the injection device for injecting the reducing agent at the opposite end of the vortex chamber of the mixing tube is arranged. For example, in the region of the bent pipe section, which serves to connect the mixing pipe to the exhaust pipe. This ensures a first mixing of the reducing agent with the exhaust gas upstream of the static flow guide elements. Further preferably, the injection device is aligned coaxially with the longitudinal axis A of the straight tube section of the mixing tube, in order to ensure that the drops of the reducing agent strike the static flow guide elements. Because when hitting the drops are broken up into smaller drops, so that the reducing agent evaporates faster.

It is also proposed that the static flow guide elements of the mixing tube are designed like a wing. This means that they are designed flat to form a sufficiently large hit area for the drops. The wing-like static flow guide elements are preferably employed with respect to a radial plane in order to set the exhaust gas flow flowing therethrough into a swirl, wherein the exhaust gas flow entrains the droplets. Preferably, the wing-like static Strömungsleitelemente protrude from radially outward to radially inward into the mixing tube, wherein they can be mounted radially outward on the inner peripheral side of the mixing tube or a tube piece inserted therein.

The additionally proposed exhaust aftertreatment system has an SCR catalyst and a device according to the invention for mixture preparation. The device for mixture preparation is upstream of the SCR catalyst in the flow direction of the exhaust gas, so that in the SCR catalyst improved exhaust gas purification is achieved due to the good mixture preparation. In this way, the efficiency of the exhaust aftertreatment system can be increased.

Advantageously, the device for mixture preparation itself is preceded by an oxidation catalyst and / or a particle filter in the flow direction of the exhaust gas, so that the exhaust gas purification is further optimized. In particular, the particulate matter load can be reduced by an upstream particle filter.

• 1 eine schematische Darstellung eines Abgasnachbehandlungssystems mit einer erfindungsgemäßen Vorrichtung zur Gemischaufbereitung,
• 2 eine schematische Seitenansicht der Vorrichtung zur Gemischaufbereitung des Abgasnachbehandlungssystems der 1 und
• 3 eine schematische Draufsicht auf die Vorrichtung zur Gemischaufbereitung des Abgasnachbehandlungssystems der 1.

Preferred embodiments of the invention are described below with reference to the accompanying drawings. These show:

• 1 a schematic representation of an exhaust aftertreatment system with a device according to the invention for mixture preparation,
• 2 a schematic side view of the device for mixture preparation of the exhaust aftertreatment system of 1 and
• 3 a schematic plan view of the device for mixture preparation of the exhaust aftertreatment system of 1 ,

Detailed description of the drawings

That in the 1 illustrated exhaust aftertreatment system for the aftertreatment of the exhaust gas of an internal combustion engine, not shown, comprises an SCR catalyst 7 , which should reduce the nitrogen oxide emissions of the internal combustion engine. The exhaust gas is a reducing agent for this purpose 3 supplied, wherein it is in the reducing agent 3 especially an aqueous one Urea solution can act. The liquid reducing agent 3 is by means of an injector 2 as a spray, that is in the form of drops, introduced, so that evaporation and mixing of the reducing agent 3 is brought about with the exhaust gas. To optimize mixing, is the SCR catalyst 7 a device 1 upstream of the mixture preparation.

The device 1 for mixture preparation comprises in addition to the injection device 2 a mixing tube 4 and a vortex chamber 5 , About the vortex chamber 5 is the device 1 with the SCR catalyst 7 connected. About the mixing tube 4 is a connection to an exhaust pipe 6 made, via which the exhaust gas into the device 1 arrives. In the transition area of the exhaust pipe 6 into the mixing tube 4 is the injector 2 arranged, in such a way that the spray in the axial direction in the mixing tube 4 is introduced.

The means of the injector 2 introduced reducing agents 3 meets in the mixing tube 4 on static flow elements 10 which cause a break up of the drops. In this way, a faster evaporation of the reducing agent in the mixing tube 4 reached. Furthermore, via the static flow guide 10 the exhaust gas flowing therethrough is set in a spin, wherein the angular momentum of the exhaust gas flow is the reducing agent 3 entrains and a uniform distribution of the reducing agent 3 effected in the exhaust. This leads to a mixture vortex 11 in the mixing tube 4 ,

How the particular 3 it can be seen, is the mixing tube 4 essentially tangential with respect to the vortex chamber 5 aligned so that the turbulence of the mixture flow in the vortex chamber 5 will continue. Through the vortex chamber 5 Accordingly, the mixing section is extended. If necessary, therefore, the mixing tube 4 be shortened to the device 1 to make the mixture preparation more compact.

The space requirement of the device 1 is further lowered, if - as in the 1 and 2 shown - the mixing tube 4 or a straight pipe section 4.2 of the mixing tube 4 at an angle α to the vortex chamber 5 is hired. That is, the longitudinal axis A of the mixing tube 4 or of the straight pipe section 4.2 with the longitudinal axis B of the vortex chamber 5 α intersects at the angle, in the present case the angle α is 45 °. The straight pipe section 4.2 of the mixing tube 4 has at its ends in each case a bent pipe section 4.1 . 4.3 on, making the transition to the vortex chamber 5 on the one hand and into the exhaust pipe 6 on the other hand is designed to optimize flow.

About the bent pipe section 4.2 can also hire a mixing tube 4 or of the straight pipe section 4.2 of the mixing tube 4 opposite the exhaust pipe 6 be achieved, so that the longitudinal axis A of the mixing tube 4 the longitudinal axis C of the exhaust pipe 6 at an angle β, which in the present case is also 45 °. In this way, the space requirement of the device can be minimized.

In addition to the reduction of nitrogen oxides also reduce the particulate matter, can - as in the 1 shown - the device 1 for mixture preparation a particle filter 9 be upstream. This can be done with an oxidation catalyst 8th be combined to make the exhaust gas purification even more efficient.

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 102014208743 A1 [0004]

Claims (7)

Device (1) for mixture preparation for an exhaust aftertreatment system, comprising an injection device (2) for injecting a liquid reducing agent (3) into an exhaust gas stream and a mixing tube (4) leading the exhaust gas flow with static flow guide elements (10) for vaporizing and mixing the reducing agent (3 ) with the exhaust gas, characterized in that the mixing tube (4) in the flow direction of the exhaust gas into a cylindrical vortex chamber (5) opens, wherein the mixing tube (4) at least in the region of the mouth substantially tangentially with respect to the cross section of the vortex chamber (5 ) is aligned. Device (1) according to Claim 1 , characterized in that the mixing tube (4) has a bent pipe section (4.1) and a straight pipe section (4.2), wherein the straight pipe section (4.2) has a longitudinal axis (A), with respect to a longitudinal axis (B) of the vortex chamber (5) is set at an angle (α), and wherein the angle (α) <90 °, preferably <60 °, further preferably 45 °. Device (1) according to Claim 1 or 2 , characterized in that the mixing tube (4) has a bent pipe section (4.2) for connection to an exhaust pipe (6), wherein preferably the exhaust pipe (6) has a longitudinal axis (C), with respect to the longitudinal axis (A) of the straight running Pipe section (4.2) of the mixing tube (4) is set at an angle (β), and wherein the angle (β) <90 °, preferably <60 °, further preferably 45 °. Device (1) according to one of the preceding claims, characterized in that the injection device (2) is arranged at the end of the mixing tube (4) opposite the vortex chamber (5), wherein preferably the injection device (2) is coaxial with the longitudinal axis (A) of the straight running pipe section (4.2) mixing tube (4) is aligned. Device (1) according to one of the preceding claims, characterized in that the static flow guide elements (10) of the mixing tube (4) are designed wing-like. Exhaust after-treatment system comprising an SCR catalytic converter (7) and a device (1) according to one of the preceding claims, wherein the device (1) is connected upstream of the SCR catalytic converter (7) in the direction of flow of the exhaust gas. Exhaust after-treatment system according to Claim 6 , characterized in that the device (1) is preceded by an oxidation catalyst (8) and / or a particulate filter (9) in the flow direction of the exhaust gas.

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