WO2019029880A1

WO2019029880A1 - Device for mixture preparation, exhaust-gas aftertreatment system

Info

Publication number: WO2019029880A1
Application number: PCT/EP2018/066105
Authority: WO
Inventors: Marco DE PELLEGRINI; Daqing JI; Christian Alt
Original assignee: Robert Bosch Gmbh
Priority date: 2017-08-10
Filing date: 2018-06-18
Publication date: 2019-02-14
Also published as: DE102017213954A1

Abstract

The invention relates to a device (1) for mixture preparation for an exhaust-gas aftertreatment system, comprising an injection device (2) for injecting a liquid reducing agent (3) into an exhaust-gas flow, and comprising a mixing pipe (4) which conducts the exhaust-gas flow and which has static flow-guiding elements (10) for the evaporation and mixing of the reducing agent (3) with the exhaust gas. According to the invention, the mixing pipe (4) opens in the flow direction of the exhaust gas into a cylindrical vortex chamber (5), wherein the mixing pipe (4) is, at least in the region of the opening-in point, oriented substantially tangentially in relation to the cross section of the vortex chamber (5). The invention also relates to an exhaust-gas aftertreatment system having an SCR catalytic converter (7) and a device (1) according to the invention.

Description

Description title

Mixture preparation device, exhaust aftertreatment system

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 help of ammonia (NH3), 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 catalyst 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 published patent application DE 10 2014 208 743 AI is an example of an exhaust aftertreatment system with an exhaust pipe and the exhaust pipe to ordered injector for an exhaust aftertreatment agent. 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 vaporizing and mixing the reducing agent with the exhaust gas. According to the invention, the mixing tube opens in the flow direction of the exhaust gas into a cylindrical vortex chamber, the mixing tube at least is aligned in the region of the mouth substantially tangential with respect to the cross section of the vortex chamber.

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.

For the purposes 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.

By virtue of the substantially tangential orientation of the mixing tube with respect to the vortex chamber, the mixture flow is caused to swirl as it flows into the vortex chamber, thereby further increasing 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.

In order 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, with respect to a longitudinal axis B of the swirl chamber in an angle α <90 ° is employed. 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 bent pipe section into the mixing tube, so that the static flow guide elements provided in the mixing pipe are optimally flown. The exhaust pipe has a longitudinal axis C, which is preferably employed with respect to the longitudinal axis A of the straight pipe section of the mixing tube at an angle ß, 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 impinge on 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 flow guide elements protrude from radially outward to radial inside into the mixing tube, wherein they may 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 S CR 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 catalytic converter 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.

Preferred embodiments of the invention are described below with reference to the accompanying drawings. 1 shows a schematic illustration of an exhaust aftertreatment system with a device according to the invention for mixture preparation,

Fig. 2 is a schematic side view of the device for mixture preparation of the exhaust aftertreatment system of Fig. 1 and

3 is a schematic plan view of the device for mixture preparation of the exhaust aftertreatment system of FIG. 1.

Detailed description of the drawings

The exhaust aftertreatment system shown in FIG. 1 for the aftertreatment of the exhaust gas of an internal combustion engine, not shown, comprises an S CR catalyst 7, which is to reduce the nitrogen oxide emissions of the internal combustion engine. For this purpose, a reducing agent 3 is supplied in advance to the exhaust gas, with the reducing agent 3 in particular being an aqueous urea. Substance solution can act. The liquid reducing agent 3 is introduced by means of an injection device 2 as a spray, that is, in drop form, so that evaporation and mixing of the reducing agent 3 with the exhaust gas is brought about. In order to optimize the mixing, the S CR catalyst 7 is preceded by a device 1 for mixture preparation.

In addition to the injection device 2, the device 1 for mixture preparation comprises a mixing tube 4 and a vortex chamber 5. Via the vortex chamber 5, the device 1 is connected to the S CR catalytic converter 7. Via the mixing tube 4, a connection with an exhaust pipe 6 is made, via which the exhaust gas enters the device 1. In the transition region from the exhaust pipe 6 in the mixing tube 4, the injection device 2 is arranged, in such a way that the spray is introduced into the mixing tube 4 in the axial direction. The introduced by means of the injector 2 reducing agent 3 meets in

Mixing tube 4 on static flow guide 10, which cause a break up of the drops. In this way, a faster evaporation of the reducing agent in the mixing tube 4 is achieved. Furthermore, the exhaust gas flowing through is set into a swirl via the static flow guiding elements 10, with the angular momentum of the exhaust gas stream entraining the reducing agent 3 and causing a uniform distribution of the reducing agent 3 in the exhaust gas. This leads to a mixture flow vortex 11 in the mixing tube 4.

As can be seen in particular from FIG. 3, the mixing tube 4 is oriented substantially tangentially with respect to the vortex chamber 5, so that the turbulence of the mixture flow in the vortex chamber 5 is continued. By the vortex chamber 5, therefore, the mixing section is extended. If necessary, therefore, the mixing tube 4 can be shortened to make the device 1 for mixture preparation more compact.

The space requirement of the device 1 is further reduced if - as shown in Figures 1 and 2 - the mixing tube 4 and a straight pipe section 4.2 of the mixing tube 4 is made at an angle α relative to the vortex chamber 5. This means that the longitudinal axis A of the mixing tube 4 or of the straight tube section 4. 2 is aligned with the longitudinal axis B of the mixing tube 4. Belkammer 5 intersects at the angle α, wherein in the present case the angle α is 45 °. The straight running pipe section 4.2 of the mixing tube 4 has at its ends in each case a bent pipe section 4.1, 4.3, so that the transition into the swirl chamber 5 on the one hand and in the exhaust pipe 6 on the other hand is designed to optimize flow.

A position of the mixing tube 4 or of the straight tube section 4.2 of the mixing tube 4 relative to the exhaust pipe 6 can also be achieved via the bent pipe section 4.2, so that the longitudinal axis A of the mixing pipe 4 intersects the longitudinal axis C of the exhaust pipe 6 at an angle .beta in the present case also 45 °. In this way, the space requirement of the device can be minimized.

In order to further reduce the particulate matter pollution in addition to the reduction of nitrogen oxides, it is possible-as shown in FIG. 1 -for the device 1 for mixture preparation to be preceded by a particle filter 9. This can be combined with an oxidation catalytic converter 8 in order to make exhaust gas purification even more efficient.

Claims

claims

1. 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 waste gas flow leading mixing tube (4) with static flow guide elements (10) for evaporation 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) is aligned at least in the region of the mouth substantially tangential with respect to the cross section of the vortex chamber (5).

2. Device (1) according to claim 1,

characterized in that the mixing tube (4) has a bent tube section (4.1) and a straight tube section (4.2), wherein the straight tube section (4.2) has a longitudinal axis (A), which relative to a longitudinal axis (B) of the vortex chamber ( 5) at an angle (a) is employed, and wherein the angle (a) <90 °, preferably <60 °, further preferably 45 °.

3. 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 pipe section (4.2) of the mixing tube (4) is set at an angle (ß), and wherein the angle (ß) <90 °, preferably

<60 °, more preferably 45 °.

4. 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), preferably the injection device (2) being coaxial to the longitudinal axis (A) of the straight tube section (4.2) mixing tube (4). is aligned.

5. 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.

6. exhaust aftertreatment system with an S CR catalyst (7) and a device (1) according to any one of the preceding claims, wherein the device (1) upstream of the SCR catalyst (7) in the flow direction of the exhaust gas.

7. exhaust aftertreatment system according to claim 6,

characterized in that the device (1) an oxidation catalyst (8) and / or a particulate filter (9) is connected upstream in the flow direction of the exhaust gas.