CN112443376A

CN112443376A - Mixing device

Info

Publication number: CN112443376A
Application number: CN202010885036.8A
Authority: CN
Inventors: B·达姆森; F·格克塔斯; F-J·特龙佩特; L·布劳恩; T·舒勒
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-08-28
Filing date: 2020-08-28
Publication date: 2021-03-05
Also published as: DE102019212883A1

Abstract

The invention relates to a mixing device (38,58) for an exhaust gas aftertreatment system (1) of a motor vehicle, wherein the mixing device has a housing with a peripheral wall (11) which surrounds a chamber (10), wherein an injection opening (44) for a fluid medium is formed in the peripheral wall, wherein a mixer surface (22) is arranged at least partially in the chamber (10) such that an exhaust gas aftertreatment agent injected into the chamber (10) through the injection opening can impinge on the mixer surface (22), characterized in that the mixer surface (22,42) is formed as a heating device.

Description

Mixing device

Technical Field

The present invention relates to a mixing device for an exhaust gas aftertreatment system.

Background

To further reduce the number of machines driven by the internal combustion engineExhaust gas emissions in motor vehicles, not only in commercial vehicles but also in passenger vehicles, are aimed at, in particular, taking into account CO₂The chemical conversion of nitrogen oxides in exhaust gas aftertreatment components for selective catalytic reduction of nitrogen oxides is further improved with an optimized engine design. For this purpose, it is known to either increase the temperature in the catalytic converter, in particular in the SCR catalytic converter, more quickly in order to reach the operating temperature early, or to configure the exhaust gas aftertreatment system in such a way that it already provides a higher efficiency even at lower operating temperatures.

To achieve this, the catalyst must already have increased activity at lower temperatures. This has been achieved in part by existing catalyst technology. One limiting factor in efficacy may be hydrolysis by which a precursor solution of the exhaust gas aftertreatment agent is converted into the exhaust gas aftertreatment agent. In this case, it is known, in particular, to use an aqueous urea solution as a precursor solution, from which ammonia is provided by means of hydrolysis. Since the low temperature limits the conversion of urea to ammonia, a reactor is proposed in which the hydrolysis is effected independently of the exhaust gas stream and also geometrically separately from the exhaust gas stream. Thus, for example, it is known to divide a part of the exhaust gas flow and supply it to the reactor, into which a precursor solution is injected, mixed with the exhaust gas flow and heated by means of a heating device, so that a flow of ammonia is formed, which is supplied upstream to the catalyst. The chamber together with the injection valve, the heating device and the exhaust gas bypass inlet constitutes such a reactor for the manufacture of an exhaust gas aftertreatment agent. The disadvantage of the proposed solution is that complicated bypass lines for the exhaust gas to the reactor and from the reactor to the catalytic converter are required, and in addition additional installation space for the reactor is required.

The droplets usually formed when dosing an aqueous urea solution into the exhaust system of an internal combustion engine by means of an injector have such a high velocity that they do not evaporate directly in the exhaust gas for the most part, but rather impinge on the wall of the exhaust system or on an impingement plate, which is often referred to as a mixer, in front of the wall. In this case, problems can occur in the exhaust gas system, mainly when the exhaust gas temperature is low, due to incomplete evaporation of AdBlue (exhaust gas aftertreatment agent), in particular due to the formation of deposits, which can lead to an interruption of the conversion of nitrogen oxides, but can also lead to corrosion and, in extreme cases, to a blockage of the exhaust gas system.

DE 102008001212 a1 discloses a device for supplying a reactant into an exhaust gas line of an exhaust gas system, which device is provided with a collecting medium, which can be heated, and which is situated opposite the injection point for the reactant at a distance.

A mixing device is also known from DE 102016211703 a1, which has a cylindrical housing with an outer circumferential wall, a first end wall and a second end wall, wherein a spray opening is formed in the outer circumferential wall. At least one collision surface for the exhaust gas flow or the exhaust gas aftertreatment agent is provided. In the mixing device, a further design measure is provided which imparts a swirl to the exhaust gas flow.

Disclosure of Invention

In contrast to the prior art, the invention proposes a mixing device for an exhaust gas aftertreatment system of a motor vehicle, wherein the mixing device has a housing with a peripheral wall which surrounds a chamber, wherein an injection opening for a fluid medium is formed in the peripheral wall, wherein a mixer surface is arranged at least partially in the chamber, such that an exhaust gas aftertreatment agent injected into the chamber through the injection opening can impinge on the mixer surface, wherein the mixer surface is designed as a heating device. The mixing device according to the invention has the advantage of optimized exhaust gas aftertreatment when the carbon dioxide content of the exhaust gas is further minimized or the exhaust gas denitrification is further improved or good exhaust gas purification should be achieved even at low exhaust gas temperatures.

Advantageous embodiments and further developments of the mixing device are also described below.

In this case, it is particularly advantageous to provide a special design of the mixer surface, in particular a special type of current supply for electrically heating the mixer surface, which combines a heating and wear-resistant electrical contact over as large an area as possible.

According to one embodiment, the mixer face has a current guide in addition to a collision face for the fluid medium, wherein the collision face is located in the chamber, and wherein the current guide extends through the peripheral wall.

According to one embodiment, the current guide is also embodied as heatable, in particular electrically heatable, like the impact surface.

According to one embodiment, the impact surface and the current guide are of the same type of construction, in particular, they differ essentially in their functionally dependent shape.

According to one embodiment, the outer circumferential wall is gas-tight at the location where the current lead penetrates the outer circumferential wall.

In an advantageous manner, the current guide or current guide is in this case designed as part of the mixer surface and is connected outside the chamber of the mixing device to a cable for applying a heating current to the mixer surface. This connection to the cable may be provided outside the mixing device or may be provided outside the chamber of the mixing device in a projection of the mixing device which is in fluidic communication with the chamber.

According to one embodiment, the outer circumferential wall is connected in the region of the current guide through the outer circumferential wall with a projection which preferably projects radially outward, the inner space of the projection being in fluidic communication with the chamber.

According to one embodiment, the projection is embodied as a tube.

According to one embodiment, the current guide is connected within the protrusion with a cable for supplying heating current.

According to one embodiment, the cable is guided out in a gas-tight manner from the end of the projection opposite the chamber of the mixing device.

Drawings

Embodiments of the invention are illustrated in the drawings and are explained in detail in the following description. The figures show:

in figure 1 there is shown an exhaust gas after-treatment system,

FIG. 2 mixing arrangement for an exhaust aftertreatment system

FIG. 3 additional mixing device

FIG. 4 shows a further mixing device in a further view, and

fig. 5 a second additional mixing device.

Detailed Description

Fig. 1 shows an exhaust gas aftertreatment system 1 for an internal combustion engine 2 of a motor vehicle, which is not shown in detail here, in a simplified representation. The internal combustion engine 2 is here an internal combustion engine which operates on diesel fuel. The exhaust gas outlet of the internal combustion engine is connected to the exhaust gas system 3 of the exhaust gas aftertreatment system 1. The exhaust gas system 3 has a diesel oxidation catalyst 4, a mixing device 8, an SCR catalyst 6 and a diesel particulate filter 7, which are flowed through in succession by the exhaust gas flow of the internal combustion engine 2.

The diesel oxidation catalyst 4 as well as the SCR catalyst 6 and the diesel particulate filter 7 are produced in particular in a known manner, so that their more precise structure and configuration should not be discussed in detail here.

The mixing device 8 is designed, for example, as a spiral mixing device and has one or more air guiding elements 9, which can be designed, in particular, as a spiral in order to introduce the exhaust gas flow from the internal combustion engine 2 into a swirling motion. The mixing device 8 is in particular designed as a static mixing device.

In the present case, a mixing device 8 is arranged between the diesel oxidation catalyst 4 and the SCR catalyst 6 and serves on the one hand to provide an exhaust gas aftertreatment agent, which contains ammonia, for example, and on the other hand to mix this exhaust gas aftertreatment agent with the exhaust gas.

Fig. 2 shows a simplified perspective view of the mixing device 8. The mixing device 8 has a chamber 10 connected upstream of the SCR catalytic converter, which is surrounded by a cylindrical housing 11, which can be designed as part of an exhaust gas line or exhaust gas system. In the chamber 10, an air guiding element 9 and an electrically operable heating device 12 are arranged. Furthermore, an opening is formed in the outer circumferential wall 11, through which the injection valve 13 can inject the medium into the chamber 10. The heating device 12 is connected downstream of the injection valve 13 in such a way that the injected medium is first guided through the heating device 2 or passes in the vicinity thereof before being conveyed through the air guiding element 9 and/or the exhaust gas flow of the latter in order to be heated when the heating device 12 is activated. The heating device is also used here as an impingement surface for the exhaust gas or the injected medium, and is therefore also referred to below as an electrically heatable mixer surface 22.

The injection valve 13 is connected to a delivery device 14, which is connected on the suction side to a tank 15, which supplies a precursor solution of the exhaust gas aftertreatment agent, in particular an aqueous urea solution. The injection valve 13 is designed for the metered injection of the precursor solution into the mixing device 8.

The precursor solution of the exhaust gas aftertreatment agent injected into the exhaust gas flow by the injection valve 13 reacts with the exhaust gas flow due to the heat of the exhaust gas flow and the heat supplied by the electric heating device 12 in such a way that pyrolysis or hydrolysis takes place and ammonia is formed, which is then mixed with the exhaust gas flow in the mixing device 8.

The injection valve 13 and the mixing device 8 with the heating device 12 thus together form a device 16 for producing an exhaust gas aftertreatment agent containing ammonia. The chamber 10 forms a pre-chamber of the SCR catalyst 6, so that the exhaust gas flow leaving the chamber 10 is supplied directly to the SCR catalyst 6. In this connection, the device 16 forming the reactor for producing ammonia is realized in a particularly space-saving manner by the integration of the mixing device 8. Since the entire exhaust gas flow of the internal combustion engine 2 is also supplied to the device, the reactor or device 16 obtains a high heat fraction from the exhaust gas flow, which can also be used for the hydrolysis of the precursor solution. The heating device 12 is therefore preferably activated or energized only when required. In particular, the heating device 12 or the mixer surface 22 is energized when the exhaust gas flow and/or the temperature of the SCR catalytic converter 6 is below a predefinable first limit value. The first limit value is selected in accordance with the temperature required for the hydrolysis, so that the heating device 12 is actuated if the heat of the exhaust gas flow which is present in the system is insufficient for the hydrolysis. If the temperature of the exhaust gas flow and/or the SCR catalyst 6 exceeds the second limit value, the heating device 12 is deactivated and the hydrolysis is continued on the basis of the heat present in the exhaust gas flow. The electrical energy consumption for the ammonia production is thereby reduced to a minimum, whereby the overall energy balance of the motor vehicle is optimized. The first and second limit values are selected to be identical or different, wherein the second limit value is preferably greater than the first limit value, so that a hysteresis function is formed which avoids an early switching of the electric heating operation.

Fig. 3 shows a perspective view of a mixing device 38, which can be integrated or installed in the exhaust gas aftertreatment system 1 according to fig. 1 instead of the mixing device 8 according to fig. 2. The basic structure of such a spiral mixing device 38 is known from DE 102016211703 a 1. Fig. 3 shows a view of an inlet region of the mixing device 38 or an inlet plate 50 of the mixing device, which inlet plate 50 has an inlet opening 52, through which inlet opening 52 the exhaust gas can flow into the mixing device 38. I.e. the exhaust gas flows from front to back in the illustration. The same or similar components as those shown in fig. 2 are provided with the same reference numerals and are not described again. The mixing device 38 has an injection opening which is provided by a connection 44 of the mixing device and is used to supply a fluid medium, in particular an aqueous urea solution, into the chamber 10, preferably by means of an injector or a dosing module which can be arranged on the connection. Downstream of the inlet plate, viewed in the flow direction of the exhaust gas, there is an electrically heatable mixer surface 42, the impingement surface 43 of which, located completely in the chamber, is charged with the urea-water solution in a schematically illustrated injection region 54, for example by means of the aforementioned dosing module. The schematically illustrated spray region 54 can also be better seen in fig. 4, since the port plate 50 is not shown here to better illustrate the interior of the mixing device. In this case, the mixer surface is designed as a heating device in order to ensure that it can be electrically heated, wherein the heatable mixer surface also comprises current guides 48 which can also be heated and are guided through the through-openings 46 of the housing 11 or the outer circumferential wall to the outside. Thus, the outer peripheral wall is penetrated so that the outer peripheral wall is kept airtight for a long time.

In an alternative embodiment, when using the mixer surface 42, the gas-tight current guides can also be displaced into the cooler region together with the current guides 48 of the mixer surface, as shown in fig. 5. In such a mixing device 58, the heated end region of the mixer surface, i.e. the current guide 48 of the mixer surface, extends through the housing to the outside only in such a way that the current guide is decoupled from the exhaust gas flow and from the pressure fluctuations inherent in the exhaust gas flow. The current guide is mainly decoupled from the high temperatures of the exhaust gas and temperature fluctuations in the exhaust gas. Outside the chamber 10 of the mixing device, the extension of the current guide 48 of the mixer surface is surrounded by a tube or a tube projection 60, which is welded, for example, in a gas-tight manner to the outer circumferential wall, wherein the tube projection is closed off in a gas-tight manner at its end facing away from the outer circumferential wall, i.e. has a gas-tight through-guide 64 for a cable 62, which is connected to the current guide 48 within the tube projection, for applying a heating current to the mixer surface. In this case, the interior or the interior space of the tube 60 is in fluidic communication with the chamber 10.

The invention can be used in an advantageous manner in exhaust gas systems of diesel internal combustion engines, in particular in exhaust gas systems optimized for minimum carbon dioxide emissions, which require high dosing rates of aqueous urea solutions due to strong nitrogen oxide emissions, but also in the case of particularly low legal extremes of nitrogen oxides for rapid start-up of dosing of aqueous urea solutions, or in vehicles which are operated frequently and for long periods at very low exhaust gas temperatures, for example in postal vehicles.

Claims

1. A mixing device (38,58) for an exhaust gas aftertreatment system (1) of a motor vehicle, wherein the mixing device has a housing with a peripheral wall (11) which surrounds a chamber (10), wherein an injection opening (44) for a fluid medium is formed in the peripheral wall, wherein a mixer face (22) is arranged at least partially in the chamber (10) such that an exhaust gas aftertreatment agent injected into the chamber (10) through the injection opening can impinge on the mixer face (22), characterized in that the mixer face (22,42) is formed as a heating device.

2. Mixing device according to claim 1, wherein the mixer face (42) has current guides (48) in addition to a collision face (43) for the fluid medium, wherein the collision face (43) is located in the chamber, and wherein the current guides (48) extend through the peripheral wall (11).

3. Mixing device according to claim 2, characterized in that the current guide (48) is also embodied as heatable, in particular electrically heatable, like the impact surface (43).

4. Mixing device according to claim 3, characterized in that the impact surface (43) and the current guide (48) are of the same type of construction, in particular they differ substantially in their function-dependent shaping.

5. Mixing device according to claim 2, 3 or 4, characterised in that the peripheral wall (11) is made airtight at the points where the current guides (48) penetrate the peripheral wall.

6. Mixing device according to claim 2, 3 or 4, characterized in that the peripheral wall (11) is connected, in the region of the current guide (48) passing through it, with a preferably radially outwardly projecting protrusion (60), the inner space of which is in fluid communication with the chamber.

7. Mixing device according to claim 6, characterized in that the projection (60) is embodied as a tube.

8. Mixing device according to claim 6 or 7, wherein the current guide (48) is connected within the protrusion (60) with a cable (62) for supplying heating current.

9. Mixing device according to claim 8, characterized in that the cable (62) is guided out in a gas-tight manner from the end (64) of the projection opposite the chamber (10) of the mixing device (58).