DE102012008556B4 - Apparatus and method for exhaust aftertreatment - Google Patents

Abstract

Device (1) for the exhaust aftertreatment of an exhaust gas mass flow in an exhaust line, wherein in the exhaust line, an injector (9.1, 9.2) for supplying reducing agent is disposed in the exhaust gas mass flow, and wherein a cylindrical exhaust line segment (5) has a tangential inlet (8) downstream of the tangential inlet (8) is disposed a mixer (11) for reversing the direction of rotation of the exhaust gas mass flow and upstream of the mixer (11) the injector (9.1; 9.2) in the cylindrical exhaust tract segment (5) on the central axis (6) of the mixer (11) or upstream of the inlet (8) in a cross-sectional narrowed region of an exhaust line segment (4) which is immediately upstream of the tangential inlet (8) disposed upstream, wherein the mixer (11) has at least one radially extending guide element (16) , wherein relative to the central axis (6) of the mixer (11), the guide element (16) in an inner guide element section (17) and an outer baffle portion (18), and wherein the inner baffle portion (17) is inclined against the direction of rotation (P2) of the flow, and wherein the outer baffle portion (18) is inclined in the direction of rotation (P2) of the flow ,

Description

Technical area

The invention relates to an apparatus and a method for exhaust aftertreatment.

State of the art

From the US 2009/0000287 A1 For example, an exhaust gas flow device is known. In one embodiment, an exhaust gas mass flow offset with a reducing agent flows via a tangential inlet into a cylindrical exhaust pipe section, whereby a swirling flow arises about the longitudinal axis of the cylindrical exhaust pipe section. Due to central forces, unboiled or unhydrolyzed reductant components settle on the inner wall of the exhaust pipe section. In addition, due to a diaphragm-shaped baffle plate, these reducing agent components are prevented from continuing to flow to a downstream exhaust gas aftertreatment device.

The publication DE 42 03 807 A1 describes a device for the catalytic reduction of NO _x from oxygen-containing exhaust gases using urea, which contains a hydrolysis catalyst consisting of fine flow channels, which allow by deflection and apertures or slits partial flows, which are directed approximately perpendicular to the main flow.

The publication DE 199 22 959 A1 discloses an exhaust gas purification system with nitrogen oxide reduction with addition of reducing agent. In this case, a nitrogen oxide reduction catalyst for the reduction of nitrogen oxides contained in the exhaust gas with the participation of a introduced into the exhaust stream, vaporous reducing agent and a reducing agent metering device is arranged in the exhaust line, which comprises a arranged in the exhaust line upstream of the nitrogen oxide reduction catalyst evaporator. The evaporator has as a heat source a heatable baffle on which the supplied from the supply unit reducing agent is directed under pressure, or a microwave generator.

The Japanese patent application JP 2009 228 484 A describes an exhaust gas purification device in which reducing agent upstream of an SCR catalyst is introduced tangentially and perpendicular to the center axis of the SCR catalyst.

Finally, the disclosure document describes DE 10 201 0 045 751 A1 an exhaust system with an injection device, which for introducing a fluid, in particular a water-urea mixture or a liquid fuel, in the exhaust gas flow has an opening in front of an SCR catalyst in the exhaust line injection nozzle. The injection nozzle opens at an injection point in the injection section of the exhaust line. The exhaust gas coming from a supply section of the exhaust gas line flows into the injection section substantially tangentially in order to impart an angular momentum to the exhaust gas around the injection point.

Object of the invention

The invention has for its object to provide an apparatus and a method for exhaust aftertreatment device, which ensures an improved mixing of the exhaust gas mass flow with the reducing agent.

Solution of the task

The object is achieved by a device according to claim 1. Furthermore, the invention is achieved by a method according to claim 6.

Advantages of the invention

According to the invention, a mixer for reversing the direction of rotation of the exhaust gas mass flow is arranged downstream of the tangential inlet. Furthermore, the injector is arranged upstream of the mixer. The injector is disposed in the cylindrical exhaust tract segment on the central axis of the mixer. The reducing agent is thereby atomized in the entire cylindrical exhaust tract segment. With this arrangement, the short mixing distance is advantageous. In addition, the mixer is wetted with the reducing agent, so that evaporates on the surface of the mixer, the reducing agent. Alternatively, the injector is located upstream of the tangential inlet in a cross-sectional narrowed portion of an exhaust tract segment immediately upstream of the tangential inlet. By means of this injector arrangement, a longer mixing distance is achieved, whereby the period of time for mixing the reducing agent is prolonged. The mixer has at least one radially extending guide element. The guide element is divided into an inner and an outer guide element section upstream of the central axis of the mixer. The inner guide element section is inclined counter to the direction of rotation of the exhaust gas mass flow. In contrast, the outer guide element section is inclined in the direction of rotation. Due to the respective inclination of the exhaust gas mass flow is prevented from an external flow into the mixer and facilitates an internal inflow.

In an advantageous embodiment, the radial length of the inner guide element section a ratio of 2: 1 to the radial length of the outer baffle section.

In a further advantageous embodiment, a first exhaust gas aftertreatment device is arranged upstream of the tangential inlet, wherein the center axis of the first exhaust gas aftertreatment device is perpendicular to the central axis of the mixer.

In a further advantageous embodiment, a second exhaust gas aftertreatment device is arranged downstream of the mixer, wherein the center axis of the second exhaust gas aftertreatment device is eccentric to the central axis of the mixer.

In a further advantageous embodiment, a cross-sectional widening region immediately adjoins the mixer downstream of the mixer.

In the method according to the invention, a swirl around the flow direction is impressed on the exhaust gas mass flow flowing through the tangential inlet, as a result of which the exhaust gas mass flow rotates downstream of the inlet about the flow direction in a first direction of rotation. Subsequently, the exhaust gas mass flow offset with the reducing agent is supplied to the mixer. In the mixer, the first direction of rotation of the exhaust gas mass flow is reversed in a second direction of rotation opposite to the first direction of rotation. Thus, the exhaust gas mass flow rotates downstream of the mixer in the second direction of rotation. Furthermore, the exhaust gas mass flow is conducted from outside to inside in relation to the central axis of the mixer. For this purpose, the mixer has at least one radially extending guide element, wherein, based on the central axis of the mixer, the guide element is subdivided into an inner guide element section and into an outer guide element section. The inner guide element section is inclined counter to the first direction of rotation and the outer guide element section is inclined in the first direction of rotation. The exhaust gas mass flow is prevented from flowing into the mixer in the region of the outer guide element section and facilitated in the region of the inner guide element section.

There is a 90 ° deflection and twisting of the exhaust gas mass flow in a confined space compared to an example of the US 2009/0000287 A1 known 90 ° bend and subsequent swirl generator. Due to the eccentric arrangement of the mixer, the required space does not exceed the outer dimensions of the exhaust aftertreatment devices, since the tangential supply of the exhaust gas mass flow is offset to the mixer. Due to the twisted flow of the offset of the center axis of the mixer and the center axis of the second exhaust aftertreatment device is compensated until it enters the second exhaust aftertreatment device.

drawings

Show it:

1 a perspective view of a device according to the invention;

2 a sectional view of the device according to 1 ;

3 : a cross-sectional view of a detail of 1 ;

4 a perspective view of a mixer according to the invention;

5 : a front view of the mixer according to 4 ;

6 a side view of the mixer according to 4 ;

7 : a rear view of the mixer according to 4 ,

The 1 and 2 show a perspective view of an embodiment of a device according to the invention 1 for exhaust aftertreatment. An exhaust gas mass flow flows in the direction of the arrow P1 through a first exhaust gas aftertreatment device 2 in a first exhaust gas segment 3 is arranged. The first exhaust aftertreatment device 2 is, for example, a diesel oxidation catalyst (DOC).

Downstream of the first exhaust aftertreatment device 2 the exhaust gas mass flow flows through a second exhaust gas segment 4 , which directly adjoins the first exhaust gas segment 3 followed. The cross-sectional size of the second exhaust gas segment 4 decreases continuously in the flow direction of the exhaust gas mass flow, so that as a result of the flow velocity of the exhaust gas mass flow is increased.

Downstream of the second exhaust line segment 4 closes immediately a third exhaust gas segment 5 at. The central axis 6 of the third exhaust gas segment 5 is perpendicular to the central axis 7 of the first exhaust gas segment 3 arranged so that the third exhaust gas segment 5 at an angle α of 90 ° to the first exhaust line segment 3 and thus also to the first exhaust aftertreatment device 2 is arranged. The third exhaust gas segment 5 has a tangential inlet 8th via which the exhaust gas mass flow from the second exhaust gas line segment 4 in the third Exhaust train segment 5 flows in the direction of the arrow P2 and merges into a helical movement with a first direction of rotation.

An injector 9.1 . 9.2 for supplying reducing agent, for example a liquid urea solution, is optionally in the second exhaust line segment 4 at the level of the narrowed section or in the third exhaust gas segment 5 on the central axis 6 arranged. The position of the injector 9.1 . 9.2 is located in a highly turbulent flow area of the exhaust gas mass flow with a pronounced swirl.

To the third exhaust gas segment 5 closes immediately downstream of a fourth exhaust line segment 10 at. In the fourth exhaust gas segment 10 is a mixer 11 arranged. Both the fourth exhaust gas segment 10 as well as the mixer 11 lie in extension of the central axis 6 of the third exhaust gas segment 5 , When flowing through the mixed with the reducing agent exhaust gas mass flow through the mixer 11 the first direction of rotation is reversed in the direction of the arrow P2 in a second direction of rotation opposite to the first direction of rotation in the direction of the arrow P3.

Downstream of the fourth exhaust gas segment 10 closes immediately a fifth exhaust gas segment 12 at. The fifth exhaust gas segment 12 is funnel-shaped, wherein in the flow direction of the initial diameter is smaller compared to the final diameter. In the flow direction is the fifth exhaust line segment 12 thus formed cross-sectional widening. The initial diameter of the fifth exhaust line segment 12 agrees with the diameter of the fourth exhaust gas segment 10 match.

A sixth exhaust gas segment 13 closes downstream directly to the fifth exhaust line segment 12 at, wherein the final diameter of the fifth exhaust gas segment 12 with the diameter of the sixth exhaust line segment 13 matches. In the sixth exhaust gas segment 13 is a second exhaust aftertreatment device 14 arranged. The second exhaust aftertreatment device 14 is, for example, a selective catalytic reduction (SCR) catalyst or a diesel particulate filter with SCR coating (SDPF).

The central axis 15 the second exhaust aftertreatment device 14 is eccentric compared to the central axis 6 of the mixer 11 , In the 3 the eccentricity is also shown.

Downstream of the mixer 11 the exhaust gas mass flow offset with the reducing agent flows through the funnel-shaped fifth exhaust gas line segment 12 , thereby homogenizing the velocity field, to the second exhaust aftertreatment device 14 ,

The exhaust gas mass flow becomes homogeneous over the inflow surface of the second exhaust gas aftertreatment device 14 distributed. By means of the homogeneous distribution on the inflow surface, the conversion rate of the second exhaust aftertreatment device 14 elevated.

The device 1 allows a close-coupled exhaust aftertreatment in a 90 ° arrangement of the first exhaust aftertreatment device 2 and the second exhaust aftertreatment device 14 , In addition, a very short mixing distance can be realized.

In the 4 to 7 is an embodiment of the mixer according to the invention 11 shown. The mixer 11 has radially extending guide elements 16 with a curvature variable along the flow direction. Relative to the central axis 6 is the guiding element 16 upstream into an inner baffle section 17 and in an outer guide element section 18 divided. The number of guide elements 16 is for a mixer 11 preferably 16 , Due to a higher number of guide elements 16 will increase the efficiency of the mixer 11 increases, whereby also the component costs of the guide elements 16 increase.

The inner guide element section 17 has a radial length L1. In addition, the outer guide element section 18 a radial length L2. The length L1 has a ratio of 2: 1 compared to the length L2. The ratio is on the expression of the swirl upstream of the mixer 11 dependent. The expression of the twist influences, for example, the detailed shape and size of the second exhaust gas segment 4 , the inlet 8th , the third exhaust gas segment 5 and the impact angle of the exhaust gas mass flow on the inner guide element section 17 / outer guide element section 18 ,

The inner guide element section 17 is inclined against the direction of the arrow P2, so that an inflow of the exhaust gas mass flow into the mixer 11 is relieved. The outer guide element section 18 is inclined in the direction of the arrow P2, so that an inflow of the exhaust gas mass flow into the mixer 11 is difficult. The inclination angle of the inner guide element section 17 and the outer guide element section 18 is in turn of the expression of the swirl upstream of the mixer 11 dependent.

By means of the inner guide element section 17 and the outer guide element section 18 is the exhaust gas mass flow relative to the central axis 6 directed from outside to inside. In front of the mixer 11 creates a strong spin around the central axis 6 , This is characterized by a very high flow rate near the pipe wall and a lower flow rate in the interior. As a result, the exhaust gas mass flow (based on mass per unit of time) near the pipe wall is greater in comparison to the immediate vicinity of the center axis 6 ,

This unequal distribution would negatively affect the conversion rate of the second exhaust aftertreatment device 14 As exhaust components flowing at the edge have a shorter duration (reaction time) in the second exhaust aftertreatment device 14 would linger compared to exhaust components that are near the center axis 6 stream. By the shape of the mixer 11 , in particular of the inner guide element section 17 and the outer guide element section 18 , this inequality is counteracted.

The outer guide element sections 18 are inclined in the flow direction of the swirl, so that flowing exhaust gas from flowing into the mixer 11 is prevented. The inner guide element sections 17 are inclined against the flow direction of the swirl, so that the exhaust gas flow thus easier in the mixer 11 can flow in.

Downstream of the inner Leitelementabschnitts 17 and the outer guide element section 18 is through the guide element 16 a total deflection of the now equally distributed flow (based on the output spin) achieved, resulting in improved mixing. The exhaust gas is downstream of the mixer 11 Homogenized with respect to the distribution of the exhaust gas mass flow and the reducing agent.

Due to the geometric design of the guide 16 when flowing through the exhaust gas mass flow through the mixer 11 the direction of rotation reversed. This direction of rotation change and the conduction of the exhaust gas mass flow from outside to inside, which primarily by the inner Leitelementabschnitt 17 and the outer guide element section 18 is generated, contributes to an improvement in the mixing of the vaporized reducing agent with the exhaust gas mass flow.

LIST OF REFERENCE NUMBERS

1

contraption

2

first exhaust aftertreatment device

3

first exhaust gas segment

4

second exhaust gas segment

5

third exhaust gas segment

6

central axis

7

central axis

8th

inlet

9.1

injector

9.2

injector

10

fourth exhaust gas segment

11

mixer

12

fifth exhaust gas segment

13

sixth exhaust gas segment

14

second exhaust aftertreatment device

15

central axis

16

vane

17

inner guide element section

18

outer guide element section

L1

length

L2

length

P1

arrow

P2

arrow

P3

arrow

α

angle

Claims (6)

Contraption ( 1 ) for the exhaust aftertreatment of an exhaust gas mass flow in an exhaust line, wherein in the exhaust line an injector ( 9.1 . 9.2 ) is arranged for supplying reducing agent in the exhaust gas mass flow, and wherein a cylindrical exhaust gas strand segment ( 5 ) a tangential inlet ( 8th ), wherein downstream of the tangential inlet ( 8th ) a mixer ( 11 ) is arranged to reverse the direction of rotation of the exhaust gas mass flow, and upstream of the mixer ( 11 ) the injector ( 9.1 ; 9.2 ) in the cylindrical exhaust gas segment ( 5 ) on the central axis ( 6 ) of the mixer ( 11 ) or upstream of the inlet ( 8th ) in a cross-section narrowed region of an exhaust gas line segment ( 4 ), which immediately upstream of the tangential inlet ( 8th ) is arranged, wherein the mixer ( 11 ) at least one radially extending guide element ( 16 ), wherein with respect to the central axis ( 6 ) of the mixer ( 11 ) the guiding element ( 16 ) in an inner guide element section ( 17 ) and an outer guide element section ( 18 ), and wherein the inner guide element section ( 17 ) is inclined against the direction of rotation (P2) of the flow, and wherein the outer guide element section ( 18 ) is inclined in the direction of rotation (P2) of the flow. Contraption ( 1 ) according to claim 1, characterized in that the radial length (L1) of the inner guide element section ( 17 ) a ratio of 2: 1 to the radial length (L2) of the outer guide element section (FIG. 18 ) having. Contraption ( 1 ) according to one of the preceding claims, characterized in that upstream of the inlet ( 8th ) a first exhaust aftertreatment device ( 2 ), wherein the central axis ( 7 ) the first Exhaust aftertreatment device ( 2 ) perpendicular to the central axis ( 6 ) of the mixer ( 11 ). Contraption ( 1 ) according to one of the preceding claims, characterized in that downstream of the mixer ( 11 ) a second exhaust aftertreatment device ( 14 ), wherein the central axis ( 15 ) of the second exhaust aftertreatment device ( 14 ) eccentric to the central axis ( 6 ) of the mixer ( 11 ). Contraption ( 1 ) according to one of the preceding claims, characterized in that downstream of the mixer ( 11 ) immediately adjoins a cross-sectional widening region. A method for exhaust aftertreatment of an exhaust gas mass flow in an exhaust line, wherein the exhaust gas mass flow, a reducing agent is supplied, and wherein the exhaust gas mass flow through a tangential inlet ( 8th ) into a cylindrical exhaust gas segment ( 5 ), characterized in that the exhaust gas mass flow as it flows through the inlet ( 8th ) in a spiral movement about the central axis ( 6 ) of the cylindrical exhaust gas segment ( 5 ) is transferred in a first rotational direction (P2), and then the exhaust gas mass flow offset with the reducing agent is fed to a mixer ( 11 ), and wherein in the mixer ( 11 ) the first direction of rotation (P2) of the exhaust gas mass flow is reversed in a second direction of rotation (P3) opposite to the first direction of rotation (P2), the mixer ( 11 ) at least one radially extending guide element ( 16 ), wherein with respect to the central axis ( 6 ) the guiding element ( 16 ) in an inner guide element section ( 17 ) and an outer guide element section ( 18 ), wherein the inner guide element section ( 17 ) is inclined against the direction of rotation (P2) of the flow, and wherein the outer guide element section ( 18 ) is inclined in the direction of rotation (P2) of the flow, wherein at the outer guide element section ( 18 ) the exhaust gas mass flow at an inflow into the mixer ( 11 ) is prevented, and wherein at the inner guide element section ( 17 ) an inflow of the exhaust gas mass flow into the mixer ( 11 ), so that the exhaust gas mass flow relative to the central axis ( 6 ) of the mixer ( 11 ) is directed from outside to inside.

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