DE102011079906A1 - Exhaust gas system for internal combustion engine of motor vehicle, has device for introduction of ammonia in exhaust gas flow, and mixing section for distributing ammonia in exhaust gas flow with mixing section axis - Google Patents

Abstract

The exhaust gas system (1) has an introducing device (3) for introduction of ammonia in an exhaust gas flow, a mixing section (5) for distributing the ammonia in the exhaust gas flow with a mixing section axis, where a mixing section-discharge cross section is provided. A selective catalytic reduction catalyst (7) is provided with a catalyst axis, which encloses with the mixing section axis. A hopper section (6) is provided for exhaust flow guidance of the mixing section-discharge cross section for catalyst-inlet transverse section.

Description

The invention relates to an exhaust system for a motor vehicle having an internal combustion engine having a catalyst with a catalyst inlet cross section and a funnel section upstream of this in the exhaust gas flow direction for exhaust gas flow guidance to the catalyst inlet cross section.

From the DE 196 33 563 A1 is an exhaust system of an internal combustion engine with a circular or oval-cylindrical catalyst housing with large diameter or with large radii, an input side circular or oval cylindrical exhaust pipe with small diameter or with small radii and with an inlet fitting therebetween provided with at least one flow-influencing guide is known, in the axis of the catalyst housing and the axis of the exhaust pipe at an angle between 100 ° and about 185 ° to each other, wherein the inflow to the flow path has a shorter inner portion and a longer outer portion, and wherein the guide device on the outside is arranged section to improve an exhaust system of an internal combustion engine to the effect that a uniform application of the catalyst housing or the catalyst support over the entire end face is ensured even if the Katalysatoranströmung occurs obliquely, ie when the axes of the catalyst housing or the catalyst carrier and the input side exhaust pipe are not aligned or parallel to each other.

The invention is based on the object in an exhaust system mentioned above, in which the catalyst is an SCR catalyst, upstream of a device for introducing ammonia (NH ₃ ) into an exhaust gas flow and a mixing section for distributing the ammonia in the exhaust gas flow in the exhaust gas flow direction are to improve a uniform loading of the catalyst with ammonia.

The object is achieved with an exhaust system for a motor vehicle having an internal combustion engine having a device for introducing ammonia (NH ₃ ) into an exhaust gas stream, a mixing section following in the exhaust gas flow direction for distributing the ammonia in the exhaust gas stream with a mixing section axis and a mixing section outflow cross section, an exhaust gas downstream SCR catalyst having a catalyst axis including an obtuse interior angle with the mixing section axis and a catalyst inflow section, the mixing section flow area having a smaller area than the catalyst inflow section, and one between the mixing section flow area and Catalyst inlet cross-section arranged funnel portion for exhaust gas flow guide from the mixing section Ausströmquerschnitt to the catalyst inlet cross-section, wherein the funnel section from the mixing section to the K analyzer expanded discontinuously.

An SCR catalyst enables selective catalytic reduction (SCR) of nitrogen oxides (NO _x ), in particular of NO and NO ₂ , while undesired secondary reactions, for example oxidation of sulfur dioxide to sulfur trioxide, can be largely suppressed.

With the exhaust system according to the invention, a better uniform distribution of the exhaust gas flow velocity at the catalyst inflow cross section and thereby a reduced pressure loss catalyst can be achieved. It can be achieved a better ammonia uniform distribution at the catalyst inlet cross section. A load point dependency can be avoided. A high ammonia uniform distribution at the mixing section outflow cross section can be transferred to the catalyst inflow cross section. In the funnel section recirculations can be reduced or prevented. It is possible to generate a back pressure upstream of the catalyst inflow cross section which reduces or prevents exhaust flow separation.

With the funnel section, the mixing section outflow cross section may initially be continued, and a flow cross-sectional widening to the catalyst inlet cross-section can only take place near the catalyst. The relative term "near" is to be understood in particular as meaning that the flow cross-section extension does not take place over the entire funnel section, but essentially at an end section of the funnel section facing the catalyst.

The funnel section may have a steeply sigmoid expanding flow cross section towards the catalyst inflow cross section. The Stömungsquerschnitt extended extending s-shaped running.

The mixing section axis and the catalyst axis can run at least approximately skewed relative to one another and the flow cross section of the funnel section can expand asymmetrically from the mixing section towards the catalyst.

The funnel portion may have a flank portion with which a substantial extension is achieved.

In summary, in other words, the invention provides, among other things, an optimized inlet funnel for SCR systems. The inlet funnel has a special shape - according to a steep fishing funnel - on. The inlet funnel retains the shape of a mixing section and opens shortly before the SCR catalyst in a steep sigmuiden course.

Hereinafter, an embodiment of the invention will be described with reference to figures. From this description, further features and advantages. Concrete features of this embodiment may represent general features of the invention. Features associated with other features of this embodiment may also represent individual features of the invention.

They show schematically and by way of example:

1 an exhaust system for an internal combustion engine-powered motor vehicle with an inlet, a device for introducing ammonia, a mixer, a mixing section, a funnel section, an SCR catalyst and an outlet in perspective view,

2 a funnel section and an SCR catalytic converter of an exhaust system in plan view,

3 a hopper section and an SCR catalytic converter of an exhaust system in perspective view and

4 a funnel section and an SCR catalytic converter of an exhaust system in a side view.

1 shows an exhaust system 1 for an internal combustion engine-powered motor vehicle with an inlet 2 , a facility 3 for the introduction of ammonia, a mixer 4 , Mix section 5 a funnel section 6 , an SCR catalyst 7 and an outlet 8th in perspective view.

The exhaust system 1 serves for the removal and purification of combustion exhaust gases of a lean-burn diesel engine, not shown here. About the inlet 2 During operation of the internal combustion engine, the exhaust gases in the exhaust system 1 initiated. With the exhaust system 1 a catalytically assisted reduction of NO _x can take place in an oxidizing environment.

In the present case, the reducing agent used is ammonia in the form of an aqueous urea solution, for example a 32.5 percent urea solution. The urea solution can be carried in a storage tank and supplied with compressed air or with the aid of a valve without air support. The urea solution is supplied by means of the device 3 , The supply of urea solution is discontinuous. To achieve thorough mixing and uniform distribution of the urea solution in the exhaust stream, the mixer is 4 intended. The mixer 4 is designed here as a swirl element. With the mixer 4 a strong swirl flow is achieved.

In the exhaust gas flow direction subsequently closes to the mixer 4 a mixing section 5 at. At the end of the mixing section 5 is the urea solution in the exhaust stream very evenly distributed. The mixing section 5 has a mixing section outflow cross section. Using the funnel section 6 the exhaust gas flow from the mixing section 5 to the SCR catalyst 7 directed. The SCR catalyst 7 has a catalyst inflow cross section. On the SCR catalyst 7 the urea solution is converted into ammonia essentially by hydrolysis. The reduction of NO _X then takes place on the SCR catalyst.

2 shows a funnel section 9 and an SCR catalyst 10 an otherwise not shown exhaust system in plan view, a perspective view of the funnel section 9 and the SCR catalyst 10 is in 3 and a side view of the funnel section 9 and the SCR catalyst 10 is in 4 shown.

The funnel section 9 has a funnel inlet cross section 11 and a funnel vent cross section 12 on. The funnel section 9 is using the funnel inflow section 11 with the mixing section and with the funnel outlet cross section 12 connected to the SCR catalyst. The funnel inflow cross section 11 corresponds to the mixing section Ausströmquerschnitt. The funnel outlet cross section 12 corresponds to the catalyst inflow cross section.

The funnel inflow cross section 11 has an approximately elliptical shape. In the exhaust gas flow direction approximately at right angles to the funnel inlet cross section 11 is a funnel inflow axis 13 arranged. The funnel outlet cross section 12 has a slot-like shape with a straight top edge, a parallel to this straight bottom edge and semi-circular sides. In the exhaust gas flow direction approximately at right angles to the funnel inlet cross section 11 is a funnel discharge axis 14 arranged. The funnel inflow axis 13 and the funnel discharge axis 14 close together a dull interior angle. The funnel inflow axis 13 and the funnel discharge axis 14 run in parallel planes. The funnel inflow axis 13 and the funnel discharge axis 14 are skewed to each other.

The funnel section 9 has an inflow section 15 , an outflow section 16 and one between inflow section 15 and Ansströmabschnitt 16 arranged transition section 17 on. With the transition section 17 a transition occurs from the shape of the funnel inflow cross section 11 to the shape of the funnel Ausströmquerschnitts 12 , With the transition section 17 there is a deflection of the exhaust gas flow from one of the Trichtereinströmachse 13 corresponding flow direction to one of the Funnelausströmachse 14 corresponding flow direction.

In the area of the funnel inflow axis 13 and the funnel discharge axis 14 enclosed blunt interior angle, the transition section 17 an inner radius 18 on. With the inner radius 18 an improved uniform distribution of the urea solution is achieved in the exhaust stream. The shape of the funnel inflow cross section 11 is maintained as far as possible in the exhaust gas flow direction. The flat, elliptical shape of the funnel inflow cross section 11 is maintained as far as possible in the exhaust gas flow direction. In the exhaust gas flow direction subsequently takes place with the transition section 17 then a steep sigmoidal extension of the flow channel to the shape of the funnel Ausströmquerschnitts 12 ,

The extension of the flow channel takes place, in particular in 4 apparent, asymmetrical. A bottom 19 the inflow section 15 is about the same height as a bottom 20 the outflow section 16 , At the bottom is the transition section 17 only slightly extended. A top 22 the outflow section 16 is well above a top 21 the inflow section 15 , At the top is the transition section 17 greatly expanded. The transition section 17 has a flank section 23 which has achieved a significant expansion. The flank section 23 is at the transition section 17 in the 4 arranged above.

LIST OF REFERENCE NUMBERS

1

exhaust system

2

inlet

3

Facility

4

mixer

5

mixing section

6

funnel section

7

SCR catalyst

8th

outlet

9

funnel section

10

SCR catalyst

11

Funnel inflow

12

Funnel outflow

13

Trichtereinströmachse

14

Trichterausströmachse

15

inflow

16

outflow

17

Transition section

18

inner radius

19

bottom

20

bottom

21

top

22

top

23

flank section

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 19633563 A1 [0002]

Claims (5)

Exhaust system ( 1 ) for a motor vehicle with an internal combustion engine having a device ( 3 ) for introducing ammonia (NH ₃ ) into an exhaust gas flow, a mixing section following in the exhaust gas flow direction (US Pat. 5 . 15 ) for distributing the ammonia in the exhaust gas stream with a mixing section axis ( 13 ) and a mixing section outflow cross section ( 11 ), a downstream in the exhaust gas flow direction SCR catalyst ( 7 . 10 ) with a catalyst axis ( 14 ) associated with the mixing section axis ( 13 ) includes an obtuse inner angle, and a catalyst inflow ( 12 ), wherein the mixing section outflow cross-section ( 11 ) has a smaller area than the catalyst inlet cross section ( 12 ), and one between the mixing section Ausströmquerschnitt ( 11 ) and the catalyst inlet cross section ( 12 ) arranged funnel section ( 6 . 9 ) to the exhaust flow guide from the mixing section outflow section (FIG. 11 ) to the catalyst inlet cross section ( 12 ), wherein the funnel section ( 6 . 9 ) from the mixing section ( 5 . 15 ) to the catalyst ( 7 . 10 ) discontinuously expanded. Exhaust system ( 1 ) according to claim 11, characterized in that with the funnel section ( 6 . 9 ) the mixing section outflow cross section ( 11 ) is continued first and only near the catalyst ( 7 . 10 ) a flow cross-sectional extension to the catalyst inlet cross-section ( 12 ) he follows. Exhaust system ( 1 ) according to one of the preceding claims, characterized in that the funnel section ( 6 . 9 ) to the catalyst inlet cross section ( 12 ) has a steeply sigmoid expanding Strömungsquerschnitt. Exhaust system ( 1 ) according to one of the preceding claims, characterized in that the mixing section axis ( 13 ) and the catalyst axis ( 14 ) run at least approximately skewed to each other and the flow cross section of the funnel section ( 6 . 9 ) from the mixing section to the catalyst ( 7 . 10 ) expanded asymmetrically. Exhaust system ( 1 ) according to one of the preceding claims, characterized in that the funnel section ( 6 . 9 ) a flank section ( 23 ), with which a substantial extension is achieved.

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