DE102009036511A1 - Exhaust system for e.g. diesel engine, has waste gas duct provided between input and exhaust gas treatment devices, and including deflection device for partial feedback of exhaust gas flow against main exhaust gas flow direction - Google Patents

Abstract

The system (1) has an input device (3) flowing into a tubular waste gas duct (2) for introducing an additive i.e. water urea mixture. The duct is provided between the input device and an exhaust gas treatment device i.e. selective catalytic reduction catalyst subordinate. The duct has a deflection device (5) for a partial feedback of an exhaust gas flow against a main exhaust gas flow direction (I), where the deflection device has a labyrinth-like flow guidance. A mixing device (21) is arranged between an opening of the input device and the deflection device in the gas flow direction.

Description

The The present invention relates to an exhaust system for internal combustion engines, in particular diesel engines, with a particular tubular design Exhaust duct, an opening into the exhaust duct input device for introducing additives, in particular a water-urea mixture, and an exhaust gas treatment device arranged downstream of the exhaust gas channel, in particular SCR catalyst.

by virtue of the sharper Becoming exhaust gas regulations for Diesel engines require the reduction of nitrogen oxides in the exhaust gas. It is known that the nitrogen oxides in a so-called selective catalytic reduction to reduce nitrogen and water. This is done in an SCR catalyst using a reducing agent injected into the exhaust gas. In particular, this is for this used a water-urea mixture, from which in the exhaust ammonia forms, which in turn reacts with the nitrogen in the exhaust gas. There Among other things, ammonia in a so-called hydrolysis reaction forms in the exhaust duct, the between the input device and the catalytic converter located exhaust gas section also as a hydrolysis route designated. It is important that in the field of hydrolysis a preferably good evaporation of the additive takes place and that the vaporized Additive or the resulting ammonia as possible evenly with the exhaust mixed to maximize efficiency to have in the reduction.

Therefore the hydrolysis must have a certain length, because at a Too short hydrolysis distance too much water-urea mixture and / or too poorly mixed exhaust gas enters the catalyst, so that the efficiency in the reduction is deteriorated. therefore known exhaust systems have a relatively large length between the input device and the catalyst.

Of the Invention is based on the object, a compact exhaust system specify which, in particular, a shorter length between the input device and the downstream exhaust treatment device, without that while essential disadvantages in terms of efficiency have to be accepted in the reduction.

These The object is solved by the features of claim 1 and in particular in that the exhaust duct between the input device and the downstream exhaust treatment device at least one deflection for at least partial repatriation of the Exhaust flow contrary to the original Main exhaust gas flow direction has.

Advantageous at the exhaust system according to the invention is that the geometric distance between the input device and the exhaust treatment device due to the deflection can be relatively short, without a shortening of the Hydrolysestrecke must be accepted, because of the return of the Exhaust stream in the deflection an additional section for the hydrolysis is available. In particular, in the case of the exhaust system according to the invention, because deflected in the deflection of the exhaust and against the original main exhaust gas flow direction guided is, even with a relatively short geometric distance between the Input device and the exhaust treatment device ensured be that the hydrolysis distance is sufficiently long to one good mixing of the vaporized additive with the exhaust gas too guarantee.

preferred Refinements and developments of the invention are specified in the dependent claims.

Preferably is the deflection such for multiple deflection of the exhaust stream formed, that the exhaust gas flow eventually returns to the original Main exhaust gas flow direction has. Due to the multiple deflection the exhaust gas flow in the region of the exhaust gas channel between the input device and the exhaust treatment device can be a relatively long Hydrolysestrecke realize, although the input device and the exhaust treatment device in a relatively short geometric Distance in relation to the original Arrange main exhaust gas flow direction one behind the other, so that a particularly compact exhaust system can be realized.

Preferably the deflection device has a labyrinthine flow guidance. By doing so leaves the exhaust gas flow in sections in different flow directions to lead, in particular alternately in the main exhaust gas flow direction or opposite the main exhaust gas flow direction, each between each other Following sections a diversion of the exhaust gas flow takes place. Preferably are the respective, consecutive exhaust duct sections nested in order to the deflection as possible compact. The advantage of this is that a relatively long Hydrolysestrecke between the input device and the exhaust treatment device can be realized, but still only a relatively short space for the exhaust system between the input device and the exhaust gas treatment device is needed.

To Another preferred embodiment of the invention is in the exhaust duct in the main exhaust gas flow direction behind the input device, a mixing device arranged. This results in a particularly good mixing of the introduced Additive achieved with the exhaust. Special advantage is it, when the mixing device between the mouth of the input device and the deflecting device is arranged. In particular, the mixing device also act as an evaporator, since liquid additive on the surface the mixing device can accumulate, which is particularly good there because of the hot Exhaust gas and / or evaporated because of the highly heated exhaust gas surface becomes.

Preferably the mixing device comprises a particularly cylindrical cross-flap mixer, which is a particularly good mixing of the additives and the Exhaust gas causes.

Prefers let yourself achieve a particularly good mixing result, if an exhaust gas inlet opening of Mixing device of the mouth the input device is facing and if further preferred inlet opening on the dosing cone of the mouth the input device is tuned. In this regard, it is advantageous if the input device is arranged in the exhaust passage such that the Additive is injected in the main exhaust gas flow direction. It would be also an injection oblique or transversely to the main exhaust gas flow conceivable.

To A further embodiment of the invention, the mixing device a swirl turbine, in particular in addition to the cross-flap mixer. Preferably, the swirl turbine is exhaust upstream to the flapper mixer arranged. By the swirl turbine is the injected additive along with the exhaust gas rotated, causing the mixing the exhaust gas is further improved with the additive. Additionally done due to inertia effects at the flow deflection through the swirl turbine a liquid phase separation, whereby the not yet evaporated additive on the preferably abgasstromabwärtig precipitates to the swirl turbine arranged mixing device and there evaporated. This can prevent that not evaporated Add additive enters the SCR catalyst.

To Another preferred embodiment of the invention is in particular centrically into the exhaust duct a main exhaust downstream at least partially closed or closable intermediate tube used, its outer diameter smaller than the inner diameter of the surrounding exhaust gas passage. By doing so leaves itself manufacturing technology particularly simple a deflection realize.

To In a further development of the invention, the main exhaust gas downstream end the intermediate tube by a flat or profiled, in particular arched in the middle Closed bottom. By doing so leaves in a simple way a possibility for deflecting the exhaust gas flow from the original one Main exhaust gas flow direction in the opposite flow direction create.

Of the Exhaust gas duct may have a main exhaust gas upstream of the intermediate pipe especially jet-like at the end trained, radially tapered Section have, which opens into the intermediate tube. By the rejuvenation can advantageously be achieved nesting of the exhaust system, without the outer circumference gets too big while the nozzle-like Training supports the turbulence of the exhaust gas.

Preferably are in the wall of the intermediate tube and / or the tapered section Back pressure relief holes available. The back pressure relief holes can in the area of the gas outlet openings arranged and in particular distributed uniformly in the circumferential direction in each case. Due to the back pressure relief holes too high exhaust back pressure avoided due to the exhaust deflection. In addition, the flow of the Further improved exhaust gas in the region of the deflection.

To a further embodiment of the invention, the gas outlet opening of the tapered section and / or the intermediate tube on a profiled final contour, in particular in the form of triangular, trapezoidal or wave-shaped indentations. By the profiled final contour become increasingly trailing vortices on the gas outlet opening of the tapered section and / or the intermediate tube, whereby the mixing of the Exhaust gas is further improved.

Preferably are the indentations viewed in the flow direction at least nearly, especially with a maximum offset of approx. +/- 15 °, in extension the back pressure relief holes. This has been for the vortex formation proved to be particularly advantageous.

According to another preferred embodiment of the invention, the tapered portion is formed at a portion of the exhaust passage upstream of the main exhaust gas flow direction, which is inserted with its tapered end in a main exhaust gas downstream portion of the exhaust passage. This makes it possible, in particular in combination with the aforementioned intermediate tube, to manufacture particularly easily and cost-effective to realize an exhaust system according to the invention.

Preferably the mixer is inside the tapered section. Therefore needed the mixing device no separate section in the exhaust duct, so that the exhaust system can be kept compact.

To still overlap a preferred embodiment of the invention the rejuvenated Section and the intermediate tube by more than half their length, in particular at least about two thirds of its length. This can be in a simple way, a relatively long section between the outside of the tapered Implement section and the inner intermediate tube wall, in the a return of the exhaust gas takes place against the actual exhaust gas flow direction.

To Another preferred embodiment of the invention is the exhaust duct in the region of the deflection relative to an adjacent channel section radially expanded. The flow cross section for the exhaust gas is thereby the deflection not too small.

embodiments The invention is illustrated in the drawings and will be described below described. They show, in each case in a schematic representation,

1 a side view in partial sectional view of an exhaust system according to the invention,

2 a perspective view in partial sectional view of the exhaust system of 1 .

3 a perspective view of a mixing device of the exhaust system of 1 .

4 a simplified plan view of the exhaust gas downstream side of the exhaust system of 1 and

5 another perspective view of the exhaust system of 1 ,

The illustrated exhaust system 1 has an exhaust duct 2 in which an input device 3 for the introduction of additives, which is in particular a water-urea mixture, flows and is followed by an exhaust treatment device, not shown, such as an SCR catalyst, downstream. In the area of the input device 3 and before the SCR catalyst, the exhaust gas flows through the exhaust passage 2 in the main exhaust gas flow direction I ,

Between the input device 3 and the downstream exhaust treatment device has the exhaust passage 2 a deflection device 5 on, which for the at least partial return of the exhaust gas flow against the actual exhaust gas flow direction I , ie in the direction of the exhaust gas flow II , is trained.

In particular, the exhaust duct 2 an upstream upper section 7 with a downstream, tapered lower end 9 and another downstream lower portion 11 on. As in particular from 1 it can be seen, is the lower end 9 in the lower section 11 guided. Further, it is centered in the lower section 11 an intermediate pipe 13 used, whose outer diameter is smaller than the inner diameter of the lower portion 11 , The gas outlet opening of the lower end 9 of the upper section 7 flows into the intermediate pipe 13 , Here, the inner diameter of the intermediate tube 13 again larger than the outer diameter of the lower end 9 , and the intermediate pipe 13 has a flat or profiled bottom 15 on which of the gas outlet opening of the lower end 9 facing and is arched in the middle of this.

By the nesting of the lower end 9 , of the intermediate pipe 13 and the lower section 11 will be in the diverter 5 a first exhaust passage section 17 formed, which is between the outer wall of the lower end 9 and the inner wall of the intermediate tube 13 extends and through which the exhaust gas against the main exhaust gas flow direction I , so in main countercurrent direction II , to be led. Further, exhaust gas downstream becomes the first exhaust passage portion 17 between the outer wall of the intermediate tube 13 and the inner wall of the lower section 11 a second exhaust passage section 19 formed in which the exhaust again in about the original main exhaust gas flow direction I is guided and in an area 20 the exhaust duct 2 opens, the downstream of the exhaust treatment device, in particular the SCR catalyst, or in which this is arranged.

In the lower end 9 of the upper section 7 is a mixing device 21 used. The mixing device 21 comprises a so-called cylindrical flap valve mixer 23 and a swirl turbine 25 (see in particular 3 ), which in the main exhaust gas flow direction I looked at in front of the flapper mixer 23 in an entrance opening 27 the mixing device 21 is arranged. In this case, the inlet opening 27 in particular to one of the input device 3 Dosing cone formed during introduction of the water-urea mixture 29 matched, so that the introduced mixture substantially completely into the mixing device 21 and thus in that of the mixing device 21 downstream exhaust duct sections passes.

How out 3 it can be seen has the swirl turbine 25 the mixing device 21 several, in the region of the inlet opening of the cross-flap mixer 23 arranged gas guide vanes. Furthermore, in particular 4 and 5 seen that the flapper mixer 23 several, oblique to the main exhaust gas flow direction I Asked flaps, which cause a flow deflection, whereby the mixing of the exhaust gas is improved with the additive.

In addition, in particular, the area of the lower end 9 formed nozzle-like manner in front of the gas outlet opening by this radially tapers towards the gas outlet opening. Furthermore, both the final contours of the lower end 9 as well as the intermediate tube 13 profiled formed by the respective final contour wave-shaped indentations 31 having. However, other shapes are possible, such as triangular or trapezoidal indentations.

Due to the nozzle-like configuration of the lower end 9 on the one hand and the profiled final contour of the lower end 9 On the other hand, particularly good wake in the exhaust gas flow at the gas outlet opening of the lower end 9 generated. This will cause a mixing of the in the intermediate tube 13 inflowing exhaust additive mixture supported. The deflection of the mixture into the first exhaust gas duct section 17 In addition, by the aforementioned, curved floor 15 of the intermediate pipe 13 supports, allowing a particularly good flow deflection of the exhaust flow from the lower end 9 in the first exhaust passage section 17 he follows.

In addition, due to the profiled final contour of the intermediate tube 13 Produces improved after-run, which in turn further improves the mixing of the exhaust gas additive mixture.

To support the flow in the exhaust passage are also back pressure relief holes 33 in the wall of the intermediate tube and in the wall of the lower end 9 available. These are each in the circumferential direction of the wall of the intermediate tube 13 and the wall of the lower end 9 arranged evenly distributed. In addition, there are the indentations 33 in the flow direction I preferably contemplates approximately in extension to the respective backpressure relief wells 33 , Through the back pressure relief holes 33 a pressure equalization takes place between the interior of the lower end 9 and the first channel section 17 and between the first channel section 17 and the second channel section 19 as a result of which an excessively high back pressure is avoided and, in addition, the diversion of the exhaust gas flow downstream of the exhaust gas outlet opening of the lower end 9 or the intermediate tube 13 (See the curved arrows in 1 ) is improved.

When the exhaust system is used as intended 1 this is the one in the upper section 7 in the main exhaust gas flow direction I flowing exhaust gas by means of the input device 3 added a water-urea mixture. The exhaust gas and the injected mixture then pass into the mixing device 21 Where these are on the one hand put into a swirling motion, which favors a mixing of the additive with the exhaust gas, and on the other hand, an improved mixing between the exhaust gas and the additive due to the swirl turbine 25 downstream cross-hatch mixer 23 he follows.

Subsequently, the exhaust gas additive mixture passes through the lower end 9 of the upper section 7 and enters the intermediate tube from the gas outlet opening of the lower end 13 , As previously mentioned, the lower end design helps 9 as well as the ground 15 of the intermediate pipe 13 a deflection of the flow direction of the exhaust gas additive mixture.

The exhaust gas additive mixture then enters the first exhaust gas passage section 17 moving in main counterflow direction II is flowed through. After leaving the gas outlet opening of the intermediate tube 13 in turn, a deflection of the exhaust gas additive mixture, so that this in the second exhaust duct section 19 in which the exhaust gas additive mixture again in the main exhaust gas flow direction I to be led. The second exhaust passage section 19 opens into the exhaust gas channel area 20 , downstream of which the SCR catalyst or in which the SCR catalyst is arranged.

Through the labyrinthine design of the exhaust passage 2 in the area of the deflection device 5 can be an exhaust system 1 with a relatively short length between the input device 3 and realize the SCR catalyst without a shortening of the exhaust gas channel between the input device 3 and the catalyst formed hydrolysis must be accepted.

LIST OF REFERENCE NUMBERS

1

exhaust system

2

exhaust duct

3

input device

5

deflecting

7

upper section

9

lower End of 7

11

lower section

13

intermediate pipe

15

ground of the intermediate pipe

17

first Exhaust duct section

19

second Exhaust duct section

20

Exhaust duct area

21

mixing device

23

Cross trap mixer

25

swirl turbine

27

inlet opening

29

metering cone

31

indentation

33

Back pressure relief bore

I

Main exhaust gas flow direction

II

Main exhaust downstream,

Claims (15)

Exhaust system for internal combustion engines, in particular diesel engines, with a particular tubular exhaust channel ( 2 ), one in the exhaust duct ( 2 ) input device ( 3 ) for introducing additives, in particular a water-urea mixture, and an exhaust gas channel ( 2 ) downstream exhaust treatment device, in particular SCR catalytic converter, characterized in that the exhaust gas channel ( 2 ) between the input device ( 3 ) and the downstream exhaust treatment device at least one deflection device ( 5 ) for the at least partial return of the exhaust gas flow against the original main exhaust gas flow direction ( I ) having. Exhaust system according to claim 1, characterized in that the deflection device ( 5 ) is designed in such a way for multiple deflection of the exhaust gas flow, that the exhaust gas flow finally returns to the original main exhaust gas flow direction ( I ) having. Exhaust system according to claim 1 or 2, characterized in that the deflection device ( 5 ) has a labyrinthine flow guide. Exhaust system according to one of the preceding claims, characterized in that in the exhaust duct ( 2 ) in the main exhaust gas flow direction ( I ) behind the input device ( 3 ) a mixing device ( 21 ) is arranged, in particular between the mouth of the input device ( 3 ) and the deflection device ( 5 ). Exhaust system according to claim 4, characterized in that the mixing device ( 21 ) a particularly cylindrical cross-flap mixer ( 23 ) and / or a swirl turbine ( 25 ) having. Exhaust system according to at least one of the preceding claims, characterized in that in the exhaust duct ( 11 ), in particular centric, a main exhaust downstream at least partially closed or optionally closable intermediate tube ( 13 ) is used, whose outer diameter is smaller than the inner diameter of the surrounding exhaust gas channel ( 11 ). Exhaust system according to claim 6, characterized in that the main exhaust gas downstream end of the intermediate pipe ( 13 ) by a flat or profiled, in particular in the center curved floor ( 15 ) is closed. Exhaust system according to claim 6 or 7, characterized in that the exhaust duct ( 7 ) main exhaust gas upstream of the intermediate tube a at the end in particular nozzle-like, radially tapered portion ( 9 ), which opens into the intermediate tube. Exhaust system according to one of claims 6 to 8, characterized in that in the wall of the intermediate tube ( 13 ) and / or the tapered section ( 9 ) Backpressure relief wells ( 33 ) are present, in each case in the region of the gas outlet openings and preferably evenly distributed in the circumferential direction. Exhaust system according to at least one of claims 6 to 9, characterized in that the gas outlet end of the tapered portion ( 9 ) and / or the intermediate tube ( 13 ) a profiled final contour, in particular in the form of triangular, trapezoidal or wave-shaped indentations ( 31 ) having. Exhaust system according to claim 10, characterized in that the indentations ( 31 ) viewed in the flow direction at least approximately in extension of the back pressure relief holes ( 33 ) are located. Exhaust system according to at least one of claims 8 to 11, characterized in that the tapered section ( 9 ) at one with respect to the main exhaust gas flow direction ( I ) upstream section ( 7 ) of the exhaust duct ( 2 ) is formed with its tapered end in a main exhaust gas downstream portion ( 11 ) of the exhaust duct ( 2 ) is used. Exhaust system according to at least one of claims 8 to 12, characterized in that the mixing device ( 21 ) within the tapered section ( 9 ) is located. Exhaust system according to one of claims 8 to 13, characterized in that the tapered portion ( 9 ) and the intermediate tube ( 13 ) overlap by more than half their length, in particular by at least about 2/3 of their length. Exhaust system according to one of the preceding claims, characterized in that the exhaust duct ( 11 ) in the region of the deflection device ( 5 ) opposite an adjacent channel section ( 7 . 20 ) is radially expanded.

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