DE102010045750B4 - Exhaust system of an internal combustion engine - Google Patents

Abstract

Exhaust system of an internal combustion engine with means for generating a swirl flow in the exhaust stream, characterized in that the means for generating a swirl flow in the exhaust line of the exhaust system pipe section (18) comprise, which has an elongated cross-section and in the form of a helical coil about the central longitudinal axis (20 ) of the pipe section (18) is twisted.

Description

The present invention relates to an exhaust system of an internal combustion engine with means for generating a swirl flow in the exhaust stream.

Due to stricter exhaust gas regulations for internal combustion engines, nitrogen oxides (NOx) in the exhaust gas must be reduced. A known possibility is to reduce the nitrogen oxides in a so-called selective catalytic reduction (SCR) to nitrogen and water. This takes place in a so-called SCR catalyst using a reducing agent injected into the exhaust gas. For this purpose, in particular a water-urea mixture can be used, the urea decomposes in the exhaust gas to ammonia, which reacts with the nitrogen oxides. Furthermore, liquid fuel in the form of different hydrocarbon compounds (HC) can also be injected into the exhaust gas.

It is desirable in such reduction methods in principle that on the one hand, the reducing agent is mixed as uniformly as possible with the exhaust gas and on the other hand the most complete evaporation or thermolysis of the liquid reducing agent is achieved in order to achieve high efficiency in the reduction and a deposit-free operation.

The distribution of the fluid in the exhaust stream is usually supported by a swirl flow, which has been generated by previously used in a pipeline of the exhaust line swirl generator and mixer. However, such internal swirl generator and mixer are not only relatively expensive, they also bring a relatively high cross-sectional interlocking with it.

In the DE 100 38 796 A1 is a module for exhaust systems of internal combustion engines with gasoline Dirketeinspitzung described which comprises a tubing designed as a tube piece whose tube wall is profiled thread.

In the DE 102 01 044 A1 is described an exhaust system for internal combustion engines, which comprises a helical profiled pipe following an upstream swirler, with which the peripheral speed component of the cross flow is further increased. In this case, the tube is provided on its inside with an inwardly projecting helical ridge.

The invention has for its object to provide an improved exhaust system of the type mentioned, in which the aforementioned problems are eliminated. In particular, the effort for the generation of swirls should be reduced and a cross-sectional block should be avoided as far as possible.

According to the invention, this object is solved by the features of claim 1. In this case, provision is made in particular for the means for generating a swirl flow to comprise a pipe section located in the exhaust line of the exhaust system, which has an oblong cross section and is twisted around the central longitudinal axis of the pipe section in the manner of a helical coil.

Due to this design, a particular swirl flow can be generated in particular even without internal swirl generators and / or mixers only by the shape of the tube geometry. It is thus in particular a replacement of a conventional internal mixer z. B. for SCR and HCl applications possible.

In addition, due to the lack of cross-sectional blocking results in a lower back pressure. In particular, a CFD-based (CFD = computational fluid dynamics) optimization to avoid dead water areas is possible. In addition, the outer tube geometry may also function as a phase separator, secondary atomizer, evaporator and / or turbulence generator, i. H. meet conventional SCR mixer functions. In this case, a phase separation over a relatively large cross-sectional area is possible. For example, depending on the length-to-width ratio of the elongate cross-section, over 50% of the cross-sectional area may be without free passage. With such a tube geometry, a conventional swirl turbine mixer can be replaced, in particular when using center-hollow-cone nozzles for injecting the fluid.

To get the cross-sectional area 100% "opaque", z. As well as a combination of the helically coiled pipe section with a relatively small, turbine-like stationary Gasumlenkschaufeln having sidestream swirler or mixer possible. Thus, virtually all marketable dosing systems such. As Denoxtronic, Departronic, etc. for injecting the fluid can be used. Under a 100% "opaque" cross-sectional area is to be understood that at any point of the exhaust pipe cross section, a view from the inlet side of the SCR or HCl line to its outlet side is possible. It is thus conceivable, for example, to incorporate a small sidestream swirler or mixer with turbine-type stationary gas deflecting vanes in the previously freely continuous interior region of the exhaust pipe cross-section, the swirl direction of which coincides with that of the external swirl mixer or helically coiled pipe section. This results in a separation of the liquid droplets ( Liquid phase separation) for secondary atomization and evaporation over the entire cross section of the exhaust pipe, thus avoiding penetration of non-vaporized particles. A sidestream twist generator is to be understood as meaning that part of the exhaust gas mass flow flows past the swirl generator laterally. The inner cross-sectional area of the helically coiled tube section is thus greater than the cross-sectional area of the bypass current twist generator.

According to a preferred practical embodiment of the exhaust system according to the invention, the helically coiled pipe section has a cross-section having two mutually perpendicular axes of symmetry. In this case, the cross section may in particular be elliptical or rectangular.

Advantageously, the ratio of the two axes of symmetry of the elongate cross-section of the helically coiled tubing section ranges from about 1.5: 1 to about 3: 1.

Preferably, the ratio of the two axes of symmetry of the helically coiled tube section is at least substantially constant over the length of the tube section. In principle, however, a variable over the length of the pipe section ratio of the two axes of symmetry is conceivable.

The elongate cross-section of the tube section is advantageously rotated about an angle in the range of about 90 ° to about 180 ° about the central longitudinal axis of the tube section to form the helical helix.

The swirl intensity is decisively determined by the helical pitch of the helical coil section measured over the helical pitch of the longitudinal section of the tube section. According to a preferred practical embodiment of the device according to the invention, this helical pitch of the elongated cross-section, helically coiled tube section is in a range of about 35 ° to about 55 °, in particular, may be 45 °.

Preferably, the screw pitch of the oblong cross-section of a helically coiled tubular section measured over the central longitudinal axis is at least substantially constant over its length. In principle, however, a variable over the length of the pipe section screw pitch is conceivable.

Conveniently, in the exhaust line, a pipe section comprising the elongated cross section pipe section is provided, which has a circular cross-section in the region of its upstream end viewed in the exhaust gas flow direction and the cross section in a transition region between the circular end having a circular cross-section and the helically coiled Pipe section continuously merges from the circular to the elongated cross section, wherein the transition is preferably carried out without rotation about the central longitudinal axis.

It is particularly advantageous if in the exhaust line, a pipe section is provided with the elongated cross-section tube part, which has a circular cross section in the region of its downstream viewed in the exhaust flow direction and whose cross section in a transition region between the elongated cross-section possessing helically coiled pipe section and continuously transitioning from the elongated to the circular cross-section having a circular cross-section, said transition preferably maintaining the previous pitch of the screw, i. H. in particular, the screw pitch which is present at the downstream end of the pipe section takes place.

Preferably, a combination of the two latter embodiments is provided, according to which the pipe section with the elongated cross-section comprising both in the region of its downstream end viewed in the exhaust gas flow direction and in the downstream end viewed in the exhaust gas flow direction has a circular cross-section and the transition between the upstream end portion and the helical coiled pipe section having an oblong section, and the transition between it and the downstream end portion is preferably performed as indicated.

According to an expedient practical embodiment of the exhaust system according to the invention, a device for injecting a fluid, in particular a water-urea mixture or a liquid fuel, is provided in an exhaust gas stream.

In this case, the injection device comprising at least one nozzle can be arranged and designed, for example, such that the fluid can be injected into the exhaust gas flow in the region of the upstream end of the tube part. The geometry of the pipe part according to the invention can therefore in particular fulfill the function of a mixer after injection.

However, it is also conceivable, for example, such an embodiment in which the Eindüseinrichtung comprising at least one nozzle is arranged and designed so that the fluid in the region of the downstream end of the pipe part is hineinüsbar in the gas stream. The geometry of the pipe part according to the invention can therefore in this case in particular fulfill the function of a turbulence generator prior to injection.

According to a further advantageous embodiment of the device according to the invention, however, the Eindüseinrichtung comprising at least one nozzle can also be arranged and designed so that the fluid is slidable in a viewed in the exhaust gas flow direction central region of the pipe part in the exhaust stream.

The invention will be explained in more detail below with reference to exemplary embodiments with reference to the drawing; in this show:

1 FIG. 2 shows a side view of an exemplary embodiment of a pipe part according to the invention lying in the exhaust system of an exhaust system, FIG.

2 a plan view of the pipe part according to 1 .

3 a perspective view of the pipe part according to 1 .

4 a further perspective view of the pipe part, wherein the pipe part relative to the representation in 3 but rotated 90 ° about its central longitudinal axis,

5 a front view of the pipe part according to 1 on the upstream end,

6 a rear view of the pipe part according to 1 on the downstream end,

7 a perspective view of the pipe part according to 1 with an associated injection device for injecting the fluid in the region of the upstream end of the tubular part,

8th a perspective view of the pipe part according to 1 with an associated injection device for injecting the fluid in the region of the downstream end of the tubular part,

9 a perspective view of the pipe part according to 1 with an associated injection device for injecting the fluid in an exhaust gas flow in the middle region of the pipe part, and

10 to 12 different schematic representations of an exemplary embodiment of the pipe part according to the invention in combination with a turbine-like Gasumlenkschaufeln having sidestream swirler or mixer to achieve a 100% "opaque" cross-sectional area.

The illustrated pipe part 10 is part of an exhaust system of an internal combustion engine, in particular a diesel engine, with a device 12 for injecting a fluid (cf. 7 to 9 ), in particular a water-urea mixture or a liquid fuel, in an exhaust gas stream and a distributor device for distributing the fluid in the exhaust gas stream. In this case, the distributor device comprises the pipe section lying in the exhaust system of the exhaust system 10 , The exhaust gas flows through this pipe part 10 in exhaust flow direction A.

The pipe section located in the exhaust system of the exhaust system 10 has in the region of its upstream end viewed in the exhaust flow direction A. 14 and in the region of its downstream end viewed in the exhaust flow direction A. 16 each a circular cross-section. Between the two ends 14 . 16 includes the pipe part 10 a pipe section 18 which has an elliptical cross-section and to form a helical coil about the central longitudinal axis 20 of the pipe part 10 is twisted. In the pipe section having an elliptical cross-section 18 thus results in a cross-sectional entanglement.

The elliptical cross-section of the helically coiled tube section 18 may be defined in particular by an ellipse whose half-axis ratio while maintaining the tube cross-sectional area in a range of about 1.5: 1 to about 3: 1, wherein it may be for example 2: 1.

Conveniently, the half-axis ratio of the elliptical cross section of the helically coiled tube section 18 defining ellipse over the length L of the pipe section 18 at least essentially constant. In principle, however, is also an over the length L of the pipe section 18 variable half-axis ratio conceivable.

The elliptical cross-section possessing pipe section 18 of the pipe part 10 can be used to form the helical coil, in particular by an angle in the range of about 90 ° to about 180 ° about the central longitudinal axis 20 of the pipe part 10 be twisted. Preferably, the cross-sectional entanglement is thus at least 90 °, with 180 ° being sufficient in each case.

The opposite the central longitudinal axis 20 measured helical pitch of the elliptical cross section possessing, helically coiled tube section 18 is in particular in a range of about 35 ° to about 55 °, in particular, may be 45 °.

Preferably, the opposite to the central longitudinal axis 20 measured helical pitch of the elliptical cross section possessing, helically coiled tube section 18 over its length L at least substantially constant. In principle, however, one over the length L of the pipe section 18 Variable screw pitch conceivable.

In a transition area 22 (cf., in particular 1 and 2 ) between the circular section having the upstream end portion 14 and the helical coil section having the ellipsoidal section 18 goes the cross section of the pipe part 10 in particular continuously from the circular to the elliptical cross section over. The transition takes place in particular without rotation about the central longitudinal axis 20 ,

In a transition area 24 (see in particular 1 and 2 ) between the elliptical cross-section possessing helically coiled pipe section 18 and the circular-sectioned downstream end portion 16 goes the cross section of the pipe part 10 in particular continuously from the elliptical to the circular cross-section, wherein this transition preferably while maintaining the previous pitch of the screw, ie in particular the at the downstream end of the pipe section 18 existing screw pitch, takes place.

In the transition area 22 For example, a transition from a circular cross-section to an elliptical cross-section with a half-axis ratio of 2: 1 without rotation can take place. In the transition area 24 For example, a transition from an elliptical cross section with a half-axis ratio of 2: 1 can be made to a circular cross section while maintaining the helical pitch.

When in the 7 illustrated embodiment, the at least one nozzle 26 comprehensive injection device 12 arranged and designed so that the fluid in the region of the upstream end 14 is arranged. The geometry of the pipe part according to the invention 10 So here, in particular, can fulfill the function of a mixer after the injection.

In the in the 8th reproduced embodiment is the at least one nozzle 26 comprehensive injection device 12 arranged and designed so that the fluid in the region of the downstream end 16 of the pipe part 10 can be injected into the exhaust stream. In the present case, the geometry of the pipe part according to the invention 10 So in particular fulfill the function of a turbulence generator before the injection.

In the in the 9 reproduced embodiment is the at least one nozzle 26 comprehensive injection device 12 arranged and designed so that the fluid in a viewed in the exhaust gas flow direction A central portion of the pipe part 10 can be injected into the exhaust stream.

With the geometry of the pipe part according to the invention 10 results from the lack of cross-sectional blocking a lower back pressure. In particular, a CFD-based optimization for avoiding dead water areas and according to deposits is possible. The outer geometry of the pipe part 10 In particular, it can also fulfill the function of a liquid phase separator, secondary atomizer, evaporator and turbulence generator and thus classic SCR mixer functions.

It is possible a liquid phase deposition over a large cross-sectional area. Thus, depending on the elliptical main axis ratio, more than 50% of the cross-sectional area can be without free passage and thus serve for phase separation.

The geometry of the pipe part according to the invention 10 can replace a classic swirl turbine mixer, especially in the case of axially-centered hollow cone nozzles.

To get the cross-sectional area 100% "opaque", for example, is a combination of the helically coiled tube section 18 with a relatively small, turbine-like, gas-directing vanes 30 having side stream swirl generator or mixer 28 (see the 10 to 12 ) or the like possible, whereby in particular the use of all common metering systems such. As Denoxtronic, Departronic etc. is made possible. Under a 100% "opaque" cross-sectional area is to be understood that at any point of the exhaust pipe cross section, a view from the inlet side of the SCR or HCl line to its outlet side is possible. It is therefore conceivable, for example, in the hitherto freely continuous interior region of the exhaust gas pipe cross section, a small sidestream twist generator or mixer 28 (see the 10 to 12 ) with turbine-type stationary gas deflection vanes 30 to install, whose swirl direction with that of the external swirl mixer or pipe section 18 matches. This results in a separation of the liquid droplets (liquid phase separation) for secondary atomization and evaporation over the entire cross section of the exhaust pipe, whereby a penetration of non-evaporated particles is avoided. A sidestream twist generator is to be understood as meaning that part of the exhaust gas mass flow flows past the swirl generator laterally (cf. 11 ). Here, the inner cross-sectional area of the pipe section 18 greater than the cross-sectional area of the bypass eddy generator.

LIST OF REFERENCE NUMBERS

10

pipe part

12

injection device

14

upstream end

16

downstream end

18

pipe section

20

central longitudinal axis

22

Transition area

24

Transition area

26

jet

28

By-pass twist generator or mixer

30

Gasumlenkschaufel

A

Exhaust gas flow direction

L

length

Claims (13)

Exhaust system of an internal combustion engine with means for generating a swirl flow in the exhaust stream, characterized in that the means for generating a swirl flow lying in the exhaust line of the exhaust system pipe section ( 18 ), which has an elongate cross-section and in the form of a helical coil about the central longitudinal axis ( 20 ) of the pipe section ( 18 ) is twisted. Exhaust system according to claim 1, characterized in that the helically coiled pipe section ( 18 ) has a two mutually perpendicular axes of symmetry having, in particular elliptical or rectangular cross-section. Exhaust system according to claim 2, characterized in that the ratio of the two axes of symmetry of the elongated cross section of the helically coiled pipe section ( 18 ) ranges from about 1.5: 1 to about 3: 1. Exhaust system according to claim 2 or 3, characterized in that the ratio of the two axes of symmetry of the helically coiled tube section ( 18 ) over the length (L) of the pipe section ( 18 ) is at least substantially constant. Exhaust system according to one of the preceding claims, characterized in that the elongate cross section of the pipe section ( 18 ) for forming the helical coil by an angle in the range of about 90 ° to about 180 ° about the central longitudinal axis ( 20 ) of the pipe section ( 18 ) is twisted. Exhaust system according to one of the preceding claims, characterized in that the relative to the central longitudinal axis ( 20 ) measured screw pitch of an elongate cross-section possessing, helically coiled tube section ( 18 ) is in a range of about 35 ° to about 55 ° and preferably 45 °. Exhaust system according to one of the preceding claims, characterized in that the relative to the central longitudinal axis ( 20 ) measured screw pitch of an elongate cross-section possessing, helically coiled tube section ( 18 ) over whose length (L) is at least substantially constant. Exhaust system according to one of the preceding claims, characterized in that in the exhaust line a pipe section ( 18 ) with the elongate cross-section comprising the tubular part ( 10 ), which, in the region of its upstream end (A) considered in the exhaust gas flow direction (A) ( 14 ) has a circular cross section and its cross section in a transition region ( 22 ) between the circular cross-section having upstream end portion ( 14 ) and having an oblong cross-section helically coiled pipe section ( 18 ) preferably without rotation about the central longitudinal axis ( 20 ) continuously changes from circular to oblong cross-section. Exhaust system according to one of the preceding claims, characterized in that in the exhaust line a pipe section ( 18 ) with the elongate cross-section comprising the tubular part ( 10 ), which, in the region of its downstream end, viewed in the exhaust gas flow direction (A), ( 16 ) has a circular cross section and its cross section in a transition region ( 24 ) between the helically coiled tubular section (15) having an oblong cross-section ( 18 ) and having a circular cross-section downstream end portion ( 16 ) preferably continuously passes from the elongated to the circular cross section while maintaining the helical pitch. Exhaust system according to one of the preceding claims, characterized in that a device ( 12 ) for injecting a fluid, in particular a water-urea mixture or a liquid fuel, is provided in an exhaust gas stream. Exhaust system according to claim 10, characterized in that the at least one nozzle ( 26 ) comprehensive injection device ( 12 ) is arranged and designed so that the fluid in the region of the upstream end ( 14 ), in the region of the downstream end ( 16 ) or in a direction of the exhaust gas flow direction (A) middle portion of the pipe part ( 10 ) can be eingesüsbar in the exhaust stream. Exhaust system according to one of the preceding claims, characterized in that within the helically coiled tube section ( 18 ) a turbine-like stationary gas deflection vanes ( 30 ) by-pass swirl generator or mixer ( 28 ) is provided. Exhaust system according to claim 12, characterized in that the twisting direction of the secondary flow twist generator or mixer ( 28 ) with the helically coiled tube section ( 18 ) matches.

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