DE102018125006A1 - Exhaust gas aftertreatment system and method for exhaust gas aftertreatment of an internal combustion engine - Google Patents

Abstract

The invention relates to an exhaust gas aftertreatment system for an internal combustion engine (10), in particular for a self-igniting internal combustion engine based on the diesel principle. The internal combustion engine (10) is connected to an exhaust gas system (20) which has an exhaust gas duct (22) in which a first catalyst close to the engine, in particular a NOx storage catalyst () in the flow direction of an exhaust gas of the internal combustion engine (10) through the exhaust gas duct (22). 26), and a particle filter (34) with an SCR coating (36) is arranged downstream of the first catalytic converter (26). A deflection element (28) is provided, with which the exhaust gas flow downstream of the first catalytic converter (26) and upstream of the particle filter (34) is deflected by approximately 180 °. A metering element (30) for metering a reducing agent (70) into the exhaust system (20) is arranged in the region of the deflecting element (28). It is provided that a mixing body (42) is arranged downstream of the metering element (30) and upstream of the particle filter (34), the mixing body (42) having a roof-shaped geometry (44) and the injection openings (32) of the metering element ( 30) are oriented in the direction of a gable (46) of the roof-shaped mixing body (42). The invention further relates to a method for exhaust gas aftertreatment of an internal combustion engine (10) with such an exhaust gas aftertreatment system.

Description

The invention relates to an exhaust gas aftertreatment system for exhaust gas aftertreatment of an internal combustion engine and a method for exhaust gas aftertreatment according to the preamble of the independent claim.

The current exhaust gas legislation, which will become increasingly stringent in the future, places high demands on raw engine emissions and exhaust gas aftertreatment of internal combustion engines. The demands for a further decrease in consumption and the further tightening of the exhaust gas standards with regard to the permissible nitrogen oxide emissions represent a challenge for engine developers. In gasoline engines, exhaust gas cleaning is carried out in a known manner using a three-way catalytic converter and the three-way Catalyst upstream and downstream further catalysts. Exhaust gas aftertreatment systems are currently used in diesel engines, which have an oxidation catalytic converter, a catalytic converter for the selective catalytic reduction of nitrogen oxides (SCR catalytic converter) and a particle filter for the separation of soot particles and, if appropriate, further catalytic converters. Ammonia is preferably used as the reducing agent. Because the use of pure ammonia is complex, a synthetic, aqueous urea solution is usually used in vehicles, which is mixed with the hot exhaust gas stream in a mixing device upstream of the SCR catalytic converter. This mixing heats the aqueous urea solution, the aqueous urea solution releasing ammonia in the exhaust gas duct. A commercially available, aqueous urea solution generally consists of 32.5% urea and 67.5% water.

In order to achieve the best possible mixing of the exhaust gas flow with the reducing agent before entering the catalytic converter for the selective catalytic reduction of nitrogen oxides (hereinafter referred to as SCR catalytic converter), exhaust gas mixers are known which include the evaporation of a liquid reducing agent and the mixing of this reducing agent promote the exhaust gas flow. Furthermore, this mixture should be distributed as homogeneously as possible on the SCR catalytic converter in order to enable the most efficient possible conversion of ammonia with the nitrogen oxides in the exhaust gas and to minimize the slip of nitrogen oxides and ammonia downstream of the SCR catalytic converter.

Pipe mixer systems are known from the prior art, which are arranged in the exhaust duct in an underbody area of a motor vehicle. However, due to their geometry and the space required, these tube mixer systems are not suitable for close-coupled SCR catalytic converters or close-coupled particle filters with an SCR coating.

A device for mixing two mass flows is known from utility model application G 92 04 547 U1, with which a first gas flow can be mixed with a second gas flow, a mixing body being arranged in a mixing space, the mixing body being in the form of a roof without a gable , with its ridge facing a first channel and its gable facing a second channel, from which the gas flows flow to the mixing body.

From the EP 1 681 089 A1 An exhaust gas aftertreatment system is known in which a reducing agent for selective, catalytic reduction is introduced into the exhaust gas duct of an internal combustion engine and mixes there with the exhaust gas stream of the internal combustion engine, a flow element being introduced into the exhaust gas duct for improved mixing of the exhaust gas stream and the reducing agent, which on its side facing away from the upstream side, causes a flow separation, which generates a targeted turbulence for mixing the reducing agent with the exhaust gas flow of the internal combustion engine.

The object of the invention is to improve the mixing of the reducing agent with the exhaust gas flow in an arrangement close to the engine of an SCR catalytic converter and thus to further increase the efficiency of the exhaust gas aftertreatment.

According to the invention, this object is achieved by an exhaust gas aftertreatment system for an internal combustion engine, in particular for a self-igniting internal combustion engine based on the diesel principle. The internal combustion engine is connected to an exhaust gas system which has an exhaust gas duct, in which a first catalytic converter close to the engine, in particular a NOx storage catalytic converter, and a particle filter with an SCR coating are arranged downstream of the first catalytic converter in the flow direction of an exhaust gas of the internal combustion engine through the exhaust gas duct. A deflection element is provided with which the exhaust gas flow downstream of the first catalytic converter and upstream of the particle filter is deflected by 150 ° to 210 °, preferably by approximately 180 °. A metering element for metering a reducing agent into the exhaust system is arranged in the region of the deflecting element. It is provided that a mixing body is arranged downstream of the metering element and upstream of the particle filter, the mixing body having a roof-shaped geometry, and the injection openings of the metering element being oriented in the direction of a gable and / or the ridge of the roof-shaped mixing body. Preferably that Dosing element three or more injection openings, wherein in one metering element with three injection openings preferably two injection jets are directed at the gable of the roof-shaped mixing body and a third injection jet is directed at the ridge of the roof-shaped mixing body. Such an exhaust gas aftertreatment system enables particularly efficient mixing of the reducing agent with the exhaust gas stream before entering the particle filter with the SCR coating. As a result, the nitrogen oxides can be completely reacted with the ammonia obtained from the reducing agent, which means that the use of the reducing agent can be reduced and the risk of ammonia emissions which can be attributed to unreacted reducing agent is reduced. In this context, an arrangement of the first catalytic converter close to the engine means a position in the exhaust system in which an inlet of the first catalytic converter has an exhaust gas run length of less than 80 cm, preferably less than 50 cm, from the exhaust valves of the internal combustion engine.

Advantageous further developments and non-trivial improvements of the exhaust gas aftertreatment system specified in the independent claim are possible due to the features mentioned in the dependent claims.

In a preferred embodiment of the invention, it is provided that the mixing body has a fastening section with which the mixing body can be fastened to a receiving section of the exhaust system, the fastening section being oriented at right angles to the roof-shaped geometry of the mixing body. A fastening section, which is formed perpendicular to the roof-shaped geometry of the mixing body, enables the mixing body to be easily attached to the exhaust duct. The fastening section, in particular a fastening plate, is oriented parallel to the wall of the exhaust gas duct and thus rotated out of the exhaust gas flow, so that the fastening section has only a low flow resistance. The mixing body is preferably produced by means of a forming tool. Such a mixing body can be produced simply and inexpensively from a corresponding metallic sheet by means of a forming tool.

It is preferred if the fastening section adjoins the roof-shaped geometry of the mixing body. If the fastening section connects directly to the roof-shaped geometry of the mixing body, particularly simple and precise positioning of the mixing body in the exhaust duct is possible.

In a further improvement of the invention it is provided that at least two holes are made in the fastening section, with which the mixing body is fixed to the exhaust gas duct of the internal combustion engine. Holes in the fastening section make it easy to fasten the mixing body to the exhaust duct by means of screws, rivets or welding. The holes also allow clear positioning for error-free installation.

It is preferred if the mixing body is fastened in a transition funnel of the exhaust system.

In an advantageous embodiment of the exhaust gas aftertreatment system, it is provided that radii are formed at the respectively open ends of the roof-shaped geometry, which promote flow separation and vortex formation downstream of the mixing body. The radii at the ends of the legs of the roof-shaped geometry additionally promote eddy formation and flow separation on the mixing body, which results in improved mixing of the exhaust gas flow and reducing agent with the same running length between the mixing body and entry into the particle filter with an SCR coating. This leads to an improved uniform distribution of the reducing agent over the cross section of the particle filter and thus increases the efficiency of the selective catalytic reduction of nitrogen oxides.

In a preferred embodiment of the invention it is provided that the roof-shaped geometry has a first leg and a second leg which are connected to one another in the gable, an opening angle between the two legs being 45 ° to 120 °, preferably 60 ° to 90 °. The opening angle between the two legs and the length of the legs are chosen so that the best possible compromise between good mixing of the exhaust gas flow and reducing agent and low flow resistance is achieved.

According to the invention, a method for exhaust gas aftertreatment of an internal combustion engine with an exhaust gas aftertreatment system according to the invention is proposed, two opposing flow vortices being formed downstream of the mixing body in the exhaust gas stream, by which the exhaust gas stream of the internal combustion engine is mixed with the reducing agent. The two opposing vortices enable particularly good mixing of the exhaust gas flow and reducing agent over a short mixing section. The particle filter can thus be arranged closer to the outlet of the internal combustion engine, which increases the temperature of the particle filter during operation and thus the conversion rates the selective catalytic reduction of nitrogen oxides. In addition, regeneration of the particle filter is facilitated by the position of the particle filter closer to the engine, since the heat losses through the walls of the exhaust gas duct are reduced. In addition, the position of the mixing body in the exhaust system means that the flow distribution between the two vortices is essentially independent of the engine operating point of the internal combustion engine and stable vortices are formed at all operating points.

In an advantageous improvement of the method it is provided that the reducing agent is metered into the exhaust gas duct in such a way that a plurality of reducing agent jets hit the mixing body in the area of the gable of the roof-shaped geometry. This can ensure that approximately the same amount of reducing agent is contained in both vortices, which further improves the mixing of the exhaust gas stream and the reducing agent.

In a preferred embodiment variant of the method it is provided that the distance of the particle filter with the SCR coating from the mixing body is selected such that an end face of the particle filter is spaced at least two, preferably at least three, lengths of the flow vortices from the mixing body. A suitable mixing length ensures thorough mixing of the exhaust gas stream and the reducing agent for the selective catalytic reduction of nitrogen oxides.

The various embodiments of the invention mentioned in this application can be combined with one another with advantage, unless otherwise stated in the individual case.

• 1 eine schematische Darstellung eines Verbrennungsmotors mit einem erfindungsgemäßen Abgasnachbehandlungssystem;
• 2 eine dreidimensionale Darstellung eines Mischkörpers für ein erfindungsgemäßes Abgasnachbehandlungssystem;
• 3 eine schematische Darstellung, wie die Strahlen des Dosierelements auf den Mischkörper des Abgasmischers auftreffen; und
• 4 eine schematische Darstellung einer Strömungssimulation im Abgaskanalsegment stromabwärts des Abgasmischers und stromaufwärts des Partikelfilters.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. The same components or components with the same function are identified by the same reference numerals. Show it:

• 1 a schematic representation of an internal combustion engine with an exhaust gas aftertreatment system according to the invention;
• 2nd a three-dimensional representation of a mixing body for an exhaust gas aftertreatment system according to the invention;
• 3rd a schematic representation of how the rays of the metering element strike the mixing body of the exhaust gas mixer; and
• 4th is a schematic representation of a flow simulation in the exhaust duct segment downstream of the exhaust gas mixer and upstream of the particle filter.

1 shows the schematic representation of an internal combustion engine 10th which with its outlet 16 with an exhaust system 20th connected is. The internal combustion engine 10th is a direct injection diesel engine in this embodiment and has several combustion chambers 12th on. At the combustion chambers 12th is a fuel injector 14 for injecting a fuel into the respective combustion chamber 12th arranged. The internal combustion engine 10th may further comprise a high-pressure exhaust gas recirculation, via which an exhaust gas of the internal combustion engine 10th from the outlet 16 to an inlet of the internal combustion engine 10th can be traced back. At the combustion chambers 12th Inlet valves and outlet valves are arranged, with which a fluid connection from the intake tract to the combustion chambers 12th or from the combustion chambers 12th to the exhaust system 20th can be opened or closed.

The exhaust system 20th includes an exhaust duct 22 , in which in the flow direction of an exhaust gas of the internal combustion engine 10th through the exhaust duct 22 a turbine 24th of an exhaust gas turbocharger 18th and downstream of the turbine 24th a first catalytic converter as the first component of the exhaust gas aftertreatment 26 , in particular a NOx storage catalytic converter or an oxidation catalytic converter, are arranged. The exhaust gas turbocharger 18th is preferably used as an exhaust gas turbocharger 18th designed with variable turbine geometry. For this are a turbine wheel of the turbine 24th adjustable guide vanes upstream, through which the flow of the exhaust gas onto the blades of the turbine 24th can be varied. Downstream of the first catalyst 26 is a particle filter 34 with a coating 36 arranged for the selective catalytic reduction of nitrogen oxides. Alternatively, you can also use a particle filter 34 and an SCR catalyst 38 be provided as two separate components. Downstream of the first catalyst and upstream of the particulate filter 34 becomes the exhaust gas flow 68 of the internal combustion engine 10th on a deflection element 28 deflected by about 180 °. It is in the area of the deflecting element 28 a dosing element 30th for dosing a reducing agent 70 in the exhaust duct 22 intended. Downstream of the dosing element 30th and upstream of the particulate filter 34 with the SCR coating 36 is in the exhaust duct 22 a mixed body 42 an exhaust mixer 40 arranged. The mixing body 42 has a roof-shaped geometry 44 with a gable 46 on, from which there are two legs 48 , 50 of the roof towards the particle filter 34 extend. The two legs 48 , 50 close an opening angle α a, which is preferably between 60 ° and 90 °. The dosing element 30th has several injection openings 32 for introducing the reducing agent 70 in the exhaust duct 22 on, the injection ports 32 towards the gable 46 the roof-shaped geometry 44 of the mixing body 42 are oriented. At the gable 46 opposite ends 62 the thigh 48 , 50 are radii 52 trained which the vortex formation in the exhaust gas stream 68 downstream of the mixing body 42 promote additionally. The mixing body 42 additionally has a fastening section 54 on, which is preferably designed as a mounting plate and substantially perpendicular to the roof-shaped geometry 44 of the mixing body 42 runs. On the attachment section 54 are multiple holes 58 trained with which the mixing body 42 by means of suitable fastening elements on a receiving section 56 of the exhaust duct 22 , preferably on a transition funnel 60 , can be attached. Downstream of the particle filter 34 a NOx sensor 78 can be provided, with which the effectiveness of the SCR coating 36 of the particle filter 34 can be checked as part of an on-board diagnosis. Furthermore, the amount of the reducing agent metered in can be determined by the NOx sensor 78 70 be regulated to overdose or underdose of reducing agent 70 to avoid and further improve the efficiency of the use of reducing agents. Also on the particle filter 34 a differential pressure sensor 76 provided with which the soot loading of the particle filter 34 is monitored and if a loading threshold is exceeded, regeneration of the particle filter 34 is initiated. Furthermore, in the exhaust duct 22 a temperature sensor may be provided to measure the temperature of the exhaust aftertreatment components 26 , 34 , 38 monitor and combustion of the internal combustion engine 10th and the metering of reducing agents 70 to control the exhaust aftertreatment components 26 , 34 , 38 be operated in the most efficient temperature range possible.

The internal combustion engine 10th as well as the exhaust gas sensors 76 , 78 and the dosing element 30th are via signal lines with an engine control unit 80 connected.

In the operation of the internal combustion engine 10th becomes the exhaust gas of the internal combustion engine 10th through the exhaust system 20th and the exhaust aftertreatment components arranged therein 26 , 34 , 36 , 38 headed. The nitrogen oxides are removed from the exhaust gas stream 68 in the NOx storage catalyst 26 stored or by the SCR catalyst 38 or the SCR coating 36 of the particle filter 34 converted to unlimited exhaust components. The reducing agent is metered in as required 70 through the injection ports 32 of the dosing module 30th .

In 2nd is a three-dimensional representation of a mixing body 42 shown for an exhaust gas aftertreatment system according to the invention. The mixing body 42 includes a roof-shaped geometry 44 and an attachment portion 54 . The roof-shaped geometry 44 has a first leg 48 and a second leg 50 on which on a gable 46 are interconnected. At the gable 46 opposite end 62 the roof-shaped geometry 44 is a tear-off edge in the form of a radius 52 provided which has a flow separation at the end 62 favored and thus the vortex formation downstream of the mixing body 42 promotes. On the attachment section 54 are preferably two holes 58 provided that easy attachment of the mixing body 42 on a receiving section 54 in the exhaust duct 22 enable.

In 3rd is a schematic representation of how the rays of the metering element strike the mixing body of the exhaust gas mixer. You can see how three reducing agent jets 72 in the area of the gable 46 the roof-shaped geometry 44 on the mixing body 42 hit and be atomized there. The fastening section 54 is sufficiently far from the reducing agent jets 72 removed and is therefore not and only insignificantly by the reducing agent 70 wetted so that as little deposits as possible on the mixing body 42 form.

4th shows a schematic representation of a flow simulation in an exhaust duct segment downstream of the mixing body 42 of the exhaust mixer 40 and upstream of the particulate filter 34 . It can be seen that downstream of the mixing body 42 two opposing flow vortices 64 , 66 form. The flow vortex 64 , 66 have a length L and ensure that the exhaust gas flow is mixed appropriately 68 with the reducing agent 70 . A correspondingly homogeneous distribution of reducing agents 70 across the cross section of the exhaust duct 22 before the exhaust gas flow occurs 68 in an entry area 74 of the particle filter 34 to achieve is a distance A between the mixing body 42 and this entrance area 74 of the particle filter 34 preferably at least three times the length L the flow vortex 64 , 66 intended.

An exhaust gas aftertreatment system according to the invention can be used with a simple and inexpensive exhaust gas mixer 40 a correspondingly homogeneous distribution of the reducing agent 70 before entering the particle filter 34 with SCR coating or an SCR catalyst 38 can be achieved. In addition, the particle filter can be located downstream 34 , in particular in an underbody position of a motor vehicle, another SCR catalytic converter 38 be arranged to expand the operating range for the selective catalytic reduction of nitrogen oxides and to further improve the conversion performance of nitrogen oxides.

Reference list

10th

Internal combustion engine

12th

Combustion chamber

14

Fuel injector

16

Outlet

18th

Exhaust gas turbocharger

20th

Exhaust system

22

Exhaust duct

24th

turbine

26

NOx storage catalytic converter

28

Deflecting element

30th

Dosing element

32

Injection ports

34

Particle filter

36

SCR coating

38

SCR catalytic converter

40

Exhaust mixer

42

Mixing body

44

roof-shaped geometry

46

gable

48

first leg

50

second leg

52

radius

54

Fastening section

56

Receiving section

58

Holes

60

Transition funnel

62

The End

64

first flow vortex

66

second vortex

68

Exhaust gas flow

70

Reducing agent

72

Reductant jet

74

Entrance area

76

Differential pressure sensor

78

NOx sensor

80

Engine control unit

A

distance

L

Length of the vertebra

α

Opening angle

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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.

Patent literature cited

• EP 1681089 A1 [0006]

Claims (10)

Exhaust gas aftertreatment system for an internal combustion engine (10), comprising an exhaust gas system (20) with an exhaust gas duct (22), in which a first catalytic converter (26) close to the engine in the flow direction of an exhaust gas of the internal combustion engine (10) and a particle filter downstream of the first catalytic converter (26) close to the engine (34) with a coating (36) for the selective catalytic reduction of nitrogen oxides, the exhaust system (20) having a deflection element (28) with which the exhaust gas stream (68) downstream of the first catalyst (26) and upstream of the particle filter ( 34) is deflected by 150 ° to 210 °, and a metering element (30) for metering a reducing agent (70) into the exhaust system (20) is arranged in the region of the deflecting element (28), characterized in that downstream of the metering element (30 ) and upstream of the particle filter (34) a mixing body (42) of an exhaust gas mixer (40) is arranged, the mixing body (42) having a roof has a geometry (44), the injection openings (32) of the metering element (30) being oriented in the direction of a gable (46) and / or the ridge of the roof-shaped mixing body (42). Exhaust aftertreatment system after Claim 1 characterized in that the mixing body (42) has a fastening section (54) with which the mixing body (42) can be fastened to a receiving section (56) of the exhaust system (20), the fastening section (54) being perpendicular to the roof-shaped geometry ( 44) of the mixing body (42) is oriented. Exhaust aftertreatment system after Claim 2 , characterized in that the fastening section (54) adjoins the roof-shaped geometry (44) of the mixing body (42). Exhaust aftertreatment system according to one of the Claims 2 or 3rd , characterized in that holes (58) with which the mixing body (42) is fixed to the exhaust gas duct (22) of the internal combustion engine (10) are made in the fastening section (54). Exhaust aftertreatment system according to one of the Claims 2 to 4th , characterized in that the mixing body (42) is fastened in a transition funnel (60) of the exhaust system (20). Exhaust aftertreatment system according to one of the Claims 1 to 5 , characterized in that at the respectively open ends (62) of the roof-shaped geometry (44) radii (52) are formed which promote flow separation and vortex formation downstream of the mixing body (42). Exhaust aftertreatment system according to one of the Claims 1 to 6 , characterized in that the roof-shaped geometry (44) has an opening angle (α) of 45 ° to 120 °. Method for exhaust gas aftertreatment of an internal combustion engine (10) with an exhaust gas aftertreatment system according to one of the Claims 1 to 7 , characterized in that two opposing flow vortices (64, 66) are formed downstream of the mixing body (42) in the exhaust gas flow (68), through which the exhaust gas flow (68) of the internal combustion engine (10) is mixed with the reducing agent (70). Exhaust gas aftertreatment process after Claim 8 , characterized in that the reducing agent (70) is metered into the exhaust gas channel (22) such that a plurality of reducing agent jets (72) hit the mixing body (42) in the area of the gable (46) of the roof-shaped geometry (44). Exhaust gas aftertreatment process after Claim 8 or 9 , characterized in that the distance (A) of the particle filter (34) to the mixing body (42) is selected such that an end face (74) of the particle filter (34) has at least two lengths (L) of the flow vortices (64, 66) is spaced from the mixing body (42).

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