DE102008046439A1 - Device for inserting medium for waste gas treatment for pollutant control equipment in exhaust gas flow guided in exhaust strand of internal combustion engine, has mixing chamber for mixing medium with exhaust gas flow - Google Patents

Abstract

The device (5) has a mixing chamber (6) for mixing a medium with the exhaust gas flow. The mixing chamber has an input area (7) with a flow cross section and a diameter and an output area (8) with another flow cross section and another diameter. The mixing chamber has a third flow cross section with a third diameter between the input area and the output area over an area with a length in main direction (H) of the exhaust gas flow. The third flow cross section is extended opposite to the former flow cross section. Independent claims are included for the following: (1) a pollutant control equipment with a catalyst unit; and (2) a method for inserting a medium for waste gas treatment in an exhaust gas flow guided in an exhaust strand of an internal combustion engine.

Description

The The invention relates to a device for introducing a medium for exhaust gas treatment in one in an exhaust line of an internal combustion engine guided exhaust stream, with a designed as a mixing chamber Area of the exhaust gas line for mixing the medium with the exhaust gas flow, wherein the mixing chamber has an entrance area and an exit area for the exhaust gas flow and an inlet section for having the medium.

Further The invention relates to a method for operating such Contraption.

Such a device is for example from the DE 199 22 959 A1 known.

Such Devices are used in emission control systems of Motor vehicles with a diesel engine.

Due to imperfect combustion, the exhaust gas of a motor vehicle contains, in addition to carbon dioxide CO ₂ , water H ₂ O, oxygen O ₂ and nitrogen N ₂ harmful components such as unburned or partially combusted hydrocarbons C _n H _m , carbon monoxide CO, nitrogen oxides NO _x and particles. In order to reduce the amount of harmful components already mentioned in the exhaust of motor vehicles, different exhaust aftertreatment measures are made, it being understood that in modern cars, especially catalytic processes are used.

at a known catalytic process is a 3-way catalyst used. However, the 3-way catalyst can only be used on motor vehicles be used with a gasoline engine, as for the process a nearly constant air-fuel mixture in the stoichiometric Ratio (λ = 1) is assumed.

Since the diesel engine inherently works with excess air, in motor vehicles with a diesel engine, the gasoline engine known 3-way catalyst technology for emission control can not be used. In such motor vehicles, the exhaust gas limit values for carbon monoxide CO and hydrocarbons C _n H _{m are} reduced by means of oxidation catalysts, in which the oxidation of carbon monoxide CO and hydrocarbons C _n H _m in excess oxygen (λ> 1) is performed. To comply with the limit values for nitrogen oxides NO _x can be used in motor vehicles with a diesel engine, a selectively operating SCR catalyst.

SCR catalyst technology uses a reducing agent that selectively reduces the nitrogen oxides NO _x to nitrogen N ₂ . For use in internal combustion engines of motor vehicles, a system is favored in which urea is used as ammonia-splitting precursor to the application, which is completely harmless to health.

In SCR systems, the urea is brought into contact with the exhaust gas to be treated as an aqueous solution or in powder form directly in front of the SCR catalyst. When urea is used as the ammonia-releasing precursor, the energy of the exhaust gas is utilized for its thermal decomposition. The first reaction step (thermolysis), in which the urea decomposes into ammonia NH ₃ and isocyanic acid HNCO, can proceed completely before the SCR catalyst. If aqueous urea solution is used, the water must first be evaporated. In the subsequent catalytic hydrolysis, the isocyanic acid reacts with gaseous water present in the exhaust gas to ammonia NH ₃ and carbon dioxide CO ₂ .

In order to promote the conversion of the urea into the reducing agent, ammonia NH ₃ , and to accelerate the reduction of nitrogen oxides NO _x by the reducing agent (NH ₃ ) obtained from the urea, the urea-containing medium has to be added to the exhaust gas be completely mixed with the exhaust gas. For this purpose, the devices mentioned above are used.

From the above DE 199 22 959 A1 is an emission control system with nitrogen oxide reduction with reducing agent addition known. This exhaust gas purification system has an exhaust gas line connected to an internal combustion engine and an SCR reduction catalytic converter. Further, the known exhaust gas purification system upstream of the SCR reduction catalyst comprises a reducing agent metering device consisting of a feed unit and an evaporator. About the feed unit is a reducing agent or a precursor of the same such. B. solid or liquid urea from the outside into the exhaust system, in which the exhaust gas flow is guided, injected. In the evaporator arranged downstream of the feed unit, the urea is converted into gaseous ammonia NH ₃ . A subsequent gas mixer ensures sufficient mixing of the released reducing agent with the exhaust gas.

It has now been found in practical use that it can come in conventional devices having a mixing element, which is arranged in the exhaust stream, to a hindrance of the exhaust gas flow. Furthermore, when using conventional devices, a significant pressure loss can occur. As a result, the back pressure of the emission control system is increased and thus the efficiency of the engine deteriorates. In addition, it has been found that the mixing of the reducing agent with the exhaust gas to be treated can be incomplete, which means that the very harmful nitrogen oxides NO _{x are} not reduced to nitrogen N ₂ and are therefore released into the atmosphere.

It is therefore an object of the present invention, the prior art continue to develop, leaving a constructively simple and little costly way of completely mixing the supplied medium for the exhaust gas treatment with the treated Exhaust gas is guaranteed without any direct obstruction the exhaust stream takes place.

According to the invention the object with the features of the independent claims solved.

With regard to a device, it is provided that the mixing chamber has an extended flow cross section Q ₁ in the area between the inlet area and the outlet area. The mixing chamber has between the input region and the output region over a region having a length L1 in the main direction (H) of the exhaust gas flow, a flow cross-section Q ₁ with a diameter Dmax which is wider than the flow cross-section Q ₂ . The inventive construction of the exhaust gas line in the region of the mixing chamber between the input area and the outlet area, a partial backflow of the exhaust gas is achieved, through which an improved mixing of the introduced medium with the exhaust gas is achieved, without obstructing the flow of exhaust gas takes place.

The Device according to the invention is as extended Section of the exhaust system particularly simple design and inexpensive produced.

Preferably is to improve the mixing of medium and exhaust gas L1> Dmax - D2 and optional L1 <4 · D2 selected. The mixing chamber also has over the Area with the length L1 along an x-axis a diameter Dmin and along a preferably perpendicular to the x-axis y-axis the diameter Dmax, where Dmin <Dmax.

It is particularly preferred if the length L ₁ is greater than the difference between the maximum diameters of the cross sections Q ₁ and Q ₂ by a factor of 1.2, 1.5 or 1.8.

The mixing chamber designed according to the invention provides a space with limited flow rate, which space is limited by the entrance area and the exit area, in which physicochemical processes between the medium for the exhaust gas treatment and the exhaust gas to be treated can take place over a longer time. By extending the exposure time of the medium, for example, urea as ammonia-releasing precursor of the reducing agent ensures that the present in the exhaust gas nitrogen oxides NO _x can be completely reduced in a downstream SCR catalyst to nitrogen N ₂ .

In advantageous embodiment of the invention, the mixing chamber with respect to a flow area of the entrance area and a flow area of the output area is an unbalanced one Expansion on.

These Measure has the advantage that the flowing through Exhaust gas increasingly partially flows back.

In Furthermore, an advantageous embodiment of the invention is a cross-sectional change section from the flow area of the entrance area to the extended flow cross-section of the mixing chamber with a provided jump-like course in the main direction of the exhaust stream.

In Furthermore, an advantageous embodiment of the invention is a cross-sectional change section from the expanded flow area of the mixing chamber to the flow area of the exit area with a provided jump-like course in the main direction of the exhaust stream.

By a sudden cross-sectional enlargement or cross-sectional reduction can be an even higher backflow the exhaust gas to be treated in the mixing chamber and in particular are generated in their asymmetrical expansion to the medium for the treatment of exhaust gas to be mixed with the exhaust gas to be treated.

In Furthermore, an advantageous embodiment of the invention is the inlet section for the medium downstream of the entrance area the mixing chamber arranged.

In Furthermore, an advantageous embodiment of the invention, the inlet portion a connection point for a metering device for the medium up.

In Furthermore, an advantageous embodiment of the invention is the connection point arranged in the region of asymmetrical widening of the mixing chamber.

These measures, individually or in combination, have the advantage that they are brought in by the introduction of the medium directly into the mixing chamber, regions with a turbulent flow are generated, which contribute to the mixing of the medium with the exhaust gas. Furthermore, it is achieved by the reduced flow rate that the exposure time between the medium and the exhaust gas to be treated is prolonged.

In Furthermore, an advantageous embodiment of the invention is the metering device arranged such that the introduction of the medium into the mixing chamber takes place in the main direction of the exhaust stream.

One such introduced medium is through the backflow Exhaust gas directed in the main direction of the exhaust stream. simultaneously it is against the partially backflowing exhaust gas guided. These two effects support the Mixing of the medium with the exhaust gas.

In addition, the backflowing exhaust gas causes a flushing of the connection point ( 12 ) and the dosing nozzle ( 13 ) of residues of the introduced medium and thus counteracts the deposition of reaction products.

In Furthermore, an advantageous embodiment of the invention, the exhaust line in a downstream of the exit region and spaced from this region arranged an extended flow cross-section on. Preferably, in this area is a reduction catalyst arranged.

The aforementioned Task is - especially in conjunction with the above Features - continue through an emission control system for an internal combustion engine, with an exhaust gas line, through which an exhaust gas to be treated is guided or feasible is, with at least one catalyst device with exhaust gas cleaning Function comprising at least one reduction catalyst, characterized solved that a device according to one of the claims 1 to 10 is provided.

In Advantageous embodiment of the invention is in the cleaning system at least one oxidation catalyst arranged.

The object is further provided by a method for introducing a medium for the treatment of exhaust gas in a guided in an exhaust line of an internal combustion engine exhaust gas flow, in which a mixing of the medium with the exhaust gas flow takes place in a mixing chamber of the exhaust system. The mixing chamber has an inlet region and an outlet region for the exhaust gas flow and an inlet section for the medium, wherein the exhaust gas flows in the region of the mixing chamber between the inlet region and the outlet region in an enlarged flow cross section Q ₁ , wherein in the mixing chamber a backflow in the exhaust gas relative to the main flow direction (H) takes place.

The Invention will be described below with reference to a selected embodiment described and explained in connection with the drawing. It shows:

1 : a schematic representation of an exhaust gas purification system with a device according to the invention;

2 : an enlarged view of the device according to the invention in 1 , wherein here a partial return of the exhaust gas is shown.

3 : a configuration along the section AA of 2 ,

In 1 is an emission control system 1 for an internal combustion engine 2 shown, wherein the internal combustion engine 2 preferably a diesel engine. One from the internal combustion engine 2 Exhaust gas containing, in addition to carbon dioxide CO ₂ , water H ₂ O, oxygen O ₂ and nitrogen N ₂ harmful components such as unburned or partially combusted hydrocarbons C _n H _m , carbon monoxide CO, nitrogen oxides NO _x and particles, is in a tubular exhaust line 3 directed.

In the exhaust system 3 Several components are arranged for exhaust aftertreatment. In particular, the emission control system has 1 an oxidation catalyst 4 on, which carries out the oxidation of carbon monoxide CO and hydrocarbons C _n H _m in excess of oxygen (λ> 1). Downstream of the oxidation catalyst 4 is in the exhaust system 3 a reduction catalyst 15 arranged. In the reduction catalyst 15 it is a selective SCR catalyst which, with the participation of a reducing agent, preferably ammonia NH ₃ , nitrogen oxides NO _x from the exhaust gas in nitrogen N _{2 can} convert, as will be described in more detail later. The exhaust system 1 may also include a number of sensors, which are not shown here for the sake of clarity.

Downstream of the oxidation catalyst 4 and upstream of the reduction catalyst 15 is a device 5 arranged. The device 5 serves to introduce a medium for exhaust gas treatment in the exhaust gas purification system 2 , as will be explained later. The medium, that of the mixing chamber 6 is supplied either urea as an aqueous solution or in powder form, wherein It is understood here that the metered addition of the liquid urea or urea in powder form can be carried out in a manner known from the prior art.

As in particular from the enlarged view in 2 indicates the device 5 a mixing chamber 6 on. The mixing chamber 6 with an axial length L ₁ , preferably as a region of the exhaust gas line 3 designed, used for mixing the medium for the exhaust gas treatment with the exhaust gas. The mixing chamber 6 has an entrance area 7 and an exit area 8th on. The flow of exhaust gas inside the mixing chamber 6 and the immediately adjacent to the mixing chamber upstream and downstream areas of the exhaust line 3 is illustrated with arrows.

The mixing chamber 6 has in the region of the length L1 a flow cross section Q ₁ with a (not shown) diameter Dmax, which is greater than a flow cross section Q _{2 of} the input area 7 and / or as a flow cross section Q _{3 of} the exit region 8th , In the entrance area, the mixing chamber has a (not shown) diameter D2 and in the output area a (not shown) diameter D3. The by mixing chamber 6 flowing exhaust gas undergoes a partial return flow relative to the main flow direction H, which increases the mixing of the medium for the exhaust gas treatment with the exhaust gas to be treated. The mixing chamber 6 is preferably designed so that in the region of the output range 8th a lateral deflection of exhaust gas takes place relative to the main flow direction H. Preferably, a guidance of the deflected exhaust gas through the wall of the mixing chamber 6 back to the entrance area 7 ,

At the in 2 illustrated embodiment, the flow cross-section Q _{2 of} the input area 7 and the flow area Q _{3 of} the exit area 8th comparably large. It is of course possible, the device according to the invention 5 such that the already mentioned flow cross sections Q ₂ and Q _{3 are of} different sizes, wherein the flow cross section Q ₁ in the region of the mixing chamber 6 is greater than the flow cross sections Q ₂ and Q ₃ .

The illustrated mixing chamber 6 indicates an asymmetrical widening 9 on. In 3 is a preferred geometric configuration of the mixing chamber 6 along the section AA the 2 shown. The expansion 9 extends laterally in the direction of a Y-axis laterally to a longitudinal axis 10 the exhaust line 3 or to the main direction H of the exhaust line 3 , It is understood that the expansion in other embodiments can also extend on both sides to the Y-axis, such that the asymmetrical widening 9 on both sides of the longitudinal axis 10 the exhaust line 3 is arranged. Furthermore, an expansion in the direction of an X-axis is conceivable.

A cross section change section between entrance area 7 and the expanded flow area Q _{1 of} the mixing chamber 6 indicates a sudden course in the main direction H of the exhaust gas flow 3 on. A cross-sectional change section between the expanded flow area Q _{1 of} the mixing chamber 6 and the exit area 8th can also be a sudden course in the main direction H of the exhaust stream 3 exhibit. The partial backflow of the exhaust gas is thereby reinforced and stabilized.

The mixing chamber 6 has an entrance section 11 with a connection point 12 for a metering device 13 for the medium. The metering device 13 is in the range of, preferably asymmetrical expansion 9 the mixing chamber 6 arranged. It is preferred, the metering device 13 to arrange such that the introduction of the medium into the mixing chamber 6 takes place in the main direction H of the exhaust stream. However, one can also imagine that the introduction of the medium into the mixing chamber 6 takes place against the main direction H of the exhaust stream.

The exhaust system 3 points in a downstream of the exit area 8th and spaced from this arranged area 14 an expanded flow cross-section Q ₁ , followed by the reduction catalyst 15 is arranged.

An inventive method for exhaust aftertreatment is described below in connection with 1 and 2 explained.

From the internal combustion engine 2 incoming exhaust gas is pressurized in the tubular exhaust line 3 directed. First, the exhaust gas becomes in the oxidation catalyst 4 treated by oxidizing components such as carbon monoxide CO and hydrocarbons C _n H _m . Furthermore, downstream of the oxidation catalyst 4 a particulate filter, not shown here, can be arranged, which filters off soot particles from the exhaust gas. Then the already partially treated exhaust gas passes through the entrance area 7 into the mixing chamber 6 , Part of the exhaust gas is in the mixing chamber 6 whose flow cross section Q _{1 is} greater than the flow cross section Q _{2 of} the input area 7 , along the wall of the mixing chamber against the main direction H flow. The formation of the backflow of the exhaust gas is due to the sudden flow cross-sectional widening between the input area 7 and the area with increased flow cross-section Q ₁ supported.

In the area of the mixing chamber 6 with increased flow cross-section Q ₁ , the flow velocity of the exhaust gas is reduced. For exhaust aftertreatment is the mixing chamber 6 in the main direction H of the exhaust gas, the medium for the exhaust gas treatment via the metering device 13 fed.

When urea in powder form is used as the medium, it takes place in the mixing chamber 6 First, a thermal decomposition of urea with the help of the energy in the mixing chamber 6 located exhaust gas instead. In this reaction step (thermolysis), the urea decomposes into ammonia NH ₃ and isocyanic acid HNCO. In the subsequent hydrolysis, the isocyanic acid reacts with gaseous water present in the exhaust gas to ammonia NH ₃ and carbon dioxide CO ₂ . With regard to the second reaction step, it should be noted that in the gas phase, the catalytic hydrolysis proceeds only with a corresponding catalyst at a significant rate. By using a hydrolysis catalyst which precedes the SCR catalyst in the overall system, the rate of isocyanic acid hydrolysis can be increased in such a way that undesired side reactions are suppressed. If an aqueous urea solution is used as a precursor of the reducing agent, the water must first be evaporated.

Because in the mixing chamber 6 the flow rate of the exhaust gas is reduced, that of the mixing chamber 6 supplied precursor of the reducing agent over a long time react with the exhaust gas. The extended exposure time increases the conversion of the medium into the actual reducing agent ammonia NH ₃ . Further, by introducing the medium into the mixing chamber 6 in the main direction H of the exhaust gas, the medium out against the direction of the backflowing exhaust gas.

1

emission control system

2

Internal combustion engine

3

exhaust gas line

4

oxidation catalyst

5

contraption

6

mixing chamber

7

entrance area

8th

output range

9

widening

10

longitudinal axis

11

entry section

12

junction

13

Eindosiervorrichtung

14

Area

15

reduction catalyst

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 19922959 A1 [0003, 0011]

Claims (14)

Device for introducing a medium for the treatment of exhaust gas into a waste gas stream guided in an exhaust line of an internal combustion engine, having a mixing chamber ( 6 ) for mixing the medium with the exhaust gas flow, the mixing chamber having an inlet area with a flow cross section Q2 and a diameter D2 and an outlet area with a flow gap Q3 and a diameter D3 <1.5 · D2 for the exhaust gas flow and an inlet section (FIG. 11 ) for the medium, characterized in that the mixing chamber ( 6 ) between the entrance area ( 7 ) and the exit area ( 8th ) over a region having a length L1 in the main direction (H) of the exhaust gas stream has a relation to the flow cross section Q2 extended flow cross-section Q ₁ with a diameter Dmax. Device according to claim 1, characterized in that L1> Dmax - D2 and optionally L1 <4 · D2 and / or the mixing chamber ( 6 ) has a diameter Dmin along the x-axis along the region of length L1 and the diameter Dmax along a y-axis which is preferably perpendicular to the x-axis, where Dmin <Dmax. Apparatus according to claim 1 or 2, characterized in that a cross-sectional change section between the input area ( 7 ) and the expanded flow area Q1 of the mixing chamber (FIG. 6 ) is provided with a sudden course, preferably over a length of <0.3 * D2 in the main direction (H) of the exhaust gas flow and / or that a cross-sectional change section between the region of the length 1 of the mixing chamber ( 6 ) to the exit area ( 8th ) is provided with a sudden course, preferably over a length of 0.3 · D3 in the main direction (H) of the exhaust gas stream. Device according to one of claims 1 to 3, characterized in that the mixing chamber is a geometric Form in the region of the mixing chamber, the formation of a Return flow in the exhaust gas relative to the main flow direction (H) allowed. Device according to one of claims 1 to 5, characterized in that the mixing chamber ( 6 ) laterally to a longitudinal axis ( 10 ) of the exhaust gas line ( 3 ) or to the main direction (H) of the exhaust gas flow has an asymmetric cross-sectional widening. Device according to one of claims 1 to 5, characterized in that the inlet section ( 11 ) for the medium downstream of the entrance area ( 7 ) of the mixing chamber ( 6 ) is arranged. Device according to one of claims 1 to 6, characterized in that the inlet section ( 11 ) a connection point ( 12 ) for a metering device ( 13 ) for the medium. Device according to claim 7, characterized in that the connection point ( 12 ) in the area of asymmetrical expansion ( 9 ) of the mixing chamber ( 6 ) is arranged. Apparatus according to claim 7 or 8, characterized in that the metering device ( 13 ) is arranged such that the introduction of the medium into the mixing chamber ( 6 ) takes place in the main direction (H) of the exhaust gas flow. Device according to one of claims 1 to 9, characterized in that the exhaust gas line ( 3 ) in a downstream of the exit region ( 8th ) and spaced from this arranged area ( 14 ) has an extended flow cross-section (Q4). Exhaust gas purification system for an internal combustion engine, with an exhaust gas line through which an exhaust gas to be treated is guided or can be guided, with at least one catalyst device with an exhaust-gas-cleaning function, characterized in that at least one device ( 5 ) is provided according to one of claims 1 to 10. Emission control system according to claim 11, characterized characterized in that the exhaust system at least one reduction catalyst and / or at least one oxidation catalyst. Method for introducing a medium for the treatment of exhaust gas in a guided in an exhaust line of an internal combustion engine exhaust gas flow, wherein a mixing of the medium with the exhaust gas flow takes place in a mixing chamber of the exhaust line, the mixing chamber has an input area and an outlet area for the exhaust stream and an inlet portion for the medium, characterized in that the exhaust gas in the region of the mixing chamber ( 6 ) between the entrance area ( 7 ) and the exit area ( 8th ) flows in an extended flow cross-section Q ₁ , wherein in the region of the mixing chamber, a backflow of exhaust gas takes place relative to the main flow direction (H). Method for introducing a medium for the exhaust gas treatment in a guided in an exhaust line of an internal combustion engine exhaust gas flow, wherein a mixing of the medium with the exhaust gas flow takes place in a mixing chamber of the exhaust line, the mixing chamber an input Be rich and an exit area for the exhaust stream and a connection point ( 12 ) and a metering nozzle ( 13 ) for the medium, characterized in that the backflowing exhaust gas for flushing the connection point ( 12 ) and the dosing nozzle ( 13 ) is used by residues of the introduced medium.