CN112096489A - Exhaust gas system for exhaust gas aftertreatment - Google Patents

Abstract

The invention relates to an exhaust system (1) in a motor vehicle, comprising: a dosing module (4) for feeding a fluid, in particular a fluid reducing agent, into the exhaust system (1); and at least two mixing elements (3) which are designed to mix exhaust gas flowing through the exhaust gas system (1) with the fed fluid, wherein a dosing module (4) is designed to feed a portion of the fluid into the exhaust gas system (1) substantially opposite to a gas flow direction (10) and to feed another portion of the fluid into the exhaust gas system (1) substantially in the gas flow direction (10), wherein at least one mixing element (3) is arranged in the exhaust gas system (1) upstream of the dosing module (4) and at least one mixing element (3) is arranged in the exhaust gas system (1) downstream of the dosing module (4).

Description

Exhaust systems for exhaust aftertreatment

technical field

The invention relates to an exhaust gas system in a motor vehicle having at least one metering module for feeding or injecting a fluid, in particular a fluid reducing agent, into the exhaust gas system; and at least two mixing elements , the mixing element is designed to mix at least one gas, in particular exhaust gas, flowing through the exhaust gas system with the supplied fluid. The fluid is, for example, a fluid reducing agent, especially a urea solution.

Background technique

In order to keep the air pollution produced by the exhaust gases as low as possible, aftertreatment of the exhaust gases is necessary. For such exhaust gas aftertreatment of internal combustion engines, in particular diesel engines, in particular so-called SCR systems (SCR = "Selective Catalytic Reduction"), with which nitrogen oxides ( NOx).

In order to reduce nitrogen oxides in the exhaust gas, a reducing agent containing urea is usually injected into the exhaust gas flowing through the exhaust gas system. In order to achieve optimal mixing of the injected reducing agent with the exhaust gas flowing through the exhaust gas system, mixing elements arranged in the exhaust gas system can be provided.

However, it has been shown that there is a risk that part of the reducing agent injected or fed into the exhaust gas system does not evaporate completely and adheres, for example, to mixing elements and/or boundaries of the exhaust gas system and forms deposits which can negatively affect the reduction of harmful substances , so that the deposits increase, for example, fuel consumption and/or emission of harmful substances, and even lead to blockage of the exhaust system.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to improve the exhaust gas aftertreatment in the exhaust gas system and in this case in particular to reduce or even prevent the deposition of reducing agents in the exhaust gas system.

This task is solved according to the invention in an exhaust gas system of this type. Therefore, in one embodiment of the exhaust gas system according to the invention in a motor vehicle, a dosing module is provided for feeding fluid into the exhaust gas system; and at least two mixing elements for flowing at least one through the exhaust gas system The gas, especially the exhaust gas, is mixed with the feed fluid. The dosing module is designed to feed a part of the fluid into the exhaust gas system substantially opposite the gas flow direction and to feed another part of the fluid into the exhaust gas system substantially in the gas flow direction. Here, at least one mixing element, in particular for stopping the flow in the direction opposite to the gas flow direction, is arranged upstream of the dosing module in the exhaust gas system and at least one mixing element, in particular for stopping the flow in the gas flow direction The fluid-stopping mixing element is arranged downstream of the dosing module in the exhaust gas system.

With this arrangement, the thermal energy of the exhaust gas, known as the enthalpy of the exhaust gas, used for evaporating the fluid, in particular the fluid reducing agent, is used better than in conventional systems, by virtue of the fact that in two cross-sections through the exhaust gas system utilize this thermal energy. Thus, the formation of deposits is significantly reduced or completely avoided. By arranging the dosing module between the two mixing elements, a second injector can be dispensed with, which avoids further expenditure on a separate connection in the form of such a second injector for the fluid and avoids this separate connection of cooling.

Further developments of the exhaust gas system according to the invention described below are the subject of preferred embodiments.

In one embodiment, the mixing element is arranged in the exhaust gas system orthogonal to the flow direction of the exhaust gas. As a result, the fluid in the exhaust gas system can be distributed over two planes which extend transversely with respect to the flow direction and are thus each flowed through by the entire enthalpy flow of the exhaust gas. As a result, either the dosing amount of fluid fed or injected by the dosing module can be significantly increased without deposits; The temperature range extends to lower temperatures.

In one embodiment, the mixing element is configured as a baffle. The baffle plate is a particularly simple form of a mixing element that can be produced at low cost and is simple to install.

In one embodiment, the orientation of the dosing module and the cross-section of the exhaust gas system in the region of the mixing elements, in particular the configuration of the cross-section, are selected in such a way as to ensure that the supplied fluid is distributed as equally as possible to the individual mixing elements. Equal distribution is to be understood as the distribution of the fluid sprayed into droplets by the dosing module to the mixing elements as uniformly as possible.

This also means that the distance of the mixing element from the dosing module is chosen such that the opening angle of the jet of fluid to be fed in is chosen such that the jet reaches the entire mixing element, but only a small amount of the injection reaches beyond the mixing element Boundary walls, in particular pipe walls, of the exhaust gas system. If the distance of the mixing element from the dosing module cannot be changed, the opening angle of the jet can alternatively also be selected accordingly. It is also possible to direct multiple jets to one mixing element. In this case, the entire area of the spray must impact the entire mixing element face.

In an alternative embodiment, the dosing module is oriented and the cross-section of the exhaust gas system in the region of the mixing elements is designed in such a way that a non-uniform distribution of the feed in relation to the distribution of the exhaust gas heat flow of the exhaust gas to the individual mixing elements is ensured. incoming fluid. This means that more droplets impinge on the mixing element area with higher temperature than the mixing element area with lower temperature. Therefore, the thermal energy of the exhaust gas can be used more efficiently for the evaporation of the fluid, whereby the dosing amount of the fluid can be further increased.

This can be implemented in a structural manner, for example, in that the region that is more loaded with fluid is also more flowed through by the exhaust gas. A simple structural way conceivable for this is a perforated plate in which more holes are used to transfer heat from the exhaust gas to the mixing element in the region of increased fluid impingement. Another embodiment provides that the orientation of the dosing module and the cross-section of the exhaust gas in the region of the mixing element are coordinated so that a combination of a distribution that is as uniform as possible and a higher impact density of the droplets onto the hotter region of the mixing element is achieved.

One embodiment provides that the dosing module is a porous injector having at least two orifices provided for feeding fluid into the exhaust gas system, wherein the at least one orifice is substantially opposite to the gas flow direction, also That is, it is oriented upstream and the at least one hole is oriented substantially in the direction of gas flow, that is, downstream. Thus, fluid can be injected simultaneously through a single dosing module, so that it impinges on both mixing elements. As a result, the enthalpy of the exhaust gas can be utilized more efficiently and substantially complete evaporation of the fluid can be ensured.

Another embodiment provides that the dosing module and the mixing element are arranged in a straight section of the exhaust gas system. In the straight section of the exhaust gas system, the exhaust gas flow is very uniform and uniform, that is to say hardly any turbulence occurs. As a result, the amount of heat introduced by the exhaust gas to the mixing element can be well predicted, and the fluid feed can be coordinated accordingly, so that the heat energy of the exhaust gas is used optimally for the evaporation of the fluid.

An alternative embodiment provides that the dosing module and the mixing element are arranged in curved sections of the exhaust gas system, for example in pipe bends. Here, the mixing elements arranged upstream of the dosing module are arranged shortly before the exhaust gas system bend and the mixing elements arranged downstream of the dosing module are arranged behind the exhaust system bend, ie shortly behind. The dosing module is arranged in particular in the region of the bend, preferably at the apex of the bend. With this arrangement, the angle between the two different injection directions of the dosing module is smaller than in the case of an arrangement in a straight section of the exhaust gas system. Smaller angles between different injection directions of the fluid are structurally easier to achieve than larger angles.

Another embodiment provides that at least one SCR catalytic converter is provided in the exhaust gas system, which is arranged in the flow direction behind the at least one mixing element downstream of the dosing module. The real reduction of nitrogen oxides (NOx) takes place in the SCR catalyst. With improved evaporation of the reductant, nitrogen oxides can be converted even at lower temperatures, and also higher concentrations of nitrogen oxides, which are often associated with improved engine efficiency (CO ₂ reduction) is generated.

In a further embodiment, at least one diesel oxidation catalyst is provided in the exhaust gas system, which is arranged in the flow direction upstream of the at least one mixing element upstream of the dosing module. In addition to the oxidation of hydrocarbons and CO, the diesel oxidation catalyst is also used to convert NO to NO ₂ , which simplifies the catalytic reaction on the SCR catalyst.

Description of drawings

FIG. 1 shows a schematic diagram of an exemplary embodiment of an internal combustion engine exhaust system of the present invention.

FIG. 2 shows a schematic diagram of another exemplary embodiment of an internal combustion engine exhaust system of the present invention.

Detailed ways

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The same reference numerals denote the same or corresponding elements.

FIG. 1 shows a first embodiment of an exhaust gas system 1 having a straight section 2 through which the exhaust gas flows in the direction of gas flow indicated by arrow 10 . Two mixing elements 3 are arranged at a distance from each other in the straight section 2 of the exhaust gas system 1 .

Arranged between the two mixing elements 3 is a dosing module 4 which is provided for injecting or feeding in fluid. The fluid may be a fluid reducing agent, especially a urea solution, which should be mixed with the exhaust gas. For this purpose, the dosing module 4 sprays the fluid in the form of fine droplets into the exhaust gas in the direction of the mixing element 3 . The dosing module 4 is arranged such that one mixing element 3 is arranged upstream of the dosing module 4 in the exhaust gas system 1 and one mixing element 3 is arranged downstream of the dosing module 4 in the exhaust gas system 1 . Here, the mixing element 3 is arranged such that the fluid fed in by the dosing module 4 impinges on the mixing element 3 .

The mixing element 3 is oriented orthogonally to the gas flow direction 10 and preferably extends over the entire cross section of the straight section 2 of the exhaust gas system 1 . The mixing element 3 is provided with openings through which the exhaust gas can flow. In an alternative embodiment not shown in the figures, the mixing element 3 has no openings, does not extend over the entire cross-section and is flowed around by the exhaust gas.

The dosing module 4 is arranged for injecting the fluid into the straight section 2 in two different directions, ie substantially opposite to the gas flow direction 10, which is shown in FIG. 1 by the arrow 20, so that the fluid impinges on the arrangement On the mixing element 3 upstream of the dosing module 4 and substantially in the gas flow direction 10 , which is shown in FIG. 1 by arrows 30 , the fluid impinges on the mixing element 3 arranged downstream of the dosing module 4 .

This can be achieved, for example, by designing the dosing module 4 as a porous injector provided with at least two orifices for feeding the fluid into the exhaust gas system 1 , wherein at least one orifice is substantially connected to the The gas flow direction 10 is oriented oppositely, ie upstream (corresponding to the fluid feed direction 20 ), and the at least one hole is oriented substantially in the gas flow direction 10 , ie downstream (corresponding to the fluid feed direction 30 ). Also conceivable are a plurality of holes oriented substantially opposite to or along the gas flow direction 10 , respectively, as well as having different numbers of holes in each direction 20 or 30 .

An opening angle 100 is defined between the two fluid feed directions 20 , 30 , which opening angle in the straight section 2 depends on the distance of the two mixing elements 3 relative to each other. This means that the smaller the distance between the two mixing elements 3, the smaller the angle 100, and the larger the distance between the two mixing elements 3, the larger the angle 100.

Also provided in the exhaust gas system 1 is a diesel oxidation catalyst (DOC) 5 which is arranged in the gas flow direction 10 upstream of the mixing element 3 upstream of the dosing module 4 . An SCR catalytic converter 6 is also provided in the exhaust gas system 1 , which is arranged in the gas flow direction 10 behind the mixing element 3 arranged downstream of the dosing module 4 .

The diesel oxidation catalyst 5 reduces carbon monoxide (CO) and hydrocarbons contained in the exhaust gas of the diesel engine by oxidation reaction with residual oxygen contained in the exhaust gas. The SCR catalyst 6 reduces nitrogen oxides (NOx) contained in the exhaust gas.

FIG. 2 shows a second embodiment of the exhaust gas system 1 which substantially corresponds to the first embodiment. In order to avoid unnecessary repetition, only the differences from the previous embodiments are mentioned below.

The exhaust gas system 1 shown in FIG. 2 has a curved section 7 through which the exhaust gas flows in the gas flow direction 10 . The curved section 7 has two subsections 7a, 7b which form a built-in angle 102 between them which is greater than 0° and less than 180°.

A mixing element 3 is arranged in the first subsection 7a and a further mixing element 3 is arranged in the second subsection 7b. The dosing module 4 is arranged in the region of the bend, preferably at the outer apex of the bend as shown in FIG. 2 . As already explained with reference to FIG. 1 , the dosing module 4 is provided for injecting fluid into the exhaust gas system 1 in two different directions, ie essentially opposite to the gas flow direction, which is indicated in FIG. 2 by the arrow 20 It is shown that the fluid impinges on the mixing element 3 arranged upstream of the dosing module 4 , and substantially in the gas flow direction 10 , which is shown by arrow 30 in FIG. on the downstream mixing element 3 .

By arranging the mixing element 3 and the dosing module 4 in the region of the curved section 7 , the angle 101 between the fluid feeding directions 20 and 30 is smaller than the angle 100 in the straight section 2 in FIG. 1 .

Claims (10)

1. An exhaust system (1) in a motor vehicle, the exhaust system having: a dosing module (4) for feeding a fluid, in particular a fluid reducing agent, into the exhaust gas system (1); and at least two mixing elements (3) which are designed for mixing the exhaust gas flowing through the exhaust gas system (1) with the fed fluid, characterized in that the dosing module (4) is designed for feeding a portion of the fluid into the exhaust gas system (1) substantially opposite to a gas flow direction (10) and for feeding another portion of the fluid into the exhaust gas system (1) substantially in the gas flow direction (10), wherein at least one mixing element (3) is arranged in the exhaust gas system (1) upstream of the dosing module (4) and at least one mixing element (3) is arranged in the exhaust gas system (1) downstream of the dosing module (4).

2. The exhaust system (1) according to claim 1, characterized in that the mixing element (3) is arranged orthogonally to the gas flow direction (10) of the exhaust gases in the exhaust system (1).

3. The exhaust system (1) according to claim 1 or 2, characterized in that the mixing element (3) is configured as a baffle.

4. The exhaust system (1) according to one of the preceding claims, characterized in that the dosing module (4) is oriented in such a way and the cross section of the exhaust system (1) in the region of the mixing elements (3) is configured in such a way that a substantially equal distribution of the fed fluid over the respective mixing elements (3) is ensured.

5. The exhaust system (1) according to one of claims 1 to 3, characterized in that the dosing module (4) is oriented in such a way and the cross section of the exhaust system (1) in the region of the mixing elements (3) is configured in such a way that an uneven distribution of the fed fluid in relation to the distribution of the exhaust heat flow of the exhaust gas over the respective mixing elements (3) is ensured.

6. The exhaust system (1) according to any one of the preceding claims, characterized in that the dosing module (4) is a multi-hole injector having at least two holes provided for feeding fluid into the exhaust system (1), wherein at least one hole is oriented substantially opposite to the gas flow direction (10) and at least one hole is oriented substantially along the gas flow direction (10).

7. The exhaust system (1) according to any one of the preceding claims, characterized in that the dosing module (4) and the mixing element (3) are arranged in a straight section (2) of the exhaust system (1).

8. The exhaust system (1) according to any one of claims 1 to 6, characterized in that the dosing module (4) and the mixing element (3) are arranged in a curved section (7) of the exhaust system (1).

9. The exhaust system (1) according to any one of the preceding claims, characterized in that at least one SCR catalyst (6) is provided, which is arranged behind at least one mixing element (3) downstream of the dosing module (4) in the gas flow direction (10).

10. The exhaust system (1) according to any one of the preceding claims, characterized in that at least one diesel oxidation catalyst (5) is provided, which is arranged in front of at least one mixing element (3) upstream of the dosing module (4) in the gas flow direction (10).

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