DE102021102926A1 - Catalyst system with radially inhomogeneous oxygen storage capacity - Google Patents

Abstract

Catalytic converter system (12) for an internal combustion engine with a first catalytic converter section (14) which has an oxygen storage capacity and a second catalytic converter section (15) which has an oxygen storage capacity, and with an exhaust gas probe (16) which is located in a transition between the catalytic converter sections (14 , 15) is arranged, wherein the specific oxygen storage capacity of the oxygen storage capacity of the first catalytic converter section (14) is greater in a first flow cross-sectional area (17) than in a second flow cross-sectional area (18).

Description

The invention relates to a catalytic converter system which is provided for after-treatment of exhaust gas from an internal combustion engine.

The control of the mass ratio of the air and fuel components of a mixture that is fed to the internal combustion engine of an internal combustion engine for combustion is not only of central importance for the operation of the internal combustion engine but also for after-treatment of exhaust gas generated by the internal combustion engine. This mass ratio is usually described with the dimensionless characteristic number Ä (lambda), which is also referred to as the combustion air ratio. The combustion air ratio specifically indicates the mass ratio of the mixture components air and fuel relative to the stoichiometrically ideal mass ratio for a theoretically complete combustion process.

Gasoline engines that are spark-ignited and quantity-controlled are often operated with a fundamentally stoichiometric air-combustion ratio, i.e. with λ ≈ 1. To realize such a stoichiometric air-combustion ratio, the residual oxygen content in the exhaust gas is analyzed using a so-called lambda probe and the air-fuel mass ratio is controlled for subsequent combustion processes is used. Such a reactive control means that the actual combustion air ratio fluctuates in a relatively narrow range around the stoichiometric combustion air ratio. In this regard, it is known to actively implement a so-called natural frequency control for the combustion air ratio, in which the combustion engine is defined alternately slightly rich, i.e. with a slightly sub-stoichiometric combustion air ratio (Ä < 1), and slightly lean, i.e. with a slightly more than stoichiometric combustion air ratio (Ä > 1), is operated. Switching between rich and lean operation takes place when there are defined deviations from the stoichiometric combustion air ratio.

A typical configuration of an exhaust gas aftertreatment device integrated into the exhaust line of a spark-ignition engine comprises, viewed in the flow direction of the exhaust gas, first a first lambda probe, then a first three-way catalytic converter, then a second lambda probe and finally a second three-way catalytic converter. A three-way catalytic converter is characterized in that it converts carbon monoxide (CO), nitrogen oxides (NOx) and unburned hydrocarbons (HC) into carbon dioxide (CO ₂ ), nitrogen (N ₂ ) and water (H ₂ O). In addition, such a three-way catalytic converter usually has what is known as an oxygen storage capacity. As a result, it can store oxygen to a limited extent. In lean operation of the internal combustion engine of an internal combustion engine that includes such an exhaust gas aftertreatment device, excess oxygen contained in the raw exhaust gas is stored in the first three-way catalytic converter, while in rich operation the stored oxygen is used for the conversions mentioned. To form a three-way catalytic converter, a catalytic converter material is usually applied as a coating to a carrier body which has a large number of through-openings in order to enable the exhaust gas to flow through. The oxygen storage capacity is often integrated into the catalytically active coating, for example in that it comprises a material suitable for storing oxygen.

In the case of a three-way catalytic converter, the catalytically active coating, which may also have the oxygen storage capacity, is generally radially homogeneous, i.e. distributed with (possibly) the same composition and the same layer thickness over the entire flow cross-sectional area of the carrier body. With such three-way catalytic converters, it can happen that they do not convert nitrogen oxides completely or not sufficiently during dynamic mixture change processes during operation of the gasoline engine, such as switching operations, injection suppression, and overrun fuel cut-offs, although the signals from the lambda probe, which are arranged downstream of the three-way catalytic converters, indicate this leave that a corresponding conversion should be possible.

the U.S. 2009/0301069 A1 discloses an exhaust gas cleaning component for cleaning exhaust gas from an internal combustion engine, having a support body through which a plurality of flow channels for the exhaust gas pass, wherein at least some of the walls of the flow channels have a coating with oxygen storage capacity. The coating with oxygen storage capacity is provided for a first delimited partial area of the carrier body and a second delimited partial area of the carrier body is designed without a coating with oxygen storage capacity or has a coating with a greatly reduced oxygen storage capacity compared to the first partial area. This configuration of the exhaust gas cleaning component is intended to reduce its aging and thus achieve improved operational reliability, because the thermal loads resulting from redox reactions in connection with stored oxygen are locally limited.

the US 2011/0237428 A1 discloses a catalytic converter system for exhaust gas from an internal combustion engine with two catalytic converter sections arranged directly one behind the other, of which at least one catalytic converter section located first in the flow direction of the exhaust gas has an oxygen storage capacity. The specific oxygen storage capacity of the oxygen storage capacity of this first catalyst section is greater than the specific oxygen storage capacity of the storage capacity, if any, of the second catalyst section. This is intended to prevent the formation of hydrogen sulfide (H ₂ S) or at least keep it low.

the US 2016/0288096 A1 discloses a catalytic converter system for exhaust gas from an internal combustion engine with two catalytic converter sections arranged directly one behind the other, each having an oxygen storage capacity. The oxygen storage capacity of the catalyst portion located first in the flow direction of the exhaust gas has an oxygen storage rate smaller than that of the subsequent catalyst portion.

The invention was based on the object, in a catalytic converter system for an internal combustion engine, which comprises at least two catalytic converter sections located one behind the other, in particular in the form of a three-way catalytic converter, and an exhaust gas probe arranged between the catalytic converter sections, to ensure sufficient conversion of nitrogen oxides even during dynamic mixture change processes.

This object is achieved with a catalytic converter system according to patent claim 1 . An internal combustion engine with such a catalytic converter system is the subject of patent claim 10. Advantageous embodiments of the catalytic converter system according to the invention and the internal combustion engine according to the invention are the subject of the further patent claims and result from the following description of the invention.

According to the invention, a catalytic converter system for an internal combustion engine is provided, which comprises at least a first catalytic converter section, preferably in the form of a three-way catalytic converter, which has an oxygen storage capacity, and a second catalytic converter section, preferably in the form of a three-way catalytic converter, which also has an oxygen storage capacity. The first catalytic converter section lies in front of the second catalytic converter section in an intended direction in which the exhaust gas flows through the catalytic converter system. Furthermore, the catalytic converter system has at least one exhaust gas probe, which is arranged in a transition between the catalytic converter sections. An arrangement in the transition between the catalytic converter sections is understood to mean an arrangement which is such that exhaust gas flowing against the exhaust gas probe has already flowed through the first catalytic converter section and only then flows into the second catalytic converter section. According to the invention, the specific oxygen storage capacity of the first catalytic converter section is greater in a first flow cross-sectional area than in a second flow cross-sectional area.

“Specific oxygen storage capacity” is understood to mean the oxygen storage capacity per unit volume of the corresponding catalyst section. Different specific oxygen storage capacities can be realized, for example, by providing a support body (e.g. made of ceramic and/or metal), which is provided with through openings for exhaust gas to flow through, of the corresponding catalytic converter section with a coating capable of storing oxygen (which is preferably catalytically active at the same time). , wherein the proportions of the material specifically capable of storing oxygen or of the corresponding materials of the coating are different in the different flow cross-sectional areas. In addition or as an alternative, it can also be provided that different specific coating surface sizes, i.e. related to a unit volume, are provided for the coating in the different flow cross-sectional areas, for example by the carrier body having different porosities of the carrier body in the different flow cross-sectional areas. Different coating thicknesses can also be provided in the different flow cross-sectional areas.

According to the invention, a “flow cross-sectional area” is understood to mean an area or section of a flow cross-sectional area of the/a catalytic converter section at at least one (axial) point in the direction of flow of the exhaust gas. The subdivision of at least the first catalytic converter section into different flow cross-sectional areas therefore does not have to extend over the entire length (extension in the direction in which the exhaust gas flows through), even if this is preferably provided. A varying division or a changing size ratio of the flow cross-sectional areas can also be provided over the length or a partial length of the/a catalytic converter section.

An essentially strict separation between the flow cross-sectional areas can be provided by means of a sudden change in terms of the specific oxygen storage capacity in the transition between the flow cross-sectional areas. However, smooth transitions are also possible between the flow cross-section areas with regard to the specific oxygen storage capacity through to specific oxygen storage capacities that change constantly or linearly over the flow cross-section areas of the catalyst section, which in principle results in an infinite number of flow cross-section areas that differ in terms of specific oxygen storage capacities.

A catalytic converter system according to the invention enables sufficient conversion of nitrogen oxides even during dynamic mixture change processes in the internal combustion engine. The reason for this is that, in particular during these dynamic mixture change processes, the exhaust gas can flow onto the first catalytic converter section in a radially inhomogeneous manner. The inhomogeneous distribution of the oxygen storage capacity of the first catalytic converter section according to the invention can prevent relevant pollutant breakthroughs from occurring as a result of the inhomogeneous flow onto the first catalytic converter section, which are not (quickly enough) detected by the exhaust gas probe. According to the invention, it can be ensured that in the area or areas of the first catalytic converter section in which (in each case) there is a relatively large exhaust gas mass flow with correspondingly large amounts of pollutants, there is also a correspondingly large specific oxygen storage capacity, so that there is sufficient Measures a conversion of the pollutants can take place.

The invention also relates to an internal combustion engine with an internal combustion engine and an exhaust system in which a catalytic converter system according to the invention is integrated. The internal combustion engine can preferably be externally ignited at least at times and can also be operated with quantity control (ie then as an Otto engine). In the operation of such an internal combustion engine, provision can be made for the internal combustion engine to run alternately (slightly) rich and (slightly) lean (preferably with defined unchangeable or changeable deviations from the stoichiometric combustion air ratio (λ=1), for example in the range λ=1±0, 05 or λ=1±0.03 or λ=1±0.01), which can be used in particular to achieve stoichiometric operation of the internal combustion engine on average. It can also be provided that there is a switch between rich operation and lean operation when there are defined deviations from the stoichiometric combustion air ratio. Such deviations can be determined using the exhaust gas probe, which is preferably designed in the form of a lambda probe. However, it is also possible to configure the exhaust gas probe as an NOx sensor, in particular also as a combined NO _x -NH ₃ sensor.

Flow onto the first catalytic converter section can in particular be such that a larger exhaust gas mass flow flows onto a central region than applies to a region located at the edge. Accordingly, it can preferably be provided that the first flow cross-sectional area of the first catalytic converter section is located centrally and the second flow cross-sectional area is located at the edge, wherein the second flow cross-sectional area can be designed in particular to run around the edge or be annular.

The specific oxygen storage capacity of the second catalytic converter section of a catalytic converter system according to the invention can be configured the same or with a homogeneous distribution over the entire flow cross section or the entire flow cross-sectional area of the second catalytic converter section at at least one axial point, preferably at all axial points, resulting in relatively low production costs for this second catalytic converter section be able. The specific oxygen storage capacity of the oxygen storage capacity of the second catalytic converter section can then preferably be greater than the specific oxygen storage capacity of the second flow cross-sectional area of the first catalytic converter section and in particular essentially correspond to the specific oxygen storage capacity in the first flow cross-sectional area of the first catalytic converter section.

Alternatively, it can be provided that the specific oxygen storage capacity of the oxygen storage capacity of the second catalyst section also differs in at least two flow cross-sectional areas, which in turn can be provided over a portion of the length or over the entire length of the second catalyst section. In particular, it can be provided that the specific oxygen storage capacity is smaller in a first flow cross-sectional area than in a second flow cross-sectional area. It can also be provided that the first flow cross-sectional area is located centrally and the second flow cross-sectional area of the second catalytic converter section is located at the edge. If the second flow cross-sectional area is located at the edge, it can preferably have a configuration running all the way around the edge.

According to a preferred development of such a catalytic converter system according to the invention, it can be provided that the first flow cross-sectional areas of the catalytic converter sections are arranged to overlap at least partially, preferably completely, and/or the second cross-sectional flow areas of the catalytic converter sections are arranged to overlap at least partially, preferably completely, so that, based on the ( intended) flow direction of the exhaust gas through the exhaust system, the first flow cross-sectional area of the second catalytic converter section is at least partially, preferably completely, in the flow shadow of the first flow cross-sectional area of the first catalytic converter section and/or the second flow cross-sectional area of the second catalytic converter section is at least partially, preferably completely in the flow shadow of the second flow cross-sectional area of the first Catalyst section is located.

According to a preferred embodiment of a catalytic converter system according to the invention, it can be provided that the exhaust gas probe is arranged in the area of the second flow cross-sectional area of the first catalytic converter section. Accordingly, the exhaust gas probe as a whole or at least one of its sensors is arranged in the flow shadow of the second flow cross-sectional area of the first catalytic converter section, so that exhaust gas that previously flowed through this second flow cross-sectional area of the first catalytic converter section primarily flows against it. As a result, possible breakthroughs of exhaust gas components through the first catalytic converter section, which are due to the fact that the oxygen storage capacity of the first catalytic converter section is either largely filled up or largely emptied locally in the area of the second flow cross-sectional area, can be detected as quickly as possible. Such a breakthrough can then be counteracted by appropriately influencing combustion processes in the internal combustion engine of the internal combustion engine, for example by appropriately changing from slightly rich to slightly lean operation or vice versa.

According to a preferred embodiment of a catalyst system according to the invention, it can be provided that the catalyst sections are structurally separated from one another. This makes it relatively easy to produce them with different oxygen storage capacities. Alternatively, the catalyst sections can also be designed integrally and thus in particular comprise a common, preferably one-piece carrier body, the different oxygen storage capacities being realized, for example, by a corresponding local variation of a coating of the carrier body having an oxygen storage capacity.

In a structurally separate configuration of the two catalytic converter sections, it can be provided that the exhaust gas probe is arranged in a free space over which the catalytic converter sections are spaced apart from one another over their entire surface. However, it is also possible to design the free space for the exhaust gas probe in such a way that the catalytic converter sections are only spaced apart from each other in each case in a partial area of the flow cross-sectional area, but otherwise bear directly against one another.

In the case of a structurally separate configuration of the two catalytic converter sections, they can be arranged in a common housing. As an alternative to this, they can also be arranged in different housings with an exhaust gas routing section lying in between, which can have a smaller circumferential dimension compared to the housings.

In the case of an integral design of the two catalytic converter sections, the exhaust gas probe can preferably be positioned in a free space of the common support body, which is located in the transition between the two catalytic converter sections.

At least one of the catalytic converter sections of a catalytic converter system according to the invention can also have the function of a particle filter. If this catalytic converter section then also has the function of a three-way catalytic converter, it can, as usual, be referred to as a four-way catalytic converter. A four-way catalytic converter is therefore an extension of a three-way catalytic converter.

If the exhaust gas probe is configured as a lambda probe, it can preferably be configured as a jump lambda probe (also known as a two-point lambda probe), whereby a deviation from stoichiometric operation of the internal combustion engine of an internal combustion engine according to the invention can be determined as quickly as possible. In addition, such a jump lambda probe is characterized by relatively low production costs. However, an embodiment of the lambda probe as a broadband lambda probe is also possible.

The internal combustion engine of an internal combustion engine according to the invention can preferably be operated with liquid fuel (i.e. in particular petrol). Operation with a gaseous fuel (in particular natural gas, LNG or LPG) is also possible.

The invention further relates to a motor vehicle, in particular a wheel-based and non-rail-bound motor vehicle (preferably a car or a truck), with an internal combustion engine according to the invention. The internal combustion engine of the internal combustion engine can be provided in particular for the (direct or indirect) provision of the driving power for the motor vehicle.

• 1: eine erfindungsgemäße Brennkraftmaschine;
• 2: ein erfindungsgemäßes Katalysatorsystem gemäß einer ersten Ausgestaltungsform;
• 3: ein erfindungsgemäßes Katalysatorsystem gemäß einer zweiten Ausgestaltungsform; und
• 4: ein erfindungsgemäßes Katalysatorsystem gemäß einer dritten Ausgestaltungsform.

The invention is explained in more detail below with reference to exemplary embodiments shown in the drawing. It shows, each in a simplified representation:

• 1 : an internal combustion engine according to the invention;
• 2 : a catalyst system according to the invention according to a first embodiment;
• 3 : a catalyst system according to the invention according to a second embodiment; and
• 4 : a catalyst system according to the invention according to a third embodiment.

the 1 shows an internal combustion engine according to the invention for a motor vehicle. This comprises an internal combustion engine 1, which is designed, for example, in the form of a reciprocating piston engine with four cylinder openings 2 arranged in a row. The cylinder openings 2 each delimit a combustion chamber 4 with reciprocating pistons 3 guided therein and a cylinder head. During operation of the internal combustion engine 1 and thus the internal combustion engine, these combustion chambers 4 are supplied with fresh gas via a fresh gas line 5, with the fresh gas being supplied by means of inlet valves 6, which are connected to the individual combustion chambers 4 are assigned is controlled. The fresh gas is exclusively or mainly air that is sucked in from the environment. Exhaust gas is generated during the combustion of mixture quantities consisting of fresh gas and fuel injected directly into combustion chambers 4 via fuel injectors 7 . This exhaust gas is discharged via an exhaust system 8 of the internal combustion engine, the outlet of the exhaust gas from the individual combustion chambers 4 being controlled by means of outlet valves 9 . The quantities of mixture in the combustion chambers 4 are ignited by means of electrical ignition devices 10 which, for example, generate ignition sparks (spark plugs). The exhaust gas flows through an exhaust gas after-treatment device 11, which is intended to remove components of the exhaust gas that are regarded as pollutants from the exhaust gas or to convert them into harmless components. This exhaust gas aftertreatment device 11 consists of or includes a catalytic converter system 12 according to the invention.

the 2 until 4 show different embodiments of the invention catalytic converter systems 12, for example, in an internal combustion engine according to 1 can be used.

These catalytic converter systems 12 each comprise two catalytic converter sections 14, 15 within a common housing 13, first a first catalytic converter section 14 and then a second catalytic converter section 15 being provided, viewed in the flow direction of the exhaust gas. These two catalytic converter sections 14, 15 are designed to be separate from one another and each comprise a preferably cylindrical support body and a coating which acts as a three-way catalytic converter and has an oxygen storage capacity. Furthermore, the catalytic converter systems 12 each include an exhaust gas probe 16 , for example in the form of a lambda probe, which is arranged in the transition between the catalytic converter sections 14 , 15 . In the catalyst systems 12 according to the 2 and 4 the exhaust gas probe 16 is in each case arranged in a free space over which the two catalytic converter sections 14, 15 are spaced apart from one another over the entire surface. In the catalyst system 12 according to the 3 In contrast, this free space only separates a relatively small, edge-side section, so that the mutually facing boundary surfaces of the catalytic converter sections 14, 15 make direct contact for the most part. Alternatively, there is also the possibility of designing the catalyst sections 14, 15 integrally, so that in particular a common carrier body can be provided for both catalyst sections 14, 15, with the coatings in the regions of the carrier body representing the different catalyst sections 14, 15 corresponding differentiate. An arrangement of the exhaust gas probe 16 would then be particularly comparable to that according to FIG 3 , ie in a free space formed by the individual carrier body and located at the edge.

According to the invention, it is provided that at least the first catalytic converter section 14 has two flow cross-sectional areas 17, 18 which differ in terms of their specific oxygen storage capabilities. Specifically, a first, centrally located flow cross-section area 17 and a second, circumferential or ring-shaped flow cross-section area 18 are provided. The first flow cross-sectional area 17 has a greater specific oxygen storage capacity than the second flow cross-sectional area 18 . The relatively large specific oxygen storage capacity is thereby in the 2 until 4 with OSC-high and the relatively small spec Fish oxygen storage capacity labeled OSC-low.

In the catalyst systems 12 according to the 2 and 3 Furthermore, the second catalytic converter section 15 is also divided into a first, centrally located flow cross-section area 19 and a second, peripheral or ring-shaped flow cross-section area 20 . In this case, however, the first flow cross-sectional area 19 has a lower specific oxygen storage capacity in comparison to the second flow cross-sectional area 20 . The distribution of the specific oxygen storage capabilities of the second catalyst section 15 is then consequently opposite to that of the first catalyst section 14.

In the catalyst system 12 according to the 4 the second catalytic converter section 15 has a homogeneous distribution of the oxygen storage capacity, the specific oxygen storage capacity, which is constant over the entire volume of the second catalytic converter section 15, preferably roughly corresponds in terms of size to that provided in the first flow cross-sectional area 17 of the first catalytic converter section 14.

Reference List

1

combustion engine

2

cylinder opening

3

reciprocating

4

combustion chamber

5

fresh gas line

6

intake valve

7

fuel injector

8th

exhaust line

9

outlet valve

10

ignition device

11

exhaust aftertreatment device

12

catalyst system

13

Housing

14

first catalyst section

15

second catalyst section

16

flue gas probe

17

first flow cross-sectional area of the first catalyst section

18

second flow cross-sectional area of the first catalyst section

19

first flow cross-sectional area of the second catalyst section

20

second flow cross-sectional area of the second catalyst section

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely 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

• US 2009/0301069 A1 [0006]
• US 2011/0237428 A1 [0007]
• US 2016/0288096 A1 [0008]

Claims (10)

Catalytic converter system (12) for an internal combustion engine with a first catalytic converter section (14) which has an oxygen storage capacity and a second catalytic converter section (15) which has an oxygen storage capacity, and with an exhaust gas probe (16) which is located in a transition between the catalytic converter sections (14 , 15) is arranged, characterized in that the specific oxygen storage capacity of the oxygen storage capacity of the first catalyst section (14) is greater in a first flow cross-sectional area (17) than in a second flow cross-sectional area (18). Catalyst system (12) according to claim 1 , characterized in that the first catalytic converter section (14) and/or the second catalytic converter section (15) is/are designed as a three-way catalytic converter. Catalyst system (12) according to claim 1 or 2 , characterized in that the specific oxygen storage capacity of the second catalyst section (15) is the same over the entire flow cross section. Catalyst system (12) according to any one of Claims 1 or 2 , characterized in that the specific oxygen storage capacity of the second catalyst section (15) in a first flow cross-sectional area (19) is smaller than in a second flow cross-sectional area (20). Catalyst system (12) according to claim 4 , characterized in that the first flow cross-sectional areas (17, 19) and/or the second flow cross-sectional areas (18, 20) of the catalytic converter sections (14, 15) are arranged to overlap one another. Catalyst system (12) according to one of the preceding claims, characterized in that in the first catalyst section (14) the first flow cross-sectional area (17) is located centrally and the second flow cross-sectional area (18) is located at the edge. Catalyst system (12) according to claim 6 , characterized in that the second flow cross-sectional area (18) is designed to run around the edge. Catalyst system (12) according to one of the preceding claims, characterized in that the exhaust gas probe (16) is arranged in the region of the second flow cross-sectional region (18) of the first catalyst section (14). Catalyst system (12) according to any one of the preceding claims, characterized in that the catalyst sections (14, 15) are structurally separated from one another. Internal combustion engine with an internal combustion engine (1) and an exhaust system (8) in which a catalyst system (12) according to one of the preceding claims is integrated.

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