DE102013204405A1 - System for exhaust aftertreatment for an internal combustion engine, method for influencing an exhaust gas composition and internal combustion engine - Google Patents

Abstract

A system for exhaust gas aftertreatment for an internal combustion engine, in particular for a diesel internal combustion engine, is provided with an exhaust line (1) in which an oxidation catalytic converter (3) is arranged, which has a coated support body (5) with an upstream end face (7) and a Comprises downstream end face (9), proposed. The system is characterized in that the carrier body (5) comprises a coating that varies along at least one direction, an adjusting device (11) being provided in such a way that the adjusting device (11) is used to allow at least one region of the carrier body (5) through which exhaust gas can flow. is selectable.

Description

The invention relates to a system for exhaust aftertreatment for an internal combustion engine, in particular for a diesel internal combustion engine, according to the preamble of claim 1, a method for influencing an exhaust gas composition according to claim 8, and an internal combustion engine, in particular a diesel internal combustion engine according to the preamble of claim 10 ,

Exhaust aftertreatment systems for an internal combustion engine typically include an exhaust line in which an oxidation catalyst is disposed. This serves on the one hand to oxidize unburned hydrocarbons and carbon monoxide to carbon dioxide and water, on the other hand, it is used to condition the exhaust gas for downstream, so provided downstream of the oxidation catalyst exhaust aftertreatment devices. If, for example, a particle filter is provided downstream of the oxidation catalytic converter, this must be regenerated at regular intervals. This is done by burning soot particles accumulated in the particulate filter. According to a first procedure, which is also referred to as active regeneration, an increased conversion of hydrocarbons and carbon monoxide to carbon dioxide and water is carried out in the oxidation catalyst, wherein the released during these exothermic reactions heat of reaction is used in the particulate filter to reacting the soot particles with residual oxygen comprising the exhaust gas. In the context of a second procedure, which is also referred to as passive regeneration, in the oxidation catalytic converter nitrogen monoxide, NO, which is comprised of the exhaust gas emitted by the internal combustion engine, is partially converted to nitrogen dioxide, NO ₂ . The NO ₂ is used in the particulate filter as an oxidant or oxygen supplier, and the soot particles react with the NO ₂ by oxidation, wherein the NO _{2 is} reduced. Preferably, only as much NO _{2 is} generated as is needed to regenerate the particulate filter.

Is downstream of the oxidation catalyst, a selective catalyst, also called SCR catalyst, provided for the selective catalytic reduction of nitrogen oxides, it is advantageous if in the oxidation catalyst as possible 50% of the NO included in the exhaust gas is oxidized to NO ₂ , so that the SCR catalyst Exhaust gas is flowed through which comprises NO and NO ₂ in equal parts. In this case, the SCR catalyst shows an optimal effect.

Accordingly, the following constellations are possible in which different objectives with regard to the exhaust gas aftertreatment result: in a first case, a downstream particle filter without an SCR catalytic converter is provided. In a second case, a downstream SCR catalyst without particle filter is provided. In a third case, a particulate filter and an SCR catalyst are provided. In the first case, ideally only as much NO _{2 should be} formed as is needed for the regeneration of the particulate filter, while in the second case a ratio of 1: 1 between the species NO and NO ₂ should be set. In the third case, namely in an exhaust line comprising both a particulate filter and an SCR catalyst downstream of the oxidation catalyst, the SCR catalyst determines the optimum ratio of NO to NO ₂ , so that a ratio of 1: 1 is desired.

For the catalytic oxidation of the various species encompassed by the exhaust gas, the oxidation catalyst has a carrier body with a typically noble metal-containing coating. To vary the Umsatzeigenschaften the oxidation catalyst are essentially an exhaust gas temperature in the oxidation catalyst, its space velocity and the coating of the carrier body as a parameter available. The exhaust gas temperature and the space velocity vary with the operating conditions of the internal combustion engine, which may result in unfavorable conditions in the oxidation catalyst, for example for the formation of NO ₂ . Thus, with increasing exhaust gas velocity in the oxidation catalyst, the NO ₂ formation decreases. The coating of the oxidation catalyst is typically optimally adjusted for one of the aforementioned constellations. However, it always represents a compromise, since it is typically not possible to achieve optimal conversion rates in all operating states of the internal combustion engine.

From the international patent application with the publication number WO 2007/098514 A2 shows a system for exhaust aftertreatment for an internal combustion engine, in which in an exhaust line both a first and a second oxidation catalyst is arranged, wherein the oxidation catalysts each have a coated carrier body with an upstream end face and a downstream face. The exhaust gas flows through the carrier body from the upstream end face to the downstream end face. While the first oxidation catalyst is always traversed by exhaust gas, an actuator is provided either upstream of the second oxidation catalyst or in a bypass bypassing the second oxidation catalyst, through which the amount of exhaust gas flowing through the second oxidation catalyst is variable. In this way, the Umsatzeigenschaften the arrangement of two oxidation catalysts especially with regard to a conversion of nitrogen oxides during operation can be varied. A disadvantage of this solution is that it absolutely requires two oxidation catalysts, whereby it is complicated and expensive.

The invention has for its object to provide a system for exhaust aftertreatment, a method for influencing an exhaust gas composition and an internal combustion engine, in particular influencing the exhaust gas composition downstream of an oxidation catalyst in a simple, cost-effective manner is possible.

The object is achieved by providing a system having the features of claim 1. This is characterized in that the carrier body of the oxidation catalyst comprises a coating varying along at least one direction. An adjusting device is provided in such a way that at least one region of the carrier body through which exhaust gas can flow is selectable by means of the adjusting device. In particular, two properties of the system contribute to a flexible influencing of the exhaust gas composition: Firstly, the support body is not homogeneously coated, but has a coating varying along at least one direction, so that the Umsatzeigenschaften the oxidation catalyst along the at least one direction vary. Different regions of the oxidation catalyst accordingly have different conversion properties, for example different conversion rates for nitrogen oxides.

On the other hand, an adjusting device is provided such that it can be selected by this at least one area of the carrier body through which exhaust gas can flow. With the aid of the adjusting device, it is therefore possible to influence in a targeted manner which exhaust gas flow area actually flows through the region of the carrier body. These two properties cooperate in particular in the following way: By means of the adjusting device, it is possible to selectively select a region of the carrier body for flowing through with exhaust gas which has a specific coating or specific coating properties. Thus, an exhaust gas composition can be obtained downstream of the oxidation catalyst, which satisfies certain conditions. If the conditions which the exhaust gas composition has to meet change, it is possible to use the adjusting device to select a different region of the carrier body, which then flows through exhaust gas. Again, another coating or other coating properties are present, resulting in a different exhaust gas composition downstream of the oxidation catalyst, which in turn meets the new conditions. Thus, it is thus possible, during operation of the internal combustion engine and during operation of the oxidation catalytic converter, to flexibly adapt its properties to currently required conditions, in particular to a current operating state of the internal combustion engine.

The system preferably comprises only one oxidation catalyst. It is possible to dispense with a second oxidation catalytic converter because the system makes it possible to influence the exhaust gas composition in a simple and cost-effective manner without the need for a complicated structure with a second oxidation catalytic converter. The system is therefore particularly cost-effective.

A system is preferred which is characterized in that the carrier body comprises a coating which varies in a direction lying in the at least one end face. This means that a vector indicating the at least one variation direction lies in a plane defined by the end face. Preferably, the coating is formed zoned, so that the carrier body has different zones with different coating or different coating properties. Particularly preferably, the carrier body has a coating which - seen in the circumferential direction - varies. The carrier body is in this case preferably divided into sectors, which are formed in a cylindrically symmetrical carrier body as cylinder segments with different coating or different coating properties.

Alternatively or additionally, the carrier body preferably has a coating which-seen in the radial direction-varies. The coating therefore changes starting from a center of the carrier body with increasing distance from the center, wherein preferably different zones with different coating or different coating properties are provided. If the carrier body has a cylindrically symmetrical shape, these zones are preferably designed as ring segments.

With the aid of the adjusting device, the exhaust gas can preferably be introduced into at least one specific zone of the carrier body, so that downstream of the oxidation catalytic converter a certain exhaust gas composition is achieved which corresponds to the coating or the coating properties in the selected zone.

A system is preferred, which is characterized in that the adjusting device comprises at least one covering device, with which at least one end face of the carrier body can be covered in certain areas. The covering device is preferably arranged directly on the end face of the carrier body. This means, in particular, that the exhaust gas can not possibly be distributed in a gap between the covering device and the end face of the carrier body, so that it does not flow into zones of the carrier body actually covered by the covering device, but rather only in the at least one, released by the covering device Area.

In one embodiment, it is provided that a covering device is arranged only on the upstream end face of the carrier body. In this case, exhaust gas is prevented from entering certain regions of the carrier body, or only exhaust gas is introduced into at least one selected region of the carrier body. In another embodiment, it is provided that a covering device is arranged only on the downstream side of the end face. In this case, although exhaust gas can enter all areas of the carrier body, the carrier body is actually only traversed by exhaust gas in the at least one region selected with the aid of the adjusting device. In yet another embodiment, a cover is provided both on the downstream end face and on the upstream end face. These are preferably operatively connected and / or synchronized with one another such that the same region of the carrier body is released on the inflow and outflow side, wherein the active connection and / or synchronization is configured such that as far as possible all the exhaust gas flowing into the at least one selected region is also downstream the at least one area can escape again.

A system is also preferred, which is characterized in that the covering device is designed as a rotatable, segmented diaphragm. This embodiment is particularly advantageous, although the coating of the carrier body in segments - in the circumferential direction - varies. It is possible that the aperture identifies only an open segment, wherein the opening is geometrically matched to the coating segments of the carrier body. By rotation of the diaphragm, a segment of the carrier body to be flowed through by exhaust gas can then be selected, while all other segments are covered. Alternatively, it is possible that the diaphragm has more than one open segment, so that a plurality of coating regions or zones of the carrier body can be selected at the same time. It is also possible that the rotatable, segmented diaphragm comprises at least two mutually rotatable diaphragm elements, so that different opening areas are flexibly selectable, so that at least one, but preferably also several segments are flexibly openable or coverable.

In another embodiment, it is provided that the diaphragm is designed as an iris diaphragm. This embodiment is particularly advantageous when the carrier body has a coating which varies in the radial direction, in particular ring-segment-shaped zones are provided. The iris diaphragm can preferably be adjusted continuously from a minimum opening cross-section to a maximum opening cross-section, wherein different areas of the carrier body can be released. In a preferred embodiment, at least two diaphragms arranged one behind the other can be combined with one another so that not only an opening that becomes larger towards the outside can be reached, but at the same time internal areas which are released by one diaphragm can be covered by the other diaphragm, so that it too is possible specifically targeted only radial outer annular areas, without necessarily at the same time act on radially inner regions with exhaust gas.

Also preferred is a system which is characterized in that a control device is provided which is operatively connected to the adjusting device for selecting the at least one region of the carrier body through which exhaust gas can flow. The control device is preferably designed as an engine control unit, or in an engine control unit, an algorithm for controlling the adjusting device is implemented. Preferably, a detection means is provided for detecting at least one characteristic of the exhaust gas composition downstream of the oxidation catalyst size, which is operatively connected to the control device. In this way, the exhaust gas composition of the control device is preferably adjustable. Alternatively or additionally, a map is stored in the control device, which assigns corresponding functional positions of the adjusting device to certain exhaust gas compositions. Furthermore, operating point-dependent desired exhaust gas compositions are preferably stored in this case, so that the control device can in each case select a functional position of the adjusting device for achieving a predetermined exhaust gas composition as a function of an operating point of the internal combustion engine and / or of the exhaust gas aftertreatment system. Particularly preferably, this procedure is combined with an above-described control or regulation of the exhaust gas composition by means of the detection means, so that at any time a predetermined exhaust gas composition can be achieved or constantly regulated.

Also preferred is a system characterized in that the coating of the carrier body is made to vary with respect to a conversion efficiency of nitrogen monoxide to nitrogen dioxide. The exhaust gas composition is thus specifically adjusted with regard to the requirements of downstream exhaust treatment devices. If, for example, only one particulate filter which is to be passively regenerated is present in the exhaust gas line after the oxidation catalyst, a coating region in the carrier body can be selected for the flow through exhaust gas by means of the adjusting device, in which only as much NO _{2 is} produced as is required for regeneration. If, on the other hand, NOx is to be converted in an SCR catalytic converter, a coating region of the carrier body for flowing through exhaust gas can be selected by means of the adjusting device, in which a ratio of NO to NO ₂ of 1: 1, ie in equal parts, is established.

In this context, a system is preferred which is characterized in that an SCR catalyst is arranged downstream of the oxidation catalyst. Alternatively or additionally, a particle filter is preferably arranged downstream of the oxidation catalytic converter. Above all, a system is preferred in which both a particulate filter and an SCR catalyst are provided downstream of the oxidation catalyst.

Particularly preferred is an embodiment of the system in which a passively regenerating particulate filter is located downstream of the oxidation catalyst and upstream of the SCR catalyst. At least one region of the carrier body through which exhaust gas flows is selected such that the exhaust gas flowing into the particle filter contains so much NO ₂ that this is available in an ideal ratio to NO after the oxidation of the soot particles in the particle filter at the inlet of the SCR catalytic converter stands. In this respect, improved properties of the overall system result in the arrangement described here, and thus synergy effects in the context of exhaust aftertreatment. The arrangement of a passively regenerating particulate filter - seen in the flow direction - between the oxidation catalyst and the SCR catalyst also has the advantage that in this case an SCR system comprising the SCR catalyst and a reducing agent injection device can be controlled particularly well.

The object is also achieved by providing a method with the steps of claim 8. The method for influencing an exhaust gas composition downstream of an oxidation catalyst in an exhaust line of an internal combustion engine, in particular a diesel internal combustion engine is performed using an oxidation catalyst comprising a carrier body with a coating varying along at least one direction. An adjusting device is controlled in such a way that at least one region of the carrier body through which exhaust gas flows is selected with its aid, an exhaust gas composition being influenced on account of the coating of the carrier body provided in the throughflow region. For this purpose, it is preferably provided that the coating of the carrier body varies along at least one direction. With regard to the method, the advantages already described in connection with the system result. In particular, a method which is carried out in a system according to one of the previously described embodiments is preferred.

Very particular preference is given to a method in which a ratio of nitrogen monoxide to nitrogen dioxide in the exhaust gas is controlled or regulated. In this case, the exhaust gas composition is in particular matched as needed to the conditions in a particulate filter on the one hand and in an SCR catalytic converter on the other hand.

The method is also preferably feasible in connection with an actively regenerating particle filter arranged downstream of the oxidation catalytic converter. In this case, a region of the carrier body is preferably selected for the regeneration of the particulate filter, which has a coating or coating properties in which an increased oxidation of hydrocarbons and carbon monoxide to carbon dioxide and water takes place. In this case, compared to the normal operation of the oxidation catalyst, larger amounts of heat of reaction are released, which are used for heating the particulate filter and for reacting the soot particles with the oxygen contained in the exhaust gas. After completion of active regeneration, in turn, a region of the carrier body is selected for the flow of exhaust gas, which has set for normal operation, preferably optimized Umsatzeigenschaften for hydrocarbons and carbon monoxide. It turns out that the method is not limited to the control and / or regulation of a ratio of nitrogen monoxide to nitrogen dioxide, but that in general properties of an exhaust gas composition are adjustable by selecting at least one area of the carrier body through which exhaust gas flows.

The description of the system on the one hand and the method on the other hand are to be understood as complementary to one another. In particular, an embodiment of the method is preferred, which is characterized by at least one method step, which is characterized by at least one feature of Systems, preferably combinations thereof, is conditional. Conversely, an embodiment of the system is preferred, which is characterized by at least one feature, which is due to at least one process step of the method described herein, preferably combinations thereof. In particular, the method steps described explicitly or implicitly in connection with the system, individually or in combination with one another, are also preferred steps of an embodiment of the method addressed here. In this respect, reference is therefore made to the description of the system. Conversely, in particular the features described explicitly or implicitly in connection with the method, individually or in combination with one another, are also preferred features of an embodiment of the system addressed here. In that regard, reference is therefore made to the description of the method.

The object is finally solved by an internal combustion engine having the features of claim 10 is created. This is characterized in that it comprises a system according to one of the embodiments described above. This also results in the advantages already described in connection with the system.

The internal combustion engine is preferably designed as a diesel internal combustion engine. This is particularly indicative that the internal combustion engine is operated with diesel fuel. In general, however, this also indicates that the internal combustion engine preferably operates according to the diesel combustion method, with diesel not being used as fuel as necessary. In this respect, an exemplary embodiment of the internal combustion engine which is operated with gas, in particular lean gas, is preferred. Alternatively, it is possible that the internal combustion engine is designed as an Otto internal combustion engine, in particular as a gasoline engine. In this case, it preferably comprises a three-way catalyst, in particular additionally or alternatively to a pure oxidation catalyst. In particular, when the three-way catalyst is provided as an alternative to an oxidation catalyst, it is to be understood as an oxidation catalyst in the sense described herein.

The invention will be explained in more detail below with reference to the drawing. Showing:

1 an embodiment of a portion of an exhaust system with an oxidation catalyst, and

2 an embodiment of a covering.

1 shows a schematic representation of a portion of an exhaust line 1 in which an oxidation catalyst 3 is arranged. This comprises a coated carrier body 5 , which is an upstream end face 7 and a downstream end surface 9 having. Along an arrow P, exhaust gas flows into the oxidation catalyst 3 one, where it is due to the upstream end face 7 in the carrier body 5 entry. Through the downstream end face 9 the exhaust gas in turn comes out of the carrier body 5 and leaves the oxidation catalyst 3 along an arrow P '.

The carrier body 5 is provided with a coating which varies in the illustrated embodiment in the circumferential direction, in particular in the form of cylinder segments. It is an adjusting device 11 provided with an area of the carrier body through which exhaust gas can flow 5 is selectable. The adjusting device comprises a covering device 13 in the illustrated embodiment as about a central axis M rotatable, segmented aperture 15 is trained. By means of a drive device, not shown, which is preferably controlled by a control device, also not shown, the aperture 15 be rotated about the central axis M, whereby different, cylinder-segment-shaped areas of the carrier body 5 can be covered or released. In this way, it is possible during operation of the internal combustion engine and in particular during operation of the oxidation catalyst 3 select which area or which areas of the carrier body 5 currently be flowed through by exhaust gas. Since the regions are provided with different coatings or different coating properties, such an exhaust gas composition can be downstream of the oxidation catalyst 3 to be influenced.

In the illustrated embodiment is only on the upstream end face 7 a cover device 13 intended. In another embodiment, it is possible that alternatively or additionally at the downstream end face 9 a covering device is provided.

In particular, the in 1 shown, on the upstream end face 7 provided covering device 13 or the aperture 15 is preferably immediately in front of the upstream end face 7 arranged so that no or at most a negligible proportion of exhaust gas over one between the diaphragm 15 and the upstream end face 7 existing gap on actually from the aperture 15 covered areas of the carrier body 5 can distribute. As a result of this embodiment, only that or at least essentially only that through the diaphragm is actually caused 15 shared areas of the carrier body 5 be traversed by exhaust gas.

Downstream of the carrier body 5 is preferably a detection means 17 , in particular an exhaust gas sensor or a probe, provided by means of which the exhaust gas composition downstream of the oxidation catalyst 3 is determinable. Here is the detection means 17 preferably operatively connected to the control device, not shown. In this way it is possible, the functional position of the aperture 15 to vary so that in each case a predetermined exhaust gas composition in the range of the detection means 17 is present. The exhaust gas composition is controllable in this case by the control device.

2 shows a schematic representation of an embodiment of a rotatable, segmented aperture 15 as a cover device 13 , This has three segments here 19 . 21 . 23 on. It is possible that the aperture 15 comprises only two segments or more than three segments. Preferably, the segments are to corresponding coating segments of the carrier body 5 geometrically adapted. Particularly preferred are the segments 19 . 21 . 23 symmetrical over the circumference of the aperture 15 distribute or take equal angular ranges. The same is preferably true for the coating segments of the carrier body 5 , In particular, as many segments are preferred on the panel 15 provided, such as coating segments on the carrier body 5 are provided, which are chosen with respect to their angular extent and distribution over the circumference to match each other.

In the embodiment according to 2 For example, is it possible for the first segment 19 having an opening while the segments 21 . 23 are closed. Exhaust gas can only pass through the first segment 19 stream.

Alternatively, it is possible for the first segment 19 and the second segment 21 open, with only the third segment 23 is closed, so that no exhaust gas can flow through this. This corresponds approximately to the illustration according to 1 ,

Other embodiments of concretely opened or closed segments with regard to 2 correspond to the embodiments described here and differ from this only by an irrelevant phase position, so that an explicit list of possible variations in 2 open or closed segments can be dispensed with. In any case, it is obvious that for carrying out the method or for the effective implementation of the system always at least one segment 19 . 21 . 23 must be open, while always at least one other segment 19 . 21 . 23 must be closed.

Indicates the aperture 15 more than three segments, there are more diverse combination options, wherein more than two segments can be open and / or closed more than two segments.

A series arrangement of at least two rotatable, segmented diaphragms is also possible in order to produce variable, more complex patterns of open and closed segments.

By means of the system, the method and the internal combustion engine, it is also possible to achieve a constant conversion of the oxidation catalyst 3 to ensure its duration or service life by aging of the oxidation catalyst 3 or the coating of the carrier body 5 targeted segments with higher coating or other coating properties are selected to compensate for the aging.

Overall, it has been found that by means of the system, the method and the internal combustion engine, a simple and inexpensive possibility has been created for influencing an exhaust gas composition downstream of the oxidation catalytic converter and thus, in particular, creating favorable conditions for downstream exhaust gas treatment devices.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• WO 2007/098514 A2 [0006]

Claims (10)

System for exhaust aftertreatment for an internal combustion engine, in particular for a diesel internal combustion engine, with an exhaust gas system (US Pat. 1 ), in which an oxidation catalyst ( 3 ) is arranged, which is a coated carrier body ( 5 ) with an upstream end face ( 7 ) and a downstream face ( 9 ), characterized in that the carrier body ( 5 ) comprises a coating varying along at least one direction, wherein an adjusting device ( 11 ) is provided such that by means of the adjusting device ( 11 ) at least one area of the carrier body through which exhaust gas can flow ( 5 ) is selectable. System according to claim 1, characterized in that the carrier body ( 5 ) one in one in the at least one end face ( 7 . 9 ), wherein it preferably comprises a - varying in the circumferential direction - varying coating, or wherein it comprises a - seen in the radial direction - varying coating. System according to one of the preceding claims, characterized in that the adjusting device ( 11 ) at least one covering device ( 13 ), with the at least one end face ( 7 . 9 ) of the carrier body ( 5 ) is partially coverable, preferably a cover device ( 13 ) only on the upstream end face ( 7 ), only at the downstream end face ( 9 ) or both on the upstream and on the downstream end face ( 7 . 9 ) is provided. System claim 3, characterized in that the covering device ( 13 ) as a rotatable, segmented aperture ( 15 ) or is designed as an iris diaphragm. System according to one of the preceding claims, characterized by a control device connected to the adjusting device ( 11 ) for selecting the at least one area of the carrier body through which exhaust gas can flow ( 5 ) is selectable. System according to one of the preceding claims, characterized in that the coating of the carrier body ( 5 ) is designed to vary with respect to a conversion efficiency of nitrogen monoxide to nitrogen dioxide. System according to one of the preceding claims, characterized in that downstream of the oxidation catalyst ( 3 ) an SCR catalyst and / or a particulate filter is / are arranged, wherein preferably a passively regenerating particulate filter downstream of the oxidation catalyst and upstream of the SCR catalyst is arranged. Method for influencing an exhaust gas composition downstream of an oxidation catalytic converter ( 3 ) in an exhaust gas line ( 1 ) an internal combustion engine, in particular a diesel internal combustion engine, wherein the oxidation catalyst ( 3 ) a carrier body ( 5 ) comprising a coating varying along at least one direction, and wherein an adjusting device ( 11 ) is controlled such that by means of the adjusting device ( 11 ) at least one area of the carrier body through which exhaust gas flows ( 5 ) is selected, wherein due to the provided in the flow-through area coating an exhaust gas composition is influenced. A method according to claim 8, characterized in that a ratio of nitrogen monoxide to nitrogen dioxide in the exhaust gas is controlled and / or regulated.  Internal combustion engine, in particular diesel internal combustion engine, characterized by a system according to one of claims 1 to 7.

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