DE10051361C1 - Exhaust gas cleaning system for a diesel engine and method for exhaust gas cleaning in a diesel engine - Google Patents

Abstract

The invention relates to an exhaust gas cleaning system for a diesel engine with a catalytic converter arrangement and at least one supply device (10) for supplying a reducing agent to the exhaust gas stream, the catalytic converter arrangement at least one oxidation catalytic converter (12) and at least one storage catalytic converter arranged downstream of the oxidation catalytic converter (12) in the flow direction of the exhaust gas (14) or at least one storage catalytic converter (12, 14) taking over the function of an oxidation catalytic converter, at least one partial exhaust gas stream flowing into the catalytic converter arrangement after the supply of the reducing agent and first flowing through a storage catalytic converter (14). The invention further relates to a method for exhaust gas purification which can advantageously be carried out on an exhaust gas purification system according to the invention.

Description

The invention relates to an exhaust gas purification system for a Diesel engine with a catalytic converter arrangement and at least a feeding device for feeding a Reducing agent to an exhaust gas stream, the Catalyst arrangement at least one oxidation catalyst and at least one in the flow direction of the exhaust gas arranged behind the oxidation catalyst Storage catalyst or at least one at the same time Function of an oxidation catalyst Storage catalyst has. The invention further relates to a method for exhaust gas purification in a diesel engine, at an exhaust gas flow through at least one Oxidation catalyst and at least one in Flow direction behind the oxidation catalytic converter arranged storage catalyst or by at least one at the same time the function of a Oxidation catalyst taking storage catalyst is passed and in which the exhaust gas flow Reducing agent is supplied.  

State of the art

A generic exhaust gas cleaning system is known for example from DE 197 31 865 C2. Such catalytic converters are used primarily to reduce nitrogen oxides (NO _x ) in the exhaust gas of diesel engines. The NO present in the exhaust gas is first converted into NO ₂ in the oxidation catalytic converter of the catalytic converter arrangement. The nitrogen oxides are then stored, for example, as barium nitrate in the subsequent storage component. In order to keep the storage component functional for a long time, it is advantageous to regenerate it from time to time. For this regeneration, it is necessary to realize fat phases in the exhaust gas stream, which is particularly problematic with diesel engines. It has proven useful to enrich the exhaust gas flow for the regeneration of the storage catalytic converter. The enrichment, that is to say the provision of a reducing agent, can be achieved by admixing urea, which decomposes to ammonia, or fuel (HC). It has proven to be disadvantageous that undesirable by-products are produced when a catalyst which is too heavily loaded is regenerated. The formation of these undesirable by-products is also favored by insufficient enrichment of the exhaust gas flow. However, an increase in the enrichment of the exhaust gas flow entails additional fuel consumption, this additional fuel consumption being determined, inter alia, by the amount of oxygen that is stored in the oxidation catalytic converter. It is therefore desirable to minimize the amount of fuel that is necessarily to be added and at the same time to reduce the emission of undesirable by-products. Furthermore, the exhaust system should be permanently available for exhaust gas purification, that is to say also during regeneration.

Advantages of the invention

The invention builds on the generic Exhaust gas purification system according to claim 1 characterized in that at least one partial exhaust gas stream after the supply of Reducing agent flows into the catalyst arrangement and first flows through a storage catalytic converter. Through the Fact that the one enriched with the reducing agent Exhaust gas flow first flows into the storage catalytic converter, the reducing agent immediately stands for the degradation of the Storage catalyst stored substances available. In particular, the reducing agent does not have to be the first Flow through the oxidation catalyst, where it otherwise the in Oxidation catalyst breaks down stored oxygen. On this way the amount of reducing agent needed reduced. Furthermore, the entire exhaust gas flow does not have to be included loaded with the reducing agent; rather it is enough off, a partial exhaust gas flow to the storage catalytic converter supply.

The invention is particularly advantageous in that the Feed device in the flow direction of the exhaust gas behind the storage catalyst is arranged and that the Inflow of the partial exhaust gas flow into the catalyst arrangement by reversing flow in the reverse direction. The normal operation of the catalyst can be practical unaffected by the arrangement of the feed device with regard to the catalyst arrangement because the Regeneration of the storage catalytic converter in a separate one Branch takes place in which the flow direction of the exhaust gas is reversed.  

In this context, it is particularly advantageous if the Exhaust gas partial flow after flowing through a Storage catalyst an oxidation catalyst flows through. As a result, by-products which arise during the regeneration of the storage catalytic converter Oxidation catalyst to be converted before being in the Environment are emitted.

The invention unfolds its advantages particularly in that that the catalyst assembly two pairs of catalysts has that each pair of catalysts one Oxidation catalyst and a storage catalyst has and that after flowing through the exhaust gas stream through one of the pairs of catalytic converters the partial exhaust gas flow flows through another pair of catalysts. That way it is possible during normal operation of the diesel engine with a pair of catalysts, i.e. one Oxidation catalyst and a storage catalyst To perform exhaust gas cleaning during the Storage catalyst of the other pair of catalysts Recirculation of a partial exhaust gas stream is regenerated.

Is preferably in the flow direction before A switchover device is provided, which at least essentially one the exhaust gas flow Catalyst pair feeds. This, for example, as a valve designed switching device ensures that the Main exhaust gas flow the path required for exhaust gas purification through the oxidation catalyst and the storage catalyst of a pair of catalysts.

Is preferred behind in the flow direction Catalyst arrangement a switchable flow divider provided which the exhaust gas partial flow from the exhaust gas flow  divides. The switchable flow divider makes it possible so, a major part of the cleaned exhaust gas flow into the To emit a partial exhaust flow into the environment other pair of catalysts is returned. The Switchability of the flow divider makes it easier Possible way, either either a pair of catalysts or the other pair of catalysts for exhaust gas purification use while the storage catalyst of each other couple is regenerated.

The feed device is preferably in the region of the Flow direction behind the catalyst arrangement arranged flow divider provided. Thus, the Exhaust gas partial flow separated from the exhaust gas flow immediately with the Reducing agents are added so that until reached of the storage catalyst to be regenerated advantageous mixing of the partial exhaust gas flow with the Reducing agent can take place.

It can be useful if a separate exhaust path is provided, via which the exhaust gas partial flow to the Exhaust gas flow is at least partially feedable again, wherein the feed in the flow direction behind the switchable Flow divider takes place. This way the normal one remains Exhaust gas flow of the exhaust gas to be cleaned through the Oxidation catalyst and the storage catalyst one Catalyst pair from the exhaust gas partial flow, which after the Regeneration is emitted into the environment, unaffected, since a separate exhaust gas path is available for this.

But it can also be useful in the direction of flow a switchable in front of the catalyst arrangement Flow divider is provided, which is the exhaust gas flow at least essentially leads to a pair of catalysts  and via which the exhaust gas partial flow returns to the exhaust gas flow is feedable. This has advantages in terms of Reducing the amount of piping required, because in this embodiment there is no separate exhaust gas path required for the partial exhaust gas flow. Rather, the Exhaust gas partial flow immediately after leaving the Oxidation catalyst of the regenerated catalyst pair via a switchable flow divider Exhaust gas stream are fed, which in the other The catalyst pair is cleaned. Due to the switchability the flow divider can be either Catalyst pair or the other catalyst pair for the Use normal exhaust gas cleaning during the Storage catalyst of the other pair of catalysts is regenerated. It is also possible through the Introduction of the partial exhaust gas flow in the to be cleaned Exhaust gas flow to the heat balance of the catalysts improve. Due to the exothermic reactions during the The partial flow is heated during regeneration. This energy will then used in the other pair of catalysts to Storage catalytic converter, which is currently being loaded to maintain its working temperature.

In a preferred embodiment, the in Flow direction behind the catalyst arrangement arranged switchable flow divider by two Check valves and a 2/2 valve realized. This is a variant, which is particularly with regard to the Arrangement of additional components is particularly advantageous is.

For example, arranging additional components consist of that in the area of the flow direction flow divider and  behind the feeder of the partial exhaust gas flow flows through the catalytic mixer. It is also conceivable that an additional pump to compensate for flow losses is positioned in the area of the valve arrangement.

With regard to a further embodiment, it should be mentioned as a particular advantage that part of the partial exhaust gas stream flows through the catalytic converter arrangement several times in the reverse direction. Here, too, the advantages are above all an optimized utilization of the heat, which is released when NO _{2 is} reduced. Furthermore, due to the multiple flow through the catalyst arrangement, a smaller amount of reducing agent is required.

The invention is based on the generic method in that at least one exhaust gas partial flow after the Feeding the reducing agent to the catalyst device is supplied and first a storage catalyst flows through. The fact that the one with the Reductant-enriched exhaust gas flow first in the Incoming storage catalyst flows, the reducing agent immediately for the dismantling of the in the storage catalytic converter stored substances available. In particular, it must Reducing agent not the oxidation catalyst first flow through where it is otherwise in the oxidation catalyst degrades stored oxygen. In this way the Reduced the amount of reducing agent required. Further the entire exhaust gas flow does not have to contain the reducing agent be loaded; rather it is enough to have one Feed partial exhaust gas flow to the storage catalytic converter.

Preferably for the inflow of the exhaust gas partial flow in the catalyst arrangement reverses the flow  vice versa. The normal operation of the catalyst in Forward direction can therefore be practically unaffected by the Regeneration of the storage catalytic converter in a separate one Branch take place in which the flow direction of the exhaust gas is reversed.

The partial exhaust gas flow is preferred after flowing through a storage catalytic converter by a Oxidation catalyst passed. As a result, By-products that are involved in the regeneration of the Storage catalyst arise in the oxidation catalyst be converted before being emitted into the environment become.

The invention is particularly advantageous in that the Exhaust gas flow after flowing through a pair of catalysts, which is an oxidation catalyst and one Storage catalyst has, is divided and the Exhaust gas partial flow passed through another pair of catalysts which has an oxidation catalyst and a Storage catalyst has. That way it is possible during normal operation of the diesel engine with a pair of catalysts, i.e. one Oxidation catalyst and a storage catalyst To perform exhaust gas cleaning during the Storage catalyst of the other pair of catalysts Recirculation of a partial exhaust gas stream is regenerated.

Preferably, the exhaust gas stream is essentially one Catalyst pair supplied. This can be a satisfactory operation of the exhaust system ensured be unaffected by the regeneration processes the main part of the exhaust gas is cleaned.  

It is useful if the exhaust gas partial flow is the exhaust gas flow via a separate exhaust gas path in the flow direction behind is supplied to the catalyst arrangement. In this way remains the normal exhaust gas flow of the exhaust gas to be cleaned through the oxidation catalyst and the storage catalyst a pair of catalysts from the exhaust gas partial flow, which is emitted into the environment after regeneration, Unaffected, since there is a separate exhaust gas path for this Available.

But it can also be useful if the exhaust gas partial flow in Flow direction upstream of the catalyst arrangement switchable flow divider is supplied. this has Benefits in terms of reducing required amount of piping because with this Embodiment is not a separate exhaust path for the Exhaust gas partial flow required. Rather, the Exhaust gas partial flow immediately after leaving the Oxidation catalyst of the regenerated catalyst pair via a switchable flow divider Exhaust gas stream are fed, which in the other The catalyst pair is cleaned. Due to the switchability the flow divider can be either Catalyst pair or the other catalyst pair for the Use normal exhaust gas cleaning during the Storage catalyst of the other pair of catalysts is regenerated. It is also possible through the Introduction of the partial exhaust gas flow in the to be cleaned Exhaust gas flow to the heat balance of the catalysts improve. Due to the exothermic reactions during the The partial flow is heated during regeneration. This energy will then used in the other pair of catalysts to Storage catalytic converter, which is currently being loaded to maintain its working temperature.  

In a preferred embodiment, the Exhaust gas partial flow after the supply of the reducing agent fed to a catalytic mixer. This can Mixing of the exhaust gas and the reducing agent improve what in terms of regeneration result is an advantage.

In a further preferred embodiment, part of the partial exhaust gas stream flows through the catalyst arrangement several times in the reverse direction. Here, too, the advantages are above all an optimized utilization of the heat, which is released when NO _{2 is} reduced. Furthermore, due to the multiple flow through the catalyst arrangement, a smaller amount of reducing agent is required.

Preferably, the reducing agent is already used Available diesel fuel is used. alternative this can be done with urea or another ammonia precursor be used. Urea is one odorless and environmentally compatible raw material, which disintegrates and the ammonia suitable for the reduction Provides.

The invention is based on the surprising finding that due to the return of the reducing agent offset exhaust gas flow the regeneration of a Storage catalyst can be done in a more efficient manner. Due to the fact that with the reducing agent loaded exhaust gas flow does not first the oxidation catalyst must flow through where otherwise reducing agents are lost would go, the amount of reducing agent used be minimized. At the same time the emission  unwanted by-products due to an unnecessarily high Fuel admixture reduced. Because preferably only one Partial flow for the regeneration of a storage catalytic converter is required, the exhaust gas purification in parallel System continued under normal operating conditions become.

drawings

The invention will now be described with reference to the accompanying Drawings based on preferred embodiments described as an example.

Show:

. Figure 1 is an exhaust gas purification system, which is flowed through by exhaust gas from a first flow direction;

FIG. 2 shows an exhaust gas purification system, which is flowed through by exhaust gas to a second flow direction;

Fig. 3 shows a first embodiment of an exhaust gas purification system according to the invention;

Fig. 4 shows a second embodiment of an exhaust gas purification system according to the invention;

Fig. 5 is a part of an exhaust gas purification system according to the invention;

Fig. 6 shows a third embodiment of an exhaust gas purification system according to the invention;

FIG. 7 shows another embodiment of an exhaust gas purification system;

Fig. 8 shows another embodiment of an exhaust gas purification system; and

Fig. 9 shows another embodiment of an exhaust gas purification system.

Description of the preferred embodiment

Fig. 1 shows an exhaust gas purifying system having an oxidation catalyst 12 and a storage catalytic converter 14. The arrows indicate a first flow direction of the exhaust gas, which is present, for example, during normal operation of an exhaust system. In the oxidation catalytic converter 12 , the NO present in the exhaust gas is converted into NO ₂ . This is then stored, for example, as barium nitrate in the storage component 14 , so that exhaust gas cleaned from the exhaust system is emitted into the environment. If the exhaust gas purification system is charged with a greased exhaust gas stream in the flow direction indicated in FIG. 1 for regeneration of the exhaust gas stream, exhaust gas, nitrogen (N ₂ ), water (H ₂ O), carbon dioxide (CO ₂ ), fuel (HC), carbon monoxide (CO) and nitrogen oxide (NO) are emitted into the environment. Unwanted by-products are thus emitted, especially if the storage catalytic converter is too heavily loaded or if the partial exhaust gas stream is not sufficiently enriched.

FIG. 2 shows the exhaust gas purification system according to FIG. 1, but here the arrows indicate a reverse flow in the reverse direction. This reverse flow direction illustrates the principle according to the invention. A enriched partial flow of, for example, 10% of the total exhaust gas flow is first passed into the storage catalytic converter 14 . The partial flow then flows through the oxidation catalytic converter 12 . A mixture of exhaust gas, nitrogen (N ₂ ), water (H ₂ O) and carbon dioxide (CO ₂ ) is then present at the outlet of the oxidation catalytic converter 12 . The advantage of operating the exhaust gas purification system with a backward-directed exhaust gas flow is that the enriched partial flow first flows through the storage catalytic converter 14 in this flow direction, so that the reducing agent is still completely available for the regeneration of the storage catalytic converter 14 . Subsequently, the partial flow flows through the oxidation catalytic converter 12 , where by-products are converted before they are emitted into the environment.

In Fig. 3, an exhaust gas purification system is shown schematically. The percentages in the figures are relative approximations which relate to the total exhaust gas flow. The exhaust gas purification system comprises a switchover device 16 , to which three separate exhaust gas paths connect. Two of these exhaust gas paths each comprise a pair of catalysts 12 , 14 , each pair of catalysts 12 , 14 consisting of an oxidation catalytic converter 12 and a storage catalytic converter 14 . Behind the storage catalytic converters 14 of the respective catalytic converter pairs 12 , 14 , the two exhaust gas paths are combined in a switchable flow divider 18 . The third exhaust gas path 30 opens behind the switchable flow divider 18 . A feed device 10 for feeding a reducing agent, for example HC, is arranged in the region of the switchable flow divider 18 . The feed device 10 comprises a metering unit and optionally also a catalytic mixer for producing carbon monoxide (CO). A pump can also be provided.

In the arrangement according to FIG. 3, the exhaust gas flow is passed through the switching device 16 into one of the catalyst pairs 12 , 14 . In the position of the switching device 16 shown by way of example, 100% of the exhaust gas flow is conducted into the lower pair of catalysts 12 , 14 . Behind the switching device 16 , the entire exhaust gas flow initially flows through the lower pair of catalysts 12 , 14 . There, the exhaust gas stream is first passed through an oxidation catalytic converter 12 and subsequently through a storage catalytic converter 14 , so that the exhaust gas stream is cleaned. After the storage catalytic converter 14 , the exhaust gas flow meets a switchable flow divider 18 , where part of the exhaust gas flow, for example 10%, is returned to the upper pair of catalysts 12 , 14 . The returned part is mixed with a reducing agent, here HC, by the feed device 10 . The remaining 90% of the exhaust gas flow is led out of the exhaust gas cleaning system. The recirculated partial exhaust gas stream first flows through the storage catalytic converter 14 of the upper pair of catalysts 12 , 14 , so that the storage catalytic converter can be regenerated efficiently without the reduction potential of the partial exhaust gas flow having been reduced by previously flowing through an oxidation catalytic converter. After flowing through the storage catalytic converter 14 , the exhaust gas partial flow is fed to the oxidation catalytic converter 12 of the upper catalytic converter pair 12 , 14 , by-products being reacted in an advantageous manner. After flowing through the oxidation catalytic converter 12 , the partial exhaust gas stream hits the switching device 16 again and is passed there into a separate exhaust gas path 30 . This separate exhaust gas path 30 feeds the exhaust gas partial stream behind the switchable flow divider to the exhaust gas stream, so that the exhaust gas partial stream can be emitted into the environment together with the exhaust gas stream. In the present illustration shown in FIG. 3 thus 12, 14, the lower catalyst pair performs a cleaning function during the storage catalytic converter 14 of the upper catalyst pair 12, 14 is regenerated. On the other hand, if the storage catalytic converter 14 of the lower catalytic converter pair 12 , 14 is to be regenerated, the switchover device 16 is adjusted in such a way that the main exhaust gas flow initially flows through the upper catalytic converter pair 12 , 14 . Likewise, the switchable flow divider 18 is brought into a position so that the exhaust gas partial flow mixed with reducing agent flows through the lower pair of catalysts 12 , 14 .

Fig. 4 shows another embodiment of an exhaust gas purification system. In the case of a switchable flow divider 20, the exhaust gas path branches to an upper catalyst pair 12 , 14 and a lower catalyst pair 12 , 14 . Each of the catalyst pairs 12 , 14 consists of an oxidation catalyst 12 and a storage catalyst 14 . The exhaust gas paths merge behind the storage catalytic converters 14 to form a further switchable flow divider 18 . In the area of the switchable flow divider 18 , a feed device 10 is provided, which is used to feed a reducing agent, for example fuel (HC).

The exhaust gas flowing into the exhaust gas purification system according to FIG. 4 is almost completely conducted to the lower pair of catalysts 12 , 14 in the position of the switchable flow divider 20 shown . There, the exhaust gas flow first flows through the oxidation catalytic converter 12 and then through the storage catalytic converter 14 , so that the exhaust gas flow is cleaned. After leaving the storage catalytic converter 14 , the exhaust gas flow is divided in the switchable flow divider 18 . A partial exhaust gas stream is generated, which is returned to the upper pair of catalysts 12 , 14 . The partial exhaust gas stream is enriched by the feed device 10 with a reducing agent, here HC. The main exhaust gas stream leaves the exhaust gas purification system and is emitted into the environment. In the upper pair of catalysts, the partial exhaust gas stream first flows through the storage catalyst 14 , which is regenerated by the presence of the reducing agent. The partial exhaust gas stream subsequently flows through the oxidation catalytic converter 12 , by-products being converted. After leaving the oxidation catalytic converter 12 , the partial exhaust gas stream again meets the switchable flow divider 20 , where it is combined with the exhaust gas stream originally flowing into the exhaust gas cleaning system. In the embodiment shown in FIG. 4, it is therefore not necessary to provide a separate exhaust gas path for expelling the partial exhaust gas flow, since this is supplied to the main exhaust gas flow in the region of the switchable flow divider 20 arranged upstream of the catalytic converter arrangement. The arrangement according to FIG. 4 has the further advantage that the heat balance of the catalysts is improved. The exhaust gas partial flow is heated by the exothermic reactions during regeneration. This energy is used to keep the other storage catalytic converter 14 , which is not being regenerated but loaded, at its working temperature.

In Fig. 5, an example for the realization of which is arranged downstream of the catalyst arrangement switchable flow divider is shown.

The arrangement comprises a 2/2-way valve 22 , the position of which determines which catalytic converter pair performs which function. Furthermore, two check valves 24 are provided. Between the check valves 24 there is an exhaust gas path to the 2/2 valve, in which a feed device 10 and a catalytic mixer 26 are arranged.

In the present position of the 2/2 valve 22 according to FIG. 5, the main exhaust gas flow is in the lower exhaust gas path. The lower one of the check valves 24 opens due to the exhaust gas pressure, so that a partial exhaust gas flow can flow into the area of the supply device 10 . There, a reducing agent, here fuel (HC), is added so that the mixture subsequently flows through a catalytic mixer 26 . The mixture reaches the 2/2 valve and is returned to the upper exhaust gas path. The upper check valve 24 is closed in the present position of the 2/2 valve 26 due to the pressure conditions. If the 2/2 valve is brought into its other switching position, the lower check valve 24 closes and the upper check valve opens, since the main exhaust gas flow now follows the upper exhaust gas path.

In FIG. 6, a further embodiment of an exhaust gas purification system is shown. A switchable flow divider 20 is located at the entrance of the exhaust gas cleaning system. From here, the exhaust gas cleaning system branches into three exhaust gas paths, a pair of catalysts 12 , 14 being arranged on a lower exhaust gas path and on an upper exhaust gas path. Each pair of catalysts 12 , 14 contains an oxidation catalyst 12 and a storage catalyst 14 . Behind the catalytic converter means open the three-way exhaust gas at two successive switching devices 28, 22 each other can be achieved so that at a suitable position of the switching devices 28, 22 is a multiple flow through the regeneration path. The supply device 10 for supplying a reducing agent is located on the exhaust gas path, on which no catalyst pair is arranged.

The exhaust gas purification system according to FIG. 6 operates in the shown setting so that the inflowing exhaust gas stream is first completely introduced into the lower exhaust path. There, the exhaust gas first flows through an oxidation catalytic converter 12 and subsequently through a storage catalytic converter 14 . The exhaust gas flowing out of the storage catalytic converter 14 is divided at a first branch, an exhaust gas partial flow of, for example, 5% being formed. This partial exhaust gas stream strikes a first switching device 28 . In the present position, this changeover device 28 directs the partial exhaust gas flow to a second changeover device 22 , where a return of the partial exhaust gas flow is initiated. The recirculated exhaust gas partial flow then flows through the storage catalytic converter 14 and the oxidation catalytic converter 12 of the upper catalytic converter pair. There is therefore an exhaust gas recirculation, which is also advantageous with regard to the heat balance of the arrangement. The recirculated exhaust gas stream, which emerges from the oxidation catalytic converter 12 , is now partly fed to a separate exhaust gas path without a catalyst and partly to the lower exhaust gas path with the lower pair of catalysts 12 , 14 . In the separate exhaust gas path, a reducing agent is supplied to the partial exhaust gas stream by the feed device 10 . The partial exhaust gas flow is diverted by the first switchover device 28 and combined with the partial exhaust gas flow which was diverted by the second switchover device 22 . A mixture of the recirculated exhaust gas and the partial exhaust gas stream enriched with the reducing agent thus flows through the storage catalyst 14 of the upper catalyst pair 12 , 14 to be regenerated. Due to the multiple flow, the arrangement according to FIG. 6 has the advantage, in addition to the improved heat balance, that the amount of reducing agent to be supplied is further reduced. A fuel-air ratio of λ <1 is generated more quickly.

In Fig. 7 a further exhaust gas cleaning system is illustrated. This includes a first oxidation catalytic converter 12 and a second oxidation catalytic converter 12 , which is connected upstream of a storage catalytic converter 14 in the flow direction. Furthermore, a DENOX catalytic converter is provided, which is arranged parallel to the second oxidation catalytic converter 12 and the storage catalytic converter 14 . To generate a partial exhaust gas flow, an adjustable flow divider in the form of a flap 34 is provided, the flap optionally being able to be positioned in front of the catalytic converter arrangement or behind the catalytic converter arrangement. The first oxidation catalytic converter 12 serves to oxidize NO to NO ₂ . Oxidation of HC to CO takes place in the second oxidation catalytic converter 12 .

In the embodiment having a flap 34 in front of the catalyst arrangement in the illustrated position of the flap 34 is 12 supplied to an exhaust gas stream, after flowing through the first oxidation catalyst for purifying exhaust gas to the second oxidation catalyst 12 and the storage catalyst fourteenth If the flap 34 is pivoted upward in front of the catalytic converter arrangement, the main exhaust gas flow flows through a conventional DENOX catalytic converter 32 , so that exhaust gas purification can take place in the DENOX catalytic converter. In this regeneration position of the flap 34, a partial exhaust gas flow flows through the second oxidation catalytic converter 12 and the storage catalytic converter 14 , so that regeneration of the storage catalytic converter 14 and exhaust gas purification of the main exhaust gas flow in the DENOX catalytic converter can take place simultaneously. For the purpose of regeneration, a reducing agent is added to the partial exhaust gas flow from the feed device 10 , in the present case fuel (HC).

If the flap 34 , which realizes the adjustable flow divider, is located behind the catalytic converter arrangement in the exhaust gas purification system according to FIG. 7, the storage catalytic converter 14 is likewise regenerated in the illustrated position of the flap 34 , while the main exhaust gas flow is cleaned in the DENOX catalytic converter 32 he follows. If the flap 34 is pivoted behind the catalytic converter arrangement such that the main exhaust gas flow passes through the second oxidation catalytic converter 12 and the storage catalytic converter 14 , the exhaust gas purification takes place in this way. In the variant with the flap behind the catalytic converter arrangement, it is to be mentioned as advantageous that, owing to the absence of the flap 34 in front of the catalytic converter arrangement, exhaust gas flows through the entire catalytic converter arrangement, which results in a better heat balance.

FIG. 8 shows a further embodiment of an exhaust gas cleaning system, which largely corresponds to the embodiment according to FIG. 7. In contrast to the embodiment according to FIG. 7, no DENOX catalytic converter is provided. Rather, two second oxidation catalysts 12 and storage catalysts 14 arranged in parallel are provided. Due to the arrangement of a second feed device 10 , one pair of oxidation catalytic converter 12 and storage catalytic converter 14 can optionally be regenerated, while the other pair of oxidation catalytic converter 12 and storage catalytic converter 14 is used for exhaust gas purification.

If one considers the embodiment according to FIG. 8 with a flap 34 in front of the catalytic converter arrangement, with no flap being provided behind the catalytic converter arrangement, regeneration of the storage catalytic converter 14 of the upper catalyst pair 12 , 14 takes place in the illustrated flap position, with a reducing agent from the upper Feed device 11 is supplied. The lower feed device does not supply any fuel during this time, and the lower pair of catalysts 12 , 14 is used for exhaust gas purification.

FIG. 9 shows a variant of an exhaust gas cleaning system with DENOX catalytic converter, which is comparable to the exhaust gas cleaning system according to FIG. 7. In contrast to FIG. 7, the second oxidation catalytic converter 12 and the storage catalytic converter 14 are surrounded by a DENOX catalytic converter 32 . The position of the flap 34 shown is the regeneration position of the flap 34 , since only a partial exhaust gas flow, which is mixed with a reducing agent from a centrally arranged feed device 10 , flows through the storage catalytic converter 14 . The main exhaust gas stream is cleaned by the DENOX catalytic converter 32 surrounding the storage catalytic converter 14 . The central arrangement of the storage catalytic converter 14 , surrounded by a DENOX catalytic converter 32 , in turn has advantages with regard to the heat balance of the arrangement, which favors exhaust gas purification in the storage catalytic converter.

The preceding description of the exemplary embodiments according to the present invention is for illustrative purposes only Purposes and not for the purpose of restricting the Invention. Various are within the scope of the invention Changes and modifications possible without the scope of Invention as well as leaving its equivalents.

Claims (22)

1. exhaust gas purification system for a diesel engine with a catalytic converter arrangement and at least one feeding means (10) for supplying a reducing agent to the exhaust stream, wherein the catalyst arrangement has at least an oxidation catalyst (12) and at least one arranged in flow direction of the exhaust gas downstream of the oxidation catalyst (12) storage catalytic converter (14 ) or at least one storage catalytic converter ( 12 , 14 ) taking over the function of an oxidation catalytic converter, characterized in that at least one partial exhaust gas stream flows into the catalytic converter arrangement after the supply of the reducing agent and first flows through a storage catalytic converter ( 14 ). 2. Emission control system according to claim 1, characterized in that
that the feed device ( 10 ) is arranged in the flow direction of the exhaust gas behind the storage catalytic converter ( 14 ) and
that the inflow of the partial exhaust gas flow into the catalyst arrangement takes place by reversing the flow in the reverse direction. 3. emission control system according to claim 1 or 2, characterized in that the partial exhaust gas stream after passing through a storage catalyst (14) flows through an oxidation catalyst (12). 4. Emission control system according to one of the preceding claims, characterized in
that the catalyst arrangement has two catalyst pairs ( 12 , 14 ),
that each pair of catalysts ( 12 , 14 ) has an oxidation catalyst ( 12 ) and a storage catalyst ( 14 ) and
that after flowing through the exhaust gas stream through one of the catalyst pairs ( 12 , 14 ), the partial exhaust gas stream flows through the other catalyst pair ( 12 , 14 ). 5. Exhaust gas purification system according to one of the preceding claims, characterized in that a switching device ( 16 ) is provided in the flow direction in front of the catalyst arrangement, which switches the exhaust gas flow at least substantially to a pair of catalysts ( 12 , 14 ). 6. Exhaust gas purification system according to one of the preceding claims, characterized in that a switchable flow divider ( 18 ) is provided in the flow direction behind the catalyst arrangement, which divides the partial exhaust gas flow from the exhaust gas flow. 7. Exhaust gas cleaning system according to one of the preceding claims, characterized in that the feed device ( 10 ) is provided in the region of the flow divider ( 18 ) arranged downstream of the catalyst arrangement in the flow direction. 8. Exhaust gas purification system according to one of the preceding claims, characterized in that a separate exhaust gas path ( 30 ) is provided, via which the partial exhaust gas flow can be at least partially fed back to the exhaust gas flow, the supply taking place in the flow direction behind the switchable flow divider ( 18 ). 9. Exhaust gas purification system according to one of the preceding claims, characterized in that a switchable flow divider ( 20 ) is provided in the flow direction in front of the catalyst arrangement, which at least essentially feeds the exhaust gas flow to a pair of catalysts ( 12 , 14 ) and via which the exhaust gas partial flow can be fed back to the exhaust gas flow is. 10. Exhaust gas purification system according to one of the preceding claims, characterized in that the switchable flow divider ( 18 ) arranged behind the catalytic converter arrangement in the flow direction is realized by two check valves ( 24 ) and a 2/2 valve ( 22 ). 11. Exhaust gas purification system according to one of the preceding claims, characterized in that in the region of the flow divider ( 18 ) arranged downstream of the catalytic converter arrangement and behind the feed device ( 10 ), the partial exhaust gas flow flows through a catalytic mixer ( 26 ). 12. Emission control system according to one of the preceding Claims, characterized in that part of the Exhaust gas partial flow the catalyst arrangement several times in Flows backwards.   13. Method for exhaust gas purification in a diesel engine, in which an exhaust gas flow through at least one oxidation catalytic converter ( 12 ) and at least one storage catalytic converter ( 14 ) arranged downstream of the oxidation catalytic converter ( 12 ) in the flow direction or through at least one storage catalytic converter ( 12 , 14 ), and in which a reducing agent is fed to the exhaust gas stream, characterized in that at least one partial exhaust gas stream is fed to the catalyst device after the reducing agent has been fed and first flows through a storage catalytic converter ( 14 ). 14. The method according to claim 13, characterized in that for the inflow of the exhaust gas partial flow into the Catalyst arrangement the flow in the reverse direction is reversed. 15. The method according to claim 13 or 14, characterized in that the exhaust gas partial flow after flowing through a storage catalyst ( 14 ) is passed through an oxidation catalyst ( 12 ). 16. The method according to any one of claims 13 to 15, characterized in that the exhaust gas stream after passing through a catalyst pair (12, 14) comprising an oxidation catalyst (12) and a storage catalytic converter (14) is divided and the partial exhaust gas stream by another Catalyst pair ( 12 , 14 ) is passed, which has an oxidation catalyst ( 12 ) and a storage catalyst ( 14 ). 17. The method according to any one of claims 13 to 16, characterized in that the exhaust gas stream is essentially fed to a pair of catalysts ( 12 , 14 ). 18. The method according to any one of claims 13 to 17, characterized characterized in that the exhaust gas partial flow over the exhaust gas flow a separate exhaust gas path in the flow direction behind the Catalyst arrangement is supplied. 19. The method according to any one of claims 13 to 18, characterized in that the partial exhaust gas flow is fed to the exhaust gas flow in the flow direction upstream of the catalyst arrangement via a switchable flow divider ( 20 ). 20. The method according to any one of claims 13 to 19, characterized in that the partial exhaust gas stream is supplied to a catalytic mixer ( 26 ) after the supply of the reducing agent. 21. The method according to any one of claims 13 to 20, characterized characterized in that part of the partial exhaust gas flow Multiple catalytic converter arrangement in the reverse direction flows through. 22. The method according to any one of claims 13 to 21, characterized characterized that as a reducing agent diesel fuel or urea is used.