DE102018101665A1 - Device and method for exhaust aftertreatment of an internal combustion engine - Google Patents

Abstract

The invention relates to an exhaust aftertreatment device for an internal combustion engine (10). The exhaust aftertreatment device can be connected to an outlet (14) of the internal combustion engine (10) and comprises an exhaust system (20) with an exhaust gas channel (32). The exhaust passage (32) flows downstream of the outlet (14) and then divides at a junction into two parallel sub-channels (34, 36). In the first sub-channel (34), an oxidation catalyst (24) and in the second sub-channel (36) an NO storage catalyst (22) is arranged. Downstream of the two catalytic converters (22, 24), the two partial channels are again brought together to form a common exhaust gas channel (32), wherein an SCR catalytic converter (26) or a particle filter (28) with a coating (30) is provided in the common exhaust gas channel (32). It is provided that the exhaust gas stream of the internal combustion engine (10) at low exhaust gas temperatures through the second sub-channel (36) is guided and at least a partial flow through the first sub-channel (34) when exceeding a threshold temperature becomes.

Description

The invention relates to a device for exhaust aftertreatment of an internal combustion engine and to a method for the exhaust aftertreatment of an internal combustion engine according to the preamble of the independent claims.

The current and increasingly stringent future exhaust gas legislation places high demands on the engine raw emissions and the exhaust aftertreatment of internal combustion engines. The demands for a further reduction in consumption and the further tightening of emission standards with regard to permissible nitrogen oxide emissions pose a challenge for the engine developers. Diesel engines currently use exhaust aftertreatment systems which contain an oxidation catalyst, a catalyst for the selective catalytic reduction of nitrogen oxides (SCR). Catalyst) and a particulate filter for the separation of soot particles and optionally further catalysts, in particular a NO _x storage catalytic converter have. The reducing agent used for the SCR catalyst is preferably ammonia. Because the handling of pure ammonia is complicated, in vehicles usually a synthetic, aqueous urea solution is used, which is mixed in a SCR catalyst upstream mixing device with the hot exhaust gas stream. By this mixing, the aqueous urea solution is heated, wherein the aqueous urea solution releases ammonia in the exhaust gas passage. A commercial aqueous urea solution generally consists of 32.5% urea and 67.5% water.

From the DE 10 2015 219 028 A1 an exhaust aftertreatment device with an exhaust system is known in which a close-coupled three-way catalytic converter is arranged with a storage capacity for nitrogen oxides. Downstream, the exhaust gas channel branches into a main channel and a bypass channel, wherein in the main channel another NO _x storage catalytic converter and in the bypass channel another three-way catalyst are arranged. In this case, the internal combustion engine is operated with a lean combustion air ratio, wherein in this lean operation the first NO _x storage catalytic converter and the second NO _x storage catalytic converter are loaded with nitrogen oxides. When the NO _x storage catalytic converters have reached their loading limit, the internal combustion engine is briefly operated with a rich mixture, the first NO _x storage catalytic converter and the second NO _x storage catalytic converter being regenerated. In order to minimize emissions during the regeneration of the first NO _x storage catalyst, the exhaust gas flow is directed through the bypass passage during regeneration of the first NO _x storage catalyst and emissions through the second three-way catalyst are minimized.

In diesel engines, exhaust aftertreatment systems are known which have a near-engine NO _x storage catalytic converter and an SCR catalytic converter arranged downstream of the NO _x storage catalytic converter. This has the advantage that the nitrogen oxides can be stored in the NO _x storage catalytic converter at low exhaust gas temperatures, in particular after a cold start of the internal combustion engine. The disadvantage, however, is that in the later normal operation of the internal combustion engine by the NO _X storage catalyst for the downstream selective, catalytic reduction of nitrogen oxides unfavorable ratio of nitrogen monoxide and nitrogen dioxide is formed, whereby the effectiveness of the SCR catalyst is reduced. Furthermore, the NO _x storage catalytic converter must be regenerated periodically, the internal combustion engine for regeneration with a rich combustion air mixture and a consequent poorer efficiency must be operated.

The invention is based on the object to reduce the NO _x emissions of an internal combustion engine, in particular a self-igniting internal combustion engine according to the diesel principle, and to avoid the disadvantages known from the prior art.

According to the invention this object is achieved by a device for exhaust aftertreatment of an internal combustion engine, which is connected with its outlet to an exhaust system, wherein the exhaust system has an exhaust passage in which a NO _x storage catalyst, an oxidation catalyst and an SCR catalyst or a particulate filter with a Coating for selective, catalytic reduction of nitrogen oxides (SCR coating) is arranged. According to the invention, the exhaust gas duct branches downstream of the outlet at a branch into a first subchannel and a second subchannel, the oxidation catalytic converter being arranged in the first subchannel and the NO _x storage catalytic converter in the second subchannel. The two subchannels are merged downstream of the oxidation catalyst and downstream of the NO _x storage catalyst at a junction to a common exhaust passage, wherein in the common exhaust passage downstream of the oxidation catalyst and downstream of the NO _x storage catalytic converter, the SCR catalyst or the particulate filter with the selective coating , Catalytic reduction of nitrogen oxides is arranged. As a result, the NO _x storage catalytic converter is during normal operation of the internal combustion engine 10 decoupled from the exhaust stream, so that the regeneration of the NO _X storage catalytic converter only comparatively rarely needs to be performed. As a result, the operating situations of the internal combustion engine can be reduced with a poorer efficiency for the regeneration of the NO _x storage catalytic converter, resulting overall in lower consumption of the internal combustion engine. Furthermore, the NO _x storage catalytic converter can be designed with a comparatively small volume, as a result of which the NO _x storage catalytic converter reaches its activation temperature more rapidly after a cold start of the internal combustion engine, from which an efficient incorporation of nitrogen oxides into the NO _x storage catalytic converter is possible. Further, in normal operation, a favorable ratio of nitrogen monoxide (NO) to nitrogen oxide nitrogen (NO ₂ ) is achieved, so that the efficiency of the SCR catalyst or the particulate filter with the coating for selective, catalytic reduction of nitrogen oxides can be increased and the reducing agent used can be reduced. Another advantage results from the fact that the NO _x storage catalytic converter is regenerated during operation and has a best possible storage behavior for nitrogen oxides in the case of a renewed cold start of the internal combustion engine.

By the features listed in the dependent claims advantageous developments and improvements of the independent claim exhaust gas aftertreatment system are possible.

In a preferred embodiment of the invention, it is provided that at the junction or at the merger, an actuating element is arranged, with which an exhaust gas stream of the internal combustion engine optionally exclusively by the oxidation catalyst, exclusively by the NO storage catalyst or proportionally by both the oxidation catalyst and by the NO _X storage catalyst is passed. As a result, an efficient exhaust aftertreatment of the exhaust gas of the internal combustion engine is possible in any operating situation of the internal combustion engine. In particular, the NO _x storage catalyst can be regenerated after the cold start phase and then decoupled from the exhaust gas flow, so that the number of consumption-increasing regeneration cycles can be minimized. Furthermore, it is ensured in this way that the NO _x storage catalytic converter in each case has its complete storage capacity during a cold start, so that a comparatively small catalyst volume can be selected.

It is particularly preferred if the actuating element is designed as an exhaust flap. By an exhaust valve, a division of the exhaust gas flow to the respective sub-channels of the exhaust system is possible in a comparatively simple and reliable manner. In addition, a comparatively fast switching between the individual operating modes of the exhaust gas aftertreatment system is possible by means of an exhaust gas flap.

In an advantageous embodiment of the exhaust gas aftertreatment system, it is provided that the oxidation catalytic converter and the NO _x storage catalytic converter are arranged in a common housing. By an embodiment in a common housing, a particularly compact and space-optimized embodiment of the device according to the invention for exhaust aftertreatment is possible. This also weight can be reduced, whereby the consumption of a motor vehicle can be reduced. Furthermore, in one embodiment with a common housing for NO _x storage catalytic converter and oxidation catalyst, an operating state in which the exhaust gas flow is passed through the NO _x storage catalytic converter leads to a heating of the oxidation catalytic converter, so that it reaches its operating temperature more quickly. In addition, the installation of the exhaust system is facilitated because fewer individual components are to be mounted.

Alternatively, an embodiment is proposed, wherein the oxidation catalyst and the NO _x storage catalyst are arranged in separate housings. Although this solution requires more space overall, however, the NO _x storage catalyst and the oxidation catalyst can be arranged separately from each other, which can be an advantage especially in tight space conditions. In addition, the components can be replaced individually, which reduces the repair costs.

Preferably, the internal combustion engine is designed as a self-igniting internal combustion engine according to the diesel principle. The exhaust gas aftertreatment device according to the invention is primarily intended for the exhaust aftertreatment problem occurring in a diesel engine. Since a diesel engine does not have a reducing agent for converting nitrogen oxides due to the excess of air in normal operation, the combination of NO _x storage catalytic converter and SCR catalytic converter offers a very efficient way of reducing nitrogen oxide emissions, especially for a diesel engine.

Alternatively, the internal combustion engine can also be embodied as a spark ignition spark ignited spark ignition engine, in particular as a gasoline engine operated with a lean combustion air ratio. As a rule, gasoline engines are operated with a stoichiometric combustion air ratio. At a stoichiometric combustion air ratio is usually sufficient amount of reducing agent in the form of unburned hydrocarbons to the nitrogen oxides by means of a three-way catalyst in molecular To convert nitrogen. In a running in lean-burn gasoline engine, however, this reducing agent is missing, so that the proposed device for exhaust aftertreatment brings in a lean-running gasoline engine similar advantages as in a diesel engine with it.

According to the invention, a method for exhaust aftertreatment of an internal combustion engine with a device according to the invention for exhaust aftertreatment is proposed, wherein an exhaust gas stream of the internal combustion engine is passed at an exhaust gas temperature below a threshold temperature exclusively through the NO _x storage catalytic converter. Below this first threshold temperature, which is about 200 ° C, the SCR catalyst has only a very low conversion performance for nitrogen oxide emissions. Therefore, in this temperature range, the NO _x storage catalyst serves to store the nitrogen oxide emissions occurring during the combustion, as long as the SCR catalytic converter has not yet reached its operating temperature.

In a further preferred embodiment of the method, it is provided that the exhaust gas stream above this threshold temperature is passed proportionately or completely through the oxidation catalyst. Once the SCR catalyst has reached its operating temperature, it is advantageous to pass the exhaust stream through the oxidation catalyst to achieve an optimum ratio of nitrogen monoxide and nitrogen dioxide for the SCR catalyst. This can improve the efficiency of the SCR catalyst and reduce the use of reducing agent.

In a preferred embodiment of the method, it is provided that, for the regeneration of the NO _x storage catalytic converter, a first partial flow of the exhaust gas flow through the NO _x storage catalytic converter and a second partial flow of the exhaust gas flow through the oxidation catalytic converter. As a result, the NO _x storage catalytic converter can be regenerated after the cold start phase, so that this catalyst is available again with full storage volume during the next cold start phase. Subsequently, the NO _x storage catalyst may be decoupled from the exhaust stream to minimize the number of regeneration cycles for the NO _x storage catalyst and, associated therewith, fuel consumption.

According to a preferred embodiment of the method, it is provided that the exhaust gas flow is passed in parallel proportionately through the NO _x storage catalyst and the oxidation catalyst when a threshold value for the exhaust gas mass flow is exceeded. In order to minimize the exhaust back pressure at high load ranges and thus to increase the efficiency of the internal combustion engine, it is provided that, when a threshold value for the exhaust gas mass flow is exceeded, the exhaust gas flow of the internal combustion engine is conducted proportionally through both catalytic converters. Thus, the flow area can be increased and the exhaust back pressure can be minimized. Furthermore, in this operating state, the NO _x storage catalytic converter acts like an oxidation catalytic converter, so that the catalyst volume available for the oxidation of unburned fuel components is increased.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

• 1 ein erstes Ausführungsbeispiel einer erfindungsgemäßen Vorrichtung zur Abgasnachbehandlung eines Verbrennungsmotors in einem ersten Betriebszustand;
• 2 die in 1 dargestellte Vorrichtung zur Abgasnachbehandlung in einem zweiten Betriebszustand;
• 3 die in 1 dargestellte Vorrichtung zur Abgasnachbehandlung in einem dritten Betriebszustand;
• 4 ein weiteres Ausführungsbeispiel einer erfindungsgemäßen Vorrichtung zur Abgasnachbehandlung eines Verbrennungsmotors in einem ersten Betriebszustand;
• 5 die in 4 dargestellte Vorrichtung zur Abgasnachbehandlung in einem zweiten Betriebszustand; und
• 6 die in 4 dargestellte Vorrichtung zur Abgasnachbehandlung in einem dritten Betriebszustand.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

• 1 a first embodiment of a device according to the invention for the exhaust aftertreatment of an internal combustion engine in a first operating state;
• 2 in the 1 illustrated device for exhaust aftertreatment in a second operating state;
• 3 in the 1 illustrated device for exhaust aftertreatment in a third operating state;
• 4 a further embodiment of a device according to the invention for the exhaust aftertreatment of an internal combustion engine in a first operating state;
• 5 in the 4 illustrated device for exhaust aftertreatment in a second operating state; and
• 6 in the 4 illustrated device for exhaust aftertreatment in a third operating state.

1 shows an internal combustion engine 10 , preferably a diesel engine, which with its outlet 14 with an exhaust system 20 connected is. The internal combustion engine 10 has an inlet 12 on, over which fresh air into several combustion chambers 16 of the internal combustion engine 10 can flow in. The combustion chambers 16 is each a fuel injection valve 18 for metering fuel into the respective combustion chamber 16 assigned. The exhaust system 20 has an exhaust duct 32 on, which downstream of the outlet 14 is formed einflutig. The exhaust duct 32 Branches at a junction 38 in a mutually parallel first sub-channel 34 and into a second subchannel 36 , In the first subchannel 34 is an oxidation catalyst 24 arranged. In the second subchannel 36 is a NO _x storage catalyst 22 arranged. The two catalysts 22 . 24 are in a common housing 46 arranged and fluidically separated by a gas-tight barrier. At the junction 38 is an actuator 42 in the form of a swiveling exhaust flap 44 arranged, with which an exhaust gas stream of the internal combustion engine 10 optionally by the oxidation catalyst 24 , through the NO _X storage catalyst 22 or proportionately by both catalysts 22 . 24 can be directed. Downstream of the two catalysts 22 . 24 become the two subchannels 34 . 36 at a merge 40 again to a common exhaust duct 32 merged. Downstream of the merger is at the common exhaust passage 32 a metering element 62 for metering in a reducing agent, in particular aqueous urea solution. Further downstream is in the common exhaust passage 32 an SCR catalyst 26 which is independent of the flow guidance of the exhaust gas flow through the sub-channels 34 . 36 in each case flows through the entire exhaust stream. On the actuator 42 is an actuator 52 , In particular an electric servomotor, provided, with which the actuating element 42 can be brought into the desired switching position. Downstream of the SCR catalyst 26 is in the exhaust duct 32 a temperature sensor 54 arranged, with which an exhaust gas temperature T _EC can be determined. The dosing element 62 , the actuator 52 are via signal lines 56 with a control unit 60 of the internal combustion engine 10 connected. The temperature sensor 54 is over another signal line 58 also with the control unit 60 connected.

In 1 the exhaust aftertreatment system is shown in a first operating state. This first operating state is in particular after a cold start of the internal combustion engine 10 before when the SCR catalyst 26 not yet reached its operating temperature and it is not yet possible, nitrogen oxide emissions using the SCR catalyst 26 to convert. Here is the actuator 42 placed so that the entire exhaust stream of the engine 10 through the NO _X storage catalyst 22 is directed. The nitrogen oxides from the exhaust gas stream are temporarily stored in the NO _x storage catalytic converter 22 stored. At the same time, the NO _X storage catalytic converter takes over 22 in this operating state, the function of an oxidation catalyst for unburned fuel components. The NO _x storage catalyst can be made with respect to solutions known in the art with a comparatively small volume, resulting in faster heating of the NO _x storage catalyst and faster achievement of its operating temperature. This first operating state is maintained until the exhaust gas temperature or the temperature of the SCR catalyst 26 reaches a threshold temperature T _S.

In 2 is the exhaust aftertreatment system of the internal combustion engine 10 shown in a second operating state. This second operating state is then initiated when the exhaust gas temperature or the temperature of the SCR catalyst 26 the threshold temperature T _S exceeds. This is the actuator 42 through the actuator 52 brought into a second switching position, in which the entire exhaust gas flow of the internal combustion engine 10 through the oxidation catalyst 24 is directed. This results in an optimal ratio of nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) for the exhaust aftertreatment through the downstream SCR catalyst 26 on. The oxidation catalyst 24 can be optimized for a medium temperature range and thus be executed with the same performance with less volume. Furthermore, no loading of the NO _x storage catalytic converter takes place in this second operating state 22 with more nitrogen oxides, reducing the number of regeneration cycles for the NO _X storage catalyst 22 can be reduced and the storage capacity of the NO _X storage catalytic converter 22 for the next cold start of the internal combustion engine 10 can be restored.

In 3 is shown a third operating state of the exhaust aftertreatment system. This is the actuator 42 through the actuator 52 placed in a middle position, so that in each case a partial flow of the exhaust gas flow through the NO _X storage catalytic converter 22 and by the oxidation catalyst 24 to be led. This operating state is selected in particular at high exhaust gas mass flows in order to reduce the flow resistance. In addition, in this operating state, both the NO _x storage catalytic converter act 22 as well as the oxidation catalyst 24 as catalysts for the oxidation of unburned fuel components, so that both catalysts 22 . 24 can be performed with a comparatively small volume. Furthermore, in this operating state, a regeneration of the NO _x storage catalytic converter 22 be performed. Alternatively, such a regeneration even at a switching position of the actuating element 42 as performed in the first operating state. Alternative to an SCR catalyst 26 can also use a particle filter 28 with a coating 30 be used for the selective catalytic reduction of nitrogen oxides.

In 4 to 6 is another embodiment of a device according to the invention for the exhaust aftertreatment of an internal combustion engine 10 shown. With essentially the same structure as 1 to 3 executed, in this embodiment, the NO _x storage catalyst 22 and the oxidation catalyst 24 in two separate housings 48 . 50 arranged. Here are the first subchannel 34 and the second subchannel 36 spaced apart. Instead of an SCR catalyst 26 is downstream of the merge in this embodiment 40 a particle filter 28 with a coating 30 for the selective, catalytic reduction of nitrogen oxides arranged. Alternatively, in this embodiment, the particulate filter 28 through an SCR catalyst 26 be replaced.

LIST OF REFERENCE NUMBERS

10

internal combustion engine

12

inlet

14

outlet

16

combustion chamber

18

Fuel injection valve

20

exhaust system

22

NO _x storage catalyst

24

oxidation catalyst

26

SCR catalyst

28

particulate Filter

30

Coating for selective, catalytic reduction

32

exhaust duct

34

first subchannel

36

second subchannel

38

branch

40

together

42

actuator

44

exhaust flap

46

common housing

48

first housing

50

second housing

52

actuator

54

temperature sensor

56

signal line

58

signal line

60

control unit

62

metering

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

• DE 102015219028 A1 [0003]

Claims (10)

A device for exhaust aftertreatment of an internal combustion engine (10), which is connected with its outlet (14) to an exhaust system (20), wherein the exhaust system (20) has an exhaust passage (32), in which a NO _x storage catalyst (22), a Oxidation catalyst (24) and an SCR catalyst (26) or a particulate filter (28) is arranged with a coating (30) for the selective, catalytic reduction of nitrogen oxides, characterized in that the exhaust channel (32) downstream of the outlet (14) branches at a junction (38) in a first sub-channel (34) and a second sub-channel (36), wherein in the first sub-channel (34) of the oxidation catalyst (24) and in the second sub-channel (36) of the NO _x storage catalytic converter (22 ), and wherein the two sub-channels (34, 36) downstream of the oxidation catalyst (24) and the NO _x storage catalytic converter (22) are brought together at a junction (40) to a common exhaust duct (32) where in the common exhaust passage (32) downstream of the oxidation catalyst (24) and downstream of the NO _x storage catalyst (22), the SCR catalyst (26) or the particulate filter (28) with the selective catalytic reduction reduction coating (30) is arranged. Device for exhaust aftertreatment after Claim 1 , characterized in that at the branch (38) or at the junction (40) an adjusting element (42) is arranged, with which an exhaust gas stream of the internal combustion engine (10) optionally exclusively by the oxidation catalyst (24), exclusively by the NO _X - Storage catalyst (22) or proportionally through both the oxidation catalyst (24) and by the NO _x storage catalyst (22) is passed. Device for exhaust aftertreatment according to Claim 2 , characterized in that the adjusting element (42) is designed as an exhaust flap (44). Device for exhaust aftertreatment according to one of Claims 1 to 3 , characterized in that the oxidation catalyst (24) and the NO _x storage catalytic converter (22) are arranged in a common housing (46). Device for exhaust aftertreatment according to one of Claims 1 to 3 , characterized in that the oxidation catalyst (24) and the NO _x storage catalytic converter (22) are arranged in separate housings (48, 50). Device for exhaust aftertreatment according to one of Claims 1 to 5 , characterized in that the internal combustion engine (10) is designed as a self-igniting internal combustion engine (10) according to the diesel principle. A method for exhaust aftertreatment of an internal combustion engine (10) with an apparatus for exhaust aftertreatment according to one of Claims 1 to 6 , characterized in that an exhaust gas stream of the internal combustion engine (10) at an exhaust gas temperature below a threshold temperature T _{S is passed} exclusively through the NO _x storage catalytic converter (22). Process for exhaust aftertreatment after Claim 7 , characterized in that the exhaust gas stream above this clamp temperature T _{S is} proportionally or completely passed through the oxidation catalyst (24). Process for exhaust aftertreatment after Claim 7 or 8th , characterized in that for the regeneration of the NO _x storage catalytic converter (22) a first partial flow of the exhaust gas flow through the NO _x storage catalytic converter (22) and a second partial flow of the exhaust gas flow through the oxidation catalyst (24) is passed. Process for exhaust aftertreatment according to one of Claims 7 to 9 , characterized in that the exhaust gas stream is passed in parallel proportionately through the NO _x storage catalyst (22) and the oxidation catalyst (24) when exceeding a threshold value for the exhaust gas mass flow.

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