DE102016112363B4 - exhaust aftertreatment system - Google Patents

Abstract

Exhaust aftertreatment system for an internal combustion engine (11) comprising an exhaust gas passage (12), an SCR-F catalytic converter for the selective catalytic reduction of nitrogen oxides with a filter and a nitrogen oxide storage catalytic converter, characterized in that in the flow direction of the exhaust gas through the exhaust gas passage (12) the nitrogen oxide storage catalytic converter (37, LNT) is arranged behind the SCR-F catalytic converter (18, SCR-F), and that the exhaust gas aftertreatment system (10) is designed to use the exhaust gas to regenerate the nitrogen oxide storage catalytic converter (37, LNT) secondly adding a reducing agent, and that in the flow direction of the exhaust gas through the exhaust gas passage (12) in front of the SCR-F catalytic converter (18, SCR-F) a passive nitrogen oxide adsorber (30, PNA) is additionally arranged, which is designed for this purpose store nitrogen oxides in a first low temperature range and release the stored nitrogen oxides again in a second temperature range.

Description

The invention relates to an exhaust aftertreatment system for an internal combustion engine.

Out of DE 10 2015 213 617 A1 a device and a method for the exhaust aftertreatment of a gasoline engine with a three-way catalytic converter is known.

Out of DE 10 2013 212 802 A1 an arrangement for exhaust gas aftertreatment for an internal combustion engine with a first and a second NOx storage catalyst is known.

Out of DE 10 2013 019 025 A1 a method for operating an exhaust gas cleaning system of an internal combustion engine is known, which has an ammonia formation catalytic converter, an ammonia SCR catalytic converter and a nitrogen oxide storage catalytic converter connected immediately downstream in the direction of flow.

Out of U.S. 2010/0 058 742 A1 an exhaust emission control apparatus using ozone injecting means is known.

In practice, it is customary to provide an SCR-F catalytic converter for the selective catalytic reduction of nitrogen oxides, which also contains a filter, and a nitrogen oxide storage catalytic converter in an exhaust gas aftertreatment system, in particular on a diesel engine. In the previously known systems, the nitrogen oxide storage catalytic converter is arranged upstream of the SCR-F catalytic converter in the flow direction of the exhaust gas, so that exhaust gas first flows through the nitrogen oxide storage catalytic converter and then through the SCR-F catalytic converter. This design of an exhaust aftertreatment system is used in particular to bring nitrogen oxide emissions below the limit values that are prescribed for the so-called Real Driving Emission Test.

The nitrogen oxide storage catalytic converter is used to store nitrogen oxides at low exhaust gas temperatures, especially after a cold start. With increasing exhaust gas temperatures, nitrogen oxides can be reduced to nitrogen in the SCR-F catalytic converter arranged downstream. In previous systems, the nitrogen oxide storage catalytic converter was frequently regenerated by raising the exhaust gas temperature and creating a rich mixture in the exhaust gas. The nitrogen oxides contained in the nitrogen oxide storage catalytic converter are released again and reduced to nitrogen by reacting with the rich exhaust gas.

Urea (urea/urea solution) or a solution containing ammonia is added upstream of the SCR-F catalytic converter, which reacts in the SCR-F catalytic converter. However, ammonia can pass through the SCR-F catalytic converter or the SCR-F catalytic converter can become oversaturated with ammonia, with excess ammonia escaping at the outlet of the SCR-F catalytic converter (so-called ammonia slip). In the previously known systems, an additional ammonia slip catalyst is required in the flow direction of the exhaust gas downstream of the SCR-F catalyst, through which any (toxic) ammonia escaping from the SCR-F catalyst is reduced to nitrogen and water.

A further problem of the previously known systems is that the conversion efficiency of an SCR-F catalytic converter can be impaired in transient operating states of the internal combustion engine (transient operation), so that there is insufficient removal of nitrogen oxides in the exhaust gas. Undesirable nitrogen oxide peaks can therefore occur in the exhaust gas escaping into the atmosphere.

It is the object of the present invention to provide an improved exhaust gas aftertreatment system and an associated operating method.

The invention solves this problem through the characterizing features of the independent claims.

According to the present disclosure, it is proposed to arrange the nitrogen oxide storage catalyst downstream of the SCR-F catalyst in the flow direction of the exhaust gas through the exhaust gas passage. Furthermore, it is proposed that the exhaust gas aftertreatment system be designed to temporarily add a reducing agent to the exhaust gas for the purpose of regenerating the nitrogen oxide storage catalytic converter. Active regeneration of the nitrogen oxide storage catalytic converter, which is arranged essentially in the end area of the exhaust gas passage, is particularly preferably carried out selectively or as required depending on the detection of nitrogen oxides downstream of the nitrogen oxide storage catalytic converter. In other words, regeneration is only performed if this is necessary to comply with prescribed limit values. Otherwise, with a nitrogen oxide storage catalytic converter that is almost or completely saturated, active regeneration can be delayed or only passive regeneration can be carried out, in which stored nitrogen oxides are discharged but not converted or only converted to a very small extent.

The aforementioned arrangement of SCR-F catalytic converter and nitrogen oxide storage catalytic converter has the advantage that the nitrogen oxide storage catalytic converter behind the SCR-F catalytic converter can also take on the task of reducing excess ammonia. It is therefore not necessary to provide an additional ammonia slip catalyst. Due to the arrangement behind the SCR-F catalytic converter, the nitrogen oxide storage catalytic converter, where a fundamentally lower concentration of nitrogen oxides and other emissions in the exhaust gas is to be expected, can continue to have smaller dimensions, which means that cost savings can be achieved.

Furthermore, a particularly good conversion efficiency for nitrogen dioxide is achieved, which is particularly important in the Real Driving Emission Test.

Further advantageous refinements of the invention are contained in the dependent claims, the following description and the attached drawings.

• 1: Ein Abgasnachbehandlungssystem gemäß dem Stand der Technik;
• 2: ein Abgasnachbehandlungssystem gemäß der vorliegenden Offenbarung;
• 3 und 4: Ablaufdiagramme zur Erläuterung eines Vorgangs zur selektiven Regenerierung eines Stickoxid-Speicherkatalysators.

The invention is shown by way of example and schematically in the drawings. Show it:

• 1 : A prior art exhaust aftertreatment system;
• 2 : an exhaust aftertreatment system according to the present disclosure;
• 3 and 4 : Flow charts explaining a process for selective regeneration of a nitrogen oxide storage catalyst.

1 shows an exhaust gas aftertreatment system (10') according to the prior art. Exhaust gas from an internal combustion engine (11) is discharged through a multi-part exhaust gas passage (12). Several after-treatment units are arranged on or in the exhaust gas passage (12) in the flow direction of the exhaust gas. In the example of 1 are in sequence: a high-pressure turbine (13), a low-pressure turbine (14), a first NOx sensor (21), a nitrogen oxide storage catalytic converter (17, LNT), a urea injector (23), an SCR F catalytic converter, ie a catalytic converter for carrying out a selective catalytic reduction of nitrogen oxides, which further comprises a filter, in particular a particle filter, a second NOx sensor (22) and an ammonia slip catalytic converter (20). Behind the SCR-F catalytic converter (18, SCR-F), there is also a branch to a low-pressure exhaust gas recirculation (19).

in the in 1 shown exhaust gas aftertreatment system (10 ') according to the prior art, a bypass (15) is also provided with a bypass valve (16). Through the bypass, exhaust gas can be routed past the high-pressure turbine (13) at times. The function of such an exhaust aftertreatment system according to the prior art was explained above.

2 Figure 12 shows an exhaust aftertreatment system (10) according to the present disclosure. to the system 1 matching components and parts bear the same reference number. Components or parts that differ in design or arrangement are marked with new reference numbers.

The exhaust aftertreatment system (10) according to 2 comprises in the flow direction of the exhaust gas through the exhaust gas passage (12) first an SCR-F catalytic converter (18, SCR-F), and behind it a nitrogen oxide storage catalytic converter (37, LNT). Furthermore, the exhaust gas aftertreatment system (10) is designed to temporarily add a reducing agent to the exhaust gas to regenerate the nitrogen oxide storage catalytic converter (37, LNT). The reducing agent can be the fuel of the internal combustion engine (11) or a separate reducing agent.

According to a first embodiment variant, the reducing agent is added in an area upstream of the SCR-F catalytic converter (18, SCR-F), in particular by adding unburned fuel to the exhaust gas in the area of the internal combustion engine (11). This can be done in particular by carrying out post-injections. According to another embodiment variant, a reducing agent injector (34) can be provided as an alternative or in addition, which is actuated to regenerate the nitrogen oxide storage catalytic converter (37, LNT) in order to add fuel or a separate reducing agent to the exhaust gas. This reducing agent injector (34) is preferably in an area of the exhaust gas pas say (12) between the SCR-F catalytic converter (18, SCR-F) and the nitrogen oxide storage catalytic converter (37, LNT).

Modern SCR-F catalytic converters (18, SCR-F) can already efficiently convert nitrogen oxides (NOx) over a wide temperature range. However, it is known that in transient conditions of the internal combustion engine, there is poor uniformity in the exhaust gas, which can affect the conversion efficiency of the SCR-F catalyst. For this reason, so-called NOx peaks can occur when the engine is in non-stationary states, which cannot be adequately intercepted by the SCR-F catalytic converter.

The arrangement of the nitrogen oxide storage catalyst (37, LNT), in the flow direction of the exhaust gas behind the SCR-F catalyst (18, SCR-F), offers the advantage that the nitrogen oxide storage catalyst (37, LNT), this NOx -Capable of absorbing spikes. Since the nitrogen oxide storage catalytic converter (37, LNT) is arranged towards the end of the exhaust gas passage (12), where exhaust gas with a significantly reduced temperature flows through it, storage of nitrogen oxides can be achieved for almost all operating states of the internal combustion engine (11). become. Furthermore, the treatment units arranged in the initial and central area of the exhaust gas passage (12) contribute to good mixing, which promotes a reaction in the nitrogen oxide storage catalytic converter (37, LNT).

A passive nitrogen oxide absorber (30) (PNA—passive NOx adsorber) can preferably also be arranged upstream of the SCR-F catalytic converter (18, SCR-F) in the flow direction of the exhaust gas. Compared to a nitrogen oxide storage catalytic converter (LNT-Lean NOx Trap / Active NOx Adsorber), the passive nitrogen oxide adsorber does not need to provide a rich exhaust gas mixture in order to release stored nitrogen oxides (NOx) again. Rather, the passive nitrogen oxide adsorber (30, PNA) can store nitrogen oxides in a first low temperature range, for example up to about 200° Celsius. In a second temperature range of the exhaust gas, which is above approximately 200° Celsius, for example, the passive nitrogen oxide adsorber (30, PNA) can release the stored nitrogen oxides (NOx) again without (directly or itself) carrying out a catalytic reduction or to support.

On the other hand, the passive nitrogen oxide adsorber (30, PNA) can offer the functionality of a diesel oxidation catalyst (DOC), ie it can at least convert hydrocarbons (HC) and carbon monoxide (CO).

The exhaust gas aftertreatment system according to the present disclosure is preferably designed to store nitrogen oxides (NOx) occurring after a cold start of the internal combustion engine (11) until an exhaust gas temperature of approximately 200° Celsius is reached in the passive nitrogen oxide adsorber (30) PNA. As soon as the exhaust gas temperature exceeds the value of around 200° Celsius, the nitrogen oxides generated by the internal combustion engine (11) and any nitrogen oxides (NOx) stored and released again from the passive nitrogen oxide adsorber (30, PNA) can be stored in the SCR-F -Catalyst (18, SCR-F) to be converted. This can be done in a manner known per se with the addition of a urea solution (urea). Correspondingly, in the direction of flow of the exhaust gas, a urea injector/urea injector/ Ammonia injector can be arranged.

The passive nitrogen oxide adsorber (30, PNA) is significantly cheaper than an ammonia slip condenser (20). The formation of the exhaust aftertreatment system (10) according to 2 with the arrangement first of a passive nitrogen oxide adsorber (30, PNA), behind it an SCR-F catalytic converter (18, SCR-F), and at the end of a nitrogen oxide storage catalytic converter (37, LNT), offers an overall higher nitrogen oxide conversion efficiency as the in 1 illustrated exhaust gas aftertreatment system with lower costs at the same time.

According to a preferred development of the disclosure, an ozone injector (35) (also called a plasma injector) is arranged upstream of the SCR-F catalytic converter and in particular downstream of the passive nitrogen oxide adsorber (30, PNA) in the flow direction of the exhaust gas. The addition of ozone (O ₃ ) to the exhaust gas serves to convert nitrogen monoxide (NO) into nitrogen dioxide (NO2), particularly in the area upstream of the SCR-F catalytic converter. This further favors the conversion efficiency in the SCR-F catalyst (18, SCR-F). If the ozone is only added after the passive nitrogen oxide adsorber (30, PNA), which also has the function of a diesel oxidation catalyst, the ozone (03) is added to an exhaust gas that essentially consists of hydrocarbons (HC) and carbon monoxide ( CO) is cleaned (because the passive nitrogen oxide adsorber can act as an oxidation catalyst). Thus, a maximum proportion of the added ozone is available for the desired reaction with nitrogen monoxide. It will avoid that one Percentage of added ozone (03) reacts to carbon dioxide (CO2) and water (H2O) through an undesired reaction with hydrocarbons (HC) in the exhaust gas, or through another undesired reaction with carbon monoxide (CO) to form carbon dioxide (CO2) and oxygen (02 ) reacted.

Alternatively or additionally, in the exhaust aftertreatment system (10) according to the present disclosure, an ozone injector (36) (also called plasma injector) in an area behind the SCR-F catalyst (18, SCR-F), and before the nitrogen oxide - Storage catalytic converter (37, LNT) can be arranged. The addition of ozone (03) at this point has the advantage that the storage efficiency of the nitrogen oxide storage catalytic converter (37, LNT) is increased for low temperatures, i.e. in particular for a period after a cold start of the internal combustion engine (11) or in stop-and-go traffic .

In the exhaust aftertreatment system (10) according to the present disclosure - in particular with regard to compliance with the limit values for the real driving emission test - the SCR-F catalytic converter (18, SCR-F), the nitrogen oxide storage catalytic converter (37, LNT ), and the passive nitrogen oxide adsorber (30, PNA), can be used particularly efficiently. In particular, this enables a particularly conservative injection strategy for the addition of urea or ammonia. If the amount of ammonia (NH3) currently contained in the SCR-F catalyst (18, SCR-F), should not be sufficient to ensure a high nitrogen oxides conversion rate, especially during transient operating conditions of the engine, when insufficient uniformity of the exhaust gas is present, nitrogen oxides (NOx)) that have passed through the SCR-F catalytic converter can be trapped in the nitrogen oxide storage catalytic converter (37, LNT) arranged downstream.

By adding urea or ammonia as conservatively as possible, the operating costs of the exhaust aftertreatment system are lowered and the risk of toxic ammonia emissions is further reduced.

Since the nitrogen oxide storage catalytic converter (37) is located behind the SCR-F catalytic converter (18), and at low exhaust gas temperatures, nitrogen oxides (NOx) are already stored in the passive nitrogen oxide absorber (30, PNA), even before the SCR -F catalytic converter (18) can take place, compared to the exhaust gas aftertreatment system (10') known from the prior art 1 a significantly lower amount of nitrogen oxides (NOx) in the nitrogen oxide storage catalyst (37, LNT), stored during engine operation. It is therefore significantly less necessary to carry out a regeneration cycle for the nitrogen oxide storage catalytic converter (37, LNT), or a smaller size of the nitrogen oxide storage catalytic converter is required. Accordingly, compared to the previously known system 1 enables a cost reduction and it is much less common or to a much lesser extent to provide a rich exhaust gas mixture or to add a reducing agent through a reducing agent injector (34) upstream of the nitrogen oxide storage catalytic converter (37, LNT).

In particular, it is possible to dispense with a separate reducing agent injector (34). Thus, a significantly lower fuel consumption or consumption of reducing agent for the operation of the exhaust gas aftertreatment system (10) according to the present disclosure is necessary and, if necessary, the costs of a reducing agent injector (34) can be saved. On the other hand, advantageous configurations of the exhaust gas aftertreatment system (10) according to the present disclosure are also possible with a reducing agent injector.

Below are from 3 and 4 two preferred embodiment variants for a process for the selective or needs-based regeneration of the nitrogen oxide storage catalytic converter (37, LNT) arranged behind the SCR-F catalytic converter (18, SCR-F) are described.

In the example of 3 it is assumed that a reducing agent injector (34) is arranged in the flow direction of the exhaust gas after the SCR-F catalytic converter (18) and before the nitrogen oxide storage catalytic converter (37), which uses a fuel from the internal combustion engine or another reducing agent for carrying out of a regeneration cycle.

the inside 3 or. 4 The sequence shown can be repeated as often as desired after the start of engine operation or run as an endless sequence. It can be carried out, for example, by a control device (not shown), which is connected to the exhaust gas aftertreatment system (10) and/or the internal combustion engine (11).

Insofar as a method or process for regenerating the nitrogen oxide storage catalytic converter (37, LNT) is explained within the scope of the present disclosure, this also applies to the fact that the exhaust gas aftertreatment system (10) is designed to carry out such a method and vice versa. The design of the exhaust aftertreatment system can consist, for example, in that it is connected to the aforementioned control device or has such a device.

In the first step (S10) of 3 it is checked whether the nitrogen oxide adsorption capacity of the nitrogen oxide storage catalytic converter (37, LNT) has been reached. This can be done in any way. A first and a second NOx sensor (31, 32) can particularly preferably be arranged upstream and downstream of the nitrogen oxide storage catalytic converter (37, LNT) in the flow direction of the exhaust gas. Furthermore, an exhaust gas temperature in the area of the nitrogen oxide catalytic converter (37, LNT) can be recorded. Based on a known temperature-dependent adsorption efficiency and adsorption capacity of the nitrogen oxide storage catalytic converter (37, LNT) and on the basis of the current measured values of the NOx sensors (31, 32), it can be determined to what extent the current adsorption capacity has already been affected by the nitrogen oxides (NOx) supplied. is exhausted. If the current adsorption capacity is almost or completely reached, no or only a few more nitrogen oxides (NOx) can be adsorbed by the surface of the nitrogen oxide storage catalytic converter (37, LNT) and thus stored. It is therefore to be expected that supplied nitrogen oxides (NOx) will pass through the nitrogen oxide storage catalytic converter (37, LNT). Accordingly, according to step (S11), it is concluded that the nitrogen oxide storage catalytic converter (37, LNT) would have to be regenerated.

According to the present disclosure, however, it is proposed that when the adsorption limit of the nitrogen oxide storage catalytic converter (37, LNT) has been reached or is about to be reached, active regeneration of the nitrogen oxide storage catalytic converter (37, LNT) is only carried out by adding a reducing agent if this is necessary to comply of prescribed limit values is required, in particular to submit the limit values for nitrogen monoxide (NO) and/or nitrogen dioxide (NO2) prescribed in accordance with the Real Driving Emission Test. If the values for the nitrogen oxide content measured or calculated in the exhaust gas downstream of the nitrogen oxide storage catalytic converter (37, LNT) are below and in particular significantly below the required limit values, active regeneration of the nitrogen oxide storage catalytic converter (37, LNT) can initially be delayed. In this case, nitrogen oxides (NOx) are deliberately allowed to pass through the nitrogen oxide storage catalytic converter (37, LNT). Alternatively or additionally, the nitrogen oxides (NOx) contained in the nitrogen oxide storage catalytic converter (37, LNT) can be released without converting them, for example by raising the exhaust gas temperature without providing a rich exhaust gas or without adding a reducing agent to the exhaust gas. As a result, the consumption for the addition of reducing agent or fuel is reduced without having to accept an impermissible increase in nitrogen oxide emissions. At the same time, the production of other undesirable emissions that could result from the addition of a reductant is reduced.

In the flow chart of 4 it is assumed that no reducing agent injector is provided between the SCR-F catalytic converter (18) and the nitrogen oxide catalytic converter (37, LNT). In particular, it is assumed that no reducing agent is added to the exhaust gas between the internal combustion engine (11) and the SCR-F catalytic converter (18), although this is possible within the scope of the disclosure. Rather, it is preferably assumed that a reducing agent takes place in the area of the internal combustion engine (11), in particular through the execution of post-injections.

If the nitrogen oxide storage catalytic converter (37, LNT) is to be regenerated under the aforementioned conditions, the added reducing agent or the added fuel must first pass through the SCR-F catalytic converter (18, SCR-F) in order to get to the nitrogen - Storage catalytic converter (37, LNT) to arrive and to be able to be used there for regeneration. However, the supply of reducing agent to the SCR-F catalytic converter (18) can impair its function (so-called hydrocarbon poisoning - HC poisoning).

According to the present disclosure, it is therefore proposed to monitor the content of reducing agent, in particular hydrocarbons (HC), in the SCR-F catalytic converter (18). The monitoring can be done in any way, preferably by simulation or a computer model. If exceeding an allowable limit for the hydrocarbon content (HC) in the SCR-F catalyst (18) is detected (S21), an active HC removal is performed (S22) when or before an active regeneration of the nitrogen oxide storage catalyst (37, LNT).

According to the flowchart (4), it is determined in step (S12) whether active regeneration of the nitrogen oxide storage catalytic converter (37, LNT) is necessary because the nitrogen oxide content behind the nitrogen oxide Storage catalytic converter is no longer sufficiently lower than the permissible limit value (S12: No). In this case, step (S21) checks whether the measured or calculated HC content in the SCR-F catalytic converter falls below a known permissible limit. If this is the case, according to step (S30) (and analogously to the procedure in 3 ) the active regeneration of the nitrogen oxide storage catalytic converter by adding a reducing agent upstream of the SCR-F catalytic converter (18, SCR-F) can be carried out. The addition preferably takes place according to a conservative addition scheme, ie only to such an extent as is necessary to comply with the respective permissible limit values for nitrogen oxides downstream of the nitrogen oxide storage catalytic converter (37, LNT).

If, on the other hand, it is determined in step (S21) that the HC content is no longer below the permissible limit (S21: No), active HC removal is carried out before or in parallel with step (S30). This is done, for example, by raising the exhaust gas temperature. The active HC removal can advantageously be combined with a process for regenerating the filter in the SCR-F catalytic converter (37, SCR-F), or a possibly separately arranged diesel particulate filter (DPF).

According to a preferred embodiment variant, the exhaust gas aftertreatment system (10) can be formed in a modular design. For light and/or low-powered vehicles, only a passive nitrogen oxide adsorber (30, PNA) and an SCR-F catalytic converter (18, SCR-F) with the upstream ozone injector (35) and/or a upstream reducing agent injector (33) or urea injector may be provided.

An additional module with the nitrogen oxide storage catalytic converter (37, LNT) , to be arranged in the exhaust gas passage (12) behind the SCR-F catalytic converter (18) SCR-F. The additional module can preferably include an integrated ozone injector (36) and/or an integrated reducing agent injector (34) and possibly a downstream NOx sensor (32). The additional module can also be used to retrofit existing vehicles, for example to subsequently convert them to comply with statutory limit values. The scope of the additional module can also include a control unit for carrying out the selective or needs-based regeneration of the nitrogen oxide storage catalytic converter (37, LNT).

Due to the modular design, considerable simplifications can be achieved for the packaging and the assembly of the exhaust gas aftertreatment system (10) for different engine versions of a vehicle series. Furthermore, significant cost savings can be achieved through the greater use of identical parts in the modular system.

REFERENCE LIST

10 exhaust aftertreatment system Exhaust gas after treatment system 10' State-of-the-art exhaust aftertreatment system Exhaust gas after treatment system according to prior art 11 combustion engine Internal combustion engine 12 exhaust passage Exhaust gas passage 13 high pressure turbine High pressure turbine 14 low pressure turbine Low pressure turbine 15 bypass bypass 16 bypass valve bypass valve 17 LNT / Lean NOx Trap / Active NOx Adsorber LNT / Lean NOx Trap / Active NOx adsorber 18 SCR-F / Selective Catalytic Reduction Catalyst with filter SCR-F / Catalyst for selective catalytic reduction including a filter 19 Low-pressure exhaust gas recirculation Low pressure exhaust gas recirculation 20 ASC / Ammonia Slip Catalyst ASC / Ammonia slip catalyst 21 First NOx sensor First NOx sensor 22 Second NOx sensor Second NOx sensor 23 urea injector urea injector 30 PNA / Passive NOx Adsorber PNA / Passive NOx adsorbers 31 First NOx sensor First NOx sensor 32 Second NOx sensor Second NOx sensor 33 Urea injector / ammonia injector Urea injector / Ammonia injector 34 reducing agent injector Reductant injector 35 Ozone Injector / Plasma Injector Ozone injector / plasma injector 36 Ozone Injector / Plasma Injector Ozone injector / plasma injector 37 LNT / Lean NOx Trap / Active NOx Adsorber LNT / Lean NOx Trap / Active NOx adsorber 38 SCR layer SCR slice

Claims (7)

Exhaust gas aftertreatment system for an internal combustion engine (11) comprising an exhaust gas passage (12), an SCR-F catalytic converter for the selective catalytic reduction of nitrogen oxides with a filter and a nitrogen oxide storage catalytic converter, characterized in that in the flow direction of the exhaust gas through the exhaust gas passage (12) the nitrogen oxide storage catalytic converter (37, LNT) is arranged behind the SCR-F catalytic converter (18, SCR-F), and that the exhaust gas aftertreatment system (10) is designed to use the exhaust gas to regenerate the nitrogen oxide storage catalytic converter (37, LNT) secondly adding a reducing agent, and that in the flow direction of the exhaust gas through the exhaust gas passage (12) in front of the SCR-F catalytic converter (18, SCR-F) a passive nitrogen oxide adsorber (30, PNA) is additionally arranged, which is designed for this purpose store nitrogen oxides in a first low temperature range and release the stored nitrogen oxides again in a second temperature range. exhaust aftertreatment system claim 1 , characterized in that an ozone injector (35, 36) is arranged in the flow direction of the exhaust gas before the nitrogen oxide storage catalytic converter (37, LNT) and/or before the SCR-F catalytic converter (18, SCR-F). Exhaust gas aftertreatment system according to one of the preceding claims, wherein the exhaust gas aftertreatment system (10) is designed to regenerate the nitrogen oxide storage catalytic converter (37, LNT) by adding unburned fuel to the exhaust gas in the area of the internal combustion engine (11), in particular by performing Post -Injections. Exhaust gas aftertreatment system according to one of the preceding claims, wherein the exhaust gas aftertreatment system (10) has a reducing agent injector (34) which is actuated to regenerate the nitrogen oxide storage catalytic converter (37, LNT) in order to add a reducing agent to the exhaust gas. Exhaust gas aftertreatment system according to one of the preceding claims, wherein the exhaust gas aftertreatment system (10) is designed to - A nitrogen oxide component (NOx) in the exhaust gas behind the nitrogen oxide storage catalytic converter (37, LNT) to detect and - If the adsorption limit of the nitrogen oxide storage catalytic converter (37, LNT) (S10, S11) has been reached or is about to be reached, only carry out an active regeneration of the same by adding a reducing agent if this is necessary to comply with prescribed limit values (S12, S20), and releasing nitrogen oxides (NOx) otherwise contained in the nitrogen oxide storage catalyst (37, LNT) without conversion or letting nitrogen oxides (NOx) through (S12, S30). exhaust aftertreatment system claim 5 , wherein the addition of reducing agent to the exhaust gas takes place in a region upstream of the SCR-F catalytic converter (18, SCR-F), and wherein the exhaust gas aftertreatment system (10) is also designed to contain hydrocarbons (HC) in the SCR -F catalytic converter (18, SCR-F) and, if a permissible limit for the hydrocarbon content (HC) is exceeded, to carry out active HC removal (S22) if or before active regeneration of the nitrogen oxide storage catalytic converter (37, LNT ) he follows. Method for regenerating a nitrogen oxide storage catalyst (37, LNT) in an exhaust gas aftertreatment system (10) according to claim 1 , characterized in that a regeneration of the stick oxide storage catalyst (37, LNT) is carried out selectively depending on the detection of nitrogen oxides in the exhaust gas downstream of the nitrogen oxide storage catalyst (37, LNT).

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