DE102019124728A1 - Process for exhaust aftertreatment of an internal combustion engine and exhaust aftertreatment system - Google Patents

Abstract

The invention relates to a method for exhaust gas aftertreatment of an internal combustion engine, the exhaust gas aftertreatment device having a first SCR catalytic converter and a second SCR catalytic converter, wherein after determining the ammonia level on the second SCR catalytic converter, the operating strategy of the internal combustion engine is adapted to the effect that the amount of NOx in the exhaust gas of the internal combustion engine is increased. The invention also relates to an exhaust system.

Description

The invention relates to a method for exhaust gas aftertreatment of an internal combustion engine and an exhaust gas aftertreatment system for carrying out such a method.

The current exhaust gas legislation, and one that will become ever more stringent in the future, place high demands on the engine-related raw emissions and the exhaust gas aftertreatment of internal combustion engines. The demands for a further decrease in consumption and the further tightening of the exhaust gas standards with regard to the permissible nitrogen oxide emissions represent a challenge for the engine developers. In gasoline engines, the exhaust gas purification takes place in the known manner via a three-way catalytic converter and a three-way catalytic converter - and downstream further catalytic converters. Exhaust gas aftertreatment systems are currently used in diesel engines, which have an oxidation catalytic converter or a NO _x storage catalytic converter, a catalytic converter for the selective catalytic reduction of nitrogen oxides (SCR catalytic converter) and a particle filter for separating out soot particles and, if necessary, further catalytic converters. Ammonia is preferably used as the reducing agent. Because dealing with pure ammonia is complex, a synthetic, aqueous urea solution is usually used in vehicles, which is mixed with the hot exhaust gas flow in a mixing device upstream of the SCR catalytic converter. As a result of this mixing, the aqueous urea solution is heated, the aqueous urea solution releasing ammonia in the exhaust gas duct. A commercially available, aqueous urea solution generally consists of 32.5% urea and 67.5% water.

Exhaust gas aftertreatment systems are known from the prior art which have a first SCR catalytic converter close to the engine, in particular a particle filter with an SCR coating, and a second SCR catalytic converter which is arranged in an underbody position of the motor vehicle remote from the engine. The close-coupled particle filter with the SCR coating can be heated up to its operating temperature more quickly after a cold start of the internal combustion engine and can therefore be used for an efficient conversion of nitrogen oxide emissions shortly after a cold start of the internal combustion engine. The second SCR catalytic converter remote from the engine is used at high engine loads and / or during regeneration of the particulate filter, in which the close-coupled particulate filter with the SCR coating is operated above the temperature range required for selective, catalytic reduction and thus only for insufficient conversion of nitrogen oxides cares. The arrangement of the particulate filter with the SCR coating close to the engine also means that there is only a short mixing section for mixing the reducing agent and exhaust gas before entering the particulate filter and thus the uniform distribution over the cross section of the particulate filter is restricted. This effect is intensified in the case of high exhaust gas mass flows and the associated high flow velocities in the exhaust gas duct. This can mean that, regardless of the temperature, the conversion capacity of the particulate filter is insufficient and the conversion capacity of the second SCR catalytic converter is also necessary.

It is also known that the conversion performance of the two SCR catalytic converters can be increased if a defined amount of ammonia is stored, in particular adsorbed, on the catalytically active surface of the respective SCR catalytic converter. Depending on the current operating state of the internal combustion engine, reducing agent is metered into the exhaust gas duct upstream of the coated particle filter, upstream of the SCR catalytic converter in the underbody position or upstream of both SCR catalytic converters.

A disadvantage of the solutions known from the prior art, however, is that ammonia slip can occur even in spite of the use of a second SCR catalytic converter and the associated increase in the conversion performance and ammonia storage capacity. This leads to an undesirable increase in ammonia emissions.

From the DE 10 2010 026 317 A1 an exhaust gas aftertreatment system for a diesel engine is known in which an oxidation catalytic converter is arranged in the exhaust system and an SCR catalytic converter is arranged downstream of the oxidation catalytic converter. _{A first NO x} sensor is provided upstream of the oxidation _{catalytic converter and a second NO x} sensor is provided downstream of the SCR catalytic converter in order to be able to assess the efficiency of the SCR catalytic converter and thus to avoid ammonia slip.

From the DE 10 2010 026 373 A1 An exhaust gas aftertreatment system and a method for determining the ammonia slip are known, in which the nitrogen oxide concentration in the exhaust gas duct is determined upstream of the SCR catalyst and downstream of the SCR catalyst and the amount of reducing agent is adjusted in such a way that the nitrogen oxide emissions are minimized.

In addition, the DE 10 2014 019 483 A1 Another method for determining the ammonia slip in an exhaust gas aftertreatment system of an internal combustion engine with an SCR catalytic converter. Upstream and downstream of a particle filter with a SCR coating determines the nitrogen oxide concentration in the exhaust gas duct and calculates the ammonia slip based on the nitrogen oxide concentration in connection with the metered amount of reducing agent.

From the US 2010/242454 A1 and the US 2015/151251 A1 It is known to change the operating strategy of the engine in order to avoid ammonia slip in systems with a simple SCR catalytic converter.

It has been shown that the strategies known from the prior art for reducing or avoiding ammonia slip work only inadequately.

The invention is therefore based on the object of efficiently reducing ammonia emissions or at best avoiding them entirely in an exhaust gas aftertreatment system with at least two SCR catalytic converters.

• Eindosieren des Reduktionsmittels in den Abgaskanal des Verbrennungsmotors; Ermitteln des Ammoniakfüllstandes des zweiten SCR-Katalysators; und Anpassen der Betriebsstrategie des Verbrennungsmotors in Abhängigkeit vom Ammoniak-Füllstand des zweiten SCR-Katalysators dahingehend, dass die Menge an NO_x im Abgas des Verbrennungsmotors erhöht wird.

To solve this problem, a method for exhaust gas aftertreatment of an internal combustion engine is described, the outlet of which is connected to an exhaust system, a first SCR catalytic converter or a particle filter with a coating for the selective catalytic reduction of nitrogen oxides being arranged in the exhaust system downstream of a turbine of an exhaust gas turbocharger and wherein a second SCR catalytic converter is arranged downstream of the first SCR catalytic converter or particulate filter with a coating, and wherein the method further comprises the following steps:

• Metering the reducing agent into the exhaust gas duct of the internal combustion engine; Determining the ammonia level of the second SCR catalytic converter; and adapting the operating strategy of the internal combustion engine as a function of the ammonia fill level of the second SCR catalytic converter in such a way that the amount of NO _x in the exhaust gas of the internal combustion engine is increased.

The operating strategy is preferably adapted as a function of the ammonia fill level to the effect that the operating strategy is adapted when the fill level of the second SCR catalyst is at least 50%, preferably at least 70%, more preferably at least 80% based on the maximum ammonia fill level.

The first SCR catalytic converter or particle filter with a coating is preferably an SCR catalytic converter or particle filter close to the engine, the particle filter or the SCR catalytic converter having an inlet with an exhaust gas run length of a maximum of 80 cm, preferably a maximum of 50 cm, from the outlet of the Internal combustion engine is spaced.

The close-coupled particle filter with the SCR coating can be heated up to its operating temperature more quickly after a cold start of the internal combustion engine and can therefore be used for an efficient conversion of nitrogen oxide emissions shortly after a cold start of the internal combustion engine. At high engine loads and temperatures, however, the ammonia storage capacity decreases. This particularly affects the first SCR catalytic converter, since it is preferably arranged close to the engine and thus heats up quickly at high engine loads, so that the ammonia storage capacity decreases. If a high temperature gradient occurs due to acceleration, the ammonia, which is present as a fill level on the first SCR catalytic converter, slips “down” onto the second SCR catalytic converter. This leads to an increased fill level of the second catalytic converter. Especially at high temperatures, ammonia can hardly be stored in the first SCR catalytic converter. This leads to an excessive ammonia level in the second catalytic converter. As soon as this is overloaded and the ammonia can no longer be stored, ammonia “tailpipe” emissions occur, which must be limited. In order to avoid ammonia emission, it is necessary to reduce the fill level of the second catalytic converter as quickly as possible. The previous strategy, which only reduced the reducing agent dosage, is in itself insufficient. In particular, this strategy takes too long in high-speed driving situations to prevent ammonia slip in the event of a steep temperature gradient on the second SCR catalytic converter. The method according to the invention therefore achieves a reduction in the ammonia filling amount by adapting the operating strategy of the internal combustion engine in such a way that the amount of NO _x in the exhaust gas of the internal combustion engine is increased.

Furthermore, according to a preferred embodiment, a method for exhaust gas aftertreatment of an internal combustion engine is described, wherein the adaptation of the operating strategy of the internal combustion engine takes place in that the amount of exhaust gas returned to the internal combustion engine by means of an exhaust gas recirculation system is adapted, preferably reduced.

With exhaust gas recirculation, exhaust gas is added to the air used in order to lower the temperature during combustion in the engine. The oxygen concentration decreases and the heat capacity of the mixture increases, which leads to a lower temperature increase in the combustion chamber when the fuel is burned. This in turn reduces the combustion temperature, which is why fewer nitrogen oxides are formed. By reducing the amount of recirculated exhaust gas through the exhaust gas recirculation system within the meaning of the invention Process, conversely, the oxygen concentration increases and the heat capacity of the mixture decreases, which leads to a greater increase in temperature in the combustion chamber when the fuel is burned. This in turn increases the combustion temperature, which is why more nitrogen oxides are formed. The exhaust gas that reaches the first SCR catalytic converter and in particular the second SCR catalytic converter is thus more highly enriched with nitrogen oxides. The increased amount of nitrogen oxides in the exhaust gas leads to a rapid conversion of the excess ammonia and can thus efficiently end an ammonia slip or prevent an ammonia slip from occurring at all.

Furthermore, according to a further preferred embodiment, a method for exhaust gas aftertreatment of an internal combustion engine is described, the exhaust gas recirculation system being designed as a low-pressure exhaust gas recirculation system which branches off exhaust gas downstream of the first SCR catalytic converter or particle filter with a coating and upstream of the second SCR catalytic converter and returns it to the internal combustion engine The operating strategy of the internal combustion engine is adjusted in that the amount of exhaust gas that is diverted downstream of the first SCR catalytic converter or particle filter with a coating and upstream of the second SCR catalytic converter is dependent on the ammonia level of the second SCR catalytic converter is adjusted.

According to a preferred embodiment, a method for exhaust gas aftertreatment is described, characterized in that the adaptation of the operating strategy takes place as a function of the temperature of the second SCR catalytic converter.

According to a preferred embodiment, a method for exhaust gas aftertreatment is described, characterized in that the adaptation of the operating strategy only takes place when a defined limit value of the temperature at the second SCR catalytic converter is exceeded.

The adaptation of the operating strategy depending on the temperature of the second SCR catalytic converter ensures that the temperature at the second SCR catalytic converter is sufficiently high so that the required conversion of the increased amount of nitrogen oxides with the stored ammonia can actually take place - in particular, it cannot at the same time there is an increased emission of ammonia and unconverted nitrogen oxides. It should be noted here that the first SCR catalytic converter, as a close-coupled catalytic converter, heats up to sufficiently high temperatures significantly faster than the second SCR catalytic converter, which is preferably made from an underbody catalytic converter. The temperature control therefore plays a special role in the present two-catalyst system.

According to a particularly preferred embodiment, a method for exhaust gas aftertreatment is described, characterized in that the adaptation of the operating strategy only takes place when a defined limit value of the temperature on the second SCR catalytic converter is exceeded and further only after a limit value for the ammonia level on the second catalytic converter has been exceeded.

The adaptation of the operating strategy depending on the temperature and the fill level of the second SCR catalytic converter ensures that the temperature at the second SCR catalytic converter is sufficiently high for the catalytic reduction and that there is sufficient reducing agent at the second catalytic converter so that the required conversion of the increased amount is available of nitrogen oxides can actually take place with the stored ammonia - in particular, there is no increased emission of unconverted nitrogen oxides.

Furthermore, according to a preferred embodiment, a method for exhaust gas aftertreatment of an internal combustion engine is described, the adaptation of the operating strategy taking place as a function of the reducing agent metering strategy. This advantageously enables both the reducing agent metering strategy, which is used to adapt the metered amount of ammonia to the fill level of the first SCR catalytic converter or the second SCR catalytic converter, and the operating strategy of the internal combustion engine to be coordinated with one another. In this way, a particularly efficient reduction in the fill level on the second SCR catalytic converter can be achieved.

Furthermore, according to a preferred embodiment, a method for exhaust gas aftertreatment of an internal combustion engine is described, wherein the adaptation of the operating strategy takes place as a function of the amount of ammonia released.

According to a further aspect of the invention, an exhaust system for an internal combustion engine is described, wherein the internal combustion engine can be connected with its outlet to the exhaust system, and wherein in the exhaust system, downstream of a turbine of an exhaust gas turbocharger, a first SCR catalyst or particle filter with a coating for selective catalytic Reduction of nitrogen oxides is arranged, and wherein a second SCR catalyst is arranged downstream of the first SCR catalyst, wherein the exhaust system is designed to carry out a method according to one of the preceding claims.

Furthermore, according to a preferred embodiment, an exhaust system for an internal combustion engine is described, the first SCR catalytic converter or particle filter with a coating being an SCR catalytic converter or particle filter close to the engine. In this case, the particle filter or the SCR catalytic converter has an inlet which is spaced apart from the outlet of the internal combustion engine with an exhaust gas run length of a maximum of 80 cm, preferably a maximum of 50 cm.

Furthermore, according to a preferred embodiment, an exhaust system for an internal combustion engine is described, wherein the second SCR catalytic converter is an underbody catalytic converter which is arranged near the underside of the vehicle.

In connection with the present invention, there is a first or a second catalyst which enables a selective catalytic reduction of nitrogen oxides to ammonia. This can in particular either be a “pure” SCR catalytic converter and / or an SCR-coated particle filter. If a first (coated) particle filter is mentioned in connection with the present invention, it can be assumed, unless expressly stated otherwise, that a first “pure” SCR catalytic converter can also be used as an alternative, that is an SCR catalytic converter without a particulate filter.

The first SCR-coated particle filter or the first SCR catalytic converter is preferably a close-coupled particle filter or a close-coupled SCR catalytic converter. A particle filter close to the engine is to be understood in this context as a particle filter or an SCR catalytic converter, the inlet of which is spaced from the outlet of the internal combustion engine with an exhaust gas run length of a maximum of 80 cm, preferably a maximum of 50 cm.

The second SCR-coated particulate filter or the second SCR catalytic converter is preferably a particulate filter remote from the engine. An SCR catalytic converter remote from the engine is preferably to be understood as an SCR catalytic converter which is arranged downstream of the first SCR catalytic converter.

In order to enable complete nitrogen oxide conversion, a further SCR catalytic converter, that is to say a second SRC catalytic converter, is provided according to the invention. Despite an efficiency of less than 1 of the first SCR catalytic converter, this enables essentially complete conversion of the nitrogen oxides.

A NO _x sensor is preferably arranged downstream of the second SCR catalytic converter. This advantageously serves to determine the ammonia concentration downstream of the second SCR catalytic converter. It can thus be determined for the second catalytic converter whether an ammonia slip occurs.

According to a preferred embodiment, an exhaust gas aftertreatment system for an internal combustion engine is described, a diesel oxidation catalytic converter and / or a nitrogen oxide storage catalytic converter being arranged downstream of the particle filter.

The ratio of nitrogen monoxide and nitrogen dioxide can be changed by means of an oxidation catalytic converter, whereby the efficiency of the selective catalytic reduction of nitrogen oxides can be increased and the operating strategy can also be adapted.

In order to enable complete nitrogen oxide conversion, a further SCR catalytic converter is provided, as already described, according to the invention. Despite an efficiency of less than 1 of the first SCR catalytic converter, this enables essentially complete conversion of the nitrogen oxides. A third NO _x sensor downstream of the second SCR catalytic converter is advantageously used to determine the ammonia concentration downstream of the second catalytic converter. This makes it easier to determine for the second catalytic converter whether an ammonia slip is occurring.

In a further embodiment of the exhaust gas aftertreatment system, it is provided that a low-pressure exhaust gas recirculation branches off from the exhaust gas duct downstream of the particle filter and upstream of the second SCR catalytic converter. The particle filter allows soot particles and other solid particles to be filtered out of the exhaust gas flow so that they are not returned to the air supply system via the low-pressure exhaust gas recirculation and can lead to damage there, in particular to damage to the compressor of the exhaust gas turbocharger. In addition, the raw emissions of the internal combustion engine can be minimized in a known manner by exhaust gas recirculation via the low-pressure exhaust gas recirculation, whereby the use of reducing agent in the exhaust gas aftertreatment can also be reduced.

According to a preferred embodiment of the exhaust gas aftertreatment system, provision is made for a second metering element to be arranged downstream of the particle filter and upstream of the second SCR catalytic converter. The operating range of the exhaust gas aftertreatment system can be expanded with a second metering element. It is therefore particularly at high exhaust gas temperatures at the particle filter, for example during a high load phase of the internal combustion engine or during a Regeneration of the particle filter, possible to enable an efficient conversion of the nitrogen oxides by the second SCR catalytic converter and to avoid thermal decomposition of the ammonia obtained from the reducing agent.

It is particularly preferred if the first metering element and the second metering element are supplied with reducing agent from a common reducing agent container. A common reducing agent container enables a particularly simple and inexpensive supply of the two metering elements with the reducing agent.

In a further embodiment of the invention it is provided that an exhaust gas mixer is arranged in the exhaust gas duct downstream of the first metering element and upstream of the particle filter with the coating for the selective catalytic reduction of nitrogen oxides. An exhaust gas mixer can achieve a homogeneous distribution of the reducing agent in the exhaust gas flow before it enters the particle filter. The length of the mixing section can be shortened by the exhaust gas mixer in order to achieve such a homogeneous distribution. As a result, the particle filter can be arranged closer to the outlet of the internal combustion engine, which promotes heating of the particle filter after a cold start of the internal combustion engine or for regeneration of the particle filter.

The various embodiments of the invention mentioned in this application can be combined with one another, unless stated otherwise in the individual case.

The features listed in the dependent claims allow advantageous improvements and non-trivial further developments of the method listed in the independent claim for exhaust gas aftertreatment of the internal combustion engine.

• 1 einen Verbrennungsmotor mit einem erfindungsgemäßen Abgasnachbehandlungssystem gemäß einer ersten Ausführungsform;
• 2 einen Verbrennungsmotor mit einem erfindungsgemäßen Abgasnachbehandlungssystem gemäß einer zweiten Ausführungsform;
• 3a, 3b und 3c eine schematische Darstellung des Füllstands des ersten SCR-Katalysators und des zweiten SCR-Katalysators sowie der geschlupften Menge Ammoniak in Abhängigkeit von der Temperatur; und
• 4 eine schematische Darstellung des Füllstands des ersten SCR-Katalysators in Abhängigkeit von der Fahrsituation.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. The same components or components with the same function are identified by the same reference numbers in the different figures. Show it:

• 1 an internal combustion engine with an exhaust gas aftertreatment system according to the invention according to a first embodiment;
• 2 an internal combustion engine with an exhaust gas aftertreatment system according to the invention according to a second embodiment;
• 3a , 3b and 3c a schematic representation of the fill level of the first SCR catalytic converter and the second SCR catalytic converter and the amount of ammonia released as a function of the temperature; and
• 4th a schematic representation of the fill level of the first SCR catalytic converter as a function of the driving situation.

1 shows a schematic representation of an internal combustion engine 10 with an air supply system 20th and an exhaust system 40 . The internal combustion engine 10 is designed as a direct injection diesel engine and has several combustion chambers 12th on. At the combustion chambers 12th each is a fuel injector 14th for injecting a fuel into the respective combustion chamber 12th arranged. The internal combustion engine 10 is with his inlet 16 with an air supply system 20th and with its outlet 18th with an exhaust system 40 connected. The internal combustion engine 10 further comprises a high pressure exhaust gas recirculation with a high pressure exhaust gas recirculation valve, via which an exhaust gas of the internal combustion engine 10 from the outlet 18th to the inlet 16 can be traced back. At the combustion chambers 12th inlet valves and outlet valves are arranged with which a fluidic connection from the air supply system 20th to the combustion chambers 12th or from the combustion chambers 12th to the exhaust system 40 can be opened or closed.

The air supply system 20th includes an intake duct 28 , in which in the direction of flow of fresh air through the intake duct 28 an air filter 22nd , downstream of the air filter 22nd an air mass meter 24 , in particular a hot film air mass meter, downstream of the air mass meter 24 a compressor 26th of an exhaust gas turbocharger 36 , downstream of the compressor 26th a throttle valve 30th and further downstream an intercooler 32 are arranged. The air mass meter can do this 24 also in a filter housing of the air filter 22nd be arranged so that the air filter 22nd and the air mass meter 24 forms an assembly. Downstream of the air filter 22nd and upstream of the compressor 26th is a confluence 34 provided on which an exhaust gas recirculation line 86 a low pressure exhaust gas recirculation 80 in the intake duct 28 flows out.

The exhaust system 40 includes an exhaust duct 42 , in which in the flow direction of an exhaust gas of the internal combustion engine 10 through the first exhaust duct 42 a turbine 44 of the exhaust gas turbocharger 36 is arranged, which the compressor 26th in the air supply system 20th drives over a shaft. The exhaust gas turbocharger 36 is preferably used as an exhaust gas turbocharger 36 designed with variable turbine geometry. To do this are a turbine wheel of the turbine 44 adjustable guide vanes are connected upstream, via which the flow of the exhaust gas onto the blades of the turbine 44 can be varied. Downstream of the turbine 44 are several Exhaust aftertreatment components 46 , 48 , 50 , 52 , 54 intended. This is immediately downstream of the turbine 44 the first component of exhaust gas aftertreatment is an oxidation catalytic converter 46 or a NO _x storage catalytic converter is arranged. Downstream of the oxidation catalyst 46 or the NO _x storage catalytic converter is a particulate filter 48 with a coating 50 arranged for the selective catalytic reduction of nitrogen oxides (SCR coating). Downstream of the particulate filter 48 is preferably a second SCR catalytic converter in the underbody position of a motor vehicle 52 in the exhaust duct 42 arranged. The second SCR catalytic converter 52 has an ammonia barrier catalyst 54 on. Downstream of the oxidation catalyst 46 and upstream of the particulate filter 48 with the SCR coating 50 is a first metering element 56 for metering in a reducing agent 78 in the exhaust duct 42 intended. Downstream of the particulate filter 48 branches off an exhaust gas recirculation line 86 a low pressure exhaust gas recirculation 80 at a branch 72 from the exhaust duct 42 from. Downstream of the branch 72 and upstream of the second SCR catalyst 52 is a second metering element 58 arranged to the reducing agent 78 in the exhaust duct 42 to be dosed. The first metering element 56 and the second metering element 58 are each via a reducing agent line 74 with a common reducing agent tank 76 connected in which the reducing agent 78 is in stock. It also includes the exhaust system 40 an exhaust flap 60 , with which the exhaust gas recirculation via the low pressure exhaust gas recirculation 80 can be controlled.

The exhaust gas recirculation 80 includes in addition to the exhaust gas recirculation line 86 an exhaust gas recirculation cooler 82 and an exhaust gas recirculation valve 84 , via which the exhaust gas recirculation 80 through the exhaust gas recirculation line 86 is controllable. On the exhaust gas recirculation line 86 the exhaust gas recirculation 80 is a temperature sensor 88 provided, over which an exhaust gas temperature in the exhaust gas recirculation 80 can be determined to the exhaust gas recirculation 80 to activate as soon as the exhaust gas temperature in the exhaust gas recirculation 80 has exceeded a defined threshold. It can thus be prevented that water vapor or reducing agent contained in the exhaust gas for the selective catalytic reduction of nitrogen oxides, in particular liquid urea solution, condenses out and in the exhaust gas recirculation 80 or in the air supply system 20th leads to damage or deposits. Downstream of the junction and upstream of the EGR cooler 82 A filter can be provided to prevent the entry of particles into the exhaust gas recirculation 80 to minimize. The exhaust gas recirculation line 86 opens at a confluence 34 into the suction line 28 of the air supply system 20th .

In the exhaust system 40 is downstream of the oxidation catalyst 46 and upstream of the first metering element 56 a first NO _x sensor 62 arranged. Downstream of the particulate filter 48 and upstream of the branch 72 is a second NO _x sensor 64 arranged. Furthermore, the particle filter 48 a differential pressure sensor 66 on, with which a pressure difference Δp across the particle filter 48 is determined. In this way, the loading state of the particle filter 48 and a regeneration of the particle filter when a defined load level is exceeded 48 be initiated. It is also in the exhaust system 40 a temperature sensor 38 provided to determine the exhaust gas temperature.

Downstream of the first metering element 56 and upstream of the particulate filter 48 can be a first exhaust mixer 68 be provided in order to mix the exhaust gas flow of the internal combustion engine 10 and reducing agents 78 before entering the particle filter 48 with the SCR coating 50 to improve and to shorten the length of the mixing section. Downstream of the second metering element 58 and upstream of the second SCR catalyst 52 can use a second exhaust mixer 70 be arranged to the mixing of exhaust gas flow and reducing agent 78 to improve and the evaporation of the reducing agent 78 in the exhaust duct 42 to support.

The internal combustion engine 10 is with an engine control unit 90 connected, which via signal lines, not shown, with the NO _x sensors 62 , 64 , the differential pressure sensor 66 , the temperature sensors 38 , 88 as well as with the fuel injectors 14th of the internal combustion engine 10 and the dosing elements 56 , 58 connected is.

As soon as now on the second SCR catalytic converter 52 an ammonia slip has been determined or it has been determined that there is a threat of ammonia slip, the operating strategy of the internal combustion engine is adapted 10 , in that the amount of NO _x in the exhaust gas of the internal combustion engine 10 is increased. Adjusting the operating strategy of the internal combustion engine 10 , takes place in that the means of the exhaust gas recirculation system 80 to the internal combustion engine 10 recirculated amount of exhaust gas is adjusted. Adjusting the operating strategy of the internal combustion engine 10 takes place in that the amount of exhaust gas, which is downstream of the first SCR catalytic converter or particulate filter 48 with a coating 50 and upstream of the second SCR catalyst 52 is branched off, is reduced proportionally to the ammonia level of the second SCR catalytic converter.

In 2 is an internal combustion engine with an exhaust gas aftertreatment system according to the invention shown according to a second embodiment. As in the case of the embodiment shown in 1 is shown, has the exhaust aftertreatment system of the internal combustion engine 10 a particulate filter 48 with a coating 50 for the selective catalytic reduction of nitrogen oxides. Upstream of the particulate filter 48 are a first NO _x sensor 62 arranged, as well as a first metering element 56 , with which a reducing agent 78 upstream of the particulate filter 48 in the exhaust duct 42 is metered. Downstream of the metering element is an exhaust mixer 68 arranged.

It is also downstream of the particulate filter 48 a second NO _x sensor 64 arranged. Further is downstream of the second NO _x sensor 64 a second SCR catalytic converter 52 arranged and downstream of the second SCR catalyst 52 is a third NO _x sensor 110 arranged. Downstream to the second NO _x sensor 64 are a second metering element 58 arranged and a second exhaust mixer 70 . A first NO _x concentration NO _x _1 is measured upstream of the particle filter 48 , 50 by means of the first NO _x sensor 62 . A second NO _x concentration NO _x _2 is also measured downstream of the particle filter 48 , 50 by means of the second NO _x sensor 64 . A third NO _x concentration NO _x _3 is optionally measured downstream of the second SCR catalytic converter 52 by means of the third NO _x sensor 110 .

The NO _x sensors are generally cross-sensitive to ammonia. In other words, the sensors not only detect nitrogen oxides but also ammonia. In an alternative embodiment, the NO _x sensors have no cross-sensitivity to ammonia. In _{this case, the NO x} sensors are designed in such a way that they can also determine an ammonia concentration _{independently of the NO x concentration.}

Using the measured values obtained by the NO _x sensors, ammonia slip on the first SCR catalytic converter and / or on the second SCR catalytic converter can be determined. Furthermore, the amount of nitrogen oxides on the first SCR catalytic converter and / or on the second SCR catalytic converter can be determined by means of the sensors. If the sensors are cross-sensitive for nitrogen oxides and ammonia, additional parameters such as the consumption of reducing agent solution, the aging of the catalytic converters and / or an efficiency model of the catalytic converters can be used _{to calculate the amount of ammonia and the amount of NO x} in the exhaust gas separately.

As soon as the amount of ammonia and the amount of NO _x in the exhaust gas have been determined separately from one another, preferably on the first SCR catalytic converter and on the second SCR catalytic converter, these values can be used to adapt the operating strategy of the internal combustion engine. In particular, if it is determined that there is ammonia slip on the second SCR catalytic converter, the operating strategy is adapted to the effect that the amount of NO _x in the exhaust gas of the internal combustion engine is increased. This can be done, for example, by an exhaust gas recirculation system (not shown) to the effect that the amount of recirculated exhaust gas is reduced.

The 3a , 3b and 3c show a schematic representation of the fill level of the first SCR catalytic converter and the second SCR catalytic converter as well as the amount of ammonia that has escaped as a function of the temperature. 3a shows a situation at low temperatures T on the first SCR catalytic converter 48 , 50 . 3b shows a situation at medium temperatures T on the first SCR catalytic converter 48 , 50 . 3c shows a situation at high temperatures T on the first SCR catalytic converter 48 , 50 .

If there is a high temperature gradient due to acceleration and / or the first SCR catalytic converter 48 , 50 heats up to high absolute temperatures, the ammonia slips, which is the level on the first SCR catalytic converter 48 , 50 is present, "down" on the second SCR catalytic converter 52 . This leads to an increased fill level of the second catalytic converter 52 .

At low temperatures, as in 3a can be shown a large amount of ammonia in the first SCR catalytic converter 48 , 50 and second SCR catalyst 52 get saved. There is essentially no ammonia slip.

At medium temperatures, as in 3b shown, decreases the amount of ammonia in the first SCR catalytic converter 48 , 50 can be saved. There is an increased shift of ammonia to the second SCR catalytic converter 52 .

At high temperatures, as in 3c shown, there is hardly any ammonia left in the first SCR catalytic converter 48 , 50 get saved. Almost all of the ammonia is shifted to the second SCR catalytic converter 52 .

Over time, the fill level of the second SCR catalytic converter increases. In order to avoid ammonia emissions, it is necessary to check the fill level of the second catalytic converter 52 dismantle as soon as possible. The operating strategy of the internal combustion engine is adapted 10 , in that the amount of NO _x in the exhaust gas of the internal combustion engine 10 is increased. Adjusting the operating strategy of the internal combustion engine 10 takes place in that the amount of exhaust gas that is downstream of the first SCR Catalyst or particle filter 48 with a coating 50 and upstream of the second SCR catalyst 52 is branched off for exhaust gas recirculation, is reduced proportionally to the ammonia level of the second SCR catalyst. The operating strategy is also adapted as a function of the temperature of the second SCR catalytic converter. It is necessary that the temperature at the second SCR catalytic converter is sufficiently high so that the required conversion of the increased amount of nitrogen oxides with the stored ammonia can actually take place - in particular, there is no increased emission of ammonia and unconverted nitrogen oxides at the same time .

The operating strategy of the internal combustion engine is preferably adapted 10 that is, depending on the temperature of the second SCR catalytic converter and the fill level of the second SCR catalytic converter. For this purpose, on the one hand the fill level of the second SCR catalytic converter and the temperature of the second SCR catalytic converter are determined.

4th shows a schematic representation of the fill level of the first SCR catalytic converter as a function of the driving situation.

When driving in the city ( S. ) there are lower accelerations and therefore lower temperatures at the first SCR catalytic converter. The amount of ammonia that is in the first SCR catalyst 48 , 50 is stored is essentially constant high. When driving overland on a country road ( L. ) there are medium accelerations and thus also higher temperature gradients or temperatures at the first SCR catalytic converter. The temperature of the first catalyst rises above a limit value T _G . Ammonia is increasingly slipping from the first SCR catalytic converter 48 , 50 on the second SCR catalytic converter 52 . When driving on a motorway ( A. ) there are high accelerations and thus also high temperatures at the first SCR catalytic converter. There is an increasing shift of ammonia to the second SCR catalytic converter, the level of which rises.

In summary, depending on the driving situation, ammonia is shifted from the first SCR catalytic converter to the second SCR catalytic converter. This happens especially in such driving situations with strong accelerations. This leads to an increased level of ammonia in the second catalytic converter 52 . If this process is repeated, the second SCR catalytic converter threatens 52 overflow and ammonia slip occurs. By adapting the internal combustion engine's operating strategy 10 can reduce the level of the second SCR catalytic converter 52 can be achieved.

List of reference symbols

10

Internal combustion engine

12th

Combustion chamber

14th

Fuel injector

16

inlet

18th

Outlet

20th

Air supply system

22nd

Air filter

24

Air mass meter

26th

compressor

28

Intake duct

30th

throttle

32

Intercooler

34

Confluence

36

Exhaust gas turbocharger

38

Temperature sensor

40

Exhaust system

42

Exhaust duct

44

turbine

46

Oxidation catalyst / NO _x storage catalyst

48

Particle filter

50

Coating for the selective catalytic reduction of nitrogen oxides

52

second SCR catalytic converter

54

Ammonia barrier catalyst

56

first metering element

58

second metering element

60

Exhaust flap

62

first NO _x sensor

64

second NO _x sensor

66

Differential pressure sensor

68

first exhaust mixer

70

second exhaust mixer

72

branch

74

Reducing agent line

76

Reducing agent tank

78

Reducing agent

80

Low pressure exhaust gas recirculation

82

Exhaust gas recirculation cooler

84

Exhaust gas recirculation valve

86

Exhaust gas recirculation line

88

Temperature sensor

90

Engine control unit

105

Diesel oxidation catalyst

110

third NO _x sensor

T _G

Temperature limit

S.

Inner-city driving

L.

Country road trip

A.

Highway driving

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102010026317 A1 [0006]
• DE 102010026373 A1 [0007]
• DE 102014019483 A1 [0008]
• US 2010242454 A1 [0009]
• US 2015151251 A1 [0009]

Claims (9)

A method for exhaust gas aftertreatment of an internal combustion engine (10) which is connected with its outlet (18) to an exhaust system (40), wherein in the exhaust system (40) downstream of a turbine (44) of an exhaust gas turbocharger (36) a first SCR catalytic converter or a A particle filter (48) with a coating (50) for the selective catalytic reduction of nitrogen oxides is arranged, and a second SCR catalyst (52) is arranged downstream of the first SCR catalyst or particle filter (48) with the coating (50), wherein the method further comprises the following steps: metering the reducing agent (78) into the exhaust gas duct (42) of the internal combustion engine (10); Determining the fill level of the second SCR catalytic converter (52); Adapting the operating strategy of the internal combustion engine (10) as a function of the ammonia fill level of the second SCR catalytic converter (52) in such a way that the amount of NO _x in the exhaust gas of the internal combustion engine (10) is increased. Procedure according to Claim 1 , characterized in that the adaptation of the operating strategy of the internal combustion engine (10) takes place in that the amount of exhaust gas returned to the internal combustion engine (10) by means of an exhaust gas recirculation system (80) is adapted. Method for exhaust gas aftertreatment according to one of the preceding claims, characterized in that the exhaust gas recirculation system (80) is designed as a low-pressure exhaust gas recirculation system, which is provided with a coating (50) downstream of the first SCR catalytic converter or particle filter (48) and upstream of the second SCR catalytic converter (52) Exhaust gas branches off and returns to the internal combustion engine (10), the adaptation of the operating strategy of the internal combustion engine (10) taking place in that the amount of exhaust gas which is downstream of the first SCR catalytic converter or particle filter (48) is coated with a coating (50 ) and is branched off upstream of the second SCR catalytic converter (52), is adapted as a function of the ammonia fill level of the second SCR catalytic converter (52). Method for exhaust gas aftertreatment according to one of the preceding claims, characterized in that the adaptation of the operating strategy takes place as a function of the temperature of the second SCR catalytic converter (52). Method for exhaust gas aftertreatment according to the preceding claim, characterized in that the adaptation of the operating strategy only takes place when a defined limit value of the temperature at the second SCR catalytic converter is exceeded. Method for exhaust gas aftertreatment according to one of the preceding claims, characterized in that the adaptation of the operating strategy takes place as a function of the reducing agent metering strategy. Method for exhaust gas aftertreatment according to one of the preceding claims, characterized in that the adaptation of the operating strategy takes place as a function of the amount of ammonia released. Exhaust system (40) for an internal combustion engine (10), wherein the internal combustion engine (10) can be connected with its outlet (18) to the exhaust system (40), and wherein in the exhaust system (40) downstream of a turbine (44) of an exhaust gas turbocharger ( 36) a first SCR catalytic converter or particle filter (48) with a coating (50) for the selective catalytic reduction of nitrogen oxides is arranged, and a second SCR catalytic converter (52) is arranged downstream of the first SCR catalytic converter (48), thereby characterized in that the exhaust system (40) is designed to carry out a method according to one of the preceding claims. The exhaust system (40) for an internal combustion engine (10) according to the preceding claim, wherein the first SCR catalytic converter or particle filter (48) with a coating (50) is a close-coupled SCR catalytic converter or particle filter (48) with a coating (50).

Images