AT522751A1 - Method for regulating an exhaust gas aftertreatment system for an exhaust gas flow of an internal combustion engine and an exhaust gas aftertreatment system - Google Patents

Abstract

The invention relates to a method for regulating an exhaust gas aftertreatment system (1) of an exhaust gas flow of an internal combustion engine with an internal combustion engine (2), the exhaust gas aftertreatment system (1) comprising at least two SCR units (3, 4), with an in particular urea-containing aftertreatment fluid in the exhaust gas flow is metered in, which reacts in the SCR units (3, 4) with the exhaust gas flow, the metered amount of aftertreatment fluid being dependent on a total loading amount of the SCR units (3, 4) and a loading amount of a second SCR unit (4) , an NH3 concentration being determined between a first SCR unit (3) and the second SCR unit (4). The invention also relates to an exhaust gas aftertreatment system (1) for an exhaust gas flow from an internal combustion engine with an internal combustion engine (2).

Description

Method for regulating an exhaust gas aftertreatment system of an exhaust gas flow of an internal combustion engine and

Exhaust aftertreatment system

The invention relates to a method for regulating an exhaust gas aftertreatment system of an exhaust gas flow of an internal combustion engine, the exhaust gas aftertreatment system comprising at least two SCR units, an NHs fill level of the SCR units being determined and an in particular urea-containing aftertreatment fluid being metered into the exhaust gas flow, which is then fed into the

SCR units reacts with the exhaust gas flow.

The invention also relates to the exhaust gas aftertreatment system of an exhaust gas flow of an internal combustion engine, the exhaust gas aftertreatment system comprising at least two SCR units, with at least one injection device for metering a particularly urea-containing aftertreatment fluid into the exhaust gas flow and a control unit for regulating an amount of the injected exhaust gas aftertreatment fluid, the control unit with the injection device

connected is.

Various methods for controlling SCR systems are known from the prior art. For example, methods are known in which the desired efficiency of the overall system is only regulated via the degree of loading of the first SCR catalytic converter. In most cases, several control loops are necessary in order to be able to meet the legal requirements, for example with regard to NOx emissions or reducing agent slip. This consideration of two SCR units as an overall system, with only an average load being controlled with a corresponding method, also has a very high error rate, since the loading of a second, downstream SCR unit is not sufficient

Accuracy can be determined.

In addition, methods known from the prior art are often insufficient to meet all legal requirements, especially when

several SCR units have different coatings.

The object of the invention is to overcome the disadvantages of the prior art. In particular, the object of the invention is to create a method by means of which the loading quantities of SCR units can be regulated simply and reliably

can.

It is also an object of the invention to provide an exhaust gas aftertreatment system

to provide the load quantities of SCR units that can be reliably regulated.

The object according to the invention is achieved in particular in that, in a method of the type mentioned at the outset, a metered amount of aftertreatment fluid is dependent on a total charge amount of the SCR units and a charge amount of a second SCR unit, with a first

SCR unit and the second SCR unit an NH: concentration is determined.

In the method according to the invention, it is particularly advantageous that an amount of ammonia is also determined between the two SCR units, as a result of which, in addition to the total load, a load of the first and second SCR units can also be determined. This makes it possible to determine the amount of ammonia (NH3a) that reaches the second SCR unit and can be stored there. In particular, this NHs determination makes it possible to see whether the first SCR unit is possibly much more NH; has or is more loaded than the second SCR unit. As in the prior art, only a medium load

regulated, it is not possible to distinguish between the two SCR units.

With the method according to the invention, the amount of NH that is converted (i.e. reacts with NOx) and / or the amount of NHes that “disappears” due to oxidation or slip can be used to determine the dosage amount. This can

the metering of the fuel can also be set, controlled and / or regulated.

It is particularly advantageous if, by determining an NH: amount between the SCR units (i.e. downstream of the first and upstream of the second SCR unit), an amount of ammonia between the two SCR units is determined in such a way that the loading amount of the second SCR unit Unit is determined independently of the first SCR unit and / or independently of a total load.

It is determined how much NH3 from the first into the second SCR unit.

If several SCR units are provided, it can be advantageous if an NHs concentration or an NHs amount is determined between each SCR unit. It can, however, also be provided that an NH: quantity is determined only once, this being done in particular upstream in front of a last SCR unit (arranged downstream in the exhaust tract). It can also be provided that an NHs: concentration is determined several times per SCR unit, for which purpose per SCR unit

several especially virtual sensors are provided.

In the context of the invention, the second SCR unit is arranged in particular immediately downstream of the first SCR unit. These preferably have a different coating, for example iron zeolite and copper zeolite. However, it can also be provided that both SCR units have a single (identical)

Have coating, whereby a common SCR unit is formed.

In order to determine a quantity of NH3s or an NH3 concentration between the SCR units, in particular a virtual sensor is provided between the SCR units. I.e. an NH: concentration is simulated at this point. However, it can also be provided that a physical sensor is arranged between the SCRE units. If more than two SCR units are provided, NHs sensors (virtual and / or physical) are arranged as described above. In the context of the invention, the terms NH: amount and NHs concentration

used equivalently.

According to the invention, it is advantageous if, in normal operation, in particular in normal operation, an operating material suitable for selective catalytic reduction, such as in particular a urea-containing aftertreatment fluid, a urea solution or AdBlue®, is metered in upstream of the SCR units. The fuel can contain a reducing agent, such as in particular ammonia (NHs), or it can be converted into a reducing agent, such as in particular NHs. A urea-containing mixture, in particular a urea-water solution such as, for example, AdBlue®, or a gaseous or solid reducing agent, is preferably used as the fuel, the fuel optionally being used as follows

The reactions shown are converted into the reducing agent, especially NH:

Thermolysis: (NH2) 2CO 3 NH3 + HNCO hydrolysis: HNCO + H2O0> NHs + CO2

In a first step, the urea (NH2) 2CO can be converted into ammonia NHz3 and isocyanic acid HNCO in the thermolysis reaction. In a second step, the isocyanic acid HNCO can be mixed with water H20O in the hydrolysis reaction

Ammonia NHz3 and carbon dioxide CO2 are converted.

The reducing agent, in particular NHs, can optionally be at least temporarily stored and / or stored in at least one SCR unit. If necessary, the ammonia accumulates on the active centers of the SCR unit. The at least temporarily stored reducing agent, in particular the ammonia NHes, can then reduce nitrogen oxides NOx, such as in particular nitrogen monoxide NO and nitrogen dioxide NO2.

In the context of the invention, an aftertreatment fluid is understood to mean a liquid, gaseous or solid fluid. Amminex, for example, is used as the gaseous fluid. The aftertreatment fluid can also be partially liquid and / or partially gaseous and / or partially solid. In particular, it contains urea. We particularly prefer a given amount of ammonia

dosed.

The metering of the fuel can be done via a metering device, such as in particular

via an injector or an injection nozzle.

In the context of the present disclosure, an SCR unit can in particular be understood to mean an sSDPF catalytic converter, an SCR catalytic converter and / or an ASC catalytic converter. In particular, it can be provided that the second SCR unit comprises an SCR catalytic converter and an ASC catalytic converter, and / or that the second SCR unit is formed from an SCR catalytic converter and an ASC catalytic converter. It can be provided that both SCR units and possibly also the ASC form an SCR system.

Furthermore, the SCR unit and / or the SCR units can be the device for

Dosing of the operating material and, if necessary, also the operating material and / or

include the operating fluid container as such. The SCR system can

optionally also include an NH: sensor.

In the context of the invention, the internal combustion engine is in particular a diesel internal combustion engine, albeit also a gasoline engine

Internal combustion engine can be provided.

It can be provided that a desired, in particular previously defined, total charge quantity of the first and the second SCR unit is specified. In the context of the present disclosure, the total charge amount can be understood to mean the combination of the charge amount of the or all SCR units. This means that the modeled load quantity of the first SCR unit and the second SCR unit may be considered together, in particular as a modeled total load quantity. In particular, it can be provided that the modeled load quantity of the first SCR unit and the second SCR unit are added in order to determine the modeled total load quantity

can.

To adjust the metering of the fuel, the desired total charge can be compared with the modeled total charge

whereby deviations can be determined.

So that the desired total load can be achieved, the metering of the fuel can be set using the modeled total load. This means that, if necessary, based on the determined deviation between the desired modeled total charge amount and the modeled total charge amount of the SCR units, the metering of the operating substance

regulated and / or controlled.

In addition, it is advantageous if a desired, in particular previously defined, charge quantity is also specified for the second SCR unit. So that the desired loading amount of the second SCR unit can be achieved, the metering of the fuel to achieve the desired loading amount of the second SCR unit can be based on the modeled loading amount of the second SCR unit.

Unit can be set. This means that the dosage of the

Operating material is regulated and / or controlled on the basis of the deviation between the desired loading amount of the second SCR unit and the modeled loading amount of the second SCR unit. In particular, both SCR units are modeled and the total load quantity and the load of the second SCR unit are regulated and / or adjusted. However, it can also be provided that only

the loading of the second SCR unit is regulated and / or adjusted.

The reactions that are decisive for the process can be calculated in a mathematical and / or physical model. For example, such a kinetic model is in "Hollauf, Bernd: Model-Based Closed-Loop Control of SCR Based DeNOx Systems. Master’s thesis, University of Applied Science Technikum Kärnten, 2009. "revealed. It is preferably provided that the relevant reactions are mapped mathematically and physically by the kinetic models. The reactions can thus be based on physical conditions, whereby estimates and / or uncertainties can be reduced and the accuracy of the modeled values can be increased. For example, the oxidation of the reducing agent, in particular the oxidation of NHs, can also be mapped with the kinetic models. With conventional methods without kinetic models, the oxidation of the reducing agent, if this is taken into account at all, can usually only be estimated, which is associated with great uncertainties or

is imprecise.

It is expedient if the reactions of the first SCR unit that are decisive for the method are calculated in addition to the real operation in a first kinetic model, the first kinetic model corresponding in particular to a mathematical mapping of the physical model of the first SCR unit, the for the method relevant reactions of the second SCR unit are calculated in addition to the real operation in a second kinetic model, the second kinetic model in particular corresponds to a mathematical mapping of the physical model of the second SCR unit, and a desired total load of the first SCR unit and the second SCR unit and a desired amount of load of the second SCR unit can be specified. The kinetic models allow the loading quantities of the

SCR units are modeled and / or calculated. This can, in particular

modeled, loading amount of each individual SCR unit is calculated and / or determined at any point in time, in particular independently of any other SCR unit

will.

The metering of the fuel to achieve the second desired load is preferably set based on the modeled load of the second SCR unit and the metered of the fuel to achieve the desired total load is set based on the modeled load of the

first and second SCR units set.

The first SCR unit and the second SCR unit are modeled using the NHs determination. As a result, the modeled reducing agent slip can be calculated and / or determined at any point in time, and this can serve as a control parameter. Due to the fact that the modeled reducing agent slip serves as a control parameter, a breakthrough of the reducing agent through the second

SCR system can be prevented.

In order to reduce the time between the beginning of the metering and the build-up of the loading of the second SCR unit, a so-called cascade control can be used. The cascade control uses two cascaded controllers. The first (outer) regulator is used to regulate the loading of the second SCR unit. For this purpose, a nominal load value is specified, with which an actual load value is compared. As a manipulated variable, this controller outputs a desired NH: quantity upstream of the second SCR component, that is to say in the direction of flow between the first SCR component and the second SCR component. This corresponds to a desired NHs slip of the first SCR component. This desired NHs slip of the first SCR component serves as a setpoint for the second (internal) controller. The second controller then compares the desired NHs slip with the actual NHs slip and outputs an NHs dosage as the manipulated variable

(before the first SCR component).

The modeled reducing agent slip of the first SCR system is in particular only

used in combination with cascade control.

It is advantageous if, as input variables for calculating the relevant reactions in the kinetic models, an exhaust gas mass flow, an exhaust gas temperature, a NOx concentration downstream of the internal combustion engine and / or a NOx concentration downstream of the exhaust gas treatment system, in particular downstream of an ammonia slip catalytic converter, a NO2 concentration, an NH3 concentration and an outside temperature can be used. As a result, the exhaust gas mass flow, the exhaust gas temperature, the NOx concentration downstream of the internal combustion engine and / or the NOx concentration downstream of the exhaust gas aftertreatment system and an NH: concentration can be taken into account in the kinetic models. In particular, the time course of the measured values serves as an input variable for the kinetic models. The NO2 / NOx changes are preferred over the entire

Modeled exhaust aftertreatment system.

It is advantageous if the input variables for calculating the relevant reactions in the kinetic models are real and / or simulated measured values, the values being recorded by at least one real and / or virtual sensor of the exhaust gas aftertreatment system. A physical sensor is understood as a real sensor in the context of the invention; one or more simulated values are understood as a virtual sensor. As a result, values, in particular real measured values, preferably values recorded over time, can be included in the calculation of the kinetic models or taken into account. However, it can also be provided that some or all of the values are additionally or alternatively also modeled, for example the NOx value downstream of the engine and in particular the NH3 value. This means that values can either be exclusively real measured values or exclusively modeled values or a combination of real and modeled values. A single value from the measured value and

modeled value.

It is useful if the aftertreatment fluid, which in particular contains urea, is metered into the exhaust gas flow via at least one injection device, the injection device being arranged upstream of the SCR units. It can also be beneficial if there is another in the exhaust gas aftertreatment system

Injection device, upstream of the first injection device, is provided.

It is advantageous if the injection device is controlled via a control unit, the control unit prescribing an amount of aftertreatment fluid to be dosed in such a way that a desired total charge amount and the charge amount of the second SCR unit are achieved. In principle, it can also be provided that a

desired load of the first SCR unit is reached.

According to the invention, the exhaust gas aftertreatment system can have a further closed-coupled SCR unit upstream of the SCR units, with one also

Loading of this unit is regulated by an NH: value.

The method according to the invention creates an intelligent control strategy for the exhaust gas aftertreatment system: If sufficient NH3 loading is ensured in the second SCR unit and the catalyst temperature of the second SCR unit is in a previously defined range, a metering in of reducing agent in a near-engine, closed coupled SCR unit should be reduced as much as possible. This ensures that there is sufficient NO in front of a particle filter (in particular DPF) located between the closed-coupled SCR unit and the SCR units in order to ensure passive (NO2-based) soot burn-off. The soot loading of the particle filter is used as a further control variable. If there is no soot cake in the particle filter, the dosage closed coupled SCR unit is not reduced - even if the above-mentioned release condition is met - in order to prevent passive soot burn-up in the particle filter (almost no NO2 available in front of the particle filter) and thus build up soot burn-off . The intelligent control strategy therefore takes into account the temperatures of all the catalytic converters arranged in the exhaust gas aftertreatment system as well as the particulate filter soot load and the NH3 load status of the

Catalysts.

The further goal is achieved if, in an exhaust gas aftertreatment system of the type mentioned at the outset, an in particular virtual NHs sensor for determining an NHs concentration is arranged between the SCR units, with a metered amount of aftertreatment fluid from a total load of the SCR units and a loading amount of a second SCR unit is dependent.

An exhaust gas aftertreatment system according to the invention thus brings the same advantages as have been described in detail with regard to the method according to the invention. The advantages according to the invention can be achieved in particular in that an in particular virtual NHz3 sensor is arranged between the SCR units. In the context of the invention, a virtual NH3 sensor is understood to mean a simulation of a sensor between the SCR units, which provides simulated NH3 simulations (measured values calculated using simulations) for further steps. Even if a virtual sensor is preferred according to the invention, a physical sensor can also be provided, which real measured values

supplies.

It is advantageous if the first SCR unit and the second SCR unit have different coatings, these being arranged in particular in a common housing. Particularly preferably, these therefore form a common device, with the two units being coated differently. For coating, for example, a first side of the SCR device (first SCR unit) can be immersed in a first solution and a second side of the SCR device (second SCR unit) in a second solution. Particularly preferably, an ASC is also arranged in the common housing of the two SCR units downstream of the second SCR unit. It can also be provided that the SCR device in addition to the

SCR units also includes an ASC.

It is advantageous if the NH3 sensor is a real or a virtual sensor. In any case, the sensor determines an NH3s concentration downstream of the first SCR unit and upstream of the second NH3 concentration or outputs this to the

kinetic model.

According to the invention, the exhaust gas aftertreatment system can have a further closed-coupled SCR unit upstream of the SCR units. A further, in particular virtual, NH3s sensor can be provided downstream thereof. As described above, the NH3 value can be used in a kinetic model of this closed-coupled SCR unit in order to regulate a fill level of the closed-coupled SCR unit. The kinetic model of the closed coupled SCR unit can be combined with the kinetic models of the SCR units to create a

Total amount of aftertreatment fluid injected through two injectors

is metered to regulate. For this purpose, an injection device is arranged upstream of the SCR units and upstream of the closed-coupled SCR unit. The SCR units and the closed coupled SCR unit can also

can be regulated independently of each other.

Further advantages, features and effects are the following exemplary embodiment

described. It shows

Fig. 1 is a schematic representation of an inventive

Exhaust aftertreatment system.

1 shows a schematic representation of an exhaust gas aftertreatment system 1 according to the invention. The exhaust gas aftertreatment system 1, which is formed on an internal combustion engine with an internal combustion engine 2, comprises a first optional diesel oxidation catalytic converter 8, a first SCR unit 3, a second SCR unit 4, an NH3: sensor 6, an injection device 5, a further injection device 9, an SCR-ASC device 10, a second diesel oxidation catalytic converter 12, several temperature sensors 13, a pressure sensor 16, several NOx sensors, an ASC 15 and a housing 7 for the SCR units 3, 4 and the ASC 15. The SCR units 3, 4 and the ASC 15 form an SCR system 17. The catalytic converters 8, 10, 13 and the injection device 9 are to be regarded as optional. The invention thus also encompasses a classic DOC-DPF-SCR-ASC (11, 12, 3, 4, 7) system.

In normal operation, an operating material, such as AdBlue® in particular, is metered in upstream of the first SCR unit 3 via the injection device 5. The fuel contains a reducing agent or can be converted into a reducing agent. According to this embodiment, the reducing agent is ammonia (NHa). The reducing agent is at least temporarily in at least one SCR unit 3, 4

saved.

To determine the dosing amount, the amount of NHe that is converted (reacts with NOx) or the amount of NHe that "disappears" due to oxidation or slip

used.

The SCR-ASC device 10 comprises a closed coupled SCR and, downstream thereof, advantageously a closed coupled ASC. According to the invention, a further NH3 sensor 6 can be arranged downstream thereof. This is used to deliver an NH3 as an input value to a kinetic model of the closed coupled SCR or the SCR-ASC device 10. As described further above with regard to the method according to the invention, a level of the closed coupled SCR or the SCR-ASC device 10 is regulated.

It can further be provided that all kinetic models are combined in order to achieve a total metering of aftertreatment fluid into the entire exhaust gas aftertreatment system 1, i.e. via the injection device 5 and the further injection device 9 Total loading amount of the SCR units 3, 4 and a loading amount of a second SCR unit 4 as well as a loading amount of the SCR-ASC device 10, with an NHs concentration and between a first SCR unit 3 and the second SCR unit 4

an NHs concentration is determined downstream of the SCR-ASC device 10.

The exhaust gas aftertreatment system 1 shown in the figure thus includes, inter alia, an SCR-ASC device 10 and the SCR system 17. The SCR-ASC device 10 and the SCR system 17 each include individual injection devices 5, 9 upstream thereof and can be independent of one another be managed. A higher-level dosing coordinator can be provided which, depending on different influencing variables such as individual temperature curves, DeNOx efficiencies and current DPF soot loads, the

specifies the respective dosing strategy.

In the exhaust gas aftertreatment system 1, the downstream SCR system 17 is divided into two SCR units 3, 4 with a virtual or real NH3 sensor 6 in between. This subdivision into two or more units and the associated control strategy can of course also be applied to other elements with an SCR coating, such as SCR-ASC device 10.

Claims (9)

Claims 1. A method for regulating an exhaust gas aftertreatment system (1) of an exhaust gas stream of an internal combustion engine with an internal combustion engine (2), wherein the exhaust gas aftertreatment system (1) comprises at least two SCR units (3, 4), an in particular urea-containing aftertreatment fluid being metered into the exhaust gas stream, which reacts with the exhaust gas flow in the SCR units (3, 4), characterized in that a metered amount of aftertreatment fluid is dependent on a total loading amount of the SCR units (3, 4) and a loading amount of a second SCR unit (4) , wherein between a first SCR unit (3) and the second SCR unit (4) an NHs concentration is determined. 2. The method according to claim 1, characterized in that the reactions of the first SCR unit (3) relevant to the method are calculated in addition to the real operation in a first kinetic model, the first kinetic model in particular a mathematical mapping of the physical model corresponds to the first SCR unit (3), the reactions of the second SCR unit (4) relevant for the method being calculated in addition to the real operation in a second kinetic model, the second kinetic model in particular a mathematical mapping of the physical model of the second SCR unit (4) corresponds, and wherein a desired total amount of charge of the first SCR unit (3) and the second SCR unit (4) and a desired amount of charge second SCR unit (4) can be specified. 3. The method according to claim 1 or 2, characterized in that as input variables for calculating the relevant reactions in the kinetic models, an exhaust gas mass flow, an exhaust gas temperature, a NOx concentration after the internal combustion engine and / or a NOx concentration after the exhaust gas aftertreatment system (1 ), especially after an ammonia slip catalytic converter (15), a NO2 concentration, an NH3s concentration and a Outside temperature can be used. 4. The method according to claim 3, characterized in that the input variables for the calculation of the relevant reactions in the kinetic models real and / or simulated measured values, the values from at least one real and / or virtual sensor (6, 13, 14) of the exhaust gas aftertreatment system (1) be included. 5. The method according to any one of claims 1 to 4, characterized in that the particular urea-containing aftertreatment fluid is metered into the exhaust gas flow via at least one injection device (5), the Injection device (5) is arranged upstream of the SCR units (3, 4). 6. The method according to claim 5, characterized in that when the injection device (5) is controlled via a control unit, wherein a metered amount of aftertreatment fluid is specified via the control unit such that a desired total load and the Loading amount of the second SCR unit (4) is reached. 7. Exhaust aftertreatment system (1) of an exhaust gas stream of an internal combustion engine with an internal combustion engine (2), wherein the exhaust aftertreatment system (1) comprises at least two SCR units (3, 4), with at least one injection device (5) for metering a particularly urea-containing aftertreatment fluid into the Exhaust gas flow and a regulating unit for regulating a quantity of the injected exhaust gas aftertreatment fluid, the regulating unit being connected to the injection device, characterized in that between the SCR units (3, 4) an in particular virtual NH3 sensor (6) for determining an NH: Concentration between the SCR units (3, 4) is arranged, wherein a metered amount of aftertreatment fluid is dependent on a total loading amount of the SCR units (3, 4) and a loading amount of a second SCR unit (4). 8. exhaust gas aftertreatment system (1) according to claim 7, characterized in that the first SCR unit (3) and the second SCR unit (4) have different coatings, these in particular in a common one Housing (7) are arranged. 9. exhaust gas aftertreatment system according to claim 7 or 8, characterized characterized in that the NH3: sensor (6) is a real or a virtual sensor.