AT522752B1 - Method for checking the function of an exhaust aftertreatment system of an internal combustion engine and an exhaust aftertreatment system - Google Patents

Abstract

The invention relates to a method for checking the function of an exhaust gas aftertreatment system (1) of an internal combustion engine with an internal combustion engine (2), wherein the exhaust gas aftertreatment system (1) comprises an SCR system (17) with at least two SCR units (3, 4), wherein in an aftertreatment fluid, in particular containing urea, is metered into the exhaust gas flow, which reacts with the exhaust gas flow in the SCR units (3, 4), with an NH3 concentration between a first SCR unit (3) and the second SCR unit (4) being increased by a NH3 sensor (6), the metering of the after-treatment fluid being stopped before the predetermined diagnostic quantity of after-treatment fluid has been metered in if a reducing agent slip is detected downstream of the first SCR unit (3), as a result of which no reducing agent emission occurs as planned.

Description

description

PROCEDURE FOR CHECKING THE FUNCTIONALITY OF AN EXHAUST GAS AFTER-TREATMENT SYSTEM OF AN INTERNAL COMBUSTION ENGINE

The invention relates to a method for checking the function of an exhaust gas aftertreatment system of an internal combustion engine with an internal combustion engine, the exhaust gas aftertreatment system comprising an SCR system with at least two SCR units, with an aftertreatment fluid, in particular containing urea, being metered into the exhaust gas flow and contained in the SCR units reacts with the exhaust gas flow, an NHs concentration being determined by an NH: sensor between a first SCR unit and the second SCR unit.

Different methods for checking the function of exhaust gas aftertreatment systems are known from the prior art. For example, methods are known in which an SCR catalytic converter is first fully loaded with ammonia and then the SCR storage capacity of the SCR catalytic converter is determined by completely emptying it. A mass balance is used to calculate how much ammonia the SCR catalytic converter could still store.

Methods are also known in which urea is metered into a completely emptied SCR catalytic converter until ammonia slip is detected after the SCR catalytic converter—that is, the SCR catalytic converter is fully loaded. This allows a mass balance to be used to determine how much ammonia can still be stored in the SCR catalytic converter.

Other methods for checking the function of an exhaust gas aftertreatment system are known, for example, from DE 102013203580 A1, EP 2317091 A1 and EP 2295750 A1.

[0005] In addition, methods known from the prior art are often not sufficient to meet all legal requirements, especially when 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 functionality of an exhaust gas aftertreatment system can be checked quickly and reliably.

The object of the invention is achieved in particular in that, in a method of the type mentioned at the outset, the aftertreatment fluid is stopped before the predetermined diagnostic quantity of aftertreatment fluid is metered in if a reducing agent slip is detected downstream of the first SCR unit, as a result of which the reducing agent emissions are minimized .

In the method according to the invention, it is particularly advantageous that an amount of ammonia is also determined between the two SCR units, whereby an NHs slip can be measured downstream of the first SCR unit and thereby a storage capacity of the first SCR unit can be determined. As a result, based on the storage capacity of the SCR unit, aging and/or contamination of the same can be detected and an appropriate response can then be made. For this purpose, for example, a loading control can be adjusted accordingly or a desulfurization can be carried out.

[0009]Since the metering of the aftertreatment fluid and thereby also the introduction of reducing agent is stopped as soon as a reducing agent slip is detected after the first SCR unit, emissions, in particular reducing agent emissions, can be essentially prevented or reduced. This means that the entire predetermined diagnosis amount of operating fluid may not or does not have to be metered in during the method. The method according to the invention makes it possible to use the NHs sensor to replace an aged and/or damaged SCR unit which has a limited storage capacity

early detection so that reversible damage can be reversed, irreversible damage can be detected and/or an SCR unit can be defined as defective.

About the NHs measurement between the two SCR units is also a loading of a second SCR unit downstream of the first SCR unit can be deduced. Consequently, the functional capability of the second SCR unit can also be determined later on. This is preferably done via the NH3 sensor in combination with at least one NOx sensor.

The method according to the invention can therefore be used to diagnose the state of an SCR unit, the amount of NHs that has been converted (i.e. reacts with NOx), stored and oxidized, and the amount that is measured as slip can be determined the metering of the fuel can be set, controlled and/or regulated.

If several SCR units are provided, it can be advantageous if an NHs concentration or an NH3 quantity is determined by an NHs3 sensor between each SCR unit. However, provision can also be made for an NHs quantity to be determined only once, with this taking place in particular upstream of a last SCR unit (arranged downstream in the exhaust gas tract).

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.

A physical sensor is provided between the SCR units to determine an NHs amount or an NHs concentration between the SCR units. i.e. an NHs concentration is actually measured at this point; the NH: sensor delivers a real measured value. If more than two SCR units are provided, NH: sensors are arranged as described above.

According to the invention, it is advantageous if, in normal operation, in particular in normal operation, a fuel suitable for selective catalytic reduction, such as in particular a urea-containing aftertreatment fluid, a urea solution or AdBlue®, is metered in front of the SCR units. The fuel can contain a reducing agent, such as in particular ammonia (NHs), or can be converted into a reducing agent, such as in particular NHs. A urea-containing mixture, in particular a urea-water solution, such as AdBlue®, is preferably used as the fuel, with the fuel being optionally converted into the reducing agent, in particular NHa, by the reactions described below:

Thermolysis: (NH2)2CO > NH3 + HNCO Hydrolysis: HNCO + H;:O > NHs + CO»

In a first step, the urea (NH2)2CO can be converted into ammonia NHs and isocyanic acid HNCO in the thermolysis reaction. In a second step, in the hydrolysis reaction, the isocyanic acid HNCO can be mixed with water H;O in ammonia NH; and carbon dioxide CO» are converted.

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

[0018] The fuel can be metered via a metering device, such as in particular via an injector or via an injection nozzle.

In the context of the invention, an aftertreatment fluid is to be understood as meaning a fuel that contains a reducing agent or can be converted into a reducing agent. The reducing agent is stored at least temporarily in the SCR units.

In the context of the invention, an after-treatment fluid is understood to mean a liquid or gaseous or solid fluid. Amminex®, for example, is used as the gaseous fluid. The aftertreatment fluid may also be partially liquid and/or partially gaseous and/or partially solid. In particular, this contains urea. It is particularly preferred that a predetermined amount of ammonia is always metered in.

[0021] Within the scope of the present disclosure, an SCR unit can in particular be understood to mean an sDPF 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.

[0022] Furthermore, the SCR unit and/or the SCR units can comprise the device for metering in the fuel and possibly also the fuel and/or the fuel container as such.

In the context of the invention, the internal combustion engine is in particular a diesel internal combustion engine, although an Otto internal combustion engine can also be provided.

Aging and/or damage to the first SCR unit can be passively determined based on the comparison of modeled NH3 values and actually measured NH3 values in normal operation.

It is favorable if the SCR system is defined as functional if no reducing agent slip is detected by the NHs sensor after the first SCR unit during the entire course of the metering of a predetermined diagnostic quantity of aftertreatment fluid, with which essentially the entire After-treatment fluid is at least temporarily stored in the first SCR unit, and that the SCR system is defined as being partially functional or non-functional if, during the course of metering the predetermined diagnostic amount of after-treatment fluid, a reducing agent slip through the NH3 sensor after the first SCR Unit is detected before the entire predefined diagnostic amount of aftertreatment fluid is metered, whereby a reduced aftertreatment fluid storage capacity of the first SCR unit is detected. The predetermined diagnosis amount of fuel that is metered in defines the amount of reducing agent introduced, since the fuel can be converted into the reducing agent and/or the fuel contains the reducing agent. If the SCR system is defined as having limited functionality or not being functional, this means that the introduced quantity of reducing agent, in particular NHe, cannot be stored by the first SCR unit. If necessary, the reduced reducing agent storage capacity, in particular the NHs storage capacity, of the SCR unit can be reduced due to aging of the SCR unit and/or due to a defect in the SCR unit.

If the SCR system is defined as having limited functionality or not being functional, it is expedient if the exhaust gas aftertreatment system is desulfurized. As a result, after a reduced storage capacity of the SCR unit(s) has been recognized, reversible damage can be healed.

Furthermore, the NHs measurement downstream of the first SCR unit and upstream of the second SCR unit makes it possible to distinguish between normal, generic aging of the SCR units and poisoning of the SCR units and between a defective SCR unit distinguish unit. No methods are known from the prior art by which the occurrence of an NHs slip can be detected so early in time. A particularly important area of application of the method according to the invention is when checking the function of an exhaust gas aftertreatment system with two or more SCR units, with at least two of them having a different coating.

The predetermined amount of aftertreatment fluid usually corresponds to an amount of reducing agent, which must still be storable in the SCR unit so that the SCR

Unit, the SCR system and / or the exhaust aftertreatment system, a limit, in particular a legal limit of pollutant emissions, especially NOx emissions, can be met. This can mean that if the predetermined amount of reducing agent can no longer be stored in the SCR unit, the SCR catalytic converter will not be able to meet the nitrogen oxide conversion rate required for the statutory limit values.

[0029] A reducing agent slip is to be understood in particular as an NH3 slip. The reducing agent slip is detected at least by the NHs sensor. It can also be provided that the NHs slip is additionally detected by an increased measured value of the NOx sensor, since the concentration of NHsz can influence a NOx sensor.

When defining the SCR system as functional or not or only partially functional, a diagnostic mode can optionally be activated in advance. The supply of aftertreatment fluid is reduced or stopped in the so-called emptying phase, so that the SCR system is supplied with little or no new reducing agent. The emptying of the first and/or second SCR unit can be based on the fact that the reducing agent still contained in the SCR units is consumed by the reduction of nitrogen oxides (NOx), which means that less reducing agent is introduced than is consumed. It can be provided that the amount of reducing agent required for sufficient cooling of the metering device is always introduced. Provision can be made for the reducing agent still contained in the SCR units to be emptied by means of an emptying mode, such as in particular by increasing the temperature of the SCR catalytic converter. After the first and/or second SCR units have been emptied, they can be tempered, in particular heated, in order to bring the SCR system to a predetermined temperature. Provision can be made for the SCR system to be brought to a previously defined temperature during emptying, as a result of which emissions can be kept low. This tempering step can be omitted if the temperature of the SCR system is already within a predetermined temperature window. After-treatment fluid is then metered in again in the so-called loading phase. The reducing agent contained in the aftertreatment fluid or formed from the operating substance is optionally at least temporarily taken up by the SCR units and/or at least temporarily stored. The determined functionality of the exhaust aftertreatment system can then be output and/or stored as status information. The diagnosis mode can then be ended if necessary.

The SCR system can be assessed as non-functional if an NH3s slip is detected after the first SCR unit before the predetermined diagnostic amount of fuel is metered. This makes it possible to determine that the reducing agent storage capacity of the SCR unit is reduced and that a limit value, in particular a legal limit value for pollutant emissions, can no longer be met with such an SCR unit.

It is favorable if the predetermined diagnostic amount of aftertreatment fluid for the diagnostic mode is dimensioned in such a way that, when the SCR unit is functional, the reducing agent introduced by the diagnostic amount of aftertreatment fluid can be stored at least temporarily in the SCR unit, which means that when the SCR is functional -Unit no reducing agent emissions occur as planned. As soon as the predetermined amount of aftertreatment fluid has been metered in, the aftertreatment fluid supply can optionally be stopped or greatly reduced, as a result of which no or only very little reducing agent is introduced. If no NHs slip is detected downstream of the first and upstream of the second SCR unit during metering of the predetermined diagnostic quantity of aftertreatment fluid, the SCR system can be assessed as being functional. This means that essentially the entire amount of reducing agent, which is defined by the amount of fuel introduced, was stored at least temporarily in the SCR units. It may therefore not be necessary to introduce so much fuel or reducing agent before (upstream) the SCR units that a slip of reducing agent after the first SCR unit inevitably occurs during the function check. As a result, on the one hand, emissions can be reduced or prevented, as planned with a functional SCR system

no reducing agent emissions occur. On the other hand, the functionality of the SCR system can be determined quickly because, in contrast to conventional methods, less fuel has to be metered in and therefore the metering time and the duration of the functional check are shorter than with conventional methods.

It is advantageous if the SCR system is emptied if the SCR system is emptied by stopping or reducing the supply of aftertreatment fluid until a parameter is detected that provides information that no more aftertreatment fluid is in the SCR system is stored, this parameter being detected by the NHsSensor. As soon as a parameter is detected which indicates that no more reducing agent is stored or is present in the SCR system, the emptying of the SCR unit(s) can be regarded as completed and the emptying phase can be ended. In particular, the measured values of the NH3 sensor and optionally also the NOx sensors, which are optionally arranged upstream and downstream of the SCR system, are used as parameters. For example, it can be assumed that essentially no more reducing agent is stored in the SCR unit if the concentration of nitrogen oxides upstream of the SCR system essentially corresponds to the concentration of nitrogen oxides downstream of the SCR system. In such a case, due to the lack of reducing agent, no more nitrogen oxides can be reduced by the SCR units. From this it can be concluded that the SCR units have been emptied.

It is advantageous if the reactions of the first SCR unit which are relevant to the process are calculated in addition to 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, where the reactions of the second SCR unit that are decisive for the method are calculated in addition to real operation in a second kinetic model, the second kinetic model corresponding in particular to a mathematical representation of the physical model of the second SCR unit, and a desired total loading quantity of the first SCR -Unit and the second SCR unit and a desired loading amount of the second SCR unit are specified.

If necessary, it is provided that the predetermined diagnostic quantity of aftertreatment fluid is determined or calculated by the kinetic model and in particular corresponds to a quantity of reducing agent that can be stored at least temporarily in the SCR units according to the model calculation if it is functional. If the SCR system is defined as having only limited functionality, the kinetic model is advantageously adjusted and/or adapted.

The reactions that are decisive for the method 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." Provision is preferably made for the relevant reactions to be mapped mathematically and physically by the kinetic models. The reactions can thus be based on physical conditions, which can reduce estimates and/or uncertainties and which can increase the accuracy of the modeled values. For example, the oxidation of the reducing agent, in particular the oxidation of NH, can also be mapped with the kinetic models. With conventional methods without kinetic models, the oxidation of reducing agent, if it is taken into account at all, can usually only be estimated, which is associated with great uncertainties or is imprecise.

With the kinetic model, an amount of aftertreatment fluid can be determined, which should be able to be stored in a functional SCR unit. With the kinetic model, it may also be possible to use the predicted and / or calculated reducing agent storage capacity to determine a limit reducing agent storage capacity, the so-called limit loading, of the SCR unit, which must be at least reached so that the SCR -Units can be defined as functional. If necessary,

seen that the amount of fuel is determined by the limit reducing agent storage capacity of the SCR unit.

It is advantageous if 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 catalyst, are used as input variables for calculating the relevant reactions in the kinetic models , an NO2 concentration, an NHs concentration and an outside temperature are used. As a result, the exhaust gas mass flow, the exhaust gas temperature, the NOx concentration after the internal combustion engine and/or the NOx concentration after the exhaust aftertreatment system and an NH3 concentration can be taken into account in the kinetic models. In particular, the course of the measured values over time serves as an input variable for the kinetic models.

It is advantageous if the input variables for calculating the relevant reactions in the kinetic models are real and/or simulated measured values, with the values being recorded by at least one real NH3 sensor in the exhaust gas aftertreatment system. A physical sensor is understood as a real sensor within the scope of the invention. As a result, values, in particular real measured values, preferably values recorded over time, can be included or taken into account in the calculation of the kinetic models. However, it can also be provided that further values are additionally or alternatively also modeled, for example the NOx value downstream and/or upstream of the engine and a number of temperature values. That is, values can be either real measured values only, modeled values only, or a combination of real and modeled values. A single value can also be composed of the measured value and the modeled value.

In an exhaust aftertreatment system, an NHs sensor for determining an NH: concentration between the SCR units can be arranged between the SCR units in order to determine a reducing agent slip downstream of a first SCR unit.

It is expedient if the aftertreatment fluid, in particular containing 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 advantageous if a further injection device is provided in the exhaust gas aftertreatment system, upstream of the first injection device.

It is advantageous if the injection device is controlled via a control unit, with the control unit specifying an amount of aftertreatment fluid to be metered in such a way that a desired total loading amount and the loading amount of the second SCR unit is achieved. In principle, it can also be provided that a desired loading quantity of the first SCR unit is achieved via the control device.

It is favorable if the first SCR unit and the second SCR unit have different coatings, these being arranged in particular in a common housing. In a particularly preferred manner, 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) can be immersed in a second solution. An ASC is particularly preferably also arranged in the common housing of the two SCR units downstream of the second SCR unit. Provision can also be made for the SCR device to also include an ASC in addition to the SCR units.

The NH3 sensor is a real, physical sensor which determines an NHs concentration downstream of the first SCR unit and upstream of the second SCR unit or specifies this for the kinetic model.

It is particularly advantageous if a factor for the deterioration of the SCR system is calculated based on the function check, the dosing being determined by the factor.

tion of aftertreatment fluid is adapted. For this purpose, either the dosing can be influenced directly or actively by the factor. The control and/or the kinetic model can also be adapted by the calculated factor, with the adaptation being able to take place continuously. The SCR system degradation factor can be calculated actively or passively. It is advantageous that, following the functional check, it is also possible to react to a function of the SCR units. Either a factor for the degradation of the entire SCR system and/or a factor for each SCR unit can be calculated. It is favorable if one factor is calculated in each case, so that each SCR unit can be checked and a state can be reacted to individually.

[0046] Further advantages, features and effects are described in the following exemplary embodiment. while showing

[0047] FIG. 1 shows a schematic representation of an exhaust gas aftertreatment system.

Fig. 1 shows a schematic representation of an exhaust gas aftertreatment system 1. The exhaust gas aftertreatment system 1, which is connected to an internal combustion engine with an internal combustion engine 2, includes a first optional diesel oxidation catalyst 8, a first SCR unit 3, a second SCR unit 4, an NHs sensor 6, an injector 5, a further injector 9, an SCR-ASC device 10, a second diesel oxidation catalyst 12, several temperature sensors 13, several NOx sensors, a pressure sensor 16, 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.

In normal operation, a fuel, such as AdBlue® in particular, is metered in before the first SCR unit 3 via the injection device 9 . The fuel contains a reducing agent or can be converted into a reducing agent. According to this embodiment, the reducing agent is ammonia (NHs). The reducing agent is stored at least temporarily in at least one SCR units 3, 4.

To check a function of the exhaust aftertreatment system 1, in particular the SCR units 3, 4, the amount of NHs that is converted (reacts with NOx) or the amount of NH that "disappears" through oxidation or slip “ determined.

Claims (8)

patent claims 1. A method for checking the function of an exhaust gas aftertreatment system (1) of an internal combustion engine with an internal combustion engine (2), the exhaust gas aftertreatment system (1) comprising an SCR system (17) with at least two SCR units (3, 4), with the exhaust gas flow containing a in particular urea-containing aftertreatment fluid is metered in, which reacts in the SCR units (3, 4) with the exhaust gas flow, with an NHs concentration being measured between a first SCR unit (3) and the second SCR unit (4) by an NHs sensor (6) is determined, characterized in that the metering of the after-treatment fluid is stopped before the predetermined diagnostic amount of after-treatment fluid is metered if a reducing agent slip is detected after the first SCR unit (3), whereby no reducing agent emission occurs as planned. 2. The method according to claim 1, characterized in that the SCR system (17) is defined as functional if no reducing agent slip through the NHs sensor (6) after the first SCR during the entire course of the metering of a predetermined diagnostic amount of aftertreatment fluid unit (3) is detected, whereby substantially all of the after-treatment fluid is at least temporarily stored in the first SCR unit (3), and that the SCR system (17) is defined as being partially functional or non-functional if during the course of the metering of the predetermined diagnostic amount of aftertreatment fluid, a reducing agent slip is detected by the NHs sensor (6) after the first SCR unit (3) before the entire predefined diagnostic amount of aftertreatment fluid has been metered in, which means that the aftertreatment fluid storage capacity of the first SCR unit (3) is reduced is detected. 3. The method according to any one of claims 1 to 2, characterized in that the metering of the after-treatment fluid is stopped when the predetermined diagnostic quantity of after-treatment fluid has been metered in and no reducing agent slip after the first SCR unit (3) is detected, as a result of which no reducing agent emissions occur as planned . 4. The method according to any one of claims 1 to 3, characterized in that the predetermined diagnostic amount of after-treatment fluid for the diagnostic mode is dimensioned such that in a functional SCR unit (3, 4) the reducing agent introduced by the diagnostic amount of after-treatment fluid is at least temporarily in the SCR unit (3, 4) can be stored, which means that no reducing agent emissions occur as planned when the SCR unit (3, 4) is functional. 5. The method according to any one of claims 1 to 4, characterized in that the SCR system (17) is emptied by stopping or reducing the supply of aftertreatment fluid until a parameter is detected which provides information that no more aftertreatment fluid is in the SCR system (17) is stored, this parameter being detected by the NHs sensor (6). 6. The method according to any one of claims 1 to 5, characterized in that the relevant for the method reactions of the first SCR unit (3) are calculated in addition to real operation in a first kinetic model, the first kinetic model in particular a mathematical mapping of the physical model of the first SCR unit (3), the reactions of the second SCR unit (4) which are decisive for the method being calculated in addition to real operation in a second kinetic model, the second kinetic model in particular being a mathematical representation of the corresponds to the physical model of the second SCR unit (4), and wherein a desired total loading amount of the first SCR unit (3) and the second SCR unit (4) and a desired loading amount of the second SCR unit (4) are specified. 7. The method according to claim 6, characterized in that the input variables for calculating the relevant reactions in the kinetic models are real and/or simulated measured values, with the values being recorded by at least one real NHs sensor (6) of the exhaust gas aftertreatment system (1). will. 8. The method according to any one of claims 1 to 7, characterized in that based on the functional check, a factor for the deterioration of the SCR system (17) is calculated, the metering of aftertreatment fluid being adapted by the factor. 1 sheet of drawings