DE102017209080B4 - Method for operating an internal combustion engine device, internal combustion engine device and SCR control device - Google Patents

Abstract

A method for operating an internal combustion engine device (1) with an internal combustion engine (3) and an exhaust gas system (5) fluidly connected to the internal combustion engine (3) for discharging exhaust gas from the internal combustion engine (3), wherein an exhaust gas stream flowing in the exhaust gas system (5) is the Internal combustion engine (3) is cleaned of nitrogen oxides, nitrogen oxide emissions of the internal combustion engine device (1) being controlled by a nitrogen oxide reduction device (7) which has an SCR catalytic converter (9) arranged in the exhaust gas line (5) and one in the exhaust gas line (5) upstream of the SCR catalytic converter (9), controllable reducing agent metering device (11) are controlled or regulated, wherein an exhaust gas mass flow through the nitrogen oxide reduction device (7) based on at least one SCR parameter selected from a group consisting from a control parameter of the nitrogen oxide reduction device (7) and a Para detected on the nitrogen oxide reduction device (7) meter, is determined, and where- the exhaust gas mass flow based on a thermal model of the nitrogen oxide reduction device (7), in which an exhaust gas temperature upstream of the SCR catalytic converter (9) and an exhaust gas temperature downstream of the SCR catalytic converter (9) are entered , is determined.

Description

The invention relates to a method for operating an internal combustion engine device, an internal combustion engine device and an SCR control device which are set up to carry out such a method.

Internal combustion engine devices of the type discussed here have an internal combustion engine and an exhaust system fluidically connected to the internal combustion engine for discharging exhaust gas from the internal combustion engine. In order to comply with emission limit values, an exhaust gas stream of the internal combustion engine flowing in the exhaust system is cleaned of nitrogen oxides, with nitrogen oxide emissions of the internal combustion engine device by controlling a nitrogen oxide reduction device - hereinafter synonymously also referred to as SCR device for short - which includes an SCR catalytic converter and a controllable reducing agent metering device arranged in the exhaust gas line upstream of the SCR catalytic converter.

Limit values applicable to nitrogen oxide emissions are typically specified - either as a statutory emission target or an emission target specified by a manufacturer or operator of the internal combustion engine device - as absolute values and in particular as mass per unit of energy, preferably in grams per kilowatt hour, and stored in a control device. A sensor system of the SCR device is, however, typically set up to measure a nitrogen oxide component, in particular a concentration or a partial pressure, in the exhaust gas flow. A conversion into absolute nitrogen oxide emissions, or vice versa, the use of the absolutely specified emission target in the regulation of the SCR device is only possible if the exhaust gas mass flow along the exhaust system and in particular through the SCR device is known. Knowledge of the exhaust gas mass flow is also necessary in order to convert a control deviation of the measured nitrogen oxide content into a required reducing agent metering rate for controlling the reducing agent metering device. The exhaust gas mass flow should be known as precisely as possible, otherwise larger safety margins have to be adhered to in order to safely achieve the emission target. This and / or an imprecise knowledge of the exhaust gas mass flow can furthermore lead to the reducing agent being overdosed, which results in undesirable secondary emissions, for example an NH ₃ slip.

In internal combustion engines that are already designed for use with an SCR device, the exhaust gas mass flow is typically determined in an internal combustion engine control device from internal combustion engine parameters such as the speed, the charge air pressure, the charge air temperature, a displacement of the internal combustion engine, and / or the air consumption calculated. A measured lambda value, that is to say the instantaneous combustion air / fuel ratio in the combustion chamber of the internal combustion engine, and a fuel mass supplied to the combustion chamber can also be used to calculate the exhaust gas mass flow. For this purpose, however, values are required that are only available internally in the internal combustion engine control unit, with internal combustion engines that are not intended for use with an SCR device having no interfaces in order to communicate such values to the outside. It is therefore not possible, or only possible with considerable effort, to retrofit internal combustion engines that are not originally set up for use with an SCR device with an SCR device.

the end EP 2 681 424 B1 discloses a method for operating an internal combustion engine device with an internal combustion engine and an exhaust system fluidly connected to the internal combustion engine for discharging exhaust gas from the internal combustion engine. An exhaust gas stream of the internal combustion engine flowing in the exhaust system is cleaned of nitrogen oxides, nitrogen oxide emissions of the internal combustion engine device being controlled by a nitrogen oxide reduction device which has an SCR catalytic converter located in the exhaust system and a controllable reducing agent metering device located in the exhaust system upstream of the SCR catalyst , controlled or regulated. An exhaust gas mass flow through the nitrogen oxide reduction device is determined on the basis of a mass flow of reducing agent and on the basis of a change in the nitrogen oxide content due to the nitrogen oxide conversion.

From Reif, K. [Hrsg.]: Exhaust technology for internal combustion engines. Wiesbaden: Springer Vieweg, 2015 (Bosch Fachinformation Automobil). P. 66. - ISBN 978-3-658-09521-5, describes a method for operating an internal combustion engine device with an internal combustion engine and an exhaust system fluidly connected to the internal combustion engine to discharge exhaust gas from the internal combustion engine. An exhaust gas stream of the internal combustion engine flowing in the exhaust system is cleaned of nitrogen oxides. Nitrogen oxide emissions of the internal combustion engine device are controlled or regulated by activating a nitrogen oxide reduction device which has an SCR catalytic converter arranged in the exhaust system and a controllable reducing agent metering device arranged in the exhaust gas system upstream of the SCR catalytic converter.

the end DE 101 00 419 A1 it emerges that an exhaust gas mass flow can be determined on the basis of a current consumption of a nitrogen oxide sensor and / or on the basis of a pressure difference between an inlet and outlet of a catalytic converter. the end DE 10 2013 219 371 A1 the determination of an exhaust gas mass flow using a differential pressure also emerges.

The invention is based on the object of creating a method for operating an internal combustion engine device as well as an internal combustion engine device and an SCR device for carrying out such a method, the disadvantages mentioned not occurring.

The object is achieved by creating the subjects of the independent claims. Advantageous refinements result from the subclaims.

The object is achieved in particular by creating a method in which, for operating an internal combustion engine device according to the type described above, it is provided that the exhaust gas mass flow passing through the SCR device is determined on the basis of at least one SCR parameter, the at least one SCR parameter. Parameter is selected from a group consisting of a control parameter of the SCR device and a parameter recorded on the SCR device. According to the invention, the exhaust gas mass flow is determined using a thermal model of the SCR device, with an exhaust gas temperature upstream of the SCR catalyst and an exhaust gas temperature downstream of the SCR catalyst being included in the thermal model. In this way, it is possible to calculate the exhaust gas mass flow on the basis of at least one variable that can be measured at the SCR device or is known in the SCR device. It is therefore easily possible to retrofit internal combustion engines with an SCR device in which no exhaust gas mass flow is calculated internally in a central internal combustion engine control unit or no variables are communicated to the outside via suitable interfaces that would be necessary to calculate the exhaust gas mass flow. Rather, the exhaust gas mass flow can be determined without recourse to the central internal combustion engine control unit on the basis of the variables provided by the SCR device, with the full functionality of the SCR device also being provided as a retrofit solution in a simple and cost-effective manner. There is neither a need to replace an older internal combustion engine control device nor a cumbersome and extensive installation of new software on such an internal combustion engine control device. The SCR device can then also be provided independently of a manufacturer of the internal combustion engine, so that even third-party motors can be retrofitted with such an SCR device by third-party providers.

An SCR parameter is understood here - as already stated - to be a control parameter for controlling the SCR device and / or a parameter recorded, in particular measured, on the SCR device. It is therefore either a default variable for controlling the SCR device, in particular a reducing agent metering rate with which the reducing agent metering device is controlled, or a variable measured by means of a sensor system on the SCR device, for example an exhaust gas temperature or a Nitrogen oxide content in the exhaust gas.

An SCR catalytic converter is understood to mean a catalytic device which is set up for the selective catalytic reduction of nitrogen oxides, in particular using a suitable reducing agent. It is particularly preferably a catalysis device that is set up to convert nitrogen oxides with ammonia to nitrogen and water, with urea in particular in the form of a urea-water solution being introduced into the exhaust system as a reducing agent or reducing agent precursor product via the reducing agent metering device can, wherein the urea in the exhaust gas stream is decomposed to ammonia. An SCR device is accordingly a device which has such an SCR catalysis device as an SCR catalytic converter.

According to a development of the invention, it is provided that the exhaust gas mass flow is determined exclusively on the basis of the at least one SCR parameter. In this case in particular, the method is outstandingly suitable for retrofitting internal combustion engines that have not previously been set up for operation with an SCR device.

Alternatively, however, it is also possible for at least one internal combustion engine parameter to be used to determine the exhaust gas mass flow in addition to the at least one SCR parameter, the at least one internal combustion engine parameter being selected from a group consisting of an internal combustion engine control parameter and an on the internal combustion engine detected parameters. This can possibly increase the accuracy of the calculation of the exhaust gas mass flow, with this embodiment of the method being used in particular when either the method itself is carried out on the central internal combustion engine control unit or when the internal combustion engine control unit has an interface for outputting at least one Having internal combustion engine control parameters, so that this can be used outside of the internal combustion engine control unit to carry out the method.

In particular, a fuel mass introduced into the combustion chambers of the internal combustion engine or a fuel mass flow, an instantaneous setpoint torque or the like come into consideration as internal combustion engine control parameters. A parameter detected on the internal combustion engine is, for example, an instantaneous speed of the internal combustion engine, an instantaneous charge air temperature, an instantaneous charge air pressure, an instantaneous combustion air-fuel ratio, an instantaneous torque applied by the internal combustion engine, an instantaneous stoichiometric air requirement, or the like. However, depending on the mode of operation of the internal combustion engine, such parameters can also be specified as internal combustion engine control parameters, and conversely one of the aforementioned internal combustion engine control parameters can optionally be configured as a parameter recorded on the internal combustion engine.

In a preferred embodiment, at least one additional SCR parameter can be used to determine the exhaust gas mass flow, the at least one additional SCR parameter being selected from a group consisting of a reducing agent metering rate, a nitrogen oxide content in the exhaust gas upstream of the SCR catalytic converter, a nitrogen oxide content in the exhaust gas downstream of the SCR catalytic converter, and a differential pressure that drops across the SCR catalytic converter.

As already stated above, a nitrogen oxide component is understood to mean, in particular, a nitrogen oxide concentration or a nitrogen oxide partial pressure, it being possible for the nitrogen oxide component to be given, in particular, in ppm. The nitrogen oxide component is in particular a total nitrogen oxide component, that is to say a cumulative component of nitrogen dioxide and nitrogen monoxide in the exhaust gas.

The differential pressure falling across the SCR catalytic converter can either be measured directly - using a suitable differential pressure sensor - or calculated from a first pressure measured upstream of the SCR catalytic converter and a second pressure measured downstream of the SCR catalytic converter - as a differential value will.

According to a further development of the invention, it is provided that the exhaust gas mass flow is determined in addition to the determination using the thermal model using a nitrogen oxide conversion rate measured on the SCR catalytic converter and a reducing agent metering rate used as a control parameter of the SCR device. This represents an embodiment of the method that is just as precise as it is easy to implement and particularly preferably can be carried out completely independently of internal combustion engine parameters, whereby it is by no means excluded that at least one internal combustion engine parameter can also be used to calculate the exhaust gas mass flow, in particular to increase the accuracy of the method .

The nitrogen oxide conversion rate η is defined as the difference between the nitrogen oxide component [NO _x ] 'in the exhaust gas upstream of the SCR catalytic converter and the nitrogen oxide component [NOx]''downstream of the SCR catalytic converter, divided by the nitrogen oxide component [ NO _x ] 'upstream of the SCR catalyst, expressed by the following equation: $$\eta =\frac{\left[N{O}_x\right]\text{'}-\left[N{O}_x\right]\text{'}\text{'}}{\left[N{O}_x\right]\text{'}}=1-\frac{\left[N{O}_x\right]\text{'}\text{'}}{\left[N{O}_x\right]\text{'}}$$

For the following consideration, one needs the ratio of the material flows - expressed in the amount of material per unit of time, in particular moles per second, of the reducing agent R and the accumulated nitrogen oxides (NO _x ), which is expressed by the following equation: $$\alpha =\frac{\dot{\mathrm{R.}}}{\left(N{\dot{O}}_x\right)}$$

wobei Ḋ die Reduktionsmittel-Dosierrate in Masse pro Zeiteinheit, insbesondere Gramm pro Sekunde, ist, und wobei M_R die Molmasse des Reduktionsmittels, insbesondere in Gramm pro Mol, ist. Der kumulierte Stickoxid-Stoffstrom (NȮ̇_x) ergibt sich gemäß folgender Gleichung: $$\left(N{\dot{O}}_x\right)=\frac{{\dot{m}}_A}{M_A}\left[N{O}_x\right]\text{'}$$

aus dem letztlich gesuchten Abgasmassenstrom ṁ_A dividiert durch die bekannte und zumindest in guter Näherung konstante Molmasse M_A des Abgases und multipliziert mit dem Stickoxid-Anteil [NO_X]' stromaufwärts des SCR-Katalysators. Setzt man die Gleichungen (3) und (4) in die Gleichung (2) ein, erhält man: $$\alpha =\frac{M_A}{M_R}\frac{\dot{D}}{\left[NOx\right]\text{'}}\frac{1}{{\dot{m}}_A}$$

Im stationären Fall gilt $$\alpha =\eta$$

dass nämlich die Umsatzrate η gleich dem Dosierverhältnis α ist.It is also referred to below as the metering ratio α. The reducing agent flow rate R results from the reducing agent metering rate according to the following equation: $$\dot{\mathrm{R.}}=\frac{\dot{\mathrm{D.}}}{{\mathrm{M.}}_{\mathrm{R.}}}$$

where Ḋ is the reducing agent metering rate in mass per unit of time, in particular grams per second, and where M _{R is} the molar mass of the reducing agent, in particular in grams per mole. The cumulative nitrogen oxide mass flow (NȮ̇ _x ) results from the following equation: $$\left(N{\dot{O}}_x\right)=\frac{{\dot{m}}_{\mathrm{A.}}}{{\mathrm{M.}}_{\mathrm{A.}}}\left[N{O}_x\right]\text{'}$$

from the exhaust gas mass flow ultimately sought ṁ _A divided by the known and at least in good approximation constant molar mass M _{A of} the exhaust gas and multiplied by the nitrogen oxide component [NO _X ] 'upstream of the SCR catalytic converter. Inserting equations (3) and (4) into equation (2) one obtains: $$\alpha =\frac{{\mathrm{M.}}_{\mathrm{A.}}}{{\mathrm{M.}}_{\mathrm{R.}}}\frac{\dot{\mathrm{D.}}}{\left[NOx\right]\text{'}}\frac{1}{{\dot{m}}_{\mathrm{A.}}}$$

In the stationary case, the following applies $$\alpha =\eta$$

namely that the conversion rate η is equal to the metering ratio α.

Thus, in the stationary case, the exhaust gas mass flow ṁ _A sought can ultimately be calculated in a simple manner from the measured nitrogen oxide components [NO _x ] ', [NO _x ]''and the specified reducing agent metering rate R, with - as already indicated - the molar masses of the exhaust gas M _A on the one hand and of the reducing agent M _R on the other hand are known and are constant at least in a very good approximation, so that they can be stored as fixed parameters.

For the sake of completeness, it should be added that, due to the temperature-dependent effect of the so-called direct oxidation, equation (6) does not apply without restrictions in practice even in the steady state, whereas a correction factor must be taken into account that specifies the - temperature-dependent - proportion of the reducing agent, which is without Reduction of nitrogen oxides is oxidized directly on the SCR catalyst. However, for the sake of simpler representation, this is not discussed, especially since the corresponding correction can be carried out in a simple manner by taking into account a temperature-dependent factor, the corresponding temperature-dependent factor being able to be determined in advance by means of test bench tests.

was einem PT1-Glied mit Totzeit entspricht, mit der Verstärkung K, der Zeitkonstante T, und der Totzeit T_t, wobei s in üblicher Weise die Laplace-Transformierte des Zeitparameters t darstellt. Die Parameter η₀ und α₀ geben den temperaturabhängigen Arbeitspunkt der SCR-Einrichtung an, wobei auch die Verstärkung K, die Zeitkonstante T und die Totzeit T_t temperatur- und damit arbeitspunktabhängig sind. Diese Parameter können aber vorab am Prüfstand vermessen und in Abhängigkeit von der an der SCR-Einrichtung messbaren Temperatur insbesondere in einem Kennfeld hinterlegt werden.In the dynamic case, equation (6) no longer applies without restriction, since additional effects occur due to the behavior of the SCR device over time. These result, for example, from the reducing agent storage behavior of the SCR catalytic converter. It is therefore necessary to use substitute models, preferably control-technical substitute models, for example a PT1 model, a PT1 model with dead time, or the like. One possible approach can be chosen as follows: $$\eta ={\eta }_0+\frac{K}{1+T\cdot s}{e}^{-T_t\cdot s}\left(\alpha -{\alpha }_0\right)$$

which corresponds to a PT1 element with dead time, with the gain K, the time constant T, and the dead time T _t , where s is the Laplace transform of the time parameter t in the usual way. The parameters η ₀ and α ₀ indicate the temperature-dependent operating point of the SCR device, the gain K, the time constant T and the dead time T _{t also being} temperature-dependent and thus dependent on the operating point. These parameters can, however, be measured in advance on the test bench and, depending on the temperature that can be measured on the SCR device, be stored in a characteristic map in particular.

wobei der einfacheren Darstellung wegen das Totzeitglied weggelassen wurde, zumal die Totzeit T_t durch zeitliches Verschieben aller Werte, die in die Berechnung des Dosierverhältnisses α sowie des Dosierverhältnisses α₀ am Arbeitspunkt eingehen, berücksichtigt werden kann.According to equation (5) in conjunction with equation (7), the mass flow rate ṁ _{A sought is contained in the metering ratio α.} Forming and inserting gives: $$\eta -{\eta }_0+\frac{K}{1+T\cdot s}{\alpha }_0=\frac{\frac{K}{{\dot{m}}_{\mathrm{A.}}}}{1+T\cdot s}\frac{{\mathrm{M.}}_{\mathrm{A.}}}{{\mathrm{M.}}_{\mathrm{R.}}}\frac{\dot{\mathrm{D.}}}{\left[N{O}_x\right]\text{'}}$$

The dead time element has been omitted for the sake of simplicity, especially since the dead time T _t can be taken into account by shifting all values that are included in the calculation of the metering ratio α and the metering ratio α _{0 at the operating point.}

mit den folgenden Definitionen: $$y*=\eta -{\eta }_0+\frac{K}{1+T\cdot s}{\alpha }_0$$

$$K*=\frac{K}{{\dot{m}}_A}$$

$$u*=\frac{M_A}{M_R}\frac{\dot{D}}{\left[N{O}_x\right]\text{'}}$$

leicht sieht. Gleichung (9) ist dabei einem Schätzverfahren ohne weiteres zugänglich, wobei insbesondere die Werte von K* und T aus den gemessenen und bekannten Werten der SCR-Einrichtung geschätzt werden können, und wobei sich gemäß Gleichung (11) aus dem geschätzten Wert für K* und der aus Prüfstandsversuchen bekannten Verstärkung K ohne weiteres der gesuchte Abgasmassenstrom ṁ_A berechnen lässt. Auch die Zeitkonstante T kann - wie oben ausgeführt - grundsätzlich aus Prüfstandsversuchen bekannt sein, wobei ein so erhaltener Wert ohne weiteres verwendet werden kann. Er kann aber auch im Rahmen des Schätzverfahrens mitgeschätzt werden, wobei diese Vorgehensweise auch zusätzlich angewendet werden kann, um die Genauigkeit des Verfahrens zu verbessern.Equation (8) again corresponds to the typical shape of a PT1 element, which can be seen in the following illustration: $$y*=\frac{K*}{1+T\cdot s}u*$$

with the following definitions: $$y*=\eta -{\eta }_0+\frac{K}{1+T\cdot s}{\alpha }_0$$

$$K*=\frac{K}{{\dot{m}}_{\mathrm{A.}}}$$

$$u*=\frac{{\mathrm{M.}}_{\mathrm{A.}}}{{\mathrm{M.}}_{\mathrm{R.}}}\frac{\dot{\mathrm{D.}}}{\left[N{O}_x\right]\text{'}}$$

easily sees. Equation (9) is easily accessible to an estimation method, wherein in particular the values of K * and T can be estimated from the measured and known values of the SCR device, and according to equation (11) from the estimated value for K * and the gain K known from test bench tests allows the _{exhaust gas mass flow ṁ A to be calculated without further ado.} As explained above, the time constant T can in principle also be known from test bench tests, it being possible to use a value obtained in this way without further ado. However, it can also be estimated as part of the estimation procedure, and this procedure is also used can additionally be used to improve the accuracy of the method.

The accuracy of the method can be further improved in that at least one internal combustion engine parameter can also be used. For example, instead of the exhaust gas mass flow, only a correction factor for a rough calculation value can then be determined. If, for example, the degree of delivery is not known, but the charge air temperature and charge air pressure can be measured, it is possible to transform the equations so that a rough calculation value is included for the input variables u *, where in K * the known K and then the Insert the correction factor you are looking for, which corresponds to the degree of delivery. If the charge air temperature and the charge air pressure are also not known, then fixed, typical values can be assumed for this, with deviations in real operation being able to be mapped in the correction factor. The more motor variables are known, the closer the correction factor is to the value 1 lie, and the smaller its fluctuations will be. The estimation of the correct exhaust gas mass flow ṁ _A thus works better, the more quantities are available.

Values for the exhaust gas mass flow resulting from the estimation method can also be stored - in particular as a function of measured or set parameters - and retrieved later - in particular again as a function of measured or set parameters - as starting values for the estimation method.

In particular, if at least one internal combustion engine parameter is also used to determine the exhaust gas mass flow, it is possible to store the respectively estimated exhaust gas mass flow or correction factor in at least one characteristic map as a function of the at least one internal combustion engine parameter. If an operating point corresponding to a specific value or a value combination of the at least one internal combustion engine parameter is reached again at a later point in time, the value of the exhaust gas mass flow or correction factor assigned to the specific value or the value combination of the at least one internal combustion engine parameter can be read out again and in particular as a starting value for the estimation method can be used. This can speed up the process.

According to the invention, the exhaust gas mass flow is determined using a thermal model of the SCR device, with an exhaust gas temperature upstream of the SCR catalyst and an exhaust gas temperature downstream of the SCR catalyst being included in the thermal model. The exhaust gas mass flow can be determined exclusively using the thermal model or using the thermal model in combination with the method presented above. In particular, it is possible that the thermal model is used to calculate a starting value, the exact value of the exhaust gas mass flow then being able to be determined as explained above in connection with equations (1) to (12).

mit der Abgas-Temperatur $T_A^{\text{'}}$

stromaufwärts des SCR-Katalysators, der Abgas-Temperatur $T_A^{\text{'}\text{'}}$

stromabwärts des SCR-Katalysators sowie deren zeitlicher Ableitung ${\dot{T}}_A^{\text{'}\text{'}},$

dem Abgasmassenstrom ṁ_A, der spezifischen Wärmekapazität c_p,A des Abgases, die als konstanter Parameter oder unter Berücksichtigung einer leichten Temperaturabhängigkeit fest hinterlegt sein kann, dem bekannten und fest hinterlegten Produkt h aus einem Wärmeübergangskoeffizient und der Oberfläche des SCR-Katalysators, der Wärmekapazität C_SCR des SCR-Katalysators, und der Umgebungstemperatur T_u, die als Messwert vorhanden, als fester, konstanter Wert angenommen und hinterlegt, oder auch vernachlässigt werden kann. Der modellgemäßen Gleichung (13) liegt insbesondere die Annahme zugrunde, dass die Abgas-Temperatur $T_A^{\text{'}\text{'}}$

stromabwärts des SCR-Katalysators zumindest im Wesentlichen der Temperatur des SCR-Katalysators entspricht, da diese Temperatur des Abgases aufgrund der hohen Oberfläche des SCR-Katalysators stark an die Temperatur des SCR-Katalysators gekoppelt ist. In der Praxis zeigt sich, dass detailliertere Ansätze, bei denen separat eine Katalysator-Temperatur und eine Abgas-Temperatur berechnet werden, keinen nennenswerten Unterschied zu den Ergebnissen nach Gleichung (13) ergeben.Such a thermal model can be selected as follows, for example: $${\dot{T}}_{\mathrm{A.}}^{\text{'}\text{'}}=\frac{{\dot{m}}_{\mathrm{A.}}{c}_{p,\mathrm{A.}}\left(T_{\mathrm{A.}}^{\text{'}}-T_{\mathrm{A.}}^{\text{'}\text{'}}\right)-H\left(\frac{T_{\mathrm{A.}}^{\text{'}}+T_{\mathrm{A.}}^{\text{'}\text{'}}}{2}-T_u\right)}{{\mathrm{C.}}_{\mathrm{S.}\mathrm{C.}\mathrm{R.}}}$$

with the exhaust gas temperature $T_{\mathrm{A.}}^{\text{'}}$

upstream of the SCR catalyst, the exhaust gas temperature $T_{\mathrm{A.}}^{\text{'}\text{'}}$

downstream of the SCR catalytic converter and its time derivative ${\dot{T}}_{\mathrm{A.}}^{\text{'}\text{'}},$

the exhaust gas mass flow ṁ _A , the specific heat capacity c _{p, A of} the exhaust gas, which can be permanently stored as a constant parameter or taking into account a slight temperature dependency, the known and permanently stored product h of a heat transfer coefficient and the surface of the SCR catalytic converter, the heat capacity C _{SCR of} the SCR catalytic converter, and the ambient temperature T _u , which is available as a measured value, accepted and stored as a fixed, constant value, or can also be neglected. The model equation (13) is based in particular on the assumption that the exhaust gas temperature $T_{\mathrm{A.}}^{\text{'}\text{'}}$

downstream of the SCR catalytic converter corresponds at least substantially to the temperature of the SCR catalytic converter, since this temperature of the exhaust gas is strongly linked to the temperature of the SCR catalytic converter due to the high surface area of the SCR catalytic converter. In practice, it has been shown that more detailed approaches, in which a catalytic converter temperature and an exhaust gas temperature are calculated separately, do not produce any significant difference to the results according to equation (13).

In this way, in particular, a first rough estimate of the exhaust gas mass flow can be made from the known heat capacity of the SCR catalytic converter and the measured temperature values upstream and downstream of the SCR catalytic converter. A differentiation filter is preferably used in order to generate derivation values that are as good as possible from noisy temperature measurement values.

stromabwärts des SCR-Katalysators mithilfe eines sogenannten Ableitungsfilters ein Wert für die zeitliche Temperaturableitung ${\dot{T}}_A^{\text{'}\text{'}}$

erzeugt werden. Der Ableitungsfilter sorgt dafür, dass eine ausreichende Filterung vorgenommen wird, um Effekte durch Messrauschen zu unterdrücken, die ansonsten zu falschen Ableitungswerten führen würden. Eine zu starke Filterung kann aber in unerwünschter Weise zu einer zeitlich verzögerten Ableitung der Temperatur führen. Bevorzugt werden die Temperaturmesswerte mit einem einfachen PT1-Filter gefiltert, um dann numerisch eine Ableitung zu erzeugen. Bessere Ergebnisse werden erzielt, wenn spezielle Ableitungsfilter verwendet werden, bei denen in einem Schritt Filterung und Bildung der Ableitung durchgeführt werden. Solche Filter sind aus der Signalverarbeitung für sich genommen bekannt.In particular, the measured value for the temperature $T_{\mathrm{A.}}^{\text{'}\text{'}}$

downstream of the SCR catalytic converter, a value for the temperature derivative over time with the aid of a so-called discharge filter ${\dot{T}}_{\mathrm{A.}}^{\text{'}\text{'}}$

be generated. The derivative filter ensures that sufficient filtering is carried out in order to suppress effects caused by measurement noise that would otherwise lead to incorrect derivative values. However, excessive filtering can undesirably lead to a time-delayed derivation of the temperature. The measured temperature values are preferably filtered with a simple PT1 filter in order to then generate a numerical derivative. Better results are achieved if special derivation filters are used, in which filtering and formation of the derivation are carried out in one step. Such filters are known per se from signal processing.

All the variables from equation (13) are then known except for the exhaust gas mass flow ṁ _A sought, which can be determined from the time course of the measured values with the aid of an estimation method.

As already stated, a starting value for the exhaust gas mass flow ṁ _{A is} particularly preferably determined in this way, with the subsequent determination of more precise values then being able to take place using the method described above in connection with equations (1) to (12).

Alternatively or additionally, it is also possible to determine or at least roughly estimate the exhaust gas mass flow using the differential pressure across the SCR catalytic converter, a principle relationship indicating that the exhaust gas volume flow is proportional to the square root of the differential pressure. The exhaust gas mass flow can then be calculated back from the volume flow estimated in this way, taking into account the known density of the exhaust gas. The linear relationship or the constant describing it can in particular be determined on the basis of test bench tests. However, this procedure is comparatively coarse and imprecise, in particular because the pressure drop across the SCR catalytic converter is typically small.

According to a further development of the invention, it is provided that the exhaust gas mass flow is determined by an estimation method - as already indicated above. The estimation method is preferably selected from a group consisting of the method of least squares, a maximum likelihood estimation, which in particular represents a variant of the method of least squares, the condition monitoring for systems with unknown inputs, this procedure also as "Unknown Input Observer “Or principle of the observer, and a Kalman filter.

When monitoring the status of systems with unknown inputs, in particular the measured conversion rate η can be _{compared with a calculated conversion rate η M} , the difference thus obtained being used as the actual value and compared with a target value, which is preferably determined to be 0, The resulting control deviation is fed into a controller that _{outputs a model value α M} for the dosing ratio, from which the model value _{for the conversion rate η M is} calculated using a dynamic model, for example in the form of a PT1 element with dead time. In this way, a control loop is created in which the model value for the metering ratio α _M is adapted in such a way that the deviation between the measured conversion rate η and the modeled conversion rate η _M disappears. The value optimized in this way for the modeled metering ratio α _M can then in turn be converted into the exhaust gas mass flow sought on the basis of the specified reducing agent metering rate and the measured nitrogen oxide content upstream of the SCR catalytic converter.

The controller for calculating the modeled metering ratio α _M can be, for example, a P controller or a PI controller.

A Kalman filter is, in particular, a method in which the states or parameters of a model are estimated with knowledge of the dynamic model and measured values of input and output variables. Statistical properties of the signals are taken into account. Such a Kalman filter is known per se, so that it will not be discussed in detail.

The current conversion rate η can be determined according to the relationships discussed above from the measured nitrogen oxide components [NO _x ] ', [NO _x ]''in the exhaust gas upstream and downstream of the SCR catalytic converter, the current reducing agent metering rate Ṙ also being known . With the help of an estimation method in particular, it is possible _{to determine the unknown exhaust gas mass flow ṁ A} from these values using a model context.

According to a further development of the invention, it is provided that, in addition to the exhaust gas mass flow, at least one dynamic parameter for describing a dynamic behavior of the SCR device is determined from the estimation method. Such a dynamic parameter can in particular be a dead time, a time constant of the SCR device and / or a gain.

Alternatively or additionally, it is possible that a lower limit for a confidence or confidence range of the exhaust gas mass flow is determined from the estimation method. Such a confidence range can be obtained directly from an estimation method. However, it is also possible for the confidence range and in particular its lower limit to be determined from the values that result for the exhaust gas mass flow from the estimation method using a statistical evaluation. Depending on the specific estimation method used, this directly provides a lower limit for the confidence range, or an additional statistical evaluation of the results obtained for the exhaust gas mass flow is required. As will be shown in the following, this lower limit of the confidence range can advantageously be used to specify the reducing agent metering rate.

According to a further development of the invention, it is provided that a lower estimate for the exhaust gas mass flow is used to regulate the nitrogen oxide emissions of the internal combustion engine device and in particular to control the reducing agent metering device. In particular, the current reducing agent metering rate is preferably predefined on the basis of the lower estimate for the exhaust gas mass flow. In this way, it can be effectively prevented that an excessively high amount of reducing agent is metered into the exhaust gas line, as a result of which secondary emissions, in particular an NH ₃ slip, can be avoided.

The lower limit of the confidence range of the exhaust gas mass flow already described above, which can be obtained - directly or indirectly - from the estimation method for estimating the exhaust gas mass flow, can particularly preferably be used as the lower estimate for the exhaust gas mass flow.

It is not absolutely necessary that the lower estimate is used directly as a value for the exhaust gas mass flow. Here it is also possible to provide a correction factor or a function so that ultimately the assumed exhaust gas mass flow is determined, in particular calculated, on the basis of the lower estimate. In particular, the risk of underestimating the actual exhaust gas mass flow and thus an excessively high nitrogen oxide emission and the risk of overestimating the actual exhaust gas mass flow and thus an overdose of reducing agent and the promotion of secondary emissions can be made.

The object is finally also achieved in that an internal combustion engine device is created which has an internal combustion engine and an exhaust system, the exhaust system being fluidically connected to the internal combustion engine for discharging exhaust gas from the internal combustion engine. The internal combustion engine device has a control device which is set up to carry out a method according to one of the embodiments described above. The internal combustion engine device has an SCR device in its exhaust system, which in turn has an SCR catalytic converter and a controllable reducing agent metering device. The SCR device has in particular a nitrogen oxide sensor upstream of the SCR catalytic converter and a nitrogen oxide sensor downstream of the SCR catalytic converter, which are operatively connected to the control device. The reducing agent metering device is operatively connected to the control device in such a way that the control device can specify a reducing agent metering rate for the reducing agent metering device or control the reducing agent metering device at the reducing agent metering rate.

The SCR device preferably has a first temperature sensor upstream of the SCR catalytic converter and a second temperature sensor downstream of the SCR catalytic converter in the exhaust system. The SCR device preferably has a differential pressure sensor for measuring a differential pressure across the SCR catalytic converter, or a first pressure sensor for detecting an exhaust gas pressure upstream of the SCR catalytic converter and a second pressure sensor for detecting an exhaust gas pressure downstream of the SCR catalytic converter. These sensors are also preferably operatively connected to the control device.

In connection with the internal combustion engine device, there are in particular the advantages that have already been explained in connection with the method.

According to a further development of the invention it is provided that the control device - in particular as an SCR control device - is designed separately from an internal combustion engine control device, the internal combustion engine control device being set up to control the internal combustion engine. The internal combustion engine control device can in particular be a control unit of the internal combustion engine. Since the control device is set up to carry out an embodiment of the method described above, it is possible to operate it separately from the control unit of the internal combustion engine. Alternatively, however, it is also possible for the control unit of the internal combustion engine itself to be designed as a control device which is set up to carry out an embodiment of the method described above.

The internal combustion engine is preferably designed as a reciprocating piston engine. It is possible that the Internal combustion engine is set up to drive a passenger car, a truck or a utility vehicle. In a preferred embodiment, the internal combustion engine is used to drive particularly heavy land or water vehicles, for example mining vehicles, trains, the internal combustion engine being used in a locomotive or a railcar, or ships. It is also possible to use the internal combustion engine to drive a vehicle used for defense, for example a tank. An exemplary embodiment of the internal combustion engine is preferably also used in a stationary manner, for example for stationary energy supply in emergency power operation, continuous load operation or peak load operation, the internal combustion engine in this case preferably driving a generator. Stationary use of the internal combustion engine to drive auxiliary units, for example fire pumps on drilling rigs, is also possible. It is also possible to use the internal combustion engine in the field of conveying fossil raw materials and, in particular, fuels, for example oil and / or gas. It is also possible to use the internal combustion engine in the industrial sector or in the construction sector, for example in a construction or construction machine, for example in a crane or an excavator. The internal combustion engine is preferably designed as a diesel engine, as a gasoline engine, as a gas engine for operation with natural gas, biogas, special gas or another suitable gas. In particular, if the internal combustion engine is designed as a gas engine, it is suitable for use in a block-type thermal power station for stationary energy generation.

Finally, the object is also achieved by creating an SCR control device which is set up to carry out an embodiment of the aforementioned method. In connection with the SCR control device, the advantages that have already been explained in connection with the method and the internal combustion engine device are realized in particular. Such an SCR control device can in particular be used to retrofit already existing internal combustion engines that are not designed for operation with an SCR device.

The SCR control device preferably has suitable interfaces to sensors of the SCR device, in particular an interface to nitrogen oxide sensors upstream and downstream of the SCR catalytic converter, to temperature sensors upstream and downstream of the SCR catalytic converter and / or to a differential pressure sensor or to pressure sensors upstream and downstream of the SCR catalyst. The SCR control device is also preferably set up to preset a reducing agent metering rate to the reducing agent metering device.

It is possible for the SCR control device to have an interface for connection to an internal combustion engine control device. In this case, parameters of the internal combustion engine control device can also be used in the SCR control device.

A nitrogen oxide limit value is preferably stored in the SCR control device, in particular in units of mass per unit of energy, in particular in grams per kilowatt hour.

The invention is explained in more detail below with reference to the drawing. The single FIGURE shows a schematic representation of an exemplary embodiment of an internal combustion engine device and an SCR control device, which are set up to carry out an embodiment of a method for operating the internal combustion engine device.

The single FIGURE shows a schematic representation of an exemplary embodiment of an internal combustion engine device 1 who have favourited an internal combustion engine 3 and one with the internal combustion engine 3 for discharging exhaust gas from the internal combustion engine 3 fluid-connected exhaust line 5 having. In the exhaust system 5 is a nitrogen oxide reduction device - or SCR device for short 7th - Arranged, the one in the exhaust line 5 arranged SCR catalytic converter 9 and one in the exhaust line 5 upstream of the SCR catalyst 9 arranged, controllable reducing agent metering device 11 which is set up to add a reducing agent or a reducing agent precursor product, preferably an aqueous urea solution, into the exhaust system 5 metered in, the reducing agent either directly injected or formed from the reducing agent precursor product in the exhaust gas flow being suitable for being applied to the SCR catalytic converter 9 to be reacted with nitrogen oxides contained in the exhaust gas flow, so that the nitrogen oxides are preferably reduced to nitrogen and water.

In the context of one embodiment of a method for operating the internal combustion engine device 1 becomes the one in the exhaust system 5 flowing exhaust gas stream of the internal combustion engine 3 cleaned of nitrogen oxides, with nitrogen oxide emissions of the internal combustion engine device 1 by controlling the controllable reducing agent metering device 11 controlled or regulated. For this open-loop or closed-loop control, the most precise possible knowledge of the exhaust gas mass flow through the SCR catalytic converter is required 9 , since target emission values are typically specified in absolute numbers, in particular in g / kWh, while one of the SCR facility 7th The sensor system included can detect a relative nitrogen oxide content in the exhaust gas flow, that is to say in particular a nitrogen oxide concentration or a nitrogen oxide partial pressure. In particular, an absolute amount of reducing agent to be metered in or a metering rate can only be calculated with knowledge of the exhaust gas mass flow.

In the context of the method proposed here for operating the internal combustion engine device 1 it is provided that the exhaust gas mass flow through the SCR device 7th is determined on the basis of at least one SCR parameter, the at least one SCR parameter being selected from a group consisting of a control parameter of the SCR device 7th and one at the SCR facility 7th recorded parameters. An internal combustion engine can also do this in this way 3 that were not originally designed for operation with an SCR device 7th is set up, can be retrofitted and operated with such, it being possible to determine the exhaust gas mass flow, even if this is not in a central control unit of the internal combustion engine 3 is calculated, and / or no parameters suitable for calculating the exhaust gas mass flow from the central control unit of the internal combustion engine 3 - in particular via suitable interfaces - are communicated to the outside world.

According to a preferred embodiment, the exhaust gas mass flow is determined exclusively on the basis of the at least one SCR parameter. It is also possible, however, to use at least one internal combustion engine parameter in addition to the at least one SCR parameter to determine the exhaust gas mass flow, which can in particular be selected from a group consisting of an internal combustion engine control parameter for controlling the internal combustion engine 3 and one on the internal combustion engine 3 recorded parameters. The internal combustion engine parameter can in particular be a speed of the internal combustion engine 3 , a charge air temperature, a charge air pressure, a combustion air-fuel ratio, a target or actual torque, a fuel mass introduced or to be introduced into a combustion chamber or a fuel mass flow, or a stoichiometric air requirement.

The at least one SCR parameter is preferably selected from a group consisting of a reducing agent metering rate, an exhaust gas temperature upstream of the SCR catalytic converter, an exhaust gas temperature downstream of the SCR catalytic converter 9 , a nitrogen oxide component upstream of the SCR catalytic converter 9 , a nitrogen oxide component downstream of the SCR catalytic converter 9 , and one above the SCR catalytic converter 9 falling differential pressure. In order to record such parameters, the SCR device 7th preferably different sensors. In particular, it preferably has a first nitrogen oxide sensor 12.1 upstream of the SCR catalyst 9 and a second nitrogen oxide sensor 12.2 downstream of the SCR catalyst 9 on. It also preferably has a first temperature sensor 13.1 upstream of the SCR catalyst 9 and a second temperature sensor 13.2 downstream of the SCR catalyst 9 on. It is possible to record the differential pressure across the SCR catalytic converter 9 a differential pressure sensor is provided. According to the embodiment shown here, however, the SCR device 7th a first pressure sensor 15.1 upstream of the SCR catalyst 9 and a second pressure sensor 15.2 downstream of the SCR catalyst 9 on, the one above the SCR catalytic converter 9 falling differential pressure as the difference between the signals from the pressure sensors 15.1 , 15.2 can be calculated.

The internal combustion engine device 1 has an SCR controller 17th that is set up to carry out the method described here. The SCR control device is for this purpose 17th with the various sensors of the SCR device 7th , that is, with the nitrogen oxide sensors 12.1 , 12.2 , the temperature sensors 13.1 , 13.2 and the pressure sensors 15.1 , 15.2 effectively connected. It is also connected to the reducing agent metering device 11 for their control, in particular for specifying a reducing agent metering rate, operatively connected. The SCR control device 17th is also preferred with the internal combustion engine 3 operatively connected in order to be able to use at least one internal combustion engine parameter to determine the exhaust gas mass flow.

In the exemplary embodiment shown here, the SCR control device is 17th as a separate control device, in particular independent and separate from a central control unit, not shown, of the internal combustion engine 3 educated. This is a particularly suitable embodiment for retrofitting existing internal combustion engines 3 that have not yet been set up for operation with an SCR device 7th . But it is just as possible that the SCR control device 17th as the central control unit of the internal combustion engine 3 is designed, which can ultimately mean in particular that the functionality of the SCR control device 17th , in particular the implementation of the method described here, in the central control unit of the internal combustion engine 1 integrated, in particular implemented in the form of a suitable computer program.

The exhaust gas mass flow is preferred - in particular exclusively, but not necessarily exclusively - on the basis of an on the SCR catalytic converter 9 measured nitrogen oxide conversion rate and one as a control parameter of the SCR device 7th used reducing agent metering rate is calculated. The nitrogen oxide conversion rate can be determined by comparing the signals from the nitrogen oxide sensors 12.1 , 12.2 be determined.

Alternatively or additionally, it is possible that the exhaust gas mass flow is calculated using a thermal model of the SCR device 7th , in which an exhaust gas temperature upstream of the SCR catalytic converter 9 and an exhaust gas temperature downstream of the SCR catalyst 9 received, to be determined. The exhaust gas mass flow can only be determined using the thermal model. In particular, however, it is also possible to determine the thermal model in combination with the determination of the exhaust gas mass flow on the basis of the nitrogen oxide conversion rate and the reducing agent metering rate. This can in particular also take place one after the other, a first starting value for the exhaust gas mass flow being determined using the thermal model, this value being optimized or improved on the basis of the nitrogen oxide conversion rate and the reducing agent metering rate.

The exhaust gas mass flow is preferably calculated by an estimation method, the estimation method preferably being selected from a group consisting of the least squares method, a maximum likelihood estimation method, state monitoring for systems with unknown inputs, and a Kalman filter.

In addition to the exhaust gas mass flow, at least one dynamic parameter, in particular a dead time, a time constant, and / or a gain, for describing a dynamic behavior of the SCR device is preferably also derived from the estimation method 7th determined. Alternatively or additionally, it is possible for a lower limit for a confidence range of the exhaust gas mass flow to be determined from the estimation method. This can result directly from the estimation method, or it can be calculated from the values for the exhaust gas mass flow obtained with the help of the estimation method using a statistical method.

It is preferably provided that a lower estimate for the exhaust gas mass flow is used to regulate the nitrogen oxide emissions of the internal combustion engine device. In this way, an overdosage of the reducing agent due to an overestimation of the actual exhaust gas mass flow can be avoided, which helps to prevent secondary emissions, in particular an ammonia slip. The lower limit of the confidence range obtained from the estimation method is preferably used as the lower estimate for the exhaust gas mass flow.

Overall, it can be seen that with the method proposed here and the internal combustion engine device 1 and the SCR controller 17th precise knowledge of the exhaust gas mass flow is possible even if it is not in a central control unit of an internal combustion engine 3 is calculated, and / or if the central control unit of the internal combustion engine 3 no parameter values suitable for calculating the exhaust gas mass flow are communicated to the outside world. It is thus possible in a simple, functional and operationally reliable manner, including internal combustion engines 3 with an SCR facility 7th to equip and, in particular, to retrofit, which are not originally intended for operation with an SCR device 7th are set up.

Claims (10)

A method for operating an internal combustion engine device (1) with an internal combustion engine (3) and an exhaust gas line (5) fluidly connected to the internal combustion engine (3) for discharging exhaust gas from the internal combustion engine (3), wherein - An exhaust gas stream of the internal combustion engine (3) flowing in the exhaust system (5) is cleaned of nitrogen oxides, wherein - Nitrogen oxide emissions of the internal combustion engine device (1) by controlling a nitrogen oxide reduction device (7) which has an SCR catalytic converter (9) arranged in the exhaust gas line (5) and one arranged in the exhaust gas line (5) upstream of the SCR catalytic converter (9), has controllable reducing agent metering device (11), controlled or regulated, wherein - An exhaust gas mass flow through the nitrogen oxide reduction device (7) is determined on the basis of at least one SCR parameter selected from a group consisting of a control parameter of the nitrogen oxide reduction device (7) and a parameter detected on the nitrogen oxide reduction device (7) , and where - The exhaust gas mass flow is determined on the basis of a thermal model of the nitrogen oxide reduction device (7), in which an exhaust gas temperature upstream of the SCR catalytic converter (9) and an exhaust gas temperature downstream of the SCR catalytic converter (9) are determined. Procedure according to Claim 1 , characterized in that the exhaust gas mass flow is additionally determined on the basis of a nitrogen oxide conversion rate measured on the SCR catalytic converter (9) and a reducing agent metering rate used as a control parameter of the nitrogen oxide reduction device (7). Procedure according to Claim 1 or 2 , characterized in that a) the exhaust gas mass flow is determined exclusively on the basis of the at least one SCR parameter, or that b) to determine the exhaust gas mass flow, in addition to the at least one SCR parameter, at least one internal combustion engine parameter selected from a group consisting of an internal combustion engine control parameter and a on the internal combustion engine (3) detected parameters is used. Method according to one of the preceding claims, characterized in that the exhaust gas mass flow is determined by an estimation method. Procedure according to Claim 4 , characterized in that the estimation method is selected from a group consisting of a least squares method, a maximum likelihood estimation method, a state observation for systems with unknown inputs, and a Kalman filter. Method according to one of the preceding claims, characterized in that in addition to the exhaust gas mass flow from the estimation method a) at least one dynamic parameter for describing a dynamic behavior of the nitrogen oxide reduction device (7), and / or b) a lower limit for a confidence range of the exhaust gas mass flow is determined. Method according to one of the preceding claims, characterized in that a lower estimate for the exhaust gas mass flow is used to regulate the nitrogen oxide emissions of the internal combustion engine device (1). Internal combustion engine device (1), with an internal combustion engine (3) and an exhaust line (5) fluidly connected to the internal combustion engine (3) for discharging exhaust gas from the internal combustion engine (3), characterized in that the internal combustion engine device (1) has a control device (17), which is set up to carry out a method according to one of the Claims 1 until 7th . Internal combustion engine device (1) according to Claim 8 , characterized in that the control device (17) is designed separately from an internal combustion engine control device of the internal combustion engine (3). SCR control device (17), set up to carry out a method according to one of the Claims 1 until 7th .

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