INTERNAL COMBUSTION ENGINE WITH EXHAUST GAS AFTERTREATMENT AND CONTROL OF THE NITROGEN OXIDE EMISSIONS

Abstract

An internal combustion engine (1), with an engine regulating device (3) and an exhaust gas aftertreament device (16) with an SCR catalytic converter (4) for the reduction of at least one NO.sub.x component, and with a catalytic converter regulating device (6), wherein the engine regulating device (3) is prescribed a target value for an NO.sub.x mean value of the NO.sub.x component of the exhaust gases, which mean value results at an outlet point (7) of the exhaust gas aftertreatment device (16) in relation to a predefinable time period, and the engine regulating device (3) is configured at least in one operating mode to continuously calculate an NO.sub.x reference value for the catalytic converter regulating device (6) with consideration of No.sub.x components which have already been emitted and the predefined target value, which reference value is selected in such a way that the predefined target value results at the outlet point of the exhaust gas aftertreatment device (16) at the end of the predefinable time period when the calculated NO.sub.x reference value of the catalytic converter regulating device (6) is fed as NO.sub.x setpoint value to the regulating means.

Claims

1. A system, comprising: an internal combustion engine, comprising: an engine block having a plurality of piston-cylinder units configured to combust an air-fuel mixture to produce exhaust gases containing a NO.sub.x proportion or component; an exhaust gas aftertreatment apparatus (16) configured to aftertreat the exhaust gas to reduce the NO.sub.x proportion or component, wherein the exhaust gas aftertreatment apparatus has at least one SCR catalytic converter and a catalytic converter closed-loop control configured to open-loop or closed-loop control the at least one SCR catalytic converter; and an engine closed-loop control unit configured to control operation of the engine block, wherein: the engine closed-loop control unit is configured to be prescribed a target value (NO.sub.x.sub.,Tar) for a NO.sub.x average value (NO.sub.x) of the NO.sub.x proportion or component of the exhaust gases, that occurs in relation to a predeterminable or predetermined period of time (t.sub.av) at a discharge from the exhaust gas aftertreatment apparatus; the engine closed-loop control unit is configured at least in one operating mode to continuously calculate a NO.sub.x reference value (NO.sub.x,Ref(t)) for the catalytic converter closed-loop control having regard to already emitted NO.sub.x proportions or components and the predeterminable or predetermined target value (NO.sub.x.sub.,Tar), wherein the NO.sub.x reference value is so selected that at the end of a predeterminable or predetermined period of time (t.sub.av) the predeterminable or predetermined target value (NO.sub.x.sub.,Tar) results at the discharge of the exhaust gas aftertreatment apparatus; and the calculated NO.sub.x reference value (NO.sub.x,Ref(t)) is fed to the catalytic converter closed-loop control as an NO.sub.x setpoint value.

2. The system of claim 1, wherein the engine closed-loop control unit is configured to calculate the NO.sub.x reference value (NO.sub.x,Ref(t)) for the catalytic converter closed-loop control continuously in accordance with the following formula: ${\mathrm{NO}}_{x,\mathrm{Ref}}\left(t\right)=\frac{1}{t_2-t}\left(t_{\mathrm{av}}.Math.\stackrel{\_}{N}{\stackrel{\_}{O}}_{x,\mathrm{Tar}}-{\int }_{t_1}^t{\mathrm{NO}}_x\left(t^{\prime }\right){\mathrm{dt}}^{\prime }\right)$ or having regard to NO proportions or components in the exhaust gases that have already occurred prior to the beginning of the period of time t.sub.av in cumulated form (cumulNO.sub.x) in accordance with the following formula: ${\mathrm{NO}}_{x,\mathrm{Ref}}\left(t\right)=\frac{1}{t_2-t}\left(t_{\mathrm{av}}.Math.\stackrel{\_}{N}{\stackrel{\_}{O}}_{x,\mathrm{Tar}}-{\int }_{t_1}^t{\mathrm{NO}}_x\left(t^{\prime }\right){\mathrm{dt}}^{\prime }-{\mathrm{cumulNO}}_x\right)$

3. The system of claim 1, wherein the engine closed-loop control unit is configured to control operation of the engine block based on a state of the engine block and a state of the exhaust gas aftertreatment apparatus.

4. The system of claim 1, wherein the engine closed-loop control unit is configured to control operation of the engine block based on a state of the exhaust gas aftertreatment apparatus comprising a current conversion rate (R.sub.conv(t)).

5. The system of claim 1, wherein the engine closed-loop control unit is configured, at least after an expiry of a starting time of the internal combustion engine, to provide for open-loop and/or closed-loop control of a current operating point of the engine block in dependence on a conversion rate (R.sub.conv(t)) of the exhaust gas aftertreatment apparatus.

6. The system of claim 1, wherein the engine closed-loop control unit is configured to move a current operating point of the engine block away from a first operating point to a transient operating point with lower NO.sub.x emissions if the at least one SCR catalytic converter of the exhaust gas aftertreatment apparatus reduces fewer NO.sub.x proportions or components than is required to attain the NO.sub.x reference value (NO.sub.x,Ref(t)) at the discharge of the exhaust gas aftertreatment apparatus.

7. The system of claim 1, wherein the engine closed-loop control unit is configured to take account of a mechanical actual power output (P.sub.m,ist) of the internal combustion engine or an electrical actual power output (P.sub.el,ist) of an electrical generator coupled to the internal combustion engine in control of the engine block and the catalytic converter closed-loop control.

8. The system of claim 1, comprising an injector configured to inject a reducing agent into an exhaust gas manifold before a catalytic zone of the at least one SCR catalytic converter and the catalytic converter closed-loop control provides for open-loop or closed-loop control of an amount (Redux) of the reducing agent converted in the at least one SCR catalytic converter.

9. The system of claim 1, wherein the engine closed-loop control unit, for reduction of the exhaust gas NO proportion or component emitted during a starting time of the internal combustion engine, is configured during the starting time of the internal combustion engine to predetermine a power ramp for the engine block in a first time portion, after a power output reaches a minimum power output, until the power output reaches a predetermined limit value with a first lesser gradient and in a second time portion until the power output reaches a nominal power output of the internal combustion engine with a second greater gradient, wherein the second greater gradient is calculated in dependence on a remaining time until the starting time is reached.

10. The system of claim 1, wherein the engine closed-loop control unit, for reduction of the exhaust gas NO.sub.x proportion or component emitted during a starting time of the internal combustion engine is configured within the starting time of the internal combustion engine to increase an air excess number (λ) of the air-fuel mixture available for combustion in the piston-cylinder units from a lower first value (λ.sub.1) to a higher second value (λ.sub.2).

11. The system of claim 1, wherein the engine closed-loop control unit is configured, after a power output reaches a nominal power output of the internal combustion engine for a predeterminable or predetermined period of time: to reduce a charging pressure of the engine block, and/or to set an ignition time of ignition in the piston-cylinder units to late.

12. The system of claim 11, wherein the predeterminable or predetermined period of time (t.sub.av) begins to run: with a start of the internal combustion engine, and/or at an established moment in time after a synchronization of a genset with a power supply grid or during a power output ramp of the internal combustion engine, wherein the genset comprises an electrical generator driven by the internal combustion engine, and/or after of the power output reaches the nominal power output of the internal combustion engine when there is a change in a load.

13. The system of claim 1, wherein the engine closed-loop control unit is configured not to exceed a predetermined or predeterminable limit value dependent on a mode of operation for a momentary mass flow or for a momentary concentration of the NO.sub.x proportions or components of the exhaust gases in an exhaust manifold.

14. The system of claim 1, comprising one or more sensors, wherein the engine closed-loop control unit, via the one or more sensors, is configured to acquire or determine information about a state of the engine block and a state of the exhaust gas aftertreatment apparatus, wherein the one or more sensors comprise at least one NO.sub.x sensor and/or at least one temperature sensor.

15. The system of claim 1, wherein the engine closed-loop control unit is configured to control conversions and/or the NO.sub.x proportions or components in the exhaust gas to achieve optimization of a reducing agent and/or a total operating resources consumption of the reducing agent.

16. The system of claim 1, wherein the engine closed-loop control unit is configured to control NO.sub.x emissions to control a charging pressure of the engine block to provide a desired air excess number (λ).

17. The system of claim 1, wherein the engine closed-loop control unit is configured, in a selection of a desired air excess number (λ), to take account of a synchronization duration of a genset with a power supply grid, wherein the genset comprises an electrical generator driven by the internal combustion engine.

18. The system of claim 1, wherein the exhaust gas aftertreatment apparatus comprises at least one oxidation catalytic converter connected fluidically upstream or downstream of the at least one SCR catalytic converter.

19. The system of claim 1, comprising a common controller having the engine closed-loop control unit and the catalytic converter closed-loop control.

20. The system of claim 1, comprising a genset having an electric generator configured to couple to the internal combustion engine by a mechanical coupling.

Description

[0080] Embodiments of the invention are discussed with reference to the Figures in which:

[0081] FIG. 1 shows an internal combustion engine according to the invention,

[0082] FIG. 2 shows a view of the state of the internal combustion engine in relation to time on the basis of selected parameters,

[0083] FIG. 3 shows a further view of the state of the internal combustion engine in relation to time on the basis of selected parameters with adaptation of a load ramp,

[0084] FIG. 4 shows an open-loop and closed-loop control movement of the operating point of the engine block in a combustion diagram,

[0085] FIG. 5 shows a view of the state of the internal combustion engine in relation to time on the basis of selected parameters when using the open-loop and closed-loop control strategy shown in FIG. 4, and

[0086] FIG. 6 shows a genset according to the invention.

[0087] The moments in time identified by the same references in FIGS. 1, 3 and 5 are identical.

[0088] FIG. 1 diagrammatically shows an embodiment of an internal combustion engine 1 according to the invention with the following proportions or components: [0089] 2 piston-cylinder units [0090] 3 engine closed-loop control unit [0091] 4 SCR catalytic converter [0092] 5 engine block [0093] 6 catalytic converter closed-loop control device [0094] 7 discharge from the exhaust gas aftertreatment apparatus [0095] 8 electric generator of a genset including the internal combustion engine [0096] 9 turbocharger (optional) [0097] 10 wastegate (optional) [0098] 11 ignition device [0099] 12 NO.sub.x sensor (optional), in particular NO.sub.x sensors do not have to be provided at all illustrated positions, [0100] 13 temperature sensor (optional), in particular temperature sensors do not have to provided at all illustrated positions, [0101] 14 oxidation catalytic converter (optional), in particular alternatively or additionally there can be an ammonia slip catalytic converter and/or oxidation catalytic converter upstream of the SCR catalytic converter [0102] 15 injection device for reducing agent [0103] 16 exhaust gas aftertreatment apparatus [0104] 17 exhaust manifold [0105] 18 charging air temperature control device (optional)

[0106] FIG. 6 shows a genset which is or can be electrically connected to a power supply grid 23 and having an internal combustion engine 1 according to the invention which is coupled to an electric generator 8 by means of a mechanical coupling 24.

[0107] The term state of the engine block 5 is used to denote in particular (individually or in any combination, naturally not all the following variables have to be taken into account): [0108] the temperature of the exhaust gases directly after a turbine of a possibly provided turbocharger 9 and/or directly after exhaust valves of the piston-cylinder units 2; [0109] temperature of operating means (like oil, cooling water, . . . ) or a material of the engine block 5 itself; [0110] NO.sub.x proportion or component in the exhaust gases in an exhaust manifold 17 after a possibly provided low-pressure turbine of a turbocharger 9 before an injection device 15 for reducing agent of the at least one SCR catalytic converter 4 (preferably for each engine bank of the engine block 5); [0111] NO.sub.x proportion or component in the exhaust gases at a discharge 7 from the at least one SCR catalytic converter; [0112] ratio of NO proportion or component to NO.sub.2 in the exhaust gas or the NO.sub.2 proportion or component to NOR or the NO proportion or component to NOR, that can be converted as desired, as the following applies: NO.sub.x=NO+NO.sub.2; [0113] actual speed of a crankshaft of the internal combustion engine 1, driven by the piston-cylinder units 2 of the engine block 5; [0114] speed of a turbocharger 9 which is possibly provided; [0115] exhaust gas pressure ensuing from a degree of opening of a wastegate 10 which is possibly provided; [0116] selected ignition times for the piston-cylinder units 2; [0117] on/off state of ignition devices for the piston-cylinder units 2; [0118] charging pressure (pressure in front of the inlet valves of the piston-cylinder units 2); [0119] charging temperature (temperature in front of the inlet valves of the piston-cylinder units 2); [0120] induction air temperature; [0121] fuel mass flow or mixture mass flow to the piston-cylinder units 2; [0122] air mass flow; [0123] currently produced mechanical and/or electrical (in the case of a genset) power; and [0124] valve control times (in the case of a variable valve drive).

[0125] The state of the engine block 5 can be influenced by way of the engine closed-loop control unit 3 by means of actuators known in the state of the art (and therefore not shown). For example: [0126] the temperature of the exhaust gases can be influenced directly after outlet valves of the piston-cylinder units 2 by the selection of an ignition time and/or the air excess number of the fuel-air mixture and/or exhaust gas recycling, total amount of fuel, temperature of the charging air or the fuel-air mixture in front of inlet valves of the piston-cylinder units 2, skip firing, valve control times and so forth; [0127] the NO.sub.x proportion or component in the exhaust gases in the exhaust manifold 17 can be influenced by the choice of a combustion temperature and/or combustion speed, in particular by the choice of an ignition time and/or the air excess number λ of the fuel-air mixture and/or exhaust gas recycling, total amount of fuel, temperature of the charging air or the fuel-air mixture in front of inlet valves of the piston-cylinder units 2, valve control times and so forth; [0128] the exhaust gas backpressure can be influenced by the degree of opening of an optionally provided wastegate 10 or by a variable turbine geometry (VTG); and [0129] the selected ignition times and/or the on/off state (skip firing) of ignition devices for the piston-cylinder units 2 can be influenced by appropriate actuation of the ignition devices of the piston-cylinder units 2.

[0130] The term state of the exhaust gas aftertreatment apparatus 16 is used to mean in particular (individually or in any combination, naturally not all the following variables have to be taken into consideration): [0131] the exhaust gas mass flow fed to the at least one SCR catalytic converter 4; [0132] a temperature of a catalytic zone and/or a temperature of the exhaust gas at an inlet location and/or a temperature of the exhaust gas at a discharge location of the at least one SCR catalytic converter 4; [0133] a mass flow Redux of reducing agent introduced into the at least one SCR catalytic converter 4; [0134] an amount of reducing agent reacted in the catalytic zone of the at least one SCR catalytic converter 4; [0135] an NH.sub.3 storage state of the at least one SCR catalytic converter 4; [0136] the state of a possibly provided heating device for the at least one SCR catalytic converter 4; and [0137] state of a possibly provided oxidation catalytic converter 14.

[0138] The state of the exhaust gas aftertreatment apparatus 16 can be influenced by the catalytic converter closed-loop control device 6 by way of actuators known in the state of the art (and therefore not shown). By way of example the following can be influenced: [0139] the exhaust gas mass flow fed to the at least one SCR catalytic converter 4, influenced by the selection of a power output or an operating point of the engine block 5; [0140] the temperature of the catalytic zone of the at least one SCR catalytic converter 4, influenced by a temperature of the supplied exhaust gas and/or a heating device and/or a change in the exhaust gas mass flow; [0141] the temperature at the inlet to the at least one SCR catalytic converter 4, influenced by a temperature of the supplied exhaust gas and/or a heating device; [0142] a mass flow Redux of reducing agent introduced into the at least one SCR catalytic converter 4, being influenced by suitable actuation of an injection device 15 for reducing agent; [0143] the NH.sub.3 storage state in the catalytic zone of the at least one SCR catalytic converter 4, being influenced by the supplied amount of reducing agent, the temperature of the catalytic zone, a change in the exhaust gas mass flow, a change in the NO.sub.x proportion or component and/or the NO.sub.2 proportion or component of the exhaust gas.

[0144] The engine closed-loop control unit 3 can be or is prescribed a target value NO.sub.x.sub.,Tar for an NO.sub.x average value NO.sub.x of the NO.sub.x proportion or component of the exhaust gases in relation to a predetermined or predeterminable period of time t.sub.av at a discharge 7 from the exhaust gas aftertreatment apparatus 16.

[0145] The engine closed-loop control unit 3 at least during the period t.sub.av is in an operating mode in which it is configured to continuously calculate an NO.sub.x reference value NO.sub.x,Ref(t) for the catalytic converter closed-loop control device 6 having regard to already emitted NO.sub.x proportions or components and the predeterminable or predetermined target value NO.sub.x.sub.,Tar, which reference value is so selected that at the end of the predeterminable or predetermined period of time t.sub.av the predeterminable or predetermined target value NO.sub.x.sub.,Tar results at the discharge of the exhaust gas aftertreatment apparatus 16, and to feed the calculated NO.sub.x reference value NO.sub.x,Ref(t) to the catalytic converter closed-loop control device 6 as an NO.sub.x setpoint value.

[0146] FIG. 2 shows a typical operating situation in relation to the FIG. 1 embodiment of an internal combustion engine 1 according to the invention, the starting point here being a start of the internal combustion engine 1 by actuating a start button at the moment in time t.sub.1.

[0147] At the moment in time t.sub.3 the internal combustion engine 1 has reached the nominal power output (here in the form of an electrical nominal power output P.sub.e, of a genset afforded by way of a coupled electric generator—not shown in FIG. 1 as it corresponds to the state of the art, but see FIG. 6) so that the following applies for the starting time: t.sub.Start=t.sub.3−t.sub.1. The starting operation is therefore concluded at the moment in time t.sub.3 (here for example approximately 5 minutes).

[0148] Within the starting time t.sub.Start in relation to the NO.sub.x proportions or components occurring in the engine block 5 at NO.sub.x,in of the exhaust gases (the index “in” is adopted because this involves the NO.sub.x proportions or components flowing into the exhaust gas aftertreatment apparatus 16) it is possible to see two clear peaks, namely a first peak by virtue of the increase in the speed v to a nominal value (synchronous speed in relation to a power supply grid) and—after coupling of the genset to the power supply grid and the load uptake resulting therefrom—a second peak because of the build-up in torque during the turbo lag (which can be seen in the electrical power output as a divergence which remains behind the predetermined ramp). After overcoming the turbo lag (as soon as the turbocharger or turbochargers is or are brought up to speed) the NO.sub.x proportions or components NO.sub.x,in in the exhaust gases occurring the engine block 5 fall to a first value which is constant for the rest of the starting time t.sub.Start.

[0149] The reduction in the NO.sub.x proportions or components NO.sub.x,in in the exhaust gases occurring in the engine block 5, that can be seen after the conclusion of the starting operation, is to be attributed to the fact that the engine closed-loop control unit 3 is configured after the attainment of a nominal power output of the internal combustion engine 1, for a predetermined or predeterminable period of time, to increase a charging pressure of the engine block 5 and/or to set an ignition time of the ignition in the piston-cylinder units to late (see also the combustion diagram in FIG. 4).

[0150] The engine closed-loop control unit 3 monitors a conversion rate R.sub.conv(t) of the exhaust gas aftertreatment apparatus as an absolute value or—preferably—relative to an expected target value. The SCR catalytic converter 4 begins to work at the moment in time t.sub.4 as the temperature necessary for reduction of the NO.sub.x in the catalytic zone is reached and reducing agent is injected with a mass flow Redux by the injection device 15 (controlled by the catalytic converter closed-loop control device 6) into the exhaust manifold 17. Therefore the conversion rate R.sub.conv(t) begins to rise from the value zero and the NO.sub.x proportions or components NO.sub.x,out of the exhaust gases at the discharge from the SCR catalytic converter 4 begin to diverge from the NO.sub.x proportions or components NO.sub.x,in (the expected target value of the conversion rate R.sub.conv(t) is first reached at the moment in time t.sub.5).

[0151] As from the moment in time t.sub.4 the engine closed-loop control unit 3 begins to enrich the air-fuel mixture again and to set the ignition time back to earlier (see also the combustion diagram in FIG. 4). Therefore the NO.sub.x proportions or components NO.sub.x,in increase again to the value at the moment in time t.sub.3, this however can be accepted as now in fact the SCR catalytic converter 4 is working.

[0152] At the moment in time t.sub.2 the predetermined period of time t.sub.av (here for example 30 minutes) has expired and the NO.sub.x reference value NO.sub.x,Ref(t) for the catalytic converter closed-loop control device 6 has reached the predetermined target value NO.sub.x.sub.,Tar (see FIG. 5).

[0153] The illustration as from the moment in time t.sub.6 (here for example 2 hours) to the moment in time t.sub.7 (here for example 24 hours) shows by way of example that here a 24 hours—target value NO.sub.x.sub.,Tar which is increased in relation to the 30 minutes—target value NO.sub.x.sub.,Tar—is accepted in order to minimize a consumption of reducing agent.

[0154] FIG. 3 shows an optional control diagram in which the engine closed-loop control unit 3 of the internal combustion engine 1 in FIG. 1, to reduce the NO.sub.x proportion or component in the exhaust gases that is emitted during a starting time by the internal combustion engine 1 is additionally configured during the starting time t.sub.Start of the internal combustion engine 1 to predetermine a power output ramp (dotted line which covers over a long period of time with the solid line) for the engine block 5 (here for the electrical power output P.sub.el) in a first time portion, preferably after reaching a minimum power output (moment in time t.sub.8) until reaching a predetermined limit value for the power output (moment in time t.sub.11) with a first lesser gradient and in a second time portion (from the moment in time t.sub.11) until reaching a nominal power output of the internal combustion engine 1 (at the moment in time t.sub.3) with a second greater gradient, wherein it is preferably provided that the greater gradient is calculated in dependence on the remaining time (period t.sub.3-t.sub.11) until the starting time t.sub.Start is reached.

[0155] The solid line represents the actual power output. It can be seen that the engine block 5 can follow the power output ramp only after overcoming the turbo lag, which occupies the greatest part of the period of time t.sub.9−t.sub.8.

[0156] A power ramp is shown in dashed-line form without the optional control scheme, and it can be seen that from the outset a steeper power output ramp is adopted, which during the turbo lag leads to increased NO.sub.x emissions which as from the moment in time t.sub.9 would have to be compensated by a drop in the power output ramp in order to be able to reach the predetermined NO.sub.x average value NO.sub.x of the NO.sub.x proportion or component of the exhaust gas for the period of time t.sub.av.

[0157] FIG. 4 shows a combustion diagram in which it can be seen that the engine closed-loop control unit 3 of the internal combustion engine 1 in FIG. 1 is optionally configured to move a current first operating point 19 of the engine block 5 which occurs after attainment of a nominal power output of the internal combustion engine 1 to a transient operating point 20 with lower NO.sub.x emissions (the NO.sub.x emissions occurring in the engine block 5, for which straight lines involving constant values are shown, decrease upwardly in FIG. 4), for example to an operating point at higher temperatures (the temperatures of the piston-cylinder units, for which straight lines involving constant values are shown, increase towards the left in FIG. 4), of the exhaust gases immediately after exhaust valves of the piston-cylinder units (preferably in that respect the temperature T of the hottest piston-cylinder unit is used by the engine closed-loop control unit 3). That can be achieved for example by adjusting an ignition time of ignition in the piston-cylinder units to late and/or (preferably at the same time leaning of the fuel-air mixture available for combustion in the piston-cylinder units from the first value λ.sub.1 to a second value λ.sub.2 (naturally in such a way that no misfires or knocking occurs). In the combustion diagram (with the coordinate axes “air excess number λ” and ignition time measured at the “crankshaft angle θ”) the operating point thereby moves within the knock limit and the misfire limit in the direction of higher exhaust gas temperatures.

[0158] That can optionally occur in a first step (along a first trajectory 21 in the combustion diagram) by means of a pre-control in order to cause rapid first adjustment of the operating point of the engine block 5. That can be followed in a second step (along a second trajectory 22 in the combustion diagram) by a control action in order to be able to more accurately select the ensuing transient operating point 20.

[0159] When the at least one SCR catalytic converter begins to reduce the NO.sub.x proportion or component in the exhaust gas (because the catalytic zone has reached the required temperature) the engine closed-loop control unit provides for open-loop and/or closed-loop control of the engine block in such a way that the current operating point moves away from the transient operating point back in the direction of the first operating point (preferably on the same trajectory as for the movement from the nominal operating point to the steady-state operating point, but in the reverse direction) and reaches same.

[0160] FIG. 5 shows once again the most important above-discussed parameters in the course of time t. It can be clearly seen how the time-dependent NO.sub.x reference value NO.sub.x,Ref(t) increasingly approaches the predetermined target value NO.sub.x.sub.,Tar and finally reaches it at the time t.sub.2 (right-hand dark point). By way of example shown for an earlier time (left-hand dark point) in a shape with a gray background are rectangles which correspond to the average NO.sub.x proportions or components in the exhaust gases, that have already been emitted by the internal combustion engine 1 up to that moment in time, and the average NO.sub.x proportions or components in the exhaust gases, that are thus still available to reach the predetermined target value NO.sub.x.sub.,Tar.

[0161] With reference to FIG. 3 the synchronization duration is measured (here equal: t.sub.8−t.sub.1) and in dependence on the synchronization duration it is decided (immediately after the moment in time t.sub.8) whether the mixture is to be more or less greatly enriched, and therefore a desired air excess number λ is established in dependence on the synchronization duration.

LIST OF REFERENCES

[0162] 1 internal combustion engine [0163] 2 piston-cylinder units [0164] 3 engine closed-loop control unit [0165] 4 SCR catalytic converter [0166] 5 engine block [0167] 6 catalytic converter closed-loop control device [0168] 7 discharge of the SCR catalyst [0169] 8 electric generator [0170] 9 turbocharger [0171] 10 wastegate [0172] 11 ignition device [0173] 12 NO.sub.x sensor [0174] 13 temperature sensor [0175] 14 oxidation catalytic converter [0176] 15 injection device for reducing agent [0177] 16 exhaust gas aftertreatment apparatus [0178] 17 exhaust manifold [0179] 18 charging air temperature control device [0180] 19 first operating point [0181] 20 transient operating point [0182] 21 first trajectory in the combustion diagram [0183] 22 first trajectory in the combustion diagram [0184] 23 power supply grid [0185] 24 mechanical coupling between internal combustion engine and electric generator [0186] t.sub.av predetermined or predeterminable period of time [0187] t.sub.1,t.sub.2,t.sub.3, . . . first, second, third . . . moment in time [0188] t current moment in time [0189] t.sub.Start starting time of the internal combustion engine [0190] NO.sub.x(t) rate of the NO.sub.x proportion or component (mass flow or concentration) at the moment in time t [0191] NO.sub.x NO.sub.x average value [0192] NO.sub.x.sub.,Tar predeterminable or predetermined (constant) target value [0193] NO.sub.x,Ref(t) time-dependent NO.sub.x reference value (mass flow) at the moment in time t [0194] cumulNO.sub.2 cumulated NO.sub.x proportion or component [0195] R.sub.conv(t) conversion rate of the exhaust gas aftertreatment apparatus at the moment in time t [0196] NO.sub.x,in(t) mass flow entering the exhaust gas aftertreatment apparatus at the moment in time t [0197] NO.sub.x,out(t) mass flow issuing from the exhaust gas aftertreatment apparatus at the moment in time t [0198] Redux(t) mass flow of reducing agent at the moment in time t [0199] λ air excess number [0200] λ.sub.1 first value of the air excess number [0201] λ.sub.2 second value of the air excess number [0202] P.sub.m mechanical power output of the internal combustion engine [0203] P.sub.el electrical power output of the internal combustion engine [0204] V speed of a crankshaft of the engine block [0205] T temperature [0206] θ crankshaft angle