Method for operating an internal combustion engine, control device for an internal combustion engine and internal combustion engine with a control device of this type

Abstract

The invention relates to a method for operating an internal combustion engine (1), wherein a combustion gas with a fluctuating hydrogen portion is introduced into an air path (5) of the internal combustion engine (1), wherein a combustion air ratio for a combustion chamber (15) of the internal combustion engine (1) is adjusted via a predefinable combustion gas mass flow into the air path (5), wherein a power variable of the internal combustion engine (1) is adjusted by a throttle valve (9) arranged in the air path (5), wherein a nitrogen oxide concentration is detected in an exhaust path (11) of the internal combustion engine (1), wherein the combustion air ratio is adjusted according to the detected nitrogen oxide concentration, wherein a throttle valve reserve is detected in the air path (5), and wherein an ignition time in the combustion chamber (15) of the internal combustion engine (1) is selected according to the detected throttle valve reserve.

Description

[0001] Rolls-Royce Solutions GmbH

[0002] DESCRIPTION

[0003] Method for operating an internal combustion engine, control unit for an internal combustion engine and internal combustion engine with such a control unit

[0004] The invention relates to a method for operating an internal combustion engine, a control unit for an internal combustion engine for carrying out such a method and an internal combustion engine with such a control unit.

[0005] Particularly with a view to climate protection, a progressive move towards a so-called hydrogen economy, in particular the use of hydrogen as a fuel or fuel gas, is planned. In this context, it is specifically planned to mix hydrogen with other fuel gases, particularly to feed it into distribution networks for other fuel gases, especially the natural gas grid. However, this will almost inevitably result in hydrogen concentrations that fluctuate over time, which causes problems in the operation of internal combustion engines that use such fuel gas mixtures (hereinafter also referred to as fuel gas). In particular, this can lead to strongly fluctuating nitrogen oxide emissions during operation of such an internal combustion engine, even exceeding legally prescribed limits.A simple way to account for the fluctuating hydrogen content in the fuel gas mixture is to use a suitable sensor, particularly a hydrogen sensor. However, this requires an additional component and additional control measures, which is complex and expensive. Regulating the fluctuating hydrogen content also faces the problem that, in the course of adapting to an increasing hydrogen content, a throttle valve reserve that is essential for any load jumps with regard to the dynamics of the internal combustion engine can be consumed.

[0006] The invention is therefore based on the object of providing a method for operating an internal combustion engine, a control unit for an internal combustion engine for implementing such a method, and an internal combustion engine with such a control unit, wherein the aforementioned disadvantages are at least reduced, preferably not occurring at all. This object is achieved by providing the present technical teaching, in particular the teaching of the independent claims and the preferred embodiments disclosed in the dependent claims and the description.

[0007] The object is achieved in particular by providing a method for operating an internal combustion engine, wherein a fuel gas with a fluctuating hydrogen content is introduced into an air path of the internal combustion engine, wherein a combustion air ratio for a combustion chamber of the internal combustion engine is set via a predeterminable fuel gas mass flow to be introduced or introduced into the air path, wherein a power variable of the internal combustion engine is set by means of a throttle valve arranged in the air path, wherein a nitrogen oxide concentration in an exhaust gas path of the internal combustion engine is detected, wherein the combustion air ratio is set as a function of the detected nitrogen oxide concentration, wherein a throttle valve reserve is detected in the air path, and wherein an ignition point in the combustion chamber of the internal combustion engine is selected as a function of the detected throttle valve reserve.By adjusting the combustion air ratio depending on the detected nitrogen oxide concentration, the internal combustion engine can be advantageously controlled to a fluctuating hydrogen content in the fuel gas without the need for a separate hydrogen sensor. In particular, it is advantageously possible to comply with a legally prescribed nitrogen oxide limit. By additionally selecting the ignition timing in the combustion chamber depending on the detected throttle valve reserve, exhaustion of the throttle valve reserve is advantageously avoided, and the necessary or desirable dynamics of the internal combustion engine for any load surges are maintained.

[0008] In the context of the present technical teaching, a fuel gas is understood in particular to be a combustible gas or gas mixture that is gaseous at room temperature and ambient pressure, in particular at 25 °C and 1013 mbar. In particular, a fuel gas is understood to be a mixture of natural gas, in particular liquefied natural gas (LNG), and hydrogen—in particular with a variable hydrogen content.

[0009] In the context of the present technical teaching, a hydrogen content is understood in particular to mean a hydrogen concentration or a hydrogen partial pressure. In the context of the present technical teaching, a combustion air ratio is understood in particular to mean a lambda value. In particular, the combustion air ratio is thus the ratio of an actual air mass to a stoichiometric air mass required for complete combustion, or - equivalently - the quotient of an actual ratio of air mass to fuel mass and a stoichiometric ratio of air mass to fuel mass.

[0010] In the context of the present technical teaching, a power quantity is understood to be a physical quantity, a measured value, or a parameter that is characteristic of the power of an internal combustion engine. In particular, the power quantity can be the power itself. Alternatively or additionally, the power quantity can also be a torque of the internal combustion engine—or another suitable quantity.

[0011] The fact that the combustion air ratio is adjusted depending on the detected nitrogen oxide concentration means in particular that the predeterminable fuel gas mass flow is adjusted depending on the detected nitrogen oxide concentration.

[0012] In the context of the present technical teaching, a throttle valve reserve is understood to mean, in particular, a pressure difference in the air path across the throttle valve, in particular a pressure drop across the throttle valve, in particular a difference between a first pressure in the air path - in particular directly - upstream of the throttle valve and a second pressure in the air path - in particular directly - downstream of the throttle valve.

[0013] The internal combustion engine is operated in particular in a characteristic map with a combustion air ratio of 1 at idle and 1.75 to 2, in particular up to 1.8, at rated load, wherein the internal combustion engine is operated in a load range, i.e. in particular above idle speed, in the lean range, in particular with a combustion air ratio of up to 2, in particular up to 1.8. This means in particular that the internal combustion engine is preferably operated at least at full load such that the combustion air ratio does not fall below 1.8 or below 1.75. Thus, the internal combustion engine is in particular a lean-burn gas engine. According to a development of the invention, the power variable is regulated to a setpoint value by means of the throttle valve. The internal combustion engine can thus advantageously be operated in a manner guided by the power variable. The setpoint value can in particular be constant or variable over time.

[0014] According to a further development of the invention, the combustion air ratio is increased, i.e., in particular, the predeterminable fuel gas mass flow is reduced, if the detected nitrogen oxide concentration is greater than a target nitrogen oxide concentration, and the combustion air ratio is reduced, i.e., in particular, the predeterminable fuel gas mass flow is increased, if the detected nitrogen oxide concentration is less than the target nitrogen oxide concentration. Alternatively or additionally, the combustion air ratio is not changed if the detected nitrogen oxide concentration is equal to the target nitrogen oxide concentration.

[0015] An increase in the hydrogen content in the fuel gas leads, in particular, to a faster combustion process in the combustion chamber, i.e., to faster and hotter combustion, so that the nitrogen oxide concentration in the exhaust gas increases. If the combustion air ratio is then appropriately increased, the combustion process slows down again, and the nitrogen oxide concentration decreases. At the same time, however, the power of the internal combustion engine decreases; to compensate for this, the throttle valve is opened further by the power control, which results in a decrease in the throttle valve reserve. If, on the other hand, the hydrogen content in the fuel gas decreases, the combustion process slows down; the nitrogen oxide concentration decreases, and the combustion air ratio can be lowered; this means that the fuel gas mass flow into the air path is increased.This simultaneously increases the engine's power output. To compensate for this, the power control closes the throttle valve slightly, increasing the throttle valve reserve. This regulates the engine to the fluctuating hydrogen content; at the same time, the hydrogen content in the fuel gas and its regulation influence the throttle valve reserve.

[0016] In particular, the target nitrogen oxide concentration corresponds to the legally prescribed nitrogen oxide limit. With a view to achieving the highest possible efficiency of the internal combustion engine, the measures explained here are implemented in such a way that the instantaneous nitrogen oxide concentration corresponds as closely as possible to the legally prescribed nitrogen oxide limit. In particular, the nitrogen oxide concentration in the exhaust gas is increased if the instantaneous nitrogen oxide contraction is lower than the nitrogen oxide limit. In one embodiment, the target nitrogen oxide concentration corresponds to the legally prescribed nitrogen oxide limit less a safety margin. This safety margin takes into account, in particular, possible aging effects, sensor scatter, or other emissions-related effects.With a view to achieving the highest possible efficiency of the internal combustion engine, the measures described here are implemented in such a way that the instantaneous nitrogen oxide concentration corresponds as closely as possible to the legally prescribed nitrogen oxide limit less the safety margin. In particular, the nitrogen oxide concentration in the exhaust gas is increased if the instantaneous nitrogen oxide contraction is lower than the nitrogen oxide limit less the safety margin.

[0017] In one embodiment, the combustion air ratio is incrementally increased—particularly starting from a current value—if the detected nitrogen oxide concentration is greater than the target nitrogen oxide concentration. Alternatively or additionally, the combustion air ratio is incrementally decreased—particularly starting from a current value—if the detected nitrogen oxide concentration is less than the target nitrogen oxide concentration.

[0018] In one embodiment, the combustion air ratio is varied in the load range from 1.8 to 2, in particular up to 2.0.

[0019] Alternatively or additionally, an increment for the change in the combustion air ratio (lambda increment) is from 0.01 to 0.03, in particular 0.02.

[0020] According to a further development of the invention, the ignition timing is retarded when the detected throttle valve reserve reaches or falls below a predetermined minimum reserve value—in particular from above, i.e., from higher values. The ignition timing is advanced after a retarded adjustment if the detected throttle valve reserve exceeds the predetermined minimum reserve value—in particular plus a predetermined hysteresis value. In particular, the ignition timing is advanced only if it has already been retarded and, in particular, if a preceding retarded adjustment has not already been compensated for by subsequent advance adjustments.If the ignition timing is retarded, this results in combustion in the combustion chamber occurring at a lower temperature, which reduces the nitrogen oxide concentration in the exhaust gas. At the same time, however, the exhaust gas temperature rises due to less expansion cooling in the expansion stroke. This means that more enthalpy is supplied to a turbine of an exhaust gas turbocharger arranged in the exhaust path of the internal combustion engine, which in turn provides more power to a compressor of the exhaust gas turbocharger arranged upstream of the throttle valve in the air path and connected to the turbine for driving purposes. This in turn increases the pressure in the air path; at the same time, the power of the internal combustion engine increases, which is in turn compensated for by the power control by closing the throttle valve slightly. This in turn increases the throttle valve reserve.Conversely, if the ignition timing is advanced, combustion occurs at a higher temperature in the combustion chamber, increasing the nitrogen oxide concentration in the exhaust gas. At the same time, the exhaust gas temperature drops due to the increased expansion cooling; this results in less enthalpy being supplied to the turbine, so the compressor receives less power. This, in turn, lowers the pressure in the air path; at the same time, the engine's power decreases, which is compensated for by the power control by opening the throttle valve further. This reduces the throttle valve reserve.

[0021] The inventors have particularly recognized that the ignition timing adjustment has an advantageous effect with regard to the nitrogen oxide concentration on the one hand and the throttle valve reserve on the other hand, in exactly the opposite way to the change in the combustion air ratio, so that the ignition timing adjustment can be advantageously used to reduce the nitrogen oxide concentration and at the same time to restore the throttle valve reserve when this has been almost used up by a change in the combustion air ratio to reduce the nitrogen oxide concentration, i.e. when in particular a further change in the combustion air ratio in the direction of decreasing the nitrogen oxide concentration is no longer possible or is associated with serious disadvantages with regard to the dynamics of the internal combustion engine.

[0022] In the context of the present technical teaching, retarding the ignition timing is understood in particular to mean that a crankshaft angle value at which ignition occurs within a working cycle is shifted closer to a top dead center of a piston or is changed to a higher value. Correspondingly, advancing the ignition timing is understood in particular to mean that the crankshaft angle value at which ignition occurs within the working cycle is further away from top dead center or is changed to a smaller value. In the case of an internal combustion engine designed as a four-stroke engine, a working cycle extends in particular from 0° CA (crankshaft angle) to 720° CA, but in the case of a two-stroke engine, it extends from 0° CA to 360° CA.

[0023] In one embodiment, the ignition timing is incrementally retarded—particularly starting from a current value—when the detected throttle valve reserve reaches or falls below the predetermined minimum reserve value. Alternatively or additionally, the ignition timing is incrementally advanced—particularly starting from a current value—when the detected throttle valve reserve exceeds the predetermined minimum reserve value—particularly plus the predetermined hysteresis value.

[0024] In one embodiment, the predetermined reserve minimum value is from 100 mbar to 300 mbar, preferably up to 250 mbar, preferably up to 200 mbar, preferably up to 150 mbar. Alternatively or additionally, the predetermined hysteresis value is from 30 mbar to 70 mbar, in particular from 40 mbar to 60 mbar, in particular 50 mbar.

[0025] In one embodiment, an adjustment range for retarding the ignition timing is from 0.1° CA to 15° CA, in particular up to 12° CA, in particular up to 10° CA, in particular up to 8° CA. In one embodiment, an increment for adjusting the ignition timing is 0.5° CA (ignition timing increment).

[0026] According to a further development of the invention, the ignition timing is only advanced as long as previous retardations have not yet been compensated for. This advantageously prevents the ignition timing from being selected too early, particularly starting from a value intended for normal operation, which could lead in particular to knocking combustion or to damage or even destruction of the internal combustion engine. According to a further development of the invention, an alarm is issued when the detected throttle valve reserve reaches or falls below the predetermined minimum reserve value - particularly from above, i.e. from higher values ​​- and at the same time the ignition timing reaches or exceeds a predetermined maximum ignition timing, and at the same time the detected nitrogen oxide concentration is greater than the predetermined target nitrogen oxide concentration.In particular, in this case, all measures to reduce the nitrogen oxide concentration have been exhausted: A further increase in the combustion air ratio is out of the question, as this would completely deplete the throttle valve reserve, and a further retardation of the ignition timing is also out of the question, as the predetermined maximum ignition timing is selected in such a way that an even later ignition timing would no longer ensure operation of the internal combustion engine with acceptable power or efficiency, or complete combustion or even any combustion at all in the combustion chamber. This, in turn, means that the legally prescribed nitrogen oxide limit can no longer be met. The alarm can be used to advantageously alert an operator of the internal combustion engine to this situation.The operator can then take appropriate measures, such as intervening in the fuel gas supply or fuel gas composition, or shutting down the engine. This can also happen automatically, without the need for manual intervention.

[0027] According to a further development of the invention, the throttle valve reserve is adjusted via a bypass path adjusting device arranged in a compressor bypass path bypassing the compressor arranged in the air path. Controlling the bypass path adjusting device changes the flow cross-section of the compressor bypass path. Advantageously, changing the flow cross-section of the compressor bypass path allows adjustment, in particular regulation, of the throttle valve reserve during operation of the internal combustion engine with a changed throttle valve position.In particular, the throttle valve reserve increases when the bypass path control device is controlled, in particular closed, in the direction of reducing the flow cross-section of the compressor bypass path; conversely, the throttle valve reserve decreases when the bypass path control device is controlled, in particular opened, in the direction of increasing the flow cross-section of the compressor bypass path. The bypass path control device can also be used to compensate for aging or contamination of the compressor, in particular by progressively closing the bypass path control device over the course of the compressor's service life.

[0028] In one embodiment, the bypass path adjusting device is designed as a valve or as a bypass flap.

[0029] According to a further development of the invention, it is provided that the ignition timing is only retarded when a predetermined closed position of the bypass path actuating device - in particular starting from an open position - is reached or - in particular in the direction of a closed position, that is to say a completely closed position - is exceeded.

[0030] Advantageously, the throttle valve reserve is initially controlled by the bypass path control device, and the ignition timing is only adjusted once this option has been exhausted. This initially provides a milder means of maintaining the throttle valve reserve before a measure that intervenes more deeply in the functioning of the internal combustion engine is taken.

[0031] The object is also achieved by providing a control unit for an internal combustion engine that is configured to carry out a method according to the invention or a method according to one or more of the previously described embodiments. In connection with the control unit, the advantages that were already explained in connection with the method arise, in particular.

[0032] The object is also achieved by providing an internal combustion engine having a gas injection device, in particular a gas injection valve, wherein the gas injection device is arranged and configured to introduce a combustion gas into an air path of the internal combustion engine. The internal combustion engine also has a throttle valve arranged in the air path, and a nitrogen oxide sensor arranged in an exhaust gas path of the internal combustion engine. Furthermore, the internal combustion engine has an ignition device arranged in a combustion chamber of the internal combustion engine, and a control unit according to the invention or a control unit according to one or more of the previously described embodiments. The control unit is operatively connected to the gas injection device, the throttle valve, and the nitrogen oxide sensor. In connection with the internal combustion engine, the advantages that were already explained above in connection with the method or the control unit arise in particular.

[0033] According to a further development of the invention, it is provided that the internal combustion engine has a compressor in the air path, wherein the internal combustion engine also has a compressor bypass path around the compressor, wherein a bypass path adjusting device is arranged in the compressor bypass path, which is designed to change a flow cross-section of the compressor bypass path, and wherein the control unit is operatively connected to the bypass path adjusting device.

[0034] In one embodiment, the internal combustion engine has a turbine in an exhaust path that is operatively connected to the compressor drive. In particular, the internal combustion engine has an exhaust-gas turbocharger, which, on the one hand, has the compressor arranged in the air path and, on the other hand, has the turbine arranged in the exhaust path and operatively connected to the compressor.

[0035] In one embodiment, the internal combustion engine has - in particular upstream of the nitrogen oxide sensor - a catalyst for reducing nitrogen oxides, in particular for selective catalytic reduction (SCR catalyst).

[0036] The invention is explained in more detail below with reference to the drawings, which show:

[0037] Figure 1 is a schematic representation of an embodiment of an internal combustion engine with an embodiment of a control unit;

[0038] Figure 2 shows a first schematic representation of an embodiment of the method in the form of a flow chart, and

[0039] Figure 3 shows a second schematic representation of the process.

[0040] Fig. 1 shows a schematic representation of an embodiment of an internal combustion engine 1 with an embodiment of a control unit 3.

[0041] The internal combustion engine 1 has an air path 5 and in the air path 5 a gas

[0042] Injection device 7, in particular a gas injection valve, wherein the gas injection device 7 is arranged and configured to introduce a fuel gas having a temporally fluctuating hydrogen content into the air path 5. In addition, the internal combustion engine 1 has a throttle valve 9 arranged in the air path 5, and a nitrogen oxide sensor 13 arranged in an exhaust gas path 11 of the internal combustion engine 1. Furthermore, the internal combustion engine 1 has an ignition device 17 arranged in a combustion chamber 15 of the internal combustion engine 1. For the sake of better clarity, only one combustion chamber 15 and only one ignition device 17 are each identified here with the corresponding reference numeral. The control unit 3 is operatively connected to the gas injection device 7, the throttle valve 9, and the nitrogen oxide sensor 13. It is configured, in particular, to carry out a method described in more detail below.

[0043] In particular, the internal combustion engine 1 has a compressor 19 in the air path 5, as well as a compressor bypass path 21 around the compressor 19. A bypass path adjusting device 23, in particular a bypass flap, is arranged in the compressor bypass path 21. This bypass flap is configured to change a flow cross-section of the compressor bypass path 21. The control unit 3 is operatively connected to the bypass path adjusting device 23.

[0044] In particular, the internal combustion engine 1 also has a turbine 25 in the exhaust path 11, which is operatively connected to the compressor 19 drive. In particular, the internal combustion engine 1 has an exhaust gas turbocharger 27, which, on the one hand, has the compressor 19 arranged in the air path 5 and, on the other hand, the turbine 25 arranged in the exhaust path 11 and operatively connected to the compressor 19 drive.

[0045] Fig. 2 shows a first schematic representation of an embodiment of the method in the form of a flow chart.

[0046] Identical and functionally identical elements are provided with the same reference symbols in all figures, so that reference is made to the preceding description in each case.

[0047] In the embodiment shown here, the method starts in a first step S1.

[0048] In a second step S2, it is checked whether a nitrogen oxide concentration [NO X ] in the exhaust gas, that is to say in particular an actual nitrogen oxide concentration, is greater than a predetermined target nitrogen oxide concentration [NO X ] S , where the predetermined target nitrogen oxide concentration [NO X ] Sin particular a legally prescribed limit value - optionally less a safety margin. If this is the case, in a third step S3 the combustion air ratio X is increased starting from a current value - in particular by a predetermined lambda increment - in particular by suitably controlling the gas injection device 7 in order to reduce a fuel gas mass flow into the air path 5 - in particular incrementally. Subsequently, in a fourth step S4, it is checked whether a throttle valve reserve DKR, in particular an actual throttle valve reserve, reaches or exceeds a predetermined reserve minimum value DKRmin. If this is the case, the method continues in the second step S2.

[0049] If, however, the throttle valve reserve DKR falls below the predetermined reserve minimum value DKRmin, a fifth step S5 checks whether an ignition timing ZP, in particular a current actual ignition timing, reaches or exceeds a predetermined maximum ignition timing ZPmax. If this is not the case, in a sixth step S6 the ignition timing ZP is retarded starting from its current value—in particular by a predetermined ignition timing increment. Preferably, however, the ignition timing ZP is only retarded in the sixth step S6 if the bypass path actuating device 23 has reached or exceeded a predetermined closed position. The method then continues in the second step S2.

[0050] If it is determined in the second step S2 that the nitrogen oxide concentration [NO X ] is not greater than the target nitrogen oxide concentration [NO X ] S, in a seventh step S7 it is checked whether the nitrogen oxide concentration [NO X ] is smaller than the target nitrogen oxide concentration [NO X ] SIf this is the case, the combustion air ratio X is reduced in an eighth step S8 starting from its current value - in particular by the predetermined lambda increment - in particular by suitably controlling the gas injection device 7 in order to increase the fuel gas mass flow into the air path 5 - in particular incrementally. Then, in a ninth step S9, it is checked whether the throttle valve reserve DKR reaches or exceeds the predetermined reserve minimum value DKRmin plus a predetermined hysteresis value DKRuyst. If this is not the case, the method continues in the second step S2. If, on the other hand, the throttle valve reserve DKR exceeds the predetermined reserve minimum value DKRmin plus the predetermined hysteresis value DKRuyst, a check is carried out in a tenth step S10 to determine whether the ignition timing ZP has already been retarded.If this is the case, and in particular if the retardation has not already been compensated for by subsequent advances, the ignition timing ZP is advanced back to the previous position in an eleventh step S1, starting from its current value—in particular, by the predetermined ignition timing increment. The method then continues in the second step S2.

[0051] If, however, it is determined in the tenth step S10 that no change in the ignition timing ZP has previously taken place towards retardation, the method is continued in the second step S2 directly after the tenth step S10.

[0052] If it is determined in the seventh step S7 that the nitrogen oxide concentration [NO X ] is not less than the target nitrogen oxide concentration [NO x ]s, in a twelfth step S12 it is checked whether the nitrogen oxide concentration [NO X ] equal to the target nitrogen oxide concentration [NO X ]S If this is the case, no further action is taken, and the process is restarted in the first step S1, optionally after a predetermined waiting period. If this is not the case—which should not be provided for due to the intrinsic logic of the process, but could occur exceptionally in the case of high-frequency fluctuations in the hydrogen content—the process continues in step S2.

[0053] If it is determined in the fifth step S5 that the ignition timing ZP exceeds the predetermined maximum ignition timing ZP max reaches or exceeds, a thirteenth step S13 checks again whether the nitrogen oxide concentration [NO X ] is greater than the predetermined target nitrogen oxide concentration [NO X ] S If this is not the case, the method continues in the seventh step S7.

[0054] However, if the nitrogen oxide concentration [NOX ] in the thirteenth step S13, the predetermined target nitrogen oxide concentration [NO X ] S , an alarm is issued in a fourteenth step S14. Preferably, this ends the method; alternatively, however, the method can also be restarted in the first step S1—particularly after a measure has been taken in response to the alarm. Figure 2 illustrates the method in a sequence of discrete steps carried out one after the other. While it is possible to carry out the method in this way in one embodiment, this illustration serves in particular to better understand the structure of the method. In fact, the method is preferably carried out simultaneously by a plurality of control devices, particularly in another embodiment, as will be explained below in connection with Figure 3.

[0055] Fig. 3 shows a second schematic representation of the method. In the embodiment shown here, the actual nitrogen oxide concentration [NO X ] and the target nitric oxide contraction [NO X ] S From a control deviation calculated therefrom, the nitrogen oxide control device 29 calculates an offset combustion air ratio AZ, which is compared in a first calculation element 31 with a target combustion air ratio Z, read out in particular from a characteristic map. s to a combustion air ratio X. The combustion air ratio X is used to control the gas injection device 7 in order to set the combustion air ratio X.

[0056] At the same time, the actual throttle valve reserve DKR and a target throttle valve reserve DKR are fed into a bypass valve control device 33, which is provided for adjusting the position of the bypass path control device 23. S From a control deviation calculated therefrom, the bypass valve control device 33 calculates a bypass valve position BKP, which is used to control the bypass path actuating device 23.

[0057] The bypass valve position BKP is also transmitted to an ignition timing control device 35, wherein the bypass valve position BKP is used in particular to activate or trigger the ignition timing control device 35. In particular, the ignition timing control device 35 is inactive as long as the bypass valve position BKP has not reached or exceeded a predetermined closed position. If the bypass valve position BKP reaches or exceeds the predetermined closed position, the ignition timing control device 35 is activated. Preferably, the ignition timing control device 35 is deactivated again when the bypass valve position BKP falls below the predetermined closed position again.

[0058] If the ignition timing control device 35 is active, it calculates an offset ignition timing AZP from the actual throttle valve reserve DKR and the reserve minimum value DKRmin, which is compared in a second calculation element 37 with a target ignition timing ZP read out in particular from a characteristic map. S to an ignition timing ZP, which is then used to control the ignition device 17. In particular, the predetermined hysteresis value DKRuyst is also input into the ignition timing control device 35 in order to advance the ignition timing ZP only when the throttle valve reserve DKR exceeds the reserve minimum value DKRmin plus the predetermined hysteresis value DKRuyst.

Claims

CLAIMS 1. A method for operating an internal combustion engine (1), wherein - a fuel gas with a fluctuating hydrogen content is introduced into an air path (5) of the internal combustion engine (1), wherein a combustion air ratio for a combustion chamber (15) of the internal combustion engine (1) is set via a predeterminable fuel gas mass flow into the air path (5), wherein a power variable of the internal combustion engine (1) is set by means of a throttle valve (9) arranged in the air path (5), wherein a nitrogen oxide concentration in an exhaust gas path (11) of the internal combustion engine (1) is detected, wherein the combustion air ratio is set as a function of the detected nitrogen oxide concentration, wherein a throttle valve reserve in the air path (5) is detected, and wherein an ignition point in the combustion chamber (15) of the internal combustion engine (1) is selected as a function of the detected throttle valve reserve.

2. Method according to claim 1, wherein the power variable is regulated to a desired value by means of the throttle valve (9).

3. Method according to one of the preceding claims, wherein the combustion air ratio is increased when the detected nitrogen oxide concentration is greater than a target nitrogen oxide concentration, and wherein the combustion air ratio is reduced when the detected nitrogen oxide concentration is less than the target nitrogen oxide concentration.

4. Method according to one of the preceding claims, wherein the ignition timing is retarded when the detected throttle valve reserve reaches or falls below a predetermined minimum reserve value, and wherein the ignition timing is advanced after a retardation when the detected throttle valve reserve exceeds the predetermined minimum reserve value - in particular plus a predetermined hysteresis value.

5. The method according to claim 4, wherein the ignition timing is only advanced as long as previous retardations have not yet been compensated.

6. Method according to one of the preceding claims, wherein an alarm is issued when the detected throttle valve reserve reaches or falls below the predetermined minimum reserve value, at the same time the ignition timing reaches or exceeds a predetermined maximum ignition timing, and at the same time the detected nitrogen oxide concentration is greater than the predetermined target nitrogen oxide concentration.

7. Method according to one of the preceding claims, wherein the throttle valve reserve is adjusted via a bypass path adjusting device (23) arranged in a compressor bypass path (21) around a compressor (19) arranged in the air path (5), wherein a flow cross-section of the compressor bypass path (21) is changed by controlling the bypass path adjusting device (23).

8. The method according to claim 7, wherein the ignition timing is retarded only when a predetermined closed position of the bypass path adjusting device (23) is reached or exceeded.

9. Control device (3) for an internal combustion engine (1), designed to carry out a method according to one of claims 1 to 8.

10. Internal combustion engine (1), with a gas injection device (7) which is arranged and configured to introduce a fuel gas into an air path (5) of the internal combustion engine (1), a throttle valve (9) arranged in the air path (5), a nitrogen oxide sensor (13) arranged in an exhaust gas path (11) of the internal combustion engine (1), an ignition device (17) arranged in a combustion chamber (15) of the internal combustion engine (1), and a control unit (3) according to claim 9, wherein the control unit (3) is operatively connected to the gas injection device (7), the throttle valve (9) and the nitrogen oxide sensor (13).

11. Internal combustion engine (1) according to claim 10, wherein the internal combustion engine (1) has a compressor (19) in the air path (5), wherein the internal combustion engine (1) also has a Compressor bypass path (21) around the compressor (19), wherein a bypass path adjusting device (23) is arranged in the compressor bypass path (21), which is designed to change a flow cross-section of the compressor bypass path (21), and wherein the control unit (3) is operatively connected to the bypass path adjusting device (23).

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