METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE

Abstract

Method for operating an internal combustion engine, wherein the internal combustion engine is operated by an air-fuel mixture comprising a fuel mixture and air, wherein the fuel mixture comprises a first fuel, preferably natural gas, and hydrogen as a second fuel different from the first fuel, wherein a hydrogen content of the fuel mixture is determined, and at least an ignition timing is adapted as a function of the hydrogen content of the fuel mixture independent of a target power output of the internal combustion engine,
wherein the higher the amount of hydrogen in the fuel mixture the later the ignition timing is set for at least partially compensating a shift of a center of combustion due to higher flame speed of hydrogen compared to the first fuel.

Claims

1. A method for operating an internal combustion engine, wherein the internal combustion engine is operated by an air-fuel mixture comprising a fuel mixture and air, wherein the fuel mixture comprises a first fuel including natural gas, and hydrogen as a second fuel different from the first fuel, wherein the method comprises: obtaining a hydrogen content of the fuel mixture, and controlling at least an ignition timing as a function of the hydrogen content of the fuel mixture independent of a target power output of the internal combustion engine, wherein the higher an amount of hydrogen in the fuel mixture the later the ignition timing is set for at least partially compensating a shift of a center of combustion due to a higher flame speed of hydrogen compared to the first fuel.

2. The method according to claim 1, wherein the higher the amount of hydrogen in the fuel mixture the higher a boost pressure target value is set to meet a target NOx amount in an exhaust gas of the internal combustion engine.

3. The method according to claim 1, wherein a lambda value of the air-fuel mixture supplied to the internal combustion engine is adapted during a change of the amount of hydrogen in the fuel mixture for at least partially compensating an increase of a boost pressure without changing an actual power output of the internal combustion engine.

4. The method according to claim 1, wherein a lambda value of the air-fuel mixture supplied to the internal combustion engine is increased during an increase of the amount of hydrogen in the fuel mixture beyond an increase of the lambda value when using only the first fuel.

5. The method according to claim 1, wherein depending on the amount of hydrogen in the fuel mixture a target NOx amount in an exhaust gas of the internal combustion engine is held constant or decreased.

6. The method according to claim 5, wherein the target NOx amount in the exhaust gas of the internal combustion engine is set below a target NOx amount compared to a corresponding target NOx amount when using only the first fuel.

7. The method according to claim 1, wherein an amount of the fuel mixture is adapted to compensate a difference in a heating value of the hydrogen compared to the first fuel including the natural gas.

8. The method according to claim 1, wherein a boost pressure target value is adapted depending on the amount of hydrogen in the fuel mixture.

9. The method according to claim 8, wherein the higher the hydrogen amount in the fuel mixture the higher the boost pressure target value is set.

10. The method according to claim 1, wherein a boost pressure is adapted in a feedback control as a function of a continuously measured NOx content of an exhaust gas of the internal combustion engine.

11. The method according to claim 1, wherein a boost pressure or a boost pressure offset is adapted as a function of the amount of hydrogen in the fuel mixture.

12. The method according to claim 1, wherein the hydrogen content of the fuel mixture is determined by a hydrogen sensor.

13. The method according to claim 1, wherein the hydrogen content of the fuel mixture is estimated by an in-cylinder pressure sensor and/or an exhaust gas temperature sensor.

14. A system, comprising: a controller configured to control operation of an internal combustion engine using an air-fuel mixture comprising a fuel mixture and air, wherein the controller is configured to: obtain a hydrogen content of the fuel mixture comprising first and second fuels, wherein the first fuel comprises natural gas and the second fuel comprises hydrogen; and control at least an ignition timing as a function of the hydrogen content of the fuel mixture independent of a target power output of the internal combustion engine, wherein the higher an amount of hydrogen in the fuel mixture the later the ignition timing is set for at least partially compensating a shift of a center of combustion due to a higher flame speed of hydrogen compared to the first fuel.

15. The system of claim 14, comprising the internal combustion engine controlled by the controller.

16. The system of claim 14, wherein the controller is configured to control a boost pressure of an intake into the internal combustion engine based on the amount of hydrogen in the fuel mixture.

17. The system of claim 14, wherein the controller is configured to control a lambda value of the air-fuel mixture in response to changes in the amount of hydrogen in the fuel mixture.

18. A system, comprising: an internal combustion engine; and a controller configured to control operation of the internal combustion engine using an air-fuel mixture comprising a fuel mixture and air, wherein the controller is configured to: obtain a hydrogen content of the fuel mixture comprising first and second fuels, wherein the first fuel comprises natural gas and the second fuel comprises hydrogen; and control at least an ignition timing as a function of the hydrogen content of the fuel mixture, wherein the ignition timing is adjusted later in response to an increase in the amount of hydrogen in the fuel mixture.

19. The system of claim 18, wherein the controller is configured to control a boost pressure of an intake into the internal combustion engine based on the amount of hydrogen in the fuel mixture.

20. The system of claim 18, wherein the controller is configured to control a lambda value of the air-fuel mixture in response to changes in the amount of hydrogen in the fuel mixture.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Further details and advantages of the invention are apparent from the accompanying figures and the following description of the drawings. The figures show:

[0063] FIG. 1 is a schematic of an internal combustion engine.

[0064] FIG. 2 is a schematic of an internal combustion engine operated by a method according to certain aspects of the invention.

[0065] FIG. 3 is a diagram illustrating a method for operating an internal combustion engine during a change of a hydrogen content in the fuel mixture.

DETAILED DESCRIPTION

[0066] FIG. 1 illustrates a first embodiment of an internal combustion engine 1. This internal combustion engine has a combustion chamber 3 in which a fuel-air mixture is combusted.

[0067] This invention is, of course, not restricted to a single combustion chamber 3 and the combustion chamber 3 used in the Figures serves only as an example. The invention can be used on an internal combustion engine 1 for one or more combustion chambers 3 selectively and/or globally for all applications.

[0068] The fuel-air mixture is supplied to at least one combustion chamber through a compressor 11 of a turbocharger 14, wherein the fuel-air mixture can be cooled after compression by the compressor 11 in a mixture cooler 15.

[0069] The air-fuel mixture supplied can be mixed by a gas mixer (not illustrated in FIG. 1) upstream of the compressor 11, wherein a fuel or a fuel mixturee.g., provided by a natural gas supply gridcan be mixed with air and passed to the compressor 11.

[0070] The mixture cooler 17 and the compressor 11 can be bypassed by means of a bypass line with a compressor bypass valve 10, wherein a boost pressure p2 can be adjusted by this compressor bypass valve 10 and with that boost pressure p2 least one combustion chamber 3 can be filled.

[0071] By changing the boost pressure p2, it is possible to vary the filling of at least one combustion chamber 3.

[0072] In addition, the turbocharger 14 has an exhaust turbine 13 that can be bypassed by a bypass line along with the turbine bypass valve 12.

[0073] By means of this turbine bypass valve 12, an exhaust backpressure p3 can be set which acts on the at least one combustion chamber 3.

[0074] A control unit 2 (e.g., controller) is provided which is signal conductively connected by means of signal conducting connections 6, on the one hand to the compressor bypass valve 10 of the compressor 11 and on the other hand to the turbine bypass valve 12 of the exhaust turbine 13.

[0075] Furthermore, the control unit 2 is signal conductively connected with the combustion chamber 3 to control or monitor the combustion process. Via this signal connection 6, it would also be possible for the control unit 2, e.g., to vary or control an ignition timing of the combustion by an ignition source, preferably a spark plug.

[0076] The compressor bypass valve 10 of the compressor 11 (and also of the mixture cooler 15) in this embodiment is configured as an actuator 4 that influences combustion parameters.

[0077] The turbine bypass valve 12 of the exhaust turbine 13 in this embodiment forms the actuator 5 that influences the exhaust backpressure p3.

[0078] The control unit 2 is configured to actuate the at least one actuator 4 (in this embodiment the compressor bypass valve 10 of the compressor 11) that influences the boost pressure p2.

[0079] As already described in the beginning, fuel sources such as natural gas from a public supply grid can contain a certain amount of hydrogen, and a method for operating the internal combustion engine is provided to react on varying contents of hydrogen in the air-fuel mixture according to certain aspects of the invention.

[0080] An embodiment of such a method for operating an internal combustion engine 1 is shown by FIG. 2.

[0081] FIG. 2 illustrates a schematic overview of a method for operating an internal combustion engine 1.

[0082] In this embodiment, the control unit 2 is split up into an ignition timing control module 16 and a boost pressure control module 17, wherein an ignition timing of the combustion in the combustion chamber 3 and a boost pressure of the air-fuel-mixture delivered to the combustion chamber 3 can be controlled by the control unit 2.

[0083] The boost pressure setpoint p2 is provided by a calculation unit 18 to the boost pressure control module 17, wherein the calculation unit 18 calculates a boost pressure setpoint based on a given NOx setpoint and a power requirement of the internal combustion engine 1.

[0084] The calculation unit 18 could for example be embodied as the regulating device disclosed in EP 2 977 596 B1.

[0085] The ignition timing setpoint is given by the hydrogen control unit 19.

[0086] The hydrogen control unit 19 is configured to: [0087] determine a hydrogen content of the fuel mixture, [0088] adapt an ignition timing as a function of the hydrogen content of the fuel mixture independent of a target power output of the internal combustion engine 1,
wherein the higher the amount of hydrogen in the fuel mixture the later the ignition timing is set to compensate a shift of center of combustion due to higher flame speed of hydrogen compared to the first fuel.

[0089] Independent of a target power output in this context is to be understood that the ignition timing is not adapted in order to change a target power output of the internal combustion engine, e.g., in the case of a change in load, but is adapted depending on the hydrogen amount in the fuel mixture. Of course, it can be necessary to adapt the ignition timing in reaction of a change in load, but such a reaction is different to the adaption of the ignition timing depending on the hydrogen amount in the fuel mixture to compensate for a change of combustion speed of the fuel mixture.

[0090] Furthermore, it can be provided that the hydrogen control unit 19 is configured to influence the target NOx amount, wherein the higher the amount of hydrogen in the fuel mixture the higher a boost pressure target value is set to meet a target NOx amount in the exhaust gas of the internal combustion engine 1, wherein indirectly via the calculation unit 18 the boost pressure setpoint p2 is controlled to meet the requirements of the NOx setpoint.

[0091] It can also be provided that the hydrogen control unit 19 is configured to directly vary the boost pressure setpoint p2 to influence the lambda value.

[0092] The [0093] ignition timing control module 16, [0094] boost pressure control module 17, [0095] calculation unit 18 and/or [0096] hydrogen control unit 19
can be embodied as separate hardware components and/or software modules. In other preferred embodiments, these modules are partially or fully integrated with each other as one or more software modules being executed on one or more hardware components.

[0097] FIG. 3 illustrates a method for operating an internal combustion engine 1 during a change of a hydrogen content in the fuel mixture by a diagram.

[0098] The diagram shows therefore a connection between a boost pressure setpoint p2 (ordinate) and a power output (abscissa) of an internal combustion engine 1 for different air-fuel mixtures (indicated by the lines a, b and c).

[0099] Line 7 discloses an operation by an air-fuel mixture of charged air and natural gas, wherein the internal combustion engine 1 is operated at an operating point I to reach a required power output P.

[0100] If the fuel provided, e.g., by a public supply grid, changes to a fuel mixture comprising natural gas and a content of hydrogen (as shown by line 8), then the internal combustion engine 1 has to be transferred to operation point II to deliver continuous power output P.

[0101] As such, a variation of the hydrogen content in the fuel mixture of the air-fuel mixture appears, according to certain aspects of the invention, it is provided to control the ignition timing, wherein the higher the amount of hydrogen in the fuel mixture the later the ignition timing is set to compensate a shift of center of combustion due to higher flame speed of hydrogen compared to the first fuel, i.e., operation point I in this example.

[0102] Furthermore, as can be seen in FIG. 3, the boost pressure is increased during the increase of hydrogen, wherein the lambda value is changed. By this increase of the boost pressure p2, the control of the ignition timing to late and the increase of hydrogen content can be compensated to keep the power output constant and reach operation point II, line 8, indicating a specific lambda value for a specific hydrogen content of a fuel mixture.

[0103] Starting from the operating point II, the boost pressure p2 can be increased further, wherein line 9indicating an air-fuel mixture with a different lambda value but the same fuel-mixture as line 8can be reached.

[0104] As the boost pressure p2 of an air-fuel mixture starting in operation point II is increased, wherein the certain fuel mixture mass is kept constant, also the lambda value is increased until an operation point III is reached, wherein the NOx emissions can be reduced while still having the same power output P.

[0105] The different relationships between the boost pressure p2, the power output P, a lambda value, and a NOx content can be stored in the control unit 2, e.g., in the form of FIG. 3.

LIST OF USED REFERENCE SIGNS

[0106] 1 internal combustion engine [0107] 2 control unit [0108] 3 combustion chamber [0109] 4 actuator [0110] 5 actuator [0111] 6 signal conductive connection [0112] 7 line [0113] 8 line [0114] 9 line [0115] 10 compressor bypass valve [0116] 11 compressor [0117] 12 turbine bypass valve [0118] 13 exhaust turbine [0119] 14 turbocharger [0120] 15 mixture cooler 15 [0121] 16 ignition timing control module [0122] 17 boost pressure control module [0123] 18 calculation unit [0124] 19 hydrogen control unit