Internal combustion engine, as well as method and computer program product for operating the same

Abstract

Internal combustion engine comprising - a control unit (2) for controlling the internal combustion engine (1), - at least one combustion chamber (3) for combusting at least one fuel, and - an exhaust gas recirculation system (4) for recirculating exhaust gas from the combustion into the at least one combustion chamber (3), wherein the control unit (2) is configured to control an exhaust gas recirculation amount, preferably an exhaust gas recirculation rate, by actuating the exhaust gas recirculation system (4) according to a reference exhaust gas recirculation amount, preferably a reference exhaust gas recirculation rate, wherein the control unit (2) is configured to set or correct the reference exhaust gas recirculation amount in dependence on - a first parameter at least partially indicative of a stability of the combustion in the at least one combustion chamber (3) and / or - a second parameter at least partially indicative of a gas state, in particular a state of the recirculated exhaust gas.

Description

[0001] Internal combustion engine, as well as method and computer program product for operating the same The present disclosure concerns internal combustion engines, methods for operating internal combustion engines, and computer program products for operating internal combustion engines. Internal combustion engines according to this disclosure are primarily stationary engines for driving generators. Combinations of internal combustion engines, in particular gas engines, driving generators for the creation of electrical energy are known as gensets. It is however also conceivable to apply the current disclosure to other types of engines.Internal combustion engines for automotive applications, e.g.operated with gaseous hydrogen, and with exhaust gas recirculationare in principle known for example from DE 102021121214 A1. Thisdisclosure suggests adjusting the amount of recirculated exhaustgas based on the engine speed. A disadvantage of coupling the amount of recirculated exhaust gas to the engine speed is of course that the engine speed does not completely define the operation point of an engine. Depending for example on power demand, environmental conditions, fuel conditions, and age of the internal combustion engine different amounts of recirculated exhaust gas can be optimal at the same engine speed. This is a particularly pronounced disadvantage for internal combustion engines coupled to generators for creating electrical energy because these engines need to perform at a speed which is as stable as possible in order to keep the frequency and phase of the produced electricity in close correlation to the distribution grid into which the electricity is fed. The result is that the engine is operated in a non-optimal way from the point of view of energy efficiency and / or power output. Advanced controls of internal combustion engines are described inEP 2977596 A1, unpublished International Patent Application no.PCT / AT2023 / 060134, unpublished European Patent Application no. 22209889, and unpublished International Patent Application no. PCT / AT2023 / 060230. The object of the disclosure is therefore to provide internal combustion engines as well as methods and computer program products for operating internal combustion engines in which or with which the amount of recirculated exhaust gas can be controlled for an operation of the internal combustion engine which is optimal or closer to the optimum compared to the prior art with regard to energy efficiency and / or power output. One aspect of the present disclosure is an internal combustion engine comprising -an electronic control unit for controlling the internalcombustion engine, -at least one combustion chamber for combusting at leastone fuel, and -an exhaust gas recirculation system for recirculatingexhaust gas from the combustion into the at least one combustion chamber, wherein the control unit is configured to control an exhaust gas recirculation amount, preferably an exhaust gas recirculation rate, by actuating the exhaust gas recirculation system according to a reference exhaust gas recirculation amount, preferably a reference exhaust gas recirculation rate, and wherein the control unit is configured to set or correct the reference exhaust gas recirculation amount in dependence on -a first parameter at least partially indicative of astability of the combustion in the at least one combustion chamber and / or -a second parameter at least partially indicative of a gasstate, in particular a state of the recirculated exhaust gas. Another aspect of the current disclosure is an internal combustion engine comprising at least one combustion chamber, an exhaust gas recirculation system, and an electronic control unit, wherein thecontrol unit is configured to control at least one engine variablefor an operation of the internal combustion engine, and the control unit is configured to control an amount of exhaust gas recirculated into the at least one combustion chamber, and wherein the controlunit is configured to calculate or estimate an intake gas amountand / or an intake gas coefficient indicative of the amount of intakegas, which is a mixture of the recirculated exhaust gas and aspirated fresh air, necessary for a stoichiometric combustion given an actual and / or reference exhaust gas recirculation amount, preferably an actual and / or reference exhaust gas recirculationrate, and to use the intake gas amount and / or intake gascoefficient as input for the control of the at least one engine variable of the internal combustion engine. Another aspect of the current disclosure is a method for operating an internal combustion engine the method comprising -measuring and / or otherwise determining a first parameterat least partially indicative of a stability of a combustion in at least one combustion chamber and / or a second parameter at least partially indicative of a gas state, in particular a state of the recirculated exhaust gas, -setting or correcting a reference exhaust gas recirculationamount, preferably a reference exhaust gas recirculation rate, in dependence on the first parameter at least partially indicative of a stability of a combustion in theat least one combustion chamber and / or in dependence on the second parameter at least partially indicative of a gas state, in particular a state of the recirculated exhaust gas, and -controlling an exhaust gas recirculation amount, inparticular an exhaust gas recirculation rate, by actuatingan exhaust gas recirculation system according to the reference exhaust gas recirculation rate. Another aspect of the current disclosure is a method for operating an internal combustion engine the method comprising -measuring and / or otherwise determining an actual and / orreference exhaust gas recirculation amount, preferably an actual and / or reference exhaust gas recirculation rate, -calculating or estimating an intake gas amount and / or anintake gas coefficient indicative of the amount of intakegas, which is a mixture of the recirculated exhaust gas and aspirated fresh air, necessary for a stoichiometric combustion given the actual and / or reference exhaust gas recirculation amount, preferably the actual and / or reference exhaust gas recirculation rate, and -using the intake gas amount and / or intake gas coefficientas input for a control of at least one engine variable ofthe internal combustion engine. Another aspect of the present disclosure is a computer programproduct for operating an internal combustion engine comprising instructions causing an executing computer to perform the following: -setting or correcting a reference exhaust gas recirculationamount, preferably an exhaust gas recirculation rate, in dependence on a parameter at least partially indicative of a stability of a combustion in at least one combustion chamber and / or in dependence on a second parameter at least partially indicative of a gas state, in particular a stateof the recirculated exhaust gas, and -controlling an exhaust gas recirculation amount, inparticular an exhaust gas recirculation rate, by actuatingan exhaust gas recirculation system according to the reference exhaust gas recirculation amount. Another aspect of the present disclosure is a computer programproduct for operating an internal combustion engine comprisinginstructions causing an executing computer to perform the following: -calculating or estimating an intake gas amount and / or anintake gas coefficient indicative of the amount of intakegas, which is a mixture of the recirculated exhaust gas and aspirated fresh air, necessary for a stoichiometric combustion given an actual and / or reference exhaust gas recirculation amount, preferably an actual and / or reference exhaust gas recirculation rate, and -using the intake gas amount and / or intake gas coefficientas input for a control of at least one engine variable ofthe internal combustion engine. Another aspect of the present disclosure is transitory or non- transitory storage device with a computer program product as mentioned before stored thereon.Another aspect of the present disclosure is a data carrier signalcarrying at least one of -one or more of the computer program products as mentionedbefore -a reference exhaust gas recirculation amount, preferablyan exhaust gas recirculation rate, and / or a correction therefor, calculated in dependence on a parameter at least partially indicative of a stability of a combustion in at least one combustion chamber and / or in dependence on a second parameter at least partially indicative of a gas state, in particular a state of the recirculated exhaustgas -an intake gas amount and / or an intake gas coefficientindicative of the amount of intake gas, which is a mixture of recirculated exhaust gas and aspirated fresh air, necessary for a stoichiometric combustion given an actual and / or reference exhaust gas recirculation amount, preferably an actual and / or reference exhaust gas recirculation rate One effect of the different aspects of the present disclosure is a control of an internal combustion engine which is optimal or closer to the optimum compared to the prior art with regard to energy efficiency and / or power output. Another major advantage of the present disclosure is that a stable combustion can be realised even with higher exhaust gas recirculation rates. The first parameter at least partially indicative of a stability of the combustion in the at least one combustion chamber can for example be- a burn duration parameter of the combustion in the at leastone combustion chamber and / or -a mass fraction of burnt fuel parameter of the combustionin the at least one combustion chamber and / or -a peak firing pressure parameter of the combustion in theat least one combustion chamber and / or -a knock magnitude parameter and / or- a misfire detection parameter and / or- a glow ignition detection parameter and / or- a backfire detection parameter.These parameters offer a quantification of the stability of the combustion in the at least one combustion chamber. Since exhaust gas recirculation is included in internal combustion engines often for the reason of improving the stability of the combustion using the first parameter at least partially indicative of a stability of the combustion can result in a very accurate control of the exhaust gas recirculation. The second parameter at least partially indicative of a gas state, in particular the state of the recirculated exhaust gas, can also have a significant effect on the optimum amount of exhaust gas recirculation. On the one hand the second parameter can be a parameter of the recirculated exhaust gas, such as for example an oxygen parameter and / or a humidity parameter thereof. On the other hand, the second parameter can alternatively or additionally be for example a humidity parameter of the aspirated air. As mentioned, one aspect of the present disclosure concerns anintake gas amount and / or an intake gas coefficient indicative ofthe amount of intake gas, which is a mixture of the recirculated exhaust gas and aspirated fresh air, necessary for a stoichiometric combustion given an actual and / or reference exhaust gas recirculation amount, preferably an actual and / or reference exhaust gas recirculation rate.Such a parameter can be helpful for determining an optimumoperating point in the presence of recirculated exhaust gas. Forexample, the overall control of an internal combustion engine isin many cases reliant on a control of the lambda value (also called air fuel equivalence ratio) which is the ratio of air to fuel normalised so that a lambda value of 1 indicates stoichiometric combustion. Since recirculated exhaust gas has in general significantly less oxygen than aspirated fresh air due to the combustion from which it results, exhaust gas recirculation in general has a significant effect on the lambda value at which the internal combustion engine operates. The control of other engine variables than lambda can alternativelyor additionally also benefit from an intake gas amount and / or anintake gas coefficient indicative of the amount of intake gas,which is a mixture of the recirculated exhaust gas and aspirated fresh air. For example, a power and / or boost pressure control can additionally or alternatively be dependent on the intake amount or intake gas coefficient. The control of the internal combustion engine according to the present disclosure can include a control and / or control scheme asdisclosed in EP 2977596 A1, unpublished International PatentApplication no. PCT / AT2023 / 060134, unpublished European Patent Application no. 22209889, and / or unpublished International Patent Application no. PCT / AT2023 / 060230. Exhaust gas recirculation systems can be classified in internal and external exhaust gas recirculation systems, wherein the recirculated exhaust gas does not leave the at least one combustion chamber in the internal variant, but remains in the at least one combustion chamber, for example via an overlap of the open periods of the intake and exhaust valves. External exhaust gas recirculation means that the recirculated exhaust gas is taken from the at least one combustion chamber and mixed with the aspirated fresh air designated for the at least one combustion chamber, and potentially fuel, and delivered to the at least one combustion chamber. External exhaust gas recirculation can furthermore be divided into low pressure and high pressure exhaust gas recirculation systems. In low pressure exhaust gas recirculation systems, the exhaust gas first passes through at least one exhaust gas turbine, e.g. of one or more turbo chargers, and is then mixed in with the aspirated fresh air at a lower pressure than upstream of the at least one exhaust gas turbine, preferably before at least one compressor of the one or more turbo chargers. In high pressure exhaust gas recirculation the recirculated exhaust gas is branched of the rest of the exhaust gas before an exhaust gas turbine and preferably mixed in with the aspirated fresh air at a boost pressure created by a compressor of the one or more turbo chargers. Mixed versions are of course conceivable, e.g. where the recirculated exhaust gas is taken from a volume between two exhaust gas turbines and mixed with the aspirated fresh air in a volume between two compressors. In many cases exhaust gas recirculation systems comprise a exhaust gas recirculation valve which can be used to regulate or open loop control or closed loop control the amount of recirculated exhaust gas, preferably the exhaust gas recirculation rate. Alternatively, or additionally, other actuators can be used to regulate or control the amount of recirculated exhaust gas, e.g. a blower. In preferred embodiments the term that a parameter is set or corrected “in dependence on” certain other parameters can be understood to mean that the other parameter is an input in a control scheme for controlling the parameter. The internal combustion engine can be a gas engine. Internal combustion engines of the present disclosure can be aninternal combustion engines, preferably a gas engine, coupled toa generator generating electrical energy (so-called genset). The internal combustion engine can be a stationary engine. In other embodiments, the internal combustion engine can for example be an engine for naval applications. The internal combustion engine can be of a piston-cylinder type, preferably -with an even number of cylinders, particularly preferablybetween 6 and 24, and / or -with the cylinders in a row or V-configuration. The internal combustion engine can be configured for combusting molecular hydrogen as fuel. Alternatively, or additionally, other gases, such as for example natural gas, methane, and / or other types of hydrocarbons, can be used as fuel. The amount of recirculated exhaust gas can for example be expressed as concentration of the recirculated exhaust gas in the complete gas mass supplied to a combustion chamber, such as a cylinder, and / or in absolute terms and / or as so-called exhaust gas recirculation rate which is the fraction of the complete gas mass supplied to a combustion chamber, such as a cylinder. The electronic control unit can be arranged directly at the internal combustion engine and in wire and / or wireless signal connection with the rest of the internal combustion engine. In certain embodiments the control unit can be partly or wholly embodied by a computer server in a long-distance data transmission connection with the rest of the internal combustion engine. In certain embodiments the control unit can be embodied by distributed computing. Mixed forms for the arrangement and / or connection of the control unit with the rest of the internal combustion engine are of course conceivable. The control unit can be an electronic control unit. The control unit can be the computer executing the mentioned computer program products.It should be noted that the control unit can be embodied as one ormore software and / or hardware modules.The control unit can be embodied in a distributed fashion wheresome sub-modules are present or run at the internal combustion engine and others are present or run at a computer distanced from the internal combustion engine, e.g., in a cloud server or the like. The computer program product can be executed on the control unit. In other embodiments, the computer program product can for example be used to control a virtual internal combustion engine, for example as part of a simulation of the internal combustion engine. The computer program products can receive a measurement and / or other values, such as setting or reference values, as input.The measurement and / or other determination can concern the firstparameter at least partially indicative of a stability of a combustion in at least one combustion chamber and / or the second parameter at least partially indicative of a gas state, in particular the state of the recirculated exhaust gas, Alternatively, or additionally, the measurement and / or otherdetermination can concern the actual and / or reference exhaust gasrecirculation amount, preferably the actual and / or reference exhaust gas recirculation rate. The internal combustion engine can in particularly preferred embodiments be an engine configured for molecular hydrogen as fuel, exhaust gas recirculation, and lean burn operation. Further preferred embodiments of the invention are defined in the dependent claims. As mentioned before, the first parameter at least partially indicative of the combustion stability can be at least one of -a burn duration parameter of the combustion in the at leastone combustion chamber and / or -a mass fraction of burnt fuel parameter of the combustionin the at least one combustion chamber and / or -a peak firing pressure parameter of the combustion in theat least one combustion chamber and / or -a knock magnitude parameter and / or- a misfire detection parameter and / or- a glow ignition detection parameter and / or- a backfire detection parameter.The second parameter at least partially indicative of a state of the recirculated exhaust gas can be at least one of -an oxygen parameter of the recirculated exhaust gas and / or- a humidity parameter of the recirculated exhaust gas and / or- a humidity parameter of aspirated fresh air.The control unit can preferably be configured to set the reference exhaust gas recirculation amount in dependence on an engine power output and / or a boost pressure and / or a fuel type. Formulated differently, there can be a feed forward control of the exhaust gas recirculation amount, wherein the reference is set in dependence on an engine power output and / or a boost pressure and / or a fuel type. In particularly preferred embodiments the control unit can have stored a reference for the first parameter at least partiallyindicative of the stability of the combustion and / or the at leastone second parameter at least partially indicative of a gas state, and the control unit can be configured to subtract an actual value of the first parameter and / or the second parameter from the respective reference, and preferably the respective difference between the first parameter and / or the second parameter and the respective reference can be subjected to a proportional–integral– derivative controller. Said difference, preferably after being subjected to the proportional–integral–derivative controller, can be added to the reference exhaust gas recirculation amount as the correction. The internal combustion engine, and in particular the control unit, can be configured for lean burn operation, and / or the internal combustion engine can be a gas engine. In particular for hydrogen and / or natural gas or other hydrocarbons lean burn operation of the internal combustion engine can be preferred due to the ignition and emission behaviour under these conditions. There can be provided -an intake tract for delivering air and / or an air-fuelmixture to the at least one combustion chamber, and -an exhaust gas tract for discharging exhaust gas from theat least one combustion chamber. The exhaust gas recirculation system can comprise -an exhaust gas recirculation conduct which connects theexhaust gas tract with the intake tract in a fluid communication sense for recirculating exhaust gas into the at least one combustion chamber, and- an exhaust gas recirculation valve configured to adjust amass flow and / or a volume flow through the exhaust gas recirculation conduct. Formulated in other words, the exhaust gas recirculation system can be configured for external exhaust gas recirculation. The exhaust gas recirculation system can comprise a blower (or more blowers) configured to increase a mass flow of recirculated exhaust gas, and wherein the control unit is configured to activate the blower in dependence on the reference exhaust gas recirculation amount. In situations where the exhaust gas is not in condition to provide a recirculated exhaust gas mass flow said blower can increase the mass flow in order to bring the operating point of the internal combustion engine closer to the optimum. There can be provided an oxygen sensor configured for measuring an oxygen concentration or amount of oxygen of the recirculated exhaust gas and / or the electronic control unit can be configured to estimate the oxygen concentration or amount of oxygen in the recirculated exhaust gas. The estimate of the oxygen concentration or the amount of oxygen in the recirculated exhaust gas can for example be made with a dynamical engine model with which concentrations of fuel, air, and recirculated exhaust gas are estimated. There can be provided a fuel valve, and the at least one engine variable can comprise a command variable for the fuel valve, preferably a command value for the mass flow through the fuel valve and / or an opening time duration of the fuel valve. The at least one engine variable can particularly preferably comprise a fuel air equivalence ratio (also called lambda) and / ora boost pressure, in particular a command value for the fuel airequivalence ratio and / or the boost pressure. In some embodiments the control unit can employ PID control for controlling the operating point of the internal combustion engine. For example, in connection with Fig. 4 below an embodiment is disclosed in which the power of the internal combustion engine is controlled with a PID controller. The control unit can particularly preferably comprise a model- based controller and an engine model of the model-based controllercan comprise a correction based on the intake gas amount and / or anintake gas coefficient indicative of the amount of intake gasnecessary for the stoichiometric combustion. The engine model according to the invention may be a linear version or a non-linear version of a model of the internal combustion engine. The model-based controller can preferably comprise lower-level controllers configured to perform lower-level control of actuators, preferably a throttle valve, a compressor bypass valve,a wastegate valve, an ignition system, a fuel (metering) valve,and / or an exhaust gas recirculation valve and / or a blow-off valve. This can be a preferred way for controlling the boost pressure by actuating the compressor bypass valve, the throttle valve, the wastegate valve, and / or the blow off valve. The model-based controller may be configured to output command values, preferably for the boost pressure and / or the air-fuel equivalence ratio, and wherein the lower-level controllers may be configured to use the command values outputted by the model-based controller as reference values for the lower-level control of the actuators. Formulated differently, in preferred embodiments there is a cascaded control scheme. According to the invention a control can be embodied in different ways, for example as open loop control or closed loop control, with one input and / or one output variable. However, in particularthe model-based controller can be a multi-input / multi-outputcontroller. The low-level controls can be preferably implemented as open loop control or PID control (potentially with any of the PID gains zero). It furthermore can include models for feedforward or for open loop control that are possibly inverted. Preferred measurement values which can be taken at the internal combustion engine and / or the generator and which can be used in any of the controls of the cascaded control according to thepresent disclosure as feedback are for example:- engine speed and / or equivalent grid frequency and / or- generator power and / or crankshaft torque and / or- generator voltage and / or- boost pressure before and / or after the throttle valveand / or -boost temperature (i.e., the temperature of the air and / orair / fuel mixture downstream of a compressor). -NOx concentration- air-fuel equivalence ratio A cascaded control is understood as a control with at least one high-level control and at least one low-level control wherein at least one output variable of the at least one high-level control is used as at least one setpoint for the at least one low-level control. For the purposes of this invention the air-fuel equivalence ratio(also called lambda) is the ratio of the masses of air and fuel inthe mixture divided by the stoichiometric air / fuel ratio. As mentioned, the at least one control unit can comprise a model- based controller, preferably model predictive controller and / or a state space controller, for performing the at least one high-level control, preferably during the load transient operation and / or substantially during all operation. Instead of a model predictive controller and / or a state space controller the model-based controller can be another controller configured to output the at least one setpoint for the at least one low-level controller by solving a mathematical optimization problem based on actual measurements and a dynamic engine model to minimize the control error. The model-based controller can comprise a cost function to beminimised, wherein the cost function is based on the engine modelof the internal combustion engine, potentially together with a generator coupled to the internal combustion engine and / or a power supply grid and / or participants of the power supply grids, such as other generators for creating electrical energy or loads. In particular, the model-based controller can be configured for solving an optimization problem that makes use of a dynamic engine model to predict the evolution of relevant engine variables (e.g., speed, boost pressure, power, torque, lambda, EGR concentration) over a finite or infinite prediction horizon in response to the selected setpoints to the low level controllers and therefore is able to coordinate the setpoints in a preferably optimal way (e.g. linear quadratic regulator, model predictive controller). The model-based controller can apply nonlinear control techniques such as nonlinear model predictive control, feedback linearization or backstepping, or linear control techniques that work with a model that is linearized around the actual / reference operation point or around the actual / reference trajectory of state / system variables. The controller may receive measurements of power that provide the feedforward of the measured disturbance that is responsible for a fast reaction and saturation of the references to the at least one low-level control in case of a load transient. A feedback control based on the speed and boost pressure and / or other measurements can provide the additional control action for stabilizing the system at the desired references. As mentioned, the basis for the model-based controller is preferably a dynamic engine model that describes the evolution of relevant engine variables (speed, boost pressure, air fuel ratio, torque and / or power and possibly others) depending on the control inputs and external disturbances such as electrical loads on the generator that is coupled to the engine. An example for such a model is provided by J. Huber, H. Kopecek, and M. Hofbaur. In “Nonlinear model predictive control of an internal combustion engine exposed to measured disturbances”, Control Engineering Practice 44, (2015) for the lean burn case without exhaust gas recirculation or as a minimum formulation given by the following equations including EGR. A torque balance between engine torque τeand generator load τggoverns the engine speed is given by Guzzella, Lino, and Christopher Onder in “Introduction to modelling and control of internal combustion engine systems”, Springer Science & Business Media, (2009) as with the engine torque ^^computed as depending on volumetric efficiency ^^^^, brake efficiency ^^^^^^, displacement volume ^^,lower heating value ^^, gas constant of the mixture ^^^, intakemanifold temperature ^^^, stoichiometric air fuel ratio ^^^^, as well as the controlled variables engine speed omega, intakemanifold pressure ^^′, air fuel equivalence ratio ^ and the exhaustgas recirculation fraction ^^^^, leading to with The following assumptions for the closed loop control of the lower-level controls may be taken for the design of the model-basedcontroller control. Here ^^^^^ is the intake gas amount indicative of the amount ofintake gas, which is a mixture of the recirculated exhaust gas and aspirated fresh air, necessary for a stoichiometric combustion given an actual and / or reference exhaust gas recirculation amountand it can be computed with the following equation. One central aspect of the present disclosure is that the intake gas amount, or the intake gas coefficient, can be used to correct the engine model for the different oxygen concentration in the recirculated exhaust gas compared to the ambient air, in this particular example by correcting the torque balance. The intake gas coefficient could for example be defined as However, in this document the equations are formulated in terms of the intake gas amount. It can also be beneficial to adapt the constraints for the lambda command value using the intake gas amount (or the intake gas coefficient), for example as This makes it more likely that a correct fuelling state can be maintained in the internal combustion engine. The boost pressure has a decisive effect on the performance of the internal combustion engine because it has a strong influence on the relative amounts of fuel and oxygen in the at least one combustion chamber. One example of correcting the boost pressure reference using the intake gas amount would be as follows: The LEANOX module sets a reference boost pressure p2,ref’ based on the estimated power or load of the genset so as to achieve a desired level of NOx emissions. An embodiment for how the LEANOX module functions can be found inEP 2977596 A1.The tracking behaviour of boost pressure, with boost pressure ^ reference ^′^,^^^ ≡ ^^ and measurement ^^′ can be modelled with timeconstant ^ and slope ^ with (see Fig. 6) Or further simplified, e.g., The tracking behaviour of air fuel equivalence ratio ^ can bemodelled with a dependence on the delay between the gas dosage / fuelmetering and the cylinders ^ as well as a mixing time constant ^^with The tracking behaviour of exhaust gas recirculation concentration^^^^can be modelled with a dependence on the transport delay between the EGR valve and the cylinders ^^^^as well as a mixing time constant ^^^^, Further relations for implementing the current example of theengine model and the corresponding model predictive control arecollected in the following. Constraints: Boost pressure command value constraint: EGR command value constraint: References: Engine speed reference: ^^,^^^ = const = 1500^ 30 Base boost pressure reference: ^^^,^^^,^ = ^^^^^^^^^^, ^^^ , ^^^^, ^^^EGR reference: Lambda reference: Optimisation: st. model equations and constraints.Based on these prerequisites an example control strategy for ahydrogen engine with exhaust gas recirculation configured for lean burn operation could be formulated as follows: 1) Power setpoint / actual power is converted to boost pressure reference (as LEANOX curve) defines basic reaction of CBV,TV in transients 2) Power controlled to setpoint via actuation of lambda command.3) L_min depends on EGR concentration ^^ ^^^4) Corrections depending on ^ ^ ^^^- Option 1: Correction of boost pressure setpoint: tomaintain lambda at same reference -Option 2: Correction of lambda setpoint and limits: tomaintain same boost pressure: -Option 3: combination of Option 1 + 2: select ^^^,^^^and then correct ^^^^^to maintain power5) Compute gas mass flow from lambda command with updated ^^ ^^^ 6) EGR concentration controlled by feedforward depending on load / ^^ ^and gas type: ^ = ^(^^^^^,^^^,^^ ^ , ^^^ ^^^^)Feedback correction: -Option 1: estimate combustion parameter from cylinderpressure: -Option 2: estimate / measure O2 concentration in EGR:O2 set - O2 act ^^^^,^^^,^^EGR concentration command: ^^^^,^^^ = ^^^^,^^^,^^ + ^^^^,^^^,^^7) EGR concentration command controlled as feedforward via inverse valve equation rPosEgr = ^^^^8) Additionally an EGR blower is activated depending on the desired egr massflow ^^̇^^,^^^(option: control massflow with blower instead of or in addition to valve)Further details and advantages of the present disclosure are apparent from the figures and the accompanying description. The figures show:Fig. 1 a schematic depiction of an example internalcombustion engine,Fig. 2 a schematic depiction of an example genset coupledto a power grid,Fig. 3 a table concerning the intake gas amount,Fig. 4 an embodiment of a control scheme for an internalcombustion engine,Fig. 5 an embodiment of a control scheme for an internalcombustion engine, andFig. 6 and 7 diagrams showing simulation results.Fig. 1 shows a schematic depiction of an embodiment of an internalcombustion engine 1 according to the invention.A fuel valve 12 is provided for mixing a fuel and air to producea combustible air / fuel mixture. The fuel can for example be natural gas including methane and / ormolecular hydrogen. Alternatively, or additionally, the fuel maycomprise other hydrocarbons.The air / fuel mixture is compressed in compressor 14 of theturbocharger 15 so that the air / fuel mixture is charged into thecombustion chamber 3 or a plurality of combustion chambers 3 while under a boost pressure p2’ (potentially together with recirculated exhaust gas, see below).In a bypass conduct bypassing the compressor 14 of the turbocharger15 there is a compressor bypass valve 16 which can be used todirect an amount of the air / fuel mixture around the compressor 14 so as to lower the boost pressure p2’.In the intake tract 6 connecting the compressor 14 of theturbocharger 15 to the combustion chamber 3 there is a throttlevalve 17. In this embodiment the engine is mixture charged as the fuel valve12 is upstream of the compressor 14. In other embodiments the fuelvalve 12 can be arranged downstream of the compressor 14 (aircharged engine).The turbocharger 15 in this example is a single stage turbocharger15. In other embodiments according to the invention there can two,three, four or more turbocharger 15 stages.The internal combustion engine 1 could also include a blowoff valve for rapidly discharging charged air and / or charged air / fuel mixture into the environment or other separate volumes. However, in this embodiment such a blowoff valve is not included. The cylinder charge, which is the air / fuel mixture charged intothe combustion chambers 3 under the boost pressure p2’ is ignitedusing an ignition system 18, in this case a system comprising aspark plug for each combustion chamber 3.In principle, the present disclosure can also be used withcompression ignition engines and / or engines operated with liquid fuel and / or dual fuel engines.The combustion chambers 3 can comprise a pre-combustion chamber.After combustion in the combustion chambers 3 the exhaust gasesremaining in the combustion chambers 3 are expelled therefrom.The embodiment of Fig. 1 comprises an exhaust gas recirculation system 4.There is an exhaust gas recirculation conduct 8 in which an exhaustgas recirculation valve 9 is arranged.The exhaust gas recirculation valve 9 can be used to recirculatepart of the exhaust gas into the mass flow of the air / fuel mixture directed into the combustion chambers 3, such that the charge comprises recirculated exhaust gas next to the air / fuel mixture. Optionally there can be a blower 10 in the exhaust gas recirculation conduct 8. The exhaust gas which is not recirculated is decompressed in theexhaust gas turbine 19 of the turbocharger 15. The exhaust gasturbine 19 drives the turbocharger shaft 20 which in turn drivesthe compressor 14 of the turbocharger 15.Alternatively, or additionally, to the exhaust gas turbine 19 thecharging system can comprise an electric drive for the compressor14 of the turbocharger 15.There is a bypass conduct bypassing the exhaust gas turbine 19 anda waste gate valve 21 is arranged in this bypass of the exhaustgas turbine 19 so that part of the exhaust gas can be routed pastthe exhaust gas turbine 19.The exhaust gas passing through the exhaust gas turbine 19 and / orthe wastegate valve 21 is then subjected to aftertreatment in theexhaust gas aftertreatment system 23 which can comprise differentkinds of catalytic converters. For example, if the internal combustion engine 1 is operated with essentially stoichiometric lambda the exhaust gas aftertreatmentsystem 23 can comprise a three-way catalytic converter.In other embodiments where the internal combustion engine 1 is operated with a lean burn concept the exhaust gas aftertreatmentsystem 23 can comprise a selective catalytic reaction catalyticconverter and / or an oxidation catalytic converter and / or a thermal oxidiser.The control unit 2 is in signal communication with the actuatorsof the internal combustion engines, which in this embodiment comprise the fuel valve 12, the exhaust gas recirculation valve 9, the ignition system 18, the compressor bypass valve 16, the throttle valve 17, and the wastegate valve 21. However, the signal communication of the control unit 2 with theactuators is not depicted in Fig. 1 for the sake of clarity of thefigure.The control unit 2 of this embodiment is also in signalcommunication with a multitude of measurement devices which can be used to implement closed loop control, both for the model-basedcontroller 13 and the lower-level controllers.Measurement devices which can for example be used in this capacityare -pressure sensors, upstream and / or downstream of thecompressor 14 and / or upstream and / or downstream of theexhaust turbine 19, and / or -temperature sensors, upstream and / or downstream of thecompressor 14 and / or upstream and / or downstream of theexhaust turbine 19, and / or -in cylinder pressure sensors and / or- knock sensors and / or- lambda sensors in the exhaust gas conduct and / or- oxygen concentration sensors, in particular oxygen sensors11 in the exhaust gas recirculation conduct 8, and / or- engine speed sensors- NOx sensorsThese sensors can be embodied as in principle known in the prior art.Also here, the signal communication of the control unit 2 with thesensors is not depicted in Fig. 1 for the sake of clarity thefigure.In the embodiment of Fig. 1 the exhaust gas recirculation valve 9recirculates exhaust gas from downstream of the exhaust gas turbine19 to a volume upstream of the compressor 14 when at least partially opened. This is called low-pressure exhaust gas recirculation.In other embodiments the exhaust gas is recirculated from upstreamof the exhaust gas turbine 19 to downstream of the compressor 14,i.e., a low-pressure exhaust gas recirculation.Fig. 2 schematically shows a genset with an internal combustionengine 1 according to the present disclosure which is coupledmechanically to a generator 24 for creating electrical energy.The generator 24 may be connected to a power grid 25. The powergrid 25 can for example be a public power supply grid, an island grind, or a microgrid. Fig. 3 shows a table which visualises the effect of recirculated exhaust gas and possible ways for compensating these effects. The first row of the table shows an example without recirculated exhaust gas (cegr = 0%). For a lambda of 2 a stoichiometric air fuel ratio Lminand a certain mass flow ^^̇^^for the fuel into the engine is given. The second row of the table shows an example with 50% recirculatedexhaust gas. With the formula given earlier the intake gas amountindicative of the amount of intake gas, which is a mixture of the recirculated exhaust gas and aspirated fresh air, necessary for a stoichiometric combustion given a concentration of 50% exhaust gas. Because of the higher intake amount ^^^^^that would be necessary for a given lambda and because of the unchanged lambda and boost pressure the amount of fuel gas entering the at least one combustion chamber the power of the engine is lower in the example of the second row of the table. Formulated differently, for a constant lambda (and boost pressure) less fuel will be used if there is recirculated exhaust gas containing less oxygen than ambient air. The third row of the table shows a first example of how the lowerpower can be compensated (Option 1 for the correction based on ^^ ^^^mentioned above). In this example the command value for lambda (air fuel equivalence ratio) is scaled using the ratio of the air fuel ratio (Lmin) and the amount of intake gas ^^^^^. Formulated differently, a fatter mixture can be used together with recirculated exhaust gas which contains less oxygen than ambient air. As can be seen in the table this is a first way of reaching thefuel gas flow of the first row and therefore the same power.The fourth row of the table shows another example of how the lowerpower due to recirculated exhaust gas can be compensated (Option2 for the correction based on ^^^^^mentioned above). In this example the command value for the boost pressure p2’ is scaled such that the same fuel mass flow is reached. The idea here is to use a higher boost pressure so that enough oxygen is delivered into the at least one combustion chamber so that also the appropriate amount of fuel gas can be delivered to the at least one combustion chamber. In summary, the power does then not change. It should be noted that the compensations schemes explained in connection with the third and fourth rows can also be combined (Option 3 for the correction based on ^^^^^mentioned above), i.e., mixed versions are possible where some of the potential power loss is compensated by a scaled lambda and some of it is compensated by a higher boost pressure. Fig. 4 shows control scheme according to an embodiment of thepresent disclosure. The control scheme can broadly be divided intoa boost pressure control, a power control, and an EGR control. The control scheme as depicted can be implemented on the control unit 2 of the internal combustion engine 1. In this embodiment the boost pressure control comprises a ReferenceLoadramp module which outputs a power setpoint (PowerSet) of theinternal combustion engine 1 based on the power of a generator 24 driven by the internal combustion engine 1 and a base power command value. According to the disclosure of EP 2977596 A1 (see block 2 in Fig. 2 therein) a functional relationship can be used to output a boost pressure setpoint (also called boost pressure reference, IntPresSet or p’2,ref). This is visualised in Fig. 4 with the LEANOX module.It is optionally possible to make the boost pressure setpointdependent on the ignition time (IgnTime), the temperature in theintake manifold (intake tract 6, IntTmp), and / or the engine speed(EngSpd). Based on the boost pressure setpoint a boost pressure control can be used for example to output command values for actuators, in particular of of a turbo charger, such as for example a compressor bypass valve, a wastegate valve, and / or a throttle valve. The power control starts from the power setpoint mentioned above, and a current generator power (GenPower) is deducted from the power setpoint. The resulting value is subjected to a PID control (proportional integral derivative) which is in and of itself known to persons skilled in the art. The PID control outputs a command value u^ which is subjected to a correction by a multiplication with the ratio of the air fuel ratio Lminand the intake amount ^^^^^.Further, a lambda limiter 26 limits the lambda command value tothe lambda limits ^^^^^ / ^^^mentioned above. The resulting value is used as input for a Gas flow function which outputs a gas flow (GasFlow) parameter which can be used directly for controlling the fuel valve 12.The Gas flow function can optionally be made dependent on theintake amount ^^^^^, intake pressure (IntPres) in the intake tract, the engine speed (EngSpd), and / or the intake temperature (IntTemp). In the embodiment of Fig. 4 the EGR control starts with the setting of exhaust gas recirculation concentration command value cegr,cmdwhich is a function of the boost pressure and the type of fuel (gas type). This can be viewed as a feed forward control of the recirculated exhaust gas.The command value can be corrected in dependence on a firstparameter indicative of the stability of the combustion in the at least one combustion chamber 3, in this case a burn duration parameter. In this example the burn duration parameter (BurnDur) is the output of a combustion analysis module (Comb. Analysis) which has as input the measurement signals (CylPres) of an in-cylinder pressure sensor. How the burn duration parameter can be extracted from the measurements of an in-cylinder pressure sensor is in and of itself known to persons skilled in the art. The burn duration parameter is subtracted from a reference burnduration parameter (BurnDurSet), stored in the control unit 2, andthe resulting value subjected to PID control.The value resulting from the PID control can be combined with theexhaust gas recirculation concentration command value. The exhaust gas recirculation concentration command value can be corrected in dependence on a second parameter at least partially indicative of a gas state, in particular a state of the recirculated exhaust gas. In tis concrete example the gas state is the oxygen concentration parameter in the recirculated exhaust gas. The oxygen concentration (O2 meas / est) can be measured using the oxygen sensor 10 in the exhaust gas recirculation conduct 8. Alternatively, or additionally, an estimate of the oxygen concentration or the amount of oxygen in the recirculated exhaust gas can for example be made with a dynamical engine model with which concentrations of fuel, air, and recirculated exhaust gas are estimated. The oxygen concentration is subtracted from a set or referenceoxygen concentration (O2 set) and the resulting value is subjectedto PID control. The value resulting from the PID control can be combined with the exhaust gas recirculation concentration command value. Summarising, the exhaust gas recirculation concentration command value can be corrected in dependence on a burn duration parameterand / or an oxygen concentration parameter of the recirculatedexhaust gas. The corrected exhaust gas recirculation concentration commandvalue is subjected to an egr limiter 27 which limits the egrcommand value to certain pre-defined minimal and / or maximal egr command values. The scaled corrected exhaust gas recirculation concentration command value is subsequently converted to a mass flow parameter ^^̇^^. The mass flow parameter ^^̇^^can be used directly by an EGR valve control module to output a command value (uegr,valve) for the exhaust gas recirculation valve 9. It is optionally possible to make the command value for the exhaust gas recirculation valve 9 dependent on a temperature (Tegr) of the recirculated exhaust gas, the pressure (pegr,in) of the recirculated exhaust gas upstream the exhaust gas recirculation valve 9, and / or the pressure (pegr,out) of the recirculated exhaust gas downstream the exhaust gas recirculation valve 9.For example, when the exhaust gas recirculation valve 9 is alreadycompletely open and / or when the mass flow parameter ^^̇^^for the recirculated exhaust gas indicates that a larger mass flow of recirculated exhaust gas is needed or beneficial, the blower 10 can be activated by an EGR blower control module. The corrected exhaust gas recirculation concentration commandvalue cegr,cmd, preferably after being subjected to an egr limiter 27, and the measured or estimated O2 meas / est can be used tocalculate the intake gas amount ^^^^^indicative of the amount of intake gas, which is a mixture of the recirculated exhaust gas and aspirated fresh air, necessary for a stoichiometric combustion with the equation given above. This is indicated in Fig. 4 with a Lmin_est module. The calculated intake amount ^^^^^can be used to compensate for the potential power loss as described in conjunction with the table in Fig. 3. For example, the intake amount ^^^^^can be used to make a correction to the IntPresSet parameter (boost pressure) output by the LEANOXmodule as explained in connection with the third row of the tableof Fig. 3. For this embodiment a LEANOX correction module is provided which outputs a correction factor Fact EGR based on the intake amount ^^^^^and the following formula. Alternatively, or additionally, the intake amount ^^^^^can be used to correct the power control, in particular the Gas flow functionand / or the lambda limiter 26 and / or the correction by amultiplication with the ratio of the air fuel ratio Lminand the intake amount ^^^^^, as indicated by the arrows. The compensation as explained in connection with the fourth row of the table of Fig. 3 can be implemented in this way. Fig. 5 shows another control scheme according to an embodiment of the present disclosure. This control scheme can broadly be dividedinto a EGR control, physical components and model-based controller13 in the box in the upper left. The control scheme as depicted can be implemented on the control unit 2 of the internal combustion engine 1. The EGR control is setup like the embodiment of Fig. 4 so that a repetition of the detailed description thereof can be omitted. The model-based controller 13 comprises a LEANOX module as described in connection with Fig. 4. The model-based controller 13 comprises an optimal control module which implements the model and cost function for the optimal control as discussed in the latter part of the general part of the description. The model-based controller 13 comprises a gas dosage control and a boost pressure control, which are in and of themselves known to persons skilled in the art. The physical components include the internal combustion engine 1,fuel valves 12 (in this case in particular a fuel metering valveor gas dosage valve), rotating parts of the internal combustion engine 1, and the generator 24 driven by the internal combustion engine 1.The SAFI is an interface between the engine control system and theactuators at each cylinder. It provides the inputs to the ignitionsystem to actuate the ignition at the specified ignition timing (ITi) and optionally to a port injection system in order to command port injection opening parameters (PIi) for an appropriate gas dosage. The parameters used in Fig. 5 are the following: PGGenerator power neengine speed Ttemperature measurements at different positionsIT intake temperaturene,refreference engine speed p’2,refreference boost pressure p2sactual boost pressure u^lambda command value uitignition timing command value Nskipnumber of cylinders for which ignition is skipped up’2boost pressure command value ppressure measurements at different engine positions^^̇^^desired fuel gas mass flow Topen,ifuel valve opening time uTJ gas mass flow injected to the systemPIiport injection actuation (current) Itiactuated ignition timing point utvthrottle valve command value ucbvcompressor bypass valve command value uwgv waste gate valve command value ^eactual torque produced by the engine ^gactual torque of generator on the crankshaft ^L equivalent torque related to the electrical loadV generator voltageThe compensation of potential power loss due to the exhaust gas recirculation can be done with the intake amount ^^^^^which is a mixture of the recirculated exhaust gas and aspirated fresh air, necessary for a stoichiometric combustion as described in conjunction with the engine model described in the general part of the description as well as Fig. 3 and 4.Referring to Fig. 6 there are diagrams of the engine speed, lambda,mass flow, engine power, boost pressure p’2, and several factorsconcerning the exhaust gas recirculation for an engine with exhaustgas recirculation from a simulation where the control of the enginehas not been adapted. The simulation models an internal combustion engine configured for combusting molecular hydrogen as fuel, exhaust gas recirculation, and lean burn operation. Due to the recirculated exhaust gas, there is an offset of the actual speed of the engine compared to the reference engine speed. There is also an offset between the actual lambda value and the actual lambda. Additionally, it can be seen that the offsets increase at the 45 second mark, when the mass flow of recirculated exhaust gas is increased. In comparison Fig. 7 shows the same diagrams as in Fig. 6 from a simulation with the same setup, but with adapted control of the engine according to the embodiment of Fig. 5. As can be seen the offsets are not present anymore.

[0002] List of references1 internal combustion engine2 control unit3 combustion chamber4 exhaust gas recirculation system5 proportional–integral–derivative controller6 intake tract7 exhaust gas tract8 exhaust gas recirculation conduct9 exhaust gas recirculation valve10 blower11 oxygen sensor12 fuel valve13 model-based controller14 compressor15 turbocharger16 compressor bypass valve17 throttle valve18 ignition system19 exhaust gas turbine20 turbocharger shaft21 waste gate valve22 engine speed sensor23 exhaust gas aftertreatment system24 generator25 power grid26 lambda limiter27 egr limiter

Claims

Claims1. Internal combustion engine comprising- a control unit (2) for controlling the internal combustionengine (1), -at least one combustion chamber (3) for combusting at leastone fuel, and -an exhaust gas recirculation system (4) for recirculatingexhaust gas from the combustion into the at least one combustion chamber (3), wherein the control unit (2) is configured to control an exhaust gas recirculation amount, preferably an exhaust gas recirculation rate, by actuating the exhaust gas recirculation system (4) according to a reference exhaust gas recirculation amount, preferably a reference exhaust gas recirculation rate, characterised in that the control unit (2) is configured to set or correct the reference exhaust gas recirculation amount in dependence on -a first parameter at least partially indicative of astability of the combustion in the at least one combustion chamber (3) and / or -a second parameter at least partially indicative of a gasstate, in particular a state of the recirculated exhaust gas.

2. Internal combustion engine according to claim 1, wherein thefirst parameter at least partially indicative of the combustion stability is at least one of -a burn duration parameter of the combustion in the at leastone combustion chamber (3) and / or -a mass fraction of burnt fuel parameter of the combustionin the at least one combustion chamber (3) and / or- a peak firing pressure parameter of the combustion in theat least one combustion chamber (3) and / or -a knock magnitude parameter and / or- a misfire detection parameter and / or- a glow ignition detection parameter and / or- a backfire detection parameter.

3. Internal combustion engine according to one of the precedingclaims, wherein the second parameter at least partially indicative of a state of the recirculated exhaust gas is at least one of -an oxygen parameter of the recirculated exhaust gas and / or- a humidity parameter of the recirculated exhaust gas and / or- a humidity parameter of aspirated fresh air.

4. Internal combustion engine according to one of the precedingclaims, wherein the control unit (2) is configured to set the reference exhaust gas recirculation amount in dependence on an engine power output and / or a boost pressure and / or a fuel type.

5. Internal combustion engine according to one of the precedingclaims, wherein the control unit (2) has stored a reference for the first parameter at least partially indicative of the stability of the combustion and / or the at least one second parameter at least partially indicative of a gas state, and wherein the control unit (2) is configured to subtract an actual value of the first parameter and / or the second parameter from the respective reference, and preferably wherein the respective difference between the first parameter and / or the second parameter and the respective reference is subjected to aproportional–integral–derivative controller (5).

6. Internal combustion engine according to claim 5, whereincontrol unit (2) is configured correct the reference exhaust gas recirculation amount by adding the difference, preferably after being subjected to the proportional–integral–derivative controller (5), to the reference exhaust gas recirculationamount.

7. Internal combustion engine according to one of the precedingclaims, wherein the internal combustion engine (1), and in particular the control unit (2), is configured for lean burn operation, and / or the internal combustion engine (1) is a gas engine.

8. Internal combustion engine, according to one of the precedingclaims, wherein there is provided -an intake tract (6) for delivering air and / or an air-fuelmixture to the at least one combustion chamber (3), and -an exhaust gas tract (7) for discharging exhaust gas fromthe at least one combustion chamber (3).

9. Internal combustion engine according to claim 8, wherein theexhaust gas recirculation system (4) comprises -an exhaust gas recirculation conduct (8) which connectsthe exhaust gas tract (7) with the intake tract (6) in a fluid communication sense for recirculating exhaust gas into the at least one combustion chamber (3), and -an exhaust gas recirculation valve (9) configured to adjusta mass flow and / or a volume flow through the exhaust gas recirculation conduct (8).

10. Internal combustion engine according to one of the precedingclaims, wherein the exhaust gas recirculation system (4) comprises a blower (10) configured to increase a mass flow ofrecirculated exhaust gas, and wherein the control unit (2) is configured to activate the blower (10) in dependence on the reference exhaust gas recirculation amount.

11. Internal combustion engine, in particular according to one ofthe preceding claims, comprising at least one combustion chamber (3), an exhaust gas recirculation system (4), and a control unit (2), wherein the control unit (2) is configured to control at least one engine variable for an operation of the internal combustion engine (1), and the control unit (2) is configured to control an amount of exhaust gas recirculated into the at least one combustion chamber (3), characterised in that the control unit (2) is configured to calculate or estimate an intake gas amount and / or an intake gas coefficientindicative of the amount of intake gas, which is a mixture of the recirculated exhaust gas and aspirated fresh air, necessary for a stoichiometric combustion given an actual and / or reference exhaust gas recirculation amount, preferably an actual and / or reference exhaust gas recirculation rate, and to use the intake gas amount and / or intake gas coefficient asinput for the control of the at least one engine variable of the internal combustion engine (1).

12. Internal combustion engine according to one of the precedingclaims, wherein there is provided an oxygen sensor (11) configured for measuring an oxygen concentration or amount of oxygen of the recirculated exhaust gas and / or the control (2) unit is configured to estimate the oxygen concentration or amount of oxygen in the recirculated exhaust gas.

13. Internal combustion engine according to one of the precedingclaims, wherein there is provided a fuel valve (12), and wherein the at least one engine variable comprises a commandvariable for the fuel valve (12), preferably a command value for the mass flow through the fuel valve (12) and / or an opening time duration of the fuel valve (12).

14. Internal combustion engine according to one of the precedingclaims, wherein the at least one engine variable comprises a fuel air equivalence ratio and / or a boost pressure, preferably a command value of the fuel air equivalence ratio and / or the boost pressure.

15. Internal combustion engine according to one of the precedingclaims, wherein the control unit (2) comprises a model-based controller (13) and an engine model of the model-based controller (13) comprises a correction based on the intake gas amount and / or an intake gas coefficient indicative of theamount of intake gas necessary for the stoichiometric combustion.

16. Method for operating an internal combustion engine, inparticular according to one of the preceding claims, wherein the method comprises -measuring and / or otherwise determining a first parameterat least partially indicative of a stability of a combustion in at least one combustion chamber (3) and / or a second parameter at least partially indicative of a gas state, in particular a state of the recirculated exhaust gas, -setting or correcting a reference exhaust gas recirculationamount, preferably a reference exhaust gas recirculation rate, in dependence on the first parameter at least partially indicative of a stability of a combustion in the at least one combustion chamber (3) and / or in dependence on the second parameter at least partially indicative of agas state, in particular a state of the recirculated exhaust gas, and -controlling an exhaust gas recirculation amount, preferablya exhaust gas recirculation rate, by actuating an exhaustgas recirculation system (4) according to the reference exhaust gas recirculation rate.

17. Method, in particular according to claim 16, for operating aninternal combustion engine, in particular according to one of the claims 1 to 15, wherein the method comprises -measuring and / or otherwise determining an actual and / orreference exhaust gas recirculation amount, preferably an actual and / or reference exhaust gas recirculation rate, -calculating or estimating an intake gas amount and / or anintake gas coefficient indicative of the amount of intakegas, which is a mixture of the recirculated exhaust gas and aspirated fresh air, necessary for a stoichiometric combustion given the actual and / or reference exhaust gas recirculation amount, preferably the actual and / or reference exhaust gas recirculation rate, and -using the intake gas amount and / or intake gas coefficientas input for a control of at least one engine variable of the internal combustion engine (1).

18. Computer program product for operating an internal combustionengine, in particular according to one of the claims 1 to 15, comprising instructions causing an executing computer to perform the following: -setting or correcting a reference exhaust gas recirculationamount, preferably an exhaust gas recirculation rate, in dependence on a parameter at least partially indicative of a stability of a combustion in at least one combustion chamber (3) and / or in dependence on a second parameter atleast partially indicative of a gas state, in particular astate of the recirculated exhaust gas, and -controlling an exhaust gas recirculation amount, inparticular an exhaust gas recirculation rate, by actuating an exhaust gas recirculation system according to the reference exhaust gas recirculation amount.

19. Computer program product, in particular according to claim 18,for operating an internal combustion engine, in particular according to one of the claims 1 to 15, comprising instructions causing an executing computer to perform the following: -calculating or estimating an intake gas amount and / or anintake gas coefficient indicative of the amount of intakegas, which is a mixture of the recirculated exhaust gas and aspirated fresh air, necessary for a stoichiometric combustion given an actual and / or reference exhaust gas recirculation amount, preferably an actual and / or reference exhaust gas recirculation rate, and -using the intake gas amount and / or intake gas coefficientas input for a control of at least one engine variable of the internal combustion engine (1).

20. Transitory or non-transitory storage device with a computerprogram product according to one of the claims 18 or 19 stored thereon.

21. Data carrier signal carrying at least one of- the computer program product of claim 18- the computer program product of claim 19- a reference exhaust gas recirculation amount, preferablyan exhaust gas recirculation rate, and / or a correction therefor, calculated in dependence on a parameter at least partially indicative of a stability of a combustion in atleast one combustion chamber (3) and / or in dependence on a second parameter at least partially indicative of a gas state, in particular a state of the recirculated exhaustgas- an intake gas amount and / or an intake gas coefficientindicative of the amount of intake gas, which is a mixture of recirculated exhaust gas and aspirated fresh air, necessary for a stoichiometric combustion given an actual and / or reference exhaust gas recirculation amount, preferably an actual and / or reference exhaust gas recirculation rate

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