Method for controlling an internal combustion engine

A method for controlling an internal combustion engine is disclosed. The method may include receiving knock data corresponding to knock levels over a time period. The method may also include determining from the knock data whether the knock levels change over the time period. Further, the method may include determining that a variation in the gas composition of the gaseous fuel supplied to the internal combustion engine has occurred when the knock levels change over the time period. In addition, the method may include adjusting an operating condition of the internal combustion engine to adapt a knock susceptibility of the internal combustion engine to the varying gas composition.

CLAIM FOR PRIORITY

This application claims benefit of priority of European Patent Application No. 14176648.5, filed Jul. 11, 2014, which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to internal combustion engines. More particularly, the present disclosure relates to a method for controlling an internal combustion engine supplied with gaseous fuel of a varying gas composition.

BACKGROUND

Gaseous fuel operated internal combustion engines typically use natural gas or bio-gas as an energy source for combustion. Those gaseous fuels commonly comprise a blend of different hydrocarbons such as methane and higher hydrocarbons as well as inert gases. The composition of gaseous fuel may vary during the operation of the internal combustion engine, for example, when gaseous fuel from a gas field or other gas reservoirs is used. The variation of the gas composition may occur over a long time period, for instance over minutes or hours and may be caused by changes in the gas quality present in those gas reservoirs.

Variations of the gas composition may also affect the energy content of the gaseous fuel, for example, by varying amounts of higher hydrocarbons. As a result, the internal combustion engine is operated with gaseous fuel of a varying energy content. Thus, variations of the gas composition may have an impact on the operation of the internal combustion engine.

The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of prior systems.

SUMMARY OF THE DISCLOSURE

According to one aspect of the present disclosure, a method for controlling an internal combustion engine operating at least partly on gaseous fuel with a varying gas composition is disclosed. The method comprises receiving a knock data corresponding to knock levels over a time period of a varying gas composition, determining from the knock data that the knock levels have a tendency to change over the time period and accordingly that a variation in the gas composition of the gaseous fuel supplied to the internal combustion engine has occurred. The method further comprises adjusting an operating condition of the internal combustion engine (such as one or more operation parameters) to adapt a knock susceptibility of the internal combustion engine to the varying gas composition.

According to another aspect of the present disclosure, a control system for an internal combustion engine operating at least partly on gaseous fuel with a varying gas composition is disclosed. The control system comprises a knock sensor configured to continuously detect knock levels of the internal combustion engine or of each individual cylinder of the internal combustion engine, and a control unit connected to the knock sensor and configured to perform the method as exemplary disclosed herein.

According to yet another aspect of the present disclosure, an internal combustion engine operating at least partly on gaseous fuel with a varying gas composition comprises the control system as exemplary disclosed herein.

DETAILED DESCRIPTION

The following is a detailed description of exemplary embodiments of the present disclosure. The exemplary embodiments described therein and illustrated in the drawings are intended to teach the principles of the present disclosure, enabling those of ordinary skill in the art to implement and use the present disclosure in many different environments and for many different applications. Therefore, the exemplary embodiments are not intended to be, and should not be considered as, a limiting description of the scope of patent protection. Rather, the scope of patent protection shall be defined by the appended claims.

The present disclosure is based in part on the realization that a change in gas composition can be associated with a changing lower heating value (LHV) and/or Methane Number of a gaseous fuel supplied to an internal combustion engine. The LHV commonly represents the energy content of a gaseous fuel and is a measure of the heat release of combustion. The Methane Number indicates a knock susceptibility of the gaseous fuel and is typically in the range from 0 to 140, where higher Methane Numbers indicate a lower knock susceptibility of the fuel.

It was further realized that a changing LHV and/or Methane Number may cause a change of knock levels of the internal combustion engine. In particular, it was found that in case of rising LHVs and/or decreasing Methane Numbers, the knock levels of the internal combustion engine may have a tendency to increase. Likewise, decreasing LHVs and/or increasing Methane Numbers may correspond to a tendency of decreasing knock levels. Those tendencies of increasing or decreasing knock levels may typically occur over, for example, a time period of several 10 seconds to 120 min. That time period is longer than a time period usually associated with engine knock caused by other phenomena than the described varying gas composition, which would require instant countermeasures.

The present disclosure is further based in part on the realization that—once it has been determined that the knock levels have a tendency to increase or decrease and accordingly that a change in the LHV and/or Methane Number of the gaseous fuel has occurred—an operating condition of the internal combustion engine is adjusted to adapt a knock susceptibility of the internal combustion engine to the varying gas composition. The operating condition may be adjusted, for example, by increasing an intake manifold air pressure (IMAP) of intake air, delaying an ignition timing of a cylinder of the internal combustion engine, and/or substituting a portion of gaseous fuel with liquid fuel, in case the knock levels have a tendency to increase. Likewise, if the knock levels have a tendency to decrease, the operating condition may be adjusted, for example, by decreasing an IMAP of intake air, advancing an ignition timing of a cylinder, and/or substituting a portion of liquid fuel with gaseous fuel.

In the following, an internal combustion engine operable at least partly on gaseous fuel and exemplary methods for controlling the same are described in connection withFIG. 1toFIG. 3andFIG. 4toFIG. 7, respectively.

FIG. 1shows schematically an exemplary internal combustion engine100operating at least partly on gaseous fuel, such as a DF engine (illustrated schematically inFIG. 2) or a gaseous fuel engine (illustrated schematically inFIG. 3).

Internal combustion engine100comprises an engine block2, a charge air system4, an exhaust gas system5, a gaseous fuel system6including a purge gas system7and/or a liquid fuel system8. Internal combustion engine100can be powered with a liquid fuel such as, for example, diesel fuel in a liquid fuel mode (LFM), and with a gaseous fuel such as natural gas provided, for example, by an LNG-system, in a gaseous fuel mode (GFM).

Engine block2comprises a plurality of cylinders. Exemplarily, four cylinders9are depicted inFIG. 1. Engine block2may be of any size, with any number of cylinders, such as 6, 8, 12, 16 or 20, and in any configuration, for example, “V”, in-line or radial configuration.

Each cylinder9is equipped with at least one inlet valve16and at least one outlet valve18. Inlet valves16are fluidly connected to charge air system4and configured to provide charge air, or a mixture of charge air and gaseous fuel into cylinders9. Analogous, outlet valves18are fluidly connected to exhaust gas system5and configured to direct exhaust gas out of respective cylinder9.

Charge air is provided by charge air system4including an air intake20, a compressor22to charge air, a compressor outlet21and a charge air cooler24. A intake manifold26is fluidly connected downstream of charge air cooler24and guides charge air via cylinder specific inlet channels28into respective cylinders9.

Charge air system4may further comprise a blow-off system44. Blow-off system44includes, for example, a blow-off line441and at least one blow-off valve442disposed within blow-off line441. Blow-off line441may be fluidly connected to compressor outlet21upstream or downstream of charge air cooler24and to air intake20upstream of compressor22. Alternatively, blow-off line441may not be connected to air intake20but may be open to the environment. Blow-off valve442may be configured to allow a portion of charge air to return to air intake20, thereby bypassing compressor22via blow-off line441, in case for example a pressure in compressor outlet21exceeds a preset threshold level. Blow-off valve442may also help to control a desired fuel-to-air ratio of a fuel-air mixture admitted to cylinder9. When blow-off line441is not connected to air intake20, the portion of charge air bypassing compressor22may be released to the environment.

Exhaust gas system5includes an exhaust gas turbine30connected to compressor22via shaft32and an exhaust gas manifold34guiding exhaust gas from individual exhaust gas outlet channels35to exhaust gas turbine30and further to exhaust gas outlet33.

Exhaust gas system5may further comprise a wastegate system55. Wastegate system55includes, for example, a wastegate line551and at least one wastegate valve552disposed within wastegate line551. Wastegate line551may be fluidly connected to exhaust gas manifold34upstream of exhaust gas turbine30and to exhaust gas outlet33downstream of exhaust gas turbine30. The skilled person may appreciate that wastegate line551and wastegate valve552may be provided in different configurations than the one shown here. Wastegate valve552may be configured to allow a portion of exhaust gas bypassing exhaust gas turbine30via wastegate line551, if, for example, a compression of intake air shall not exceed a preset compression rate.

Charge air system4may further comprise one or more intake manifolds26. Similarly, exhaust gas system5may comprise one or more exhaust gas manifolds34.

In addition, inlet valves16and outlet valves18may be installed within inlet channels28and outlet channels35, respectively. Inlet channels28as well as outlet channels35may be provided within a common cylinder head or individual cylinder heads covering cylinders9.

Gaseous fuel system6comprises a gaseous fuel source36connected to gaseous fuel piping42. Gaseous fuel source36constitutes a gaseous fuel feed for supplying gaseous fuel for combustion in GFM. For example, gaseous fuel source36comprises a gas valve unit and a gaseous fuel tank that contains, for example, natural gas in a pressurized state.

Gas valve unit is configured to allow, to block, and to control flow from gaseous fuel tank into gaseous fuel piping42. The gas valve unit may comprise gaseous fuel control valves, gaseous fuel shut-off valves and venting valves.

Gaseous fuel piping42is fluidly connected to a gaseous fuel manifold54, which splits into a plurality of gaseous fuel channels56. Each gaseous fuel channel56is fluidly connected to one of the plurality of inlet channels28. To dose gaseous fuel into individual inlet channels28, in each gaseous fuel channel56, a gaseous fuel admission valve58is installed. In some embodiments, internal combustion engine100may comprise more than one gaseous fuel manifold54.

Each gaseous fuel admission valve58is configured to allow or to block flow of gaseous fuel into an individual inlet channel28to mix with charge air from charge air system4in GFM. Thus, cylinder specific mixing zones downstream of each gaseous fuel admission valve58are generated. For example, gaseous fuel admission valves58may be solenoid actuated plate valves in which springs hold a lower surface of a movable disk against an upper surface of a stationary disk or plate, the two surfaces being configured to provide a sealed relationship in a closed state of gaseous fuel admission valve58. Each gaseous fuel admission valve58may be mounted to a cylinder head covering at least one cylinder9.

Purge gas system7(indicated inFIG. 1by a dashed-dotted box) comprises a purge gas tank60, a purge gas control valve62, and a purge gas shut-off valve64connected in series. Purge gas tank60constitutes a purge gas source to flush gaseous fuel piping42, gaseous fuel manifold54, etc. with a purge gas, such as nitrogen in a pressurized state.

Purge gas system7may be fluidly connected to gaseous fuel system6at various locations. For example, inFIG. 1a first connection66is disposed proximal to the gaseous fuel manifold54. A second connection70is disposed proximal to gaseous fuel source36. First shut-off valve68and second shut-off valve72can block or allow a purge gas flow through first connection66and second connection70, respectively. Additional connections may be integrated in gas valve unit of gaseous fuel source36.

As previously mentioned,FIG. 1illustrates a DF internal combustion engine as well as a gaseous fuel engine. In a DF internal combustion engine, liquid fuel system8comprises a liquid fuel tank40connected to liquid fuel piping43. Liquid fuel tank40may comprise a first liquid fuel tank for storing a first liquid fuel, for example, heavy fuel oil (HFO), and a second liquid fuel tank for storing a second liquid fuel, for example, diesel fuel. Liquid fuel tank40constitutes a liquid fuel source for supplying liquid fuel for combustion in LFM. Additionally, liquid fuel tank40may constitute a liquid fuel source for supplying ignition fuel in GFM.

Liquid fuel piping43is fluidly connected to a liquid fuel manifold46, which splits into a plurality of liquid fuel inlet channels48. To dose liquid fuel into the combustion chamber of cylinder9, in each liquid fuel inlet channel48a fuel injection system50is installed.

In a gaseous fuel internal combustion engine, such as a spark ignited gaseous fuel internal combustion system, fuel injection system50is fluidly connected to gaseous fuel source36(indicated by a dashed line49) instead of liquid fuel tank40. In this embodiment fuel injection system50may comprise a pre-combustion chamber for providing spark ignited pilot flames91(seeFIG. 3) to ignite the mixture of gaseous fuel and air.

Exemplary embodiments of fuel injection system50for DF and gaseous fuel internal combustion engines are described in more detail when referring toFIG. 2andFIG. 3, respectively.

As shown inFIG. 1, internal combustion engine100may further comprise one or more knock sensors77. Knock sensors77may be mounted at cylinder9and configured to generate a signal corresponding to a knock level of cylinder9. Knock sensor77may alternatively be mounted at the cylinder head or intake manifold26of internal combustion engine100. Knock sensors77may in addition or alternatively be configured to generate a signal corresponding to a knock level of internal combustion engine100. A knock sensor is further described in connection withFIG. 2.

To control operation of internal combustion engine100, a control unit76is provided. Control unit76forms part of a control system of the engine. Control unit76is configured to receive knock data of knock sensor77via a readout connection line101. Control unit76may further be configured to control various components of internal combustion engine100such as wastegate valve552via a control connection line102, blow-off valve442via a control connection line103, gaseous fuel admission valves58via a control connection line104, fuel injection system50via a control connection line106. Control unit76may further be configured to control valves of purge gas system7via additional control lines. Alternatively, a second control unit (not shown) may be configured to control the operation of internal combustion engine100. Further description of the control system and additional control lines between control unit76and other components of the engine, such as the fuel injection system50, will be given when referring toFIGS. 2 and 3.

Control unit76may further be connected to other sensors not shown inFIG. 1, such as engine load sensors, engine speed sensors, temperature sensors, NOx-sensors, or fuel-to-air ratio sensors provided for each individual cylinder or for a plurality of cylinders. Control unit76may also be connected to an operator panel (not shown) for issuing a warning to the operator, indicating a failure of the engine or the like.

FIG. 2shows a cylinder9of a DF internal combustion engine200which is an exemplary embodiment of internal combustion engine100ofFIG. 1. Elements already described in connection withFIG. 1have the same reference numerals, such as engine block2, control unit76, knock sensor77, and cylinder9.

Cylinder9provides at least one combustion chamber10for combusting a mixture of gaseous fuel and air, a piston84, and a crankshaft80which is drivingly connected to piston84via a piston rod82. Piston84is configured to reciprocate within cylinder9.

Cylinder9is connected to intake manifold26via inlet channel28and to exhaust gas manifold34via outlet channel35(seeFIG. 1). Inlet valve16is disposed in inlet channel28, and outlet valve18is disposed in outlet channel35. Gaseous fuel admission valve58can supply gaseous fuel to combustion chamber10of cylinder9.

FIG. 2further illustrates fuel injection system50by a dashed box. When DF internal combustion engine200is operated in LFM, fuel injection system50is used to inject liquid fuel into combustion chamber10, the liquid fuel being the sole source of energy. When DF internal combustion engine200is operated in GFM, fuel injection system50may be used to inject a pilot amount of liquid fuel into combustion chamber10to ignite the mixture of gaseous fuel and air. In GFM, fuel injection system50may therefore function as a gaseous fuel ignition system.

InFIG. 2, an exemplary embodiment of such a gaseous fuel ignition system is based on a main liquid fuel injector38for injecting a large amount of liquid fuel in LFM and a pilot amount of liquid fuel into combustion chamber10to ignite the mixture of gaseous fuel and air in GFM. In other embodiments, such as for heavy duty DF internal combustion engines, gaseous fuel ignition system may comprise a separate ignition liquid fuel injector39to inject the pilot amount of liquid fuel into combustion chamber10in GFM.

As exemplarily shown inFIG. 2, cylinder9further comprises knock sensor77for detecting pressure fluctuations within combustion chamber10. In general, knock sensor77may be any type of knock sensor known to the skilled person. For example, knock sensor77may additionally or alternatively be configured to detect fluctuations indicative of engine knock, such as sound waves propagating within intake manifold26and/or engine block2, or temperature fluctuations within combustion chamber10.

Knock sensor77may detect those fluctuations and generate a signal, such as a voltage signal, which corresponds to an intensity of the detected knock.

DF internal combustion engine200further comprises a control system including control unit76. Control unit76is connected to main liquid fuel injector38via control connection line108and, in case of heavy duty DF internal combustion engines, also to ignition liquid fuel injector39via a separate control connection line (not shown).

FIG. 3shows a cylinder9of a gaseous fuel internal combustion engine300being another exemplary embodiment of internal combustion engine100ofFIG. 1. Elements already described in connection withFIGS. 1 and 2have the same reference numerals. Gaseous fuel internal combustion engine300is similar to DF internal combustion engine200ofFIG. 2, except for the components described in the following.

Fuel injection system50comprises a pre-combustion chamber90. Pre-combustion chamber is configured to receive a pre-mixture of gaseous fuel and air outside of combustion chamber10. The pre-mixture of gaseous fuel and air is ignited, for example by a spark plug, to provide pilot flames91disposed into combustion chamber10. Pilot flames91are used to ignite the mixture of gaseous fuel and air in combustion chamber10. Control unit76is connected to pre-combustion chamber90via control connection line110. Alternatively, fuel injection system50may be a spark plug for igniting the mixture of gaseous fuel and air via an electric discharge.

In general, control unit76of an engine as disclosed in connection withFIG. 1toFIG. 3may be a single microprocessor or multiple microprocessors that include means for controlling, among others, an operation of various components of DF internal combustion engine200. Control unit76may be a general engine control unit (ECU) capable of controlling numerous functions associated with DF internal combustion engine200and/or its associated components. Control unit76may include all components required to run an application such as, for example, a memory, a secondary storage device, and a processor such as a central processing unit or any other means known in the art for controlling DF internal combustion engine200and its components. Various other known circuits may be associated with control unit76, including power supply circuitry, signal conditioning circuitry, communication circuitry and other appropriate circuitry. Control unit76may analyze and compare received and stored data and, based on instructions and data stored in memory or input by a user, determine whether action is required. For example, control unit76may compare received knock data from knock sensor77with target values stored in memory, and, based on the results of the comparison, transmit signals to one or more components of the engine to alter the operation of the same.

INDUSTRIAL APPLICABILITY

Exemplary internal combustion engines suited to the disclosed control procedure are, for example, DF internal combustion engines of the series M46DF, M34DF and M43DF or gaseous fuel internal combustion engines of the series GCM34 and GCM46 manufactured by Caterpillar Motoren GmbH & Co. KG, Kiel, Germany, or other spark ignited open or pre-combustion chamber gaseous fuel engines. Respective internal combustion engines may be operated at 500-750 rpm and may be applied, for example, in medium speed power generator sets and/or compressor or pump drives. Other engines suited to the disclosed procedure are, for example, gaseous fuel engines of the series 3600 and 3500, as well as other dynamic gas blending engines manufactured by Caterpillar Inc., which are typically operated at speeds of up to 1500 rpm or even 3000 rpm. One skilled in the art would however appreciate that the disclosed procedures may also be adapted to suit other internal combustion engines.

In the following, operation and control of an internal combustion engine such as internal combustion engines described with reference toFIG. 1toFIG. 3are described in connection withFIG. 4toFIG. 7. For illustration purposes, the procedures described herein are disclosed with reference to structural elements disclosed inFIG. 1toFIG. 3. However, the skilled person will appreciate that the respective steps of the procedure can be performed on other embodiments as well.

Referring toFIG. 4, an exemplary time-knock level diagram of an internal combustion engine operating at least partly on gaseous fuel with a varying gas composition is shown. The time-knock level diagram shows a temporal development of knock levels402, which are illustrated exemplarily for selected combustion cycles by dots.FIG. 4further illustrates that the sequence of received knock levels402can be grouped in knock data400which correspond to knock levels402associated with a time period during which the gaseous fuel showed a varying gas composition. Depending on the configuration, type and speed of internal combustion engine100, the time period may be, for example, in the range from several 10 seconds to 120 min.

“Knock levels” may be determined from control unit76by performing a frequency analysis of the voltage signal received from knock sensor77. The skilled person will however appreciate that the frequency analysis may depend on the operating condition of internal combustion engine100, such as on engine speed or engine load, as well as on the type or configuration of the engine to be controlled.

Based on the frequency analysis, control unit76determines the amplitudes of those frequencies and compares the determined amplitudes with preset lower and higher amplitude threshold companions stored on the memory of control unit76.

Control unit76then associates amplitudes equal to or smaller than the preset lower amplitude threshold companion with 0% knock levels (base line404). Similarly, control unit76associates amplitudes equal to or larger than the preset higher amplitude threshold companion with 100% knock levels (top line406). Consequently, a knock level of 0% (base line404) indicates that no knocking occurs in internal combustion engine100or at least that the knock level present in the internal combustion engine is below the knock levels detectable by control unit76. A knock level of 100% (top line406) indicates that internal combustion engine experiences severe knocking. Knock levels between 0% and 100% correspond to a knock intensity between no knocking and severe knocking, i.e. amplitudes between the lower and higher amplitude threshold companions (e.g. presented in logarithmic or linear units) are projected on the 100% range.

As can be further seen inFIG. 4, the exemplary knock data400show knock levels402with a tendency to change over the time period during which the gaseous fuel varied in gas composition. For example, knock levels402may have a tendency to increase (indicated by the upward arrows403A and403B) or may have a tendency to decrease (indicated by the downward arrow403C). For example, for a medium speed engine (operating at approximately 500 rpm) the tendency may be based on a sequence of 4, 10, 20, 200, or up to 2000 combustion cycles or more, such as on a sequence of at least 4, at least 10, at least 20, at least 200, or at least 2000 combustion cycles. Control unit76associates tendencies403A,403B,403C with a variation in the gas composition and adjusts the operation condition of internal combustion engine100such that a knock susceptibility of the engine is adapted to the varying gas composition.

Referring toFIG. 5, controlling the internal combustion engine is explained in connection withFIG. 4. At step504, a knock data such as the one shown inFIG. 4is received from knock sensor77by control unit76via readout connection line101.

At step506, control unit76determines from knock data400whether knock levels402have a tendency to change over the time period, and accordingly whether a variation in the gas composition of the gaseous fuel supplied to internal combustion engine100has occurred. When determining the tendency, control unit76may further determine whether knock levels402have a tendency to increase (403A,403B) or a tendency to decrease (403C).

Control unit76may further determine, in particular for a tendency to increase (403A,403B) that knock data400fulfill the requirement that knock levels402are outside or within a preset knock level range408below a preset knock level threshold410. For example, tendency403A may not result in a control action, whereas tendency403B may result in control actions. A lower limit409of preset knock level range408and preset knock level threshold410are exemplarily shown inFIG. 4as dashed and double-dashed lines, respectively. Preset knock level range408enables control unit76to classify whether the determined tendency to increase (403A,403B) requires appropriate control actions for internal combustion engine100in response to a, for example, potentially harmful change in LHV or Methane Number. Such a determination may not be applied for a tendency to decrease (403C), as indicated by the respective knock data400crossing line409.

Alternatively or in addition, control unit76may determine a knock margin416, where knock margin416is a difference between knock level threshold410and the current knock level402. Control unit76may further determine whether knock margin416is within a preset knock margin range from knock level threshold410to classify whether the determined tendency to increase (403A,403B) may require appropriate control actions.

Preset knock level range408, preset knock level threshold410and preset knock margin range may be empirical values stored on the memory of control unit76. Preset knock level range408, preset knock level threshold410and preset knock margin range may also be set in dependence of the operating condition of internal combustion engine100, for example, in dependence of a load or a speed of the engine. In this case, control unit76may additionally be connected to a load sensor or a speed sensor of internal combustion engine100. Preferably, preset knock level threshold410may be in the range from 1% to 10%. Likewise, preset knock level range408may extend down to 0%, for example, the lower limit409is in the range from 0% to 5%, accordingly the preset knock margin range may be in the range from 0% to 10%.

Once control unit76determined at point506A that knock levels402have a tendency to change, control unit76adjusts at step510an operating condition of internal combustion engine100such that the knock susceptibility of internal combustion engine is adapted to the varying gas composition. When control unit76determined that knock levels402have a tendency to increase (403A,403B) and, for example, additionally determined that this tendency occurred within preset knock level range408, the control actions performed at step510may include any known control action appropriate to reduce the knock susceptibility of internal combustion engine100. Control actions may be, for example, increasing (step512) an IMAP of intake air admitted to cylinder9, delaying (step514) an ignition timing of cylinder9by an ignition delay time, and/or substituting (step516) a portion of gaseous fuel with liquid fuel such as diesel fuel.

In some embodiments, control unit76may additionally be configured to reduce a temperature of intake air or a mixture of gaseous fuel and air supplied to internal combustion engine100. For example, control unit76may additionally be connected to charge air cooler24(FIG. 1) and operate charge air cooler24to effect cooling of the intake air or the mixture supplied to internal combustion engine100. In some embodiments, variable camshaft timing may be applied to adapt the combustion cycle to a Miller cycle, thereby decreasing a temperature of the charge air. In some embodiments, control unit76may additionally be configured to reduce the load of internal combustion engine100. Control unit76may therefore be connected to a load sensor of internal combustion engine100.

Similarly, when control unit76determined at point506A that knock levels402have a tendency to decrease (403C), the control actions performed by control unit76at step510may include any known control action appropriate to increase the knock susceptibility, thereby adapting the operating condition of internal combustion engine100to the decreasing LHV and/or increasing Methane Number. Control actions may include, for example, decreasing (step512) an IMAP of intake air admitted to cylinder9, advancing (step514) an ignition timing of cylinder9by an ignition advance time, and/or substituting (step516) a portion of liquid fuel with gaseous fuel.

Further control actions in addition or alternative to the above mentioned control actions may be performed to adapt the knock susceptibility of internal combustion engine100.

In some embodiments, when internal combustion engine100is equipped with a NOx-sensor, control unit76may additionally or alternatively adjust at step510control actions in dependence of NOx emissions received from the NOx-sensor to comply, for example, with emission regulations.

The control actions may be performed for each cylinder9or for all cylinders9and may be performed together or individually. The person skilled in the art will however appreciate that substituting (step516) a portion of gaseous fuel with liquid fuel, or alternatively a portion of liquid fuel with gaseous fuel, may not be performed in gaseous fuel internal combustion engines.

The control steps504,506and510may further be performed in a closed loop based control520(indicated by the dashed-dotted box inFIG. 5). The closed loop based control520includes at least one control action set out in step510and is performed until the received knock data400correspond to stable knock levels (region418inFIG. 4). Stable knock levels indicate that the knock susceptibility of internal combustion engine100is adapted to the current LHV and/or Methane Number of the gaseous fuel. Once control unit76determines that the knock levels no longer have a tendency to change (point506B), e.g. by showing stable knock levels (in region418ofFIG. 4), control unit76determines at step508that no further control action is required. The procedure then returns to initial step504via loop508A.

Alternatively, once the control actions have been performed and a further change in operating condition of internal combustion engine100is required, for example, a change in engine load or engine revolution, the procedure set out above may be reset and initiated anew, thereby returning to initial step504without any further steps being performed. Resetting the procedure may include resetting preset knock level range408, preset knock level threshold410and/or preset knock margin range, as well as the control actions performed so far. A continuous control without resetting may also be applied.

In some embodiments, the procedure may additionally include an inversion section530. In inversion section530, control unit76inverts the control actions performed at step510in response to the determined stable knock levels received by control unit76during a previous run through closed loop based control520. Inversion section530may include inversion actions, such as decreasing (step532) an IMAP of intake air admitted to cylinder9, advancing (step534) an ignition timing of cylinder9, and/or substituting (step536) a portion of liquid fuel with gaseous fuel, in case control actions were performed in response to increasing knock levels.

Alternatively, inversion actions may include, for example, increasing (step532) an IMAP of intake air admitted to cylinder9, delaying (step534) an ignition timing of cylinder9, and/or substituting (step536) a portion of gaseous fuel with liquid fuel, in case control actions were performed in response to decreasing knock levels.

It should be appreciated that, similarly to the control actions set out in step510, inversion actions may be performed together or individually, for each cylinder9or for all cylinders of internal combustion engine100.

It will be appreciated that for a given control action, the procedure does not require the corresponding inversion action to be performed in response to the stable knock levels. In other words, the disclosed procedure may not be limited to, for example, advancing (step534) an ignition timing, when the operating condition was changed by delaying (step514) an ignition timing, and vice versa. Once inversion actions have been performed, the procedure returns to initial step504via loop530A.

In some embodiments, where internal combustion engine100comprises a plurality of knock sensors77mounted at each individual cylinder9, control unit76may receive separate sets of cylinder specific knock data corresponding to the respective cylinder9and may start the procedure set out above once for at least one of the cylinder specific knock data the respective knock levels402have a tendency to increase (403A,403B) or decrease (403C). The herein described procedure will be more stable, if a cylinder balancing is applied to internal combustion engine100. In that case, internal combustion engine100will run balanced and respective knock levels402should be equal for all cylinders9.

InFIG. 6, a flow diagram for controlling an internal combustion engine is shown where a respective control action is associated with a preset maximal change in operating condition. In the exemplary procedure, control unit76determines at point506A that knock levels402have a tendency to increase (403A,403B inFIG. 4) over the time period. The skilled person will however appreciate that the procedure may be performed vice versa in case control unit76determined that knock levels402have a tendency to decrease (403C inFIG. 4). Steps already described in connection withFIG. 5have the same reference numerals.

InFIG. 6, the closed loop based control520ofFIG. 5is implemented as three closed loop based controls (520A,520B,520C). Each closed loop based control is associated with a respective control action and is performed until the respective control action reaches a preset maximal change in operating condition. Once the preset maximal change in operating condition is reached for a specific control action, another closed loop based control is initiated. Alternatively, internal combustion engine100may be switched to liquid fuel mode (step518) without initiating another closed loop based control, thereby reducing the knock susceptibility of internal combustion engine100without performing further control actions set out above.

In the exemplary embodiment ofFIG. 6, closed loop based control520comprises a first closed loop based control520A which is associated with a first control action, for example, increasing an IMAP of intake air. Once control unit76determined at point506A that the knock levels have a tendency to increase (403A,403B inFIG. 4), control unit76checks at step602whether an opening area of blow-off valve442and/or wastegate valve552has already reached a preset minimal opening area. The preset minimal opening area may be, for example, in the range from 0% to 5%. In case the opening area of blow-off valve442and/or wastegate valve552has not reached the preset minimal value (point602B), control unit76further increases at step512the IMAP of intake air. The loop is repeated until at point602A control unit76determines that the preset minimal opening area is reached and that the IMAP can no longer be increased.

Control unit76then initiates a second closed loop based control520B which is associated with a second control action, for example, delaying (step514) an ignition timing of cylinder9. Control unit76checks at step604whether the ignition delay time has reached a preset maximal ignition delay time, and performs second closed loop based control520B until the maximal ignition delay time is reached (point604B). The maximal ignition delay time may be set in dependence of a load and/or a speed of internal combustion engine100and may be, for example in the range from 1 degree crank angle to 10 degrees crank angle.

When the first and second closed loop based controls520A,520B can no longer be performed because both control actions have reached their respective preset maximal change of operating condition, control unit76initiates a third closed loop based control520C with a third control action, for example, substituting (step516) a portion of gaseous fuel with liquid fuel. Similarly, the third closed loop based control520C is performed until control unit76determines at point606A that a preset maximal portion of gaseous fuel, for example up to 50%, is substituted. In other embodiments, the preset maximal portion of gaseous fuel may be 60%, 70%, or up to 100%. At that point, control unit76finally initiates a switch from GFM to LFM (step518). In some embodiments, upon performing the third closed loop based control (520C), i.e. substituting gaseous fuel with liquid fuel such as diesel fuel, control unit76may also advance ignition timing of cylinder9(and increase the portion of liquid fuel at the same time) or perform other inversion actions of inversion section530as indicated by the double-dashed line520D.

Alternatively, once control unit76has determined for any closed loop based control that the respective control action has reached its preset maximal change in operating condition, control unit76may directly proceed to the closed loop based controls that may still be performable, as indicated by the dashed lines. In some embodiments or under specific conditions, such as a very large tendency, control unit76may initiate the switch from GFM to LFM (step518) already, when just one of the closed loop based controls (520A,520B,520C) can no longer be performed, as indicated by the double-dashed lines. This may be the case, for example, when internal combustion engine100needs to react quickly to the varying gas composition.

FIG. 7shows yet another control procedure that includes a closed loop based control520AB with two control actions being performed together in the loop. Such an embodiment may be used, for example, when control unit76determined that tendency403A,403B,403C of knock levels402is beyond a preset tendency, thereby determining that a large change in LHV and/or Methane Number has occurred. The preset tendency may be stored on the memory of control unit76, or alternatively it may be set according to empirical values.

In the exemplary procedure, control unit76determines at point506A that knock levels402have a tendency to increase, thereby determining that a large rise in LHV and/or a large decrease in Methane Number has occurred. Once the large change in LHV and/or Methane Number is determined, control unit76performs, for example, the control steps of increasing (step512) an IMAP and delaying (step514) an ignition timing for one or all cylinders within one closed loop based control. In case control unit76determined at point602A that the IMAP has already reached the preset maximal IMAP value, the procedure may directly proceed to step604to check whether delaying an ignition timing has also already reached the preset maximal ignition delay time. If this is the case, at point604A, control unit76initiates the switch from GFM to LFM (step518).

Alternatively, when control unit76determines at point506A that knock levels402have a tendency to decrease, control unit76may perform, for example, the control steps of decreasing (step512) an IMAP and advancing (step514) an ignition timing together in one loop.

In some embodiments, the disclosed procedure may be performed in parallel with other known procedures for detecting and/or controlling knock in internal combustion engine100, where the detected knock may be caused by other phenomena than the described varying gas composition. For example, an ignition timing of cylinder9may be delayed, an IMAP of the intake air may be increased, and/or a portion of gaseous fuel may be substituted with liquid fuel, such as diesel fuel, when knock levels402exceed preset knock level threshold410(indicated by the dashed-dotted line420inFIG. 4). In this case, known knock control strategies will be performed, but the herein described procedure for controlling internal combustion engine100in response to the varying gas composition may stay active too.

In some embodiments, the received knock data400or sub-sets of the same may be subjected to data filtering steps and/or data smoothing steps prior to initial step504in order to improve the signal-to-noise ratio of knock data400, thereby increasing the robustness of the described procedure as well.

Multiple closed loop based controls (520A,520B and520C) may be based on a variety of operating parameters which may be changed, once a change in gas quality has been determined.

Inversion section530may ensure that for a given operating condition of internal combustion engine100, the control measures associated with closed loop based control520do not reach the respective preset maximal change in operating condition. Thus, internal combustion engine100can react to a further change in gas quality.

The herein described procedures are, for example, suitable for internal combustion engines operated in industrial power plants, such as generator sets on oil/gas platforms, where varying gas qualities may negatively affect the power output of the power plant. Using the herein disclosed aspects, internal combustion engines may run at operating conditions adapted to the current gas quality and, as a result, knock susceptibility of the internal combustion engines may be reduced and up time of the engines may be increased.

While herein some examples may only be given for increasing or decreasing knock levels (as an example of a change of gas composition), the skilled person will appreciate, that a respective situation may also be addressed for decreasing or increasing knock levels.

Although the preferred embodiments of this invention have been described herein, improvements and modifications may be incorporated without departing from the scope of the following claims.