Patent Publication Number: US-11384699-B2

Title: Method of operating a gaseous fuel internal combustion engine

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to a gaseous fuel internal combustion engine and a method of operating the same, in particular, to a method of controlling an ignition device of a gaseous fuel internal combustion engine. 
     BACKGROUND 
     Generally, a gaseous fuel internal combustion engine, for example, a diesel gas engine, a dual fuel engine or an Otto gas engine, comprises an ignition device configured to ignite a mixture of gaseous fuel and air in a combustion chamber of a cylinder of the internal combustion engine. For example, in a diesel gas engine or a dual fuel engine, a pilot injector may be provided and configured for injecting a pilot amount of liquid fuel, for example, diesel, to facilitate combustion of the mixture of gaseous fuel and air in the combustion chamber. Further, an Otto gas engine may include an ignition device such as a spark plug for igniting the mixture of gaseous fuel and air in the combustion chamber. 
     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 of operating a gaseous fuel internal combustion engine comprising an ignition device configured to ignite a mixture of gaseous fuel and air in a combustion chamber of a cylinder comprises performing at least one measurement relating to the combustion of the mixture of gaseous fuel and air in the combustion chamber in a combustion cycle of the cylinder. The method further comprises determining at least one combustion parameter based on the at least one measurement, comparing the combustion parameter to a desired combustion parameter, and controlling an ignition by the ignition device in the combustion cycle based on the comparison. 
     According to another aspect of the present disclosure, a gaseous fuel internal combustion engine comprises an engine block defining at least in part a cylinder, an ignition device configured to ignite a mixture of gaseous fuel and air in a combustion chamber of the cylinder, and a control unit configured to perform the steps of the method according to the above aspect of the present disclosure. 
     According to yet another aspect of the present disclosure, a computer program comprises computer-executable instructions which, when executed by a computer, cause the computer to perform the steps of the method according to the above aspect of the present disclosure. 
     Other features and aspects of the present disclosure will be apparent from the following description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an exemplary internal combustion engine in accordance with the present disclosure; and 
         FIG. 2  is a schematic view of a control system in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following is a detailed description of exemplary embodiments of the present disclosure. The exemplary embodiments described herein 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 protection. Rather, the scope of protection shall be defined by the appended claims. 
     The present disclosure is based at least in part on the realization that, at present, there is no option to influence or control the combustion in a combustion chamber of a gaseous fuel internal combustion engine in a single combustion cycle. Instead, it is only possible to change operating parameters of the engine for a subsequent combustion cycle, for example, based on measurements during a previous combustion cycle. 
     Accordingly, the present disclosure is based at least in part on the realization that it is possible to use measurements performed during a combustion cycle of a gaseous fuel internal combustion engine for controlling an ignition device associated with a cylinder to control the combustion in the same combustion cycle. In this respect, it has been realized that cylinder pressure measurements can be used in order to calculate characteristic values for the combustion in the cylinder and to determine whether the combustion has developed as expected. If this is not the case, appropriate counter-measures can be taken to control the combustion in the combustion cycle, for example, by controlling the ignition device in an appropriate manner. Accordingly, it is possible to form a shape of the combustion profile in a combustion cycle, for example, in order to achieve a desired cylinder pressure profile associated with the combustion. In this manner, a combustion efficiency, exhaust emissions and an operation stability can be optimized. 
     The present disclosure is also based at least in part on the realization that a control of the ignition device of the associated cylinder may also be used to react to pre-ignitions in the cylinder. For example, when a pre-ignition, i.e., a start of combustion before an actuation of the ignition device, is detected, the associated ignition device can be deactivated. This will reduce a pressure increase and a load on the affected cylinder. Additionally, the present disclosure may be based at least on part on the realization that a fast pressure relief valve could be provided in the combustion chamber, and could be opened to protect the affected cylinder when a pre-ignition is detected. Further, in case the engine is provided with a variable valve train, the protection of the cylinder could also be achieved by opening the exhaust valve of the same at an appropriate timing. 
     Further, the present disclosure is based at least in part on the realization that the above-described concept can be applied both to diesel gas engines and Otto gas engines, as well as to dual fuel engines. In this respect, the present disclosure may be based at least in part on the realization that, in case of a diesel gas engine or a dual fuel engine including a pilot injector, an additional pilot injection could be performed, for example, if the start of combustion differs from a desired start of combustion. Likewise, an amount of pilot fuel that is injected, for example, in a second pilot injection, may also be adjusted based on the above-described measurement. On the other hand, in case of an Otto gas engine comprising an ignition device such as a spark plug, one or more further ignitions by the ignition device could be performed when the start of combustion does not match a desired start of combustion. Additionally, a further gas injection and ignition could also be performed, for example, in case the engine is provided with a high pressure gas supply gas system. 
     Referring now to the drawings, an exemplary embodiment of an internal combustion engine  10  is illustrated in  FIG. 1 . Internal combustion engine  10  may include features not shown, such as fuel systems, air systems, cooling systems, peripheries, drive train components, etc. In the embodiment, internal combustion engine  10  is a diesel gas engine. One skilled in the art will recognize, however, that internal combustion engine  10  may be any type of gaseous fuel internal combustion engine that utilizes an ignition device for igniting a mixture of gaseous fuel and air for combustion, for example, a dual fuel engine or an Otto gas engine. 
     Internal combustion engine  10  may be of any size, with any number of cylinders and in any configuration (“V”, “in-line”, etc.). Internal combustion engine  10  may be used to power any machine or other device, including ships or other marine applications, locomotive applications, on-highway trucks or vehicles, off-highway machines, earth-moving equipment, generators, aerospace applications, pumps, stationary equipment such as power plants, or other engine-powered applications. 
     Still referring to  FIG. 1 , internal combustion engine  10  comprises an engine block  20  including a bank of cylinders  26 A- 26 D, a gaseous fuel supply (not shown), a liquid fuel tank (not shown), a turbocharger  40  associated with cylinders  26 A- 26 D, and an intake manifold  22 . 
     Engine block  20  includes a crank-case (not shown) within which a crank-shaft  6  (see  FIG. 2 ) is supported. Crank-shaft  6  is connected to pistons  18  (see  FIG. 2 ) that are movable within each of cylinders  26 A- 26 D during operation of internal combustion engine  10 . 
     Intake manifold  22  is at least temporarily fluidly connected to each of cylinders  26 A- 26 D. Each of cylinders  26 A- 26 D is provided with at least one inlet valve  35  (see  FIG. 2 ) that is adapted to open or close a fluid connection between an intake passage  24  and a corresponding combustion chamber  16  of cylinders  26 A- 26 D. 
     An exhaust manifold  28  is connected to each of cylinders  26 A- 26 D. Each of cylinders  26 A- 26 D is provided with at least one exhaust valve  36  disposed in an exhaust passage  37  (see  FIG. 2 ) and being configured to open and close a fluid connection between combustion chamber  16  of each cylinder  26 A- 26 D and exhaust manifold  28 . 
     Generally, when internal combustion engine  10  is operated, a mixture of gaseous fuel and air (in the following referred to as the “mixture”) is introduced into the combustion chambers of the plurality of cylinders  26 A- 26 D via an air inlet  4 , intake manifold  22 , inlet valves  35 , which supply compressed intake air, and gas admission valves  38  (see  FIG. 2 ), which supply gaseous fuel. After combustion, exhaust gases generated by the combustion process are released from cylinders  26 A- 26 D through exhaust manifold  28 . 
     An exhaust sensor  29  may be disposed in exhaust manifold  28  to detect a component of the exhaust from internal combustion engine  10 . In the exemplary embodiment described herein, exhaust gas sensor may be an NOx sensor configured to detect an amount of NOx in the exhaust from internal combustion engine  10 . 
     Turbocharger  40  is configured to use the heat and pressure of the exhaust gas of internal combustion engine  10  to drive a compressor  44  for compressing the intake air prior to being supplied to the engine. Specifically, exhaust gas passing a turbine  42  of turbocharger  40  rotates turbine  42 , thereby decreasing in pressure and temperature. Compressor  44  is rotatably connected to turbine  42  via a common shaft  46  and driven by turbine  42 . 
     Generally, an outlet of compressor  44  is fluidly connected to an inlet of intake manifold  22  via a compressor connection  21 . As shown in  FIG. 1 , an outlet of compressor  44  is connected to the inlet of intake manifold  22  via a cooler  23 . A throttle valve  27  arranged downstream of cooler  23  is configured to open or close the fluid connection between compressor connection  21  and intake manifold  22 , thereby enabling or restricting a flow of the compressed intake air from compressor connection  21  into intake manifold  22 . 
     During operation of internal combustion engine  10 , the intake air is compressed and cooled before being supplied to cylinders  26 A- 26 D. Within cylinders  26 A- 26 D, further compression and heating of the mixture may be caused by movement of pistons  18  (see  FIG. 2 ). Then, the mixture within the cylinders  26 A- 26 D may be ignited, for example, by using ignition device  90  for supplying a pilot injection of liquid fuel to initiate the combustion of the mixture at a desired ignition timing. It should be noted that herein the term “ignition timing” may be used for the timing of the start of injection of the pilot fuel by the ignition device  90 , or for any other defined point in time during the injection. The produced exhaust gas is discharged via exhaust manifold  28 . An outlet of exhaust manifold  28  is fluidly connected to an inlet of turbine  42 . An outlet of turbine  42  may be fluidly connected to, for example, an exhaust gas treatment system (not shown). 
     Additionally, as indicated in  FIG. 1 , internal combustion engine  10  may be provided with a waste gate system including a waste gate connection  80  and a waste gate valve  82 . Further, internal combustion engine  10  may include a blow-off system including a blow-off connection  66  and a blow-off valve  64 . It should be appreciated that blow-off connection  66  and blow-off valve  64  may be provided with different configurations than the one shown in  FIG. 1 , if appropriate. Alternatively, one or more of these components may be omitted. 
     Turning now to  FIG. 2 , an exemplary embodiment of a control system  100  for controlling the combustion in a cylinder  26  during a combustion cycle is shown. The person skilled in the art will recognize that the exemplary cylinder  26  shown in  FIG. 2  demonstrates the principles of the cylinders  26 A- 26 D of  FIG. 1 . Therefore, the exemplary disclosed configuration shown in  FIG. 2  also applies to the cylinders  26 A- 26 D shown in  FIG. 1 . 
       FIG. 2  shows a schematic cross-sectional view of cylinder  26 . Cylinder  26  defines a combustion chamber  16  and includes a piston  18 . Crank-shaft  6  is connected to piston  18  via piston rod  8 . Piston  18  is configured to reciprocate within cylinder  26 . 
     Cylinder  26  is connected to intake manifold  22  ( FIG. 1 ) via intake passage  24  and to exhaust manifold  28  via exhaust passage  37 . Inlet valve  35  is disposed in intake passage  24 , and exhaust valve  36  is disposed in exhaust passage  37 . Gas admission valve  38  is provided to supply gaseous fuel to combustion chamber  16  of cylinder  26 . In the exemplary embodiment, gas admission valve  38  may be a solenoid-operated gas admission valve (SOGAV). Further, in the exemplary embodiment, a pressure relief valve  70  is provided in combustion chamber  16 . In other embodiments, however, pressure relief valve  70  may be omitted. 
     Inlet valve  35  is configured to supply compressed intake air to combustion chamber  16 . Exhaust valve  36  is configured to discharge exhaust from combustion chamber  16  to exhaust manifold  28  after combustion. 
     Ignition device  90  is configured to ignite the mixture of gaseous fuel and air inside combustion chamber  16  at a desired ignition timing. In the embodiment, ignition device  90  is a pilot injector configured to inject a pilot amount of, for example, diesel fuel to ignite the mixture of gaseous fuel and air in the gas mode. In some embodiments, a pre-combustion chamber (not shown) may be provided in combustion chamber  16 , and ignition device  90  may be configured to inject a small amount of fuel into the pre-combustion chamber in order to initiate the combustion of the mixture of gaseous fuel and air in combustion chamber  16 . 
     Control system  100  includes a sensor  60  associated with cylinder  26 . Sensor  60  may be disposed at least in part within combustion chamber  16 . In other exemplary embodiments, sensor  60  may be disposed outside of combustion chamber  16 . Sensor  60  is configured to detect a parameter of the combustion in cylinder  26 . In some embodiments, sensor  60  may be a pressure sensor configured to detect a cylinder pressure in cylinder  26 . Sensor  60  may be any known pressure sensor and may be configured to detect the pressure within combustion chamber  16  in a known manner. In other embodiments, sensor  60  may be configured to detect temperature fluctuations within combustion chamber  16  or other parameters from which characteristics of the combustion in combustion chamber  16  can be derived. For example, sensor  60  may be an impact sound sensor configured to detect an impact sound propagating in engine block  20  during combustion in combustion chamber  16 . 
     Control system  100  further includes a control unit  50 . Control unit  50  is connected to sensor  60  via a communication line  54  and to gas admission valve  38  via a communication line  52 . Control unit  50  is further connected to ignition device  90  via a communication line  53  and to pressure relief valve  70  via a communication line  55 . Control unit  50  is configured to control an ignition timing of the mixture in combustion chamber  16  via ignition device  90  by injecting a predetermined amount of liquid fuel at a predetermined ignition timing. Further, control unit  50  is configured to receive the results of the detection by sensor  60  and to determine at least one combustion parameter associated with the combustion in combustion chamber  16  from the received detection results. 
     Control unit  50  may be a single microprocessor or dual microprocessors that include means for controlling, among others, an operation of various components of combustion engine  10 . Control unit  50  may be a general engine control unit (ECU) capable of controlling internal combustion engine  10  and/or its associated components. Control unit  50  may 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 internal combustion engine  10  and its components. Various other known circuits may be associated with control unit  50 , including power supply circuitry, signal conditioning circuitry, communication circuitry and other appropriate circuitry. Control unit  50  may 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 unit  50  may compare received values with target values stored in memory, and, based on the results of the comparison, transmit signals to one or more components to alter the operation status of the same. 
     Control unit  50  may include any memory device known in the art for storing data relating to the operation of internal combustion engine  10  and its components. The data may be stored in the form of one or more maps that describe and/or relate, for example, the detection results from sensor  60  and a desired combustion profile for the combustion in combustion chamber  16 . Each of the maps may be in the form of tables, graphs and/or equations, and may include a compilation of data collected from lab and/or field operation of internal combustion engine  10 . The maps may be generated by performing instrumented tests on the operation of internal combustion engine  10  under various operating conditions while varying parameters associated therewith or performing various measurements. Control unit  50  may reference these maps and control operation of one component in response to the desired operation of another component. 
     In the embodiment, control unit  50  may have one or more combustion profiles for cylinder  26  stored in the memory of the same, said combustion profiles being determined in advance for a standard or reference operating condition of internal combustion engine  10 . For example, each reference combustion profile may be determined under a reference operating condition that corresponds to one or more of a reference fuel quality of the gaseous fuel, a reference ambient air temperature, a reference ambient air pressure, a reference humidity, a reference engine load, and the like. For example, during testing of internal combustion engine  10 , internal combustion engine  10  may be operated with a standard fuel of known quality under standard or known ambient conditions such as air temperature, air pressure, humidity, etc. Under these standard conditions, injection timings and injection amounts for one or more injections by ignition device  90  may be varied, until an optimum combustion is obtained. In some embodiments, NOx values associated with the combustion may be taken into account when determining the optimum number of injections and/or injection amounts. In this manner, one or more combustion profiles characterized by, for example, reference cylinder pressure profiles can be obtained for an optimum combustion under different operating conditions. 
     During operation of in the field, internal combustion engine  10  may be operated using a standard number of injections and corresponding injection amounts for a given ambient air temperature, ambient air pressure, humidity etc. Further, a corresponding reference combustion profile for an optimum or desired combustion is selected in accordance with the current operating condition of internal combustion engine  10 . 
     Next, one or more measurements relating to the combustion in combustion chamber  16  of cylinder  26  are performed. In the embodiment, for example, the in-cylinder pressure measurement by sensor  60  is used to determine at least one combustion parameter, for example, a start of combustion, a center of combustion and/or a combustion duration for the associated combustion event. It will be appreciated that in other embodiments other measurements may be used as an alternative or in addition to the cylinder pressure measurements. 
     Control unit  50  is configured to compare the at least one combustion parameter based on the at least one measurement to a desired or reference combustion parameter associated with the selected reference combustion profile. Further, control unit  50  is configured to determine whether the determined combustion parameter differs from the desired combustion parameter, for example, by more than a predetermined amount. If so, control unit  50  is configured to take appropriate counter-measures, either to achieve a desired combustion in the current combustion cycle, or to prevent an actuation of ignition device  90  in case a pre-ignition is detected. This will be described in more detail below. 
     In one example, control unit  50  may be configured to actuate ignition device  90  at a standard ignition timing in order to supply a standard amount of pilot liquid fuel to combustion chamber  16  in order to initiate combustion of the mixture of gaseous fuel and air in combustion chamber  16 . For example, control unit  50  may be configured to inject a first amount of liquid fuel at a first ignition timing, for example, a predetermined crank angle before or after top dead center. 
     Further, control unit  50  may receive pressure measurements from sensor  60 , and may continuously compare the received pressure measurement values with desired or reference pressure values associated with the selected reference combustion profile. In addition or as an alternative, control unit  50  may be configured to determine, for example, a start of combustion based on the received pressure measurement values. 
     In some embodiments, when control unit  50  determines that the actual start of combustion during the current combustion cycle differs from the desired or reference start of combustion, for example, by more than a predetermined amount, control unit  50  may be configured to again actuate ignition device  90  to perform one or more additional pilot fuel injections in order to initiate the combustion. For example, control unit  50  may be configured to actuate ignition device  90  one more time when the start of combustion differs from the desired start of combustion by more than the predetermined amount. Control unit  50  may be configured to immediately perform the additional injection when it is determined that the start of combustion does not match the desired start of combustion, or to perform the additional injection (or several additional injections) at a predetermined timing (or predetermined timings) defined in advance, for example, with respect to the first ignition timing. In some embodiments, control unit  50  may be configured to first perform one additional injection, again evaluate the pressure measurement results received from sensor  60 , and perform one or more further injections in case the start of combustion still does not match the desired start of combustion. 
     Additionally, control unit  50  may be configured to variably control the amount of injected pilot liquid fuel based on the comparison of the determined combustion parameter with the desired combustion parameter. For example, control unit  50  may be configured to adjust the additional amount of pilot fuel that is injected by ignition device  90  based on the difference between the same. In some examples, control unit  50  may be configured to adjust the additional amount of pilot fuel in proportion to the difference between, for example, a detected in-cylinder pressure and a reference cylinder pressure at a given crank angle. In other embodiments, control unit  50  may be configured to vary the additional amount of pilot fuel in proportion to a difference between a determined start of combustion and a desired start of combustion. In some embodiments, control unit  50  may be configured to determine a heat release during the combustion in combustion chamber  16 , and compare the determined heat release to a desired heat release, for example, at a predetermined crank angle. In this case, control unit  50  may also be configured to adjust the amount of pilot fuel that is injected based on this comparison. 
     With the exemplary control described above, control unit  50  is capable of controlling a combustion within a single combustion cycle in order to achieve or approach a desired combustion profile associated with a desired or optimum combustion in a cylinder of internal combustion engine  10 . In this manner, a combustion efficiency, exhaust emissions, etc. can be optimized. 
     In another example, control unit  50  may be configured to perform the at least one measurement associated with cylinder  26  prior to a first actuation of ignition device  90  in a combustion cycle of cylinder  26 . For example, control unit  50  may be configured to receive the measured cylinder pressure from sensor  60 , and determine based on the received cylinder pressure values whether a pre-ignition is occurring in cylinder  26 , i.e., whether the mixture of gaseous fuel and air in combustion chamber  16  is ignited even though ignition device  90  has not yet supplied any pilot fuel. If so, control unit  50  is configured to abort the injection of pilot fuel by ignition device  90  (deactivate the same) in order to reduce a pressure increase and a load on cylinder  26 . 
     Additionally, control unit  50  may be configured to open pressure relief valve  70  when a start of combustion is detected prior to the actuation of ignition device  90 , i.e., in case of a pre-ignition. It will be appreciated that any appropriate pressure relief valve having a switching time that is fast enough can be used to achieve the desired effect. 
     As an alternative or in addition, control unit  50  may further be configured to open exhaust valve  36  of cylinder  26  in case of a detected pre-ignition, for example, for engines that are provided with a variable valve train. Again, it will be appreciated that any appropriate actuation mechanism that allows actuation of exhaust valve  36  at variable timings can be used. 
     In the above-described embodiment, gaseous fuel internal combustion engine  10  is a diesel gas engine. It will be readily appreciated, however, that the above-described control by control unit  50  can also be implemented in case of a dual fuel engine operating in gas mode. 
     In addition, it will be readily appreciated that the above-described control can be implemented for an Otto gas engine including an ignition device  90  such as, for example, a spark plug that is configured to ignite the mixture of gaseous fuel and air in combustion chamber  16  by generating an ignition spark at a desired ignition timing. In this case, control unit  50  may be configured to actuate ignition device  90  prior to performing the at least one measurement, and to actuate ignition device  90  at least one more time during the same combustion cycle, for example, when the combustion parameter differs from the desired combustion parameter by more than the predetermined amount. For example, control unit  50  may be configured to actuate ignition device  90  for a second time in case no start of combustion is detected after a first actuation. Of course, this can be repeated, if necessary, i.e., control unit  50  may also actuate ignition device  90  for a third time, and so on. 
     Likewise, in case of detection of a pre-ignition, control unit  50  may be configured to deactivate ignition device  90 , i.e., prevent generation of the ignition spark by the same. 
     In case gaseous fuel internal combustion engine  10  is provided with a high pressure gas supply system, control unit  50  may also be configured to actuate gas supply valve  38  to supply an additional amount of gaseous fuel in combination with the additional actuation of ignition device  90 . For example, in case of an Otto gas engine, a gas supply valve close to the ignition device may supply an additional amount of gaseous fuel, and the ignition device of the engine may perform a second ignition in the same combustion cycle when the combustion parameter differs from the desired combustion parameter by more than the predetermined amount. Control unit  50  may be configured to synchronize the additional gas injection with the additional ignition, or to supply the additional gas injection at a predetermined timing with respect to the additional ignition, for example, a predetermined crank angle before the same. 
     It will be appreciated that, apart from the above-described differences between an Otto gas engine and a diesel gas engine, the remaining control by control unit  50  in accordance with the present disclosure may be the same for both engine types. 
     INDUSTRIAL APPLICABILITY 
     The industrial applicability of the systems and methods for controlling the combustion during a combustion cycle of gaseous fuel internal combustion engine described herein will be readily appreciated from the foregoing discussion. An exemplary machine suited to the disclosure is a large internal combustion engine such as the engines of the series M46DF, M43DF, GCM46, GCM34, M32DF, M34DF, M27DF, GCM27, M3x manufactured by Caterpillar Motoren GmbH &amp; Co. KG, Kiel, Germany. Similarly, the systems and methods described herein can be adapted to a large variety of other gas or dual fuel engines used for various different tasks. 
     With the system of the present disclosure, it is possible to form the shape of the combustion profile in a cylinder of a gaseous fuel internal combustion engine in a single combustion cycle. As mentioned above, this can improve the efficiency of the combustion, reduce exhaust emissions, and increase the operation stability of the engine. An exemplary method of controlling the gaseous fuel internal combustion engine is described in the following. 
     During operation of the gaseous fuel internal combustion engine  10 , control unit  50  may actuate ignition device  90  at a predetermined ignition timing, for example, a predetermined crank angle, in order to inject a predetermined amount of ignition fuel or to actuate an ignition device such as a spark plug or the like. 
     Sensor  60  measures the in-cylinder pressure of associated cylinder  26 . Control unit  50  receives the measured cylinder pressure values, and determines whether the measured values correspond to reference values associated with, for example, a desired combustion profile for cylinder  26 . 
     In case the values do not match, for example, when a start of combustion is retarded with respect to a desired start of combustion, control unit  50  is configured to perform an appropriate counter-measure. For example, in case of a diesel gas engine, control unit  50  may be configured to perform a second injection of pilot fuel at an appropriate timing in order to further promote combustion of the mixture of gaseous fuel and air in combustion chamber  16 . In this respect, control unit  50  may also be configured to adjust the amount of additional pilot fuel that is injected based on, for example, a comparison between a current heat release and a desired heat release associated with the combustion, for example, at a predetermined crank angle. Here, the timing of the additional injection and/or the amount of the additional injection can be determined in advance for a variety of combustion profiles determined by control unit  50 . For example, appropriate timings and/or injection amounts may be related to the difference between the measured cylinder pressure and the desired cylinder pressure in one or more maps, and may be selected by control unit  50  by utilizing said maps. Of course, the same applies for the additional ignition timings in case of an Otto gas engine. 
     As an alternative or an addition, in one exemplary method disclosed herein, control unit  50  may also be configured to determine based on the received cylinder pressure measurements from sensor  60  whether a pre-ignition has occurred in combustion chamber  16 . If so, control unit  50  is configured to deactivate ignition device  90 , i.e., prevent the ignition of pilot fuel in case of a diesel gas engine, or prevent actuation of the spark plug of an Otto gas engine. 
     It will be appreciated that the foregoing description provides examples of the disclosed systems and methods. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the general disclosure. 
     Recitation of ranges of values herein are merely intended to serve as a shorthand method for referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All method steps described herein can be performed in any suitable order, unless otherwise indicated or clearly contradicted by the context. 
     Although the preferred embodiments of the present disclosure have been described herein, improvements and modifications may be incorporated without departing from the scope of the following claims.