WO2014094807A1

WO2014094807A1 - Control system for internal combustion engines

Info

Publication number: WO2014094807A1
Application number: PCT/EP2012/005346
Authority: WO
Inventors: Karl Stellwagen
Original assignee: Caterpillar Energy Solutions Gmbh
Priority date: 2012-12-21
Filing date: 2012-12-21
Publication date: 2014-06-26

Abstract

The present disclosure generally relates to a control system (50) configured to be used in a turbocharged internal combustion engine (10). The disclosed control system (50) may comprise an exhaust throttle valve (54) configured to be disposed downstream of a turbine (42) of a turbocharger and to control a flow of exhaust gas originating from at least one cylinder (26A to 26D). The disclosed control system (50) may further comprise a control unit (52) connected to the exhaust throttle valve (54) and configured to determine a differential pressure of the air/fuel-mixture across an intake throttle valve (27) disposed upstream of the at least one cylinder (26A to 26D), and, if the differential pressure exceeds a differential pressure threshold, adjust the exhaust throttle valve (54) such that the differential pressure of the air/fuel-mixture across the intake throttle valve (27) reduces.

Description

CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES Technical Field

The present disclosure generally relates to a control system for internal combustion engines and, particularly, to a control system for gaseous fuel internal combustion engines. Furthermore, the present disclosure relates to a method for controlling operation of an internal combustion engine.

Background

During operation of turbocharged engines, particularly gaseous fuel type engines with different types of fuel or varying fuel mixtures, the pressure of an air/fuel-mixture upstream of an intake throttle valve varies at constant load, whereas the pressure of the air/fuel-mixture downstream of the intake throttle valve substantially maintains constant. That effect may particularly arise if the fuels have different burning characteristics, as for example, natural gas and/or biogas. As a result, the differential pressure at the intake throttle valve disposed upstream of at least one cylinder of the internal combustion engine increases continuously. If the differential pressure across the intake throttle valve exceeds a differential pressure threshold, the compressor of the turbocharger may reach the surge line. This can result in engine faults, damages, and downtime of the internal combustion engine. In this respect, it is known to control the differential pressure at the throttle valve by means of a bypass line at the compressor or at the turbine of the turbocharger.

US 2003/0188531 A discloses a system for estimating engine exhaust pressure. The system includes a pressure sensor fluidly coupled to an intake manifold of the engine, a turbocharger having a turbine fluidly coupled to an exhaust manifold of the engine, a control actuator responsive to a control command to control either of a swallowing capacity and a swallowing efficiency of the turbine, and a control computer estimating engine exhaust pressure as a function of the pressure signal and the control command.

[04] US 5 079 921 A discloses an exhaust back pressure control system for controlling operations of an internal combustion engine. When a valve disposed in an exhaust outlet of a turbocharger is moved towards a closed position, it restricts the exhaust flow, thereby increasing back pressure and friction within the engine by producing an artificial load thereon, and thus speeds up the warming process of the engine taking place within the engine upon starting thereof.

[05] US 7 171 292 B2 discloses a system for processing vehicle powertrain torsional information resulting from vibration of the vehicle powertrain.

Specifically, techniques for monitoring any one or more powertrain torsionals, and providing diagnostic information and/or controlling one or more

engine/vehicle operation parameter as a function thereof is disclosed.

[06] The present disclosure is directed, at least in part, to improving or

overcoming one or more aspects of prior systems.

Summary of the Disclosure

[07] According to an aspect of the present disclosure, a control system

configured to be used in an internal combustion engine including at least one cylinder configured to combust an air/fuel-mixture within, an intake throttle valve disposed upstream of the at least one cylinder and configured to provide a desired amount of the air/fuel-mixture to the at least one cylinder, and a turbocharger including a compressor disposed upstream of the intake throttle valve and a turbine disposed downstream of the at least one cylinder and being mechanically coupled to the compressor may comprise an exhaust throttle valve configured to be disposed downstream of the turbine and to control a flow of exhaust gas originating from the at least one cylinder, and a control unit connected to the exhaust throttle valve. The control unit may be configured to determine a differential pressure of the air/fuel-mixture across the intake throttle valve, and, if the differential pressure exceeds a differential pressure threshold, adjust the exhaust throttle valve such that the differential pressure of the air/fuel-mixture across the intake throttle valve reduces.

According to another aspect of the present disclosure, an internal combustion engine may comprise at least one cylinder configured to combust a mixture of fuel and air within, an intake throttle valve disposed upstream of the at least one cylinder and configured to provide a desired amount of the mixture of fuel and air to the at least one cylinder, a turbocharger including a compressor disposed upstream of the intake throttle valve and a turbine disposed downstream of the at least one cylinder and being mechanically coupled to the compressor, and a control system according to the present disclosure.

According to another aspect of the present disclosure, a method for retrofitting an internal combustion engine including at least one cylinder configured to combust an air/fuel-mixture within, an intake throttle valve disposed upstream of the at least one cylinder and configured to provide a desired amount of the air/fuel-mixture to the at least one cylinder, and a turbocharger including a compressor disposed upstream of the intake throttle valve and a turbine disposed downstream of the at least one cylinder and being mechanically coupled to the compressor may comprise installing a control system according to the present disclosure at the internal combustion engine.

According to another aspect of the present disclosure, a method for controlling operation of an internal combustion engine including at least one cylinder configured to combust an air/fuel-mixture within, an intake throttle valve disposed upstream of the at least one cylinder and configured to provide a desired amount of the air/fuel-mixture to the at least one cylinder, a turbocharger comprising a compressor disposed upstream of the intake throttle valve and a turbine disposed downstream of the at least one cylinder and being mechanically coupled to the compressor, and an exhaust throttle valve disposed downstream of the turbine may comprise determining a differential pressure of the air/fuel- mixture across the intake throttle valve, and if the differential pressure exceeds a differential pressure threshold, adjusting the exhaust throttle valve such that the air/fuel-mixture across the intake throttle valve reduces.

In some embodiments, the differential pressure may be determined by a signal provided from a first pressure sensor configured to detect the pressure of the air/fuel-mixture upstream of the intake throttle valve and a signal provided from a second pressure sensor configured to detect the pressure of the air/fuel- mixture downstream of the intake throttle valve.

In some embodiments, the control system may further comprise a differential pressure sensor configured to detect the differential pressure of the air/fuel mixture across the intake throttle valve and to provide a signal indicating the detected differential pressure.

In some embodiments, the differential pressure threshold may be a pressure value. In some other embodiments, the differential pressure threshold may be a ratio expressed in percent between the predetermined differential pressure and the pressure, for example, downstream of the intake throttle valve.

Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

Brief Description of the Drawing

Fig. 1 shows a schematic diagram of an internal combustion engine comprising an exemplary disclosed control system.

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 may be based in part on the realization that, if a differential pressure across an intake throttle valve exceeds a differential pressure threshold, providing and adjusting an exhaust throttle valve disposed downstream of a turbine of a turbocharged internal combustion engine may reduce a differential pressure across an intake throttle valve disposed downstream of the compressor. Particularly, by closing the exhaust throttle valve, an exhaust gas back pressure may be generated upstream of the exhaust throttle valve, which may reduce the turbine speed and, thus, the output torque of the turbine. This may in turn reduce the power of the compressor mechanically coupled to the turbine and, thus, may reduce the output torque of the compressor, such that the pressure upstream of the intake throttle valve reduces. Therefore, the differential pressure across the intake throttle valve may also be reduced.

The present disclosure may be further based in part on the realization that retrofitting a turbocharged internal combustion engine with an exemplary disclosed control system may support in preventing engine faults, downtime of the engine, and/or damage to engine components such as, for example, the compressor or the intake throttle valve.

Referring now to the drawing, an internal combustion engine 10 is illustrated in Fig. I . The internal combustion engine 10 may include features not shown, such as fuel systems, air systems, cooling systems, peripheries, drive train components, control systems etc. For the purposes of the present disclosure, the internal combustion engine 10 is a single-stage turbocharged internal combustion engine running on gaseous fuel. Particularly, the internal combustion engine 10 is an internal combustion engine running on different gaseous fuels, such as natural gas and/or biogas, depending on specific operational states. The internal combustion engine 10 may be switched over from, for instance, biogas to natural gas during normal operation. In some embodiments, the internal combustion engine 10 may be powered down or switching over from, for instance, biogas to natural gas.

One skilled in the art will recognize, however, that the internal combustion engine 10 may be any type of engine (gas, natural gas, propane, dual fuel, etc.) that utilizes an air/fuel-mixture for combustion. Thus, the internal combustion engine 10 may also be a two-stage turbocharged internal combustion engine. Further, in some types of combustion engines, the air/fuel-mixture may be supplied to the combustion engine via an intake manifold. In other types of combustion engines, only air may be supplied to the combustion engine via the intake manifold, and fuel may be separately injected into each cylinder prior to combustion.

The internal combustion engine 10 may be of any size, with any number of cylinders and in any configuration ("V", "in-line", etc.). The internal combustion engine 10 may be used to power any machine or other device, including locomotive applications, on-highway trucks or vehicles, off-highway machines, earth-moving equipment, generators, aerospace applications, marine applications, pumps, stationary equipment such as power plants, or other engine- powered applications.

The internal combustion engine 10 comprises an engine block 20 including a bank of cylinders 26A to 26D, at least one fuel tank (not shown), a turbocharger 40 associated with the cylinders 26A to 26D, and an intake assembly 12.

The engine block 20 includes a crankcase (not shown) within which a crankshaft 6 indicated by a dot-dashed line is supported. The crankshaft 6 is connected to pistons (not shown) that are movable within each of the cylinders 26A to 26D during operation of the internal combustion engine 10. The intake assembly 12 comprises an intake manifold 22 and a plurality of intake ports 24A to 24D. The intake manifold 22 defines a flow direction of the air/fuel-mixture in the intake manifold 22 (shown by an arrow in Fig. 1) and is fluidly connected to each of the cylinders 26A to 26D via a corresponding one of the intake ports 24A to 24D of the cylinders 26 A to 26D. The inlet ports 24A to 24D are configured to receive the air/fuel-mixture from the intake manifold 22. Generally, the inlet ports 24A to 24D may be formed at least in part in respective cylinder heads or in a common cylinder head (not shown) of the cylinders 26A to 26D.

An exhaust manifold 28 is connected to each of the cylinders 26A to 26D. Each of the cylinders 26A to 26D is provided with at least one exhaust valve (not shown) configured to open and close a fluid connection between the combustion chamber of the corresponding cylinder and the exhaust manifold 28.

The turbocharger 40 is configured to use the heat and pressure of the exhaust gas of the internal combustion engine 10 to drive a compressor 44 for compressing the air/fuel-mixture prior to being supplied to the cylinders 26A to 26D. Specifically, exhaust gas passing a turbine 42 of the turbocharger 40 rotates the turbine 42, thereby decreasing in pressure and temperature. The compressor 44 is rotatably connected to the turbine 42 via a common shaft 46 and driven by the turbine 42.

The air/fuel-mixture may be supplied to the compressor 44 via an intake pipe 14 fluidly connected to an air system (not shown) and a fuel system (not explicitly shown in Fig. 1). In some embodiments, a gas admission valve may be used for mixing air with gaseous fuel for providing the air/fuel-mixture having a desired ratio of fuel to air.

The compressor 44 may compress the air/fuel-mixture to about 3 to 4 bar at 180°C and a cooler (not shown) may cool the charge air from about 180°C to 45°C. After combustion, the exhaust gas may have a pressure of about 3 to 4 bar at a temperature in the range from about 550°C to 650°C. Generally, an outlet of the compressor 44 is fluidly connected to an inlet of the intake manifold 22 via a compressor connection 21. As shown in Fig. 1 , an outlet of the compressor 44 is connected to the inlet of the intake manifold 22 via an intake throttle valve 27 arranged downstream of the compressor 44. The intake throttle valve 27 is configured to open or close the fluid connection between the compressor connection 21 and intake manifold 22, thereby enabling or restricting the flow of the combustion mixture from the compressor connection 21 into the intake manifold 22.

During operation of the internal combustion engine 10, the air/fuel- mixture is accordingly compressed prior to being supplied to the cylinders 26A to 26D. Within the cylinders 26A to 26D, further compression and, therefore, heating of the air/fuel-mixture is caused through the movement of the pistons. Therein, an ignition event may ignite the air-fuel-mixture. Then, exhaust gases, which are discharged via the exhaust manifold 28, are produced.

An outlet of the exhaust manifold 28 is fluidly connected to an inlet of the turbine 42. An outlet of the turbine 42 may be fluidly connected to, for example, an exhaust gas treatment system (not shown) configured to treat the exhaust gas.

The internal combustion engine 10 further includes a control system 50 including a control unit 52 and an exhaust throttle valve 54 configured to be disposed downstream of the turbine 42.

The control unit 52 is connected to the exhaust throttle valve 54, particularly to an exhaust throttle valve actuation means 53 via a first control line 56, and is configured to be connected to a first pressure sensor 17 configured to detect the pressure of the air/fuel-mixture within the compressor connection 21. The first control line 56 may be a conventional wire connection suitable for transmitting electric signals. In some embodiments, the first control line 56 may be a wireless connection, such as, for example, a Bluetooth connection, a WLAN connection, or an infrared connection. [34] The control unit 52 is configured to receive a signal from the first pressure sensor 17, which indicates the pressure of the air/fuel-mixture within the compressor connection 21. The control unit 52 is further configured to be connected to the intake throttle valve 27, particularly to an intake throttle valve actuation means 25.

[35] The control unit 52 may be further connected to a second pressure sensor

18 configured to detect the pressure of the air/fuel-mixture within the intake manifold 22. In such case, the control unit 52 may receive signals indicating the pressure of the air/fuel-mixture upstream of the intake throttle valve 27 and the pressure of the air/fuel-mixture downstream of the intake throttle valve 27 from the first and second pressure sensors 17, 18, respectively. Subsequently, the control unit 52 may be configured to determine a differential pressure of the air/fuel-mixture across the intake throttle valve 27 based on the pressures of the air/fuel-mixture upstream and downstream of the intake throttle valve 27.

[36] The control unit 52 may be a single microprocessor or plural

microprocessors that may include means for controlling, among others, an operation of the internal combustion engine 10 and the throttle valves 27, 54 as well as other components of the internal combustion engine 10. The control unit 52 may be a general engine control unit capable of controlling numeral functions associated with the internal combustion engine 10 and/or its associated components. In some embodiments, the control unit 52 may be a separate control unit exclusively configured to control the exhaust throttle valve 54.

[37] The control unit 52 may include all the 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 the internal combustion engine 10 and its various components. Various other known circuits may be associated with the control unit 52, including power supply circuitry, signal-conditioning circuitry, communication circuitry, and other appropriate circuitry. The control unit 52 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, the control unit 52 may compare received values with target values stored in memory, and based on the results of the comparison, the control unit 52 may transmit signals to one or more components to alter the operation status thereof, such as, for example, the operation of the throttle valves 27, 54.

The control unit 52 may include any memory device known in the art for storing data relating to operation of the 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 to, for example, operation of the throttle valves 27, 54 and/or the internal combustion engine 10. Each of the maps may be in the form of look-up tables, graphs, and/or equations, and include a compilation of data collected from lab and/or field operation of the internal combustion engine 10. The maps may be generated by performing instrumented tests on the operation of the internal combustion engine 10 under various operating conditions while varying parameters associated therewith. The control unit 52 may reference these maps and control operation of one component in response to the desired operation of another component.

The intake throttle valve 27 and the exhaust throttle valve 54 may be throttle valves known in the art. For example, the throttle valves 27, 54 may each include a known flap (not shown) configured to open or close the passage therethrough. In some embodiments, the flaps may infinitely control the amount of the air/fuel-mixture or exhaust gas passing through the respective throttle valve 27, 54.

The flap of the intake throttle valve 27 may be actuated by an intake throttle valve actuation means 25. Similarly, the flap of the exhaust throttle valve 54 may be actuated by an exhaust throttle valve actuation means 53. The intake throttle valve actuation means 25 and the exhaust throttle valve actuation means 54 are connected to the control unit 52 configured to adjust the flaps of the throttle valves 27, 54.

The control unit 52 may further determine the pressure of the air/fuel- mixture within the intake manifold 22 by receiving a signal indicating a degree of displacement of the flap of the intake throttle valve 27 via a second control line 58. The degree of displacement of the flap may, for example, indicate an opening degree of the flap. The degree of displacement of the flap may, for instance, be measured by an angle sensor (not shown) attached to the intake throttle valve 27. In such case, the control unit 52 may adjust the degree of displacement of the exhaust throttle valve flap in dependency of the degree of displacement of the intake throttle valve flap. The relationship between the degrees of displacement of the exhaust throttle valve flap and the intake throttle valve flap may be acquired by, for instance, a look-up table, a calculation using a corresponding equation, or by graphical association.

In some embodiments, the second control line 58 may be a wireless connection, such as, for example, a Bluetooth connection, a WLAN connection, or an infrared connection.

In some embodiments, the control system 50 may comprise a differential pressure sensor (not shown) connected to the control unit 52 and configured to detect the differential pressure of the air/fuel-mixture across the intake throttle valve 27 and to provide a signal indicating the detected differential pressure to the control unit 52.

In some other embodiments, the control unit 52 may determine the differential pressure of the air/fuel-mixture based on the engine load. In such embodiments, a specific engine load requires a specific pressure within the intake manifold 22, such that the control unit 52 may include a look-up table associating the engine loads to corresponding intake manifold pressures. Therefore, the first pressure sensor 17 may provide the pressure of the air/fuel-mixture upstream of the intake throttle valve 27, whereas the above-mentioned look-up table may provide the pressure of the air/fuel-mixture downstream of the intake throttle valve 27 based on the engine load.

In some other embodiments, the control unit 52 may determine the differential pressure of the air/fuel-mixture in dependency of the opening degree of the intake throttle valve flap. In such embodiments, the opening degree of the intake throttle valve flap may be proportional to the differential pressure of the air/fuel-mixture across the intake throttle valve 27.

As already mentioned above, the internal combustion engine 10 is configured to run on different fuels, such as, for instance, natural gas and or biogas. In dependency of the gaseous fuel used for running the internal combustion engine 10, a different pressure within the intake manifold 22 is required. Thus, the control unit 52 may further include any look-up tables associating the pressure within the inlet manifold 22 to the specific ratio of air to fuel within the air/fuel-mixture.

The exemplary disclosed control system 50 may be further configured to retrofit any internal combustion engine including at least one cylinder, at least one turbocharger unit, and an intake throttle valve. In such case, by retrofitting the internal combustion engine with an exemplary disclosed control system 50, the control unit 52 may be configured to prevent any engine faults or damages caused by a differential pressure of the air/fuel-mixture at the intake throttle valve which exceeds the differential pressure threshold.

Industrial Applicability

In the following, operation of the control system 50 during operation of the internal combustion engine 10 is described with reference to Fig. 1.

After combustion of the air/fuel-mixture within the cylinders 26A to 26D, the exhaust gas may be released into the exhaust manifold 28 and may drive the turbine 42, which in turn drives the compressor 44 for compressing the air/fuel- mixture prior to being supplied to the cylinders 24A to 24D. [51] The control unit 52 may continuously determine the differential pressure of the air/fiiel-mixture across the intake throttle valve 27. The control unit 52 may further compare the determined differential pressure of the air/fiiel-mixture across the intake throttle valve 27 with a differential pressure threshold. If the determined differential pressure across the intake throttle valve 27 exceeds the differential pressure threshold, the control unit 52 adjusts the exhaust throttle valve 54. Specifically, the control unit 52 may transmit a signal to the exhaust throttle valve actuation means 53, which in turn may adjust the position of the flap, thereby adjusting the opening degree of the exhaust throttle valve 54.

[52] For example, the differential pressure threshold may be a pressure value in the range from, for instance, about 0.1 bar to 0.5 bar. For example, during a part load operation of the internal combustion engine 10, the pressure

downstream of the intake throttle valve 27 may be about 0.5 bar, whereas, during a full load operation of the internal combustion engine 10, the pressure downstream of the intake throttle valve may be about 4 bar.

[53] In some other embodiments, the differential pressure threshold may be variable, such that the differential pressure threshold may be adjusted in dependency of, for instance, the engine load, the engine speed, or the compressor speed.

[54] In the case that the determined differential pressure of the air/fuel-mixture across the intake throttle valve 27 exceeds the differential pressure threshold, the control unit 52 adjusts the exhaust throttle valve 54. Particularly, the control unit 52 may at least partially close the exhaust throttle valve 54, which results in an exhaust gas back pressure within the exhaust manifold 28 and the turbine 42. The exhaust gas back pressure may retard the turbine 42 and may, thus, reduce the turbine speed and the turbine output torque.

[55] As the turbine 42 is mechanically coupled to the compressor 44 via the common shaft 46, retarding of the turbine 42 results in a reduced compressor speed and, thus, a reduced compressor output torque. Therefore, the pressure of the air/fuel-mixture downstream of the compressor 44 and, thus, upstream of the intake throttle valve 27 may be also reduced, which results in a reduced differential pressure of the air/fuel-mixture across the intake throttle valve 27.

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.

Claims

1. A control system (50) configured to be used in an internal combustion engine (10) including at least one cylinder (26 A to 26D) configured to combust an air/fuel-mixture within, an intake throttle valve (27) disposed upstream of the at least one cylinder (26A to 26D) and configured to provide a desired amount of the air/fuel-mixture to the at least one cylinder (26A to 26D), and a turbocharger (40) including a compressor (44) disposed upstream of the intake throttle valve (27) and a turbine (42) disposed downstream of the at least one cylinder (26A to 26D), the turbine (42) being mechanically coupled to the compressor (44), the control system (50) comprising:

an exhaust throttle valve (54) configured to be disposed downstream of the turbine (42) and to control a flow of exhaust gas originating from the at least one cylinder (26A to 26D); and

a control unit (52) connected to the exhaust throttle valve (54), the control unit (52) being configured to

determine a differential pressure of the air/fuel-mixture across the intake throttle valve (27), and

if the differential pressure exceeds a differential pressure threshold, adjust the exhaust throttle valve (54) such that the differential pressure of the air/fuel-mixture across the intake throttle valve (27) reduces.

2. The control system (50) of claim 1 , further comprising a first pressure sensor (17) configured to detect the pressure of the air/fuel-mixture upstream of the intake throttle valve (27) and to provide a signal indicating the detected pressure of the air/fuel-mixture upstream of the intake throttle valve (27) to the control unit (52), and a second pressure sensor (18) configured to detect the pressure of the air/fuel-mixture downstream of the intake throttle valve (27) and to provide a signal indicating the detected pressure of the air/fuel-mixture downstream of the intake throttle valve (27) to the control unit (52), wherein the control unit (52) is configured to determine the differential pressure across the intake throttle valve (27) based on the received signals from the first pressure sensor (17) and the second pressure sensor(18).

3. The control system (50) of claim 2, wherein control unit (52) is configured to determine the pressure of the air/fuel-mixture downstream of the intake throttle valve (27) based on an engine load.

4. The control system (50) of claim 1, wherein the intake throttle valve (27) includes a flap being configured to open or close the intake throttle valve (27), and wherein the control unit (52) is configured to determine the differential pressure based on a degree of displacement of the flap of the intake throttle valve (27).

5. The control system (50) of claim 1 , further comprising a differential pressure sensor configured to detect the differential pressure of the air/fuel-mixture across the intake throttle valve (27) and to provide a signal indicating the detected differential pressure to the control unit (52).

6. The control system (50) of any one of the preceding claims, further comprising an exhaust throttle valve actuation means (53) configured to control a flap of the exhaust throttle valve (54), the flap being configured to open or close the exhaust throttle valve (54).

7. The control system (50) of claim 6, wherein the exhaust throttle valve actuation means (53) is a mechanical actuation means configured to be controlled by compressed air originating from an air system of the internal combustion engine (10).

8. An internal combustion engine (10) comprising:

at least one cylinder (26A to 26D) configured to combust a mixture of fuel and air within;

an intake throttle valve (27) disposed upstream of the at least one cylinder (26A to 26D) and configured to provide a desired amount of the mixture of fuel and air to the at least one cylinder (26A to 26D);

a turbocharger (40) including a compressor (44) disposed upstream of the intake throttle valve (27), and a turbine (42) disposed

downstream of the at least one cylinder (26A to 26D) and being mechanically coupled to the compressor (44); and

a control system (50) according to any one of the preceding claims.

9. The internal combustion engine (10) of claim 8, wherein the internal combustion engine (10) is running on gaseous fuel.

10. The internal combustion engine (10) of claim 9, wherein the gaseous fuel internal combustion engine (10) is configured to run on at least two different gaseous fuels having different fuel qualities.

11. A method for retrofitting an internal combustion engine (10) including at least one cylinder (26 A to 26D) configured to combust an air/fuel-mixture within, an intake throttle valve (27) disposed upstream of the at least one cylinder (26A to 26D) and configured to provide a desired amount of the air/fuel-mixture to the at least one cylinder (26A to 26D), and a turbocharger (40) including a compressor (44) disposed upstream of the intake throttle valve (27) and a turbine (42) disposed downstream of the at least one cylinder (26A to 26D), the turbine (42) being mechanically coupled to the compressor (44), the method comprising:

installing a control system (50) according to any one of claims 1 to 7 at the internal combustion engine (10).

12. A method for controlling operation of an internal combustion engine (10) including at least one cylinder (26 A to 26D) configured to combust an air/fuel-mixture within, an intake throttle valve (27) disposed upstream of the at least one cylinder (26A to 26D) and configured to provide a desired amount of the air/fuel-mixture to the at least one cylinder (26A to 26D), a turbocharger (40) comprising a compressor (44) disposed upstream of the intake throttle valve (27) and a turbine (42) disposed downstream of the at least one cylinder (26A to 26D) and being mechanically coupled to the compressor (44), and an exhaust throttle valve (54) disposed downstream of the turbine (42), the method comprising:

determining a differential pressure of the air/fuel-mixture across the intake throttle valve (27); and

if the differential pressure exceeds a differential pressure threshold, adjusting the exhaust throttle valve (54) such that the air/fuel-mixture across the intake throttle valve (27) reduces.

13. The method of claim 12, wherein determining the differential pressure is based on a first signal indicating the pressure upstream of the intake throttle valve (27) and a second signal indicating the pressure downstream of the intake throttle valve (27).

14. The method of claim 13, wherein the pressure downstream of the intake throttle valve (27) is determined based on the engine load.

15. The method of claim 12, wherein adjusting the exhaust throttle valve (54) includes mechanically displacing a flap of the exhaust throttle valve (54), the flap being configured to open or close the exhaust throttle valve (54).