CN118188154A

CN118188154A - Method of operating a large low-speed two-stroke uniflow scavenged turbocharged internal combustion engine

Info

Publication number: CN118188154A
Application number: CN202410377007.9A
Authority: CN
Inventors: 汉斯·斯卡夫特·拉尔森; 彼得·托夫特·特耶尔
Original assignee: Mannone Solutions Mannone Solutions Germany Branch
Current assignee: Mannone Solutions Mannone Solutions Germany Branch
Priority date: 2019-11-15
Filing date: 2020-11-13
Publication date: 2024-06-14
Also published as: KR102684155B1; KR20210060338A; JP7329488B2; JP2021080920A; CN112814780A

Abstract

The present invention provides a method of operating a large low speed two-stroke uniflow scavenged turbocharged internal combustion engine having a crosshead (9). The engine includes: a plurality of cylinders (1) having: -an exhaust valve (4), -an exhaust valve actuation system (46) for actuating the exhaust valve (4), -a fuel delivery system (30) for delivering a quantity of a first fuel to the associated cylinder (1), -a pressure sensor (42) for generating a cylinder-specific pressure signal indicative of the pressure in the associated cylinder (1); and an exhaust gas driven turbocharger (5) to pressurize scavenging gas for the cylinder (1). The method comprises the following steps: at least one combustion process parameter of the cylinder (1) is closed-loop controlled in a cylinder-specific manner on the basis of a pressure signal of the specific cylinder and a setpoint of the specific cylinder, which is a compensation of the specific cylinder for a common setpoint of all cylinders (1).

Description

Method of operating a large low-speed two-stroke uniflow scavenged turbocharged internal combustion engine

The application relates to a split application of a patent application of which the application date is 11/13 in 2020, the application number is 202011271040.1 and the application name is 'a large-sized low-speed turbocharged two-stroke uniflow scavenging internal combustion engine and an operation method'.

Technical Field

The present invention relates to a large low speed turbocharged two-stroke uniflow scavenged internal combustion engine having a crosshead and having a plurality of cylinders, and to a method of operating such an engine.

Background

Large low speed turbocharged two-stroke uniflow scavenged internal combustion engines with crossheads are commonly used in propulsion systems for large vessels or as prime movers for power plants.

Modern engines of this type are fully electronically controlled, i.e. during engine operation, both the intake/injection of fuel and the opening and closing of the exhaust valves can be controlled by an electronic control system to ensure that the engine operates optimally under given operating conditions.

The engine is calibrated prior to shipment to ensure that the engine meets all performance requirements such as, for example, power, fuel efficiency, emissions, noise/vibration levels, and reliability.

Therefore, at the time of shipment, the engine exerts the best performance and meets the performance requirements. However, wear and tear occurs over time because the engine, or at least the cylinders of the engine, deviate from factory specifications, i.e. require recalibration.

Recently, there has been a need for large turbocharged two-stroke compression ignition engines capable of handling alternative types of fuels, such as natural gas, petroleum gas, methanol, coal slurry, water-oil mixtures, petroleum coke, and the like.

Several of these alternative fuels have the potential to reduce cost and emissions.

Large low-speed uniflow scavenged turbocharged two-stroke internal combustion engines are often used to propel large ocean-going cargo vessels, and reliability is therefore critical. Operation of these alternative fuel-using engines is still relatively new and redundancy in operation using gaseous fuels is at a lower level of reliability than when operating using conventional fuels. When the gas fuel is used intentionally, the normal running time of the dual-fuel engine is shortened, thereby reducing the cost. For example, for gaseous fuel systems, redundancy is low. If a fault is detected on one cylinder, the supply of gaseous fuel to all cylinders is stopped. In the normal fuel (oil) mode, only the cylinders affected by the failure are stopped. Correlation is ensured using conventional fuel operation. It is therefore important to be able to quickly switch from alternative fuel to conventional fuel, since operation with conventional fuel is considered a safe fallback measure.

Thus, existing large low-speed two-stroke diesel engines are dual-fuel engines having a fuel system for operation using an alternative fuel, such as a gaseous fuel, for example, and another fuel system for operation using a conventional fuel, such as fuel, for example, so that the engine can be operated at full power using only the conventional fuel.

In the case where there is a problem in operation using the alternative fuel, for example, there is an insufficient gas pressure in operation using the gas fuel, it is essential to be able to quickly switch from operation using the alternative fuel to operation using the normal fuel. It is also important to be able to switch back from conventional fuel to alternative fuel quickly and easily for cost and emissions savings.

However, when the fuel type changes, the combustion process is no longer the same and the engine must be recalibrated to accommodate operation with a different fuel, for example, control of the timing and duration of fuel injection, timing of exhaust valve closure, scavenging pressure, compression pressure, cylinder maximum (peak) pressure, and average indicated pressure needs to be adjusted to the fuel type used. This means that a new process balance must be achieved, especially because the properties (heating value) of the large amounts of gaseous fuel delivered by a typical gaseous fuel system may show large fluctuations.

Known engine control systems are unable to perform such recalibration in a satisfactory manner without human intervention. The known control systems either take too long or have insufficient precision to reach the optimum operating conditions of the engine immediately after a fuel switch.

Furthermore, large low-speed turbocharged two-stroke uniflow scavenged internal combustion engines have been calibrated before shipment such that the combustion process in each of the engine's cylinders is performed according to design criteria throughout the operating state of the engine. Before shipment, the cylinders are balanced (load balanced), i.e. the maximum (peak) or average indicated pressure (load) of the cylinders is as uniform as possible. Alternatively, instead of peak pressure, the average indicated pressure for each cylinder is kept as uniform as possible to ensure as optimal load balancing as possible.

However, after the factory, wear and tear will have a different impact on the engine and on each of the cylinders over time. During use, the combustion process in the cylinder deviates from factory specifications, and the cylinder balance deteriorates. Over time, such developments lead to reduced performance and increased emissions, which should be counteracted at some point in time by recalibrating the control system.

Known control systems for large two-stroke internal combustion engines require manual intervention to perform such recalibration. However, manual intervention requires expert skill because a change in one of the parameters, such as the closing angle of the exhaust valve, will affect the other parameter ranges. Typically, the engine operator does not have the skill required to perform the recalibration involving manual intervention, and thus, such recalibration does not actually occur. Some of the consequences of this lack of recalibration are increased fuel consumption and emissions.

Rolle s Wiesmann a combustion control and monitoring of two-stroke engines in the journal of the valan technology in 2011 discloses an engine with a closed-loop fuel control system in which a common load set point is provided for all cylinders, the cylinder pressure is measured for each cylinder separately and the fuel injection timing and exhaust valve closure are adjusted accordingly.

Disclosure of Invention

Against this background, it is an object of the present application to provide a large low speed turbocharged two-stroke uniflow scavenged internal combustion engine and a method of operating such an engine that overcomes or at least alleviates the above-mentioned problems.

According to a first aspect, this object is achieved by providing a large low-speed two-stroke uniflow scavenged turbocharged internal combustion engine with a crosshead, comprising:

A plurality of cylinders, the cylinders having:

the exhaust valve is arranged to be in fluid communication with the exhaust valve,

An exhaust valve actuation system for actuating an exhaust valve,

A fuel delivery system for delivering an amount of a first fuel to an associated cylinder,

A pressure sensor for generating a pressure signal of a particular cylinder representing the pressure in the associated cylinder,

An exhaust-driven turbocharger that pressurizes scavenging gas for the cylinder,

A controller that receives or is configured to determine the following actual operating conditions of the engine:

A common torque signal representing the torque to be transmitted by the engine,

A common peak pressure signal representing the peak cylinder pressure to be achieved in the cylinder,

A common compression pressure signal representing the compression pressure to be achieved in the cylinder,

The controller receives a pressure signal for a particular cylinder,

Wherein:

a) The controller is configured to: deriving from the pressure signal of the particular cylinder a torque signal of the actual particular cylinder indicative of the torque transmitted by the associated particular cylinder; and adjusting the common torque signal according to the deviation of the common torque signal and the torque signal of the actual specific cylinder to obtain the torque signal of the specific cylinder; and delivering an amount of fuel to the associated particular cylinder based on the torque signal of the particular cylinder,

And

B) The controller is configured to: deriving a peak pressure signal of the actual specific cylinder representing the peak pressure in the associated cylinder (1) from the pressure signal of the specific cylinder to adjust the common peak pressure signal in dependence of a deviation of the common peak pressure signal from the peak pressure signal of the actual specific cylinder to obtain a peak pressure signal of the specific cylinder; and determining the time at which the delivery of the quantity of fuel to the associated particular cylinder (1) starts based on the peak pressure signal of the particular cylinder,

And

C) The controller is configured to: deriving from the pressure signal of the particular cylinder a compression pressure signal of the actual particular cylinder representative of the compression pressure in the associated cylinder, to adjust the common compression pressure signal in dependence of a deviation of the common compression pressure signal from the compression pressure signal of the actual particular cylinder to obtain a compression pressure signal of the particular cylinder; and determining a time for closing the exhaust valve of the associated particular cylinder based on the compression pressure signal of the particular cylinder.

By adjusting the respective combustion process parameter(s) in a cylinder-specific manner, i.e. generating a cylinder-specific torque signal, a cylinder-specific feed pressure signal and/or a cylinder-specific compression pressure signal in the feedback loop, it is achieved that each cylinder operates strictly in accordance with the factory specifications, even in case the wear and tear of the engine or other factors change the operating state of the relevant cylinder. At the same time, it is achieved that the control of the combustion process of the cylinders in the engine is performed irrespective of the load balancing of the cylinders or the cylinders of the entire engine. This way of controlling the engine ensures that each cylinder is in an optimal operating state without concern for cylinder balancing (load balancing).

In a possible implementation of the first aspect, the engine is fuel-guided and the engine comprises at least element a).

In a possible implementation of the first aspect, the engine is air-guided and the engine comprises at least element c).

In a possible implementation of the first aspect, the engine is partly fuel-and partly air-guided and the engine comprises at least element a) and element c).

In a possible embodiment of the first aspect, the engine is a dual fuel engine and wherein the fuel delivery system is configured to handle at least two different fuels and the cylinders are each provided with at least one fuel valve for delivering a first fuel and at least one fuel valve for delivering a second fuel.

In a possible implementation of the first aspect, the engine is fuel-guided when operating on a first fuel and air-guided when operating on a second fuel.

In a possible implementation of the first aspect, the controller receives a desired engine speed and receives a measured engine speed, and wherein the controller comprises a regulator configured to determine the fuel index signal as a function of a deviation of the desired engine speed from the measured engine speed.

In a possible implementation of the first aspect, the controller is configured to convert the fuel index signal into the common torque signal by applying the fuel index signal to a first predetermined map.

In a possible implementation of the first aspect, the controller comprises a power calculation module configured to calculate an engine load signal indicative of the engine load, the power calculation module preferably receiving the fuel index signal and the measured engine speed.

In a possible implementation of the first aspect, the controller is configured to:

-determining a common peak pressure signal by applying the engine load signal to a second predetermined map, and/or

-Determining the common compression pressure by applying the engine load signal to a third predetermined map.

In a possible implementation of the first aspect, the controller comprises a fuel index signal to distribution duration module configured to convert the fuel index signal into a common fuel delivery duration signal.

In a possible implementation of the first aspect, the controller is configured to adjust the common fuel delivery duration signal in dependence of a deviation of the common fuel delivery duration signal from the torque signal of the specific cylinder to obtain the fuel delivery duration signal of the specific cylinder.

In a possible implementation of the first aspect, the controller is configured to determine the injection profile of the specific cylinder based on a torque signal of the specific cylinder or based on a fuel delivery duration signal of the specific cylinder, and wherein the fuel delivery system delivers the quantity of fuel to the relevant specific cylinder by opening one or more fuel valves according to the injection profile of the specific cylinder.

In a possible implementation of the first aspect, the fuel delivery system starts delivering the quantity of fuel to the associated specific cylinder by opening one or more fuel valves according to a start timing of delivery of the quantity of fuel determined by the controller.

Limiting the magnitude of the adjustment of the common torque signal to a first threshold when the adjustments to the other cylinders are in the same direction, and wherein the controller is configured to limit the magnitude of the adjustment of the common torque signal to a second threshold when the adjustments to the other cylinders are in opposite directions,

And/or

Limiting the magnitude of the adjustment of the common peak pressure signal to a first threshold value when the adjustment to the other cylinders (1) is in the same direction, and wherein the controller (55) is configured to limit the magnitude of the adjustment of the common peak pressure signal to a second threshold value when the adjustment to the other cylinders (1) is in an opposite direction,

And/or

-Limiting the magnitude of the adjustment of the common compression pressure signal to a first threshold when the adjustment to the other cylinders (1) is in the same direction, and wherein the controller (55) is configured to limit the magnitude of the adjustment of the common compression pressure signal to a second threshold when the adjustment to the other cylinders (1) is in the opposite direction.

In a possible implementation of the first aspect, the second threshold value is lower than the first threshold value.

In a possible implementation of the first aspect, the first, second and/or third predetermined map is preferably preset at the engine factory according to a test of the relevant engine or the same or comparable engine, the first, second and/or third predetermined map preferably comprising an algorithm and/or a table.

In a possible implementation of the first aspect, the common torque signal corresponds to an average indicated cylinder pressure for all cylinders, and wherein the torque signal for a particular cylinder corresponds to an average indicated cylinder pressure for the associated particular cylinder.

In a possible implementation of the first aspect, the controller comprises a cylinder compensation module for a specific cylinder of each cylinder, the cylinder compensation module of the specific cylinder being configured for compensating the common torque signal, the common peak pressure signal and/or the common compression pressure signal of the specific cylinder concerned.

In a possible implementation of the first aspect, the compensation module of the specific cylinder is manually or automatically controlled.

In a possible implementation of the first aspect, the controller is configured to control cylinders of the engine separately without taking into account cylinder balancing.

In a possible implementation of the first aspect,

The controller is configured to continuously calculate an error value from a difference between the torque of the specific cylinder and the torque of the actual specific cylinder, and in the case where the engine has the element a), apply correction based on the proportional term and the integral term,

The controller is configured to continuously calculate an error value from a difference between the peak pressure of the specific cylinder and the actual peak pressure of the specific cylinder, and in case the engine has element b), apply a correction based on the proportional term and the integral term,

The controller is configured to continuously calculate an error value from a difference between the compression pressure of the specific cylinder and the compression pressure of the actual specific cylinder, and to apply a correction based on the proportional term and the integral term in the case where the engine has the element c).

In a possible embodiment of the first aspect, the fuel delivery system is configured for delivering an amount of the first fuel and/or an amount of the second fuel to the associated cylinder.

According to a second aspect there is provided a method of operating a large low speed two-stroke uniflow scavenged turbocharged internal combustion engine having a crosshead, the engine comprising:

A plurality of cylinders, the cylinders having:

An exhaust valve actuation system for actuating an exhaust valve,

The method comprises the following steps:

At least one combustion process parameter of the cylinder is closed-loop controlled in a cylinder-specific manner based on a pressure signal of the particular cylinder and a set point of the particular cylinder, which is a compensation of the particular cylinder for a common set point of all cylinders.

By adjusting the respective combustion process parameter(s) in a cylinder-specific manner, i.e. generating a cylinder-specific torque signal, a cylinder-specific feed pressure signal and/or a cylinder-specific compression pressure signal in the feedback loop, it is achieved that each cylinder operates strictly in accordance with the factory specifications, even in case the wear and tear or other factors of the engine change the operating state of the relevant cylinder. At the same time, control of the combustion process of the cylinders in the engine is achieved without regard to load balancing of the cylinders or the cylinders of the whole engine. This way of controlling the engine ensures that each cylinder is in an optimal operating state without concern for cylinder balancing (load balancing).

In a possible embodiment of the second aspect, the at least one combustion process parameter comprises:

the quantity of fuel to be injected into the reactor,

-Timing of start of fuel injection, and/or

Timing of closing the exhaust valve.

In a possible embodiment of the second aspect, the closed-loop control is performed without taking into account maintaining cylinder balance.

In a possible implementation of the second aspect, the closed loop control applies the correction based on a proportional term and an integral term.

In a possible embodiment of the second aspect, the common setpoint is:

-a common torque signal representing the torque to be transmitted by the engine, and/or

-A common peak pressure signal representing the peak cylinder pressure to be achieved in the cylinder, and/or

-A common compression pressure signal representing the compression pressure to be achieved in the cylinder.

In a possible implementation of the second aspect, the closed-loop control uses the measured cylinder pressure of the specific cylinder as a reference value.

In a possible embodiment of the second aspect, the average indicated cylinder pressure of the specific cylinder is derived from the measured cylinder pressure of the specific cylinder, and/or wherein the peak pressure of the specific cylinder is derived from the measured cylinder pressure of the specific cylinder, and/or wherein the compression pressure of the specific cylinder is derived from the measured cylinder pressure of the specific cylinder.

According to a third aspect, there is provided a method of operating a large low speed two-stroke uniflow scavenged turbocharged internal combustion engine having a crosshead, the engine comprising:

A plurality of cylinders, the cylinders having:

An exhaust valve actuation system for actuating an exhaust valve,

a common torque signal, the common torque signal representing a torque to be transmitted by the engine,

A common peak pressure signal, the common peak pressure signal representing a peak cylinder pressure to be achieved in the cylinder,

A controller that receives a pressure signal of a specific cylinder,

The method comprises the following steps:

Deriving from the pressure signal of the particular cylinder a torque signal of the actual particular cylinder representing the torque transmitted by the particular cylinder concerned, and adjusting the common torque signal in dependence of a deviation of the common torque signal from the torque signal of the actual particular cylinder to obtain a torque signal of the particular cylinder,

And delivering an amount of fuel to the associated particular cylinder based on the torque signal of the particular cylinder, and/or

B) Deriving a peak pressure signal of the actual specific cylinder representing the peak pressure in the relevant cylinder from the pressure signal of the specific cylinder, adjusting the common peak pressure signal based on a deviation between the common peak pressure signal and the peak pressure signal of the actual specific cylinder to obtain the peak pressure signal of the specific cylinder, and

Determining a timing to begin delivering the quantity of fuel based on a peak pressure signal for a particular cylinder, and/or

C) Deriving from the pressure signal of the particular cylinder a compression pressure signal of the actual particular cylinder representing the compression pressure in the associated cylinder, adjusting the common compression pressure signal in dependence of a deviation of the common compression pressure signal from the compression pressure signal of the actual particular cylinder to obtain the compression pressure signal of the particular cylinder, and

The timing of the exhaust valve closure is determined based on the compression pressure signal for the particular cylinder.

According to a fourth aspect there is provided a large low speed two-stroke uniflow scavenged turbocharged internal combustion engine having a crosshead, the engine comprising:

A plurality of cylinders, the cylinders having:

An exhaust valve actuation system for actuating an exhaust valve,

A controller configured for closed-loop control of one or more combustion process parameters of the cylinder in a cylinder-specific manner according to:

-pressure signal of specific cylinder, and

O common setpoint for all cylinders, or

O set point for a particular cylinder, the set point for a particular cylinder being a compensation for the particular cylinder for the common set point.

According to a fifth aspect there is provided a large low speed two-stroke uniflow scavenged turbocharged internal combustion engine having a crosshead, the engine comprising:

-a plurality of cylinders, said cylinders having:

An exhaust valve is arranged on the inner side of the cylinder,

An exhaust valve actuation system for actuating an exhaust valve,

A fuel delivery system (30), the fuel delivery system (30) for delivering an amount of a first fuel to an associated cylinder,

An exhaust gas-driven turbocharger which pressurizes the scavenging gas for the cylinders,

A controller configured to control at least one of a combustion process parameter(s), an amount of fuel, a timing of a start of fuel injection, and a timing of a closing of an exhaust valve in a cylinder-specific manner,

The controller (55) is configured to:

The combustion process parameters of the cylinders (1) are controlled separately by cyclically adjusting the common set point of the combustion process parameter(s) or the set point of a specific cylinder in a cylinder-specific manner, depending on the operating state of the engine,

An average value of the adjustments of the particular cylinder of the combustion process parameter(s) of the cylinder is calculated,

The adjustment of a particular cylinder in a cycle of combustion process parameter(s) is limited to the addition or subtraction of a maximum predetermined deviation from the calculated average value of the adjustments of the relevant combustion process parameter.

By providing a limiter function that ensures that the adjustment of a particular cylinder in particular does not go out of range, it is possible to ensure that sufficient flexibility is provided to accommodate the large adjustments that normally occur, while suppressing the large adjustments due to errors, thereby ensuring that damage or disruption of operation is avoided.

According to a possible embodiment of the fifth aspect, the controller is configured to define the interval as the maximum predetermined deviation added or subtracted from the calculated average value of the adjustments of the relevant combustion process parameter and to limit the adjustment of the specific cylinder in the cycle of the combustion process parameter(s) to an adjustment within the interval.

According to a possible embodiment of the fifth aspect, the interval is a range having a first range in the positive direction and a second range in the negative direction relative to the calculated average value of the adjustment of the relevant combustion process parameter.

According to a possible embodiment of the fifth aspect, the interval is combustion process parameter specific.

According to a possible implementation of the fifth aspect, the positive range has a first predetermined amplitude and wherein the negative range has a second predetermined amplitude, the first predetermined amplitude not necessarily being the same as the second predetermined amplitude.

According to a possible embodiment of the fifth aspect, the controller is configured to calculate an average value of the cylinder's adjustments to the particular cylinder of the combustion process parameter(s) for one cycle or more cycles of the cyclic adjustments of the relevant combustion process parameter.

According to a possible embodiment of the fifth aspect, the adjustment of the combustion process parameter(s) is an adjustment for a single cycle.

According to a possible embodiment of the fifth aspect, the at least one combustion process parameter comprises:

the quantity of fuel to be injected into the reactor,

-Timing of start of fuel injection, and/or

Timing of closing the exhaust valve.

According to a possible embodiment of the fifth aspect, the set point for a particular cylinder of the combustion process parameter(s) is a compensation for a common set point of the combustion process parameter(s).

According to a possible implementation of the fifth aspect, the operating state of the engine is one or more of the following: engine speed, engine load, cylinder peak pressure, cylinder combustion pressure, cylinder average indicated pressure, scavenge pressure fuel type, ambient humidity, and ambient temperature.

According to a sixth aspect there is provided a method of operating a large low speed two-stroke uniflow scavenged turbocharged internal combustion engine having a crosshead, the engine comprising:

-a plurality of cylinders, said cylinders having:

An exhaust valve is arranged on the inner side of the cylinder,

An exhaust valve actuation system for actuating an exhaust valve,

The method comprises the following steps:

at least one of the combustion process parameter(s), the amount of fuel, the timing of the start of fuel injection and the timing of the closing of the exhaust valve are controlled in a cylinder-specific manner,

The combustion process parameter(s) of the cylinders (1) are controlled separately by cyclically adjusting the common set point of the combustion process parameter(s) or the set point of a particular cylinder in a cylinder-specific manner, depending on the operating state of the engine,

An average value of the adjustments to the particular cylinder of the combustion process parameter(s) is calculated,

Determining a section around the calculated average value for the adjustment of the combustion process parameter(s), and

Limiting the adjustment of a particular cylinder in a cycle of combustion process parameter(s) to the maximum predetermined deviation plus or minus the average of the calculated adjustments of the relevant combustion process parameters.

Other objects, features, advantages and characteristics of the fuel valve and engine according to the present disclosure will become apparent from the detailed description.

Drawings

In the following detailed part of the present description, the invention will be explained in more detail with reference to exemplary embodiments shown in the drawings, in which:

Figure 1 is a front view of a large two-stroke diesel engine according to an example embodiment,

Figure 2 is a side view of the large two-stroke engine of figure 1,

Figure 3 is a schematic view of a large two-stroke engine according to figure 1,

FIG. 4 is a schematic diagram of an embodiment of a controller for the engine of FIG. 1, an

FIG. 5 is a schematic diagram of another embodiment of a controller for the engine of FIG. 1, and

FIG. 6 is a schematic diagram of yet another embodiment of a controller for the engine of FIG. 1.

Detailed Description

In the following detailed description, a compression ignition internal combustion engine will be described with reference to a large two-stroke, low-speed turbocharged internal combustion (diesel) engine in an example embodiment. Fig. 1, 2 and 3 show a large low-speed turbocharged two-stroke diesel engine with a crankshaft 8 and a crosshead 9. Fig. 3 shows a large low-speed turbocharged two-stroke diesel engine with an intake system and an exhaust system. In this example embodiment, the engine has six cylinders 1 arranged in a row. Large low-speed turbocharged two-stroke diesel engines typically have between four and fourteen cylinders in a row carried by an engine frame 11. The engine may for example be used as a main engine for ocean going vessels or as a stationary engine for operating a generator in a power station. The total output of the engine may be, for example, in the range 1,000KW to 110,000 kw.

In this example embodiment, the engine is a diesel (compression ignition) engine or Otto (spark ignition) engine of the two-stroke uniflow scavenged type having scavenging ports 18 at the lower region of the cylinder 1 and a central exhaust valve 4 at the top of the cylinder 1. The scavenging air is transferred from the scavenging air receiver 2 to the scavenging air ports 18 of the respective cylinders 1. The piston 10in the cylinder 1 compresses the scavenging gas, fuel is injected from the fuel valves 50, 51 in the cylinder head 22, and then combustion is performed, and exhaust gas is generated. When the exhaust valve 4 is opened, the exhaust gas flows through the exhaust conduit associated with the cylinder 1 to the exhaust receiver 3 and onward through the first exhaust conduit 19 to the turbine 6 of the turbocharger 5, from where the exhaust gas flows through the second exhaust conduit via the economizer 20 to the outlet 21 and into the atmosphere. The turbine 6 drives a compressor 7, which is supplied with fresh air via an intake 12, by means of a shaft. The compressor 7 delivers the pressurized scavenging air to a scavenging air conduit 13, which scavenging air conduit 13 leads to the scavenging air receiver 2.

The scavenge air in the conduit 13 passes through an intercooler 14 for cooling the scavenge air. In an example embodiment, the scavenge air leaves the compressor at about 200 ℃ and is cooled to a temperature between 36 ℃ and 80 ℃ by an intercooler.

When the compressor 7 of the turbocharger 5 does not deliver sufficient pressure for the scavenge air receiver 2, i.e. in the case of low or partial load of the engine, the cooled scavenge air is passed via an auxiliary fan 16 driven by an electric motor 17, which auxiliary fan 16 pressurizes the scavenge air flow. At higher engine loads, the turbocharger compressor 7 delivers sufficient compressed scavenge air, which is then bypassed by the auxiliary fan 16 via the check valve 15.

The piston is coupled to the crosshead 9 by a piston rod. The crosshead 9 is connected to the crankshaft 8 via a connecting rod. The rotational speed and position of crankshaft 8 is measured by sensor 40. The engine speed signal measured by the sensor 40 is sent to the controller 55, for example, via a signal line.

Each cylinder 1 is provided with an exhaust valve 4, and each cylinder 1 is provided with a pressure sensor 42 and two or more fuel valves 50. The pressure signal of the specific cylinder of the pressure sensor 42 is sent to the controller 55.

In an embodiment, the engine is a dual fuel engine, and in this embodiment, two or more fuel valves 50 are dedicated to a first fuel and two or more fuel valves 50 are dedicated to a second fuel. Alternatively, two or more fuel valves are shared by two fuels.

The fuel valve 50 is controlled by a controller 55, for example, the controller 55 determines when and for how long the fuel valve is open, and in embodiments, the controller 55 also determines the opening profile of the fuel valve 50. The fuel valve 50 is part of the fuel supply system 30. The signal for opening and closing the fuel valve 50 may be a fluid signal or a hydraulic signal. In embodiments where the signal for opening and closing the fuel valve is a fluid signal, such as a hydraulic signal, the controller 55 may send an electronic signal to an electronically controlled valve or pump from which the hydraulic signal is sent to the fuel valve 55.

In an embodiment, the fuel supply system 30 is configured to be capable of supplying at least two different fuels. In an embodiment, one of the two fuels is a fuel oil, say for example a fuel oil or a heavy fuel oil or methanol. In an embodiment, one of the two fuels is a gaseous fuel such as petroleum gas or natural gas. In an embodiment, the gaseous fuel is introduced or injected into the cylinder in a gaseous state. In another embodiment, the gaseous fuel is introduced or injected into the cylinder in a liquid state.

In an embodiment, the engine is a fuel-guided engine. In a fuel-or gas-guided combustion process, the amount of fuel to be metered is determined as a function of the operating point of the internal combustion engine and of specifiable target values for the rotational speed and/or the power of the internal combustion engine. The fuel-guided combustion process is particularly applicable during variable speed operation of an internal combustion engine, in an internal combustion engine operating in isolation, during engine start-up or when the internal combustion engine is idling. The deployed engine controller includes a power controller and/or a speed controller. Engines that operate exclusively according to diesel engine processes are fuel-guided engines, regardless of whether the fuel is a liquid fuel or a gaseous fuel. Typically, fuel is injected shortly after Top Dead Center (TDC) and is ignited immediately upon injection. Therefore, the amount of fuel to be injected is a main control parameter of the fuel-guided engine.

In an embodiment, the engine is an air-guided engine. In order to avoid knock problems (premature combustion) or specific scavenging pressures, in particular specific compression pressures, the fuel quantity to be metered is determined in the air-guided combustion process, for example, as a function of the operating point of the internal combustion engine and of a specifiable target value of the fuel-air ratio. Accordingly, deployed engine control devices typically include a compression pressure controller. Engines operating exclusively according to the otto process are air-guided engines, irrespective of the type of fuel. Thus, the compressed air pressure is the main control parameter of the air-guided engine.

In an embodiment, the engine is a combination of an air intake and a fuel-directed engine. Examples of such engines are the following: in this engine, a first amount of fuel is admitted to the combustion chamber prior to the compression stroke, while a further second amount of fuel is injected near Top Dead Center (TDC). The injection of the second amount of fuel initiates ignition of both the second amount of fuel and the first amount of fuel in the combustion chamber. In large two-stroke engines, injection near TDC typically occurs shortly after TDC. In this engine, both the amount of fuel to be injected and the compression pressure are the main control parameters, and the importance of each parameter may depend on the engine load and the rotational speed.

In an embodiment, the internal combustion engine is a dual fuel engine and is fuel-directed when operating on a first fuel and air-directed when operating on a second fuel.

Each exhaust valve 4 is provided with an exhaust valve actuator 46. In an embodiment, the exhaust valve actuator 46 is a hydraulic actuator that is commanded by an electronic signal from the controller 55.

Another combustion process parameter in the combustion process in the cylinder 1 is controlled by the controller 55. The combustion process parameter is, for example, at least one of the amount of fuel, the timing of the start of fuel intake/injection, and the timing of the exhaust valve closure. The combustion process parameter fuel quantity is related to the contribution of the associated cylinder 1 to the torque transmitted by the engine. The combustion process parameters of the moment at which the fuel injection starts are related to the peak pressure in the relevant cylinder (this is particularly true for engines operating on the diesel principle, but not so much for engines operating on the otto principle, where fuel is admitted rather than injected). The combustion process parameter of the timing of the exhaust valve closure is related to the combustion pressure of the associated cylinder 1.

Fig. 4 shows a first embodiment of the controller 55. In an embodiment, the controller 55 includes an engine controller and a plurality of cylinder controllers.

The controller 55 receives a speed setting, i.e., a desired engine speed, for example, from the cab. The controller 55 receives the engine speed signal from the sensor 40 and the controller 55 compares the desired engine speed with the measured engine speed to obtain a speed deviation signal. The controller 55 comprises a regulator fed with a speed deviation signal. The regulator is configured to determine the fuel index based on a deviation of the desired engine speed from the measured engine speed, i.e., the regulator is configured to determine the fuel index based on the speed deviation signal. The fuel index signal is a signal indicating the amount of fuel to be injected/injected to achieve a desired engine speed. The amount of fuel to be injected is directly related to the amount of torque to be transmitted by the engine.

The controller 55 includes an index to a common torque signal module configured to convert the fuel index to a common torque signal by applying the fuel index to a first predetermined map. The common indicated torque/index may be considered to be proportional to the common average indicated pressure.

"Common" in this document means: is applied to all cylinders.

The first predetermined map is established by testing, for example testing performed on a test bench of a factory where the engine is developed and/or manufactured. In an embodiment, the first predetermined map includes a table or algorithm that correlates fuel indicators with commonly indicated torques.

A cylinder controller is associated with each of the cylinders 1. A common torque signal is sent to each of the cylinder controllers.

The controller 55 includes a power calculation module (load calculation) configured to calculate an engine load signal indicative of an engine load. In an embodiment, the engine load signal is representative of an actual engine load relative to a maximum engine load, such as a maximum continuous rating. The power calculation module receives the index signal and the measured engine speed. In an embodiment, the load calculation module multiplies the engine speed by the fuel index and multiplies the result by a predetermined factor that has been established by a test or empirical value to yield a percentage of the relative engine load, i.e., the maximum continuous rating.

The controller 55 includes an engine operating mode module configured to determine the common peak pressure signal by applying the engine load signal to a second predetermined map and configured to determine the common compression pressure by applying the engine load signal to a third predetermined map.

The second predetermined map and the third predetermined map are established based on tests, such as tests performed on test benches of factories that develop and/or manufacture engines. In an embodiment, the second predetermined map includes a table or algorithm that correlates peak pressure to engine load, and in an embodiment, the third predetermined map includes a table or algorithm that correlates compression pressure to engine load. The second and third maps may take into account many other parameters such as ambient pressure, ambient temperature, and engine speed, and may include compensation such as friction losses.

The common peak pressure signal and the common compression pressure signal are sent to all cylinder controllers.

Each cylinder controller receives a specific measured cylinder pressure from the pressure sensor 42 of the cylinder 1 for which the associated cylinder controller is dedicated.

The cylinder controller is configured to calculate the maximum pressure of the actual specific cylinder, the compression pressure of the actual specific cylinder, and the average indicated pressure of the actual specific cylinder from the pressure signal of the specific cylinder received from the pressure sensor 42 of the relevant cylinder 1. The average indicated pressure of a particular cylinder is hereinafter denoted as the torque of the actual particular cylinder.

Preferably, the actual pressure value of a particular cylinder is determined by an arithmetic mean, particularly preferably a median, of a plurality of successive pressure measurements, for example between 5 and 50 engine cycles, preferably about 10 engine cycles.

In order to obtain better signal quality and thus higher control performance, the pressure signal of a specific cylinder of the cylinders is a temporally filtered measured first pressure signal of the specific cylinder obtained over 5 to 50 engine cycles, preferably 7 to 15 combustion cycles.

Thus, the actual cylinder-specific pressure is the result of a statistical evaluation of the pressure measurements made by the pressure sensor 42 of the associated cylinder 1.

The cylinder controller is configured to adjust the common torque signal to obtain a torque signal for the particular cylinder based on a deviation of the common torque signal from a torque signal for an actual particular cylinder. Accordingly, the cylinder controller continuously (or intermittently) calculates an error value from the difference between the torque of the specific cylinder and the torque of the actual specific cylinder, and applies correction based on the proportional term and integral term (PI regulator) to derive a torque signal of the specific cylinder and form closed-loop control for the relevant specific cylinder 1.

In an embodiment, the controller 55 receives an adjustment of the common torque, an adjustment of the common peak pressure, and/or an adjustment of the common compression pressure. In this embodiment, the controller 55 is configured to determine an average value (average for the adjustment) of the adjustments of the common torque for all cylinders, an average value or number of adjustments of the common peak pressure for all cylinders, and/or an average value or number of adjustments of the compression pressure for the cylinders.

In this embodiment, the controller 55 is configured to allow each cylinder controller to set the range of maximum adjustments of the torque of the particular cylinder, the peak pressure of the particular cylinder, and/or the compression pressure of the particular cylinder within a window defined by the respective average value plus or minus an adjustment of a predetermined magnitude. For example, the adjustment interval is to add or subtract 5bar to the calculated average value. In this example, when the average value of the adjustment of the peak pressure for a particular cylinder for all cylinders is positive 2bar, each cylinder controller will be allowed to adjust the peak pressure adjustment for the particular cylinder between negative 3bar and positive 7 bar.

The limiter limits the maximum correction to the common torque signal. If the correction of the common torque signal is directed in the same direction for all cylinders 1, the limiter allows the maximum correction to reach the first threshold. If the correction of the common torque signal does not point in the same direction for all cylinders 1, the limiter allows the maximum correction to reach a second threshold value, which is lower than the first threshold value. Thus, erroneous signals are avoided to disrupt the stability of the system and allow for greater correction if all cylinders 1 have the same deployment.

Accordingly, the controller 55 calculates an average value of the adjustment of the specific cylinder of the torque signals for all the cylinders, and limits the adjustment of the specific cylinder in the cycle of the torque signals to the maximum predetermined deviation added or subtracted from the calculated average value of the adjusted torque signals.

The controller 55 is configured to define the interval as the average of the adjustments of the torque signal calculated plus or minus the maximum predetermined deviation, and to limit the adjustment of the particular cylinder in the torque signal cycle to adjustments within the interval. The interval is a range having a first range in the positive direction and a second range in the negative direction relative to the calculated average value of the adjustment of the torque signal. The interval is specific to the torque signal and other combustion process parameters (pressure and combustion pressure). The positive range has a first predetermined magnitude, and wherein the negative range has a second predetermined magnitude. These magnitudes can be determined, for example, at the factory by test runs. The interval should be large enough to accommodate the maximum adjustment that would normally occur, but small enough to exclude adjustments that may be caused by an error, say, for example, a wrong sensor signal.

The controller 55 is configured to calculate an average of the cylinder's adjustments to a particular cylinder of the torque signal for one or more cycles of the cyclical adjustment of the torque signal. In an embodiment, the adjustment of the combustion process parameter(s) is an adjustment for a single cycle.

The injection distribution module converts a torque signal for a particular cylinder into a fuel valve distribution signal for the particular cylinder. The injection distribution module correlates the torque signal for the particular cylinder with the injection distribution by applying the particular torque signal to a fourth predetermined map. The fourth graph may include algorithms and/or look-up tables that have been built upon the test. The fuel valve distribution signal of a specific cylinder is sent to the fuel valves 50 of the relevant cylinder, and the fuel valves 50 are indicated according to the distribution in which the fuel valves 50 should be opened and closed, i.e., the fuel valve opening duration and the distribution shape. The fuel valve 50 delivers the fuel quantity of a particular cylinder to the associated particular cylinder 1 in response to a fuel valve distribution signal of a cylinder controller associated with the associated cylinder 1.

The cylinder controller is configured to adjust the common peak pressure signal based on a deviation of the common peak pressure signal from a peak pressure signal of an actual particular cylinder to obtain a peak pressure signal of the particular cylinder. Accordingly, the cylinder controller continuously (or intermittently) calculates an error value from the difference between the torque of the specific cylinder and the pressure of the actual specific cylinder, and applies correction based on the proportional term and integral term (PI regulator) to derive a peak pressure signal of the specific cylinder and form a closed loop control for the relevant specific cylinder 1.

In the same manner, the limiter for the peak pressure signal limits the maximum correction to the common peak pressure signal, as described above with respect to the torque signal. If the correction of the common peak pressure signal is directed in the same direction for all cylinders 1, the limiter allows the maximum correction to reach the first threshold. If the correction of the common peak pressure signal does not point in the same direction for all cylinders 1, the limiter allows the maximum correction to reach a second threshold value, which is lower than the first threshold value. Thus, erroneous signals are avoided to disrupt the stability of the system and allow for greater correction if all cylinders 1 have the same deployment.

The peak pressure module converts a peak pressure signal for a particular cylinder to a fuel injection timing signal for the particular cylinder. To this end, the peak pressure module applies the peak pressure signal for the particular cylinder to a fifth predetermined map. The fifth predetermined map may include algorithms and/or look-up tables relating pressure to the start of fuel intake/injection. The algorithm and/or the look-up table of the fifth predetermined map may be established by testing.

The fuel injection timing signal of the specific cylinder is sent to the fuel valve 50 of the relevant cylinder 1, and the fuel valve 50 is indicated when the fuel valve should start to open, i.e., the time (angle) at which the fuel intake/injection is started. In response to the injection timing signal of the cylinder controller associated with the associated cylinder 1, the fuel valve 50 of the associated cylinder 1 starts to cause the fuel quantity of the particular cylinder to enter/be injected into the associated particular cylinder 1.

The cylinder controller is configured to adjust the common compression pressure signal in accordance with a deviation of the common compression pressure signal from a compression pressure signal of an actual specific cylinder to obtain a compression pressure signal of the specific cylinder. Accordingly, the cylinder controller continuously (or intermittently) calculates an error value from the difference between the compression signal of the specific cylinder and the compression pressure of the actual specific cylinder, and applies correction based on the proportional term and integral term (PI regulator) to derive the compression pressure signal of the specific cylinder, and forms closed-loop control for the relevant specific cylinder 1.

In the same manner, the limiter for the compression pressure signal limits the maximum correction to the common compression pressure signal as described above with respect to the torque signal and the peak pressure signal. If the correction of the common compression pressure signal is directed in the same direction for all cylinders 1, the limiter allows the maximum correction to reach the first threshold. If the correction of the common compression pressure signal does not point in the same direction for all cylinders 1, the limiter allows the maximum correction to reach a second threshold value, which is lower than the first threshold value. Thus, erroneous signals are avoided to disrupt the stability of the system and allow for greater correction if all cylinders 1 have the same deployment.

The compression pressure module converts a compression pressure signal of a specific cylinder into an exhaust valve closing timing signal of the specific cylinder. To this end, the compression pressure module applies the compression pressure signal of the specific cylinder to the sixth predetermined map. The sixth predetermined map may include an algorithm and/or a look-up table relating compression pressure to the timing of closing of the exhaust valve 4. The algorithm and/or the look-up table of the sixth predetermined map may be established by testing.

The exhaust valve closing timing signal of the specific cylinder is sent to the fuel valve 50 of the relevant cylinder 1, and indicates the exhaust valve actuator 46 when the exhaust valve 4 should be closed, i.e., the time (angle) at which the exhaust valve 4 is closed. The exhaust valve actuator 46 of the associated cylinder 1 is closed in response to an exhaust valve closing timing signal of the cylinder controller associated with the associated cylinder 1.

In an embodiment, the torque signal (average indicated pressure) adjustment of the specific cylinder, the peak pressure adjustment of the specific cylinder, and the combustion pressure adjustment of the specific cylinder are sent back to the controller 55, and an average "average indicated pressure adjustment", an average peak pressure adjustment, and an average combustion pressure adjustment are calculated. The adjustment is performed cyclically, for example, for every single, two, five or ten engine revolutions. The average value of the combustion process parameter for all cylinders is also calculated cyclically, preferably at the same cycle frequency as the adjustment cycle. The controller 55 sets limits for the adjustment of the particular cylinder for the corresponding combustion process parameter relative to the calculated average value of the associated combustion process parameter. The limit may be in the form of adding or subtracting a maximum predetermined deviation from the calculated average. The predetermined positive deviation may be different from the predetermined negative deviation. Thus, a section is formed around the calculated average value of the relevant process parameter. The predetermined positive and negative deviations are process parameter specific. Integrator saturation will be variable so that greater regulation is allowed when the average regulation of torque, peak pressure and combustion pressure is greater.

The cylinder controller is configured to control the cylinders 1 of the engine individually without taking into account maintaining cylinder balance, i.e. without cylinder balance. Thus, each cylinder 1 operates according to the design specifications by: a specific cylinder feedback loop control providing an average indicated pressure (torque) for a specific cylinder, and/or a specific cylinder feedback loop control providing a peak pressure for a specific cylinder, and/or a specific cylinder feedback loop control providing a compression pressure for a specific cylinder. Since all cylinders 1 will operate according to the design specifications, no cylinder balancing is required. This is particularly advantageous for dual fuel engines after changing the fuel from one fuel to another. In conventional engines, such refueling requires manual recalibration to allow the engine to operate optimally after refueling. With the controller according to this document, no manual recalibration is required after refueling. In particular peak pressures and torques are very important during the transition of fuel oil to S secondary fuel (e.g. gas) and this will be ensured/regulated automatically by the present controller.

However, in some cases, it may be necessary to operate one or more cylinders that are different from the design specifications. For example, when the cylinder 1 is in a state where it is determined that there is a significant risk of cylinder liner wear (sticking), cylinder liner wear (sticking) is sometimes caused by insufficient cylinder lubrication. It may be necessary to reduce the load on the following cylinders: the cylinder gives a signal that wear is occurring or will soon occur if the load is not reduced.

Thus, in the embodiment of the controller shown in the embodiment of fig. 5, each cylinder controller comprises a cylinder compensation module for a specific cylinder of each cylinder 1. In this embodiment, the same or similar structures and features as those previously described or illustrated herein are denoted by the same reference numerals as previously used for the sake of simplicity. This embodiment of the controller 55 is substantially the same as the embodiment of fig. 4, except that a compensation module for a particular cylinder is added.

The compensation module of a particular cylinder is configured to compensate for a common torque signal, a common peak pressure signal and/or a common compression pressure signal with respect to the associated particular cylinder 1. For example, compensation may be automatically introduced or introduced by a human operator based on signals from sensors that cause the cylinder controller or controllers to introduce compensation settings for a particular cylinder 1. For example, the detection of knocking in a specific cylinder may be detected by a sensor. In response to such a knock sensor, the compression pressure of that particular cylinder is reduced by controller 55 to reduce the temperature in the combustion chamber, thereby reducing the risk of knock. Thus, compensation for a particular cylinder will be introduced for the associated cylinder. Further, in the embodiment, the controller 55 is configured to increase the air-fuel ratio by decreasing the fuel amount by compensation of the specific cylinder compensation for the fuel amount to be injected.

Accordingly, the cylinder compensation module outputs a torque set point for the particular cylinder, a peak pressure set point for the particular cylinder, and a compression pressure set point for the particular cylinder. In the same manner as the embodiment of fig. 4 described above, the set point of the specific cylinder is adjusted according to the difference between the corresponding actual torque of the specific cylinder, the peak pressure of the specific cylinder, and the compression pressure of the specific cylinder, thereby deriving the torque of the specific cylinder, the peak pressure of the specific cylinder, and the compression pressure of the specific cylinder, respectively.

Fig. 6 shows another embodiment of the controller 55. In this embodiment, the same or similar structures and features as those previously described or illustrated herein are denoted by the same reference numerals as previously used for the sake of simplicity. This embodiment of the controller 55 is substantially the same as the embodiment of fig. 5, except that a fuel index is added to the distribution duration module. The fuel index of the distribution duration module is configured to convert the fuel index signal into a common distribution duration signal.

Each cylinder controller receives a common distribution duration signal. The cylinder controller adjusts the common fuel delivery duration signal based on a deviation between the common fuel delivery duration signal and the torque signal of the particular cylinder to obtain a fuel distribution duration signal of the particular cylinder.

The addition of the common distribution duration signal makes the engine more robust to fluctuations in fuel quality. In particular, the properties of gaseous fuels tend to vary, for example, the gaseous LCV (lower heating value) may vary up to 30% to 50%.

In an embodiment, the common torque signal corresponds to an average indicated cylinder pressure for all cylinders, and wherein the torque signal for a particular cylinder corresponds to an average indicated cylinder pressure for the associated particular cylinder.

Various aspects and embodiments have been described in connection with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed subject matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor, controller or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The reference signs used in the claims shall not be construed as limiting the scope. The drawings (e.g., hatching, arrangement of parts, proportion, degree, etc.) are intended to be read together with the specification, unless otherwise indicated, and should be considered a portion of the entire written description of this disclosure.

Claims

1. A method of operating a large low speed two-stroke uniflow scavenged turbocharged internal combustion engine having a crosshead (9), the engine comprising:

a plurality of cylinders (1), the cylinders (1) having:

An exhaust valve (4),

An exhaust valve actuation system (46), said exhaust valve actuation system (46) being adapted to actuate said exhaust valve (4),

-A fuel delivery system (30), said fuel delivery system (30) being adapted to deliver a quantity of a first fuel to the associated cylinder (1),

-A pressure sensor (42), said pressure sensor (42) being adapted to generate a pressure signal representative of a specific cylinder of the pressure in the cylinder (1) concerned,

An exhaust gas driven turbocharger (5), the exhaust gas driven turbocharger (5) pressurizing scavenging gas for the cylinder (1),

The method comprises the following steps:

-closed loop control of at least one combustion process parameter of said cylinder (1) in a cylinder specific manner depending on said cylinder specific pressure signal and a cylinder specific set point, said cylinder specific set point being a cylinder specific compensation of a common set point for all cylinders (1).

2. The method of claim 1, wherein the at least one combustion process parameter comprises:

the quantity of fuel to be injected into the reactor,

-Timing of start of fuel injection, and/or

Timing of closing the exhaust valve.

3. The method of claim 1 or 2, wherein the closed loop control is performed without regard to maintaining cylinder balance.

4. The method of claim 1 or 2, wherein the closed loop control applies correction based on a proportional term and an integral term.

5. The method of claim 1 or 2, wherein the common setpoint is:

-A common peak pressure signal representing a peak cylinder pressure to be achieved in said cylinder, and/or

-A common compression pressure signal representing the compression pressure to be achieved in said cylinder.

6. The method according to claim 1 or 2, wherein the closed-loop control uses the measured cylinder pressure of a specific cylinder as a reference value.

7. The method according to claim 6, wherein an average indicated cylinder pressure of a particular cylinder is derived from the measured cylinder pressure of the particular cylinder, and/or wherein a peak pressure of a particular cylinder is derived from the measured cylinder pressure of the particular cylinder, and/or wherein a compression pressure of a particular cylinder is derived from the measured cylinder pressure of the particular cylinder.