CN115875142B

CN115875142B - Large two-stroke turbocharged uniflow scavenged internal combustion engine and method of operating the same

Info

Publication number: CN115875142B
Application number: CN202211185872.0A
Authority: CN
Inventors: 基姆·詹森; 雅各布·席鲁普; 汉斯·拉森; 卡斯佩·尼尔森
Original assignee: Mannone Solutions Mannone Solutions Germany Branch
Current assignee: Mannone Solutions Mannone Solutions Germany Branch
Priority date: 2021-09-28
Filing date: 2022-09-27
Publication date: 2023-12-29
Anticipated expiration: 2042-09-27
Also published as: CN115875142A; JP7329670B2; DK202170475A1; DK181193B1; JP2023049015A; KR102656099B1; KR20230045546A

Abstract

A dual fuel large two-stroke turbocharged uniflow scavenged internal combustion engine and method of operating the same are provided. The engine includes: a plurality of cylinders; a piston reciprocating between BDC and TDC in each of the cylinders; at least one fuel inlet valve associated with the cylinder for admitting a first fuel during a stroke of the piston from BDC to TDC; at least one fuel injection valve associated with at least one of the cylinders for injecting a second fuel when the piston is at or near TDC; and a controller configured to operate all of the cylinders according to the premixing process by default, the controller configured to: determining whether actual combustion conditions of cylinders operating according to the premixing process are such that there is an unacceptable risk of a pre-ignition event or misfire; and changing at least one cylinder of the plurality of cylinders from operating according to a pre-mix process to operating according to a compression ignition process when the controller determines that there is an unacceptable risk of a pre-ignition event or misfire.

Description

Large two-stroke turbocharged uniflow scavenged internal combustion engine and method of operating the same

Technical Field

The present disclosure relates to dual fuel large two-stroke uniflow scavenged internal combustion engines, in particular large two-stroke uniflow scavenged internal combustion engines with a crosshead, which are run in an operating mode by means of admitting a first fuel from a fuel valve during the stroke of the piston from BDC to TDC.

Background

Large two-stroke turbocharged uniflow scavenged internal combustion engines with crossheads are used, for example, for propulsion of large ocean going vessels or as primary prime movers in power plants. Not only due to the large size, but also these two-stroke diesel engines are built differently from any other internal combustion engine. The exhaust valve of a large two-stroke turbocharged uniflow scavenged internal combustion engine can weigh up to 400kg, the diameter of the piston up to 100cm, and the maximum operating pressure in the combustion chamber is typically hundreds of bars. The forces involved at these high pressure levels and piston sizes are enormous.

The mixture of gaseous fuel and scavenging air in the combustion chamber is compressed (thus operating according to a premixing process) and the compressed mixture is ignited by a timed ignition device, such as, for example, a pilot liquid injection or a pilot gas injection, at or near Top Dead Center (TDC), with a large two-stroke turbocharged internal combustion engine operated with normally gaseous fuel admitted through a fuel valve disposed generally along the length of the cylinder liner or centrally in the cylinder head, i.e., an engine admitting gaseous fuel during the upward stroke of the piston from Bottom Dead Center (BDC) to TDC of the piston activated just prior to closure of the exhaust valve.

The use of this type of gas admission into the fuel valve (gas admission valve) arranged in the cylinder liner or in the cylinder head has the advantage that a much lower admitted fuel admission pressure (typically between about 10ba and about 25 bar) can be used, because the gaseous fuel is injected when the compression pressure is relatively low compared to a large two-stroke turbocharged internal combustion engine in which the gaseous fuel is injected when the piston is near or at Top Dead Center (TDC) of the piston, i.e. when the compression pressure in the combustion chamber is at or near its maximum. The latter type of engine requires a fuel injection pressure (typically above 300 bar) that is significantly higher than the already high maximum combustion pressure. Fuel systems that are capable of handling gaseous fuels at these extremely high pressures are expensive and complex due to the volatile nature of the gaseous fuel and the behavior of the gaseous fuel at such high pressures, including diffusion into and through the steel components of the fuel system.

Thus, the fuel supply system for an engine that injects gaseous fuel during the compression stroke is significantly cheaper when compared to an engine that injects gaseous fuel at higher pressure when the piston is at or near TDC.

However, when gaseous fuel is injected during the compression stroke, the piston compresses the mixture of gaseous fuel and scavenging air, and thus there is a risk of pre-ignition. The risk of pre-ignition may be reduced by operating with a very lean mixture, but the lean mixture increases the risk of misfire (misfire) or partial misfire/retarded ignition and the resulting unwanted fuel leakage (slip).

During steady state operation of the engine, the performance of the engine is typically laid out to ensure that pre-ignition is avoided. This is accomplished by careful selection of combustion chamber design, fuel injection timing, and exhaust valve timing. When operating according to a pre-mix process, there is a narrow window between pre-ignition risk and misfire. When a certain indicated average pressure is reached (which indicated average pressure is lower than the level/maximum for a compression ignition engine), cylinder conditions can be controlled accurately enough to avoid pre-ignition events and misfires. However, under transient load conditions, the air-fuel ratio may change rapidly, and the air-fuel ratio may incur cylinder conditions that cause a risk of a pre-ignition event when the transient load conditions are caused by an increase in the engine load, and may incur cylinder conditions that cause a risk of a misfire when the transient conditions are caused by a decrease in the engine load. In addition, external influences such as ambient temperature and pressure also cause variations in the air-fuel ratio and the overall compression temperature (bulk compression temperature), thereby changing the combustion behavior. Tropical conditions, for example, are at risk of high engine loads leading to pre-ignition.

Pre-ignition can lead to damage to the engine and misfire can lead to leakage of unburned fuel into the atmosphere and therefore needs to be avoided.

Accordingly, measures are needed to ensure that pre-ignition events and misfires can be avoided in engines operating according to the pre-mixing process.

DK201970370 discloses a large two-stroke turbocharged uniflow scavenged operating internal combustion engine having a plurality of combustion chambers, at least one controller associated with the engine configured to determine the average compression air-fuel ratio and overall compression temperature in the combustion chambers at the start of combustion, the controller configured to:

when the determined or measured average compressed air-fuel ratio is below a lower compression air-fuel ratio threshold value, at least one compression air-fuel ratio increase measure is performed,

when the determined or measured average compressed air-fuel ratio is above the upper compressed air-fuel ratio threshold, at least one compressed air-fuel ratio reduction measure is performed,

-performing at least one bulk compression temperature increasing measure when the determined or measured bulk compression temperature is below a bulk compression temperature lower threshold, and

-performing at least one integral compression temperature reduction measure when the determined or measured integral compression temperature is above an integral compression temperature upper threshold.

Disclosure of Invention

It is an object of the present invention to provide an engine that overcomes or at least reduces the above-mentioned problems.

The foregoing and other objects are achieved by the features of the independent claims. Further embodiments are evident from the dependent claims, the description and the figures.

According to a first aspect there is provided a dual fuel large two-stroke turbocharged uniflow scavenged internal combustion engine, the engine being in at least one operating mode and the engine being configured to operate on a first fuel as a primary fuel, the engine comprising: a plurality of cylinders; a piston reciprocating between BDC (bottom dead center) and TDC (top dead center) in each of the cylinders, at least one fuel admission valve associated with the cylinder for admitting a first fuel during a stroke of the piston from BDC to TDC; at least one fuel injection valve associated with at least one of the cylinders for injecting a second fuel when the piston is at or near TDC; and a controller configured to: when the engine is running in the at least one operating mode,

By default, operating all cylinders of the plurality of cylinders according to a premixing process and admitting the first fuel during a stroke of the piston (10) from BDC to TDC,

-determining whether the actual combustion conditions of the cylinders operating according to the premixing process are such that there is an unacceptable risk of a pre-ignition event or misfire, and the controller is configured to: when the controller has determined that there is an unacceptable risk of a pre-ignition event or misfire,

changing the associated at least one of the plurality of cylinders from operation according to the pre-mixing process to operation according to a compression ignition process by terminating admittance of the first fuel during a stroke of the piston from BDC to TDC for the at least one of the plurality of cylinders, an

An amount of the second fuel is injected in an associated one of the cylinders when the piston is at or near TDC.

For cylinders operating according to a compression ignition process, the air-fuel ratio is much less critical than for cylinders operating according to a pre-mixing process, and therefore, by having one or more cylinders operating according to a compression ignition process, the operating conditions of the remaining cylinders operating according to the pre-mixing process can be adjusted to avoid pre-ignition and/or misfire events.

The indicated mean effective pressure (MIP, mean Effective Pressure) is the fictive pressure acting on the piston, which pressure acts the same as the actual pressure in the operating cycle.

In a possible implementation form of the first aspect, the controller is configured to select the amount of the second fuel injected into the associated at least one cylinder such that: when determining a risk of pre-ignition, an indicated average pressure (mean indicated pressure) of remaining cylinders of the plurality of cylinders operating according to a pre-mixing process is reduced; when determining the risk of misfire, an indicated average pressure of remaining cylinders of the plurality of cylinders operating according to a premixing process is increased.

Thus, the risk of pre-ignition events and/or misfire events may be effectively mitigated by: torque (MIP) delivered by one or more cylinders operating according to a compression ignition process is adjusted such that the operating conditions of the remaining cylinders operating according to a pre-mixing process are changed such that these conditions no longer present a risk of pre-ignition or misfire. The inventors believe that this is possible because the cylinder operating according to the compression ignition process is insensitive to air-fuel ratio and also to overall compression temperature.

In a possible implementation form of the first aspect, the controller is configured to: when a predetermined time span or engine revolution has elapsed since one or more cylinders changed from operation according to the pre-mixing process to operation according to the compression ignition process, the associated cylinder is returned from operation according to the compression ignition process to operation according to the pre-mixing process.

In a possible implementation form of the first aspect, the controller is configured to: the air-fuel ratio and the overall compression temperature of the cylinders operating according to the pre-mixing process are monitored, and when these values are within acceptable ranges, the controller is configured to change the operation of one or more cylinders operating according to the compression ignition process to an operation according to the pre-mixing process; preferably, when the values are within an acceptable range for a given time span, the controller is configured to change operation of one or more cylinders operating according to the compression ignition process to operation according to the pre-mixing process.

In a possible implementation form of the first aspect, no or only a small amount of the second fuel is injected as pilot fuel to the cylinders operating according to the premixing process.

In a possible implementation form of the first aspect, each cylinder is provided with a variable timing exhaust valve actuation system for actuating an exhaust valve centrally arranged in the cylinder head, and wherein the controller is configured to determine and control the opening and closing timings of the exhaust valve, and the controller is configured to:

timing the opening and closing of an exhaust valve adapted to a premixing operation for a cylinder operating according to a premixing process among the plurality of cylinders, an

The opening and closing of the exhaust valve adapted to the compression ignition process for the cylinder operating according to the compression ignition process among the plurality of cylinders is timed.

In a possible implementation form of the first aspect, the controller is configured to determine and control an amount of the first fuel admitted to the cylinder.

In a possible implementation form of the first aspect, the controller is configured to determine or measure an air-fuel ratio of the cylinder, and the controller is configured to determine an unacceptable risk of a misfire event when the air-fuel ratio is above an air-fuel ratio maximum threshold, and the controller is configured to determine an unacceptable risk of a pre-ignition event when the air-fuel ratio is below an air-fuel ratio minimum threshold.

In a possible implementation form of the first aspect, the controller is configured to determine or measure an overall compression temperature in the cylinder at the start of combustion, and the controller is configured to determine an unacceptable risk of a misfire event when the overall compression temperature is below an overall compression temperature minimum threshold, and the controller is configured to determine an unacceptable risk of a pre-ignition event when the overall compression temperature is above an overall compression temperature maximum threshold.

In a possible implementation form of the first aspect, the controller comprises an air-fuel ratio observer for determining an average instantaneous air-fuel ratio in the cylinder, or the controller is connected to the air-fuel ratio observer for determining an average instantaneous air-fuel ratio in the cylinder.

In a possible implementation form of the first aspect, the controller comprises or is connected to an overall compression temperature observer for determining an average instantaneous overall compression temperature in the cylinder.

According to a second aspect, there is provided a method of operating a dual fuel large two-stroke turbocharged uniflow scavenged internal combustion engine, the engine being in at least one operating mode and being configured to operate on a first fuel as a primary fuel, the engine comprising: a plurality of cylinders; a piston that reciprocates between BDC and TDC in each of the cylinders; at least one fuel admission valve associated with the cylinder for admitting a first fuel during a stroke of the piston from BDC to TDC; at least one fuel injection valve associated with at least one of the cylinders for injecting a second fuel when the piston is at or near TDC,

The method comprises the following steps:

by default, operating all cylinders of the plurality of cylinders according to a premixing process and admitting the first fuel during a stroke of the piston from BDC to TDC,

-determining whether the actual combustion conditions of the cylinders operating according to the premixing process are such that there is an unacceptable risk of a pre-ignition event or misfire, and when it has been determined that there is an unacceptable risk of a pre-ignition event or misfire:

by terminating the admitted entry of the first fuel during the stroke of the piston from BDC to TDC for at least one of the cylinders, changing the associated at least one of the plurality of cylinders from operating according to a pre-mixing process to operating according to a compression ignition process, and injecting a quantity of the second fuel in the associated at least one of the cylinders when the piston is at or near TDC.

In a possible implementation form of the second aspect, the method comprises selecting the amount of the second fuel injected into the associated at least one cylinder (1) such that:

when determining the risk of pre-ignition, the indicated average pressure of the remaining cylinders of the plurality of cylinders operating according to the pre-mixing process is reduced,

When determining the risk of misfire, an indicated average pressure of remaining cylinders of the plurality of cylinders operating according to the premixing process is increased.

In a possible implementation form of the second aspect, the method comprises: when a predetermined time span or engine revolution has elapsed since one or more cylinders changed from operation according to the pre-mixing process to operation according to the compression ignition process, the associated cylinder is returned from operation according to the compression ignition process to operation according to the pre-mixing process.

In a possible implementation form of the second aspect, the method comprises: monitoring the air-fuel ratio and the overall compression temperature of the cylinders operating according to the pre-mixing process, and when these values are within acceptable ranges, changing the operation of one or more cylinders operating according to the compression ignition process to an operation according to the pre-mixing process; preferably, when these values are within an acceptable range for a given time span, the operation of one or more cylinders operating according to the compression ignition process is changed to the operation according to the premixing process.

In a possible implementation form of the second aspect, the method comprises: the second fuel is not injected or is injected only in small amounts as a pilot fuel to the cylinders operating according to the premixing process.

In a possible implementation form of the second aspect, each cylinder is provided with a variable timing exhaust valve centrally arranged in the cylinder head, and the method comprises:

These and other aspects will be apparent from and elucidated with reference to the embodiments described hereinafter.

Drawings

In the following detailed portion of the disclosure, aspects, embodiments, and implementations will be described 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 exemplary embodiment,

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

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

fig. 4 is a cross-sectional view of a cylinder head and cylinder liner of the engine of fig. 1, showing a cylinder head, an exhaust valve fitted to the cylinder head, and a piston at both TDC and BDC shown using dashed lines,

Figure 5 is a second schematic view of the engine of figure 1,

figure 6 is a schematic view of a compression temperature observer and a compression air-fuel ratio observer,

fig. 7 is a graph showing the compression air-fuel ratio on the vertical axis and the overall cylinder temperature on the horizontal axis, showing the optimum combustion condition region surrounded by the sub-optimum action region that needs to take action to return to the safe region, which in turn is surrounded by the critical region to be avoided,

FIG. 8 is a graph showing cylinder pressure versus crank angle for various combustion conditions including misfire, normal combustion and pre-ignition (knock),

FIG. 9 is a flowchart showing a process for controlling combustion conditions of the large two-stroke engine of FIG. 1, and

fig. 10 to 15 are diagrams showing operations of the respective cylinders in various cases.

Detailed Description

In the following detailed description, an internal combustion engine will be described with reference to a large two-stroke, low-speed turbocharged uniflow-scavenged internal combustion engine with a crosshead in an exemplary embodiment. Fig. 1, 2 and 3 show an embodiment of a large two-stroke low-speed turbocharged diesel engine with a crankshaft 8 and a crosshead 9. Fig. 1 and 2 are front and side views, respectively. FIG. 3 is a schematic illustration of the large two-stroke, low-speed turbocharged internal combustion engine of FIGS. 1 and 2, having its intake and exhaust systems. In this exemplary embodiment, the engine has five cylinders in-line. Large two-stroke, low-speed turbocharged uniflow-scavenged internal combustion engines typically have four to fourteen cylinders in series carried by an engine frame 11. The engine may for example be used as a main engine in a marine vessel or as a stationary engine for operating a generator in a power station. The total output of the engine may for example be in the range from 1,000kw to 110,000 kw.

The engine in this exemplary embodiment is a two-stroke uniflow scavenged type engine having scavenge ports 18 located in a lower region of the cylinder liner 1 and a central exhaust valve 4 located in a cylinder head 22 at the top of the cylinder liner 1. When the piston 10 is below the scavenging port 18, scavenging air passes from the scavenging air receiver 2 through the scavenging port 18 of the respective cylinder liner 1. During default operation with the aid of a first fuel (typically a gaseous fuel such as natural gas, petroleum gas or ammonia), the first fuel is admitted from gaseous fuel injection valve 30 under the control of electronic controller 60 while the piston is in its upward motion and before the piston passes admission valve 30 (the gas admission valve). The first fuel is admitted at a relatively low pressure, below 30bar, preferably below 25bar, more preferably below 20bar. The fuel valves 30 are preferably evenly distributed around the circumferential portion of the cylinder liner and are placed somewhere in the central region of the length of the cylinder liner 1. Thus, admission of the first fuel occurs at a relatively low compression pressure, i.e., well below the compression pressure at which the piston 10 reaches TDC, thereby allowing admission at a relatively low pressure. The first fuel is typically a gaseous fuel that is supplied in gaseous form (gas phase), such as natural gas or petroleum gas, to the fuel admission valve and admitted into the cylinder. However, the first fuel may also be a liquid fuel, such as ammonia.

The piston 10 in the cylinder liner 1 compresses the mixture of the first fuel and the scavenging air so that compression takes place and at or near TDC the ignition is triggered by, for example, injection of pilot liquid (any other suitable ignition liquid) from a dedicated pilot liquid valve (not shown) or injection of pilot liquid ((or any other suitable ignition liquid)) from a fuel injection valve 50 preferably arranged in the cylinder head 22, followed by combustion and exhaust generation, alternative forms of ignition systems may be used instead of or in addition to the pilot liquid valve, such as for example a prechamber (not shown), laser ignition (not shown) or glow plugs (not shown).

When the exhaust valve 4 is opened, the exhaust gas flows through the exhaust conduit associated with the cylinder 1 into the exhaust gas receiver 3 and continues through the first exhaust conduit 19 to the turbine 6 of the turbocharger 5, from which turbine 6 the exhaust gas flows through the second exhaust conduit via the economizer 20 to the outlet 21 and then into the atmosphere. The turbine 6 drives by means of a shaft a compressor 7 which is supplied with fresh air via an air inlet 12. The compressor 7 delivers pressurized scavenging air to a scavenging air conduit 13 leading to the scavenging air receiver 2. The scavenging air in the conduit 13 passes through an intercooler 14 for cooling the scavenging air.

The cooled scavenging air passes through an auxiliary blower 16 driven by an electric motor 17, which auxiliary blower 16 pressurizes the scavenging air flow when the compressor 7 of the turbocharger 5 is not delivering sufficient pressure to the scavenging air receiver 2, i.e. in a low or part-load state of the engine. At higher engine loads, the compressor 7 of the turbocharger delivers fully compressed scavenging air and then bypasses the auxiliary blowers 16 via the non-return valve 15.

Fig. 4 shows a cylinder liner 1 generally designated for large two-stroke engines with crossheads. The cylinder liner 1 may be manufactured in various sizes according to the size of the engine, wherein the cylinder bores are generally in the range of 250mm to 1000mm, and the corresponding typical lengths are in the range of 1000mm to 4500 mm.

In fig. 4, the cylinder liner 1 is shown mounted in a cylinder frame 23, wherein a cylinder head 22 is disposed on top of the cylinder liner 1, wherein there is an airtight joint between the cylinder head 22 and the cylinder liner 1. In fig. 4, the piston 10 is schematically shown by the dashed lines in Bottom Dead Center (BDC) and Top Dead Center (TDC), but it is of course apparent that these two positions do not occur simultaneously and are separated by a 180 degree rotation of the crankshaft 8. The cylinder liner 1 is provided with cylinder lubrication bores 25 and cylinder lubrication lines 24, which cylinder lubrication lines 24 provide a supply of cylinder lubrication oil when the pistons 10 pass through the lubrication lines 24, and subsequently piston rings (not shown) distribute the cylinder lubrication oil over the running surfaces of the cylinder liner 1.

A pilot valve (typically more than one pilot valve per cylinder) or a prechamber with a pilot valve is mounted in the cylinder head 22 and connected to a pilot liquid source or a pilot gas source (not shown). The timing of the pilot liquid injection is controlled by the electronic control unit 60.

A fuel admission valve 30 is mounted in the cylinder liner 1 (or in the cylinder head 22), wherein a nozzle of the fuel admission valve is substantially flush with an inner surface of the cylinder liner 1 and a rear end portion of the fuel valve 30 protrudes from an outer wall of the cylinder liner 1. Typically, one or two fuel valves 30 are provided in each cylinder liner 1 that are circumferentially distributed (preferably, circumferentially uniformly distributed) around the cylinder liner 1, but up to three or four fuel valves 30 are possible. In an embodiment, the fuel valve 30 is disposed substantially centrally along the length of the cylinder liner 1. The fuel injection valves 50 for injecting the second fuel at a high pressure are mounted in the cylinder head 22, and typically two or three fuel injection valves 50 are provided per cylinder 1, the two or three fuel injection valves 50 being arranged in the cylinder head 22, wherein the nozzles of the fuel valves 50 protrude slightly into the combustion chamber. The second fuel may be a liquid fuel. The second fuel may be one or more of fuel oil, heavy fuel oil, marine diesel.

Further, fig. 4 schematically illustrates a first fuel supply system comprising a first source of pressurized fuel 44, the first source of pressurized fuel 44 being connected to the inlet of each of the fuel admission valves 30, and a second fuel supply system comprising a second source of pressurized fuel 41, the second source of pressurized fuel 41 being connected to the inlet of each of the fuel injection valves 50.

Fig. 5 shows a schematic view of an engine similar to that of fig. 2, but with more details regarding the gas exchange infrastructure of the engine. Ambient air is admitted at ambient air pressure and temperature and is delivered to the compressor 7 of the turbocharger 5 through the air inlet 12. Compressed scavenging air from the compressor 7 is conveyed to the distribution point 28 via an air conduit 32.

The distribution point 28 allows the scavenge air to be branched off through the hot cylinder bypass duct 29 to a turbine connection 32 in the first exhaust duct 19. The flow through the hot cylinder bypass conduit 29 is regulated by a hot cylinder bypass control valve 31. The hot cylinder bypass control valve 31 is electronically controlled by the controller 60. The effect of opening the hot cylinder bypass conduit 29 or reducing the throttle of the control valve 31 in the hot cylinder bypass is to increase the air-fuel ratio and increase the overall compression temperature, and the effect of closing the hot cylinder bypass conduit 29 or increasing the throttle of the control valve 31 in the hot cylinder bypass is to decrease the air-fuel ratio and decrease the overall compression temperature.

The air conduit 13 further comprises a first scavenging air control valve 33 upstream of the intercooler 14. The second scavenging air control valve 34 is arranged downstream of the intercooler 14. The air duct 13 continues to the scavenging air receiver 2. A conduit comprising an auxiliary blower 16 branches off from the intermediate cooler 14.

A cold cylinder bypass duct 35 connects the scavenge air receiver 2 to the turbine connection 32 in the first exhaust duct 19. The flow through cylinder bypass 35 is regulated by a cold cylinder bypass control valve 36. The cold cylinder bypass control valve 36 is electronically controlled by a controller 60. The effect of opening the cylinder bypass 35 or reducing the throttle of the cylinder bypass valve 36 is to increase the overall compression temperature.

The cold scavenging bypass duct 37 allows scavenging air to escape from the scavenging air receiver 26 to the environment. The flow through the cold-gas bypass duct 37 is controlled by a cold-gas bypass control valve 38. The cold-gas bypass control valve 38 is electronically controlled by the controller 60. The effect of opening the cold-scavenging bypass control valve 38 or reducing the throttle of the cold-scavenging bypass control valve 38 is to reduce the scavenging air pressure and reduce the air-fuel ratio, and the effect of closing the cold-scavenging bypass control valve 38 or increasing the throttle of the cold-scavenging bypass control valve 38 is to increase the scavenging air pressure and increase the air-fuel ratio. The cold-scavenging bypass duct 37 need not branch off from the scavenging air receiver 2, but may also branch off from the air duct 13 at any point downstream of the intercooler 14.

An exhaust gas recirculation conduit 42 connects the exhaust gas receiver 3 to the scavenging air receiver 2, and the exhaust gas recirculation conduit 42 includes an exhaust gas recirculation control valve 45, an exhaust gas recirculation cooler 44, and an exhaust gas recirculation blower 43. Both the exhaust gas recirculation blower 43 and the exhaust gas recirculation control valve 45 are used to regulate flow through the exhaust gas recirculation conduit 42 under electronic control of the controller 60. Under normal operating conditions, flow through the exhaust gas recirculation conduit 42 does not occur unless the exhaust gas recirculation blower 43 is activated, because the pressure in the exhaust gas receiver 42 is typically lower than the pressure in the scavenging air receiver 2 (thus, the exhaust gas recirculation control valve 45 needs to be closed when the exhaust gas recirculation blower 43 is not activated). The exhaust gas recirculation conduit 42 need not be connected from the exhaust gas receiver 3, but may also be connected to the first exhaust gas conduit 19 at any point, and the exhaust gas recirculation conduit 42 need not be connected to the scavenging air receiver 2, but may also be connected to any location on the air conduit 13 downstream of the intercooler 14.

The activation of the exhaust gas recirculation blower 43 in the exhaust gas recirculation conduit 42 or the increase in the speed of the exhaust gas recirculation blower 43 in the exhaust gas recirculation conduit 42 causes the compression air-fuel ratio to decrease and the overall compression temperature to decrease slightly, and the deactivation of the exhaust gas recirculation blower 43 in the exhaust gas recirculation conduit 42 or the decrease in the speed of the exhaust gas recirculation blower 43 in the exhaust gas recirculation conduit 42 causes the compression air-fuel ratio to increase and the overall compression temperature to increase slightly.

An exhaust bypass 39 branches off from the exhaust gas receiver 3 or the first exhaust gas conduit 19 and is connected to the atmosphere 27 at a given back pressure. The exhaust bypass control valve 40 regulates electronically controlled flow through the exhaust bypass conduit 39 and the controller 60.

Opening the exhaust bypass control valve 40 or reducing the throttle of the exhaust bypass control valve 40 causes the compression air-fuel ratio in the cylinder to decrease, and closing the exhaust bypass control valve 40 or increasing the throttle of the exhaust bypass control valve 40 causes the compression air-fuel ratio in the cylinder to increase.

In an engine provided with a selective catalytic receiver (SVR) reactor, a reactor bypass valve (RVB) regulates the fraction of flow through the SCR reactor in the flow from the scavenger air receiver 3 to the turbine 6 of the turbocharger 5 under electronic control of a controller 60.

All the above-mentioned components are controlled by a controller 60 connected to these components by signal lines indicated by dashed lines in fig. 5.

Fig. 6 shows an air-fuel ratio observer 46 and an overall compression temperature observer 47.

Air-fuel ratio observer 46 is a computer-implemented algorithm that possesses information regarding scavenging air pressure, exhaust valve closing timing, cylinder geometry, stoichiometric air-fuel ratio, and the amount of injected gas. The compressed air-fuel ratio observer 46 may be part of the controller 60 or may be a separate computer or controller. The compressed air-fuel ratio observer 46 provides an output that is an estimate of the compressed air-fuel ratio of the (fully) compressed air-fuel mixture (when the piston 10 is at TDC) and sends the output to the controller 60. The estimate is based on the following ratio: the ratio of the mass of fresh air trapped in the combustion chamber when the exhaust valve 4 is seated on the seat of this exhaust valve 4 divided by the mass of fresh air required for stoichiometric combustion of the total injected gas mass.

The integral compression temperature observer 47 is a computer implemented algorithm that has information about the scavenging air pressure, the scavenging air temperature, the exhaust valve closing timing and the crankshaft speed. The integral compression temperature observer 47 may be part of the controller 60 or may be a separate computer or controller. The overall compression temperature observer 47 provides an output as an estimated value for Tcomp (Tc); the overall compression temperature in the combustion chamber is within a time window from the start of gas injection to the time of pilot injection. The compressed air-fuel ratio observer 47 sends the estimated value to the controller 60. In an embodiment, the estimate of Tcomp refers to the piston 10 at TDC.

Fig. 7 is a graph showing the overall compression temperature Tcomp versus the air-fuel ratio (λ). The steady-state default region 51 falls within a boundary defined by a lower air-fuel ratio threshold (λ -lower limit), an upper air-fuel ratio threshold (λ -upper limit), a lower overall compression temperature threshold (Tc-lower limit), and an upper overall compression temperature threshold (Tc-upper limit). In this steady-state default region 51, the controller 60 supplies the amount of the first fuel required for the current engine load to each cylinder 1, respectively, and the controller 60 takes no measure to change the overall compression temperature, and controls the air-fuel ratio of each cylinder to such a level, respectively, according to the engine operation conditions: the level has a safe distance in the form of a margin from a known undesired combustion condition where partial misfire events, and/or pre-ignition may occur when the air-fuel ratio exceeds a known threshold level associated with operating conditions. The level of the first margin has a first value greater than 0.

When the combustion conditions in the cylinder 1 are predicted to leave the normal operation region 51 and enter the action zone 52, the controller 60 will take measures to prevent this from happening.

For this, the controller 60 is configured to:

when the determined or measured average compression air-fuel ratio is below a compression air-fuel ratio lower limit threshold, at least one compression air-fuel ratio increase measure (calim) is performed,

when the determined or measured average compressed air-fuel ratio is above the upper compressed air-fuel ratio threshold, at least one compressed air-fuel ratio reduction measure (AERDM) is performed,

-performing at least one Bulk Compression Temperature Increase Measure (BCTIM) when the determined or measured bulk compression temperature is below a bulk compression temperature lower threshold, and

when the determined or measured overall compression temperature is above the overall compression temperature upper threshold,

at least one bulk compression temperature reduction (BCTDM) is performed.

By performing these measures, the controller 60 maintains the condition of each of the cylinder liners 1 within the normal operation region 51, and at least temporarily allows the condition to move outside the normal operation region 51 and into the action region 52. The actuation region 52 is surrounded by a critical region 53, in which critical region 53 pre-ignition and/or misfire events are highly likely to occur.

The boundaries of the regions 51, 52, and 53 may be defined by upper and lower thresholds of the overall compression temperature and upper and lower limits of the compression air-fuel ratio. These thresholds may be determined empirically through repeated experimentation or through computer simulation of engine cycles for a particular engine.

When the observer indicates that both the compression air-fuel ratio and the overall compression temperature are outside the normal operation region 51, the controller 60 will take two measures of adjusting the compression air-fuel ratio and the overall compression temperature of each cylinder, respectively, to move the conditions in the cylinder liner 1 back to the normal operation region 51.

Opening the Exhaust Gas Bypass (EGB) conduit 39 (flow from TC turbine inlet to turbine outlet or ambient) by adjusting the exhaust gas bypass control valve 40 (moving the exhaust gas bypass control valve 40 to a more open position) causes the scavenge air pressure, and thus the mass of air trapped in the combustion chamber, to be reduced. Therefore, this measure is suitable for reducing the compression air-fuel ratio with only a slight effect on the overall compression temperature. In the case of engines with more turbochargers, a single EGB from the exhaust gas receiver may still be used, provided that the location of the EGB is selected based on other potential mixing points from other flows to the exhaust gas receiver.

Opening the hot cylinder bypass control valve 31 (flow from the TC compressor outlet to the TC turbine inlet) causes the compression air-fuel ratio and overall compression temperature in the combustion chamber to increase.

The opening of the scavenging bypass control valve 38 forms a flow from the scavenging air receiver 2 to the compressor inlet or from the scavenging air receiver 2 to the environment and this opening has a similar qualitative effect on the compression air-fuel ratio as the exhaust bypass, but a different effect on the scavenging process (and thus on the overall compression temperature in the combustion chamber). Opening the scavenging bypass control valve 38 has a faster effect on combustion chamber conditions when compared to the exhaust bypass.

Opening the cold cylinder bypass valve 36 increases the flow from the scavenge air receiver to the TC turbine inlet and increases the overall compression temperature with very little effect on the compression air-fuel ratio.

The exhaust valve closing timing determines the ratio between the compressed air pressure and the scavenging air pressure in the combustion chamber. Changing the timing has a significant effect on both the compression air-fuel ratio and the overall compression temperature in the combustion chamber.

The exhaust valve opening timing has an effect on the first phase of the scavenging process of the combustion chamber: changing the timing will have an impact on the engine efficiency and the scavenging process. As the scavenging process changes, the resulting overall temperature will also change. By opening the exhaust valve 4 prematurely, there is no flow to the scavenging air receiver 2 when the piston 10 subsequently opens the scavenging port 18. When the exhaust valve 4 opens too late, there is a large flow to the scavenging air receiver 2 when the piston subsequently opens the scavenging port 18. These measures change the scavenging process and thus the fraction of "hot and dirty" gas from the previous combustion that participates in the next compression stroke.

Thus, by opening the exhaust valve 4 later, there will be more "hot-dirty" gas from the previous combustion and thus the compression air-fuel ratio will decrease and the overall compression temperature will increase. Too early opening of the exhaust valve 4 will have less "hot-dirty" gas from the previous combustion and therefore the compression air-fuel ratio will increase and the overall compression temperature will decrease. When compression is increased by closing the exhaust valve 4 earlier, less gas escapes through the exhaust valve 4 and thus more gas is trapped in the combustion chamber. This increases the air-fuel ratio. In addition, increasing compression results in the piston 10 doing more compression work on the gases in the combustion chamber. This results in a higher gas temperature in the combustion chamber.

By activating the exhaust gas recirculation blower 43 or by increasing the speed of the exhaust gas recirculation blower 43, the exhaust gas recirculation flow is increased, more exhaust gas flows from the exhaust gas receiver 3 to the outlet of the turbocharger compressor or the scavenging air receiver 2, and this will reduce the compressed air-fuel ratio.

Increasing the speed of the auxiliary blowers 16 will cause a slight increase in the compressed air-fuel ratio.

For engines with water sprays, injecting water into the combustion chamber during compression will lower the overall compression temperature.

Scavenge air cooler bypass (not shown): bypassing the intercooler 14 will cause the overall compression temperature in the combustion chamber to increase significantly with little impact on the compression air-fuel ratio.

For engines provided with a variable geometry turbine 6, the effect of reducing the turbine flow area is to increase the scavenging air pressure and thus the mass of air trapped in the combustion chamber. This measure is therefore suitable for reducing the compression air-fuel ratio with only a minor effect on the overall compression temperature.

For an engine provided with a turbocharger assist device, accelerating the turbocharger 5 by adding the assist device will cause the compression air-fuel ratio to increase with a slight effect on the compression temperature.

Another measure is to change the ratio between gaseous fuel and liquid fuel (e.g. diesel or marine diesel). Decreasing the fraction of gaseous fuel of the total injected fuel energy increases the compression air-fuel ratio during compression. The fraction of liquid fuel increases accordingly, thereby ensuring that crankshaft torque is maintained.

For engines with a heat exchanger mounted in the exhaust gas receiver (or with a heat exchanger receiving part of the exhaust gas in the exhaust gas), increasing the fraction of the exhaust gas passing through the heat exchanger, i.e. extracting more heat from the exhaust gas, causes the scavenging air pressure to decrease and thus the mass of air trapped in the combustion chamber to decrease. This measure is therefore suitable for reducing the compression air-fuel ratio with only a minor effect on the overall compression temperature. A heat exchanger may be used to generate steam.

For engines with a heat scavenging bypass, opening the heat scavenging bypass control valve establishes flow from or increases flow from or to the compressor outlet to or from the environment, thereby significantly reducing the pressure of the scavenging air and thus the mass of air trapped in the combustion chamber. Therefore, this measure is suitable for reducing the compression air-fuel ratio.

In an embodiment, the compression air-fuel ratio lower limit threshold, the compression air-fuel ratio upper limit threshold, the overall compression temperature lower limit threshold, and the overall compression temperature upper limit threshold are parameters related to engine operating conditions. The engine operating conditions are determined by parameters such as engine load, ambient temperature, ambient humidity, engine speed, etc. The values of these parameters related to the operating conditions may be used by the controller 60 by, for example, a look-up table or algorithm or a combination of a look-up table and algorithm.

When the above measures are insufficient to maintain the combustion process in the action zone 52, the controller 60 takes additional measures to ensure that the process does not enter the critical zone 53. These additional measures are taken before the conditions in the combustion chamber have moved out of the action zone 52 into the critical zone 53 surrounding the action zone 52 or when the conditions in the combustion chamber have moved out of the action zone 52 into the critical zone 53 surrounding the action zone 52. Accordingly, the controller 60 is configured to: changing at least one of the cylinders 1 from the premixing operation to the compression ignition operation, and selecting the following amount of the second fuel: this amount of the second fuel is injected at or near TDC in the cylinder 1 operating in compression ignition to assist the remaining cylinders 1 still operating in the premixing process in moving away from the critical region 53. The second fuel is, for example, a fuel that can be injected relatively easily at the very high pressures required for injection at or near TDC (typically requiring a pressure of at least 300 bar), i.e. a liquid fuel. Examples of such liquid fuels are fuel oil, heavy fuel oil, methanol, ethanol, dimethyl ether (DME) and ammonia (any of these fuels may be added with water). In addition to changing one or more cylinders 1 to operate according to the compression ignition process, the controller 60 adjusts the amount of second fuel injected to the one or more cylinders 1 operating according to the compression ignition process such that torque (MIP) required to be transferred by the remaining cylinders operating according to the pre-mixing process is reduced when the risk of a pre-ignition event is detected and increased when the risk of a misfire event is detected. Increasing the torque (MIP) of the remaining cylinders operating according to the pre-mixing process is achieved by operating the one or more cylinders operating according to the compression ignition process with a relatively smaller amount of the second fuel such that the cylinders provide a relatively lower amount of torque (MIP). Reducing the torque (MIP) of the remaining cylinders operating according to the pre-mixing process is achieved by operating the cylinders operating according to the compression ignition process with a relatively higher amount of the second fuel such that the cylinders provide a relatively higher amount of torque (MIP).

The controller 60 is configured to minimize the constraint factors, i.e., the measures described above, to move the engine back to operating conditions within the normal region 51 and to minimize operation of the cylinder 1 according to the compression ignition process. Thus, the controller is configured to: all of the above measures are terminated when the conditions in the combustion chamber have been restored to the normal operating region.

Fig. 9 is a flowchart showing a process of operating the engine according to the configuration of the controller 60 described above.

After the start of this process, the controller 60 turns on all the cylinders 1 defaulting to operate according to the premixing process, which is the case shown in fig. 10, wherein all the cylinders operate according to the premixing process, and assuming that the conditions are optimal, the air-fuel ratio of all the cylinders 1 is within the allowable range between λ -minimum and λ -maximum, and the torque (MIP) transmitted by each cylinder 1 is approximately the same as the average torque transmitted by each cylinder 1 (this is the case shown in fig. 10). It should be noted that in embodiments, each cylinder 1 is individually controlled to optimize operation of the associated cylinder 1, which may result in minor deviations in torque transmitted by each individual cylinder 1.

Next, the controller 60 checks whether the compression air-fuel ratio (λ) is lower than a lower limit threshold (λ -lower limit value), and preferably, the controller 60 checks whether the compression air-fuel ratio (λ) of each cylinder is lower than the lower limit threshold (λ -lower limit value) respectively. If the answer is no, the controller 60 checks whether the compression air-fuel ratio upper limit threshold (λ -upper limit value) is exceeded, and if the answer is yes, the controller 60 takes a compression air-fuel ratio increasing measure from one of the above measures. Next, the controller 60 checks whether the compressed air-fuel ratio is above a maximum threshold (λ -maximum value). If the answer is no, the controller will go to check if the compression air-fuel ratio upper threshold (lambda-upper limit) is exceeded, if the answer is yes (this is the case shown in fig. 11, where there is a risk of pre-ignition), the controller 60 changes the one or more cylinders 1 from operation according to the pre-mixing process to operation according to the compression ignition process, and also adjusts the amount of second fuel injected at or near TDC to increase the MIP of the one or more cylinders 1 operating according to the compression ignition process, thereby reducing the MIP of the remaining cylinders 1 operating according to the pre-mixing process, and thereby increasing the air-fuel ratio of the cylinders 1 operating according to the pre-mixing process, so there is no longer a risk of pre-ignition in the cylinders 1. This is the situation shown in fig. 12. Next, the controller 60 checks whether the air-fuel ratio is between the lower and upper limit thresholds of the cylinder 1 operating according to the premixing process and whether the overall combustion temperature is between the upper and lower limit thresholds of the cylinder 1 operating according to the premixing process. If the answer is no, the process returns to the beginning, and if the answer is yes, the other cylinder(s) 1 are changed from the operation according to the compression ignition process to the operation according to the premixing process to further reduce the torque (MIP) of the cylinder operating according to the premixing process, and then the process returns to the beginning.

If it is determined that the air-fuel ratio is above the lower threshold (lambda-lower limit), the controller 60 checks whether the compressed air-fuel ratio is above the upper threshold (lambda-upper limit). If the answer is no, the controller goes to check whether the overall compression temperature lower limit threshold (Tc-lower limit value) is exceeded, and if the answer is yes, the controller 60 takes a compression air-fuel ratio reduction measure from one of the above measures. Next, the controller 60 checks whether the compressed air-fuel ratio is above a maximum threshold (λ -maximum value). If the answer is no, the controller goes to check whether the overall compression temperature lower limit threshold (Tc-lower limit value) is exceeded, and if the answer is yes (which is the case shown in fig. 13), the controller 60 changes the one or more cylinders 1 from operating according to the premixed process to operating according to the compression ignition process, and adjusts the amount of the second fuel injected at or near TDC to reduce the MIP of the one or more cylinders 1 operating according to the compression ignition process, thereby increasing the MIP of the remaining cylinders 1 operating according to the premixed process, and thereby reducing the air-fuel ratio of the cylinders 1 operating according to the premixed process, thereby reducing the risk of misfire. This is the situation shown in fig. 14. Next, the controller 60 checks whether the air-fuel ratio of the cylinder 1 operating according to the premixing process is between the lower limit threshold and the upper limit threshold and whether the overall combustion temperature is between the upper limit threshold and the lower limit threshold. If the answer is no, the process returns to the beginning, and if the answer is yes, the one or more cylinders 1 are changed from the operation according to the compression ignition process to the operation according to the premixing process, and then the process returns to the beginning.

If it is determined that the air-fuel ratio is not above the upper threshold (lambda-upper limit), the controller 60 checks whether the overall compression temperature is lower than the lower threshold (Tc-lower limit). If the answer is no, the controller 60 goes to the next step of checking whether the overall compression temperature is above the upper limit threshold (Tc-upper limit value), and if the answer is yes, the controller 60 takes the overall compression temperature increasing measure. Thereafter, the controller 60 checks whether the overall compression temperature is lower than a minimum threshold (Tc-minimum), and if the answer is no, the process of the controller 60 goes to a step of checking whether the overall compression temperature is above a maximum threshold (Tc-maximum), and if the answer is yes, the controller 60 changes one or more cylinders 1 from operating according to the pre-mixing process to operating according to the compression ignition process, and adjusts the amount of the second fuel injected at or near TDC to reduce the MIP of the one or more cylinders 1 operating according to the compression ignition process, thereby increasing the MIP of the remaining cylinders 1 operating according to the pre-mixing process, and thereby increasing the overall combustion temperature of the cylinders 1 operating according to the pre-mixing process. Next, the controller 60 checks whether the air-fuel ratio of the cylinder 1 operating according to the premixing process is between the lower limit threshold and the upper limit threshold and whether the overall combustion temperature is between the upper limit threshold and the lower limit threshold. If the answer is no, the process returns to the beginning, and if the answer is yes, the one or more cylinders 1 are changed from the operation according to the compression ignition process to the operation according to the premixing process, and then the process returns to the beginning.

If it is determined that the overall compression temperature is not lower than the lower threshold (Tc-lower limit), the controller 60 checks whether the overall compression temperature upper threshold (Tc-upper limit) is exceeded, if the answer is no, the controller 60 goes back to the step of checking whether the compression air-fuel ratio is lower than the lower threshold, and if the answer is yes, the controller 60 takes an overall temperature reduction measure from one of the measures according to the above. Next, the controller 60 checks whether the overall compression temperature is at the maximum threshold (Tc-maximum), if the answer is no, the controller 60 switches back to the step of checking whether the compression air-fuel ratio is below the lower threshold, and if the answer is yes, the controller 60 changes one or more cylinders 1 from operating according to the pre-mixing process to operating according to the compression ignition process and adjusts the amount of the second fuel injected at or near TDC to increase the MIP in the one or more cylinders 1 operating according to the compression ignition process, thereby reducing the MIP in the remaining cylinders 1 operating according to the pre-mixing process, and thereby reducing the overall compression temperature of the cylinders 1 operating according to the pre-mixing process, thereby reducing the risk of pre-ignition events.

In an embodiment, the controller 60 is provided with an algorithm, a look-up table, or other information to decide which of the available measures for increasing or decreasing the air-fuel ratio is the most appropriate measure under the current operating conditions of the engine.

In an embodiment, the values of the upper and lower thresholds for air-fuel ratio and the values of the maximum and minimum thresholds for air-fuel ratio are determined by the engine according to a test or computer-simulated test operation. The values of the upper and lower thresholds for the air-fuel ratio and the minimum and maximum thresholds for the air-fuel ratio are not necessarily constant values and generally depend on other parameters such as engine load and speed, environmental conditions, and the like. The controller 60 stores these values in a look-up table or the like, or uses an algorithm to determine the correct values for the actual conditions.

In an embodiment, the values of the upper and lower thresholds for the overall compression temperature and the values of the minimum and maximum thresholds for the overall compression temperature are determined by the engine from test or computer simulated test runs. The values of the upper and lower thresholds for the overall compression temperature and the minimum and maximum thresholds for the overall compression temperature are not necessarily constant values and generally depend on other parameters such as engine load and speed, environmental conditions, etc. The controller 60 stores these values in a look-up table or the like, or uses an algorithm to determine the correct values for the actual conditions.

The safety region 51, the action region 52 and the critical region 53 are schematically shown in fig. 7, and these regions do not necessarily have a rounded rectangular shape, and fig. 7 is merely an example. In practice, the actuation zone 52 will always lie within the critical zone 53 and the safety zone 51 will always lie within the actuation zone 52, but the shape of the contours of these zones 51, 52 may be any form of closed line and will depend on the design and characteristics of the relevant engine.

In another embodiment, the controller determines a need to change one or more of the plurality of cylinders 1 from operating according to a premixed operation to operating according to a compression ignition operation based on a cylinder pressure curve. Fig. 8 is a graph showing examples of a pressure curve (curve having the lowest peak value) when retarded ignition/misfire occurs, a curve (curve having the middle peak value) in the case of normal combustion, and a curve (curve having the highest peak value) in the case of advanced ignition/knocking occurrence. It should be noted that these curves are examples, and in particular, the retarded ignition/misfire curves and the advanced ignition/knock curves may differ significantly from the examples shown.

In this embodiment, the controller 60 is configured to: an occurrence of an undesired combustion event, such as a misfire and/or pre-ignition event, is detected by analyzing the cylinder pressure profile and based on this information, a determination is made as to whether a pre-ignition or a misfire event occurred.

When the controller 60 detects a pre-ignition event, the controller 60 changes one or more cylinders 1 from operating according to the pre-mixing process to operating according to the compression ignition process and adjusts the amount of second fuel injected in the cylinders 1 operating according to the compression ignition process to reduce the torque (MIP) that needs to be transferred by the cylinders 1 that are still operating according to the pre-mixing process, thereby avoiding pre-ignition events occurring in the cylinders 1 that are operating according to the pre-mixing process.

When the controller 60 detects a misfire or a late ignition event, the controller 60 changes one or more cylinders 1 from operating according to the pre-mixing process to operating according to the compression ignition process and adjusts the amount of second fuel injected in the cylinders 1 operating according to the compression ignition process to increase the torque (MIP) that needs to be transferred by the cylinders 1 that are still operating according to the pre-mixing process, thereby avoiding the occurrence of a late ignition/misfire event in the cylinders 1 operating according to the pre-mixing process.

In an embodiment, the controller 60 is configured to: after a predetermined time span (or engine revolution) of the cylinder 1 operating according to the compression ignition process, the operation of the cylinder 1 operating according to the compression ignition process is returned to the operation according to the premixing process.

In another embodiment, the controller 60 is configured to: monitoring the air-fuel ratio and the overall compression temperature of the cylinder 1 operating according to the premixing process; and changing the operation of the one or more cylinders 1 operating according to the compression ignition process back to the operation according to the premixing process when these values are within an acceptable range, preferably for a given time span, for example between a TC-lower limit value and a TC-upper limit value and between a lambda-lower limit value and a lambda-upper limit value.

In an embodiment, for an engine having a large number of cylinders 1, for example, in an engine having seven or more cylinders, the controller 60 is configured to change the operation of at least two cylinders 1 from a premixed operation to a compression ignition operation, and to change the operation of at least two cylinders 1 from a compression ignition operation to a premixed operation, to have a substantial effect on the operating conditions (such as the air-fuel ratio and/or the overall compression temperature) of the remaining cylinders 1 operating according to the premixing process.

Generally, the controller 60 is configured to minimize operation of the cylinders in accordance with the compression ignition process to minimize the use of the second fuel, as minimizing the use of the second fuel generally minimizes emissions.

In the embodiment, each cylinder 1 is provided with a variable timing exhaust valve 4, the variable timing exhaust valve 4 being centrally disposed in the cylinder head 22, and the controller 60 is configured to time the opening and closing of the exhaust valve 4 for the premixing process of the cylinder 1 operating according to the premixing process among the plurality of cylinders 1, and the controller 60 is configured to time the opening and closing of the exhaust valve 4 for the compression ignition process of the cylinder 1 operating according to the compression ignition process among the plurality of cylinders 1.

FIG. 15 is a schematic diagram of an embodiment of a controller showing control of fuel delivered to an engine based on a speed set, i.e., a desired rotational speed of the engine as compared to an actual rotational speed "of the engine. The result of the comparison is sent to a regulator that produces a fuel index that is divided into a gas index and a fuel index for the gaseous fuel and the liquid fuel, respectively. Thus, as the demand for fuel is greater, the amount of gaseous oil correspondingly decreases. The fuel amount or fuel index is determined based on a series of signals. The cylinder pressure and the fuel pilot angle are processed to detect a pre-ignition event, and the fuel amount is increased by "Fo command (fuel command)".

The measured cylinder pressure is processed by monitoring the deviation over time (derivative) and when the derivative exceeds a threshold, a fixed amount of fuel is provided for a given period of time X by Fo command. If the cylinder pressure exceeds the maximum design pressure, the fuel amount is commanded to increase by Fo until the cylinder pressure is again below the maximum design pressure. The engine speed signal is compared to the speed index, if the ratio between the engine speed signal and the speed index exceeds a maximum level, it is determined that the engine is operating under load, and the amount of fuel is commanded to increase by Fo in a manner proportional to the degree of load operation. The scavenging pressure is used to limit the maximum amount of gaseous fuel so the fuel index is increased by Fo command. The signals of the various fuel commands (Fo commands) are summed and the total number (sum) of fuel commands (Fo commands) is limited to a maximum value before the fuel index is issued.

Various aspects and implementations 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 term "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.

Claims

1. A dual fuel large two-stroke turbocharged uniflow scavenged internal combustion engine, which is in at least one operating mode and is configured to operate on a first fuel as a primary fuel, the engine comprising:

a plurality of cylinders (1),

-a piston (10), the piston (10) reciprocating between BDC and TDC in each of the cylinders (1);

at least one fuel admission valve (30), said fuel admission valve (30) being associated with a cylinder (1) for admitting a first fuel during a stroke of said piston (10) from BDC to TDC,

-at least one fuel injection valve (50), the fuel injection valve (50) being associated with at least one of the cylinders (1) for injecting a second fuel when the piston (10) is at or near TDC, and

-a controller (60), the controller (60) being configured to: when the engine is running in the at least one operating mode,

-by default, operating all cylinders of the plurality of cylinders (1) according to a premixing process and admitting the first fuel during a stroke of the piston (10) from BDC to TDC,

-determining that the actual combustion conditions of the cylinder (1) operating according to the premixing process are such that there is an unacceptable risk of a pre-ignition event or misfire, characterized in that the controller (60) is configured to: when the controller (60) has determined that there is an unacceptable risk of a pre-ignition event or misfire,

the controller (60) changes the associated at least one of the cylinders (1) from operation according to the pre-mixing process to operation according to a compression ignition process by terminating admission of the first fuel during a BDC to TDC stroke of the piston (10) for the at least one of the plurality of cylinders (1), and

the controller (60) injects a quantity of the second fuel in the associated at least one of the cylinders (1) when the piston (10) is at or near TDC.

2. The engine of claim 1, wherein the controller (60) is configured to select the amount of the second fuel injected into the associated at least one cylinder (1) such that:

when determining the risk of pre-ignition, the indicated average pressure of the remaining cylinders (1) of the plurality of cylinders (1) operating according to the pre-mixing process is reduced,

When determining the risk of misfire, the indicated average pressure of the remaining cylinders (1) of the plurality of cylinders (1) operating according to the premixing process is increased.

3. The engine of claim 1 or 2, wherein the controller (60) is configured to: when a predetermined time span or engine revolution has elapsed since one or more cylinders (1) changed from operating according to the pre-mixing process to operating according to the compression ignition process, the associated cylinder (1) is returned from operating according to the compression ignition process to operating according to the pre-mixing process.

4. The engine of claim 1 or 2, wherein the controller (60) is configured to: an air-fuel ratio and an overall compression temperature of the cylinders (1) operating according to the pre-mixing process are monitored, and when the monitored air-fuel ratio and the overall compression temperature are within acceptable ranges, the controller (60) changes an operation of one or more cylinders (1) operating according to the compression ignition process to an operation according to the pre-mixing process.

5. The engine of claim 1 or 2, wherein the controller (60) is configured to: an air-fuel ratio and an overall compression temperature of the cylinders (1) operating according to the pre-mixing process are monitored, and the controller (60) changes operation of one or more cylinders (1) operating according to the compression ignition process to operation according to the pre-mixing process when the monitored air-fuel ratio and the overall compression temperature are within acceptable ranges for a given time span.

6. An engine according to claim 1 or 2, wherein no or only a small amount of the second fuel is injected as pilot fuel to the cylinders (1) operating according to the premixing process.

7. The engine of claim 1 or 2, wherein each cylinder (1) is provided with a variable timing exhaust valve actuation system for actuating an exhaust valve (4) centrally arranged in the cylinder head (22), and wherein the controller (60) is configured to determine and control the opening and closing timings of the exhaust valve (4), and the controller (60) is configured to:

timing the opening and closing of the exhaust valve (4) adapted to the premixing operation of a cylinder (1) operating according to the premixing process, of the plurality of cylinders (1), and

-timing the opening and closing of the exhaust valve (4) adapted to the compression ignition process for the cylinder (1) of the plurality of cylinders (1) operating according to the compression ignition process.

8. The engine of claim 1 or 2, wherein the controller (60) is configured to determine or measure an air-fuel ratio of the cylinder (1), and the controller (60) is configured to determine an unacceptable risk of a misfire event when the air-fuel ratio is above an air-fuel ratio maximum threshold, and the controller (60) is configured to determine an unacceptable risk of a premature combustion event when the air-fuel ratio is below an air-fuel ratio minimum threshold.

9. The engine of claim 1 or 2, wherein the controller (60) is configured to determine or measure an overall compression temperature in the cylinder (1) at the start of combustion, and the controller (60) is configured to determine an unacceptable risk of a misfire event when the overall compression temperature is below an overall compression temperature minimum threshold, and the controller (60) is configured to determine an unacceptable risk of a premature combustion event when the overall compression temperature is above an overall compression temperature maximum threshold.

10. An engine according to claim 1 or 2, wherein the controller (60) comprises an air-fuel ratio observer (46) for determining an average instantaneous air-fuel ratio in the cylinder (1), or the controller (60) is connected to an air-fuel ratio observer (46) for determining an average instantaneous air-fuel ratio in the cylinder (1).

11. An engine according to claim 1 or 2, wherein the controller (60) comprises an overall compression temperature observer (47) for determining an average instantaneous overall compression temperature in the cylinder (1), or the controller (60) is connected to an overall compression temperature observer (47) for determining an average instantaneous overall compression temperature in the cylinder (1).

12. A method of operating a dual fuel large two-stroke turbocharged uniflow scavenged internal combustion engine, the engine being in at least one operating mode and configured to operate on a first fuel as a primary fuel, the engine comprising:

a plurality of cylinders (1),

a piston (10), the piston (10) reciprocating between BDC and TDC in each of the cylinders (1),

at least one fuel injection valve (50), said fuel injection valve (50) being associated with at least one of said cylinders (1) for injecting a second fuel when said piston (10) is at or near TDC,

-the method comprises:

-by default, all cylinders of the plurality of cylinders (1) are operated according to a premixing process and the first fuel is admitted during the stroke of the piston (10) from BDC to TDC,

determining whether the actual combustion conditions of the cylinder (1) operating according to the premixing process are such that there is an unacceptable risk of a pre-ignition event or misfire,

The method is characterized in that: when it has been determined that there is an unacceptable risk of a pre-ignition event or misfire,

changing the associated at least one of the plurality of cylinders (1) from operating according to the pre-mixing process to operating according to a compression ignition process by terminating admittance of the first fuel during a stroke of the piston (10) from BDC to TDC for the at least one of the cylinders (1), and

-injecting an amount of said second fuel in the associated at least one of said cylinders (1) when said piston (10) is at or near TDC.

13. The method according to claim 12, wherein the method comprises: -selecting said amount of said second fuel injected into the associated at least one cylinder (1) such that:

when determining the risk of misfire, the indicated average pressure of the remaining cylinders (1) of the plurality of cylinders (1) operating according to the pre-mixing process is increased.

14. The method according to claim 12 or 13, wherein the method comprises: when a predetermined time span or engine revolution has elapsed since one or more cylinders (1) changed from operation according to the pre-mixing process to operation according to the compression ignition process, the associated cylinder (1) is returned from operation according to the compression ignition process to operation according to the pre-mixing process.

15. The method according to claim 12 or 13, wherein the method comprises: an air-fuel ratio and an overall compression temperature of the cylinders (1) operating according to the pre-mixing process are monitored, and when the monitored air-fuel ratio and the overall compression temperature are within acceptable ranges, an operation of one or more cylinders (1) operating according to the compression ignition process is changed to an operation according to the pre-mixing process.

16. The method according to claim 12 or 13, wherein the method comprises: an air-fuel ratio and an overall compression temperature of the cylinders (1) operating according to the pre-mixing process are monitored and when the monitored air-fuel ratio and overall compression temperature are within acceptable ranges for a given time span, operation of one or more cylinders (1) operating according to the compression ignition process is changed to operation according to the pre-mixing process.

17. The method according to claim 12 or 13, wherein the method comprises: the second fuel is not injected or is injected only in small amounts as pilot fuel to the cylinders (1) operating according to the premixing process.

18. The method according to claim 12 or 13, wherein each cylinder is provided with a variable timing exhaust valve centrally arranged in the cylinder head (22), and the method comprises:

timing the opening and closing of the variable timing exhaust valve adapted to the pre-mixing operation of a cylinder (1) operating according to the pre-mixing process, of the plurality of cylinders (1), and

the opening and closing of the variable timing exhaust valve adapted to the compression ignition process for a cylinder (1) of the plurality of cylinders (1) operating according to the compression ignition process is timed.