CN107448284B

CN107448284B - Two-stroke crosshead internal combustion engine and method for directly injecting fuel and water into combustion chamber

Info

Publication number: CN107448284B
Application number: CN201710294692.9A
Authority: CN
Inventors: 斯蒂芬·迈尔; 约翰·斯乔侯姆; 尼尔斯·谢姆特鲁普
Original assignee: MAN Diesel and Turbo Filial af MAN Diesel and Turbo SE
Current assignee: MAN Energy Solutions Filial af MAN Energy Solutions SE
Priority date: 2016-05-02
Filing date: 2017-04-28
Publication date: 2020-08-14
Anticipated expiration: 2037-04-28
Also published as: KR20170124466A; DK201670287A1; JP6657138B2; CN107448284A; KR102105635B1; JP2017207062A; DK179162B1

Abstract

A two-stroke crosshead internal combustion engine (1) comprises an oil supply system (16), a liquefied gas supply system (17) and a water supply system (18). The individual cylinder (7) has an exhaust valve (6) at the upper end and a scavenging air port (8) in the lower end region. The single cylinder (7) also has at least one set of liquefied gas fuel injectors (14) and oil fuel injectors (15) for direct injection. A water supply (18) supplies water to the liquefied gas supply system and/or directly to the liquefied gas fuel injectors.

Description

Two-stroke crosshead internal combustion engine and method for directly injecting fuel and water into combustion chamber

Technical Field

The invention relates to a two-stroke crosshead internal combustion engine comprising a fuel supply system and a water supply system and a cylinder, the single cylinder having at least a combustion chamber, a piston, an exhaust valve at the upper end of the cylinder, a scavenging air port in the lower end region of the cylinder, and valves for direct injection of fuel and water into the combustion chamber. The invention also relates to a method of injecting fuel and water directly into the combustion chamber of a cylinder in a two-stroke crosshead internal combustion engine,

background

The two-stroke crosshead engine has an exhaust valve at the upper end of the cylinder and a scavenging air port in the lower end region of the cylinder, and is uniflow scavenged. During scavenging of the cylinder, after combustion, the exhaust valve opens, compressed scavenging air flows into the cylinder through the scavenging air port and rises in a swirling motion towards the exhaust valve, while combustion gases flow out through the exhaust valve. In this way, the cylinder is filled with air from the bottom and flows unidirectionally upward (unidirectional flow), in contrast to an engine in which both the intake and exhaust ports are provided at the top of the cylinder.

Two-stroke crosshead engines have a ratio S/B between stroke S and bore B in the range from 3.2 to 4.9 and this ratio is very different from the ratio of stroke to bore in four-stroke engines where S/B is in the range from 0.8 to 1.3, typically around 1.0. Due to these differences in basic design, the conditions in the combustion chamber with respect to scavenging, compression, injection and combustion processes are specific to a two-stroke crosshead engine. Furthermore, the two-stroke crosshead engine is a low-speed rotary engine operating at a speed in the range from 55rpm to 200rpm at 100% engine load. The single combustion process in the combustion chamber of a two-stroke crosshead engine thus takes a long time and extends over a long distance of area from the injector when compared to other types of internal combustion engines.

An engine of the type mentioned at the beginning is described in EP 0967371 a1 (corresponding to JP 2000-. The cylinder is provided with a separate water injector for injecting water into the cylinder during the compression stroke in order to reduce the temperature level in the cylinder. The water injection is controlled early in the compression stroke, for example immediately after the exhaust valve is closed. At this point of the two-stroke cycle, the pressure in the cylinder is very low, so that water injection can be achieved at a low pressure of, for example, 25 bar.

Disclosure of Invention

The object of the present invention is to allow water to be injected with a simple design at the end of the compression stroke of a two-stroke cycle or in the combustion stroke of a two-stroke cycle, and to allow no water to be injected when fuel is injected.

In view of this object, the two-stroke crosshead internal combustion engine according to the invention mentioned at the beginning is characterized in that the valves on the individual cylinders for direct injection of fuel and water comprise at least one set of liquefied gas fuel injectors and oil fuel injectors, that the fuel supply system comprises a supply system connected to the oil injectors and a liquefied gas supply system connected to the liquefied gas fuel injectors, and that the supply system comprises a supply device connected to the liquefied gas supply system or directly to the liquefied gas fuel injectors.

The liquefied gas fuel injector is adapted to inject a high pressure liquid and has an atomizer sized to inject liquefied gas fuel into the combustion chamber. Supplying water from the water supply to the liquefied gas fuel injectors causes water to be injected into the combustion chamber and avoids the installation of separate water injectors. During a combustion stroke of the two-stroke cycle, the piston moves toward a bottom dead center position, wherein the piston is disposed at a distance of at least three times a diameter of the piston from the liquefied gas fuel injector. As the combustion process progresses, the combustion chamber becomes longer and the flame front can be located away from the injector. By means of the liquefied gas fuel injectors it is possible to inject water instead of liquefied gas fuel and to ensure proper combustion, since the oil injected by the oil injectors is able to maintain the combustion process while water is injected via the liquefied gas fuel injectors. The water can be fed directly to the liquefied gas fuel injector, however it is preferred to feed the water to the liquefied gas fuel injector via a liquefied gas feed system, thereby avoiding the provision of a separate feed port in this injector and an internal flow passage in this injector. When water is supplied to the liquefied gas supply system, the water flows to the liquefied gas fuel injector along the same flow path as the liquefied gas fuel, and the water is injected into the combustion chamber in the same manner as the liquefied gas fuel.

In one embodiment, the valves used to directly inject fuel and water on a single cylinder include two sets of liquefied gas and oil fuel injectors. By having two sets, two liquefied gas injectors can be used for injecting water, and this offers the possibility of switching the injection position for injecting water into the combustion chamber by switching between the two liquefied gas fuel injectors when water is supplied to both liquefied gas fuel injectors simultaneously, or only one of them at a time, and then water is supplied alternately between the two liquefied gas fuel injectors, and by this means, a volume of water is injected into the combustion chamber quickly, for example in order to improve the combustion process. In another embodiment, a single cylinder includes three sets of liquefied gas fuel injectors and oil fuel injectors, and in a further embodiment, a single cylinder includes only one set of liquefied gas fuel injectors and oil fuel injectors.

In a preferred embodiment, the exhaust valve is centrally located at the top of the cylinder between the two sets of liquefied gas fuel injectors and oil fuel injectors. Even though the exhaust valve may alternatively be arranged at one side of the top of the cylinder, a central position is preferred as it allows each liquefied gas fuel injector and oil fuel injector to be arranged at the same side, so that the spray injected from the nozzle can be directed towards the center of the cylinder and at a greater distance from the opposite inner wall of the cylinder.

In one embodiment, the liquefied gas fuel injector comprises an injector housing having a valve guide and a valve member displaceable in the valve guide, and the internal combustion engine comprises a sealing oil system for supplying sealing oil to the liquefied gas fuel injector, and the liquefied gas fuel injector has a sealing oil passage extending from a sealing oil inlet to a bore in the valve guide. The sealing oil serves to prevent leakage of the liquefied gas fuel when the liquefied gas is injected, but also serves as a lubricant between the valve member and the hole in the valve guide when water is injected through the liquefied gas fuel injector, and prevents water from damaging the injector parts. As an alternative to using sealing oil as a lubricant, the valve parts may be made of a material that is capable of acting under the influence of water, such as a PTFE-coated steel body or a ceramic-coated steel body.

In a further development, the sealing oil system is adapted to deliver sealing oil at a predetermined sealing oil pressure, and the water supply system is adapted to deliver water at a pressure below the predetermined sealing oil pressure. Because the seal oil pressure is higher than the water pressure, the seal oil tends to press out any water that may seep into the oil-filled gap between the valve member and the bore in the valve guide.

In one embodiment the injection pressure of the liquefied gas fuel injector is set to an injection opening pressure of at least 350 bar, which is higher than the highest compression pressure in the combustion chamber just before the start of combustion. Preferably, the injection pressure of the liquefied gas fuel injector is set to an injection opening pressure of at least 500 bar, which is much higher than the maximum pressure in the combustion chamber during the two-stroke cycle, so that a very fine spray of water is achieved. Alternatively, an injection opening pressure below 350 bar may be used.

The water and/or liquefied gas fuel in the liquefied gas supply system can be pressurized to a pressure higher than the injection opening pressure and then opened and closed using a simple control valve to supply to the liquefied gas fuel injectors. Preferably, however, the liquefied gas fuel injector is adapted to feed liquefied gas fuel and/or water to the inlet chamber at a preset feed pressure, and the liquefied gas fuel injector comprises a hydraulically actuated plunger adapted to pressurise the liquefied gas fuel and/or water in the inlet chamber to an injection opening pressure. In this way, the preset feed pressure in the liquefied gas supply system can be suitably low, for example in the range from 5 to 30 bar, and the plunger can be supplied with a high pressure control oil, for example in the range from 200 to 400 bar, which causes the pressure in the inlet chamber to rise to at least the opening pressure of the liquefied gas fuel injector.

In another aspect, the invention relates to a method of injecting fuel and water directly into a combustion chamber of a cylinder of a two-stroke crosshead internal combustion engine comprising a fuel supply system and a water supply system and a cylinder, the single cylinder having at least a combustion chamber, a piston, an exhaust valve at an upper end of the cylinder, a scavenging air port at a lower end region of the cylinder and injecting fuel and water directly into the combustion chamber. According to the invention, this method is characterized in that the fuel supply system supplies at least one set of liquefied gas fuel injectors and oil fuel injectors with liquefied gas fuel from a liquefied gas supply system to the liquefied gas fuel injectors and oil fuel from an oil supply system to the oil fuel injectors for direct injection into the combustion chamber, and the water supply system supplies water to the liquefied gas supply system via a water supply device and/or directly to the liquefied gas fuel injectors. The method provides the effects and advantages mentioned in the above description in connection with an internal combustion engine.

Preferably, the injection of water from the liquefied gas fuel injector is terminated before the termination of fuel injection during the combustion stroke of the two-stroke cycle. The final injection into the combustion chamber is thus a fuel injection, and this is assumed to stabilize the combustion process and reduce the amount of any residual combustion products. It is also possible to inject water after termination of fuel injection, but this is not preferred.

In a two-stroke cycle, the water injection from the liquefied gas fuel injector can be started before the fuel injection begins. In this case, water may be injected at the final stage of the compression stroke in order to lower the temperature of the hot compressed air.

The injection of water from the liquefied gas fuel injector can occur simultaneously with the injection of fuel during the combustion stroke of the two-stroke cycle, and thus the water can be used to reduce the temperature of the flame. It is also possible to add water to the liquefied gas fuel and then feed the mixture to the liquefied gas fuel injector and inject both into the combustion chamber simultaneously.

In one embodiment, an internal combustion engine has at least a first mode of operation and a second mode of operation, wherein in the first mode of operation the liquefied gas supply system supplies liquefied gas fuel and the oil supply system supplies fuel oil; in a second mode of operation, the liquefied gas supply system supplies water and the oil supply system supplies low-sulfur fuel oil. The second mode of operation allows low sulfur fuel oil to be combusted under conditions where the flame temperature has been reduced by water injection; the first mode of operation allows the engine to be operated without consuming the more expensive low sulphur fuel oil, as the fuel oil may have a higher sulphur content, such as heavy fuel oil. In the present context, low sulphur fuel oil is understood to be fuel oil having a sulphur content below 0.1% by weight. The internal combustion engine may further or alternatively have another operating mode in which the liquefied gas supply system supplies a mixture of liquefied gas fuel and water and the oil supply system supplies fuel oil.

To facilitate the design of the fuel and water supply system, the liquefied gas supply system preferably supplies liquefied gas fuel at a preset feed pressure of at most 25 bar, and the water supply system preferably supplies water at a preset feed pressure of at most 25 bar. The preset feed pressure may for example be a pressure in the range from 6 to 10 bar.

Preferably, the water supply system supplies water to the liquefied gas supply system, and the liquefied gas supply system supplies methanol and water to the liquefied gas fuel injectors. Methanol can be supplied as a liquefied gas fuel and water and methanol are well mixed without any precautions or any special equipment. All that is required is that water be added to the methanol and then the two automatically mixed.

Preferably, the liquefied gas fuel injector operates with an injection opening pressure of at least 500 bar, for example at least 550 bar. The high opening pressure ensures that the atomized fine mist enters the combustion chamber.

Drawings

Examples of embodiments of the invention are described in more detail below in connection with highly schematic drawings, in which:

FIG. 1 illustrates an upper portion of an internal combustion engine showing air and fuel flow through cylinders, according to the present disclosure;

FIG. 2 shows a schematic representation of the engine of FIG. 1;

FIG. 3 illustrates the supply of fuel to the cylinders of the engine of FIG. 2; and

fig. 4 shows a side view of the liquefied gas injector of the engine cylinder of fig. 2 in more detail.

Detailed Description

In fig. 1, a two-stroke crosshead internal combustion engine is generally designated 1. The internal combustion engine is a unidirectional flow engine, which will be explained briefly below. The turbocharger, generally designated 2, has a compressor section, which supplies compressed intake air and scavenging air via a scavenging air cooler 4 and a water mist trap 5 to a scavenging air receiver 3, as indicated by white arrows in the figure. An exhaust valve 6 is mounted on an upper end of the cylinder 7. The scavenging air ports 8 are provided in the lower end region of the cylinder 7 as openings distributed in rows across the circumference of the cylinder wall. The piston 9 is movable in the length direction of the cylinder between a Top Dead Center (TDC) position and a Bottom Dead Center (BDC) position. In the BDC position shown in fig. 1, the piston is just below the scavenging air port 8 and the scavenging air port 8 is open and both intake and scavenging air can flow into the cylinder. These ports close when the piston has moved upward beyond the scavenging air ports. Thus, the piston acts to open and close the scavenging air port. When the exhaust valve 6 is open, exhaust gas and scavenging air may flow out of the cylinder via the exhaust passage into the exhaust gas receiver 10. In a one-way (one-way flow) action up through the cylinder, intake and scavenging air flows upward in a swirling action toward the upper portion of the cylinder, while forcing out combustion gases via the open exhaust valve. As indicated by the black arrows in fig. 1, exhaust gas flows from the exhaust gas receiver 10 to the turbine section of the turbocharger. An exhaust valve 6 is mounted at the top of the cylinder, coaxial with the longitudinal central axis of the cylinder. The exhaust valves are actuated to open and close by a hydraulic actuator mounted in an exhaust valve housing on top of the cylinder.

The piston is mounted on a piston rod 11, wherein the piston rod 11 extends along the longitudinal axis of the cylinder from the piston to a crosshead (not shown) via a piston rod stuffing box fixed to the middle bottom of the engine frame 12. The crosshead is also connected to the crankshaft via a connecting rod. The crosshead mechanism moves the piston rod up and down in line with the longitudinal centerline of the cylinder 7 and enables the cylinder to have a length related to its diameter. The two-stroke crosshead internal combustion engine has a stroke/bore ratio in the range from 3.2 to 4.9. The piston thus moves along a distance from TDC to BDC position that is greater than 3 times its diameter, while the combustion chamber 13 in the cylinder above the piston changes shape to a more elongated chamber. Fuel injection takes place in the upper end of the combustion chamber and for a uniflow scavenged two-stroke crosshead internal combustion engine the combustion conditions are very different from those in a four-stroke engine, where injection and combustion take place almost at the same location and the interruption of fuel injection can be recovered by reintroduction of fuel injection.

The internal combustion engine according to the invention is a piston engine and preferably an engine having 4 to 14 in-line cylinders. The engine can be used, for example, in the manufacture of MAN Diesel&Turbo and ME-GI types, or for manufacture

Either for making Mitsubishi or for making WinGD. The cylinder can have a bore in the range of, for example, 30 to 110cm, preferably 35 to 95 cm. Two-stroke crosshead internal combustion engines can be used as main propulsion engines in ships or prime movers in stationary power plants, where the engine drives a generator to supply power to the grid. The internal combustion engine according to the invention typically has a speed (expressed as rpm) from 55 to 200 rpm.

The engine has an injection system with a valve for injecting fuel directly into the combustion chamber. These valves comprise, on each cylinder 7, a first group of one liquefied gas fuel injector 14 and one oil fuel injector 15, and a second group of one liquefied gas fuel injector 14 and one oil fuel injector 15. One of the engine cylinders is shown in fig. 3 from above, and only the injectors and their supply lines are shown in fig. 3, but no exhaust valves are shown, which are however arranged between the two groups of injectors in the centre of the cylinder.

The engine has a fuel supply system comprising an oil supply system generally designated 16 and a liquefied gas supply system generally designated 17. The engine further has a water supply system, generally designated 18. These three systems are shown in fig. 2, showing a side view of the engine with one end of a rotating wheel 19 on the left and a crankshaft 20 on the right, and 6 cylinders 7 arranged in a row on the engine frame 12.

The oil supply system 16 includes at least one fuel oil source 21 that receives oil from one or more storage tanks via a pump. The fuel oil source comprises a feed pump and an oil supply line 22 extending from the individual cylinders 7 on the engine. When the oil supply system should supply more than one type of oil to the oil fuel injectors, the engine may have more than one source of fuel oil and associated oil tanks, pumps and supply lines arranged in parallel. One type can be a typical density of 840kg/m³Another type can be a typical density of 982kg/m³By re-ignition ofAnd (7) oil.

The liquefied gas supply system 17 comprises at least one liquefied gas source 23, wherein the liquefied gas source 23 receives liquefied gas from one or more liquefied gas storage tanks via a pump. As an example, the liquefied gas fuel can be methanol, CH, having a vapour pressure of 0.13 bar at a temperature of 20 ℃₃OH, or liquefied petroleum gas, LPG, typically propane and/or butane or mixtures thereof. The source of liquefied gas comprises a liquefied gas supply line 24 extending to the individual cylinders 7 on the cylinder, and a supply pump unit 25. The liquefied gas source and supply pump unit is arranged outside the engine room, for example on board a ship, on the weather deck 26 of the ship if the engine is mounted as a main engine for driving the ship's propellers, or outside the building wall if the engine is stationary and mounted as a prime mover for driving a generator in a power station. Any gas leaking from the liquefied gas supply thus does not enter the engine compartment. From the point of entry into the engine room, the liquefied gas supply line 24 is enclosed in an external line system 27 surrounding the liquefied gas supply line, and the annular space between the two lines is used for venting air through the annular space and monitoring gas leakage from the internal line as liquefied gas supply line. The liquefied gas supply system also comprises a purge return system 28 having a return line 29, the return line 29 likewise being enclosed in an external line system until it passes through the weather deck 26. A return line 29 extends to the source of liquefied gas 23 and is capable of returning liquefied gas to the source of liquefied gas 23. Under certain conditions, such as detection of a gas leak or a requirement to stop the engine, the liquefied gas supply line has to be emptied and purged with nitrogen supplied by the purge return system 28. After the liquefied gas has been returned to liquefied gas source 23, the complete purge with nitrogen is conducted by passing the nitrogen through a double-walled piping system.

As a result of using liquefied gas as fuel, the engine further comprises a seal oil system 30, wherein the seal oil system 30 comprises a seal oil source 31 and a seal oil supply line 32, and the seal oil source 31 in turn comprises a seal oil tank and a seal oil pump, the seal oil supply line 32 extending to a single liquefied gas fuel injector on each cylinder 7. The engine further comprises a control oil system 33, wherein the control oil system 33 comprises a control oil source 34 and a control oil supply line 35, and the control oil source 34 comprises a control oil tank and a control oil pump, the control oil supply line 35 extending to a single liquefied gas injector on each cylinder 7.

The water supply system 18 includes a water source 36, such as a water tank with a water pump or pressurized water, typically a fresh water supply, and a water supply in the form of a water supply line 37 with a water control valve 38. A water supply line 37 extends to the feed pump unit 25 in the liquefied gas feed system 17. A water control valve 38 in the water supply line 37 can be opened and closed to deliver water to the supply pump unit, and a liquefied gas control 39 is provided in the liquefied gas supply line 24 connecting the water supply line upstream of the liquefied gas supply line, upstream being between this connection and the liquefied gas source 23. The water control valve 38 and the liquefied gas control valve 39 are electronically controlled valves, and the control is effected by one or both of two

electronic control units

40, 41. When the water control valve 38 is closed and the liquefied gas control valve 39 is opened, liquefied gas is supplied to the engine via the liquefied gas supply line 24. When the water control valve 38 is opened and the liquefied gas control valve 39 is closed, water is supplied to the engine via the liquefied gas supply line 24. When the water control valve 38 is fully or partially opened, for example, to 30% or 50% or 80% of the total flow rate of the valve, and the liquefied gas control valve 39 is opened, a mixture of water and liquefied gas is supplied to the engine via the liquefied gas supply line 24. The valve can be controlled to deliver any mixture of water and liquefied gas from less than 100% liquefied gas and greater than 0% water to greater than 0% liquefied gas and less than 100% water.

Fig. 3 shows in more detail the liquid supply of liquid fuel or water to the liquefied gas fuel injectors 14 and the oil fuel injectors 15 on the cylinders 7. In the engine room, the liquefied gas supply line 24 is enclosed in an external line system 27, and the external line system 27 is provided with an air intake system and a purge gas system that supplies an inert gas such as nitrogen. The air intake system ventilates the interior of the external line system 27. Air intake occurs at 42 and air outtake occurs at 43. A pair of hydrocarbon detectors 44 is arranged in the conduit leading to the air outlet 43 downstream of the engine. A source of pressurized purge gas may be connected to the external piping system and the liquefied gas supply line 24, and when the engine is off, inert gas is supplied to the liquefied gas supply line to purge the liquefied gas supply line.

The fuel oil source 21 supplies oil fuel to the oil fuel injectors 15 on each cylinder 7 of the internal combustion engine, the oil fuel being supplied to the oil fuel pump 45, the oil fuel pump 45 being electronically controlled and being a hydraulically driven pump, the oil fuel pump 45 delivering the oil fuel to the oil fuel injectors 15 when an injection sequence occurs, and the delivery pressure of the oil fuel pump exceeding the opening pressure of the oil fuel injectors and being able to lie in the range from 400 bar to 800 bar.

The liquefied gas fuel injectors 14 on each cylinder are supplied with pressurized sealing oil via the sealing oil supply line 32. The sealing oil lubricates the liquefied gas fuel injector and prevents liquefied gas from escaping from the valve. The sealing oil source provides sealing oil at a predetermined pressure, for example a pressure in the range from 15 bar to 500 bar, preferably in the range from 20 bar to 40 bar.

The liquefied gas fuel injectors 14 on each cylinder are supplied with control oil from a control oil source 34, the control oil source 34 having a control oil pump to deliver the control oil at a pressure in the range from 250 bar to 500 bar, for example a control oil pressure of about 300 bar. Liquefied gas flows from the liquefied gas supply line 24 to the reservoir 46, and when liquefied gas injection occurs, the liquefied gas control valve 47 is opened to supply liquefied gas to the liquefied gas fuel injector 14.

The liquefied gas fuel injectors 14 and the oil fuel injectors 15 are arranged in a group on the cylinder, and they can be mounted in a cylinder head on top of a cylinder liner, for example. The cylinder has two sets of one liquefied gas fuel injector 14 and one oil fuel injector 15 in the embodiment shown, and the two sets are arranged on opposite sides of an exhaust valve (not shown in fig. 3). The two injectors in each group are arranged closer to each other than the injectors of one group are to the injectors of the other group.

The liquefied gas fuel injectors 14 can inject liquefied gas and water, either individually or as a mixture. Fig. 4 shows the main components of the liquefied gas fuel injector 14. The liquefied gas fuel injector 14 is mounted in a bore of the cylinder 7, e.g. a cylinder head, the inner end of the injector being positioned inside the combustion chamber 13 and comprising a nozzle 48, the nozzle 48 having several atomizing holes 49, through which several atomizing holes 49 liquefied gas fuel or water or a mixture thereof is injected into the combustion chamber as an atomized mist.

Liquefied gas fuel injector 14 has different areas that are independently sealed by annular sealing ring 50. A single sealing ring 50 seals between the outer surface of the liquefied gas fuel injector 14 and the inner surface of the bore in the cylinder 7. In the uppermost region there is a general drain passage 51 in the cylinder, allowing any dirt to flow into this region. An inlet port 52 for sealing oil is arranged between the second and third sealing rings 50. An outlet 53 for sealing oil is arranged between the third sealing ring and the fourth sealing ring 50. A liquid inlet 54 for liquefied gas or water or a mixture thereof is arranged between the fourth and fifth sealing ring 50. The flow path connects the liquid inlet port 54 with the liquid inlet chamber 56. The lower region 55 between the fifth and sixth sealing rings is connected to the air inlet port 42 and vents air through the air inlet port 42 to the air outlet port 43 and detects the presence of hydrocarbons.

The liquefied gas fuel injectors 14 are supplied with liquefied gas or water or a mixture thereof at a relatively low supply pressure, for example in the range from 4 to 40 bar, preferably in the range from 6 to 15 bar, for example about 8 bar. Liquefied gas or water flows into the liquid inlet chamber 56 and when spraying, pressurized control oil is admitted to the control oil inlet 57, flows into the actuation chamber 58 and acts on the end surface of the actuation piston 59. The actuation piston acts on a hydraulically actuated plunger 62 to pressurize and/or liquefy gas fuel in the liquid inlet chamber 56. The hydraulically actuated plunger 56 can be a separate member that abuts the actuation piston 59, or the hydraulically actuated plunger 56 can be integral with the actuation piston 59. When the pressure in the liquid inlet chamber 56 increases above the opening pressure of the liquefied gas fuel injector, the valve member 60, which is axially movable in the bore of the valve guide 61, moves away from its valve seat and liquefied gas or water is injected into the combustion chamber.

The sealing oil ensures that water cannot damage the

valve members

60 and 61. Water is supplied to the liquefied gas fuel injectors 14 when required. Preferably the liquid is delivered as in fig. 2, where water is fed to the feed pump unit 25 and delivered to all cylinders in a common flow through the liquefied gas feed line 24, but it is also possible to feed water individually to the delivery injectors by extending the water feed line 37 to the cylinders and providing a water branch line to the liquefied gas fuel injectors on a single cylinder or providing a water branch line to a single liquefied gas fuel injector. In these embodiments, the water supply means includes a water supply line and a water branch line and a water control valve. The single water branch line may include a water control valve and be connected with the branch line of the liquefied gas supply line 24 so that water can be supplied to the injectors via the branch line of the liquefied gas supply line 24, or the water branch line may directly extend to the single liquefied gas fuel injectors, and the water branch line may be provided with a water control valve. In the case where the water branch line extends directly to a single liquefied gas fuel injector, the liquefied gas fuel injector may be provided with a separate liquid inlet port for water, which connects the liquid inlet chamber 56 via a flow passage.

The details of the described embodiments can be combined in other embodiments within the scope of the claims.

Claims

1. A two-stroke crosshead internal combustion engine comprising a fuel and water supply system (18) and cylinders, a single cylinder (7) having at least a combustion chamber (13), a piston (9), an exhaust valve (6) at the upper end of the cylinder, a scavenge air port (8) in the lower end region of the cylinder, and valves for injecting fuel and water directly into the combustion chamber, characterised in that,

the valve on the single cylinder (7) for direct injection of fuel and water comprises at least one set of liquefied gas fuel injectors (14) and oil fuel injectors (15), the fuel supply system comprising an oil supply system (16) connected with the oil fuel injectors and a liquefied gas supply system (17) connected with the liquefied gas fuel injectors, the water supply system (18) comprising a water supply device connected with the liquefied gas supply system (17) or directly connected with the liquefied gas fuel injectors (14), the liquefied gas fuel injectors (14) being adapted to be supplied with water at a preset feed pressure to the liquid inlet chamber (56), and the liquefied gas fuel injectors (14) comprising hydraulically actuated plungers (62) adapted to pressurize the liquid water in the liquid inlet chamber to an injection opening pressure, so that water can be injected into the combustion chamber through the liquefied gas fuel injectors in the absence of liquefied gas fuel .

2. The internal combustion engine according to claim 1,

the valves on the single cylinder (7) for direct injection of fuel and water comprise two groups of liquefied gas fuel injectors (14) and oil fuel injectors (15).

3. The internal combustion engine according to claim 2,

the exhaust valve (6) is centrally located at the top of the cylinder between the two sets of liquefied gas fuel injectors (14) and oil fuel injectors (15).

4. The internal combustion engine according to claim 1,

the liquefied gas fuel injector (14) comprises an injector housing having a valve guide (61) and a valve member (60) displaceable within a bore of the valve guide (61), the internal combustion engine comprises a sealing oil system (30) for supplying sealing oil to the liquefied gas fuel injector, and the liquefied gas fuel injector (14) has a sealing oil passage extending from an inlet (52) for sealing oil to the bore in the valve guide (61).

5. The internal combustion engine according to claim 4,

the sealing oil system (30) is adapted to deliver sealing oil at a predetermined sealing oil pressure, and the water supply system is adapted to deliver water at a pressure lower than the predetermined sealing oil pressure.

6. The internal combustion engine according to any one of claims 1 to 5,

the injection pressure of the liquefied gas fuel injector (14) is set to an injection opening pressure of at least 350 bar, preferably at least 500 bar.

7. The internal combustion engine according to claim 6,

the liquefied gas fuel injector (14) is adapted to be supplied with liquefied gas fuel at a preset feed pressure to the liquid inlet chamber (56), and the hydraulically actuated plunger (62) is further adapted to pressurise the liquefied gas fuel in the liquid inlet chamber to an injection opening pressure.

8. The internal combustion engine according to any one of claims 1 to 5,

the liquefied gas fuel injector (14) is adapted to be supplied with liquefied gas fuel at a preset feed pressure to the liquid inlet chamber (56), and the hydraulically actuated plunger (62) is further adapted to pressurize the liquefied gas fuel in the liquid inlet chamber to an injection opening pressure.

9. A method for injecting fuel and water directly into the combustion chamber of a cylinder of a two-stroke crosshead internal combustion engine, wherein the engine comprises a fuel supply system and a water supply system (18) and cylinders, and a single cylinder (7) having at least a combustion chamber (13), a piston (9), an exhaust valve (6) at the upper end of the cylinder, a scavenge air port (8) in the lower end region of the cylinder and injecting fuel and water directly into the combustion chamber, characterized in that,

for direct injection into the combustion chamber, the fuel supply system supplies at least one set of liquefied gas fuel injectors (14) and oil fuel injectors (15) with liquefied gas fuel from a liquefied gas supply system (17) to the liquefied gas fuel injectors and oil fuel from an oil supply system (16) to the oil fuel injectors, the water supply system (18) supplies water to the liquefied gas supply system (17) via a water supply device and/or directly to the liquefied gas fuel injectors (14), the liquefied gas fuel injectors (14) being supplied with water to a liquid inlet chamber (56) at a preset feed pressure, and the liquefied gas fuel injector (14) includes a hydraulically actuated plunger (62), the hydraulically actuated plunger causes liquid water in the liquid inlet chamber to be pressurized to a spray opening pressure, so that water can be injected into the combustion chamber through the liquefied gas fuel injector without liquefied gas fuel.

10. The method of claim 9,

terminating injection of water from the liquefied gas fuel injector (14) prior to termination of the fuel injection during a combustion stroke of a two-stroke cycle.

11. The method of claim 9,

in a two-stroke cycle, water injection from the liquefied gas fuel injector (14) is commenced before the fuel injection commences.

12. The method of claim 9,

the injection of water by the liquefied gas fuel injector (14) occurs simultaneously with the injection of fuel during the combustion stroke of the two-stroke cycle.

13. The method of claim 9,

the internal combustion engine has at least a first and a second operating mode, wherein in the first operating mode the liquefied gas supply system (17) supplies liquefied gas fuel and the oil supply system (16) supplies fuel oil; in the second mode of operation, the liquefied gas supply system (17) supplies water and the oil supply system (16) supplies low-sulphur fuel oil.

14. The method according to any one of claims 9 to 13,

the liquefied gas supply system (17) supplies liquefied gas fuel at a preset feed pressure of at most 25 bar, and the water supply system (18) supplies water at a preset feed pressure of at most 25 bar.

15. The method according to any one of claims 9 to 13,

the water supply system (18) supplies water to the liquefied gas supply system (17), and the liquefied gas supply system supplies methanol and water to the liquefied gas fuel injectors (14).

16. The method of claim 14,

the liquefied gas fuel injector (14) operates with an injection opening pressure of at least 500 bar.