DK179162B1

DK179162B1 - An internal combustion engine of two-stroke crosshead type, and a method of direct injection of fuel and water into a combustion chamber

Info

Publication number: DK179162B1
Application number: DKPA201670287A
Authority: DK
Inventors: Stefan Mayer; Johan Sjöholm; Niels Kjemtrup
Original assignee: Man Diesel & Turbo Filial Af Man Diesel & Turbo Se Tyskland
Priority date: 2016-05-02
Filing date: 2016-05-02
Publication date: 2017-12-18
Also published as: CN107448284B; KR102105635B1; CN107448284A; JP2017207062A; JP6657138B2; KR20170124466A; DK201670287A1

Abstract

An internal combustion engine (1) of two-stroke crosshead type comprises an oil supply system (16), a liquid gas supply system (17), and a water supply system (18). The individual cylinder (7) has an exhaust valve (6) at an upper end, and scavenge air ports (8) at a lower end area. The individual cylinder (7) further has at least one set of a liquid gas fuel injector (14) and an oil fuel injector (15) for direct injection. A water supply system (18) supplies water to the liquid gas supply system and/or directly to the liquid gas fuel injector.

Description

The present invention relates to an internal combustion engine of two-stroke crosshead type, comprising a fuel supply system and a water supply system and cylinders, the individual cylinder having at least a combustion chamber, a piston, an exhaust valve at an upper end of the cylinder, scavenge air ports at a lower end area of the cylinder and valves for direct injection of fuel and water into the combustion chamber. The preset invention also relates to a method of direct injection of fuel and water into a combustion chamber of a cylinder in an internal combustion engine of two-stroke crosshead type.

The two-stroke crosshead type of engine with an exhaust valve at the upper end of the cylinder and scavenge air ports at a lower end area of the cylinder is uniflow scavenged. During scavenging of the cylinder, following the combustion, the exhaust valve is open and compressed scavenge air flows into the cylinder through the scavenge air ports and up towards the exhaust valve in a swirling motion, while combustion gas flows out through the exhaust valve. In this manner the cylinder is filled with air from the bottom and upwards in a one directional flow (uniflow), in contrast to engines where both the air intake port and the exhaust port are located at the top of the cylinder.

The two-stroke crosshead type of engine has a ratio between stroke S and bore B, S/B, in the range from 3.2 to 4.9 and this ratio is very different from the stroke to bore ratios seen in four-stroke engines where S/B is in the range from 0.8 to 1.3, typically about 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 the two-stroke crosshead type of engine. The two-stroke crosshead type of engine is furthermore a slow running engine with operating speeds at 100% engine load in the range from 55 rpm to 200 rpm. The individual combustion process in the combustion chamber of a two-stroke crosshead type of engine thus takes long time and extends to areas at large distances from the injectors, when compared to other types of internal combustion engines.

An engine of the initially mentioned type is described in EP 0 967 371 A1 (corresponding to JP 2000-54843 A). The cylinder is provid- ed with a separate water injector for spraying water into the cylinder during the compression stroke in order to reduce the temperature level in the cylinder. The water injection is controlled to take place early in the compression stroke, such as immediately after closing of the exhaust valve. At this point in the two-stroke cycle, the pressure in the cylinder is low, and thus the water injection can be effected at a low pressure, such as 25 bar.

An object of the present invention is to allow injection of water at the end of the compression stroke or in the combustion stroke of the two-stroke cycle with a simple design and while injection of fuel without water occurs.

In view of this, the initially mentioned internal combustion engine of the two-stroke crosshead type according to the present invention is characterized in that the valves for direct injection of fuel and water on said individual cylinder comprise at least one set of a liquid gas fuel injector and an oil fuel injector, that the fuel supply system comprises an oil supply system connected with the oil fuel injector and a liquid gas supply system connected with the liquid gas fuel injector, and that the water supply system comprises a water supply device connected with the liquid gas supply system or directly with the liquid gas fuel injector.

The liquid gas fuel injector is adapted to inject liquid at high pressure and has an atomizer sized to inject liquid gas fuel into the combustion chamber. The supply of water from the water supply device to the liquid gas fuel injector causes the water to be injected into the combustion chamber and mounting of a separate water injector is avoided. During the combustion stroke in the two-stroke cycle, the piston moves towards the bottom-dead-centre position, in which the piston is located at least three times its piston diameter away from the liquid gas fuel injector. As the combustion process progresses, the combustion chamber becomes more and more elongate and the flame front can be located far from the injector. It is possible to inject water without liquid gas fuel through the liquid gas fuel injector and yet ensure proper combustion, because the injection of oil by the oil fuel injector can maintain the combustion process, while the water is injected via the liquid gas fuel injector. The water can be supplied directly to the liquid gas fuel injector, however it is preferred to supply the water to the liquid gas fuel injector via the liquid gas supply system so that a separate supply port on this injector and internal flow passages in this injector are avoided. When the water is supplied to the liquid gas supply system, the water flows along the same flow path as liquid gas fuel to the liquid gas fuel injector, and the water is injected in the same manner as the liquid gas fuel into the combustion chamber.

In an embodiment the valves for direct injection of fuel and water on said individual cylinder comprise two sets of the liquid gas fuel injector and the oil fuel injector. By having two sets, two liquid gas fuel injectors can be utilized for water injection, and this provides the possibility to inject a certain volume of water faster into the combustion chamber when water is supplied simultaneously to both liquid gas fuel injectors, or to supply only one of the liquid gas fuel injectors at a time with water, and then alternate the water supply between one and the other of the two liquid gas fuel injectors and in this manner shift between injection positions tor water into the combustion chamber, for example in order to improve the combustion process. In another embodiment said individual cylinder comprise three sets of the liquid gas fuel injector and the oil fuel injector, and in a further embodiment said individual cylinder comprise only a single set of the liquid gas fuel injector and the oil fuel injector.

In a preferred embodiment the exhaust valve is located centrally at the top of the cylinder in between the two sets of the liquid gas fuel injector and the oil fuel injector. Even though the exhaust valve may alternatively be located to one side on top of the cylinder, the central location is preferred because it permits each set of the liquid gas fuel injector and the oil fuel injector to be located to the side so that the atomizer sprays from the injection nozzle can be directed towards the centre of the cylinder with a larger distance to the opposite inner wall of the cylinder.

In an embodiment the liquid gas fuel injector comprises an injector housing with a valve guide and a valve member displaceable in a bore in the valve guide, and the internal combustion engine comprises a sealing oil system for supplying sealing oil to the liquid gas fuel injector, and the liquid gas fuel injector has a sealing oil passage extending from an inlet for sealing oil to the bore in the valve guide. The sealing oil serves to prevent leakage of liquid gas fuel when that is injected, however when water is injected through the liquid gas fuel injector the sealing oil also acts as a lubricant between the valve member and the bore in the valve guide and prevents the water from damaging the injector parts. As an alternative to the use of sealing oil as lubricant, the valve parts may be manufactured of materials capable of acting under influence of water, such as a PTFE coated steel body or a ceramics 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 lower than the predetermined sealing oil pressure. As the sealing oil pressure is higher than the water pressure, the sealing oil will tend to press out any water that may have penetrated into the oil-filled clearance between the valve member and the bore in the valve guide.

In one embodiment the injection pressure of the liquid gas fuel injector is set to an injection opening pressure of at least 350 bar, which is much higher than the maximum compression pressure prevailing in the combustion chamber just before combustion is initiated. Preferably, the injection pressure of the liquid gas fuel injector is set to an injection opening pressure of at least 500 bar, which is considerably higher than the maximum pressure in the combustion chamber during the two-stroke cycle, so that a very fine atomization of water is achieved. It is alternatively possible to use an injection opening pressure of less than 350 bar.

It is possible to pressurize the water and/or the liquid gas fuel in the liquid gas supply system to a pressure higher than the injection opening pressure, and then use a simple control valve to open and close for supply to the liquid gas fuel injector. However, it is preferred that the liquid gas fuel injector is adapted to be supplied with liquid gas fuel and/or water at a preset feeding pressure to an inlet chamber, and that the liquid gas fuel injector comprises a hydraulically activated plunger adapted to pressurize the liquid gas fuel and/or water in the inlet chamber to injection opening pressure. In this manner the preset feeding pressure can be conveniently low, such as a pressure in the range from 5 to 30 bar, in the liquid gas supply system, and the plunger can then be supplied with control oil at a high pressure, such as a pressure 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 liquid gas fuel injector.

In another aspect, the present invention relates to a method of direct injection of fuel and water into a combustion chamber of a cylinder in an internal combustion engine of two-stroke crosshead type, which engine comprises a fuel supply system and a water supply system and cylinders, the individual cylinder having at least a combustion chamber, a piston, an exhaust valve at an upper end of the cylinder, scavenge air ports at a lower end area of the cylinder and direct injection of fuel and water into the combustion chamber. According to the present invention this method is characterized in that for direct injection into the combustion chamber the fuel supply system supplies at least one set of a liquid gas fuel injector and an oil fuel injector with liquid gas fuel to the liquid gas fuel injector from a liquid gas supply system and with oil fuel to the oil fuel injector from an oil supply system, and that the water supply system via a water supply device supplies water to the liquid gas supply system and/or directly to the liquid gas fuel injector. The method provides the effects and advantages mentioned in the above description in relation to the internal combustion engine.

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

It is possible in the two-stroke cycle that water injection from the liquid gas fuel injector is initiated before the fuel injection is initiated. In this case water may be injected in the final part of the compression stroke in order to lower the temperature of the hot compressed air.

It is possible, during the combustion stroke of the two-stroke cycle that water injection from the liquid gas fuel injector occurs simultaneously with the fuel injection, and thus water may act to lower the flame temperature. It is furthermore possible to add the water to the liquid gas fuel and supply the mixture to the liquid gas fuel injector and inject both simultaneously into the combustion chamber.

In an embodiment the internal combustion engine has at least a first operating mode and a second operation mode, wherein the liquid gas supply system supplies liquid gas fuel and the oil supply system supplies fuel oil in the first operating mode, and the liquid gas supply system supplies water and the oil supply system supplies low sulphur fuel oil in the second operating mode. The second operating mode allows combustion of low sulphur fuel oil under conditions where the flame temperature has been lowered by water injection, and the first operating mode allows operation of the engine without consuming the more expensive low sulphur fuel oil because the fuel oil may have a higher content of sulphur, such as a heavy fuel oil. In the present context, a low sulphur fuel oil is to be understood as a fuel oil having a sulphur content of less than 0.1% by weight. The internal combustion engine may further or alternatively have another operating mode in which the liquid gas supply system supplies a mixture of liquid gas fuel and 8water, and the oil supply system supplies fuel oil.

In order to facilitate the design of the fuel and water supply systems it is preferred that the liquid gas supply system supplies liquid gas fuel at a preset feeding pressure of at the most 25 bar, and that the water supply system supplies water at a preset feeding pressure of at the most 25 bar. The preset feeding pressure may for example be a pressure in the range from 6 bar to 10 bar.

It is preferred that the water supply system supplies water to the liquid gas supply system, and that the liquid gas supply system supplies methanol and water to the liquid gas fuel injector. Methanol may be provided as a liquid gas fuel, and water blends well with methanol without any special precautions or any special equipment. All that is required is that water is added to the methanol and then the two automatically blend.

Preferably, the liquid gas fuel injector operates with an injection opening pressure of at least 500 bar, such as an injection opening pressure of at least 550 bar. The high opening pressure ensures an atomization as a fine mist into the combustion chamber.

In the following, examples of embodiments of the present invention are described in further detail with reference to the highly schematic drawings, on which

Fig. 1 illustrates an upper part of an internal combustion engine according to the present invention, illustrating air and gas flow through a cylinder,

Fig. 2 illustrates an outline of the engine in Fig. 1,

Fig. 3 illustrates a fuel supply to a cylinder of the engine in Fig. 2, and

Fig. 4 illustrates in more detail a side view of a liquid gas injector of a cylinder of the engine in Fig. 2,

An internal combustion engine of two-stroke crosshead type is generally designated 1 in Fig. 1. The internal combustion engine is a uniflow engine, which will be briefly explained in the following. A turbocharger generally designated 2 has a compressor part supplying compressed inlet and scavenge air to a scavenge air receiver 3 via a scavenge air cooler 4 and a water mist catcher 5, as illustrated by white arrows. An exhaust valve 6 is mounted at an upper end of a cylinder 7. Scavenge air ports 8 are located in a lower end area of cylinder 7 as a circumferentially distributed row of openings through the cylinder wall. A piston 9 is displaceable in the length direction of the cylinder between a top dead centre (TDC) position and a bottom dead centre (BDC) position. In the BDC position illustrated in Fig. 1 the piston is located just below the scavenge air ports 8, and the scavenge air ports are open and inflow of intake and scavenge air into the cylinder can take place. When the piston has been moved upwards past the scavenge air ports, these ports are closed. It is thus the piston that acts to open and close for the scavenge air ports. When the exhaust valve 6 is open, exhaust gasses and scavenge air may flow out from the cylinder via an exhaust passage and into an exhaust gas receiver 10. In the one-directional (uniflow) motion upwards through the cylinder the inlet and scavenge air flow in a swirling motion up towards the upper portion of the cylinder, while at the same time pressing out combustion gasses via the open exhaust valve. The exhaust gas flows from the exhaust gas receiver 10 to the turbine part of the turbocharger, as illustrated by black arrows in Fig. 1. There is a single exhaust valve 6 mounted at the top of the cylinder coaxial with the longitudinal centre axis of the cylinder. The exhaust valve is actuated to open and close by a hydraulic actuator in an exhaust valve housing mounted on top of the cylinder.

The piston is mounted on a piston rod 11 which extends along the longitudinal axis of the cylinder from the piston to a crosshead (not illustrated) via a piston rod stuffing box fixed in an intermediate bottom of an engine frame 12. The crosshead is also connected to a crankshaft via a connecting rod. The crosshead construction makes the piston rod move up and down in line with the longitudinal centre axis of cylinder 7 and makes it possible for the cylinder to have a long length in relation to its diameter. The internal combustion engine 1 of two-stroke crosshead type has a ratio between stroke and bore in the range from 3.2 to 4.9. The piston consequently moves along a distance from the TDC to the BDC position that is longer than 3 times its diameter, and at the same time a combustion chamber 13 in the cylinder above the piston changes shape into a more and more elongate chamber. The fuel injection occurs in the upper end of the combustion chamber, and for the uniflow scavenged two-stroke crosshead internal combustion engine, combustion conditions are very different from combustion conditions in four-stroke engines, in which injection and combustion takes place more or less at the same location and an interruption in injection of fuel can be remedied just by reintroducing fuel injection.

The internal combustion engine according to the present invention is a piston engine, and preferably an engine having from 4 to 14 cylinders arranged in-line. The engine can e.g. be of the make MAN Die- sel & Turbo and the type ΜΕ-GI, or of the make Wårtsilå, or of the make Mitsubishi. The cylinders can have a bore in the range of e.g. 30 to 110 cm, preferably from 35 to 95 cm. The two-stroke crosshead internal combustion engines can be used as main propulsion engine in a ship or as a prime mover in a stationary power station where the engine drives a generator providing a grid with power. The internal combustion engine according to the present invention typically has a speed indicated as rpm in the range from 55 to 200 rpm.

The engine has an injection system with valves for injecting fuel directly into the combustion chamber. These valves comprises on every cylinder 7 a first set of one liquid gas fuel injector 14 and one oil fuel injector 15, and a second set of one liquid gas fuel injector 14 and one oil fuel injector 15. One of the engine cylinders seen from above is illustrated in Fig. 3, and only the injectors and their supply lines are illustrated, but not the exhaust valve, however the exhaust valve is located in between the two sets of injectors at the centre of the cylinder.

The engine has a fuel supply system comprising an oil supply system generally denoted 16, and a liquid gas supply system generally denoted 17. The engine further has a water supply system generally denoted 18. These three systems are illustrated in Fig. 2, showing a side view of the engine with a turning wheel 19 to the left and an end of the crank shaft 20 to the right and six cylinders 7 arranged in a single line on the engine frame 12.

The oil supply system 16 comprises at least one fuel oil source 21, which receives oil from one or more oil storage tanks via a pump. The fuel oil source includes a supply pump, and an oil supply line 22 extending to the individual cylinders 7 on the engine. The engine can have more than one fuel oil source with associated tanks, pumps and supply lines, arranged in parallel, when the oil supply system should supply more than one type of oil to the oil fuel injectors. One type could be diesel oil having a typical density of 840 kg/m3 and another type could be heavy fuel oil having a typical density of 982 kg/m3.

The liquid gas supply system 17 comprises at least one liquid gas source 23, which receives liquid gas from one or more liquid gas storage tanks via a pump. As examples, the liquid gas fuel can be methanol, CH3OH, having a vapour pressure of 0.13 bar at a temperature of 20°C, or Liquid Petroleum Gas, LPG, typically propane and/or butane or mixtures thereof. The liquid gas source includes a liquid gas supply line 24 extending to the individual cylinders 7 on the engine and a supply pump unit 25. The liquid gas source and the supply pump unit are located outside the engine room, such as located above a weather deck 26 on a ship in case the engine is installed as a main engine for driving a propeller on the ship, or outside the walls of a building in case the engine is stationary and installed as a prime mover driving a generator in a power station. Any gas leakage from the liquid gas supply will thus not enter the engine room. From its point of entry into the engine room, liquid gas supply line 24 is enclosed in an outer pipe system 27 surrounding the liquid gas supply line, and an annular space between the two pipes is used for ventilating air through the annular space and for monitoring for gas leaks from the inner pipe, which is the liquid gas supply line. The liquid supply system also includes a purge return system 28 with a return line 29, likewise enclosed in the outer pipe system until it passes through weather deck 26. Return line 29 extends to the liquid gas source 23 and can return liquid gas thereto. Under certain conditions, such as detection of a gas leakage or a need for stopping the engine, the liquid gas supply line will have to be emptied and purged with nitrogen supplied by the purge return system 28. After the liquid gas has been returned to the liquid gas source 23, full purging with nitrogen is conducted by ventilating nitrogen through the double-walled piping system.

Due to the use of liquid gas as fuel, the engine further comprises a sealing oil system 30 comprising a sealing oil source 31, including a sealing oil tank and a sealing oil pump, and a sealing oil supply line 32 extending to the individual liquid gas fuel injector on each cylinder 7. The engine also comprises a control oil system 33 comprising a control oil source 34, including a control oil tank and a control oil pump, and a control oil supply line 35 extending to the individual liquid gas fuel injector on each cylinder 7.

The water supply system 18 comprises a water source 36, such as a tank with a water pump or a general fresh water supply of pressurized water, and a water supply line 37 extending to supply pump unit 25 in the liquid gas supply system 17. A water control valve 38 in water supply line 37 can open and close for delivery of water to the supply pump unit, and a liquid gas control valve 39 located in the liquid gas supply line 24 upstream of the connection of the water supply line to the liquid gas supply line, upstream meaning between this connection and the liquid gas source 23. Water control valve 38 and liquid 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 water control valve 38 is closed and liquid gas control valve 39 is open, liquid gas is supplied to the engine via liquid gas supply line 24. When water control valve 38 is open and liquid gas control valve 39 is closed, water is supplied to the engine via liquid gas supply line 24. When water control valve 38 open, either fully or partly, such as opened to 30% or 50% or 80% of the full flow capacity of the valve, and liquid gas control valve 39 is open, a mixture of water and liquid gas is supplied to the engine via liquid gas supply line 24. The valves can be controlled to deliver any mixture of water and liquid gas in the range of from less than 100% liquid gas and more than 0% water to more than 0% liquid gas and less than 1 00% water.

Fig. 3 illustrates in more detail the liquid supply of liquid fuel or water to the liquid gas fuel injectors 14 and the oil fuel injectors 15 on cylinder 7. In the engine room, the liquid gas supply line 24 is enclosed in outer pipe system 27, which is provided with an air intake system and a purge gas system supplying inert gas, such as nitrogen. The air intake system ventilates inside the outer pipe system 27. Air intake takes place at 42, and when the system is operating normally, air outlet takes place at 43. A pair of hydrocarbon detectors 44 is placed downstream of the engine in the conduit leading to air outlet 43. A source of pressurized purge gas is connectable to the outer pipe system and to liquid gas supply line 24, and at shutdown of the engine the inert gas is supplied to the liquid gas supply line for purging the same for gas.

Fuel oil source 21 supplies oil fuel to oil fuel injectors 15 on each cylinder 7 of the internal combustion engine. The oil fuel is supplied to an oil fuel pump 45, which is an electronically controlled and hydraulically driven pump that delivers oil fuel to the oil fuel injectors 15 when an injection sequence is to occur, and the delivery pressure from the oil fuel pump exceeds the opening pressure of the oil fuel injectors and may be in the range from 400 bar to 800 bar.

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

Liquid gas fuel injectors 14 on each cylinder are supplied with control oil from a control oil source 34 having a control oil pump delivering control oil at a pressure in the range from 250 to 500 bar, such as a control oil pressure of about 300 bar. Liquid gas flows from liquid gas supply line 24 to an accumulator 46, and a liquid gas control valve 47 opens for liquid gas to liquid gas fuel injectors 14 when liquid gas injection is to take place.

Liquid gas fuel injector 14 and oil fuel injector 15 are arranged as a set on the cylinder, and they can for instance be mounted in a cylinder cover mounted on top of a cylinder liner. The cylinder has in the illustrated embodiment two sets of one liquid gas fuel injector 14 and one oil fuel injector 15, and the two sets are arranged on opposite sides of the exhaust valve (not shown in Fig. 3). The two injectors in each set are located closer to each other than the location of the one set of injectors in relation to the other set of injectors.

The liquid gas fuel injector 14 is able to inject both liquid gas and water, separately or as a mixture. An illustration of the main parts of the liquid gas fuel injector 14 is presented in Fig. 4. The liquid gas fuel injector 14 is mounted in a bore in cylinder 7, such as in the cylinder cover, and the inner end of the injector is positioned inside the combustion chamber 13 and includes an injection nozzle 48 with several atomizing bores 49 through which the liquid gas fuel or the water, or mixtures thereof, is injected into the combustion chamber as atomized mists.

The liquid gas fuel injector 14 has different zones that are independently sealed off from one another by annular sealing rings 50. The individual sealing ring 50 seals between the outer surface of the liquid gas fuel injector 14 and the inner surface of the bore in cylinder 7. In an uppermost area there is a general drain 51 in the cylinder allowing drainage of anything flowing into this area. An inlet opening 52 for sealing oil is present between the second and the third sealing ring 50. An outlet opening 53 for sealing oil is present between the third sealing ring and the fourth sealing ring 50. A liquid inlet opening 54 for liquid gas or water or a mixture thereof is present between the fourth and the fifth sealing ring 50. A flow passage connects liquid inlet opening 54 with a liquid inlet chamber 56. A lower area 55 between the fifth sealing ring and a sixth sealing ring is connected to and ventilated by the air intake at 42 and the air flows to air outlet 43 and is checked for presence of hydrocarbons.

The liquid gas fuel injector 14 is supplied with liquid gas or water or a mixture thereof at a relatively low supply pressure, such as a pressure in the range from 4 to 40 bar, preferably a pressure in the range from 6 to 15 bar, such as about 8 bar. The liquid gas or water flows into liquid inlet chamber 56 and when injection is to be performed, pressurized control oil is admitted to a control oil inlet 57 and flows into an actuator chamber 58 and act on the end surface of an actuator piston 59. The actuator piston then increases the pressure in the liquid inlet chamber 56 to above the opening pressure of the liquid gas fuel injector and a valve member 60 axially displaceable in a bore in a valve guide 61 is displaced away from its valve seat and the liquid gas or water is injected into the combustion chamber.

The sealing oil ensures that water cannot damage valve members 60 and 61. Water is supplied to the liquid gas fuel injectors 14 when desired. It is preferred that the water is delivered as illustrated in Fig. 2, where water is supplied to supply pump unit 25 and delivered to all cylinders in a common flow through liquid gas supply line 24, but it is also possible to supply the water individually to the injectors by extend ing water supply line 37 to the cylinders and provide a water branch line to the liquid gas fuel injectors on the individual cylinder, or provide a water branch line to the individual liquid gas fuel injector. The individual water branch line may include a control valve connected with a branch line of liquid gas supply line 24 so that water can be supplied to the injector via that branch of liquid gas supply line 24, or the water branch line can extend directly to the individual liquid gas fuel injector and the branch may be provided with a control valve. In case the water branch line extends directly to the individual liquid gas fuel injector, the liquid gas fuel injector may be provided with a separate liquid inlet opening for water, which via a flow passage is connected with liquid inlet chamber 56.

Details of the various embodiments described can be combined into further embodiments within the scope of the claims.

Claims

A two-stroke intersection type internal combustion engine, comprising a fuel supply system and a water supply system (18) and cylinders, each cylinder (7) having at least one combustion chamber (13), a piston (9), an exhaust valve (6) at the cylinder upper end, flushing ports (8) at a lower end region of the cylinder and valves for direct injection of fuel and water into the combustion chamber, characterized in that the valves for direct injection of fuel and water on each cylinder (7) comprise at least one set of a liquid-gas fuel injection valve (14) and an oil fuel injection valve (15), the fuel supply system comprising an oil supply system (16) connected to the oil fuel injection valve and a liquid-gas supply system ) comprises a water supply device associated with liquid the gas supply system (17) or directly to the liquid-gas fuel injection valve (14).

Combustion engine according to claim 1, characterized in that the valves for direct injection of fuel and water on the individual cylinder (7) comprise two sets of liquid-gas fuel injection valve (14) and the oil fuel injection valve (15).

Combustion engine according to claim 2, characterized in that the exhaust valve (6) is located centrally at the top of the cylinder between the two sets of liquid-gas fuel injection valve (14) and the oil fuel injection valve (15).

Combustion engine according to one or more of claims 1 to 3, characterized in that the liquid-gas fuel injection valve (14) comprises a valve housing with a valve guide (61) and a valve body (60) slidable in a bore in the valve guide, the internal combustion engine comprises a barrier oil system (30) for supplying barrier oil to the liquid-gas fuel injection valve, and the liquid-gas fuel injection valve (14) has a barrier oil passage extending from a barrier oil approach (52) to the bore oil valve.

Combustion engine according to claim 4, characterized in that the barrier oil system (30) is arranged to supply barrier oil at a predetermined barrier oil pressure and that the water supply system (18) is adapted to supply water at a lower pressure than the predetermined barrier oil pressure.

Internal combustion engine according to one or more of claims 1 to 5, characterized in that the injection gas pressure of the liquid-gas fuel injection valve (14) is set to an injection opening pressure of at least 350 bar, preferably at least 500 bar.

Combustion engine according to one or more of claims 1-6, characterized in that the liquid-gas fuel injection valve (14) is adapted to supply liquid-gas fuel and / or water at a predetermined feed pressure to a liquid supply chamber (56). the fuel injection valve (14) comprises a hydraulically actuated drive piston adapted to pressurize liquid-gas fueled and / or the water in the fluid inlet chamber to the injection opening pressure.

A method of directly injecting fuel and water into a combustion chamber of a cylinder of a two-stroke intersection type combustion engine, the engine comprising a fuel supply system and a water supply system (18) and cylinders wherein each cylinder (7) has at least one combustion chamber (13), a piston (9), an exhaust valve (6) at the upper end of the cylinder, flushing air ports (8) at a lower end region of the cylinder and direct injection of fuel and water into the combustion chamber, characterized by providing for direct injection into the combustion chamber. the fuel supply system at least one set of a liquid-gas fuel injection valve (14) and an oil-fuel injection valve (15) with liquid-gas from a liquid-gas supply system (17) for a liquid-gas fuel injection valve and an oil-fuel injection system and an oil fuel from an oil fuel; that water supply The system (18) supplies water to the liquid-gas supply system (17) and / or directly to the liquid-gas fuel injection valve (14) via a water supply device.

Method according to claim 8, characterized in that in the compression stroke of the two-stroke cycle the water injection from the liquid-gas fuel injection valve (14) is terminated before the fuel injection is terminated.

Process according to claim 8 or 9, characterized in that in the two-stroke cycle, the water injection from the liquid-gas fuel injection valve (14) is initiated before the fuel injection is initiated.

Method according to one or more of claims 8-10, characterized in that in the two-stroke compression stroke of the two-cycle water injection from the liquid-gas fuel injection valve (14) is performed simultaneously with the fuel injection.

Process according to one or more of claims 8 to 11, characterized in that the internal combustion engine has at least a first operating state and a second operating state, where the liquid-gas supply system (17) supplies liquid-gas fuel and the oil supply system (16) supplies fuel oil. in the first operating mode, and the liquid gas supply system (17) supplies water and the oil supply system (16) supplies low sulfur fuel oil in the second operating state.

Process according to one or more of claims 8-12, characterized in that the liquid-gas supply system (17) supplies liquid-gas fuel at a predetermined supply pressure of not more than 25 bar and the water supply system (18) supplies water at a predetermined supply pressure. at a maximum of 25 bar.

Process according to one or more of claims 8-13, characterized in that the water supply system (18) supplies water to the liquid-gas supply system (17) and the liquid-gas supply system supplies methanol and water to the fuel injection valve (14).

Method according to one or more of claims 8-13, characterized in that the fuel injection valve (14) in operation has an injection opening pressure of at least 500 bar.