Fuel injector for injecting fuel to combustion chamber of large engine and large engine

Abstract

To provide a fuel injector more securely and safely operable when using methanol as fuel of a large engine.SOLUTION: A fuel injector for injecting fuel into a combustion chamber of a large engine includes a nozzle holder 2 and a nozzle tip part 3 with at least one nozzle hole capable injecting fuel into the combustion chamber 100. The fuel injector further includes: a pressure chamber 4; at least one high-pressure fuel hole capable of introducing the fuel into the pressure chamber 4 with high pressure; and a needle valve 6 that opens / closes fluid connection between the pressure chamber 4 and the nozzle tip part 3, is energized by a spring 7 and interacts with a valve seat 8. A purge line 9 is disposed within the nozzle holder 2 to extend from the pressure chamber 4 to a discharge passage 20 configured to discharge fluid, and a purge valve 10 for opening / closing fluid communication through the purge line 9 is provided. The large engine including the fuel injector and a method for operating the large engine are proposed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fuel injector for injecting fuel into a combustion chamber of a large engine according to the preamble of the independent patent claim. Additionally, the present invention relates to a large engine having such a fuel injector. Furthermore, the present invention relates to a method for operating such a large engine. [Background technology]

[0002] Large engines can be configured as two-stroke or four-stroke engines, e.g., longitudinally scavenged two-stroke engines, and are often used as drive units for ships or stationary operation, e.g., for driving large generators for generating electrical energy. Engines typically operate continuously for significant periods, which places high demands on operational safety and availability. As a result, particularly long maintenance intervals, low wear and tear on the operating materials, and economical handling are central criteria for operators. Large engines typically have cylinders with an internal diameter (bore) of at least 200 mm. Currently, large engines with bores up to 980 mm or even larger are in use. In the context of this application, the term "large engine" refers to an internal combustion engine with a cylinder bore of at least 200 mm, preferably at least 300 mm.

[0003] Large engines are generally configured as large diesel engines operated on heavy fuel oil. From the perspectives of economical and efficient operation, compliance with exhaust gas regulations, sustainable reduction of CO2 emissions, and resource availability, alternatives to heavy fuel oil are also sought for large diesel engines. In this respect, both liquid fuels, i.e., fuels introduced into the combustion chamber in liquid form, and gaseous fuels, i.e., fuels introduced into the combustion chamber in gaseous form, are used.

[0004] Examples of liquid fuels known as substitutes for heavy oil include other heavy hydrocarbons, especially those left as residues in petroleum refining, alcohols, especially methanol or ethanol, ammonia, gasoline, diesel, or emulsions or suspensions. For example, the use of emulsions called MSAR (Multiphase Superfine Atomized Residue) as fuel is known. A well-known suspension is made of coal dust and water, which is also used as fuel in large engines. Known gaseous fuels include natural gas, such as LNG (liquefied natural gas), liquefied gases, such as LPG (liquefied petroleum gas), or ethane.

[0005] In particular, large diesel engines are known that can be operated on at least two different fuels, where the engine is operated on one fuel or the other depending on the operating conditions or environment. It is also known to inject two different fuels simultaneously into the combustion chambers of the cylinders.

[0006] A heavy-duty diesel engine that can run on two different fuels is called a dual-fuel heavy-duty diesel engine. Depending on the two fuels, the engine can be operated in liquid mode, where liquid fuel is introduced into the cylinder and burned, or in gas mode, where gas is introduced into the cylinder as fuel.

[0007] Heavy-duty diesel engines are capable of running on at least two or even more different liquid or gaseous fuels and often operate in different operating modes depending on the fuel being used at the time. In what is often referred to as diesel operation, fuel combustion generally occurs according to the principles of compression ignition or autoignition. In what is often referred to as Otto operation, combustion occurs via inductive ignition of a premixed, ignitable air-fuel mixture. This inductive ignition can occur via an electric spark, such as a spark plug, or via the autoignition of a small amount of injected fuel, which then triggers the inductive ignition of another fuel. A small amount of fuel intended for autoignition is either injected directly into the combustion chamber or into a pre-combustion chamber connected to the combustion chamber. The process of inductive ignition via the autoignition of a small amount of liquid autoignitable fuel or another autoignitable fuel is sometimes referred to as pilot injection.

[0008] Additionally, hybrid configurations are known that utilize both Otto and Diesel operation.

[0009] There is a strong need to reduce the use of fossil fuels, especially in light of climate change, CO2 reduction and sustainability. For this reason, even in large engines, alternatives are being considered to at least reduce or even completely avoid the use of fossil fuels. Even if this is still a long way off, partially replacing fossil fuels with renewable fuels would be considered a great success.

[0010] One alternative to fossil fuels is methanol, for example. However, renewable fuels such as methanol can cause corrosion problems in the fuel distribution and injection systems, especially when the engine is shut down or running on another fuel. Stagnant methanol can have a corrosive effect on the tubing or other components of the fuel injection system. Furthermore, there is a risk that methanol could leak from the engine, for example as vapor, into spaces accessible to engine maintenance or operating personnel. This is considered a health hazard requiring comprehensive mitigation measures. Therefore, it is necessary to ensure that residual methanol is removed from the injection system after running on methanol. Summary of the Invention [Problem to be solved by the invention]

[0011] This object is met by the present invention. It is therefore an object of the present invention to propose a fuel injector for injecting fuel into the combustion chamber of a large engine, which can operate more reliably and safely when methanol is used as fuel in the large engine. It is a further object of the present invention to propose a large engine comprising such a fuel injector. Additionally, it is an object of the present invention to propose a method for operating such a large engine. [Means for solving the problem]

[0012] The subject matter of the invention, which meets these objects, is characterized by the features of the independent patent claims.

[0013] Therefore, according to a first aspect of the present invention, there is proposed a fuel injector for injecting fuel into a combustion chamber of a large engine, comprising a nozzle retainer and a nozzle tip having at least one spray hole through which fuel can be injected into the combustion chamber, the fuel injector further comprising a pressure chamber, at least one high-pressure fuel duct through which fuel can be introduced into the pressure chamber at high pressure, and a spring-loaded needle valve interacting with a valve seat for opening and closing a fluid connection between the pressure chamber and the nozzle tip. A purge line is arranged in the nozzle retainer, the purge line extending from the pressure chamber to a discharge passage configured to discharge fluid from the nozzle retainer, and a purge valve configured to open and close fluid communication through the purge line, i.e., between the pressure chamber and the discharge passage.

[0014] The fuel injector is equipped with a purge line located inside the nozzle retainer, which connects the pressure chamber with a discharge passage. In purge mode, purge fluid can be supplied to and discharged from the pressure chamber through the purge line. This facilitates reliable removal of any fuel residue from the pressure chamber. Furthermore, since the purge line is located inside the nozzle retainer, the fuel injector has a very compact design. The structure in which the purge valve opens and closes the fluid communication makes it particularly easy to switch between an operating mode in which the purge valve is closed, in which the fuel injector injects fuel into the combustion chamber, and a purge mode in which the purge valve is open, in which the fuel injector and, in particular, the pressure chamber can be reliably purged of fuel residues.

[0015] According to a preferred configuration, at least one high-pressure fuel duct is connectable to a source of purge fluid so that purge fluid can be supplied to the high-pressure fuel duct, thereby purging the high-pressure fuel duct as well. The purge fluid enters the high-pressure fuel duct, flows through the high-pressure fuel duct, thereby purging the high-pressure fuel duct, enters the pressure chamber, and is then discharged through a purge line to a discharge passage.

[0016] Preferably, the purge valve is configured as a poppet valve, as this is a simple and reliable implementation of the purge valve.

[0017] Preferably, the purge valve further comprises a purge piston and a purge valve body biased by a purge spring, and a hydraulic line configured to supply hydraulic fluid to the purge piston. In this case, the purge valve is preferably hydraulically actuated. The purge valve can be actuated to open fluid communication through the purge line by providing hydraulic fluid to the purge piston at a pressure sufficiently high to open the purge valve against the spring force of the purge spring. When the hydraulic fluid pressure is released, the purge spring closes the purge valve, thereby closing fluid communication through the purge line. This facilitates reliable operation of the purge valve.

[0018] Because hydraulic fluid, e.g., system oil, is used in large engines in multiple locations and for multiple functions, hydraulic fluid is available in the large engine anyway, and therefore additional hydraulic fluid is not needed.

[0019] As a further preferred measure, the spring for biasing the needle valve is arranged in a spring chamber, and a lubrication pipe is provided for supplying lubricant to the spring chamber, so that the spring chamber can be filled with lubricant, thereby protecting the spring from the corrosive action of the fuel.

[0020] Additionally, the nozzle retainer includes a needle guide for receiving and guiding the needle valve, and the needle guide preferably extends from the spring chamber to the pressure chamber so that lubricant can enter the needle guide from the spring chamber. Allowing the lubricant to enter the needle guide provides very good lubrication for the needle valve. This is advantageous because methanol is a very low viscosity fluid and has very low tribological properties. The lubricant in the needle guide ensures safe and reliable operation of the needle valve.

[0021] It is preferred that the fuel injector be configured to receive lubricant as hydraulic fluid to operate the purge valve. When the purge valve needs to operate in purge mode, the lubricant pressure is switched to a higher level sufficient to open the purge valve. This has the advantage of utilizing the existing lubricant supply to operate the purge valve, eliminating the need for an additional supply line to the injector.

[0022] According to a preferred configuration, the needle guide includes an annular groove extending circumferentially around the needle valve. The annular groove is connected to a low-pressure fuel line that supplies fuel to the annular groove at low pressure, e.g., 13 bar (1.3 MPa). The annular groove filled with low-pressure fuel allows for separation and sealing between the fuel side in contact with the fuel and the lubrication side in contact with the lubricant. If lubricant is provided to the spring chamber at a pressure higher than the low fuel pressure in the annular groove, e.g., 13 bar (1.3 MPa), e.g., 16 bar (1.6 MPa), it is ensured that fuel cannot leak into the spring chamber, for example, along the needle guide or needle valve. As a result, no fuel is present in the spring chamber. In this way, the lubricant additionally acts as a sealing fluid.

[0023] Preferably, the discharge passage is connected to the low pressure fuel line, in which case the purge fluid is discharged to the low pressure fuel line and no separate return line for the purge fluid is required.

[0024] Preferably, the fuel injector is configured to receive fuel at a high pressure of at least 40 MPa, which is compatible with a typical "opening pressure" of a needle valve of 375 bar (37.5 MPa).

[0025] Most preferably, the fuel injector is configured to receive methanol as the fuel.

[0026] Regarding purging, it is preferable that the fuel injector be configured to receive water as a purging fluid. Alternatives to the purging fluid include nitrogen (gas) or diesel oil. However, with nitrogen gas or any other gas, it is difficult to reliably purge the upward-flowing tubes. If the tube cross section is too large, there is a risk that only gas bubbles will rise up the tube and the fuel will not properly exit. Regarding diesel oil as a purging fluid, the solubility of methanol in diesel oil is quite low, so the mixture of diesel oil and methanol is not homogeneous. If the mixture is recycled and then injected, there is a risk that the engine will sometimes run on diesel oil and then suddenly run on methanol. Because diesel oil has twice the energy density of methanol, combustion power operation may be difficult in this case. For these reasons, water is the preferred purging fluid.

[0027] Additionally, according to a second aspect of the present invention, there is proposed a large engine comprising at least one cylinder having a combustion chamber, in which a piston is arranged to reciprocate between top dead centre and bottom dead centre positions, the cylinder comprising a fuel injector according to the first aspect of the present invention.

[0028] According to a preferred embodiment, the large engine is configured as a longitudinally scavenged two-stroke large engine.

[0029] Furthermore, at least one cylinder is provided with a second fuel injector for injecting a second fuel into the combustion chamber, the second fuel preferably being different from the fuel mentioned above. Thus, the large engine is preferably configured to be able to operate on at least two different fuels.

[0030] The second fuel is preferably a diesel fuel that self-ignites in the combustion chamber, and therefore the large engine is preferably configured as a large diesel engine.

[0031] In the framework of this application, the term "heavy-duty diesel engine" refers to an engine that is capable of operating at least in diesel mode. In particular, the term "heavy-duty diesel engine" in this case also includes multi-fuel heavy-duty engines that are capable of operating in other modes in addition to diesel mode, such as Otto mode.

[0032] Additionally, according to a third aspect of the present invention, there is proposed a method of operating such a large engine according to the second aspect of the present invention, characterized by the step of temporarily opening a purge valve of a fuel injector of the large engine such that fluid communication is established between the pressure chamber and the discharge passage through a purge line.

[0033] Further advantageous measures and embodiments of the invention result from the dependent claims.

[0034] The invention will now be explained in more detail by way of examples and with reference to the drawings. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a cross-sectional view of an embodiment of a fuel injector according to the present invention, taken along an axial cross section; [Figure 2] 2 is a cross-sectional view of the fuel injector shown in FIG. 1 with the cutting plane rotated approximately 90 degrees. [Figure 3] FIG. 3 is an enlarged view of detail I of FIG. 2. [Figure 4] 1 is a schematic representation of a large engine. DETAILED DESCRIPTION OF THE INVENTION

[0036] Figure 1 shows a cross-sectional view of an embodiment of a fuel injector according to the invention, designated in its entirety by the reference numeral 1. The cross-section is along an axial direction A defined by the central axis of the fuel injector 1. Figure 2 shows the same embodiment of the fuel injector 1 in cross-section, the cutting plane being rotated by approximately 90° compared to the representation in Figure 1. For better understanding, Figure 3 shows an enlarged representation of detail I of Figure 2.

[0037] The fuel injector 1 is used to inject fuel into the combustion chamber 100 of a cylinder 110 of a large engine 200. Figure 4 shows a schematic representation of an embodiment of the large engine 200. Only one of the cylinders 110 of the large engine 200 is shown in Figure 4. Typically, the large engine 200 comprises multiple cylinders 110, for example up to 12 cylinders 110, or even more.

[0038] The term "large engine" refers to an internal combustion engine, such as those commonly used as drive units for ships or stationary operation, e.g., to drive large generators for producing electrical energy. Typically, the cylinders 110 of a large engine each have an internal diameter (bore) of at least about 200 mm. Such large engines 200 are known in the art in a variety of different configurations, e.g., as two-stroke or four-stroke engines.

[0039] In the following description, reference will be made to, by way of example, a large engine 200 configured as a longitudinally scavenged two-stroke large engine having a plurality of cylinders 110. Each cylinder 110 has a combustion chamber 100. Furthermore, a piston 120 is disposed within each cylinder 110 so as to reciprocate between top dead center and bottom dead center.

[0040] The term "longitudinal scavenging" means that scavenging or charge air is introduced into the cylinder 110 in the region of its lower end, and the exhaust valve 130 is located in or on the cylinder cover 140 located at the upper end of the cylinder 110.

[0041] In particular, it refers to a large, longitudinally scavenged, two-stroke engine capable of operating on different fuels, i.e., one fuel and a second fuel. Preferably, the large engine 200 is configured as a large diesel engine. The term "large diesel engine" refers to an engine that is capable of operating in at least a diesel mode of operation. In particular, the term "large diesel engine" in this case also includes a large engine 200 that is capable of operating in another mode in addition to the diesel mode of operation, such as an Otto mode of operation.

[0042] According to a preferred configuration, the large-sized engine 200 can be operated using methanol as fuel or a second fuel that is an auto-ignitable liquid. Thus, when the large-sized engine 200 is operated with the second fuel, the large-sized engine 200 is operated in liquid mode, in which only the liquid second fuel is injected into the combustion chamber 100 of the cylinder 110. Typically, the liquid fuel, such as heavy fuel oil (HFO), marine diesel oil (MDO), or marine gas oil (MGO), is injected directly into the combustion chamber 100 at the appropriate time, where it is ignited according to the principle of diesel auto-ignition. To inject the second fuel into the combustion chamber 100, each cylinder is provided with a second fuel injector 150 different from the fuel injector 1. In this case, each cylinder 110 is provided with at least one, preferably multiple, fuel injectors 1 for injecting fuel and at least one, preferably multiple, second fuel injectors 150 for injecting the second fuel.

[0043] The fuel injected into the combustion chamber 100 using the fuel injector 1 is, for example, a fuel for Otto operation, i.e., a fuel with inductive ignition of the fuel. The fuel is injected into the combustion chamber 100 to form an air-fuel mixture premixed with scavenging air. The air-fuel mixture is inductively ignited in the combustion chamber 100 according to the Otto principle. This inductive ignition is usually caused by introducing a small amount of a self-igniting second fuel (e.g., diesel or heavy fuel oil) into the combustion chamber 100 or into a pre-combustion chamber at the appropriate time, which then self-ignites and causes the inductive ignition of the air-fuel mixture in the combustion chamber 100.

[0044] The introduction of a small amount of a self-igniting second fuel, liquid or gaseous, into the combustion chamber 100 or into at least one pre-combustion chamber for the induction ignition of the fuel is also called pilot ignition. In addition to diesel oil, gases or alcohols such as methanol can also be used as pilot fluids for pilot ignition.

[0045] In other embodiments, inductive ignition is achieved by spark ignition, or laser pulses, or any other means suitable for igniting fuel within the combustion chamber 100.

[0046] In the following description, reference is made to a preferred embodiment in which the fuel is methanol and the second fuel is an auto-ignition diesel fuel, such as HFO, MDO, or MGO. With regard to the fuel methanol, operation on this fuel is preferably an operation according to the Otto principle.

[0047] Additionally, the heavy-duty diesel engine 200 can be operated in a mixed mode in which both the fuel and a secondary fuel are injected into the combustion chamber 100 of the cylinder 110. In mixed mode, both the combustion of the fuel and the combustion of the secondary fuel contribute to torque production.

[0048] In the embodiment described herein, the heavy-duty engine is configured as a longitudinally scavenged, dual-fuel, two-stroke heavy-duty diesel engine capable of operating on methanol as a fuel and / or diesel fuel as a secondary fuel.

[0049] A dual-fuel heavy-duty diesel engine includes a plurality of cylinders 110. In each cylinder 110, a piston 120 is connected to a crosshead 122 via a piston rod 123 in a manner known to those skilled in the art, and the crosshead 122 is connected to a crankshaft 170 via a push rod or connecting rod 123, such that movement of the piston 120 is transmitted via the piston rod 121, crosshead 122, and connecting rod 123 to rotate the crankshaft 170. The upper side of the piston 120, together with a cylinder cover 140, defines a combustion chamber 100 into which the fuel and / or secondary fuel is introduced.

[0050] The structure and individual components of the heavy-duty diesel engine 200, such as the fuel injection system, gas exchange system, exhaust system, or turbocharger system for supplying scavenging or intake air, as well as the monitoring and control systems of heavy-duty diesel engines, both for two-stroke and four-stroke engine designs, are well known to those skilled in the art and therefore need not be described further here.

[0051] In a typical embodiment of a longitudinally scavenged, two-stroke, heavy-duty diesel engine 200, each cylinder 110 is provided with a scavenging air slot 115 in the lower region or cylinder liner, which is periodically opened and closed by the movement of the piston 120 within the cylinder 110. As a result, scavenging air provided by the turbocharger under charge pressure can flow through the scavenging air slot into the cylinder 110 as long as the slot is open. The cylinder cover 140 is provided with a typically centrally located exhaust valve 130 through which exhaust gases can be discharged from the cylinder 110 after the combustion process into an exhaust system. The exhaust system directs at least a portion of the exhaust gases to the turbocharger turbine, and the turbocharger compressor supplies scavenging air, also referred to as charge air, to a scavenging air receiver under scavenging air pressure. The scavenging air receiver is in fluid communication with the scavenging air slot 115 of the cylinder 110.

[0052] Each cylinder 110 has at least one fuel injector 1 that injects fuel into the combustion chamber 100 of the cylinder 110. Preferably, the cylinder 110 has multiple fuel injectors 1, for example, two or three fuel injectors 1, for uniformly distributing fuel within the combustion chamber 100. In the embodiment of the large engine 200 described herein, exactly three fuel injectors 1 are provided (only one fuel injector 1 is shown in the schematic representation of FIG. 4). Each fuel injector 1 is positioned within the cylinder cover 140 of the cylinder 110 in a manner known in the art. Preferably, the fuel injectors 1 are positioned within the cylinder cover 140 near the exhaust valve 130.

[0053] Each cylinder 110 further includes at least one secondary fuel injector 150 for injecting a second fuel into the combustion chamber 100 of the cylinder 110. Preferably, a cylinder includes multiple secondary fuel injectors 150, e.g., two or three, for uniformly distributing the second fuel within the combustion chamber. In the embodiment of the large engine 200 described herein, exactly three secondary fuel injectors 150 are provided (only one secondary fuel injector 150 is shown in the schematic representation of FIG. 4). Each secondary fuel injector 150 is positioned within the cylinder cover 140 of the cylinder 110 in a manner known in the art. Preferably, the second fuel injector 150 is positioned within the cylinder cover 140 near the exhaust valve 130.

[0054] Currently, large diesel engines or large engines 200 are generally operated with full electronic control. The engine control unit 180 operates and controls all functions of the large engine 200, such as the operation of the exhaust valves 130 for gas exchange, the fuel injection process, and the timing of pilot injection (if pilot injection is required), by means of electrical or electronic signals and commands. In addition, the engine control unit 180 receives information from a number of detectors, sensors, or measuring devices.

[0055] It should be noted that the present invention is not limited to this particular type of longitudinally scavenged two-stroke heavy-duty diesel engine 200 capable of operating on a fuel and / or a second fuel. The heavy-duty engine can also be any other type of heavy-duty engine. In particular, the heavy-duty engine can be configured to burn only one fuel, such as methanol.

[0056] The present invention relates to a fuel injector 1 configured to inject fuel into a combustion chamber 100. Preferably, the fuel injector 1 is configured to receive methanol as the fuel.

[0057] With reference to Figures 1 to 3, an embodiment of the fuel injector 1 will now be described in more detail.

[0058] A fuel injector 1 for injecting fuel into a combustion chamber 100 comprises a nozzle retainer 2 and a nozzle tip 3 connected to the nozzle retainer 2. By way of example, the nozzle tip 3 may be arranged in a nozzle body, which is fixedly connected to the nozzle retainer 2. The nozzle tip 3 has at least one, but usually a plurality of, spray holes 31 through which fuel can be injected into the combustion chamber 100. The fuel injector 1 further comprises a pressure chamber 4 and at least one high-pressure fuel duct 5 through which fuel can be introduced into the pressure chamber 4 at high pressure. A needle valve 6 biased by a spring 7 and interacting with a valve seat 8 is provided within the pressure chamber 4 for opening and closing the fluid connection between the pressure chamber 4 and the nozzle tip 3.

[0059] 1, there are two high-pressure fuel ducts 5 in fluid communication with a high-pressure fuel port 51. The high-pressure fuel port 51 is connected to a high-pressure fuel source (not shown), such as a fuel booster unit, which can supply high-pressure fuel to the high-pressure fuel port 51.

[0060] When methanol is used as the fuel, the fuel booster unit is configured as a methanol booster unit that delivers methanol to the high pressure fuel port 51 at a high pressure, preferably at least 400 bar (40 MPa). For example, the high pressure can be 600 bar (60 MPa), or up to 750 bar (75 MPa).

[0061] When fuel injection is required, the fuel booster unit is activated and delivers a pre-determinable amount of high-pressure fuel to the high-pressure fuel port 51 of the fuel injector 1. The high-pressure fuel enters the pressure chamber 4 through the high-pressure fuel duct 5 and lifts the needle valve 6 from its seat 8 against the force of the spring 7, thereby opening the fluid connection between the pressure chamber 4 and the nozzle tip 3. The fuel then enters the nozzle tip 3 and is injected into the combustion chamber 100. In the combustion chamber 100, the fuel is ignited by induction. Preferably, induction ignition is achieved by a pilot injection of a small amount of a self-igniting second fuel. At least one of the second fuel injectors can be used for the pilot injection of the second fuel.

[0062] Once a pre-determinable amount of high pressure fuel has been delivered to the fuel injector 1, injection is terminated, i.e., no further high pressure fuel is delivered to the high pressure fuel port 51 of the fuel injector 1. This causes the fuel pressure in the pressure chamber 4 to drop, causing the spring 7 to urge the valve needle 6 into sealing engagement with the valve seat 8, thereby closing the fluid connection between the pressure chamber 4 and the nozzle tip 3.

[0063] In accordance with the present invention, a purge line 9 is disposed within the fuel injector 1 and extends from the pressure chamber 4 to a discharge passage 20 configured to discharge fluid from the nozzle retainer 2. A purge valve 10 is provided and configured to open and close fluid communication through the purge line 9.

[0064] As will be explained in more detail below, purge line 9 is used to remove fuel residue, such as methanol, from fuel injector 1. For example, when a large engine is changed from operation with one fuel to operation with a second fuel, or when the large engine is shut down after operation with the other fuel, it may be desirable or necessary to remove fuel from fuel injector 1 by purging fuel injector 1. Purging may also be necessary, for example, when fuel is not injected for an extended period of time (e.g., more than one month), or when a malfunction is detected in the fuel system (e.g., a leak), or in the case of maintenance. Purge line 9 makes it possible to prevent any residue of fuel in fuel injector 1. Preventing any residue of fuel, especially after engine 1 has been shut down, has the advantage of avoiding health hazards to maintenance or operating personnel.

[0065] Preferably, as shown in the embodiment of fuel injector 1 of Figure 3, purge valve 10 is configured as a poppet valve including a purge piston 11 and a purge valve body 12 biased by a purge spring 13. A hydraulic line 30 is provided that supplies hydraulic fluid to purge piston 11 for operating purge valve 10. Purge valve 10 is configured as an integral valve located within nozzle retainer 2 of fuel injector 1. The hydraulic fluid may be, for example, hydraulic oil or system oil, which is used for several different functions in large engines.

[0066] Unless the purge valve 10 is actuated, the purge spring 13 maintains the purge valve 10 in a closed position in which fluid communication through the purge line 9 is closed, thereby closing the flow connection from the purge line 9 to the exhaust passage 20.

[0067] Preferably, the high pressure fuel duct 51 is connectable to a source of purge fluid so that purge fluid can be supplied to the high pressure fuel duct 5. A liquid is preferably used as the purge fluid, since gaseous purge fluids, such as nitrogen, are difficult to reliably purge upwardly directed tubes or holes. Particularly with larger diameter tubes or holes, there is a risk that only gas bubbles will rise up the tubes or holes and the fuel will not be completely removed. A particularly preferred purge fluid is water.

[0068] The drain passage 20 is connected to a low-pressure fuel line 50, as shown by the dashed line in Figures 2 and 3. During operation of a large engine on a fuel such as methanol, any leaking fuel, such as fuel leaking along the needle valve 6, is collected and returned to a low-pressure fuel supply line (not shown) through the low-pressure fuel line 50. A selector valve (not shown) is provided to alternatively connect the low-pressure fuel line 50 to the low-pressure fuel supply line or to a drain line for draining purge fluid. During operation on fuel, the pressure of the fuel created in the low-pressure fuel line 50 is substantially the same as the supply pressure at which fuel is supplied to the fuel booster unit. The pressure of the fuel in the low-pressure fuel line 50 is, for example, 13 bar (1.3 MPa).

[0069] Purging of the fuel injector 1 will now be described in more detail. The purge mode is initiated when the operation of a large engine on a fuel is stopped, for example, by switching to operation on a second fuel. To operate the purge valve 10, hydraulic fluid is supplied to the hydraulic line 30 to pressurize the purge piston 11, thereby generating a force acting on the purge valve body 12. The pressure of the hydraulic fluid in the hydraulic line 30 is such that the force exerted by the purge piston 11 on the valve body 12 is greater than the force exerted by the purge spring 13 on the purge valve body 12. As a result, the purge valve body 12 is lifted from its seat, and the purge valve 10 is switched from the closed position to the open position, which opens fluid communication through the purge line 9 and, consequently, the flow connection from the purge line 9 to the discharge passage 20. To operate the purge valve 10, the pressure of the hydraulic fluid in the hydraulic line 30 is, for example, 16 bar (1.6 MPa).

[0070] In addition, the low pressure fuel line 50 is disconnected from the low pressure fuel supply line and connected to a drain line by a changeover valve (not shown).

[0071] Purge fluid, preferably water, is supplied to high pressure fuel port 51 at a purge pressure of up to a few bar, for example up to 5 bar (0.5 MPa). This ensures that needle valve 6 maintains sealing engagement with valve seat 8 and purge fluid does not enter nozzle tip 3.

[0072] Purge fluid enters the fuel injector 1 through the high-pressure fuel port 51, passes through the high-pressure fuel duct 5 into the pressure chamber 4, and is discharged from the pressure chamber 4 through the purge line 9 and the purge valve 10 into the drain passage 20. From the drain passage 20, the purge fluid, together with the removed fuel, is discharged into the drain line. The purge fluid thus expels fuel from the fuel injector 1 through the open purge valve 10. When the fuel injector 1 has been completely purged by the purge fluid, the purge mode can be terminated. This stops the supply of hydraulic fluid to the hydraulic line 30, thereby relieving the hydraulic pressure acting on the purge piston 11. As a result, the purge spring 13 pushes the purge valve body 12 into sealing engagement with its valve seat, and the purge valve 10 is switched to the closed position.

[0073] As a further preferred measure, a lubricant is provided for the valve needle 6. Some renewable fuels, for example methanol, have poor tribological properties and very low viscosity, so it is advantageous to lubricate the valve needle 6 of the fuel injector 1 in particular.

[0074] The spring 7 that biases the valve needle 6 is disposed in a spring chamber 71. The spring 7 is mounted on a spring support 73 that abuts against the valve needle 6. The valve needle 6 is disposed in a needle guide 61 that extends in the axial direction A between the spring chamber 71 and the pressure chamber 4. The needle guide 61 surrounds the valve needle 6 with a gap therebetween, and the valve needle 6 is guided by the needle guide 61 and is movable in the axial direction A within the needle guide 61.

[0075] A lubrication line 72 is provided through which a lubricant, for example oil, can be supplied to the spring chamber 71. The lubricant is, for example, an oil such as the system oil used in large engines. Particularly preferably, the lubricant is the same system oil used to operate the purge valve 10, i.e., the lubricant is also used as the hydraulic fluid for operating the purge valve 10.

[0076] By supplying lubricant to the spring chamber 71, the spring 7 and the spring support 73, particularly the lower part of the spring support 73 adjacent to the needle valve 6, are also lubricated. In particular, the spring 7 is subjected to a large dynamic load, so lubrication of the spring 7 is advantageous. The spring 7 is preferably made of a material with high mechanical properties, such as carbon steel.

[0077] From the spring chamber 71, the lubricant can enter the needle guide 61 and fill the gap between the needle valve 6 and the needle guide 61, thereby lubricating the needle valve 6 within the needle guide 61.

[0078] Furthermore, the needle guide 61 preferably has an annular groove 62 extending circumferentially around the needle valve 6. In the axial direction A, the annular groove 62 is arranged between the spring chamber 71 and the pressure chamber 4, for example in the center of the needle guide 61. The annular groove 62 is connected to the low-pressure fuel line 50. Thus, during operation of the large engine on fuel, the annular groove 62 is filled with low-pressure fuel. As mentioned above, the low pressure generated in the low-pressure fuel line 50 is, for example, 13 bar (1.3 MPa). In this case, the same pressure is generated in the annular groove 62.

[0079] The lubricant is supplied to the spring chamber 71 at a pressure higher than the low pressure of the fuel in the annular groove 62. For example, the lubricant is supplied to the spring chamber 71 at a pressure of 16 bar (1.6 MPa), i.e., approximately 20% higher than the pressure generated in the annular groove 62. This pressure difference ensures that any leakage along the valve needle 6 between the spring chamber 71 and the annular groove 62 is always directed toward the annular groove 62. Therefore, lubricant can leak from the spring chamber 71 through the gap between the needle guide 61 and the valve needle 6 toward the annular groove 62, but fuel cannot leak from the annular groove 62 along the valve needle 6 into the spring chamber 71. Therefore, the annular groove 62, which is filled with fuel at low pressure, and the lubricant supplied to the spring chamber 71 at a higher pressure, separate and seal the fuel side in contact with the fuel and the lubricant side in contact with the lubricant. As a result, fuel is never present in the spring chamber 71. In this way, the lubricant additionally functions as a sealing fluid. In addition, the needle valve 6 is gently lubricated during operation of the large engine on fuel.

[0080] Note: Examples described with respect to an apparatus shall equally apply to the method, if any. Although not specifically described, synergistic effects may arise from various combinations of examples.

[0081] While presently preferred embodiments of the invention have been shown and described, it is to be expressly understood that the invention is not limited thereto and is capable of various other embodiments and implementations within the scope of the following claims.

Claims

1. A fuel injector for injecting fuel into a combustion chamber of a large engine, comprising: a nozzle retainer (2); a nozzle tip (3) having at least one spray hole (31) through which the fuel can be injected into the combustion chamber (100); the fuel injector further comprising: a pressure chamber (4); at least one high-pressure fuel duct (5) through which the fuel can be introduced into the pressure chamber (4) at high pressure; and a needle valve (6) biased by a spring (7) and interacting with a valve seat (8) for opening and closing a fluid connection between the pressure chamber (4) and the nozzle tip (3). a purge line (9) disposed within the nozzle retainer (2), the purge line (9) extending from the pressure chamber (4) to a discharge passage (20) configured to discharge fluid from the nozzle retainer (2), and a purge valve (10) configured to open and close fluid communication through the purge line (9).

2. 2. A fuel injector according to claim 1, wherein said at least one high pressure fuel duct (5) is connectable to a source of purge fluid so as to supply said purge fluid to said high pressure fuel duct (5).

3. 3. A fuel injector according to claim 1 or 2, wherein the purge valve (10) is configured as a poppet valve.

4. 4. The fuel injector according to claim 1, wherein the purge valve (10) comprises a purge piston (11) and a purge valve body (12) biased by a purge spring (13), and a hydraulic pipe (30) configured to supply hydraulic fluid to the purge piston (11) for operating the purge valve (10) is provided.

5. 5. The fuel injector valve according to claim 1, wherein the spring (7) biasing the needle valve (6) is arranged in a spring chamber (71), and a lubrication pipe (72) configured to supply lubricant to the spring chamber (71) is provided.

6. 6. The fuel injector of claim 5, wherein the nozzle retainer (2) comprises a needle guide (61) for receiving and guiding the needle valve (6), the needle guide (61) extending from the spring chamber (71) to the pressure chamber (4) so ​​that the lubricant can enter the needle guide (61) from the spring chamber (71).

7. A fuel injector according to any one of claims 4 and 5-6, configured to receive the lubricant as the hydraulic fluid for operating the purge valve (10).

8. 8. The fuel injector according to claim 6, wherein the needle guide (61) comprises an annular groove (62) extending circumferentially around the needle valve (6), the annular groove (62) being connected to a low-pressure fuel line (50) that supplies the fuel to the annular groove (62) at low pressure.

9. 9. The fuel injector of claim 8, wherein a discharge passage (20) is connected to the low pressure fuel line (50).

10. 10. A fuel injector according to any preceding claim, configured to receive the fuel at a high pressure of at least 40 MPa.

11. 11. A fuel injector according to any one of claims 1 to 10, configured to receive methanol as a fuel.

12. A fuel injector according to any one of claims 2 to 11, configured to receive water as the purge fluid.

13. 13. A large engine, in particular a longitudinally scavenged two-stroke large engine, comprising at least one cylinder having a combustion chamber, in which a piston is arranged to reciprocate between a top dead center position and a bottom dead center position, the cylinder comprising a fuel injector (1) according to any one of claims 1 to 12.

14. 14. A large engine according to claim 13, wherein the at least one cylinder is provided with a second fuel injector for injecting a second fuel into the combustion chamber, the second fuel being different from the fuel, in particular the second fuel being a diesel fuel that autoignites in the combustion chamber.

15. 15. A method of operating a large engine according to any one of claims 13 or 14, comprising the steps of: temporarily opening the purge valve (10) of the fuel injector (1) of the large engine so that fluid communication is established between the pressure chamber (4) and the discharge passage (20) through the purge line (9).

Images