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

Abstract

The invention discloses a fuel injector for injecting fuel into a combustion chamber of a large engine and the large engine. The invention relates to a fuel injector for injecting fuel into a combustion chamber of a large engine, comprising a nozzle holder and a nozzle tip having at least one injection opening through which fuel can be injected into the combustion chamber, further comprising a pressure chamber and a high-pressure fuel line and a valve needle, fuel may be introduced at high pressure into the pressure chamber through a high pressure fuel conduit, and a valve needle loaded by a spring and interacting with a valve seat to open and close a fluid connection between the pressure chamber and the nozzle tip. A flush line is arranged in the nozzle holder, the flush line extending from the pressure chamber to a discharge passage configured to discharge fluid from the nozzle holder, and a flush valve configured to open and close fluid communication through the flush line is provided. Furthermore, a large engine comprising such a fuel injector and a method for operating such a large engine are proposed.

Description

Technical Field

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

[0002] Large engines (which can be configured as two-stroke or four-stroke engines, for example, as longitudinally scavenging two-stroke large engines) are commonly used as propulsion units for ships or for stationary operations, such as driving large generators to produce electrical energy. Engines typically operate continuously for considerable periods, placing high demands on operational safety and availability. Therefore, exceptionally long maintenance intervals, low wear, and economical disposal of operating materials are core criteria for operators. Large engines typically have cylinders with an inner diameter (bore) of at least 200 mm. Today, large engines with bores up to 980 mm or even larger are used. Within the framework of this application, the term "large engine" refers to an internal combustion engine with a cylinder bore of at least 200 mm and preferably at least 300 mm.

[0003] Large engines are typically configured as large diesel engines, which operate on heavy fuel oil. For large diesel engines, alternatives to heavy fuel oil are being sought to improve fuel economy, compliance with emissions limits, sustainable CO2 emission reduction, and resource availability. In this regard, both liquid fuels (i.e., fuel introduced into the combustion chamber in a liquid state) and gaseous fuels (i.e., fuel introduced into the combustion chamber in a gaseous state) are being used.

[0004] Examples of liquid fuels known as alternatives to heavy fuel oils include other heavy hydrocarbons (particularly those remaining as residues from oil refining), alcohols (particularly methanol or ethanol), ammonia, gasoline, diesel, or emulsions or suspensions. For example, emulsions called MSAR (Multiphase Ultrafine Atomized Residue) are known as fuels. A well-known suspension is a suspension of coal dust and water, which is also used as fuel in large engines. As gaseous fuels, natural gas such as LNG (liquefied natural gas), liquefied gases such as LPG (liquefied petroleum gas), or ethane are known.

[0005] In particular, it is known to operate large diesel engines with at least two different fuels, whereby the engine may operate with one fuel or another fuel depending on the operating conditions or environment. It is also known to simultaneously inject two different fuels into the combustion chamber of the cylinder.

[0006] A large diesel engine that can operate on two different fuels is called a dual-fuel large diesel engine. Depending on the two fuels, the engine can operate in liquid mode and gas mode. In liquid mode, liquid fuel is introduced into the cylinders for combustion, and in gas mode, gas is introduced into the cylinders as fuel.

[0007] Large diesel engines that can operate with at least two or even more different liquid or gaseous fuels typically operate in different modes depending on the fuel currently in use. In the operating mode commonly referred to as diesel operation, combustion usually occurs based on the principle of compression ignition or auto-ignition. In the operating mode commonly referred to as Otto operation, combustion occurs through the induced ignition of a combustible premixed air-fuel mixture. This induced ignition can occur, for example, by an electric spark (e.g., using a spark plug) or also by the auto-ignition of a small amount of fuel injected, which then induces the ignition of another fuel. A small amount of fuel intended for auto-ignition is inserted directly into the combustion chamber or injected into a pre-combustion chamber connected to the combustion chamber. The process of inducing auto-ignition through a small amount of liquid or another auto-igniting fuel is sometimes referred to as pilot injection.

[0008] In addition, hybrid forms using Otto and diesel engines are also known.

[0009] Especially considering climate change, efforts are being made to reduce CO2 emissions and sustainably reduce the use of fossil fuels. Therefore, alternatives to large engines have also been studied to at least reduce or even completely eliminate the use of fossil fuels. Even though this is still a long way off, partially replacing fossil fuels with renewable fuels is considered a huge success.

[0010] One alternative to fossil fuels is methanol. However, renewable fuels such as methanol can cause corrosion problems in fuel distribution and injection systems, especially during engine shutdown or while operating with another fuel. Residual methanol can corrode pipes or other components of the fuel injection system. Furthermore, there is a risk of methanol escaping from the engine (e.g., in vapor form) into spaces accessible to engine maintenance or operating personnel. This constitutes a health hazard and requires comprehensive mitigation measures. Therefore, residual methanol should be reliably removed from the injection system after operation with methanol. Summary of the Invention

[0011] This invention solves this objective. Therefore, the object of this invention is to provide a fuel injector for injecting fuel into the combustion chamber of a large engine, which operates more reliably and safely when methanol is used as the fuel for the large engine. Furthermore, the object of this invention is to provide a large engine equipped with such a fuel injector. Additionally, the object of this invention is to provide a method for operating such a large engine.

[0012] The subject matter of the invention that satisfies these objectives is characterized by features according to the first, second, and third aspects of the invention.

[0013] Therefore, according to a first aspect of the invention, a fuel injector for injecting fuel into the combustion chamber of a large engine is provided, the fuel injector comprising a nozzle holder and a nozzle tip having at least one injection orifice through which fuel can be injected into the combustion chamber, the fuel injector further comprising a pressure chamber and at least one high-pressure fuel conduit and a valve needle, wherein fuel can be introduced into the pressure chamber at high pressure through the at least one high-pressure fuel conduit, the valve needle being spring-loaded and interacting with a valve seat to open and close the fluid connection between the pressure chamber and the nozzle tip. A purge line is arranged in the nozzle holder, wherein the purge line extends from the pressure chamber to a discharge passage configured to discharge fluid from the nozzle holder, and wherein a purge valve is provided, the purge valve being configured to open and close the fluid communication through the purge line (i.e., between the pressure chamber and the discharge passage).

[0014] The fuel injector includes a flushing line disposed within the nozzle holder, wherein the flushing line connects the pressure chamber to the discharge passage, so that in flushing mode, flushing fluid can be supplied to and discharged from the pressure chamber through the flushing line. This facilitates reliable removal of any fuel residue from the pressure chamber. Furthermore, because the flushing line is disposed within the nozzle holder, the fuel injector has a very compact design. Switching between an operating mode with a closed flushing valve and a flushing mode with an open flushing valve is particularly simple, thanks to a flushing valve configured to open and close the fluid communication. In the operating mode with the closed flushing valve, the fuel injector injects fuel into the combustion chamber; in the flushing mode with the open flushing valve, the fuel injector, and particularly the pressure chamber, can be reliably flushed to remove fuel residue.

[0015] According to a preferred configuration, at least one high-pressure fuel line can be connected to a source of flushing fluid, allowing the flushing fluid to be supplied to the high-pressure fuel line. Therefore, the high-pressure fuel line can also be flushed. The flushing fluid enters the high-pressure fuel line, flows through it, thereby flushing the high-pressure fuel line, enters the pressure chamber, and is then discharged to the discharge channel via the flushing line.

[0016] Preferably, the flushing valve is configured as a lift valve, as this constitutes a simple and reliable implementation of the flushing valve.

[0017] Furthermore, preferably, the flushing valve includes a flushing piston and a flushing valve body loaded by a flushing spring, wherein a hydraulic line is provided for supplying hydraulic fluid to the flushing piston. Therefore, it is preferable that the flushing valve is hydraulically actuated. By supplying the flushing piston with hydraulic fluid at a sufficiently high pressure to overcome the spring force of the flushing spring, the flushing valve can be actuated to open the fluid communication through the flushing line. When the pressure of the hydraulic fluid is released, the flushing spring closes the flushing valve, thereby closing the fluid communication through the flushing line. This facilitates reliable operation of the flushing valve.

[0018] Since hydraulic fluid (e.g., system oil) is used at several locations and for several functions in large engines, hydraulic fluid is available in large engines in any case, so that no additional hydraulic fluid is needed.

[0019] As a further preferred embodiment, the spring for loading the valve needle is arranged in a spring chamber, wherein a lubrication tube configured to supply lubricant to the spring chamber is provided. Therefore, the spring chamber can be filled with lubricant, which protects the spring from any corrosive damage from fuel.

[0020] Furthermore, preferably, the nozzle retainer includes a needle guide for receiving and guiding the valve needle, the needle guide extending from the spring chamber to the pressure chamber, allowing lubricant to enter the needle guide from the spring chamber. Allowing lubricant into the needle guide provides excellent lubrication of the valve needle. This is advantageous because methanol is a very low viscosity fluid with very poor frictional properties. The lubricant in the needle guide ensures safe and reliable operation of the valve needle.

[0021] A preferred approach is to configure the fuel injector to receive lubricant as hydraulic fluid for operating the flush valve. When the flush valve needs to be actuated in flush mode, the lubricant pressure switches to a higher level, high enough to open the flush valve. The advantage of this approach is that since the existing lubricant supply is used to actuate the flush valve, additional supply piping to the injector is saved.

[0022] According to a preferred configuration, the needle guide includes an annular groove extending circumferentially around the valve needle, wherein the annular groove is connected to a low-pressure fuel line for supplying fuel at a low pressure (e.g., 13 bar (1.3 MPa)) to the annular groove. The annular groove filled with fuel at the low pressure enables separation and sealing between the fuel side in contact with the fuel and the lubrication side in contact with the lubricant. When lubricant is supplied to the spring chamber at a pressure higher than the low pressure of the fuel in the annular groove (e.g., 13 bar (1.3 MPa)) (e.g., 16 bar (1.6 MPa)), it ensures that no fuel can leak into the spring chamber, for example, along the needle guide or the valve needle. Therefore, the spring chamber is free of fuel. Thus, the lubricant additionally acts as a sealing fluid.

[0023] Preferably, the discharge channel is connected to the low-pressure fuel line. Therefore, the flushing fluid is discharged into the low-pressure fuel line, and a separate return line for the flushing fluid is not required.

[0024] Preferably, the fuel injector is configured to receive fuel at a pressure of at least 40 MPa (which is suitable for the typical “opening pressure” of a valve needle of 375 bar (37.5 MPa)).

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

[0026] Regarding flushing, it is preferable that the fuel injector is configured to receive water as the flushing fluid. Alternatively, nitrogen (gas) or diesel fuel can be considered as flushing fluids. However, with nitrogen or any other gas, it is difficult to reliably flush upward-facing pipes. For large pipe sections, there is a risk that only air bubbles will climb the pipes and the fuel will not be properly vented. Regarding diesel fuel as the flushing fluid, the mixture of diesel and methanol is not homogeneous because methanol has relatively low solubility in diesel. If the mixture is subsequently recovered and injected, there is a risk that the engine will sometimes use diesel and sometimes methanol. Therefore, power handling during combustion can be difficult because diesel fuel has twice the energy density of methanol. For these reasons, water is the preferred flushing fluid.

[0027] Furthermore, according to a second aspect of the invention, a large engine is provided, the large engine comprising at least one cylinder having a combustion chamber, wherein a piston is arranged in the cylinder to reciprocate between a top dead center position and a bottom dead center position, and wherein the cylinder comprises a fuel injector according to a first aspect of the invention.

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

[0029] Furthermore, preferably, at least one cylinder includes a second fuel injector for injecting a second fuel into the combustion chamber, wherein the second fuel is different from the stated fuel. Therefore, large engines are preferably configured to operate with at least two different fuels.

[0030] The second fuel is preferably diesel fuel for auto-ignition in the combustion chamber. Therefore, it is preferable that the large engine is configured as a large diesel engine.

[0031] Within the framework of this application, the term "large diesel engine" refers to an engine that can operate at least in diesel mode. In particular, the term "large diesel engine" therefore also includes large multi-fuel engines that can operate in another mode (e.g., Otto mode) in addition to diesel mode.

[0032] Furthermore, according to a third aspect of the invention, a method for operating such a large engine according to a second aspect of the invention is proposed. The method is characterized by the following steps: temporarily opening the flushing valve of the fuel injector of the large engine, thereby establishing fluid communication between the pressure chamber and the discharge passage through a flushing line.

[0033] Other advantages and embodiments of the invention are derived from the dependent claims. Attached Figure Description

[0034] The invention will now be explained in more detail below with reference to embodiments and the accompanying drawings. The drawings show:

[0035] Figure 1 This is a cross-sectional view along the axial direction of an embodiment of the fuel injector according to the present invention.

[0036] Figure 2 yes Figure 1 The diagram shows a cross-sectional view of the fuel injector, where the cross-sectional plane is rotated approximately 90°.

[0037] Figure 3 It comes from Figure 2 Magnified details I, and

[0038] Figure 4 This is a schematic diagram of a large engine. Detailed Implementation

[0039] Figure 1 A cross-sectional view of an embodiment of a fuel injector according to the present invention is shown, which is generally indicated by reference numeral 1. The section is along the axial direction A, which is defined by the central axis of the fuel injector 1. Figure 2 The same embodiment of the fuel injector 1 is shown in cross-sectional view, wherein, with Figure 1Compared to the view in the image, the cross-sectional plane is rotated approximately 90°. For better understanding, Figure 3 It shows Figure 2 A magnified view of detail I.

[0040] Fuel injector 1 is used to inject fuel into the combustion chamber 100 of cylinder 110 of large engine 200. Figure 4 A schematic diagram illustrating an embodiment of the large engine 200 is shown. Figure 4 Only one cylinder of the large engine 200 is shown in the diagram. Typically, the large engine 200 includes multiple cylinders 110, such as up to twelve cylinders 110 or even more.

[0041] The term "large engine" refers to an internal combustion engine that is typically used as a propulsion unit for ships or for stationary operations, such as driving large generators to produce electrical energy. Typically, the cylinders 110 of a large engine each have an inner diameter (bore) of at least about 200 mm. Such large engines 200 are known in the art in various different configurations, such as as two-stroke engines or as four-stroke engines.

[0042] In the following description, reference is made by way of example to a large engine 200, which is configured as a longitudinally scavenged two-stroke large engine having a plurality of cylinders 110. Each cylinder 110 has a combustion chamber 100. Furthermore, in each cylinder 110, a piston 120 is arranged for reciprocating between top dead center and bottom dead center.

[0043] The term "longitudinal scavenging" means that scavenging air or boost air is introduced into cylinder 110 in the lower region, and exhaust valve 130 is arranged in or at cylinder head 140 located at the upper end of cylinder 110.

[0044] In particular, reference is made to a large longitudinally scavenged two-stroke engine that can operate with different fuels (i.e., with fuel oil and a second fuel oil). Preferably, the large engine 200 is configured as a large diesel engine. The term "large diesel engine" refers to an engine that can operate at least in diesel operating mode. In particular, the term "large diesel engine" therefore also includes such a large engine 200 that can operate in another mode (e.g., Otto operating mode) in addition to diesel operating mode.

[0045] According to a preferred configuration, the large engine 200 can operate using methanol as fuel or a self-igniting liquid second fuel. Therefore, when the large engine 200 operates with the second fuel, it operates in a liquid mode where only the liquid second fuel is injected into the combustion chamber 100 of the cylinder 110. Typically, the liquid fuel (e.g., heavy fuel oil (HFO), marine diesel (MDO), or marine gasoline (MGO)) is injected directly into the combustion chamber 100 at the appropriate time and ignited there according to the principle of diesel auto-ignition. To inject the second fuel into the combustion chamber 100, each cylinder includes a second fuel injector 150, different from the fuel injector 1. Therefore, each cylinder 110 includes at least one (preferably multiple) fuel injector 1 for injecting fuel, and at least one (preferably multiple) second fuel injector 150 for injecting the second fuel.

[0046] The fuel injected into the combustion chamber 100 by the fuel injector 1 is, for example, fuel used in Otto operation, i.e., fuel-induced ignition. The fuel is injected into the combustion chamber 100 to form a premixed air-fuel mixture with the scavenging air. According to the Otto principle, the air-fuel mixture is induced to ignite in the combustion chamber 100. This induced ignition is typically caused by introducing a small amount of self-igniting secondary fuel (e.g., diesel or heavy fuel oil) into the combustion chamber 100 or pre-combustion chamber at an appropriate time. This secondary fuel then self-ignites and induces the induced ignition of the air-fuel mixture in the combustion chamber 100.

[0047] Introducing a small amount of self-igniting liquid or gaseous secondary fuel into the combustion chamber 100 or at least one pre-combustion chamber for the purpose of inducing fuel ignition is also known as ignition ignition. In addition to diesel fuel, gases or alcohols (such as methanol) can also be used as ignition fluids for ignition ignition.

[0048] In other embodiments, induced ignition is performed by spark ignition or laser pulse or by any other means suitable for igniting fuel in combustion chamber 100.

[0049] In the following description, reference is made to a preferred embodiment in which the fuel is methanol and the second fuel is a diesel fuel for auto-ignition, such as HFO, MDO, or MGO. Regarding the methanol fuel, it is preferred that the operation using the fuel is based on the Otto principle.

[0050] Furthermore, the large diesel engine 200 can operate in a hybrid mode, in which both fuel and secondary fuel are injected into the combustion chamber 100 of the cylinder 110. In hybrid mode, the combustion of both fuel and secondary fuel contributes to the generation of torque.

[0051] In the embodiments described herein, the large engine is configured as a longitudinally scavenged dual-fuel two-stroke large diesel engine, which can operate with methanol as fuel and / or diesel fuel as a second fuel.

[0052] The dual-fuel large diesel engine has multiple 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. The crosshead 122 is connected to a crankshaft 170 via a pushrod or connecting rod 123, such that movement of the piston 120 is transmitted to the crankshaft 170 via the piston rod 121, the crosshead 122, and the connecting rod 123 to rotate it. The upper side of the piston 120, together with the cylinder head 140, defines a combustion chamber 100, into which fuel and / or a second fuel is introduced.

[0053] The structure and various components of the large diesel engine 200 (e.g., the fuel injection system, the gas exchange system, the exhaust system or turbocharger system for supplying scavenging air or boost air, and the monitoring and control system for the large diesel engine) are sufficiently known to those skilled in the art, whether it is a two-stroke engine design or a four-stroke engine design, and therefore no further explanation is required here.

[0054] In an embodiment of the longitudinally scavenged two-stroke large diesel engine 200, a scavenging air sump 115 is typically located in the lower region of each cylinder 110 or cylinder liner. It is periodically closed and opened by the movement of a piston 120 within the cylinder 110, allowing scavenging air supplied by the turbocharger at charging pressure to flow into the cylinder 110 whenever the scavenging air sump is open. An exhaust valve 130, typically centrally located, is provided in the cylinder head 140, through which exhaust gases can be discharged from the cylinder 110 into the exhaust system after combustion. The exhaust system directs at least a portion of the exhaust gases to the turbocharger turbine, whose compressor provides scavenging air at scavenging air pressure in a scavenging air receiver, also referred to as boost air. The scavenging air receiver is in fluid communication with the scavenging air sump 115 of the cylinder 110.

[0055] Each cylinder 110 includes at least one fuel injector 1 for injecting fuel into the combustion chamber 100 of the cylinder 110. Preferably, the cylinder 110 includes a plurality of fuel injectors 1, such as two or three fuel injectors 1, for uniformly distributing fuel in the combustion chamber 100. In the embodiment of the large engine 200 described herein, exactly three fuel injectors 1 are provided. Figure 4The schematic diagram shows only one fuel injector 1. Each fuel injector 1 is arranged in the cylinder head 140 of the cylinder 110 in a manner known in the art. Preferably, the fuel injector 1 is arranged in the cylinder head 140 near the exhaust valve 130.

[0056] Each cylinder 110 further includes at least one second fuel injector 150 for injecting a second fuel into the combustion chamber 100 of the cylinder 110. Preferably, the cylinder includes a plurality of second fuel injectors 150, such as two or three second fuel injectors, for uniformly distributing the second fuel in the combustion chamber. In the embodiment of the large engine 200 described herein, exactly three second fuel injectors 150 are provided (in... Figure 4 The schematic diagram shows only one second fuel injector 150. Each second fuel injector 150 is arranged in the cylinder head 140 of the cylinder 110 in a manner known in the art. Preferably, the second fuel injector 150 is arranged in the cylinder head 140 near the exhaust valve 130.

[0057] Today, large diesel engines or large engines 200 are typically operated in a fully electronically controlled manner. The engine control unit 180 operates and controls all functions of the large engine 200 via electrical or electronic signals and commands, such as the operation of the exhaust valve 130 for gas exchange, the fuel injection process, and ignition injection timing (when ignition injection is required). Additionally, the engine control unit 180 receives information from several detectors, sensors, or measuring devices.

[0058] It should be noted that the present invention is not limited to this specific type of longitudinally scavenged two-stroke large diesel engine 200, which can operate with fuel and / or with a second fuel. The large engine can also be any other type of large engine. In particular, the large engine can be configured for combustion of only one fuel (e.g., methanol).

[0059] 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 fuel.

[0060] refer to Figures 1 to 3 The implementation of fuel injector 1 will now be described in more detail.

[0061] Fuel injector 1 for injecting fuel into combustion chamber 100 includes nozzle retainer 2 and nozzle tip 3, the nozzle tip 3 being connected to nozzle retainer 2. As an example, nozzle tip 3 may be disposed at nozzle body, which is fixedly connected to nozzle retainer 2. Nozzle tip 3 has at least one (but typically multiple) injection holes 31 through which fuel can be injected into combustion chamber 100. Fuel injector 1 further includes pressure chamber 4 and at least one high-pressure fuel conduit 5 through which fuel can be introduced into pressure chamber 4 at high pressure. In pressure chamber 4, a valve needle 6, loaded by spring 7 and interacting with valve seat 8, is provided to open and close the fluid connection between pressure chamber 4 and nozzle tip 3.

[0062] exist Figure 1 In the illustrated embodiment, two high-pressure fuel lines 5 are provided, which are 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 fuel at high pressure to the high-pressure fuel port 51.

[0063] When methanol is used as fuel, the fuel enhancer unit is configured as a methanol enhancer unit, which delivers methanol to the high-pressure fuel port 51 at a 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).

[0064] When fuel injection is required, the fuel booster unit is actuated to deliver a preset amount of fuel at high pressure 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 line 5 and lifts the valve needle 6 from the valve seat 8 against the force of the spring 7, thus 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 induced ignition. Preferably, induced ignition is performed by igniting a small amount of self-igniting second fuel. At least one of the second fuel injectors can be used for the ignition injection of the second fuel.

[0065] After a preset amount of fuel at high pressure has been supplied to the fuel injector 1, injection is terminated, meaning no more fuel at high pressure is supplied to the high-pressure fuel port 51 of the fuel injector 1. This causes a drop in fuel pressure in the pressure chamber 4, whereby the spring 7 presses the valve needle 6 into a sealing engagement with the valve seat 8, thereby closing the fluid connection between the pressure chamber 4 and the nozzle tip 3.

[0066] According to the invention, a flushing line 9 is arranged in the fuel injector 1, wherein the flushing line 9 extends from the pressure chamber 4 to the discharge passage 20, the discharge passage 20 being configured to discharge fluid from the nozzle holder 2. A flushing valve 10 is provided, which is configured to open and close the fluid communication through the flushing line 9.

[0067] As will be explained in more detail below, flushing line 9 is used to remove fuel residues, such as methanol, from fuel injector 1. For example, it is recommended or necessary to remove the fuel from fuel injector 1 by flushing when the operation of a large engine changes from using one type of fuel to using a second type, or when the large engine is shut down after using one type of fuel. Flushing is also necessary, for example, when there has been no fuel injection for an extended period (e.g., more than a month) or when a fault (e.g., a leak) is detected in the fuel system or during maintenance. By using flushing line 9, any fuel residue in fuel injector 1 can be avoided. Avoiding any fuel residue (especially after engine 1 has been stopped) has the advantage of preventing health hazards to maintenance or operating personnel.

[0068] Preferably, and as for example Figure 3 As shown in the embodiment of the fuel injector 1, the flushing valve 10 is configured as a lift valve, which includes a flushing piston 11 and a flushing valve body 12 loaded by a flushing spring 13. A hydraulic line 30 is provided, configured to supply hydraulic fluid to the flushing piston 11 to operate the flushing valve 10. The flushing valve 10 is configured as an integrated valve arranged within the nozzle holder 2 of the fuel injector 1. The hydraulic fluid is, for example, hydraulic oil or system oil, which is used for several different functions in large engines.

[0069] As long as the flush valve 10 is not activated, the flush spring 13 holds the flush valve 10 in the closed position, in which the fluid communication through the flush line 9 is closed, thereby closing the flow connection from the flush line 9 to the discharge channel 20.

[0070] Preferably, the high-pressure fuel port 51 can be connected to a source of flushing fluid, allowing flushing fluid to be supplied to the high-pressure fuel line 5. A liquid is preferred as the flushing fluid because it is difficult to reliably flush upward-facing pipes or holes using gaseous flushing fluids (e.g., nitrogen). Especially in pipes or holes with large diameters, there is a risk that only air bubbles will climb up the pipe or hole and the fuel will not be completely removed. Water is a particularly preferred flushing fluid.

[0071] Emission passage 20 is connected to low-pressure fuel line 50, such as Figure 2 and Figure 3As shown by the dashed line. During operation of the large engine using fuel (e.g., methanol), leaked fuel (e.g., fuel leaking along valve needle 6) is collected and returned to the low-pressure fuel supply line (not shown) via low-pressure fuel line 50. A switching valve (not shown) is provided to alternatively connect low-pressure fuel line 50 to the low-pressure fuel supply line or to a discharge line to discharge flushing fluid. During operation with fuel, the pressure of the fuel that dominates in low-pressure fuel line 50 is substantially the same as the supply pressure at which fuel is supplied to the fuel booster unit. The fuel pressure in low-pressure fuel line 50 is, for example, 13 bar (1.3 MPa).

[0072] The flushing of fuel injector 1 will now be explained in more detail. After the operation of a large engine using fuel has ceased, for example by changing to operation using a second fuel, the flushing mode is initiated. To activate the flushing valve 10, hydraulic fluid is supplied to the hydraulic line 30 to pressurize the flushing piston 11, which generates a force acting on the flushing valve body 12. The pressure of the hydraulic fluid in the hydraulic line 30 is so high that the force exerted on the valve body 12 by the flushing piston 11 is greater than the force exerted on the flushing valve body 12 by the flushing spring 13. Therefore, the flushing valve body 12 is lifted from its seat and the flushing valve 10 switches from the closed position to the open position, in which the fluid communication through the flushing line 9 is opened, thus opening the flow connection from the flushing line 9 to the discharge passage 20. To activate the flushing valve 10, the pressure of the hydraulic fluid in the hydraulic line 30 is, for example, 16 bar (1.6 MPa).

[0073] Additionally, the low-pressure fuel line 50 is disconnected from the low-pressure fuel supply line and connected to the discharge line via a switching valve (not shown).

[0074] The flushing fluid (preferably water) is supplied to the high-pressure fuel port 51 at a flushing pressure of up to a few bar (e.g., up to 5 bar (0.5 MPa)). This ensures that the valve needle 6 remains in a sealed engagement with the valve seat 8, preventing the flushing fluid from entering the nozzle tip 3.

[0075] Flushing fluid enters the fuel injector 1 through the high-pressure fuel port 51, enters the pressure chamber 4 through the high-pressure fuel line 5, and is discharged from the pressure chamber 4 into the discharge passage 20 through the flushing line 9 and the flushing valve 10. The flushing fluid, along with the removed fuel in the discharge line, is discharged from the discharge passage 20. Thus, the flushing fluid discharges fuel from the fuel injector 1 via the open flushing valve 10. The flushing mode can end when the fuel has been completely removed from the fuel injector 1 by the flushing fluid. Therefore, the supply of hydraulic fluid to the hydraulic line 30 is stopped, thereby releasing the hydraulic pressure acting on the flushing piston 11. Consequently, the flushing spring 13 pushes the flushing valve body 12 to seal against its seat, causing the flushing valve 10 to switch to the closed position.

[0076] As a further preferred measure, lubrication is provided for the valve needle 6. Some renewable fuels (e.g., methanol) have poor tribological properties and very low viscosity. Therefore, it is advantageous to specifically lubricate the valve needle 6 of the fuel injector 1.

[0077] A spring 7 for loading the valve needle 6 is arranged in a spring chamber 71. The spring 7 is placed on a spring support 73, which abuts against the valve needle 6. The valve needle 6 is arranged within a needle guide 61 that extends along 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, such that the valve needle 6 is guided by the needle guide 61 and is movable within the needle guide 61 along the axial direction A.

[0078] A lubrication pipe 72 is provided through which lubricant (e.g., oil) can be supplied to the spring chamber 71. The lubricant is, for example, oil, such as the system oil used in large engines. Particularly preferably, the lubricant is the same system oil used to actuate the flush valve 10, that is, the lubricant also serves as the hydraulic fluid for actuating the flush valve 10.

[0079] By also 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 valve needle 6) are lubricated. In particular, lubrication of the spring 7 is advantageous because the spring 7 is dynamically highly loaded. The spring 7 is preferably made of a material with high mechanical properties (e.g., carbon steel).

[0080] Lubricant can enter the needle guide 61 from the spring chamber 71 and can fill the gap between the valve needle 6 and the needle guide 61, thereby providing lubrication for the valve needle 6 in the valve needle guide 61.

[0081] Furthermore, preferably, the needle guide 61 includes an annular groove 62 extending circumferentially around the valve needle 6. With respect to the axial direction A, the annular groove 62 is located between the spring chamber 71 and the pressure chamber 4, for example, in the middle of the needle guide 61. The annular groove 62 connects to the low-pressure fuel line 50. Therefore, during large engine fuel operation, the annular groove 62 is filled with fuel at a low pressure. As mentioned above, the dominant low pressure in the low-pressure fuel line 50 is, for example, 13 bar (1.3 MPa). Therefore, the same pressure dominates in the annular groove 62.

[0082] Lubricant is supplied to the spring chamber 71 at a lower pressure than 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., a pressure approximately 20% higher than the dominant pressure in the annular groove 62). This pressure difference ensures that any leakage of the valve needle 6 along the space between the spring chamber 71 and the annular groove 62 always points towards the annular groove 62. Thus, lubricant can leak from the spring chamber 71 toward the annular groove 62 through the gap between the needle guide 61 and the valve needle 6, but fuel cannot leak from the annular groove 62 along the valve needle 6 into the spring chamber 71. Therefore, the annular groove 62 filled with fuel at a low pressure and the lubricant supplied to the spring chamber 71 at a higher pressure can be separated and sealed between the fuel side in contact with the fuel and the lubricant side in contact with the lubricant. Therefore, the spring chamber 71 is always without fuel. Thus, the lubricant also serves as a sealing fluid. Furthermore, during large engine operation using fuel, the valve needle 6 is gently lubricated.

[0083] Notice:

[0084] Any implementation of the apparatus described should be similarly related to the method (if any). Although not described in detail, different combinations of implementations may produce synergistic effects.

[0085] While presently preferred embodiments of the invention have been shown and described, it should be clearly understood that the invention is not limited thereto, but may be embodied and practiced differently in other ways within the scope of the following claims.

Claims

1. A fuel injector for injecting fuel into a combustion chamber of a large engine, the fuel injector comprising a nozzle holder (2) and a nozzle tip (3) having at least one injection orifice (31) through which fuel can be injected into the combustion chamber (100), the fuel injector further comprising a pressure chamber (4) and at least one high-pressure fuel line (5) and a valve needle (6) through which fuel can be introduced at high pressure into the pressure chamber (4) via the at least one high-pressure fuel line (5), the valve needle (6) being loaded by a spring (7) and interacting with a valve seat (8) to open and close the fluid connection between the pressure chamber (4) and the nozzle tip (3). Its features are, A flushing line (9) is arranged in the nozzle holder (2), wherein the flushing line (9) extends from the pressure chamber (4) to a discharge channel (20) configured to discharge fluid from the nozzle holder (2), and wherein a flushing valve (10) is provided, the flushing valve (10) being configured to open and close the fluid communication through the flushing line (9).

2. The fuel injector according to claim 1, wherein, The at least one high-pressure fuel line (5) can be connected to a source of flushing fluid, such that the flushing fluid can be supplied to the high-pressure fuel line (5).

3. The fuel injector according to any one of the preceding claims, wherein, The flushing valve (10) is configured as a lift valve.

4. The fuel injector according to any one of the preceding claims, wherein, The flushing valve (10) includes a flushing piston (11) and a flushing valve body (12) loaded by a flushing spring (13), and wherein a hydraulic pipe (30) is provided, the hydraulic pipe (30) being configured to supply hydraulic fluid to the flushing piston (11) to operate the flushing valve (10).

5. The fuel injector valve according to any one of the preceding claims, wherein, The spring (7) that loads the valve needle (6) is arranged in a spring chamber (71), and a lubrication tube (72) is provided therein, the lubrication tube (72) being configured to supply lubricant to the spring chamber (71).

6. The fuel injector according to claim 5, wherein, The nozzle holder (2) includes a needle guide (61) for receiving and guiding the valve needle (6), the needle guide (61) extending from the spring chamber (71) to the pressure chamber (4) such that the lubricant can enter the needle guide (61) from the spring chamber (71).

7. The fuel injector according to any one of claims 5 to 6 and claim 4, wherein the fuel injector is configured to receive the lubricant as the hydraulic fluid for operating the flush valve (10).

8. The fuel injector according to any one of claims 6 to 7, wherein, The needle guide (61) includes an annular groove (62) extending in the circumferential direction around the valve needle (6), wherein the annular groove (62) is connected to a low-pressure fuel line (50) for supplying fuel to the annular groove (62) at low pressure.

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

10. The fuel injector according to any one of the preceding claims, wherein the fuel injector is configured to receive the fuel at a pressure of at least 40 MPa.

11. The fuel injector according to any one of the preceding claims, wherein the fuel injector is configured to receive methanol as fuel.

12. The fuel injector according to any one of claims 2 to 11, wherein the fuel injector is configured to receive water as the flushing fluid.

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

14. The large engine according to claim 13, wherein, The at least one cylinder includes a second fuel injector for injecting a second fuel into the combustion chamber, wherein the second fuel is different from the fuel, and in particular, wherein the second fuel is diesel fuel for auto-ignition in the combustion chamber.

15. A method for operating a large engine according to any one of claims 13 or 14, the method comprising the steps of: - Temporarily open the flush 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 flush line (9).

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