Cylinder cover structure for large engine and large engine

Abstract

To provide a cylinder cover structure for a large engine.SOLUTION: A cylinder cover structure includes: a cylinder cover (2) for defining a combustion chamber (100) of a cylinder; and a fuel injector (3) for injecting fuel into the combustion chamber (100). The fuel injector (3) extends in an axial direction (A), and includes: a nozzle holder (4); a nozzle tip (5) having at least one nozzle hole (51); a pressure chamber (6) disposed within the nozzle holder (4); at least one fuel duct (7) disposed within the nozzle holder (4); a valve needle (8) interacting with a valve seat (9) for opening / closing fluid connection between the pressure chamber (6) and the nozzle tip (5); and a holding outer shell (10) for mounting the nozzle tip (5) to the nozzle holder (4).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cylinder cover arrangement for a large engine according to the preambles of the independent claims. Additionally, the invention relates to a large engine having such a cylinder cover arrangement.

[0002] Large engines, which may be configured as two-stroke or four-stroke engines, for example as longitudinally scavenged two-stroke large engines, are often used as drive units for ships or in stationary operation, for example to drive large generators for generating electrical energy. Since engines typically operate continuously for long periods of time, operational safety and availability are highly demanding. As a result, particularly long maintenance intervals, low wear, and economical handling of operating materials are central criteria for operators. Large engines typically have cylinders with an internal diameter (bore) of at least 200 mm. Today, large engines with bores of up to 980 mm or even more are in use. Within the framework of this application, the term "large engine" designates an internal combustion engine having a bore of the cylinder(s) of at least 200 mm, preferably at least 300 mm.

[0003] Large engines are typically configured as large diesel engines that run on heavy fuel oil. From the perspectives of economical and efficient operation, compliance with exhaust gas limit values, sustainability, CO2 emission reduction, and resource availability, alternatives to heavy fuel oil are now being sought for large diesel engines. In this regard, both liquid fuels, i.e., fuels that are introduced into the combustion chamber in a liquid state, and gaseous fuels, i.e., fuels that are introduced into the combustion chamber in a gaseous state, are used.

[0004] Examples of liquid fuels known as substitutes for heavy oils are other heavy hydrocarbons, especially those remaining as residues from petroleum refining, alcohols, especially methanol or ethanol, ammonia, gasoline, diesel, or even emulsions or suspensions. For example, it is known to use an emulsion known as MSAR (multiphase ultrafine atomized residue) as a fuel. A well-known suspension is a suspension of coal dust and water, which is also used as a fuel for large engines. Known gaseous fuels include natural gases, 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, with the engine operating 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 a cylinder.

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

[0007] Large diesel engines, capable of running on at least two or more different liquid or gaseous fuels, often operate in different operating modes depending on the fuel currently being used. In what is often referred to as diesel operation, combustion of the fuel generally occurs according to the principles of compression ignition or autoignition of the fuel. In what is often referred to as Otto operation, combustion occurs via inductive ignition of an ignitable premixed air-fuel mixture. This inductive ignition can occur, for example, via an electric spark, e.g., using a spark plug, or by 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-chamber connected to the combustion chamber. The process of inductive ignition via autoignition of a small amount of liquid or another autoignition fuel is sometimes referred to as pilot injection.

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

[0009] In particular, in light of climate change, there is a demand for reduced CO2 emissions and sustainability, as well as a reduction in the use of fossil fuels. Therefore, even for 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, such renewable fuels 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 corrodes pipes and 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 poses a health hazard requiring comprehensive mitigation measures.

[0011] The leakage of gaseous methanol into the atmosphere is commonly referred to as methanol slip. When methanol is used as a fuel in large engines, most of the methanol is consumed in the combustion process. However, some of the methanol remains unburned and may leak into the atmosphere, for example, by passing through the large engine's exhaust gas system. Methanol is harmful to the environment and to humans and animals. Therefore, significant efforts have been made to reduce methanol slip in large engines, such as those used for marine propulsion.

[0012] The present invention addresses this problem of methanol slip in large engines. It is therefore an object of the present invention to propose measures to reduce the methanol slip occurring in large engines capable of operating on methanol, without compromising the reliable, safe and economical operation of the large engine.

[0013] The subject matter of the invention which meets this object is characterized by the features of the independent patent claims.

[0014] Therefore, according to a first aspect of the present invention, there is proposed a cylinder cover arrangement for a large engine having at least one cylinder, the cylinder cover arrangement comprising: a cylinder cover for defining a combustion chamber of the cylinder; and a fuel injector for injecting fuel into the combustion chamber. The fuel injector extends in an axial direction and comprises a nozzle holder and a nozzle tip having at least one spray hole through which fuel can be injected into the combustion chamber. The fuel injector further comprises a pressure chamber arranged in the nozzle holder and at least one fuel duct arranged in the nozzle holder, through which fuel can be introduced into the pressure chamber. The fuel injector further comprises: a valve needle arranged in the pressure chamber, which interacts with a valve seat to open and close a fluid connection between the pressure chamber and the nozzle tip; and a holding shell for attaching the nozzle tip to the nozzle holder. The cylinder cover has an inner surface for defining a combustion chamber and an injector bore extending through the cylinder cover and opening into the inner surface, the injector bore configured to receive a fuel injector, the injector bore having a contact surface for contacting the nozzle tip, and the nozzle tip having a support surface for supporting the fuel injector within the injector bore, the support surface abutting against the contact surface of the injector bore during operation, i.e., when the fuel injector is inserted into the cylinder cover.

[0015] The nozzle tip has a proximal end facing the nozzle holder and a distal end facing the combustion chamber when mounted, the support surface being closer to the distal end than to the proximal end.

[0016] The contact surface is preferably spaced from an inner surface defining the combustion chamber such that, in the installed condition, the support surface is within the injector bore. The distance of the contact surface from the inner surface is preferably 0.75 to 1.25 times the outer diameter of the nozzle tip, and more preferably at least as large. In this case, the contact surface preferably provides a seat for the fuel injector such that, in the installed condition, only the distal end of the nozzle tip is within the combustion chamber.

[0017] These features allow the sac volume of the fuel injector to be significantly reduced. The sac volume of a fuel injector is the volume of the fuel flow passage between the valve seat and the spray hole(s) in the nozzle tip, i.e., the volume of the flow passage downstream of the valve seat and upstream of the spray hole(s). After the fuel injection process is completed, i.e., when the fluid connection between the pressure chamber and the nozzle tip is closed by the valve needle sealingly interacting with the valve seat, the sac volume downstream of the valve seat remains filled with uninjected fuel, which can drip into the combustion chamber after the injection process is completed. In particular, when methanol is used as a fuel, the methanol remaining in the sac volume after the injection process is completed evaporates and can enter the cylinder's combustion chamber and exhaust valve directly into the exhaust gas system, i.e., unburned. This unburned methanol causes methanol slip. Therefore, reducing the sac volume of the fuel injector significantly reduces methanol slip.

[0018] Because the nozzle tip is mounted directly on the cylinder cover, the axial length of the nozzle tip can be significantly reduced compared to prior art fuel injectors. By reducing the axial length of the nozzle tip, the suction volume is reduced. Therefore, when a large engine is operated on methanol, the reduction in suction volume directly reduces methanol slip.

[0019] According to known fuel injector designs, the nozzle tip is disposed within a nozzle retainer having a central opening through which the nozzle head projects into the combustion chamber. The nozzle retainer secures the nozzle head to the injector body. In such prior art designs, the nozzle retainer abuts the cylinder cover. Therefore, the nozzle retainer is axially located between the cylinder cover and the nozzle tip. In contrast, according to the present invention, the nozzle tip is in direct contact with the cylinder cover; i.e., there is no nozzle retainer between the cylinder cover and the nozzle tip. Therefore, the length of the nozzle tip, i.e., the axial extension of the nozzle tip, can be reduced, which significantly reduces the suction volume of the fuel injector and leads to reduced methanol or fuel slippage.

[0020] Although reducing the suction volume is particularly suited to reducing methanol slip, it should be noted that it can also be advantageous for other fuels. Furthermore, when operating large engines on fuels other than methanol, such as heavy fuel oil or diesel, the clearance between the valve seat and the spray hole poses a similar problem. At the end of fuel injection, the valve needle is pressed into the valve seat, so the fuel downstream between the valve seat and the spray hole is no longer pressurized by the fuel injection pressure. At this time, this portion of the fuel may enter the combustion chamber through the spray hole after the end of fuel injection in an insufficiently atomized or underpressurized state, resulting in little or no combustion, or at least no controlled combustion. This leads to further exhaust gas contamination and the accumulation of unburned fuel in the combustion chamber and all parts of the exhaust gas system. Therefore, reducing the suction volume is an advantageous measure even for fuels other than methanol.

[0021] According to a preferred embodiment, the nozzle tip includes a shoulder axially displaced from the support surface, and the retaining shell engages the shoulder to attach the nozzle tip to the nozzle holder during operation. By providing a shoulder axially displaced from the support surface, the retaining shell can engage with the nozzle tip to attach the nozzle tip to the nozzle holder without the need to interpose the retaining shell between the nozzle tip and the cylinder cover, thereby reducing the sack volume.

[0022] In view of a simpler configuration, the preferred measure is that the retaining shell is fixed to the nozzle holder during operation by means of a dowl pin, in particular only by means of a dowl pin, which extends perpendicular to the axial direction or tangentially to the nozzle holder. Since the main function of the retaining shell is to enable the nozzle tip to be removed from the injector bore together with the nozzle holder, for example for maintenance, attachment by a dowl pin is sufficient and simplifies the design.

[0023] Since the valve seat is located closer to the combustion chamber compared to conventional designs, the injector bore preferably includes a cooling sleeve located adjacent to the inner surface of the cylinder cover, the cooling sleeve at least partially surrounding the nozzle tip, the cooling sleeve forming at least a portion of the contact surface during operation. The cooling sleeve is thus a component of the cylinder cover that dissipates heat from the nozzle holder with the valve seat. The cooling sleeve includes a cooling sleeve bore that forms at least a portion of the injector bore.

[0024] In particular, the valve seat is a sensitive component that must be adequately cooled. With regard to cooling of the nozzle holder, and in particular the valve seat, the cylinder cover is preferably provided with cooling channels for a coolant, for example water, and the cooling sleeve is in fluid communication with the cooling channels.

[0025] The bearing surface of the nozzle tip is preferably located closer to the proximal end than to the distal end of the nozzle tip so that the bearing surface is closer to the valve seat.

[0026] A cooling sleeve, which provides at least a portion of the contact surface in contact with the support surface, is preferably used to provide cooling for the valve seat.

[0027] Preferably, the cooling sleeve is configured to at least partially surround the valve seat of the fuel injector, and thus preferably extends axially while the cooling sleeve is disposed radially outwardly around the valve seat.

[0028] Even more preferably, the cooling sleeve is configured to at least partially surround the pressure chamber of the fuel injector, such that the cooling sleeve extends axially at least as high as the pressure chamber, thereby enabling the cooling sleeve to effectively cool the nozzle tip, the valve seat, and the pressure chamber.

[0029] Furthermore, the cooling sleeve preferably includes at least one cooling bore for receiving a coolant, which is disposed close to the valve seat to cool the valve seat. By "close," we mean that thermal contact is formed between the valve seat and the cooling sleeve, for example, at a distance of 5 to 15 mm. This allows the coolant to be guided very close to the valve seat. This is advantageous in ensuring that the valve seat has a controllable temperature, even though the valve seat is disposed closer to the combustion chamber than in conventional configurations.

[0030] According to a preferred configuration, the cooling sleeve rests on an annular projection of the injector bore.

[0031] A further advantageous measure is that the injector bore includes an intermediate bushing surrounding the fuel injector and arranged axially adjacent to the cooling sleeve, the intermediate bushing being configured to press the cooling sleeve toward the inner surface of the cylinder cover. The intermediate bushing is then used to press down the cooling sleeve for insertion and adjustment. This configuration makes it possible to omit any bolt or similar connection at the end of the injector bore facing the combustion chamber. Furthermore, since no press fit is required for installing the cooling sleeve, the cooling sleeve can be removed or replaced without any special tools.

[0032] For the preferred application, the fuel injector is configured to receive methanol as the fuel.

[0033] According to a second aspect of the present invention there is provided a large engine comprising at least one cylinder having a combustion chamber, a piston arranged within the cylinder for reciprocating movement between top dead centre and bottom dead centre positions, the large engine further comprising a cylinder cover arrangement according to the first aspect of the present invention.

[0034] According to a preferred embodiment, the large engine is configured as a longitudinally scavenged, two-stroke large engine.

[0035] Furthermore, at least one cylinder of the large engine is provided with a second fuel injector for injecting a second fuel into the combustion chamber, the second fuel being preferably different from the fuel. Thus, the large engine is preferably configured to be capable of operating on at least two different fuels.

[0036] The second fuel is preferably diesel fuel for auto-ignition in the combustion chamber, so that the large engine is preferably configured as a large diesel engine.

[0037] Within the framework of the present application, the term "large diesel engine" refers to such an engine that can be operated at least in diesel operation. In particular, the term "large diesel engine" therefore also includes such multi-fuel large engines that can be operated in other modes, such as Otto operation, in addition to diesel operation.

[0038] Further advantageous measures and embodiments of the invention result from the dependent claims.

[0039] In the following, the invention will be explained in more detail by means of embodiments and with reference to the drawings. [Brief explanation of the drawings]

[0040] [Figure 1] 1 is a cross-sectional view of a cross section along an axial direction A of one embodiment of a cylinder cover component according to the present invention. FIG. [Figure 2] FIG. 2 is an enlarged detail of I in FIG. [Figure 3] FIG. 3 is a cross-sectional view of the nozzle tip and valve seat of the fuel injector of FIGS. 1 and 2. [Figure 4] 4 is a cross-sectional view of the retaining shell taken along section line IV-IV of FIG. 3. [Figure 5] 1 is a schematic diagram of a large engine.

[0041] Figure 1 shows a cross-sectional view of an embodiment of a cylinder cover arrangement according to the invention, designated in its entirety by the reference numeral 1. The cylinder cover arrangement 1 comprises a cylinder cover 2 for defining a combustion chamber 100 of a cylinder, and a fuel injector 3 for injecting fuel into the combustion chamber 100. In Figure 1, the cross-section is along an axial direction A defined by the central axis of the fuel injector 3. For better understanding, Figure 2 shows an enlarged view of detail I of Figure 1.

[0042] The cylinder cover assembly 1 is used in a large engine 200, and the fuel injector 3 is used to inject fuel into the combustion chamber 100 of the cylinder 110 of the large engine 200. FIG. 5 shows a schematic diagram of one embodiment of the large engine 200. In FIG. 5, only one of the cylinders 110 of the large engine 200 is shown. Typically, the large engine 200 includes multiple cylinders 110, for example, up to 12 or more cylinders. The term "large engine" typically refers to such internal combustion engines used as drive units for marine vessels or in stationary operation, for example, to drive large generators for producing electrical energy. Typically, the cylinders 110 of the large engine 200 each have an inner diameter (bore) of at least about 200 mm. Such large engines 200 are known in the art in a variety of different configurations, for example, as two-stroke engines or four-stroke engines.

[0043] In the following description, reference will be made to 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 arranged in each cylinder 110 so as to reciprocate between top dead center and bottom dead center.

[0044] The term "longitudinal scavenging" means that scavenging or charging air is introduced into the cylinder 110 in the area of ​​the lower end and the exhaust valve 130 is located in or on the cylinder cover 2 located at the upper end of the cylinder 110.

[0045] In particular, reference is made to a large longitudinally scavenged two-stroke engine that can be operated on different fuels, i.e., a fuel and a second fuel. Preferably, the large engine 200 is configured as a large diesel engine. The term "large diesel engine" refers to such an engine that can be operated in at least diesel operation. Thus, in particular, the term "large diesel engine" also includes such a large engine 200 that can be operated in another mode, such as Otto operation, in addition to diesel operation.

[0046] According to a preferred configuration, the large engine 200 can be operated using methanol as fuel or using an auto-ignition, liquid second fuel. Thus, when the large engine 200 is operated with the second fuel, it is operated in a 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 a suitable time, where it ignites according to the diesel principle of 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 3. Thus, each cylinder 110 is provided with at least one, but preferably multiple, fuel injectors 3 for injecting fuel and at least one, but preferably multiple, second fuel injectors 150 for injecting the second fuel.

[0047] The fuel injected into the combustion chamber 100 by the fuel injector 3 is, for example, a fuel for Otto operation, i.e., 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 self-igniting second fuel (e.g., diesel or heavy fuel oil) into the combustion chamber 100 or pre-chamber at a suitable moment, which then ignites itself and causes inductive ignition of the air-fuel mixture in the combustion chamber 100.

[0048] The introduction of a small amount of a self-igniting liquid or gaseous second fuel into the combustion chamber 100 or into at least one pre-chamber for the purpose of inductive ignition of the fuel is also called pilot ignition. In addition to diesel oil, it is also possible to use gas or alcohols such as methanol as the pilot fluid for pilot ignition.

[0049] In other embodiments, inductive ignition is achieved by spark ignition or laser pulses, or by any other means suitable for igniting fuel within the combustion chamber 100 .

[0050] 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 respect to the fuel methanol, it is preferred that operation with the fuel is according to the Otto principle.

[0051] Additionally, the heavy-duty diesel engine 200 may be operated in a mixed mode in which both the fuel and the secondary fuel are injected into the combustion chamber 100 of the cylinder 110. In the mixed mode, both the combustion of the fuel and the combustion of the secondary fuel contribute to the production of torque.

[0052] In the embodiments described herein, the heavy-duty engine is configured as a longitudinally scavenged, dual-fuel, two-stroke heavy-duty diesel engine that can be operated on methanol as a fuel and / or diesel fuel as a secondary fuel.

[0053] The dual-fuel heavy-duty diesel engine has a number of cylinders 110. In each cylinder 110, a piston 120 is connected in a manner known per se via a piston rod 121 to a crosshead 122, which is connected to a crankshaft via a pushrod or connecting rod 123, so that the movement of the piston 120 is transmitted via the piston rod 121, the crosshead 122 and the connecting rod 123 to the crankshaft 170, causing it to rotate. The upper side of the piston 120, together with the cylinder cover 2, defines a combustion chamber 100 into which the fuel and / or the second fuel is introduced.

[0054] The structure and individual components of the heavy-duty diesel engine 200, such as the injection system for fuel, the gas exchange system, the exhaust system, or the turbocharger system for supplying scavenging or charging 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 do not require further explanation here.

[0055] In the longitudinally scavenged two-stroke heavy-duty diesel engine 200, scavenging air slots 115 are typically provided in the lower region of each cylinder 110 or cylinder liner. These slots are periodically opened and closed by the movement of the piston 120 within the cylinder 110, allowing scavenging air provided by the turbocharger under charge pressure to flow through the scavenging air slots 115 into the cylinder 110 as long as they are open. A typically centrally located exhaust valve 130 is provided within the cylinder cover 2, through which exhaust gases can be discharged from the cylinder 110 into the exhaust system after the combustion process. The exhaust system directs at least a portion of the exhaust gases to the turbocharger turbine, whose compressor provides scavenging air, also referred to as charge air, in a scavenging air receiver under scavenging pressure. The scavenging air receiver is in fluid communication with the scavenging air slots 115 of the cylinder 110.

[0056] Each cylinder 110 includes at least one fuel injector 3 for injecting fuel into the combustion chamber 100 of the cylinder 110. Preferably, the cylinder 110 includes multiple fuel injectors 3, for example, two or three, to distribute fuel evenly within the combustion chamber 100. In the embodiment of the large engine 200 described herein, exactly three fuel injectors 3 are provided (only one fuel injector 3 is shown in the schematic diagram of FIG. 5). Each fuel injector 3 is located within the cylinder cover 2 of the cylinder 110. The cylinder cover 2 includes an inner surface 21 for defining the combustion chamber 100 and an injector bore 22 extending through the cylinder cover 2 and opening into the inner surface 21. The injector bore 22 is configured to receive the fuel injector 3. Preferably, the fuel injector 3 is located within the cylinder cover 2 near the exhaust valve 130.

[0057] 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 110 includes multiple second fuel injectors 150, e.g., two or three, to evenly distribute the second fuel within the combustion chamber 100. In the embodiment of the large engine 200 described herein, exactly three second fuel injectors 150 are provided (only one second fuel injector 150 is shown in the schematic diagram of FIG. 5). Each second fuel injector 150 is positioned within the cylinder cover 2 of the cylinder 110 in a manner known in the art. Preferably, the second fuel injectors 150 are positioned within the cylinder cover 2 near the exhaust valve 130.

[0058] Nowadays, large diesel engines or large engines 200 are generally operated in a fully electronically controlled manner. An engine control unit 180 operates and controls, by means of electrical or electronic signals and commands, 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). In addition, the engine control unit 180 receives information from several detectors, sensors, or measuring devices.

[0059] 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, which may be operated on a fuel and / or a second fuel. The heavy-duty engine may also be any other type of heavy-duty engine. In particular, the heavy-duty engine may be configured for the combustion of only one fuel, for example methanol.

[0060] The present invention relates to a cylinder cover arrangement 1 comprising a cylinder cover 2 and a fuel injector 3 configured to inject fuel into a combustion chamber 100. Preferably, the fuel injector 3 is configured to receive methanol as fuel.

[0061] Next, an embodiment of the cylinder cover assembly 1 will be described in more detail, with particular reference to Figures 1 and 2.

[0062] The cylinder cover arrangement 1 comprises a cylinder cover 2 and a fuel injector 3 disposed in an injector bore 22 extending through the cylinder cover 2 and opening into an inner surface 21 defining a combustion chamber 100. The fuel injector 3 for injecting fuel into the combustion chamber 100 comprises a nozzle holder 4 and a nozzle tip 5 attached to the nozzle holder 4 by a retaining shell 10.

[0063] For better understanding, FIG. 3 shows an enlarged cross-sectional view of the nozzle tip 5 of the fuel injector 3 shown in FIGS. 1 and 2, and FIG. 4 shows a cross-sectional view of the retaining shell 10 along section line IV-IV in FIG. 3.

[0064] The nozzle tip 5 has at least one, but usually several, spray holes 51 through which fuel can be injected into the combustion chamber 100. The fuel injector 3 further comprises a pressure chamber 6 and at least one fuel duct 7 through which fuel can be introduced at high pressure into the pressure chamber 6. Within the pressure chamber 6 a valve needle 8 loaded by a spring 81 is provided which interacts with a valve seat 9 to open and close the fluid connection between the pressure chamber 6 and the nozzle tip 5.

[0065] 1 and 2, two fuel ducts 7 are provided in fluid communication with the high-pressure fuel port 71. The high-pressure fuel port 71 is connected to a high-pressure fuel source (not shown), such as a fuel booster unit, that can supply high-pressure fuel to the high-pressure fuel port 71.

[0066] When methanol is used as the fuel, the fuel booster unit is preferably configured as a methanol booster unit that delivers methanol at a high pressure of at least 400 bar (40 MPa) to the high pressure fuel port 71. For example, the high pressure may be 600 bar (60 MPa) or up to 750 bar (75 MPa).

[0067] When fuel injection is required, the fuel booster unit is activated to deliver a pre-determinable amount of fuel at high pressure to the high-pressure port 71 of the fuel injector 3. The high-pressure fuel enters the pressure chamber 6 through the fuel duct 7 and lifts the valve needle 8 from the valve seat 9 against the force of a spring 81, thereby opening the fluid connection between the pressure chamber 6 and the nozzle tip 5. The fuel enters the nozzle tip 5 and is injected through the spray holes 51 into the combustion chamber 100. In the combustion chamber 100, the fuel is then ignited by induction. Preferably, induction ignition is performed 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.

[0068] After a pre-determinable amount of high pressure fuel has been delivered to the fuel injector 3, injection terminates, i.e., high pressure fuel is no longer delivered to the high pressure fuel port 71 of the fuel injector 3. This causes the fuel pressure in the pressure chamber 6 to decrease, which in turn causes the spring 81 to push the valve needle 8 back into sealing engagement with the valve seat 9, thereby closing the fluid connection between the pressure chamber 6 and the nozzle tip 5.

[0069] According to the present invention, the injector bore 22 is provided with a contact surface 23 for contacting the nozzle tip 5, and the nozzle tip 5 is provided with a support surface 52 for supporting the fuel injector 3 within the injector bore 22. The support surface 52 abuts the contact surface 23 of the injector bore 22.

[0070] Therefore, the nozzle tip 5 is placed directly on the cylinder cover 2. Therefore, compared to a conventional configuration in which a nozzle retainer for holding the nozzle tip is disposed between the nozzle tip and the cylinder cover, thereby abutting the cylinder cover, the axial length of the nozzle tip 5, i.e., the extension of the nozzle tip 5 in the axial direction A, can be significantly reduced. In the configuration according to the present invention, the support surface 52 of the nozzle tip 5 itself abuts against the cylinder cover 2, i.e., the contact surface 23 of the injector bore 22.

[0071] The sack volume is reduced by shortening the axial length of the nozzle tip 5. Therefore, when a large engine is run on methanol, the reduced sack volume directly reduces methanol slip.

[0072] With respect to the retaining shell 10, as best shown in Figure 3, the retaining shell preferably engages a shoulder 53 on the nozzle tip 5, the shoulder being axially displaced from the support surface 52. The shoulder 53 is located closer to the valve seat 9 than the support surface 52. This configuration allows the nozzle tip 5 to be attached to the nozzle holder 4 without the need to position the retaining shell 10 between the nozzle tip 5 and the cylinder cover 2 in the axial direction A, which leads to the aforementioned reduction in sack volume and therefore reduced methanol slippage.

[0073] This configuration of the retaining shell 10 engaging the shoulder 53 of the nozzle tip 5 enables the retaining shell 10 to fulfill its primary function, namely, to attach the nozzle tip 5 to the nozzle holder 4 so that the nozzle tip 5 together with the nozzle holder 4 can be withdrawn from the injector bore 22, thereby allowing the nozzle holder 4 together with the nozzle tip 5 to be removed from the cylinder cover 2. Removal of the fuel injector 3 from the cylinder cover 2 may be required, for example, for maintenance or repair of these components.

[0074] Compared to known nozzle retainers for fixing the nozzle tip to the nozzle holder, the retaining shell 10 of the fuel injector 3 in the cylinder cover arrangement 1 according to the invention can be made significantly smaller, thereby reducing the required axial length of the nozzle tip 5. This, as mentioned above, results in a reduction in sack volume and methanol slip.

[0075] Preferably, as shown in Figure 4, the retaining shell 10 is fixed to the nozzle holder 4 by means of a dowel pin 11 which extends perpendicular to the axial direction A or tangentially to the nozzle holder 4. Particularly preferably, the dowel pin 11 is the only fastener for the retaining shell 10, i.e. the retaining shell 10 is fixed to the nozzle holder 4 only by the dowel pin 11. This simplifies the design.

[0076] Due to the reduced axial length of the nozzle tip 5, the valve seat 9 of the fuel injector 3 is positioned closer to the combustion chamber 100 compared to conventional designs. As the valve seat 9 is particularly sensitive to high temperatures, it is preferable to provide measures specifically for cooling the valve seat 9.

[0077] 1 and 2, the injector bore 22 is therefore provided with a cooling sleeve 25 disposed adjacent the inner surface 21 of the cylinder cover 2. The cooling sleeve 25 is part of the cylinder cover 2 and surrounds the nozzle tip 5. The cooling sleeve 25 forms a contact surface 23 against which the support surface 52 of the nozzle tip 5 abuts.

[0078] Preferably, the cooling sleeve 25 is configured such that it also surrounds the valve seat 9 of the fuel injector. In the embodiment shown in Figures 1 and 2, the cooling sleeve 25 extends in the axial direction A to a height above the pressure chamber 6 of the fuel injector 3. The cooling sleeve therefore surrounds the nozzle tip 5 and valve seat 9 of the fuel injector as well as the pressure chamber 6. The cooling sleeve 25 rests on an annular projection 26 of the injector bore 22.

[0079] The cooling sleeve 25 dissipates heat from the fuel injector 3, particularly from those components of the fuel injector that are located near the combustion chamber 100 and are therefore exposed to high temperatures therein. In particular, the cooling sleeve 25 cools the valve seat 9, which is particularly sensitive.

[0080] Preferably, the cylinder cover 2 includes cooling channels 24 for a coolant, and the cooling sleeve 25 is in fluid communication with the cooling channels 24. The coolant is a fluid, preferably a liquid, such as water. The coolant flows through the cooling channels 24, and because the cooling sleeve 25 is in fluid communication with the cooling channels 24, the coolant impinges directly on the cooling sleeve 25, dissipating heat from the cooling sleeve.

[0081] Providing the cooling sleeve 25 as a separate component of the cylinder cover 2 has the advantage that the cooling sleeve 25 can be manufactured from a different, e.g., higher-quality, material than the other components of the cylinder cover. The cooling sleeve 25 can be made of a material that is particularly well suited to dissipating heat. Preferably, the cooling sleeve 25 is made of a material with high heat resistance, such as X39CrMo17-1. The cooling sleeve is configured and optimized to be exposed to high thermal stresses.

[0082] A further advantage of providing the cooling sleeve 25 as a separate component of the cylinder cover 2 is that it is easy to provide the cooling sleeve 25 with internal cooling bores 251 to further improve cooling of the cooling sleeve 25. Because the cooling sleeve 25 is a separate component, it is easier to drill bores in the cooling sleeve 25 to create internal cooling bores in the cooling sleeve 25. The cooling bores 251 are in fluid communication with the cooling channels 24 so that coolant can enter the cooling bores 251.

[0083] 2, because the valve seat 9 is particularly heat sensitive, the cooling sleeve 25 includes at least one cooling bore 251 for receiving a coolant that is positioned near, i.e., in thermal contact with, the valve seat 9 to cool the valve seat 9. The cooling bore 251 directs the coolant near the valve seat 9. This ensures that the valve seat 9 has a controlled temperature even though the valve seat 9 is positioned closer to the combustion chamber 100 compared to conventional designs.

[0084] The injector bore 22 further includes an intermediate bushing 27 surrounding the fuel injector 3 and positioned axially adjacent to the cooling sleeve 25. The intermediate bushing 27 is configured to press the cooling sleeve 25 against the inner surface 21 of the cylinder cover 2. A connecting sleeve 28 is positioned axially adjacent to the intermediate bushing 27 and abuts against it. As is known in the art, the connecting sleeve 28 is typically used to reduce tubing connections to the fuel injector 3. In the embodiment of the invention shown in FIG. 1 , the connecting sleeve 28 has the additional function of exerting an axial force on the intermediate bushing 27, which in turn presses down on the cooling sleeve 25.

[0085] This arrangement has the advantage that no bolt connection is required at the lower end of the injector bore 22 adjacent the inner surface 21 of the cylinder cover 2. Furthermore, during maintenance or repair, the cooling sleeve 25 may be replaced without any special tools, especially since no press fit is required to secure the cooling sleeve 25.

[0086] Note: Any embodiment described with respect to an apparatus, if any, also relates to the method. Synergistic effects may arise from different combinations of embodiments, which may not be described in detail.

[0087] While presently preferred embodiments of the present invention have been shown and described, it is to be expressly understood that the invention is not limited thereto and may be variously embodied and carried out in other ways within the scope of the following claims.

Claims

1. A cylinder cover arrangement for a large engine having at least one cylinder, said cylinder cover arrangement comprising a cylinder cover (2) for defining a combustion chamber (100) of said cylinder, and a fuel injector (3) for injecting fuel into said combustion chamber (100), said fuel injector (3) extending in an axial direction (A); - a nozzle holder (4), a nozzle tip (5) having at least one spray hole (51) through which the fuel can be injected into the combustion chamber (100); a pressure chamber (6) located within said nozzle holder (4); at least one fuel duct (7) arranged in said nozzle holder (4), through which said fuel can be introduced into said pressure chamber (6); a valve needle (8) arranged in said pressure chamber (6) and interacting with a valve seat (9) to open and close the fluid connection between said pressure chamber (6) and said nozzle tip (5); - a retaining shell (10) for attaching said nozzle tip (5) to said nozzle holder (4); Equipped with the cylinder cover (2) has an inner surface (21) for defining the combustion chamber (100), and an injector bore (22) extending through the cylinder cover (2) and opening into the inner surface (21); 1. A cylinder cover arrangement, wherein the injector bore (22) is configured to receive the fuel injector (3), wherein the injector bore (22) has a contact surface (23) for contacting the nozzle tip (5), and the nozzle tip (5) has a support surface (52) for supporting the fuel injector (3) within the injector bore (22), the support surface (52) being configured to abut the contact surface (23) of the injector bore (22) during operation. Cylinder cover component.

2. 2. A cylinder cover arrangement according to claim 1, wherein the nozzle tip (5) comprises a shoulder (53) axially displaced from the support surface (52), and the retaining shell (10) is configured to engage the shoulder (53) to attach the nozzle tip (5) to the nozzle holder (4).

3. 3. A cylinder cover arrangement according to claim 1 or 2, wherein the retaining shell (10) is configured to be fixed to the nozzle holder (4) by means of a dowel pin (11) extending perpendicular to the axial direction (A) or tangentially to the nozzle holder (4), in particular by means of the dowel pin (11) alone.

4. 4. A cylinder cover arrangement according to claim 1, wherein the injector bore (22) comprises a cooling sleeve (25) arranged adjacent to the inner surface (21) of the cylinder cover (2), the cooling sleeve (25) at least partially surrounding the nozzle tip (5), and the cooling sleeve (25) forming at least a part of the contact surface (23).

5. 5. The cylinder cover arrangement according to claim 4, wherein the cylinder cover (2) comprises cooling channels (24) for a coolant, and the cooling sleeve (25) is in fluid communication with the cooling channels (24).

6. 6. A cylinder cover arrangement according to claim 4 or 5, wherein the cooling sleeve (25) is configured to at least partially surround the valve seat (9) of the fuel injector (3).

7. 7. A cylinder cover arrangement according to any one of claims 4 to 6, wherein the cooling sleeve (25) is configured to at least partially surround the pressure chamber (6) of the fuel injector (3).

8. 8. The cylinder cover arrangement according to claim 5, wherein the cooling sleeve (25) comprises at least one cooling bore (251) for receiving the coolant, the cooling bore (251) being arranged near the valve seat (9) for cooling the valve seat (9).

9. A cylinder cover arrangement according to any one of claims 4 to 8, wherein the cooling sleeve (25) is configured to rest on an annular projection (26) of the injector bore (22).

10. 10. The cylinder cover arrangement according to claim 4, wherein the injector bore (22) comprises an intermediate bush (27) surrounding the fuel injector (3) and arranged axially adjacent to the cooling sleeve (25), the intermediate bush (27) being configured to press the cooling sleeve (25) towards the inner surface (21) of the cylinder cover (2).

11. A cylinder cover arrangement according to any one of claims 1 to 10, wherein the fuel injector (3) is configured to receive methanol as fuel.

12. A large engine, in particular a longitudinally scavenged two-stroke large engine, comprising at least one cylinder having a combustion chamber (100), in which a piston is arranged in said cylinder for reciprocating movement between a top dead center position and a bottom dead center position, The large engine is characterized in that it comprises a cylinder cover arrangement (1) according to any one of claims 1 to 11. Large engine.

13. 13. A large engine according to claim 12, wherein the at least one cylinder comprises a second fuel injector for injecting a second fuel into the combustion chamber (100), the second fuel being different from the fuel, in particular the second fuel being a diesel fuel for auto-ignition in the combustion chamber (100).

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