A cylinder cover arrangement for a large engine and a large engine

Abstract

A cylinder cover arrangement for a large engine having at least one cylinder is proposed, the cylinder cover arrangement comprising a cylinder cover (2) for delimiting a combustion chamber (100) of the cylinder and a fuel injector (3) for injecting a fuel into the combustion chamber (100), the fuel injector (3) extending in an axial direction (A) and comprising a nozzle holder (4) and a nozzle tip (5) having at least one spray hole (51), through which the fuel can be injected into the combustion chamber (100), further comprising a pressure chamber (6) and at least one fuel duct (7), through which the fuel can be introduced into the pressure chamber (6), a valve needle (8) arranged in the pressure chamber (6) and interacting with a valve seat (9) for opening and closing a fluid connection between the pressure chamber (6) and the nozzle tip (5), and a retaining husk (10) for attaching the nozzle tip (5) to the nozzle holder (4), wherein the cylinder cover (2) comprises an inner surface (21) for delimiting the combustion chamber (100) and an injector bore (22) extending through the cylinder cover (2) and opening into the inner surface (21), wherein the injector bore (22) is configured to receive the fuel injector (3). The injector bore (22) comprises a contact surface (23) for contacting the nozzle tip (5), and the nozzle tip (5) comprises a support face (52) for supporting the fuel injector (3) in the injector bore (22), wherein the support face (52) abuts the contact surface (23) of the injector bore (22). Furthermore, a large engine comprising such a cylinder cover arrangement is proposed.

Description

[0001] The invention relates to a cylinder cover arrangement for a large engine according to the preamble of the independent patent claim. In addition, the invention relates to a large engine having such a cylinder cover arrangement.

[0002] Large engines, which can 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, e.g. to drive large generators for generating electrical energy. The engines usually run for considerable periods in continuous operation, which places high demands on operational safety and availability. As a consequence, particularly long maintenance intervals, low wear and an economical handling of the operating materials are central criteria for the operator. Large engines typically have cylinders, which inner diameter (bore) is at least 200 mm. Nowadays, large engines with a bore of up to 980 mm or even more are used. Within the framework of this application, the term "large engine" designates an internal combustion engine with a bore of the cylinder(s), which is at least 200 mm and preferably at least 300 mm.

[0003] Large engines are classically configured as large diesel engines, which are operated with heavy fuel oil. Under the aspects of economic and efficient operation, compliance with exhaust-gas limit values, sustainability, reduction of CO 2 emission and the availability of resources, alternatives to the fuel heavy fuel oil are now also being sought for large diesel engines. In this respect, both liquid fuels are used, i.e. fuels that are introduced into the combustion chamber in the liquid state, and gaseous fuels, i.e. fuels that are introduced into the combustion chamber in the gaseous state.

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

[0005] In particular, large diesel engines are also known which can be operated with at least two different fuels, whereby the engine is operated either with one fuel or with the other fuel depending on the operating situation or environment. It is also known to concurrently inject the two different fuels into the combustion chamber of the cylinder.

[0006] Large diesel engines that can be operated with two different fuels are referred to as dual-fuel large diesel engine. Depending on the two fuels, said engines may be operated in a liquid mode in which a liquid fuel is introduced into the cylinder for combustion and in a gas mode in which a gas is introduced into the cylinder as fuel.

[0007] Large diesel engines, which can be operated with at least two or even more different liquid or gaseous fuels, are often operated in different operating modes depending on the fuel currently in use. In the operating mode often referred to as diesel operation, the combustion of the fuel generally takes place according to the principle of compression ignition or self-ignition of the fuel. In the mode often referred to as Otto operation, combustion takes place by induced ignition of an ignitable pre-mixed air-fuel mixture. This induced ignition can take place, for example, by an electrical spark, e.g. with a spark plug, or also by the self-ignition of a small injected amount of fuel, which then causes the induced ignition of another fuel. The small amount of fuel intended for self-ignition is directly inserted into the combustion chamber or injected into a pre-chamber connected to the combustion chamber. The process of induced ignition by self-ignition of a small amount of a liquid or another self-igniting fuel is sometimes referred to as pilot injection.

[0008] Furthermore, mixed forms using both Otto and diesel operation are also known.

[0009] In particular in view of the climate change, the reduction of CO 2 production and sustainability a reduction in the use of fossil fuels is strived for. Thus, also for large engine alternatives are investigated to at least reduce or even completely avoid the use of fossil fuels. Even if this is still a long way, a partial replacement of fossil fuels by renewable fuels is considered as a large success.

[0010] One alternative to fossil fuel is for example methanol. However, such renewable fuels such as methanol can cause corrosion problems in the fuel distribution and injection system, in particular during standstill of the engine or during operation with another fuel. The stagnant methanol corrosively attacks the pipes or other components of the fuel injection system. Furthermore, there is the risk that methanol escapes from the engine, e.g. as vapor, into the space which is accessible to engine maintenance or engine operating personnel. This constitutes a health hazard requiring comprehensive mitigation measures.

[0011] The escaping of gaseous methanol into the atmosphere is usually referred to as methanol slip. When methanol is used as a fuel in a large engine, most of the methanol is consumed in the combustion process. However, some of the methanol remains unburned and may escape into the atmosphere, e.g. by passing the exhaust gas system of the large engine. Methanol is hazardous for the environment as well as for human beings and animals. Therefore, great efforts are made to reduce the methanol slip occurring in large engines, such as large engines used for ship propulsion.

[0012] The present invention addresses this problem of methanol slip in large engines. Accordingly, it is an object of the invention to propose measures for reducing the methanol slip occurring in large engines operable with methanol without reducing the reliable, safe, and economical operation of the large engine.

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

[0014] Thus, according to a first aspect of the invention, a cylinder cover arrangement for a large engine having at least one cylinder is proposed, the cylinder cover arrangement comprising a cylinder cover for delimiting a combustion chamber of the cylinder and a fuel injector for injecting a 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 the 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 duct the fuel can be introduced into the pressure chamber. The fuel injector further comprises a valve needle arranged in the pressure chamber and interacting with a valve seat for opening and closing a fluid connection between the pressure chamber and the nozzle tip, and a retaining husk for attaching the nozzle tip to the nozzle holder. The cylinder cover comprises an inner surface for delimiting the combustion chamber and an injector bore extending through the cylinder cover and opening into the inner surface, wherein the injector bore is configured to receive the fuel injector. The injector bore comprises a contact surface for contacting the nozzle tip, and the nozzle tip comprises a support face for supporting the fuel injector in the injector bore. The support face then abuts the contact surface of the injector bore in operation, i.e. when the fuel injector is inserted into the cylinder cover.

[0015] By these features the sac volume of the fuel injector can be considerably reduced. The sac volume of the fuel injector is the volume of the fuel flow path between the valve seat and the spray hole(s) in the nozzle tip, i.e. the volume of the flow path downstream of the valve seat and upstream of the spray hole(s). After the end of the fuel injection process, i.e. when the valve needle has closed the fluid connection between the pressure chamber and the nozzle tip by sealingly interacting with the valve seat, the sac volume downstream of the valve seat is still filled with uninjected fuel which can dribble into the combustion chamber after the end of the injection process. In particular, when methanol is used as fuel, the methanol remaining in the sac volume after the end of the injection process can evaporate and directly, i.e. unburned, enter the exhaust gas system through the combustion chamber and the exhaust valve of the cylinder. This unburned methanol generates methanol slip. Therefore, reducing the sac volume of the fuel injector results in a considerable reduction of the methanol slip.

[0016] Since the nozzle tip rests directly on the cylinder cover, the axial length of the nozzle tip can be considerably reduced compared to prior art fuel injectors. By reducing the axial length of the nozzle tip, the sac volume is reduced. Thus, when the large engine is operated with methanol, the reduced sac volume directly reduces the methanol slip.

[0017] According to known designs of a fuel injector, the nozzle tip is arranged in a nozzle retainer having a central opening, through which the nozzle head protrudes into the combustion chamber. The nozzle retainer fixes the nozzle head to the injector body. In such a prior art design, the nozzle retainer abuts the cylinder cover. Thus, regarding the axial direction, the nozzle retainer is arranged between the cylinder cover and the nozzle tip. In contract, according to the invention, the nozzle tip is in direct contact with the cylinder cover, i.e. without a nozzle retainer between the cylinder cover and the nozzle tip. Therefore, the length of the nozzle tip, i.e. the nozzle tip's extension in the axial direction, can be reduced, therewith considerably reducing the sac volume of the fuel injector, which leads to the reduced methanol or fuel slip.

[0018] Even if the reduced sac volume is particularly suited to reduce the methanol slip, it must be pointed out that the reduced sac volume may be advantageous for other fuels, too. Also when operating a large engine with different fuels than methanol, e.g. heavy fuel oil or a diesel oil, the spatial distance between the valve seat and the spray holes involves a similar problem. At the termination of the fuel injection, the valve needle is pressed into the valve seat so that the fuel which is located downstream between the valve seat and the spray holes is no longer pressurized by the injection pressure of the fuel. This portion of the fuel can then enter through the spray holes in a poorly atomized or unpressurized manner into the combustion chamber after the termination of the fuel injection, where it burns only slightly or not at all or at least not in a controlled manner. It thus leads to additional pollution of the exhaust gas and to deposits of unburned fuel at all parts of the combustion chamber and of the exhaust gas system. Thus, the reduction of the sac volume is an advantageous measure also for fuels different from methanol.

[0019] According to a preferred embodiment, the nozzle tip comprises a shoulder axially displaced from the support face, wherein the retaining husk, in operation, engages with the shoulder for attaching the nozzle tip to the nozzle holder. By providing the shoulder, which is axially displaced from the support face, the retaining husk can engage with the nozzle tip for attaching the nozzle tip to the nozzle holder without the need to interpose the retaining husk between the nozzle tip and the cylinder cover. This leads to a reduced sac volume.

[0020] In view of a simpler configuration, it is a preferred measure that the retaining husk is, in operation, fixed to the nozzle holder by means of a dowl pin extending perpendicular to the axial direction or tangentially to the nozzle holder, in particular solely by means of the dowl pin. Since it is the main function of the retaining husk that the nozzle tip can be removed from the injector bore together with the nozzle holder, e.g. for maintenance, the attachment by means of the dowl pin is fully sufficient and simplifies the design.

[0021] Since the valve seat is arranged closer to the combustion chamber as compared to conventional designs, it is preferred that the injector bore comprises a cooling sleeve arranged adjacent to the inner surface of the cylinder cover, wherein the cooling sleeve at least partially encompasses the nozzle tip, and wherein the cooling sleeve at least partially forms the contact surface in operation. Thus, the cooling sleeve is a component of the cylinder cover, with discharges heat from the nozzle holder which comprises the valve seat. In particular the valve seat is a sensitive component that should be sufficiently cooled.

[0022] Regarding the cooling of the nozzle holder and in particular of the valve seat, it is preferred that the cylinder cover comprises a cooling channel for a coolant, e.g. water, wherein the cooling sleeve is in fluid communication with the cooling channel.

[0023] Preferably, the cooling sleeve is configured to at least partially encompass the valve seat of the fuel injector. Thus, it is preferred that the cooling sleeve extends in the axial direction as far that the cooling sleeve is arranged radially outwardly around the valve seat.

[0024] Even more preferred, the cooling sleeve is configured to at least partially encompass the pressure chamber of the fuel injector. Thus, the cooling sleeve extends in the axial direction at least to the same level at which the pressure chamber is arranged. Therewith, the cooling sleeve can effectively cool the nozzle tip, the valve seat, and the pressure chamber.

[0025] Furthermore, it is preferred that the cooling sleeve comprises at least one cooling bore for receiving the coolant, wherein the cooling bore is arranged close to the valve seat for cooling the valve seat. By "close", it is meant that a thermal contact is formed between the valve seat and the cooling sleeve, e.g., in a distance of 5-15mm. Thus, it is possible to guide the coolant very close to the valve seat. This is advantageous to assure that the valve seat has a controllable temperature, although the valve seat is arranged closer to the combustion chamber as compared to conventional configurations.

[0026] According to a preferred configuration, the cooling sleeve rests on an annular protrusion of the injector bore.

[0027] It is a further advantageous measure that the injector bore comprises an intermediate bush encompassing the fuel injector and arranged axially adjacent to the cooling sleeve, wherein the intermediate bush is configured for pressing the cooling sleeve towards the inner surface of the cylinder cover. Thus, for inserting and adjusting the cooling sleeve, the intermediate bush is used to press down the cooling sleeve. This configuration allows to omit any bolt connection or similar connection at the combustion chamber facing end of the injector bore. Furthermore, the cooling sleeve can be removed or exchanged without any special tool, in particular, since it does not require a press fit for mounting the cooling sleeve.

[0028] In view of a preferred application, the fuel injector is configured to receive methanol as fuel.

[0029] As a second aspect of the invention, a large engine is proposed comprising at least one cylinder having a combustion chamber, wherein a piston is arranged in the cylinder for a reciprocating movement between a top dead center position and a bottom dead center position, wherein the large engine further comprises a cylinder cover arrangement according to the first aspect of the invention.

[0030] According to a preferred embodiment, the large engine is configured as a longitudinally scavenged two-stroke large engine.

[0031] Furthermore, it is preferred that the at least one cylinder of the large engine comprises a second fuel injector for injecting a second fuel into the combustion chamber, wherein the second fuel is different from the fuel. Thus, the large engine is preferably configured to be operable with at least two different fuels.

[0032] The second fuel is preferably a diesel fuel for self-ignition in the combustion chamber. Thus, it is preferred that the large engine is configured as a large diesel engine.

[0033] Within the framework of this application, the term "large diesel engine" refers to such engines, which can be operated at least in a diesel operation. In particular, the term "large diesel engine" thus also comprises such multi fuel large engines that can be operated in another mode, e.g. Otto operation, in addition to diesel operation.

[0034] Further advantageous measures and embodiments of the invention result from the dependent claims.

[0035] In the following, the invention is explained in more detail by means of embodiments and referring to the drawing. In the drawing show: Fig. 1:a cross-sectional view of an embodiment of a cylinder cover arrangement according to the invention in a section along an axial direction A. Fig. 2:an enlarged detail I from Fig 1, Fig. 3:a cross-sectional view of the nozzle tip and the valve seat of the fuel injector of Figs. 1 and 2, Fig. 4:a cross-sectional view of the retaining husk along the cutting line IV-IV in Fig. 3, and Fig. 5:a schematic representation of a large engine.

[0036] Fig. 1 shows a cross-sectional view of an embodiment of a cylinder cover arrangement according to the invention, which is designated in its entirety with reference numeral 1. The cylinder cover arrangement 1 comprises a cylinder cover 2 for delimiting a combustion chamber 100 of a cylinder and a fuel injector 3 for injecting a fuel into the combustion chamber 100. In Fig. 1 the section is along an axial direction A, which is defined by the central axis of the fuel injector 3. For a better understanding, Fig. 2 shows an enlarged representation of the detail I in Fig. 1.

[0037] The cylinder cover arrangement 1 is used for a large engine 200, and the fuel injector 3 is used for the injection of a fuel into the combustion chamber 100 of a cylinder 110 of the large engine 200. Fig. 5 shows a schematic representation of an embodiment of a large engine 200. In Fig. 5 only one of the cylinders 110 of the large engine 200 is shown. Usually, the large engine 200 comprises a plurality of cylinders 110, for example up to twelve cylinders 110 or even more. The term "large engine" refers to such internal combustion engines that are usually used as drive unit for ships or also in stationary operation, e.g. to drive large generators for generating electrical energy. Typically, the cylinders 110 of a large engine 200 each have an inner diameter (bore) of at least about 200 mm. Large engines 200 as such are known in the art in various different configurations, for example as two-stroke engines or as four stroke engines.

[0038] 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 a reciprocating movement between a top dead center and a bottom dead center.

[0039] The term "longitudinally scavenged" means that the scavenging or charging air is introduced into the cylinder 110 in the area of the lower end and an exhaust valve 130 is arranged in or at the cylinder cover 2 located at the upper end of the cylinder 110.

[0040] In particular, reference is made to a large longitudinally scavenged two-stroke engine, which can be operated with different fuels, namely with a fuel and with a second fuel. Preferably, the large engine 200 is configured as a large diesel engine. The term "large diesel engine" refers to such engines, which can be operated at least in a diesel operation. In particular, the term "large diesel engine" thus also comprises such large engines 200 that can be operated in another mode, e.g. Otto operation, in addition to diesel operation.

[0041] According to a preferred configuration, the large engine 200 can be operated with methanol as fuel or with a self-igniting and liquid second fuel. Thus, when the large engine 200 is operated with the second fuel, the large engine 200 is operated in a liquid mode, in which only the liquid second fuel is injected into the combustion chamber 100 of the cylinder 110. Usually the liquid fuel, for example 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 and ignites there according to the diesel principle of self-ignition. For injecting the second fuel into the combustion chamber 100 each cylinder comprises a second fuel injector 150, which is different from the fuel injector 3. Thus, each cylinder 110 comprises at least one, but preferably a plurality of the fuel injectors 3 for injecting the fuel, as well as at least one, but preferably a plurality of second fuel injectors 150 for injecting the second fuel.

[0042] The fuel, which is injected with the fuel injector 3 into the combustion chamber 100 is for example a fuel for an Otto operation, i.e. with induced ignition of the fuel. The fuel is injected in the combustion chamber 100 to form a premixed air-fuel mixture with the scavenging air. The air-fuel mixture is induced ignited in the combustion chamber 100 according to the Otto principle. This induced 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 into a pre-chamber at a suitable moment, which second fuel then ignites itself and causes the induced ignition of the air-fuel mixture in the combustion chamber 100.

[0043] Introducing 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 induced ignition of the fuel is also referred to as pilot ignition. Beside a diesel oil it is also possible to use a gas or an alcohol such as methanol as pilot fluid for the pilot ignition.

[0044] In other embodiments, the induced ignition is made by way of a spark ignition or a laser pulse or by any other means which is suited for igniting the fuel in the combustion chamber 100.

[0045] 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 self-ignition, for example HFO, MDO or MGO. Regarding the fuel methanol, it is preferred that the operation with the fuel is an operation according to the Otto principle.

[0046] Furthermore, the large diesel engine 200 can be operated in a mixed mode, in which both the fuel and the second 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 second fuel contribute to the generation of the torque.

[0047] In the embodiment described here, the large engine is configured as a longitudinally scavenged dual-fuel two-stroke large diesel engine, which can be operated with methanol as fuel and / or with a diesel fuel as second fuel.

[0048] The dual-fuel large diesel engine has a plurality of cylinders 110. In each cylinder 110 the piston 120 is connected in a manner known per se to a crosshead 122 via a piston rod 121, which crosshead 122 is connected to a crankshaft 170 via a push rod 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 to rotate it. The upper side of the piston 120 delimits together with the cylinder cover 2 the combustion chamber 100, into which the fuel and / or the second fuel is introduced.

[0049] The structure and the individual components of a large diesel engine 200, such as the injection system for the fuels, the gas exchange system, the exhaust system, or the turbocharger system for the supply of the scavenging or charging air, as well as the monitoring and control system for a large diesel engine are sufficiently known to the person skilled in the art both for the design as a two-stroke engine and for the design as a four-stroke engine and therefore need no further explanation here.

[0050] In the embodiment of a longitudinally scavenged two-stroke large diesel engine 200, scavenging air slots 115 are usually provided in the lower region of each cylinder 110 or cylinder liner, which are periodically closed and opened by the movement of the piston 120 in the cylinder 110, so that the scavenging air provided by the turbocharger under a charging pressure can flow into the cylinder 110 through the scavenging air slots 115 as long as they are open. In the cylinder cover 2, the usually centrally arranged exhaust valve 130 is provided, through which the exhaust gases can be discharged from the cylinder 110 into the exhaust system after the combustion process. The exhaust system guides at least a part of the exhaust gases to a turbine of the turbocharger, whose compressor provides the scavenging air, which is also referred to as charging air, in an scavenge air receiver under the scavenge air pressure. The scavenge air receiver is in fluid communication with the scavenging air slots 115 of the cylinders 110.

[0051] Each cylinder 110 comprises at least one fuel injector 3 for injecting the fuel into the combustion chamber 100 of the cylinder 110. Preferably, the cylinder 110 comprises a plurality of fuel injectors 3, for example two or three fuel injectors 3, for uniformly distributing the fuel in the combustion chamber 100. In the embodiment of the large engine 200 described here, exactly three fuel injectors 3 are provided (only one fuel injector 3 is shown in the schematic representation of Fig. 5). Each fuel injector 3 is arranged in the cylinder cover 2 of the cylinder 110. The cylinder cover 2 comprises an inner surface 21 for delimiting 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 injectors 3 are arranged in the cylinder cover 2 near the exhaust valve 130.

[0052] Each cylinder 110 further comprises at least one second fuel injector 150 for injecting the second fuel into the combustion chamber 100 of the cylinder 110. Preferably, the cylinder 110 comprises a plurality of second fuel injectors 150, for example two or three second fuel injectors, for uniformly distributing the second fuel in the combustion chamber 100. In the embodiment of the large engine 200 described here, exactly three second fuel injectors 150 are provided (only one second fuel injector 150 is shown in the schematic representation of Fig. 5). Each second fuel injector 150 is arranged in the cylinder cover 2 of the cylinder 110 in a manner which is known in the art. Preferably, the second fuel injectors 150 are arranged in the cylinder cover 2 near the exhaust valve 130.

[0053] Nowadays, a large diesel engine or a large engine 200 in general is operated in a fully electronically controlled manner. An engine control unit 180 operates and controls all functions of the large engine 200, for example the operation of the exhaust valves 130 for the gas exchange, the injection process for the fuels and the pilot injection timing (when pilot injection is required) by way of electric or electronic signals and commands. In addition, the engine control unit 180 receives information from several detectors, sensors or measuring devices.

[0054] It must be noted that the invention is not restricted to this specific type of a longitudinally scavenged two-stroke large diesel engine 200, which can be operated with the fuel and / or with the second fuel. The large engine can also be any other type of large engine. In particular, it is possible that the large engine is configured for the combustion of only one fuel, e.g. methanol.

[0055] The present invention is related to the cylinder cover arrangement 1 comprising the cylinder cover 2 and the fuel injector 3 which is configured for injecting the fuel into the combustion chamber 100. Preferably, the fuel injector 3 is configured to receive methanol as fuel.

[0056] Particularly referring to Fig. 1 and Fig. 2, the embodiment of the cylinder cover arrangement 1 will now be described in more detail.

[0057] The cylinder cover arrangement 1 comprises the cylinder cover 2 and the fuel injector 3 arranged in the injector bore 22 extending through the cylinder cover 2 and opening into the inner surface 21 which delimits the combustion chamber 100. The fuel injector 3 for injecting the fuel into the combustion chamber 100 comprises a nozzle holder 4 and a nozzle tip 5, which is attached to the nozzle holder 4 by means of a retaining husk 10.

[0058] For a better understanding, Fig. 3 shows an enlarged cross-sectional view of the nozzle tip 5 of the fuel injector 3 shown in Fig. 1 and Fig. 2, and Fig. 4 shows a cross-sectional view of the retaining husk 10 along the cutting line IV-IV in Fig. 3.

[0059] The nozzle tip 5 has at least one, but usually a plurality of spray holes 51, through which the 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 the fuel can be introduced into the pressure chamber 6 at a high pressure. In the pressure chamber 6, a valve needle 8 loaded with a spring 81 and interacting with a valve seat 9 is provided for opening and closing a fluid connection between the pressure chamber 6 and the nozzle tip 5.

[0060] In the embodiment shown in Fig. 1 and Fig. 2, two fuel ducts 7 are provided, which are in fluid communication with a high-pressure fuel port 71. The high-pressure fuel port 71 is connected to a high-pressure fuel source (not shown), for example a fuel booster unit, which can supply the fuel at the high pressure to the high-pressure fuel port 71.

[0061] When methanol is used as the fuel, the fuel booster unit is configured as a methanol booster unit delivering the methanol to the high-pressure fuel port 71 with a high pressure of 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).

[0062] When an injection of the fuel is required, the fuel booster unit is actuated to deliver a presettable amount of the fuel with the high pressure to the high-pressure port 71 of the fuel injector 3. The fuel at the high pressure enters the pressure chamber 6 through the fuel ducts 7 and lifts the valve needle 8 against the force of the spring 81 from the valve seat 9, so that a fluid connection between the pressure chamber 6 and the nozzle tip 5 is opened. 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 an induced ignition. Preferably, the induced ignition is performed by a pilot injection of a small amount of the self-igniting second fuel. At least one of the second fuel injectors can be used for the pilot injection of the second fuel.

[0063] After the presettable amount of the fuel at the high pressure has been supplied to the fuel injector 3, the injection is terminated, i.e. no more fuel at the high pressure is supplied to the high-pressure fuel port 71 of the fuel injector 3. This causes a drop of the fuel pressure in the pressure chamber 6, whereby the spring 81 presses the valve needle 8 back into a sealing engagement with the valve seat 9, so that the fluid connection between the pressure chamber 6 and the nozzle tip 5 is closed.

[0064] According to the invention, the injector bore 22 comprises a contact surface 23 for contacting the nozzle tip 5, and the nozzle tip 5 comprises a support face 52 for supporting the fuel injector 3 in the injector bore 22. The support face 52 abuts the contact surface 23 of the injector bore 22.

[0065] Thus, the nozzle tip 5 rests directly on the cylinder cover 2. Therefore, the axial length of the nozzle tip 5, i.e. the extension of the nozzle tip 5 in the axial direction A, can be considerably reduced as compared to conventional configurations, in which a nozzle retainer for holding the nozzle tip is arranged between the nozzle tip and the cylinder cover, so that the nozzle retainer abuts the cylinder cover. In the configuration according to the invention, the support face 52 of the nozzle tip 5 itself abuts the cylinder cover 2, namely the contact surface 23 of the injector bore 22.

[0066] By reducing the axial length of the nozzle tip 5 the sac volume is reduced. Thus, when the large engine is operated with methanol, the reduced sac volume directly reduces the methanol slip.

[0067] Regarding the retaining husk 10 it is preferred - as it is best seen in Fig. 3 - that the retaining husk engages with a shoulder 53 of the nozzle tip 5, wherein the shoulder is axially displaced from the support face 52. The shoulder 53 is arranged closer to the valve seat 9 than the support face 52. By means of this configuration, the nozzle tip 5 can be attached to the nozzle holder 4 without the requirement to arrange the retaining husk 10 between the nozzle tip 5 and the cylinder cover 2 regarding the axial direction A which leads to the above-describe reduced sac volume and therefore reduced methanol slip.

[0068] With this configuration of the retaining husk 10 engaging with the shoulder 53 of the nozzle tip 5, the retaining husk 10 can fulfill its main function, namely to attach the nozzle tip 5 to the nozzle holder 4 in such a manner that the nozzle tip 5 can be pulled out of the injector bore 22 together with the nozzle holder 4, so that the nozzle holder 4 can be removed from the cylinder cover 2 together with the nozzle tip 2. Removing the fuel injector 3 from the cylinder cover 2 may be required for example for servicing or repair of these components.

[0069] Compared to known nozzle retainers for fixing the nozzle tip to the nozzle holder, the retaining husk 10 of the fuel injector 3 in the cylinder cover arrangement 1 according to the invention can be configured considerably smaller, therewith reducing the required axial length of the nozzle tip 5. This leads to reduced sac volume and methanol slip as described above.

[0070] Preferably, as it is shown in Fig. 4, the retaining husk 10 is fixed to the nozzle holder by means of a dowl pin 11 extending perpendicular to the axial direction A or tangentially to the nozzle holder 4. Particularly preferred, the dowl pin 11 is the sole fixation for the retaining husk 10, i.e. the retaining husk 10 is fixed to the nozzle holder 4 only by means of the dowl pin 11. This simplifies the design.

[0071] Due to the reduced axial length of the nozzle tip 5, the valve seat 9 of the fuel injector 3 is arranged closer to the combustion chamber 100 as compared to conventional designs. Since the valve seat 9 is particularly sensitive to high temperatures, it is preferred to provide measures for cooling in particular the valve seat 9.

[0072] In the preferred embodiment shown in Fig. 1 and Fig. 2 the injector bore 22 thus comprises a cooling sleeve 25 arranged adjacent to the inner surface 21 of the cylinder cover 2. The cooling sleeve 25 is part of the cylinder cover 2 and encompasses the nozzle tip 5. The cooling sleeve 25 forms the contact surface 23, which the support face 52 of the nozzle tip 5 abuts.

[0073] Preferably, the cooling sleeve 25 is configured such, that the cooling sleeve 25 also encompasses the valve seat 9 of the fuel injector. In the embodiment shown in Fig. 1 and Fig. 2, the cooling sleeve 25 extends in the axial direction A to a level, which is above the pressure chamber 6 of the fuel injector 3. Accordingly, the cooling sleeve encompasses the nozzle tip 5 and the valve seat 9 and the pressure chamber 6 of the fuel injector. The cooling sleeve 25 rests on an annular protrusion 26 of the injector bore 22.

[0074] The cooling sleeve 25 dissipates heat from the fuel injector 3, particularly from those components of the fuel injector, which are arranged close to the combustion chamber 100 and therefore more exposed to the high temperatures there. In particular, the cooling sleeve 25 cools the valve seat 9 which is particularly sensitive.

[0075] Preferably, the cylinder cover 2 comprises a cooling channel 24 for a coolant, and the cooling sleeve 25 is in fluid communication with the cooling channel 24. The coolant is a fluid, preferably a liquid, for example water. The coolant flows through the cooling channel 24, and since the cooling sleeve 25 is in fluid communication with the cooling channel 24, the coolant directly impinges on the coolant sleeve 25, and dissipates heat from the cooling sleeve.

[0076] 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. a higher-grade material than the other components of the cylinder cover. The cooling sleeve 25 can be made of a material, which is particularly well suited for deducting heat. Preferably, the cooling sleeve 25 consists of material having a high heat resistance, e.g., X39CrMo17-1. The cooling sleeve is configured and optimized to be exposed to high thermal stresses.

[0077] It is a further advantage of providing the cooling sleeve 25 as a separate component of the cylinder cover 2, that it is easy to provide the cooling sleeve 25 with internal cooling bores 251 to even better cool the cooling sleeve 25. Since the cooling sleeve 25 is a separate component, it is easier to drill bores into the cooling sleeve 25 to generate internal cooling bores in the cooling sleeve 25. The cooling bores 251 are in fluid connection with the cooling channel 24, so that the coolant can enter the cooling bores 251.

[0078] As it can be best seen in Fig. 2, the cooling sleeve 25 comprises at least one cooling bore 251 for receiving the coolant, which is arranged close, i.e. in a thermal contact, to the valve seat 9 for cooling the valve seat 9, because the valve seat 9 is particularly sensitive to heat. By means of said cooling bore 251 the coolant is guided close to the valve seat 9. This assures that the valve seat 9 has a controlled temperature, although the valve seat 9 is located closer to the combustion chamber 100 as compared to conventional designs.

[0079] The injector bore 22 further comprises an intermediate bush 27 encompassing the fuel injector 3 and arranged axially adjacent to the cooling sleeve 25. The intermediate bush 27 is configured for pressing the cooling sleeve 25 towards the inner surface 21 of the cylinder cover 2. A connection sleeve 28 is arranged axially adjacent to the intermediate bush 27 and abuts the intermediate bush 27. As it is known in the art, the connection sleeve 28 is normally used to reduce the pipe connections to the fuel injector 3. In the embodiment of the invention shown in Fig. 1, the connection sleeve 28 has the additional function to exert an axial force on the intermediate bush 27, which in turn presses down the cooling sleeve 25.

[0080] This configuration has the advantage that there is no need for a bolt connection at the lower end of the of the injector bore 22 adjacent to the inner surface 21 of the cylinder cover 2. Furthermore, during servicing or repair, the cooling sleeve 25 can be exchanged without any special tools since the cooling sleeve 25 in particular does not require a press fit to be fixed.Note:

[0081] Any embodiments described with respect to the devices shall similarly pertain to the methods, if any. Synergetic effects may arise from different combinations of the embodiments although they might not be described in detail.

[0082] While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

1. A cylinder cover arrangement for a large engine having at least one cylinder, the cylinder cover arrangement comprising a cylinder cover (2) for delimiting a combustion chamber (100) of the cylinder and a fuel injector (3) for injecting a fuel into the combustion chamber (100), the fuel injector (3) extending in an axial direction (A) and comprising - 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) arranged in the nozzle holder (4), - at least one fuel duct (7) arranged in the nozzle holder (4), through which fuel duct (7) the fuel can be introduced into the pressure chamber (6), - a valve needle (8) arranged in the pressure chamber (6) and interacting with a valve seat (9) for opening and closing a fluid connection between the pressure chamber (6) and the nozzle tip (5), and - a retaining husk (10) for attaching the nozzle tip (5) to the nozzle holder (4), wherein the cylinder cover (2) comprises an inner surface (21) for delimiting the combustion chamber (100) and an injector bore (22) extending through the cylinder cover (2) and opening into the inner surface (21), wherein the injector bore (22) is configured to receive the fuel injector (3), characterized in that the injector bore (22) comprises a contact surface (23) for contacting the nozzle tip (5), and in that the nozzle tip (5) comprises a support face (52) for supporting the fuel injector (3) in the injector bore (22), wherein the support face (52) is configured to abut the contact surface (23) of the injector bore (22) in operation.

2. The cylinder cover arrangement according to claim 1, wherein the nozzle tip (5) comprises a shoulder (53) axially displaced from the support face (52), and wherein the retaining husk (10) is configured to engage with the shoulder (53) for attaching the nozzle tip (5) to the nozzle holder (4).

3. The cylinder cover arrangement according to any one of the preceding claims, configured such that the retaining husk (10) is fixed to the nozzle holder (4) by means of a dowl pin (11) extending perpendicular to the axial direction (A) or tangentially to the nozzle holder (4), in particular solely by means of the dowl pin (11).

4. The cylinder cover arrangement according to any one of the preceding claims, wherein the injector bore (22) comprises a cooling sleeve (25) arranged adjacent to the inner surface (21) of the cylinder cover (2), wherein the cooling sleeve (25) at least partially encompasses the nozzle tip (5), and wherein the cooling sleeve (25) forms at least a part of the contact surface (23).

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

6. The cylinder cover arrangement according to any one of claims 4-5, wherein the cooling sleeve (25) is configured to at least partially encompass the valve seat (9) of the fuel injector (3).

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

8. The cylinder cover arrangement according to any one of claims 5-7, wherein the cooling sleeve (25) comprises at least one cooling bore (251) for receiving the coolant, wherein the cooling bore (251) is arranged close to the valve seat (9) for cooling the valve seat (9).

9. The cylinder cover arrangement according to any one of claims 4-8 configured such that the cooling sleeve (25) rests on an annular protrusion (26) of the injector bore (22).

10. The cylinder cover arrangement according to any one of claims 4-9, wherein the injector bore (22) comprises an intermediate bush (27) encompassing the fuel injector (3) and arranged axially adjacent to the cooling sleeve (25), wherein the intermediate bush (27) is configured for pressing the cooling sleeve (25) towards the inner surface (21) of the cylinder cover (2).

11. The cylinder cover arrangement according to any one of the preceding claims, 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), wherein a piston is arranged in the cylinder for a reciprocating movement between a top dead center position and a bottom dead center position, characterized in that the large engine comprises a cylinder cover arrangement (1) according to any one of the preceding claims.

13. The 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), wherein the second fuel is different from the fuel, and in particular wherein the second fuel is a diesel fuel for self-ignition in the combustion chamber (100).

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