Large engine and fuel booster unit for pressurizing fuel for a large engine

Abstract

A fuel booster unit for pressurizing fuel for a large engine from a low pressure to a high pressure.SOLUTION: A fuel booster unit comprising a pressure chamber (4) for fuel, a fuel inlet (5) for supplying fuel at low pressure to the pressure chamber (4), a fuel outlet (6) for discharging fuel at high pressure from the pressure chamber (4), a plunger (2) movable back and forth in an axial direction (A) in a plunger cylinder (25), a hydraulic piston (3) extending in a hydraulic cylinder (35) and movable back and forth in the axial direction (A), and a working port (7) for supplying working fluid to a low pressure end (31) of the hydraulic piston (3) and to the plunger (2).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel booster unit for pressurizing fuel from low pressure to high pressure for a large engine according to the preambles of the independent claims. Furthermore, the invention relates to a large engine equipped with such a fuel booster unit.

[0002] Large engines can be configured as two-stroke or four-stroke engines, for example as longitudinally scavenged two-stroke large engines, and are often used as drive units for ships or in stationary operation, for example to drive large generators for producing electrical energy. Since engines usually operate continuously for considerable periods of time, operational safety and availability are highly demanding. As a result, long maintenance intervals, low wear, and economical handling of operating materials, among others, 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" refers to an internal combustion engine whose cylinders have a bore 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. Substitutes for heavy fuel oil for large diesel engines are currently being sought in terms of economical and efficient operation, compliance with exhaust gas limit values, sustainable reduction of CO2 emissions, and resource availability. In this regard, both liquid fuels, i.e., fuels introduced into the combustion chamber in a liquid state, and gaseous fuels, i.e., fuels introduced into the combustion chamber in a gaseous state, are used.

[0004] Examples of liquid fuels known as alternatives to heavy oil include other heavy hydrocarbons, especially those left as residues from petroleum refining, alcohols, especially methanol or ethanol, ammonia, gasoline, diesel, or emulsions or suspensions. For example, the use of an emulsion known as MSAR (Multiphase Superfine Atomized Residue) as a fuel is known. 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), and 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 run on two different fuels is called a dual-fuel heavy-duty diesel engine. Depending on the fuel, the engine can operate in liquid mode, where liquid fuel is introduced into the cylinder for combustion, and in 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 through inductive ignition of an ignitable premixed air-fuel mixture. This inductive ignition can occur, for example, via an electric spark, e.g., a spark plug, or it can also occur through the autoignition of a small amount of injected fuel, which then causes the inductive ignition of another fuel. A small amount of fuel intended for autoignition is either injected directly into the combustion chamber or injected into a pre-combustion chamber connected to the combustion chamber. The process of inductive ignition through the autoignition of a small amount of liquid or other autoignition fuel is sometimes referred to as pilot injection.

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

[0009] In particular, climate change, CO2 emission reduction and sustainability considerations call for a reduction in the use of fossil fuels. Therefore, alternatives are being considered to at least reduce or completely avoid the use of fossil fuels, even for large engines. Even if this is still a long way off, replacing a portion of fossil fuels with renewable fuels would be considered a great success.

[0010] One alternative to fossil fuels is methanol, for example. However, renewable fuels such as methanol must be carefully removed from the fuel distribution injection system, especially during engine shutdown or operation on another fuel, because otherwise there is a risk that methanol will leak from the engine, e.g., as vapor, into spaces accessible to engine maintenance or engine operators. This poses a health hazard that requires comprehensive mitigation measures. Therefore, after operation with methanol, residual methanol should be reliably removed from the injection system, for example, by purging the fuel distribution injection system with a liquid such as water or a gas such as nitrogen.

[0011] For efficient, economical, and reliable operation of large engines using renewable fuels such as methanol, it is advantageous to inject the fuel into the combustion chamber at high pressure, for example, at a pressure of 600 bar (60 MPa) or higher. It is known in the art to use a fuel booster unit to pressurize fuel from low pressure to high pressure, thereby injecting the fuel into the combustion chamber. The fuel booster unit includes a hydraulic cylinder having a plunger for pressurizing fuel in a pressure chamber. The pressurized fuel is then supplied to a fuel injector for injection into the combustion chamber. According to known methods, the fuel booster unit is configured for batch mode operation, i.e., the plunger in the hydraulic cylinder performs one stroke for each injection. When a cylinder includes multiple fuel injectors, it is known to provide a separate hydraulic cylinder for each fuel injector. Because the fuel booster unit pressurizes fuel, such as methanol, to high pressure, there is a risk of fuel leakage, which may unintentionally escape from the fuel booster unit, for example, into the environment or surroundings of the fuel booster unit.

[0012] Starting from such prior art fuel booster units, it is an object of the present invention to propose a fuel booster unit for pressurizing fuel, for example methanol, from low pressure to high pressure for large engines, which fuel booster unit has improved reliability and / or operational safety. Furthermore, it is an object of the present invention to propose a large engine equipped with such a fuel booster unit.

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

[0014] Therefore, according to a first aspect of the present invention, there is proposed a fuel booster unit for pressurizing fuel from low pressure to high pressure for a large engine, the fuel booster unit comprising: a pressure chamber for fuel, a fuel inlet for supplying low-pressure fuel to the pressure chamber, and a fuel outlet for discharging high-pressure fuel from the pressure chamber; a plunger extending into the plunger cylinder and movable axially back and forth within the plunger cylinder, the plunger having a high pressure end at least partially delimiting a pressure chamber and a plunger connection end opposite the high pressure end for establishing a plunger-piston connection; - a hydraulic piston extending into the hydraulic cylinder and axially movable back and forth within the hydraulic cylinder, the hydraulic piston having a low pressure end for actuating the plunger and a piston connection end for establishing a plunger-piston connection; an actuation port for supplying actuation fluid to a low-pressure end of the hydraulic piston for actuating the hydraulic piston and to the plunger through a plunger-piston connection; Equipped with.

[0015] The surface area of ​​the low pressure end of the hydraulic piston is greater than the surface area of ​​the high pressure end of the plunger, allowing the fuel to be compressed from low pressure to high pressure.

[0016] The plunger cylinder further includes a low-pressure fuel groove disposed between the high-pressure end and the plunger connection end of the plunger, the low-pressure fuel groove configured to collect fuel residue leaking from the pressure chamber between the plunger and the plunger cylinder, and the fuel booster unit further includes a fuel return line configured to connect the low-pressure fuel groove to the fuel inlet for directing at least a portion of the fuel residue back to the fuel inlet.

[0017] Therefore, at least a portion of the fuel residue can be returned to the fuel inlet, thereby suppressing unintentional fuel leakage from the fuel booster unit.

[0018] During operation of the fuel booster unit, the plunger performs a compression stroke, pressurizing the fuel in the pressure chamber and supplying it to the high-pressure fuel injector. During this compression stroke, some of the fuel leaks from the pressure chamber along the plunger through a gap between the plunger and the plunger cylinder. This fuel residue is collected in the low-pressure fuel groove and recirculated to the fuel inlet via the fuel return line. Because the low-pressure fuel groove is in fluid communication with the fuel inlet, the pressure generated in the low-pressure fuel groove is calibrated to the low pressure of the fuel. Therefore, a clear pressure drop exists along the plunger from the pressure chamber to the low-pressure fuel groove. This pressure drop ensures an induced leakage flow along the plunger, which is effective for cooling the plunger. This further improves the operational safety of the fuel booster unit.

[0019] Preferably, the fuel booster unit further includes a sealing fluid supply configured to insert a sealing fluid between the plunger and the plunger cylinder at an axial sealing position between the plunger connection end and the low-pressure fuel groove. The sealing fluid is, for example, system oil or hydraulic oil. By supplying the sealing fluid to the gap between the plunger and the plunger cylinder at the position between the low-pressure fuel groove and the plunger connection end, reliability in preventing fuel leakage along the plunger is further improved.

[0020] According to another preferred embodiment, the seal fluid supply unit is configured to insert the seal fluid at a seal fluid pressure higher than the low pressure of the fuel. Specifically, the seal fluid pressure is 10% to 50% higher, for example, 20% higher, than the low pressure of the fuel. Therefore, the seal fluid is supplied to the plunger at a seal fluid pressure higher than the low pressure of the fuel, i.e., the pressure of the fuel at the fuel inlet. Because the low-pressure fuel groove is fluidly connected to the fuel inlet, the pressure generated in the low-pressure fuel groove is essentially the same as the low pressure. Therefore, when the seal fluid is supplied to the gap between the plunger and the plunger cylinder when the seal fluid pressure is higher than the low pressure of the fuel, a constant flow of seal fluid is ensured from the sealing position to the low-pressure fuel groove and from there through the fuel return line. Therefore, fuel cannot leak along the plunger farther than the low-pressure fuel groove. For example, the seal fluid is supplied to the sealing position at a pressure approximately 20% higher than the low pressure. The low pressure at which fuel is supplied to the fuel booster unit is, for example, 13 bar (1.3 MPa), and the supply pressure of the sealing fluid is, for example, 16 bar (1.6 MPa).

[0021] According to a further preferred embodiment, the fuel booster unit includes an annular plunger seal (rod seal) surrounding the plunger to provide a seal between the plunger and the plunger cylinder, the plunger seal being axially disposed between the seal position and the plunger connecting end. The annular plunger seal is advantageous in directing the flow of sealing fluid toward the low-pressure fuel groove, which further improves the reliability of preventing fuel leakage along the plunger.

[0022] The plunger seal is preferably positioned so that the axial distance between the low-pressure fuel groove and the plunger seal is near, preferably below, the maximum stroke of the plunger. In a preferred configuration, the fuel booster unit includes a cooling groove for cooling the plunger, the cooling groove being axially disposed between the seal location and the plunger connection end. A cooling fluid can be supplied to the cooling groove to cool and / or lubricate the plunger. The cooling fluid can be a system oil, e.g., the same fluid used as the seal fluid (see above).

[0023] Particularly preferably, the actuating fluid, sealing fluid, and cooling fluid are all the same fluid, such as system oil, which is supplied to the fuel booster unit at different pressures. For example, when the low pressure of the fuel is 13 bar (1.3 MPa), the actuating fluid for actuating the hydraulic piston is system oil supplied to the actuation port at a pressure of 300 bar (30 MPa), the sealing fluid is system oil supplied to the sealing position at a pressure of 16 bar (1.6 MPa), and the cooling fluid is system oil supplied to the cooling groove at a pressure of 16 bar (1.6 MPa).

[0024] Preferably, cooling grooves are arranged in the plunger cylinder, in particular in the wall of the plunger cylinder facing the plunger, for efficiently cooling and / or lubricating the plunger. Preferably, the cooling grooves are open towards the plunger.

[0025] It is particularly preferred that the cooling grooves are configured as spiral grooves.

[0026] The fuel booster unit further preferably includes a sleeve surrounding the plunger cylinder, with the seal fluid supply disposed between the sleeve and the plunger cylinder. Thus, an annular gap is formed between the sleeve and the plunger cylinder, through which the plunger reciprocates. During operation, the annular gap between the sleeve and the plunger cylinder is filled with seal fluid. The seal fluid stabilizes the temperature by thermally isolating the plunger cylinder, thereby protecting the plunger cylinder and plunger from external temperature fluctuations. The seal fluid, e.g., system oil, creates an oil film that is supplied at a low flow rate to the annular gap between the sleeve and the plunger cylinder. This oil film provides thermal insulation and temperature equilibrium along the sleeve and the plunger cylinder.

[0027] The sleeve may be configured as an axial extension of the hydraulic cylinder, in particular the sleeve may be formed integrally with the hydraulic cylinder such that the hydraulic cylinder and the sleeve are formed as one piece.

[0028] Preferably, the sealing fluid supply is arranged between the sleeve and the plunger cylinder wall so that the sealing fluid also provides thermal insulation for the sleeve. Thermal stability ensures high geometric accuracy in the axial and circumferential directions of the plunger cylinder.

[0029] Most preferably, the fuel booster unit is configured to receive methanol as fuel, which helps reduce harmful exhaust emissions from large engines.

[0030] According to a preferred configuration, the low pressure is at least 1 bar (0.1 MPa) and at most 100 bar (10 MPa), in particular at least 5 bar (0.5 MPa) and at most 20 bar (2 MPa), and / or the high pressure is at least 300 bar (30 MPa) and at most 1500 bar (150 MPa), in particular at least 400 bar (40 MPa) and at most 700 bar (70 MPa).

[0031] More preferably, the low-pressure fuel groove is an annular fuel groove that annularly surrounds the plunger.

[0032] Preferably, the plunger-piston connection comprises one of the group consisting of: an axial abutment between the piston connection end and the plunger connection end; and a clamp between the piston connection end and the plunger connection end.

[0033] Therefore, in a structurally very simple configuration, the plunger and hydraulic piston are each cylindrical, the diameter of the hydraulic piston is larger than the diameter of the plunger, and the plunger connection end of the plunger abuts the piston connection end of the hydraulic piston. In another embodiment, the plunger is formed integrally with the hydraulic piston, so that the plunger and hydraulic piston are formed as a single part. The plunger and hydraulic piston are formed, for example, as a stepped piston having two axial faces with different surface areas. The axial face with the larger surface area constitutes the low-pressure end, and the axial face with the smaller surface area constitutes the high-pressure end.

[0034] According to a second aspect of the present invention, there is proposed a large engine, in particular a longitudinally scavenged two-stroke large engine, comprising at least one cylinder having a combustion chamber, a piston arranged in the cylinder for reciprocating movement between top dead centre and bottom dead centre positions, the cylinder comprising at least one fuel injector for injecting fuel into the combustion chamber, the large engine comprising a fuel booster unit according to the first aspect of the present invention, a fuel outlet of the fuel booster unit being connected or connectable to the fuel injector.

[0035] In some embodiments, the large engine includes multiple fuel injectors for injecting fuel into the combustion chamber, and the fuel booster unit includes a separate hydraulic cylinder, a separate plunger, and a separate fuel outlet for each of the fuel injectors.

[0036] According to a preferred embodiment, at least one cylinder is provided with a second fuel injector for injecting a second fuel into the combustion chamber, the second fuel being different from the fuel. Thus, the large engine is preferably configured to be capable of operating on at least two different fuels.

[0037] The second fuel is preferably a diesel fuel for auto-ignition in the combustion chamber, the fuel advantageously comprising methanol, and the heavy duty engine is therefore preferably configured as a dual fuel heavy duty diesel engine.

[0038] A large engine may have multiple cylinders and multiple fuel booster units, i.e., one for each cylinder, which may be connected to each other or to one or more common rails to supply fluids, such as working fluid, fuel, and / or seal fluid, to the fuel booster units.

[0039] Within the framework of the present application, the term "large diesel engine" refers to such an engine that is capable of operating at least in diesel operation. In particular, the term "large diesel engine" therefore also includes such multi-fuel large engines that, in addition to diesel operation, are capable of operating in another mode, for example Otto operation.

[0040] Further advantageous measures and embodiments of the invention emerge from the dependent claims. 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]

[0041] [Figure 1] 1 is a schematic diagram of one embodiment of a fuel booster unit according to the present invention; [Figure 2] FIG. 2 is a cross-sectional view of the fuel booster unit taken along an axial direction. [Figure 3] 3 is a cross-sectional view of the fuel booster unit shown in FIG. 2, with the cross-sectional plane rotated approximately 90 degrees. [Figure 4] 4 is an enlarged detail I of FIG. 3 without the sleeve. [Figure 5] 1 is a schematic diagram of one embodiment of a large engine according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0042] FIG. 1 shows a schematic diagram of one embodiment of a fuel booster unit according to the present invention, generally designated 1. The fuel booster unit 1 is configured to pressurize fuel from low pressure to high pressure for a large engine 100 (see FIG. 5). For ease of understanding, FIG. 2 shows a cross-sectional view of the fuel booster unit 1 taken along axial direction A. FIG. 3 is a cross-sectional view of the fuel booster unit shown in FIG. 3, with the cross-sectional plane rotated approximately 90 degrees. FIG. 4 is an enlarged view of detail I of FIG. 3, but showing only the plunger cylinder.

[0043] The fuel booster unit 1 comprises a pressure chamber 4 for fuel, a fuel inlet 5 for supplying low-pressure fuel to the pressure chamber 4, and a fuel outlet 6 for discharging high-pressure fuel from the pressure chamber 4. The fuel outlet 6 is connected to a fuel injector 110. The fuel injector 110 is used to inject fuel into the combustion chamber 120 of a cylinder 130 of the large engine 100. Figure 5 shows a schematic diagram of one embodiment of a large engine 100 according to the present invention. Note that Figure 5 shows only one cylinder 130 of the large engine 100. Typically, the large engine 100 comprises multiple cylinders 130, for example up to 12 cylinders 130 or more.

[0044] The term "large engine" typically refers to such internal combustion engines used as drive units for marine vessels or even in stationary operation, for example to drive large generators for producing electrical energy. Typically, the cylinders 130 of the large engine 100 each have an internal diameter (bore) of at least about 200 mm. Such large engines 100 are known in the art in a variety of different configurations, such as two-stroke engines or four-stroke engines.

[0045] In the following description, reference is made to a large engine 100 configured as a longitudinally scavenged, two-stroke large engine having a plurality of cylinders 130. Each cylinder 130 has a combustion chamber 120. Furthermore, each cylinder 130 contains a piston 125 that reciprocates between top dead center and bottom dead center.

[0046] The term "longitudinally scavenged" means that scavenging or charge air is introduced into the cylinder 130 in the region of the lower end, and the exhaust valve 135 is located in or on the cylinder cover 140 located at the upper end of the cylinder 130.

[0047] In particular, reference is made to a large, longitudinally scavenged, two-stroke engine capable of operating on different fuels, i.e., a fuel and a second fuel. Preferably, the large engine 100 is configured as a large diesel engine. The term "large diesel engine" refers to an engine capable of operating in at least a diesel mode of operation. Thus, in particular, the term "large diesel engine" also includes a large engine 100 that can operate in another mode, e.g., an Otto mode of operation, in addition to the diesel mode of operation.

[0048] According to a preferred configuration, the large engine 100 can operate using methanol as fuel or using a liquid, auto-igniting secondary fuel. Thus, when the large engine 100 is operated using the secondary fuel, it is operated in a liquid mode in which only the liquid secondary fuel is injected into the combustion chamber 120 of the cylinder 130. 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 120 at the appropriate time, where it ignites according to the diesel principle of auto-ignition. To inject the secondary fuel into the combustion chamber 120, each cylinder 130 is equipped with a second fuel injector 150, different from the fuel injector 110. Thus, each cylinder 130 is equipped with at least one, preferably multiple, fuel injectors 110 for injecting fuel and at least one, preferably multiple, second fuel injectors 150 for injecting the secondary fuel.

[0049] The fuel injected by the fuel injector 110 into the combustion chamber 120 is, for example, a fuel for Otto operation, i.e., with inductive ignition of the fuel. The fuel is injected into the combustion chamber 120 and forms a premixture with scavenging air. The mixture is inductively ignited in the combustion chamber 120 according to the Otto principle. This inductive ignition is usually caused by the timely introduction of a small amount of a self-igniting second fuel (e.g., diesel or heavy fuel oil) into the combustion chamber 120 or pre-combustion chamber, which then self-ignites and causes inductive ignition of the air-fuel mixture in the combustion chamber 120.

[0050] The introduction of a small amount of a self-igniting liquid or gaseous second fuel into the combustion chamber 120 or into at least one pre-combustion chamber for the induction ignition of the fuel is also called pilot ignition. In addition to diesel oil, gas or alcohols such as methanol can also be used as pilot fluids for pilot ignition.

[0051] 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 120 .

[0052] 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, operation with the fuel is preferably operation according to the Otto principle.

[0053] Additionally, the heavy-duty diesel engine 100 can operate in a mixed mode in which both the fuel and a secondary fuel are injected into the combustion chamber 120 of the cylinder 130. In the mixed mode, both the combustion of the fuel and the combustion of the secondary fuel contribute to torque production.

[0054] In the embodiments described herein, the heavy-duty engine is configured as a longitudinally scavenged, dual-fuel, two-stroke heavy-duty diesel engine capable of operating on methanol as a fuel and / or diesel fuel as a secondary fuel.

[0055] The dual-fuel heavy-duty diesel engine has a plurality of cylinders 130. In each cylinder 130, a piston 125 is connected via a piston rod 121 to a crosshead 122 in a manner known to those skilled in the art, which is connected to a crankshaft 170 via a push rod or connecting rod 123 such that movement of the piston 125 is transmitted to the crankshaft 170 via the piston rod 121, crosshead 122, and connecting rod 123, causing the crankshaft to rotate. The upper side of the piston 125, together with a cylinder cover 140, defines a combustion chamber 120 into which the fuel and / or second fuel is introduced.

[0056] The structure and individual components of the heavy-duty diesel engine 100, such as the injection system for fuel, the gas exchange system, the exhaust or turbocharger system for scavenging or charge air supply, as well as the monitoring and control systems for heavy-duty diesel engines, are well known to those skilled in the art, both for two-stroke and four-stroke engine designs, and therefore do not require further explanation here.

[0057] In the longitudinally scavenged, two-stroke, heavy-duty diesel engine 100 embodiment, scavenging slots 115 are typically provided in the lower region of each cylinder 130 or cylinder liner and are periodically opened and closed by the movement of the piston 125 within the cylinder 130, allowing scavenging air supplied by the turbocharger under boost pressure to flow through the scavenging slots into the cylinder 130 as long as the scavenging slots are open. A typically centrally located exhaust valve 135 is provided in the cylinder cover 140 to allow exhaust gases to be discharged from the cylinder 130 to an 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 receiver under scavenging pressure. The scavenging receiver is in fluid communication with the scavenging slots 115 of the cylinder 130.

[0058] Each cylinder 130 includes at least one fuel injector 110 for injecting fuel into the combustion chamber 120 of the cylinder 130. Preferably, the cylinder 130 includes multiple fuel injectors 110, for example, two or three, to evenly distribute fuel within the combustion chamber 120. In the embodiment of the large engine 100 described herein, exactly three fuel injectors 110 are provided. Only one fuel injector 110 is shown in the schematic diagram of FIG. 5. However, FIG. 1 shows three fuel injectors 110, each connected by a high-pressure line 160 to a fuel booster unit 1 for receiving fuel, here methanol, at high pressure. Each fuel injector 110 is positioned within the cylinder cover 140 of the cylinder 130 in a manner known in the art. Preferably, the fuel injectors 110 are positioned within the cylinder cover 140 near the exhaust valve 135.

[0059] Each cylinder 130 further includes at least one second fuel injector 150 for injecting a second fuel into the combustion chamber 120 of the cylinder 130. Preferably, the cylinder 130 includes multiple second fuel injectors 150, e.g., two or three, to evenly distribute the second fuel within the combustion chamber 120. In the embodiment of the large engine 100 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 140 of the cylinder 130 in a manner known in the art. Preferably, the second fuel injectors 150 are positioned within the cylinder cover 140 near the exhaust valve 135.

[0060] Nowadays, large diesel engines or large engines 100 generally operate in a fully electronically controlled manner. An engine control unit 180 activates and controls all functions of the large engine 100 by means of electrical or electronic signals and commands, such as the operation of the gas exchange exhaust valves 135, the fuel injection process, and the pilot injection timing (if pilot injection is required). Furthermore, the engine control unit 180 receives information from several detectors, sensors or measuring devices.

[0061] It should be noted that the present invention is not limited to this particular type of longitudinally scavenged two-stroke heavy-duty diesel engine 100 that can operate 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 to burn only one fuel, for example methanol.

[0062] The present invention relates to a fuel booster unit 1 for pressurizing a fuel from low pressure to high pressure. A preferred fuel is methanol. In particular, when using methanol as the fuel, the low pressure is preferably at least 1 bar (0.1 MPa) and at most 100 bar (10 MPa). Even more preferably, the low pressure is at least 5 bar (0.5 MPa) and at most 20 bar (2 MPa). The low pressure is, for example, 13 bar (1.3 MPa). The high pressure is preferably at least 300 bar (30 MPa) and at most 1500 bar (150 MPa). Even more preferably, the high pressure is at least 400 bar (40 MPa) and at most 700 bar (70 MPa). The high pressure is, for example, about 600 bar (60 MPa).

[0063] The fuel booster unit 1 hydraulically amplifies the pressure of fuel from low pressure to high pressure. The fuel booster unit 1 includes a plunger 2 extending in an axial direction A and a hydraulic piston 3 extending in the axial direction A, with the plunger 2 abutting against a hydraulic cylinder 3. Both the plunger 2 and the hydraulic piston 3 are cylindrical, and the hydraulic piston 3 has a larger diameter than the plunger 2. The cylinder axis of the hydraulic piston 3 coincides with the cylinder axis of the plunger 2. These aligned axes define the axial direction A.

[0064] The plunger 2 is disposed within the plunger cylinder 25 and is reciprocally movable within the plunger cylinder 25 in an axial direction A. With respect to the axial direction A, the plunger 2 extends from a high-pressure end 22 that at least partially defines the pressure chamber 4 to a plunger connection end 23 for establishing a plunger-piston connection.

[0065] The hydraulic piston 3 is disposed within the hydraulic cylinder 35 and is reciprocally movable within the hydraulic cylinder 25 in an axial direction A. With respect to the axial direction A, the hydraulic piston 3 extends from a low pressure end 31 to a piston connection end 33 to establish a plunger-piston connection.

[0066] In the embodiment described here, the plunger-piston connection is achieved by abutment between the plunger 2 and the hydraulic piston 3. In other words, the piston connection end 33 of the hydraulic piston 3 abuts against the plunger connection end 23 of the plunger 2.

[0067] The fuel booster unit 1 further comprises an actuation port 7 for supplying actuation fluid to the low pressure end 31 of the hydraulic piston 3 for actuating the hydraulic piston 3 and to the plunger 2 by way of the plunger-piston connection. The actuation fluid may be, for example, system oil which is also used for other purposes in the large engine 100.

[0068] Because the hydraulic piston 3 has a larger diameter than the plunger 2, the surface area of ​​the low-pressure end 31 of the hydraulic piston 3 is larger than the surface area of ​​the high-pressure end 22 of the plunger 2. This surface area ratio determines the amplification factor, i.e., the ratio of the pressure generated at the high-pressure end 22 of the plunger 2 to the pressure generated at the low-pressure end 31 of the hydraulic piston 3. Therefore, the pressure of the working fluid supplied to the low-pressure end 31 increases to the high pressure generated in the pressure chamber 4 by the amplification factor.

[0069] According to the present invention, the plunger cylinder 25 includes a low-pressure fuel groove 8 arranged between the high-pressure end 22 and the plunger connection end 23 of the plunger 2, the low-pressure fuel groove 8 being configured to collect fuel residues leaking from the pressure chamber 4 between the plunger 2 and the plunger cylinder 25. Furthermore, the fuel booster unit 1 includes a fuel return line 81 configured to connect the low-pressure fuel groove 8 to the fuel inlet 5 for guiding at least a portion of the fuel residues back to the fuel inlet 5.

[0070] Referring now to the embodiment of the fuel booster unit 1 shown in FIG. 1 , the fuel booster unit 1 preferably includes a separate hydraulic cylinder 3, a separate plunger 2, a separate pressure chamber 4, and a separate fuel outlet 6 for each fuel injector 110 in a cylinder 130. Thus, where n is the number of fuel injectors 110 in a cylinder 130, the fuel booster unit 1 includes n fuel outlets 6. Each fuel outlet 6 is provided with a separate pressure chamber 4, and each pressure chamber 4 is provided with a separate hydraulic piston 3 and a separate plunger 2 for pressurizing the fuel in the respective pressure chamber 4. In the embodiment described herein, n equals 3. Preferably, a separate fuel booster unit 1 is provided for each cylinder 130 in the large engine 100. As known to those skilled in the art, these fuel booster units 1, i.e., one for each cylinder 130, can be connected to each other or to a common rail for supplying fluid, such as hydraulic fluid, to the fuel booster units 1.

[0071] 2, 3 and 4 show only one arrangement of hydraulic cylinder 35 with hydraulic piston 3, plunger cylinder 25 with plunger 2, pressure chamber 4 and fuel outlet 6. A separate such arrangement is provided in fuel booster unit 1 for each of the three fuel injectors 110 of cylinder 130.

[0072] As shown in FIG. 1 , a separate fuel inlet 5 is provided for each pressure chamber 4 to supply low-pressure fuel to the respective pressure chamber 4. The fuel inlets 5 are connected by low-pressure lines 200 to a fuel rail 210 containing low-pressure fuel, for example, 13 bar (1.3 MPa). A fuel pump 220 is provided to transport fuel from a fuel reservoir 230 to the fuel rail 210. The fuel pump 220 pressurizes the fuel to the low pressure. Each fuel inlet 5 is provided with a check valve 240 to prevent backflow of fuel from the pressure chamber 4 to the low-pressure line 200. A fuel return line 81 is connected to the low-pressure line 200 upstream of the check valve 240.

[0073] Each fuel outlet 6 is connected to one of the fuel injectors 110 by one of the high pressure lines 160 .

[0074] Each actuation port 7 is connected by an actuation line 700 to an actuation rail 710 containing actuation fluid at actuation pressure. Preferably, the actuation pressure is between 150 bar (15 MPa) and 400 bar (40 MPa), for example about 300 bar (30 MPa). At least one pump 720, preferably several pumps 720, are provided to convey actuation fluid from an actuation fluid reservoir 730 to the actuation rail 710. The pumps 720 pressurize the actuation fluid to the actuation pressure.

[0075] Between the actuation port 7 and the actuation rail 710, an actuation valve 70 is provided for opening and closing the fluid connection between the actuation port 7 and the actuation rail 710. Preferably, each actuation valve 70 is configured as an electrically operated, spring-loaded slide valve 70 having two stable positions. In the open position, the fluid connection between the actuation port 7 and the actuation rail 710 is open, so that actuation fluid having an actuation pressure can flow from the actuation rail 710 through the actuation port 7 and act on the low-pressure end 31 of the hydraulic piston 3. In the closed position, the flow connection between the actuation port 7 and the actuation rail 710 is closed, so that actuation fluid cannot flow from the actuation rail 710 through the actuation port 7. In the closed position, the actuation port 7 is in fluid communication with a return line 740, so that actuation fluid can flow from a chamber bounded by the low-pressure end 31 of the hydraulic piston 3 into the return line 740. The return line 740 can be connected to a reservoir 730 for actuation fluid (not shown in FIG. 1 ).

[0076] The general operating mode of the fuel booster unit 1 is described below. Before the fuel injector 110 starts injecting fuel into the combustion chamber 120, the plunger 2 and hydraulic piston 3 are in their lowest positions. This position is also shown in the left half of FIG. 2. The pressure chamber 4 is filled with fuel at low pressure, e.g., 13 bar (1.3 MPa), and the actuation valve 70 is in the closed position. To start fuel injection, an electrical signal (e.g., initiated by the engine control unit 180) switches the actuation valve 70 from the closed position to the open position against a spring load. Actuation fluid at actuation pressure flows from the actuation rail 710 through the actuation port 7 and acts on the low-pressure end 31 of the hydraulic piston 3. The hydraulic piston 3 moves upward and pushes the plunger 2 upward via the plunger-piston connection. The high-pressure end 22 of the plunger 2 pressurizes the fuel in the pressure chamber 4 into high-pressure fuel. The high pressure fuel then exits through fuel outlet 6 and is supplied through high pressure line 160 to fuel injector 110 which injects the fuel into combustion chamber 120 .

[0077] When injection is complete, the plunger 2 and hydraulic piston 3 are at their top positions, as shown in the right half of Figure 2. The actuation valve 70 is then switched to a closed position. For example, the electrical signal is deactivated so that the spring load switches the actuation valve 70 from the open position to the closed position. The actuation fluid is discharged through the actuation port 7 to the return line 740.

[0078] Fuel at low pressure, for example 13 bar (1.3 MPa), enters the pressure chamber 4 through the fuel inlet 5 and refills the pressure chamber 4. The low pressure of the fuel entering the pressure chamber 4 pushes the plunger 2 downward, and as shown in the left half of Figure 2, the plunger 2 and hydraulic piston 3 again push the hydraulic piston 3 downward until they are at their lowest position.

[0079] During the upward movement of the hydraulic piston 3 and plunger 2 as described above, some fuel, referred to herein as "fuel residue," leaks from the pressure chamber 4 in the gap between the plunger 2 and the plunger cylinder 25. These fuel residues are collected in the low-pressure fuel groove 8 and recirculated through the fuel return line 81 to the low-pressure line 200, which is in fluid communication with the fluid inlet 5. Because the fuel return line 81 is connected to the low-pressure line 200 upstream of the check valve 240, fuel cannot flow back directly from the pressure chamber 4 to the fuel return line 81. Thus, unintentional fuel leakage from the fuel booster unit 1 is avoided or at least reduced.

[0080] Furthermore, the pressure created in the low-pressure fuel groove 8 is calibrated to the low pressure of the fuel by the fuel return line 81. Therefore, there is a clear pressure drop from the pressure chamber 4 along the plunger 2 to the low-pressure groove 8. This pressure drop ensures a small amount of induced leakage of fuel along the plunger 2, which is advantageous for cooling the plunger 2.

[0081] During injection, the high pressure end 22 of the plunger 2 is filled with fuel at high pressure and the low pressure end 31 of the hydraulic piston 3 is filled with working fluid at working pressure, so that the fuel can mix with the working fluid. In particularly preferred embodiments of the fuel booster unit 1, mixing of the fuel with the working fluid, e.g., system oil, should be avoided, at least to a large extent.

[0082] In the following it will be explained how such mixing can be avoided or at least reduced, in particular by using the preferred embodiment of the fuel booster unit 1 shown in Figures 2 to 4. For better understanding, in Figure 4, which shows an enlarged view of detail I, only the plunger cylinder 25 is shown.

[0083] The fuel booster unit 1 includes a seal fluid supply 9 for inserting a seal fluid between the plunger 2 and the plunger cylinder 25 at a seal position 91. The seal position 91 is arranged between the plunger connection end 23 and the low-pressure fuel groove 8 with respect to the axial direction A. The seal position 91 is arranged in the plunger cylinder 25 and configured as an annular seal groove 91 surrounding the plunger 2. With respect to the representations of Figures 2 to 4, the seal groove 91 is arranged below the low-pressure fuel groove 8. The seal fluid supply 9 further includes a seal port 92 to which a seal fluid is supplied. Preferably, the seal fluid is system oil.

[0084] The sealing fluid is supplied to the sealing port 92 at a sealing fluid pressure higher than the low pressure of the fuel. Preferably, the sealing fluid pressure is 10% to 50% higher than the low pressure of the fuel, for example, 20% higher. If the low pressure of the fuel is, for example, 13 bar (1.3 MPa), the sealing fluid pressure is, for example, 16 bar (1.6 MPa).

[0085] The fuel booster unit 1 further includes a sleeve 26 that surrounds the plunger cylinder 25, and the seal fluid supply portion 9 is disposed between the sleeve 26 and the plunger cylinder 25. An annular gap in which the plunger 2 reciprocates is formed between the sleeve 26 and the plunger cylinder 25. With respect to the axial direction A, the seal port 92 is disposed at the upper end of the plunger cylinder 25, i.e., at the end of the plunger cylinder 25 adjacent to the pressure chamber 4. As a result, the seal fluid supplied through the seal port 92 enters the gap between the plunger cylinder 25 and the sleeve 26 and flows downward along the plunger cylinder 25 into the seal groove 91.

[0086] During operation, the annular gap between the sleeve 26 and the plunger cylinder 25 is filled with a sealing fluid, which stabilizes the temperature by thermally isolating the plunger cylinder 25. This protects the plunger cylinder 25 and plunger 2 from external temperature fluctuations.

[0087] 2 and 3, the sleeve 26 may be configured as an extension of the hydraulic cylinder 35 in the axial direction A. In particular, the sleeve 26 may be formed integrally with the hydraulic cylinder 35, so that the hydraulic cylinder 35 and the sleeve 26 are formed integrally.

[0088] Furthermore, an annular plunger seal 10 is provided surrounding the plunger 2 to provide a seal between the plunger 2 and the plunger cylinder 25. With respect to the axial direction A, the plunger seal 10 is disposed between the seal groove 91 and the plunger connecting end 23. In the representations of FIGS. 2 to 4, the plunger seal 10 is disposed below the seal groove 91. It is preferable to dispose the plunger seal 10 so that the axial distance between the low-pressure fuel groove 8 and the plunger seal 10 is approximately the same as the maximum stroke of the plunger 2. The axial distance is the distance measured in the axial direction A.

[0089] Optionally, the fuel booster unit 1 further comprises a cooling groove 20 for cooling the plunger 2. The cooling groove 20 is arranged in the plunger cylinder 25 between the seal groove 91 and the plunger connecting end 23 with respect to the axial direction A. In particular, the cooling groove 20 is arranged—with respect to the axial direction A—between the plunger seal 10 and the plunger connecting end 23. With respect to the representations of Figures 2 to 4, the cooling groove 20 is arranged below the plunger seal 10. Thus, the plunger seal 10 is arranged between the seal groove 91 and the cooling groove 20.

[0090] Preferably, the cooling grooves 20 are configured as spiral grooves 20, as best shown in FIG. 4 . A cooling fluid can be supplied to the cooling grooves 20 to cool and / or lubricate the plunger 2. The cooling fluid can be system oil, i.e., the same fluid used as the sealing fluid. At least one cooling bore 201 is provided in the hydraulic cylinder 35 to supply the cooling fluid to the cooling grooves 20. A cooling port 202 is located at an axial end of the hydraulic cylinder 35 adjacent the low-pressure end 31 of the hydraulic piston 35. The cooling bore 201 extends from the cooling port 202 in the axial direction A through the entire hydraulic cylinder 35 to the axial end of the hydraulic cylinder 35 adjacent the plunger 2.

[0091] The plunger cylinder 25 includes at least one feed bore 203 extending from the radially outer surface of the plunger cylinder 25 to the radially inner surface of the plunger cylinder 25 .

[0092] 3 shows two cooling ports 202, two cooling bores 201, and two supply bores 203. Cooling fluid is supplied to the cooling ports 202, flows through the cooling bores 201, and enters the annular gap between the plunger cylinder 25 and the sleeve 26. From there, the cooling fluid is directed through the supply bores 203 to the beginning of the spiral cooling groove 20, which is the end closest to the plunger seal 10.

[0093] The cooling fluid is supplied to the cooling port 202 at a cooling fluid pressure higher than the low fuel pressure. Preferably, the cooling fluid pressure is 10% to 50% higher than the low fuel pressure. If the low fuel pressure is, for example, 13 bar (1.3 MPa), the cooling fluid pressure is, for example, 16 bar (1.6 MPa). A particularly preferred cooling fluid pressure is at least approximately the same as the seal fluid pressure. This has the advantage that the plunger seal 10, located between the seal groove 91 and the cooling groove 20, is pressure balanced and lubricated from both sides.

[0094] During operation of the fuel booster unit 1, sealing fluid is supplied to the sealing port 92 at a sealing fluid pressure, for example, 16 bar (1.6 MPa), cooling fluid is supplied to the cooling port 202 at a cooling fluid pressure preferably equal to the sealing fluid pressure, and fuel is supplied to the fuel inlet 5 at a low pressure less than the sealing fluid pressure and less than the cooling fluid pressure, for example, 13 bar (1.3 MPa).

[0095] Sealing fluid supplied through sealing port 92 enters the gap between plunger cylinder 25 and sleeve 26 and flows downward along plunger cylinder 25 to seal groove 91 surrounding plunger 2. From there, the sealing fluid flows upward toward low-pressure fuel groove 8 and is discharged along fuel return line 81 along with fuel residue. Thus, the upward flow of sealing fluid prevents fuel residue from passing downward beyond low-pressure fuel groove 8. Cooling fluid flows upward from cooling port 202 through cooling bore 201 and through supply bore 203 to the beginning of spiral cooling groove 20. The cooling fluid flows downward through spiral cooling groove 20.

[0096] Because the sealing fluid pressure and the cooling fluid pressure are at least approximately the same, the plunger seal 10 located between the seal groove 91 and the cooling groove 20 is pressure balanced and lubricated from both sides. A pressure balanced plunger seal 10 has the advantage of lower loads acting on the plunger seal 10, resulting in less wear on the plunger seal 10.

[0097] Positioning the plunger seal 10 so that the axial distance between the low pressure fuel groove 8 and the plunger seal 10 is approximately at the maximum stroke of the plunger 2 has the advantage that fuel residue is not drawn onto the plunger seal 10.

[0098] Configuring the cooling groove 20 as a spiral groove 20 is also advantageous for guiding the plunger 2 and the hydraulic piston 3. The preferred fuel, methanol, has very poor tribological properties. Therefore, it is desirable to avoid any physical contact between the plunger cylinder 25 and the plunger 2, at least between the low-pressure fuel groove 8 and the high-pressure end 22 of the plunger 2, as much as possible. The pressure drop from the high-pressure end 22 of the plunger 2 to the low-pressure fuel groove 8 in the axial direction A prevents the plunger 2 from directly contacting the plunger cylinder 25. However, there is a certain risk that the plunger 2 may contact the plunger cylinder 25 close to the low-pressure fuel groove 8. To prevent such undesired contact, the plunger 2 is guided by a sealing and / or cooling fluid, preferably system oil. The oil is significantly more viscous than methanol. Therefore, the system oil prevents the plunger 2 from tilting in the plunger cylinder 25. However, due to friction, the system oil may heat up due to its high viscosity.

[0099] The spiral cooling grooves 20 located adjacent the lower end of the plunger cylinder 25, i.e., the plunger connecting end 23, allow the flow of cooling fluid (system oil) to be adjusted to the level required for sufficient cooling without increasing the clearance between the plunger 2 and the plunger cylinder 25. Having essentially the same clearance along the plunger cylinder 25 has the advantage that the plunger 2 is well guided with a stable system oil film and the constant clearance on the plunger cylinder simplifies manufacturing, especially the honing process.

[0100] It should be noted that any embodiment described with respect to an apparatus also relates to a method, if any. Synergistic effects may result from different combinations of embodiments, which may not be described in detail. While preferred embodiments of the present invention have now 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. 1. A fuel booster unit for pressurizing fuel from low pressure to high pressure for a large engine (100), comprising: a pressure chamber (4) for the fuel, a fuel inlet (5) for supplying the fuel at low pressure to the pressure chamber (4), and a fuel outlet (6) for discharging the fuel at high pressure from the pressure chamber (4); a plunger (2) extending into a plunger cylinder (25) and movable back and forth in an axial direction (A), said plunger (2) having a high-pressure end (22) at least partially delimiting said pressure chamber (4), said plunger (2) having a plunger connection end (23) opposite said high-pressure end (22) for establishing a plunger-piston connection; - a hydraulic piston (3) extending in a hydraulic cylinder (35) and movable back and forth in said axial direction (A), said hydraulic piston (3) having a low pressure end (31) for actuating said plunger (2) and a piston connection end (33) for establishing said plunger-piston connection; - an actuation port (7) for supplying actuation fluid to the low pressure end (31) of the hydraulic piston (3) for actuating the hydraulic piston (3) and to the plunger (2) by means of the plunger-piston connection; an actuation port (7) in which the surface area of ​​the low pressure end (31) of the hydraulic piston (3) is greater than the surface area of ​​the high pressure end (22) of the plunger (2); the plunger cylinder (25) has a low-pressure fuel groove (8) disposed between the high-pressure end (22) and the plunger connection end (23) of the plunger (2), and the low-pressure fuel groove (8) is configured to collect fuel residue leaking from the pressurized chamber (4) between the plunger (2) and the plunger cylinder (25); the fuel booster unit comprises a fuel return line (81) configured to connect the low pressure fuel groove (8) to the fuel inlet (5) for directing at least a portion of the fuel residue back to the fuel inlet (5), Fuel booster unit.

2. 2. The fuel booster unit of claim 1, further comprising a sealing fluid supply (9) configured to insert a sealing fluid between the plunger (2) and the plunger cylinder (25) at a sealing position (91) between the plunger connection end (23) and the low-pressure fuel groove (8) in the axial direction (A).

3. 3. A fuel booster unit according to claim 2, wherein the sealing fluid supply (9) is configured to insert the sealing fluid at a sealing fluid pressure higher than the low pressure of the fuel, in particular, the sealing fluid pressure being 10% to 50% higher than the low pressure of the fuel.

4. 4. The fuel booster unit according to claim 2, further comprising an annular plunger seal (10) surrounding the plunger (2) to provide a seal between the plunger (2) and the plunger cylinder (25), the plunger seal (10) being disposed between the seal position (91) and the plunger connection end (23) in the axial direction (A).

5. 5. The fuel booster unit according to claim 1, further comprising a cooling groove (20) for cooling the plunger (2), the cooling groove (20) being disposed between the sealing position (91) and the plunger connection end (23) in the axial direction (A).

6. 6. A fuel booster unit according to claim 5, wherein the cooling grooves (20) are arranged in the plunger cylinder (25), in particular in the wall of the plunger cylinder (25) facing the plunger, in particular the cooling grooves (20) being open towards the plunger (2).

7. 7. A fuel booster unit according to claim 5 or 6, configured to supply a cooling fluid to the cooling grooves (20) for cooling and / or lubricating the plunger (2).

8. A fuel booster unit according to any one of claims 5 to 7, wherein the cooling groove (20) is configured as a spiral groove (20).

9. 9. The fuel booster unit according to claim 2, further comprising a sleeve (26) surrounding the plunger cylinder (25), wherein the sealing fluid supply portion (9) is arranged between the sleeve (26) and the plunger cylinder (25).

10. A fuel booster unit according to any preceding claim, configured to receive methanol as fuel.

11. the low pressure is at least 1 bar and at most 100 bar, in particular at least 5 bar and at most 20 bar, and / or the high pressure is at least 300 bar and at most 1500 bar, in particular at least 400 bar and at most 700 bar; A fuel booster unit according to any one of claims 1 to 10.

12. A fuel booster unit according to any one of claims 1 to 11, wherein the low-pressure fuel groove (8) is an annular fuel groove (8) that annularly surrounds the plunger (2).

13. 13. A fuel booster unit according to any one of claims 1 to 12, wherein the plunger-piston connection comprises at least one of the group consisting of axial abutment between the piston connection end (33) and the plunger connection end (23), and clamping between the piston connection end (33) and the plunger connection end (23).

14. 14. A large engine (100), in particular a longitudinally scavenged two-stroke large engine, comprising at least one cylinder (130) having a combustion chamber (120), a piston arranged in said cylinder for reciprocating movement between a top dead center position and a bottom dead center position, said cylinder (130) comprising at least one fuel injector (110) for injecting fuel into said combustion chamber (120), said large engine comprising a fuel booster unit (1) according to any one of claims 1 to 13, said fuel outlet (6) of said fuel booster unit (1) being connected to said fuel injector (110).

15. 15. A large engine according to claim 14, comprising a plurality of fuel injectors (110) for injecting the fuel into the combustion chamber (120), the fuel booster unit (1) comprising a separate hydraulic cylinder (3), a separate plunger (2), and a separate fuel outlet (6) for each of the fuel injectors (110).

16. 16. A large engine according to any one of claims 14 to 15, wherein the at least one cylinder (130) is provided with a second fuel injector (150) for injecting a second fuel into the combustion chamber (120), the second fuel being different from the fuel, preferably the second fuel being diesel fuel for auto-ignition in the combustion chamber (120).

Images