Fuel system for large two-stroke, dual-fuel internal combustion engines with an improved purge system

Abstract

Disclosed are a dual fuel system for a large two-stroke turbocharged uniflow internal combustion engine capable of operating with a first fuel, which is fuel oil, and a second fuel, which is a liquid fuel different from the first fuel; a large two-stroke engine and a vessel equipped with the same; and a method for operating the large two-stroke engine. [Solution] A dual fuel system is provided that allows the second fuel system to be easily purged with an inert gas, by comprising a first fuel system for supplying the first fuel, a second fuel system 30 for supplying the second fuel, a purge system for discharging the second fuel, and bypass valves 34 and 35 for completely discharging the second fuel from the second fuel system 30 during purging.

Description

Technical Field

[0001] The disclosure of the present application (hereinafter referred to as the present disclosure) relates to a crosshead type large two-fuel turbocharged two-stroke uniflow internal combustion piston engine, and more particularly to a crosshead type large turbocharged two-stroke uniflow internal combustion piston engine having a first fuel system for a conventional fuel and a second fuel system for a non-conventional fuel. Background

[0002] Large two-stroke uniflow scavenging turbocharged internal combustion crosshead engines are typically used as propulsion systems for large ships and as prime movers for power generation plants. The size, weight, and output of this type of engine are quite different from those of general internal combustion engines, classifying this type of engine into a unique class.

[0003] Large two-stroke uniflow scavenging turbocharged internal combustion crosshead engines have traditionally used marine diesel fuel or heavy oil as fuel. However, in recent years, these engines have come to be manufactured as dual-fuel engines that can operate on both a conventional first fuel and a second type of liquid fuel different from it. The second fuel is usually a fuel that offers advantages related to the environment and sustainability, such as methanol, ammonia, liquefied petroleum gas, etc.

[0004] Therefore, these engines are equipped with a first fuel system for the first fuel and a second fuel system for the second fuel. The first fuel system is a conventional fuel system and is well known in the art of the present invention, so it will not be described in detail. The second fuel system has an element (e.g., a fuel tank) installed on the deck of the ship on which the engine is mounted. The second fuel system needs to connect this fuel tank to the engine's fuel valve. The engine's fuel valve is usually installed inside the engine's cylinder cover, i.e., near the top of the engine. During engine operation, this type of engine exhibits relatively large vibrations, so the fuel valve is constantly moving during engine operation. However, the fuel tank on the deck does not move. Therefore, the second fuel system must be able to absorb the movement of the fuel valve relative to the fuel tank. This is difficult. If the fuel tank and the fuel valve are connected in a straight line, the stresses generated in the fuel supply line and fuel return line can become unmanageable, and may cause leaks or ruptures, especially at the connections between sections of the fuel supply line and return line. It is known in the art of this invention to provide elbows large enough to accommodate relative movement in a manner that does not create excessive stress on the pipes forming the supply and return lines. The larger the elbow, the greater the stress reduction. Since the fuel valve is located near the top of the engine and the fuel tank is located on the deck, i.e., even higher than the fuel valve, the most effective way to create an elbow of sufficient size is to provide an elbow that extends widely downward from the fuel valve and fuel tank. However, such an elbow has a lower section where two parts extending downward from the supply and return lines, respectively, merge. This poses a problem when purging the second fuel system with an inert gas. Purge is required, for example, when the second fuel system is not in use, especially before maintenance work on the second fuel system. The problem that arises at this time is that it is difficult to push out the liquid fuel from the upward section downstream of the lower section of the supply line, which has a larger diameter. This is because when the inert gas passes through the layer of liquid fuel in that upward section, it may only foam without removing the liquid fuel.

[0005] WO2024 / 032900 discloses a dual fuel system for a large two-stroke turbocharged uniflow internal combustion engine capable of operating on a first fuel, which is heavy oil, and a second fuel, which is a different liquid fuel. The engine comprises at least one cylinder in a cylinder liner, a reciprocating piston in the cylinder liner, a cylinder cover covering the cylinder, and a combustion chamber formed in the cylinder liner between the reciprocating piston and the cylinder cover, wherein the fuel system comprises a first fuel system for supplying the first fuel and a second fuel system for supplying the second fuel, the second fuel system comprising a fuel supply line for supplying pressurized second fuel to at least one fuel valve located in the cylinder cover or the cylinder liner, and a fuel return line for returning pressurized second fuel from the at least one fuel valve. The fuel system also comprises a purge system for removing low flash point fuel from the fuel supply line and the fuel return line. The purge system comprises means for introducing a liquid, such as water or diesel, through at least the fuel supply line and return line of the low flash point fuel system. Therefore, low flash point fuels can be safely and economically discharged from the fuel system. Low flash point fuels may also be recovered in a tank for reuse as fuel. Handling mixtures of nitrogen and fuel is complex and costly, but this is eliminated because inert gases such as nitrogen are not used for purging. Summary

[0006] One of the objectives is to provide a fuel system that solves or at least mitigates the above-mentioned problems.

[0007] In a first aspect, a dual fuel system is provided for a large two-stroke turbocharged uniflow internal combustion engine capable of operating with a first fuel, which is fuel oil, and a second fuel, which is a liquid fuel different from the first fuel. However, the aforementioned organization With at least one cylinder in the cylinder liner; A reciprocating piston disposed within the cylinder liner and the cylinder cover that encloses the cylinder; Within the cylinder liner, a combustion chamber is formed between the reciprocating piston and the cylinder cover; The dual fuel system is equipped with, A first fuel system for supplying the first fuel, The device comprises a second fuel system for supplying the second fuel, the second fuel system comprising a fuel supply line for supplying pressurized second fuel to at least one fuel valve disposed in the cylinder cover or the cylinder liner, and a fuel return line for returning pressurized second fuel from the at least one fuel valve, The fuel supply line has a first supply line section running in the vertical direction and a second supply line section running in the vertical direction, with the lowest section of the fuel supply line located between the first supply line section and the second supply line section, the first supply line section located upstream of the lowest section of the supply line, and the second supply line section located downstream of the lowest section of the supply line. The fuel return line comprises a first return line section having a portion running in the vertical direction and a second return line section having a portion running in the vertical direction, the lowest return line section of the fuel return line is located between the first return line section and the second return line section, the first return line section is located upstream of the lowest return line section, and the second return line section is located downstream of the lowest return line section. The lowest section of the supply line is located below the at least one fuel valve. The system comprises a purge system for discharging the second fuel from at least one fuel valve, the fuel supply line, and the fuel return line to a drain tank, wherein the drain tank is positioned higher than the height of the lowest section of the supply line. The aforementioned purge system A first bypass valve connecting the lowest section of the supply line and the fuel return line, A second bypass valve connects the portion of the fuel supply line downstream of the second supply line section to the fuel return line, Purge gas system and The purge gas system is equipped with, When the first bypass valve is closed and the second bypass valve is open, the second fuel is pushed from the fuel supply line and the fuel return line into the drain tank in order to empty the fuel supply line and the fuel return line. Subsequently, when both the first bypass valve and the second bypass valve are open, the remaining second fuel, along with the purge gas, is drawn from the lowest section of the supply line and the second supply line section through the first bypass valve to the drain tank. It is configured in this way.

[0008] By providing a shortcut in the lowest section of the fuel supply line, liquid fuel in the section of the fuel supply line upstream of the lowest section can be drawn into the drain tank through the shortcut by purge gas, thereby effectively removing liquid fuel from the section of the fuel supply line upstream of the lowest section. Furthermore, by opening the second shortcut valve, the pressure between the fuel supply line and the fuel return line is equalized, thereby allowing the liquid fuel in the section of the fuel supply line upstream of the lowest section to flow towards the shortcut due to gravity.

[0009] In one example of the implementation of the first aspect described above, the second fuel is selected from methanol, ammonia, or liquid petroleum gas.

[0010] In one example of the implementation of the first aspect, the first bypass valve is connected to the fuel return line at the lowest point of the fuel return line.

[0011] In one example of the implementation of the first aspect described above, the purge gas system has a purge gas supply source.

[0012] In one example of the implementation of the first aspect described above, the purge gas is an inert gas.

[0013] In one example of the implementation of the first aspect described above, the first bypass valve, when open, has less resistance to flow than the second bypass valve when open.

[0014] In one example of the implementation of the first aspect, the second bypass valve, when open, equalizes the pressure between the fuel supply line and the fuel return line.

[0015] In one example of the implementation of the first aspect, the engine is installed within a structure, the at least one fuel valve moves relative to the structure due to engine vibration during engine operation, and the first supply line section and the second supply line section, as well as the first return line section and the second return line section, reduce stress on the fuel supply line and the fuel return line, wherein the stress is caused by the movement of the at least one fuel valve on the portion of the second fuel supply system that is supported by the structure.

[0016] In one example of the implementation of the first aspect described above, the first bypass valve and the second bypass valve are valves that are normally closed.

[0017] In one example of the implementation of the first aspect, the fuel system includes a liquid detection sensor for detecting the presence of liquid inside the lowest section of the supply line or the lowest section of the return line.

[0018] In one example of the implementation of the first aspect described above, the fuel valve is connected to the fuel supply line via a first control valve and to the fuel return line via a second control valve, and the first and second control valves are opened during purging of at least one fuel valve and closed during purging of the fuel supply line and the fuel return line.

[0019] In one example of the implementation of the first aspect, the cross-sectional area of ​​the second return line section is smaller than the cross-sectional area of ​​the second supply line section, preferably less than 50% of the cross-sectional area of ​​the second supply line section, and most preferably less than 25% of the cross-sectional area of ​​the second return line section. The cross-sectional area of ​​the supply line needs to be large in order to supply sufficient fuel to the engine during operation. However, since only a portion of the fuel is returned during operation, the return line can be made smaller. Therefore, the cross-sectional area of ​​the return line, and especially the second return line section, can be made significantly smaller. This prevents the purge gas from foaming the fuel in the second return line and ensures that the purge gas pushes the fuel toward the drain tank.

[0020] According to the second aspect, a large two-stroke supercharged uniflow internal combustion crosshead engine is provided, comprising the fuel system of the first aspect or any possible embodiment thereof.

[0021] According to the third aspect, a vessel equipped with the engine of the second aspect is provided.

[0022] In one example of the implementation of the third aspect described above, the engine is located in an engine room below deck, part of the second fuel supply system and the drain tank are located on deck, the fuel supply line connects part of the second fuel supply system on deck to the at least one fuel valve, and the fuel return line connects the at least one fuel valve to the drain tank on deck.

[0023] According to a fourth aspect, a method of operating a dual-fuel system for a large two-stroke turbocharged uniflow internal combustion engine operable with a first fuel that is fuel oil and a second fuel that is a liquid fuel different from the first fuel is provided. However, the engine includes at least one cylinder within a cylinder liner, a reciprocating piston disposed within the cylinder liner and a cylinder cover covering the cylinder, a combustion chamber formed between the reciprocating piston and the cylinder cover within the cylinder liner, a first fuel system for supplying the first fuel, a second fuel system for supplying the second fuel, and includes: The second fuel system includes a fuel supply line for supplying pressurized second fuel to at least one fuel valve disposed in the cylinder cover or the cylinder liner, and a fuel return line for returning pressurized second fuel from the at least one fuel valve. The fuel supply line has a first supply line section running in the height direction and a second supply line section running in the height direction. There is a supply line lowest section of the fuel supply line between the first supply line section and the second supply line section. The first supply line section is located upstream of the supply line lowest section, and the second supply line section is located downstream of the supply line lowest section. The fuel return line has a first return line section having a portion running in the height direction and a second return line section having a portion running in the height direction. There is a return line lowest section of the fuel return line between the first return line section and the second return line section. The first return line section is located upstream of the return line lowest section, and the second return line section is located downstream of the return line lowest section. The supply line lowest section is located below the at least one fuel valve. The engine has a purge system for draining the second fuel from the at least one fuel valve, the fuel supply line and the fuel return line to a drain tank, wherein the drain tank is positioned higher than the height of the lowest section of the supply line. The aforementioned purge system A first bypass valve connecting the lowest section of the supply line and the fuel return line, A second bypass valve connecting the portion of the fuel supply line downstream of the second supply line section to the fuel return line, and a purge gas system, Equipped with, The method involves closing the first bypass valve, opening the second bypass valve, and pushing the second fuel from the fuel supply line and the fuel return line to the drain tank; Subsequently, both the first bypass valve and the second bypass valve are opened, allowing the purge gas to draw the second fuel remaining in the lowest section of the supply line and the second supply line section towards the drain tank through the first bypass valve; Includes.

[0024] In one example of the implementation of the fourth aspect, the method includes using a liquid detection sensor to detect the presence of liquid in the lowest section of the supply line or the lowest section of the return line.

[0025] In one example of the implementation of the fourth aspect, the at least one fuel valve is connected to the fuel supply line via the first control valve and to the fuel return line via the second control valve, and the method includes opening the first and second control valves when purging the at least one fuel valve, and closing the first and second control valves when purging the fuel supply line and the fuel return line.

[0026] In one example of the implementation of the fourth aspect, the cross-sectional area of ​​the second return line section is smaller than the cross-sectional area of ​​the second supply line section, preferably the cross-sectional area of ​​the second return line section is less than 50% of the cross-sectional area of ​​the second supply line section, and most preferably the cross-sectional area of ​​the second return line section is less than 25% of the cross-sectional area of ​​the second supply line section.

[0027] The aforementioned and other issues are resolved by the features described in the independent claims. More specific implementations will become apparent from the dependent claims, specification, and drawings. [Brief explanation of the drawing]

[0028] The following will describe in detail various aspects, embodiments, and implementation examples with reference to the exemplary embodiments shown in the drawings. [Figure 1] This shows an overview of a large two-stroke diesel engine according to an exemplary embodiment, viewed from a front oblique angle. [Figure 2] Figure 1 shows an overview of the large two-stroke engine viewed from the rear at an oblique angle. [Figure 3] Figures 1 and 2 show a schematic representation of a first embodiment of the large two-stroke engine, along with its intake and exhaust systems. [Figure 4] Figures 1 to 3 are schematic representations of the second fuel system of a large two-stroke engine. [Figure 5] Figure 4 shows details of the second fuel system. Detailed description

[0029] The following detailed description refers to an exemplary embodiment of a large two-stroke low-speed uniflow scavenging turbocharged crosshead internal combustion engine, describing the internal combustion engine, a vessel equipped with the engine, a method of operating the engine, and a dual fuel system for the engine. The exemplary large two-stroke low-speed uniflow scavenging turbocharged internal combustion engine is of the type in which fuel is injected at or near the top dead center of the piston, i.e., high-pressure type; i.e., compression-ignited type.

[0030] This disclosure provides a large two-stroke uniflow scavenging turbocharged internal combustion engine. Figures 1 and 2 depict a large low-speed turbocharged two-stroke internal combustion engine. This engine has a crankshaft 8 and a crosshead 9. Figure 3 is a schematic representation of a turbocharged large low-speed two-stroke diesel engine in one embodiment, along with its intake and exhaust systems. This engine has six cylinders in series. A large low-speed turbocharged two-stroke internal combustion engine typically has four to fourteen cylinders in series. These cylinders are supported on a cylinder frame 23. The cylinder frame 23 is supported on an engine frame 11. Such engines can also be used, for example, as main engines in ships or as stationary engines to power generators in power plants. The total output of the engine can be, for example, in the range of 1,000 to 110,000 kW.

[0031] In the following embodiment, the engine is a two-stroke uniflow compression-ignition engine, with a scavenging port 18 provided in the lower region of each cylinder liner 1, and an exhaust valve positioned in the center of the top of the cylinder liner 1. The cylinders of the engine are formed by the cylinder liners 1.

[0032] This engine is a dual-fuel engine capable of operating by switching between a first fuel and a different second fuel. That is, it has an operating mode using the first fuel and another operating mode using the second fuel. The first fuel is typically fuel oil, such as marine diesel fuel or heavy oil. The second fuel can be, for example, methanol, ammonia, or liquefied petroleum gas.

[0033] During engine operation, scavenging air is introduced through the scavenging receiver 2 to the scavenging ports 18 of each cylinder 1. The piston 10 reciprocates between bottom dead center (BDC) and top dead center (TDC) in the cylinder liner 1, compressing the scavenging air. Fuel is injected into the combustion chamber in the cylinder liner 1 at or near TDC through a plurality of (high-pressure) fuel valves 49 located in the cylinder cover 22. Combustion occurs following the fuel injection, producing exhaust gas. Each cylinder cover 22 is provided with two or more fuel valves 49. In this embodiment, the fuel valves 49 are arranged in the cylinder cover 22 around the exhaust valve 4 located in the center of the cylinder cover 22. The fuel valves 49 receive fuel from the (high-pressure) fuel supply system 30. The engine in this embodiment is a compression-ignition engine, i.e., a diesel engine. In another embodiment not shown, the engine is an Otto engine. In this case, the fuel valve 49 is located on the cylinder liner 1, and the engine is a so-called low-pressure type, that is, a type in which fuel gas is injected at low pressure.

[0034] When the exhaust valve 4 opens, the exhaust gas flows through the exhaust ducts provided in each cylinder to the exhaust receiver 3, and then through the first exhaust pipe 19 to the turbine 6 of the turbocharger 5. From there, the exhaust gas is released into the atmosphere through the second exhaust pipe 25 and the exhaust outlet 21.

[0035] The turbine 6 drives the compressor 7 via a shaft. The compressor 9 is supplied with outside air through the air intake 12. The compressor 7 sends the compressed scavenging air to the scavenging pipe 13, which is connected to the scavenging receiver 2. The scavenging air in the scavenging pipe 13 passes through the intercooler 14 to cool the scavenging air.

[0036] The cooled scavenging air passes through an auxiliary blower 16 driven by an electric motor 17. The auxiliary blower 16 compresses the scavenging airflow when the compressor 7 of the turbocharger 5 cannot provide sufficient pressure for the scavenging tank 2, i.e., when the engine is under low or partial load. When the engine is under high load, the compressor 7 of the turbocharger can supply sufficiently compressed scavenging air, so the auxiliary blower 16 is bypassed by a check valve 15 and the electric motor 17 is stopped.

[0037] For each engine cycle, the precise amount of fuel to be administered is injected into the cylinder 1 through the fuel valve 49. In some embodiments, the electronic control unit 50 is configured to calculate the engine load as a function of the amount of fuel administered.

[0038] The engine's fuel system has a first fuel system for the first fuel, which is a conventional fuel such as fuel oil. The first fuel system is well known, so no further details will be provided.

[0039] Figure 4 is a schematic representation of the second fuel system 30 of a vessel equipped with a large two-stroke engine. The second fuel system 30 may be divided into two main sections: a deck section and an engine room section.

[0040] The second fuel system 30 includes a fuel tank 31 in the deck section for storing the second fuel. The fuel tank 31 is connected to a fuel supply line 32 and a fuel return line 36. The fuel supply line 32 and the fuel return line 36 are routed from the deck section to the engine room section.

[0041] In the engine room section, the fuel supply line 32 is composed of multiple sections, including a first supply line section 32a having a portion running in the vertical direction, a lower supply line section 32b, and a second supply line section 32c having a portion running in the vertical direction. Similarly, the fuel return line 36 may be composed of multiple sections, including a first return line section 36a, a lower return line section 36b, and a second return line section 36c. The fuel supply line 32 leads to at least one fuel valve 49 located in the cylinder cover 22. The fuel valve 49 is connected to the fuel supply line 32 via a fuel valve supply line 38 including a first control valve 40, and to the fuel return line 36 via a fuel valve return line 39 including a second control valve 41.

[0042] The system further includes a first bypass valve 34 connecting the lowest section 32b of the supply line to the fuel return line 36. A second bypass valve 35 can connect a portion of the fuel supply line 32 downstream of the second supply line section 32c to the fuel return line 36.

[0043] The fuel supply line 32 has a first supply line section 32a having a portion running in the vertical direction, and a second supply line section 32c having a portion running in the vertical direction. Furthermore, the lowest supply line section 32b of the fuel supply line is provided between the first supply line section 32a and the second supply line section 32b. The first supply line section 32a is located upstream of the lowest supply line section 32b, and the second supply line section 32c is located downstream of the lowest supply line section 32b. The fuel return line 36 has a first return line section 36a having a portion running in the vertical direction, and a second return line section 36c having a portion running in the vertical direction. Furthermore, the lowest return line section 36b of the fuel supply line 36 is provided between the first return line section 36a and the second return line section 36c. The first return line section 36a is located upstream of the lowest return line section 36b, and the second return line section 36c is located downstream of the lowest return line section 36b.

[0044] The purge system has an inert gas supply device 51 connected to the fuel supply line 32 through an inert gas supply line 37. The inert gas supply line 37 preferably includes a valve or similar element for controlling the flow of purge gas to the fuel supply line 32. The purge gas is, for example, nitrogen. The purge gas is used to push the second fuel out of the system during the purging operation. This is necessary, for example, when the engine is running on the first fuel and the second fuel system 30 is not in use. It is also particularly necessary when maintenance needs to be performed on the second fuel system 30.

[0045] The drain tank 52 is located higher than the lowest section 32b of the supply line. The drain tank 52 is used to recover the second fuel during purging operations.

[0046] The system may also include a liquid sensor 43, which is configured to detect the presence of liquid fuel in the lower section 32b of the supply line or the lower section 36b of the return line.

[0047] Additional components include a working fluid control valve 45, a one-way valve 46, a working fluid supply line 47, and a working fluid return line 48, which are part of the fuel valve actuation system. The fuel valve actuation system is configured to actuate the fuel valve 49 in a timely manner to perform fuel injection events with a precise dosage of second fuel.

[0048] This configuration of the second fuel system 30 allows for efficient supply of the second fuel during normal operation and effective purging of the system when necessary. The vertically running portions of the supply line section and return line section help to accommodate relative movement between the engine and deck components due to engine vibration. Meanwhile, the bypass valve facilitates the complete discharge of the second fuel during purging operations. All or some of the valves 34, 35, 40, and 41 of the second fuel system, as well as valves not assigned a designation, are also controllable by the electronic control unit 50.

[0049] Figure 5 shows a detailed view focusing on the arrangement of the fuel supply line 32 and fuel return line 36, as well as the bypass valves 34 and 35. This figure shows the vertical configuration of the fuel supply line 32 and fuel return line 36. As shown, they can be positioned at the same height (but not necessarily have to be). The first bypass valve 35 and the conduit connecting the lowest section of the fuel supply line 32b and the lowest section of the fuel return line 36b (if present) are configured to run substantially horizontally. It is not an absolute requirement that the first bypass valve 34 be connected to the lowest section 36b of the fuel return line, but this is preferred at present. The fuel supply line 32 mainly has two vertical sections (second section 32c and first section 32a), connected at the base by the horizontal section 32b, forming a U-shaped structure. This design is also reflected in the fuel return line 36, which similarly has a second vertical section 36c and a first vertical section 36a connected at the base by the horizontal section 36b. The arrangement of these lines ensures that vibrations typical of large ship engines (especially lateral movements) do not generate unacceptable stresses in the fuel supply line 32 and the fuel return line 36.

[0050] At the lowest point of the U-shaped structure, a first bypass valve 34 is strategically positioned to connect the horizontal sections of the fuel supply line 32b and the fuel return line 36b. This valve plays a crucial role in the purging process, enabling efficient system purging by allowing the secondary fuel to be diverted from the supply line 32 to the return line 36, and ensuring that no fuel remains in the lower section of the line during fuel switching or maintenance work.

[0051] In the initial purging phase, the fuel valves 49 are sequentially purged with the first and second shortcut valves 34 and 35 closed (each cylinder cover 22 typically has 2 to 3 fuel valves 49, and the engine typically has 4 to 12 cylinders). At this stage, the first and second control valves 40 and 41 associated with each fuel valve 49 are open, and all fuel valves 49 are sequentially purged. Once the purging of the fuel valves 49 is complete, the first and second control valves 40 and 41 are all closed, the second shortcut valve 35 is opened, and the fuel supply line 32 and fuel return line 36 are purged by blowing purge gas through the fuel supply line 35 and fuel return line 36. This removes most of the liquid second fuel, however, in the vertically running portion of the second supply line section 32, there is a risk that the purge gas will pass through the column of liquid fuel in a foamy manner against the effect of gravity on the column of liquid second fuel, and therefore there is a risk that not all of the liquid fuel in the second supply line section 32c will be removed. Therefore, in the next stage, both the first and second shortcut valves 34 and 35 are opened, allowing the purge gas to flow from the lowest section 32b of the supply line to the lowest section 36b of the return line. At this time, the liquid fuel in the second supply line section 36c flows downstream to the supply line section 32b by gravity, where it merges with the purge gas flowing from the lowest section 32b of the supply line to the first shortcut valve 34. As a result, the liquid second fuel is drawn into the drain tank 52 through the first shortcut valve 34 along with the purge gas. Thus, any second fuel remaining after the previous purging process is effectively removed. In this purging stage, the second bypass valve 35 is opened to equalize the pressure between the fuel supply line 32 and the return line 36, allowing the second fuel in the second supply line section 32c to flow to the lowest section 32b of the supply line by gravity. Preferably, when the first bypass valve 34 is open, its resistance to flow is set to be lower than when the second bypass valve 35 is open. As a result, the purge gas selects the path with the least resistance and passes through that path if the first bypass valve 34 is open.

[0052] In some embodiments, the cross-sectional area of ​​the second return line section is smaller than that of the second supply line section. The cross-sectional area of ​​the second return line section may be less than 50% of the cross-sectional area of ​​the second supply line section, and may also be less than 25% of the cross-sectional area of ​​the second supply line section. In some embodiments, the diameter of the pipes forming the second supply line section is 1 / 2 inch. The cross-sectional area of ​​the supply line needs to be large to supply sufficient fuel to the engine during operation. However, since only a portion of the fuel is returned during operation, the return line can be small. Therefore, the cross-sectional area of ​​the return line, particularly the second return line section, can be significantly reduced. This prevents the purge gas from foaming the fuel in the second return line and ensures that the purge gas pushes the fuel toward the drain tank.

[0053] Various aspects and implementation forms of the invention have been described with several embodiments. However, by examining the specification, drawings, and claims of this application, a person skilled in the art will understand and be able to realize many variations in the invention described in the claims, in addition to the embodiments described. The words “equipment,” “possess,” and “include” in the claims do not exclude the existence of undescribed elements or steps. Even if the number of elements described in the claims is not explicitly stated as multiple, this does not exclude the existence of multiple such elements. Even if several matters are described in separate dependent claims, this does not exclude the combination of these claims, and it is possible to benefit from combining them.

[0054] The reference numerals used in the claims should not be construed as limiting the scope of the invention. Unless otherwise specified, the drawings are intended to be read together with the specification and are part of the overall disclosure. In the specification, the terms “horizontal,” “vertical,” “left,” “right,” “up,” and “down,” and their adjective and adverbial forms (e.g., “horizontally,” “to the right,” “upwards,” etc.) simply describe the orientation of the illustrated structure in the direction from which the reader views it. Similarly, the terms “inward” and “outward” generally describe the direction of a surface relative to a longitudinal axis or rotational axis, depending on the context.

Claims

1. A dual fuel system for a large two-stroke turbocharged uniflow internal combustion engine capable of operating on a first fuel, which is fuel oil, and a second fuel, which is a liquid fuel different from the first fuel, wherein the engine comprises at least one cylinder in a cylinder liner, a reciprocating piston disposed within the cylinder liner and a cylinder cover covering the cylinder, and a combustion chamber formed between the reciprocating piston and the cylinder cover within the cylinder liner, wherein the dual fuel system is A first fuel system for supplying the first fuel, A second fuel system for supplying the aforementioned second fuel, The second fuel system comprises a fuel supply line for supplying a second fuel to at least one fuel valve located in the cylinder cover or the cylinder liner, and a fuel return line for returning the second fuel from the at least one fuel valve. The fuel supply line comprises a first supply line section running in the vertical direction and a second supply line section running in the vertical direction, with the lowest section of the fuel supply line located between the first supply line section and the second supply line section, the first supply line section located upstream of the lowest section of the supply line, and the second supply line section located downstream of the lowest section of the supply line. The fuel return line comprises a first return line section having a portion running in the vertical direction and a second return line section having a portion running in the vertical direction, the lowest return line section of the fuel return line is located between the first return line section and the second return line section, the first return line section is located upstream of the lowest return line section, and the second return line section is located downstream of the lowest return line section. The lowest section of the supply line is located below the at least one fuel valve. The dual fuel system comprises a purge system for discharging the second fuel from the at least one fuel valve, the fuel supply line, and the fuel return line to a drain tank, wherein the drain tank is positioned higher than the height of the lowest section of the supply line, and the purge system is A first bypass valve connecting the lowest section of the supply line and the fuel return line, A second bypass valve connects the portion of the fuel supply line downstream of the second supply line section to the fuel return line, Purge gas system and The purge gas system is equipped with, When the first bypass valve is closed and the second bypass valve is open, the second fuel is pushed from the fuel supply line and the fuel return line into the drain tank in order to empty the fuel supply line and the fuel return line. Subsequently, when both the first bypass valve and the second bypass valve are open, the remaining second fuel, along with the purge gas, is drawn from the lowest section of the supply line and the second supply line section through the first bypass valve to the drain tank. A dual-fuel system configured as follows.

2. The dual fuel system according to claim 1, wherein the second fuel is selected from methanol, ammonia, and liquid petroleum gas.

3. The two-fuel system according to claim 1, wherein the purge gas system comprises a purge gas supply unit.

4. The dual fuel system according to claim 1, wherein the purge gas is an inert gas.

5. The dual fuel system according to claim 1, wherein the first bypass valve, when open, has less resistance to flow than the second bypass valve when open.

6. The dual fuel system according to claim 1, wherein the second bypass valve, when open, equalizes the pressure between the fuel supply line and the fuel return line.

7. The engine is installed within a structure, the at least one fuel valve moves relative to the structure due to engine vibration during engine operation, the first supply line section and the second supply line section and the first return line section and the second return line section reduce stress on the fuel supply line and the fuel return line, wherein the stress is the stress caused by the movement of the at least one fuel valve on the portion of the second fuel system that is supported by the structure.

8. The dual fuel system according to claim 1, wherein the first bypass valve and the second bypass valve are valves that are normally closed.

9. The dual fuel system according to claim 1, further comprising a liquid detection sensor for detecting the presence of liquid inside the lowest section of the supply line or the lowest section of the return line.

10. The dual fuel system according to claim 1, wherein the fuel valve is connected to the fuel supply line via a first control valve and to the fuel return line via a second control valve, and the first control valve and the second control valve are opened during purging of at least one fuel valve and closed during purging of the fuel supply line and the fuel return line.

11. The dual fuel system according to claim 1, wherein the cross-sectional area of ​​the second return line section is smaller than the cross-sectional area of ​​the second supply line section.

12. A large two-stroke turbocharged uniflow internal combustion crosshead engine comprising the fuel system according to any one of claims 1 to 11.

13. A vessel equipped with the engine described in claim 12.

14. The vessel according to claim 13, wherein the engine is located in an engine room below deck, part of the second fuel system and the drain tank are located on deck, the fuel supply line connects part of the second fuel system on deck to the at least one fuel valve, and the fuel return line connects the at least one fuel valve to the drain tank on deck.

15. A method for operating a fuel system for a large two-stroke turbocharged uniflow internal combustion engine capable of operating with a first fuel, which is fuel oil, and a second fuel, which is a liquid fuel different from the first fuel, The engine comprises at least one cylinder within a cylinder liner, a reciprocating piston disposed within the cylinder liner and a cylinder cover covering the cylinder, and a combustion chamber formed between the reciprocating piston and the cylinder cover within the cylinder liner. A first fuel system for supplying the first fuel, A second fuel system for supplying the aforementioned second fuel, Equipped with, The second fuel system comprises a fuel supply line for supplying pressurized second fuel to at least one fuel valve located in the cylinder cover or the cylinder liner, and a fuel return line for returning pressurized second fuel from the at least one fuel valve. The fuel supply line comprises a first supply line section running in the vertical direction and a second supply line section running in the vertical direction, with the lowest section of the fuel supply line located between the first supply line section and the second supply line section, the first supply line section located upstream of the lowest section of the supply line, and the second supply line section located downstream of the lowest section of the supply line. The fuel return line comprises a first return line section having a portion running in the vertical direction and a second return line section having a portion running in the vertical direction, the lowest return line section of the fuel return line is located between the first return line section and the second return line section, the first return line section is located upstream of the lowest return line section, and the second return line section is located downstream of the lowest return line section. The lowest section of the supply line is located below the at least one fuel valve. The engine further comprises a purge system for draining the second fuel from the at least one fuel valve, the fuel supply line and the fuel return line to a drain tank, wherein the drain tank is positioned higher than the height of the lowest section of the supply line. The aforementioned purge system A first bypass valve connecting the lowest section of the supply line and the fuel return line, A second bypass valve connects the portion of the fuel supply line downstream of the second supply line section to the fuel return line, Purge gas system and Equipped with, The method involves closing the first bypass valve, opening the second bypass valve, and pushing the second fuel from the fuel supply line and the fuel return line to the drain tank; Subsequently, both the first bypass valve and the second bypass valve are opened, and the purge gas sweeps the second fuel remaining in the lowest section of the supply line and the second supply line section through the first bypass valve to the drain tank; Methods that include...

16. The method according to claim 15, comprising using a liquid detection sensor to detect the presence of liquid in the lowest section of the supply line or the lowest section of the return line.

17. The method according to claim 15, wherein the at least one fuel valve is connected to the fuel supply line via a first control valve and to the fuel return line via a second control valve, and the method includes opening the first and second control valves when purging the at least one fuel valve and closing the first and second control valves when purging the fuel supply line and the fuel return line.

18. The method according to claim 15, wherein the cross-sectional area of ​​the second return line section is smaller than the cross-sectional area of ​​the second supply line section.

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