Fuel system and operation method thereof, engine and marine vessel

Abstract

A dual fuel system for a large two-stroke turbocharged uniflow internal combustion crosshead engine capable of operating with a first fuel and a second, different fuel, the first fuel being fuel oil, the second fuel being fuel oil, the first fuel being fuel oil, the second fuel being fuel oil, the second fuel being fuel oil, the first fuel being fuel oil, and the second fuel being fuel oil, and a marine vessel having the same, and a method of operating the engine are disclosed. The second fuel is a liquid fuel. The dual fuel system includes: a first fuel system for supplying a first fuel; a second fuel system (30) for supplying a second fuel; a purge system for discharging a second fuel; and the bypass system is used for ensuring that the second fuel from the second fuel system is completely discharged during purging.

Description

Technical Field

[0001] This disclosure relates to a crosshead-type large dual-fuel turbocharged two-stroke single-flow internal combustion piston engine, and more particularly to a crosshead-type large turbocharged two-stroke single-flow internal combustion piston engine having a first fuel system and a second fuel system, wherein the first fuel system is used for conventional fuel and the second fuel system is used for a second unconventional liquid fuel. Background Technology

[0002] Large, two-stroke, single-flow scavenging, turbocharged internal combustion crosshead engines are typically used in the propulsion systems of large ships or as primary power sources in power plants. Their absolute size, weight, and power output make them quite different from ordinary internal combustion engines, placing them within their own class.

[0003] Large, two-stroke, single-flow scavenging, turbocharged internal combustion crosshead engines typically operate using fuel oils, such as marine diesel or heavy fuel oil. However, in recent years, these engines have been configured as dual-fuel engines, capable of operating on either a conventional primary fuel or another type of secondary liquid fuel. The secondary fuel is often one that offers advantages in terms of environmental and sustainability aspects, such as methanol, ammonia, or liquefied petroleum gas (LPG).

[0004] Therefore, these engines are equipped with a first fuel system for a first fuel and a second fuel system for a second fuel. The first fuel system is a conventional fuel system, well known in the art, and will not be described in detail here. The second fuel system includes components typically arranged on the deck of the marine vessel where the engine is mounted, such as fuel tanks, which need to be connected to the engine's fuel valves. The engine's fuel valves are located in the cylinder head of the engine cylinder, i.e., near the top of the engine. During engine operation, these types of engines exhibit relatively large vibrations, and therefore, the fuel valves move constantly during engine operation. This presents a challenge because the fuel tanks on the deck do not move; therefore, the second fuel system needs to be able to absorb the movement of the fuel valves relative to the fuel tanks. In the case of a straight connection between the fuel tank and the fuel valve, the stress generated in the fuel supply and return lines can be too high to handle and can lead to leaks (especially at the joints between the various sections of the fuel supply and return lines) and / or ruptures of the fuel supply and return lines. It is known in the art to provide bends with extensions sufficient to accommodate relative movement, thereby preventing excessive stress in the pipes forming the supply and return lines. The larger extension of the bend results in a greater reduction in stress. Since the fuel valve is positioned close to the top of the engine and the fuel tank is located on the deck—even higher than the fuel valve—the most efficient way to create a bend with a considerable extension is to extend it downwards from the fuel valve and fuel tank to a greater extent. However, this bend has a lowest point where the two downwardly extending portions of the supply and return lines intersect. This can cause problems during purging of the secondary fuel system with inert gas, for example, when the secondary fuel system is not in operation, especially before any maintenance work is performed on it. The problem is that it is difficult to expel liquid fuel from the upward-pointing portion of the large-diameter supply line downstream of the lowest portion of the supply line, because the inert gas bubbles in the liquid gas column of the upward-pointing portion of the supply line instead of removing the liquid fuel.

[0005] WO2024 / 032900 discloses a dual-fuel system for a large two-stroke turbocharged single-flow internal combustion crosshead engine capable of operating with a first fuel and a different second fuel, the first fuel being fuel oil and the second fuel being a liquid fuel. The dual-fuel system includes: at least one cylinder in a cylinder liner; a reciprocating piston in the cylinder liner; a cylinder head covering the cylinder; a combustion chamber formed within the cylinder liner between the reciprocating piston and the cylinder head; a first fuel system for supplying the first fuel; and a second fuel system for supplying the second fuel, the second fuel system including a fuel supply line and a fuel return line. The fuel supply line supplies pressurized second fuel to at least one fuel valve disposed in the cylinder head or cylinder liner, and the fuel return line returns pressurized second fuel from the at least one fuel valve. The fuel system includes a purging system for discharging low-flash-point fuel from the fuel supply line and the return line. The purging system includes means for guiding a liquid, such as water or diesel, at least through the fuel supply line and the return line of the low-flash-point fuel system. Therefore, low flash point fuels can be safely and economically removed from the fuel system, whereby they can be collected in tanks for reuse as fuel, avoiding the expensive and complicated handling of nitrogen and fuel mixtures, since no inert gases such as nitrogen are used for purging. Summary of the Invention

[0006] The goal is to provide a fuel system that overcomes or at least reduces the aforementioned problems.

[0007] According to a first aspect, a dual-fuel system is provided for a large two-stroke turbocharged single-flow internal combustion crosshead engine capable of operating using a first fuel and a different second fuel, wherein the first fuel is fuel oil and the second fuel is a liquid fuel, and the dual-fuel system includes: At least one cylinder in the cylinder liner The reciprocating piston in the cylinder liner and the cylinder head that covers the cylinder. The combustion chamber is formed within the cylinder liner between the reciprocating piston and the cylinder head. A first fuel system for supplying the first fuel; A second fuel system for supplying a second fuel, comprising a fuel supply line and a fuel return line, wherein the fuel supply line supplies pressurized second fuel to at least one fuel valve disposed in the cylinder head or cylinder liner, and the fuel return line returns the pressurized second fuel from the at least one fuel valve. The fuel supply pipeline includes a first supply pipeline section and a second supply pipeline section having vertical extensions, and a lowest supply pipeline section located between the first supply pipeline section and the second supply pipeline section, wherein the first supply pipeline section is located upstream of the lowest supply pipeline section, and the second supply pipeline section is located downstream of the lowest supply pipeline section. The fuel return pipeline includes a first return pipeline section and a second return pipeline section having a vertical extension, and a lowest return pipeline section of the fuel supply pipeline located between the first return pipeline section and the second return pipeline section, wherein the first return pipeline section is located upstream of the lowest return pipeline section and the second return pipeline section is located downstream of the lowest return pipeline section. The lowest supply line section is located below at least one fuel valve. A purging system is used to discharge a second fuel from at least one fuel valve and fuel supply line, as well as a fuel return line, to a discharge tank, which is located at a height above the lowest section of the supply line. The purging system includes: The first bypass valve connects the lowest supply line section and the fuel return line. The second bypass valve connects the downstream portion of the fuel supply line to the fuel return line, and... The purging gas system is configured as follows: 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 fuel return line to the discharge tank to empty the fuel supply line and fuel return line. Subsequently, when both the first and second bypass valves are open, any remaining second fuel is dragged from the lowest supply line section and the second supply line section toward the discharge tank via the first bypass valve using purge gas.

[0008] By installing a quick-access section at the lowest point of the fuel supply line, purge gas can effectively remove liquid fuel from the vertical section downstream of the lowest point of the fuel supply line by dragging it through the quick-access section to the discharge tank. By opening a second quick-access valve, the pressure between the fuel supply line and the fuel return line is equalized, causing the liquid fuel in the vertical section downstream of the lowest point of the fuel supply line to flow towards the quick-access section under the influence of gravity.

[0009] Depending on the possible implementation of the first aspect, the second fuel is selected from methanol, ammonia, and liquefied petroleum gas.

[0010] According to a possible implementation of the first aspect, the first bypass valve is connected to the fuel return line at the lowest part of the fuel return line.

[0011] According to a possible implementation of the first aspect, the purge gas system includes a purge gas supply.

[0012] According to the possible implementation of the first aspect, the purging gas is an inert gas.

[0013] According to a possible implementation of the first aspect, the first bypass valve imposes a smaller restriction on the flow rate when it is open than the second bypass valve imposes a smaller restriction on the flow rate when it is open.

[0014] According to a possible implementation of the first aspect, the second bypass valve, when opened, balances the pressure between the fuel supply line and the fuel return line.

[0015] According to a possible implementation of the first aspect, the engine is mounted in a structural member, and wherein at least one fuel valve moves relative to the structural member due to engine vibration during engine operation, and wherein a first supply line portion, a second supply line portion, a first return line portion, and a second return line portion reduce stress in the fuel supply line and fuel return line caused by the movement of at least one fuel valve relative to the portion of the second fuel supply system carried by the structural member.

[0016] According to the possible implementation of the first aspect, the first bypass valve and the second bypass valve are normally closed valves.

[0017] According to a possible implementation of the first aspect, the fuel system includes a liquid detection sensor for detecting the presence of liquid in the lowest supply line section or the lowest return line section.

[0018] According to a possible implementation of the first aspect, 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, wherein the first and second control valves are open during purging of at least one fuel valve, and wherein the first and second control valves are closed during purging of the fuel supply line and the fuel return line.

[0019] According to a possible implementation of the first aspect, the cross-sectional area of ​​the second return line section is smaller than that 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. The cross-sectional area of ​​the supply line must be large to allow sufficient fuel flow to the engine during operation. However, the return line can be smaller because only a portion of the fuel is returned during operation. Therefore, the return line, particularly the second return line section, can have a significantly smaller cross-sectional area, which prevents bubbling of fuel through the purge gas in the second return line, thereby ensuring that the purge gas pushes the fuel toward the exhaust canister.

[0020] According to the second aspect, a large two-stroke turbocharged single-flow internal combustion crosshead engine is provided, including a fuel system according to the first aspect or any possible implementation of the fuel system.

[0021] According to a third aspect, a marine vessel is provided, which includes an engine according to a second aspect.

[0022] According to a possible implementation of the third aspect, the engine is located in an engine room below the deck, wherein an exhaust tank and a portion of a second fuel supply system are located above the deck, and wherein a fuel supply line connects the portion of the second fuel supply system located above the deck to at least one fuel valve, and wherein a fuel return line connects at least one fuel valve to the exhaust tank located above the deck.

[0023] According to a fourth aspect, a method for operating a fuel system is provided, the fuel system being used in a large two-stroke turbocharged single-flow internal combustion crosshead engine capable of operating using a first fuel and a different second fuel, the first fuel being fuel oil and the second fuel being a liquid fuel, the engine comprising: At least one cylinder in the cylinder liner The reciprocating piston in the cylinder liner and the cylinder head that covers the cylinder. The combustion chamber is formed within the cylinder liner between the reciprocating piston and the cylinder head. The first fuel system is used to supply the first fuel. A second fuel system for supplying a second fuel, comprising a fuel supply line and a fuel return line, wherein the fuel supply line supplies pressurized second fuel to at least one fuel valve located in the cylinder head or cylinder liner, and the fuel return line returns the pressurized second fuel from the at least one fuel valve located in the cylinder head. The fuel supply pipeline includes a first supply pipeline section and a second supply pipeline section having vertical extensions, and a lowest supply pipeline section located between the first supply pipeline section and the second supply pipeline section, wherein the first supply pipeline section is located upstream of the lowest supply pipeline section, and the second supply pipeline section is located downstream of the lowest supply pipeline section. The fuel return pipeline includes a first return pipeline section and a second return pipeline section having a vertical extension, and a lowest return pipeline section of the fuel supply pipeline located between the first return pipeline section and the second return pipeline section, wherein the first return pipeline section is located upstream of the lowest return pipeline section and the second return pipeline section is located downstream of the lowest return pipeline section. The lowest supply line section is located below at least one fuel valve. A purging system is used to discharge a second fuel from at least one fuel valve and fuel supply line, as well as a fuel return line, to a discharge tank, which is located at a height above the lowest section of the supply line. The purging system includes: The first bypass valve connects the lowest supply line section and the fuel return line. A second bypass valve and a purge gas system are also included. The second bypass valve connects the downstream portion of the fuel supply line to the fuel return line. The methods include: Close the first bypass valve, open the second bypass valve, and push the second fuel from the fuel supply line and fuel return line to the discharge tank. Subsequently, both the first and second bypass valves are opened, and the purging gas drags any remaining second fuel in the minimum supply line section and the second supply line section toward the discharge tank through the first bypass valve.

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

[0025] According to a possible implementation of the fourth aspect, at least one fuel valve is connected to a fuel supply line via a first control valve and to a fuel return line via a second control valve, the method comprising: opening the first control valve and the second control valve when purging at least one fuel valve, and closing the first control valve and the second control valve when purging the fuel supply line and the fuel return line.

[0026] According to a possible implementation of the fourth aspect, the cross-sectional area of ​​the second return pipeline section is smaller than the cross-sectional area of ​​the second supply pipeline section. Preferably, the cross-sectional area of ​​the second return pipeline section is less than 50% of the cross-sectional area of ​​the second supply pipeline section. Most preferably, the cross-sectional area of ​​the second return pipeline section is less than 25% of the cross-sectional area of ​​the second supply pipeline section.

[0027] The above and other aspects are achieved through the features of the independent claims. Further embodiments are readily apparent from the dependent claims, the specification, and the drawings. Attached Figure Description

[0028] In the following detailed sections of this disclosure, these aspects, implementations, and methods will be described in more detail with reference to exemplary embodiments illustrated in the accompanying drawings, wherein: Figure 1 This is a top-down front / side view of a large two-stroke diesel engine according to an exemplary embodiment. Figure 2 yes Figure 1 A top-down rear / side view of a large two-stroke engine. Figure 3 It is based on Figure 1 and Figure 2 A schematic diagram of a first embodiment of a large two-stroke engine, showing the inlet and outlet systems. Figure 4 It is based on Figures 1 to 3 A schematic diagram illustrating the implementation of the second fuel system for a large two-stroke engine, and Figure 5 It shows Figure 4 Details of the second fuel system. Detailed Implementation

[0029] In the following detailed description, an internal combustion engine, a marine vessel having the engine, a method of operating the engine, and a dual-fuel system for the engine will be described with reference to the crosshead large two-stroke low-speed single-flow scavenging turbocharged internal combustion engine of the reference embodiment. The large two-stroke low-speed single-flow scavenging turbocharged internal combustion engine is a high-pressure type, wherein fuel is injected at or near the top dead center of the piston and ignited by compression.

[0030] This disclosure provides a large two-stroke single-flow scavenging turbocharged internal combustion engine. Figure 1 and Figure 2 This shows a large, low-speed turbocharged two-stroke internal combustion engine with a crankshaft 8 and a crosshead 9. Figure 3A schematic diagram of a large, low-speed turbocharged two-stroke diesel engine and its intake and exhaust systems, according to an embodiment, is shown. The engine has six cylinders in an inline. Large, low-speed turbocharged two-stroke internal combustion engines typically have between four and fourteen cylinders in an inline configuration, with the cylinders supported by cylinder frames 23, which in turn are supported by engine frames 11. This engine can be used, for example, as a main engine in marine vessels or as a stationary engine for operating generators in power plants. The total output of the engine can be, for example, in the range of 1,000 kW to 110,000 kW.

[0031] In this embodiment, the engine is a two-stroke, single-flow compression-ignition engine, having a scavenging air port 18 in the lower region of the cylinder liner 1 and a central exhaust valve 4 at the top of each 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 switching between a primary fuel and different secondary fuels, allowing it to operate in both a primary fuel-based and a secondary fuel-based mode. The primary fuel is typically fuel oil, such as marine diesel or heavy fuel oil. The secondary fuel can be, for example, methanol, ammonia, or liquefied petroleum gas.

[0033] During operation, scavenging air is delivered from the scavenging air receiver 2 to the scavenging ports 18 of each cylinder 1. The scavenging air is compressed by the piston 10, which reciprocates between bottom dead center (BDC) and top dead center (TDC) in the cylinder liner 1. Fuel is injected into the combustion chamber in the cylinder liner 1 at or near TDC via (high-pressure) fuel valves 49 arranged in the cylinder head 22. Combustion then occurs, generating exhaust gases. Each cylinder head 22 is provided with two or more fuel valves 49. In this embodiment, the fuel valves 49 are arranged in the cylinder head 22 around the central exhaust valve 4 and 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 fuel valves 49 are located in the cylinder liner 1 and the engine is a so-called low-pressure engine, in which fuel gas is injected at a lower pressure, and the engine is an "Otto" engine.

[0034] When the exhaust valve 4 is open, the exhaust gas flows into the exhaust gas receiver 3 through the exhaust duct associated with each cylinder, then forward through the first exhaust passage 19 to the turbine 6 of the turbocharger 5, and the exhaust gas flows out of the turbine 6 through the second exhaust passage via the exhaust outlet 21 and into the atmosphere.

[0035] Turbine 6 drives compressor 7 via shaft, and compressor 7 is supplied with fresh air through inlet 12. Compressor 7 delivers pressurized scavenging air to scavenging air passage 13, which leads to scavenging air receiver 2. The scavenging air in scavenging air passage 13 passes through intercooler 14 for cooling.

[0036] Cooled scavenging air passes through an auxiliary blower 16 driven by an electric motor 17. This auxiliary blower 16 pressurizes the scavenging air stream when the turbocharger 5 compressor 7 does not deliver sufficient pressure to the scavenging air receiver 2, i.e., under low or partial engine load conditions. Under higher engine load conditions, the turbocharger compressor 7 delivers sufficient compressed scavenging air, and then the auxiliary blower 16 is bypassed via a check valve 15, and the electric motor 17 is deactivated.

[0037] For each engine cycle, a precise dose of fuel is injected into cylinder (1) via fuel valve 49, and the return control unit 50 is configured in the embodiment to calculate the engine load based on the fuel dose.

[0038] The engine's fuel system includes a first fuel system for a first (conventional) fuel, such as fuel oil. The first fuel system is well known in the art and therefore will not be described in further detail.

[0039] Figure 4 A schematic diagram of an embodiment of a second fuel system 30 for a large two-stroke engine installed in a marine vessel is shown. The second fuel system 30 can be divided into two main parts: an on-deck section and an engine room section.

[0040] In the deck section, the system includes a fuel tank 31 for storing a second fuel. The fuel tank 31 is connected to a fuel supply line 32 and a fuel return line 36. These lines extend from the deck section to the engine room section.

[0041] In the engine compartment section, the fuel supply line 32 includes multiple sections, including a first supply line section 32a having a vertical extension, a lowest supply line section 32b, and a second supply line section 32c, also having a vertical extension. The fuel return line 36 may similarly include multiple sections, including a first return line section 36a, a lowest return line section 36b, and a second return line section 36c. The fuel supply line 32 leads to at least one fuel valve 49 disposed in the cylinder head 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 is connected to the fuel return line 36 via a fuel valve return line 39 including a second control valve 41.

[0042] The system includes a first bypass valve 34 connecting the lowest supply line section 32b and 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 32c to the fuel return line 36.

[0043] The fuel supply line 32 includes a first supply line section 32a and a second supply line section 32c having vertical extensions, and a lowest supply line section 32b located between the first supply line section 32a and the second supply line section 32b. The first supply line section 32a is upstream of the lowest supply line section 32b, and the second supply line section 32c is downstream of the lowest supply line section 32b. The fuel return line 36 includes a first return line section 36a and a second return line section 36c having vertical extensions, and a lowest return line section 36b located between the first return line section 36a and the second return line section 36c. The first return line section 36a is upstream of the lowest return line section 36b, and the second return line section 36c is downstream of the lowest return line section 36b.

[0044] The purging system includes an inert gas supplier 51 connected to a fuel supply line 32 via an inert gas supply line 37, which is preferably equipped with a valve or similar device for controlling the flow rate of the purging gas entering the fuel supply line 32. The purging gas can be, for example, nitrogen. The purging gas is used to expel a second fuel from the system during purging operations, which is necessary when, for example, the engine operating based on the first and second fuel systems 30 is not in use, and is particularly relevant when maintenance of the second fuel system 30 is required.

[0045] The discharge tank 52 is positioned above the lowest supply line section 32b. This discharge tank 52 is used to collect secondary fuel during purging operations.

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

[0047] Additional components include an actuated fluid control valve 45, a check valve 46, an actuated fluid supply line 47, and an actuated fluid return line 48, which are part of the fuel valve actuation system. The fuel valve actuation system is configured to activate the fuel valve 49 in a timely manner to perform a fuel injection event with a precise dose of second fuel.

[0048] This arrangement of the second fuel system 30 allows for efficient second fuel supply during normal operation and effective purging of the system when needed. Vertical extensions of the supply and return lines help accommodate relative movement between the engine and deck components caused by engine vibration, while bypass valves facilitate complete discharge of the second fuel during purging operations. All or some of the valves in valves 34, 35, 40, and 41 of the second fuel system, as well as those not assigned any reference numerals, can be controlled by the electronic control unit 50.

[0049] Figure 5 Detailed schematic diagrams are provided, focusing on the arrangement of fuel supply line 32, fuel return line 36, and bypass valves 34 and 35. The diagram shows the vertical configuration of fuel supply line 32 and fuel return line 36. As shown, fuel supply line 32 and fuel return line 36 can be arranged at the same height as (but not necessarily at) the first bypass valve 35. If the first bypass valve 35 is present, the channel connecting the lowest portion of fuel supply line 32b to the lowest portion of fuel return line 36b extends approximately horizontally. It is not absolutely required that the first bypass valve 34 be connected to the lowest portion 36b of the fuel return line, but this is currently preferred. Fuel supply line 32 is depicted as having two main vertical portions: a second portion 32c and a first portion 32a, which are connected at their bases by a horizontal portion 32b, forming a U-shaped configuration. This design is reflected in the fuel return line 36, which is also characterized by a second vertical section 36c and a first vertical section 36a connected at the base by a horizontal section 36b. The positioning of these lines ensures that motion (especially lateral motion) caused by vibration, which is typically found in large marine engines, does not create unacceptable stress in the fuel supply line 32 and the fuel return line 36.

[0050] At the lowest point of the U-shaped configuration, a first bypass valve 34 is strategically placed to connect the horizontal portion of the fuel supply line 32b and the fuel return line 36b. This valve plays a crucial role during purging, allowing secondary fuel to be redirected from the supply line 32b to the return line 36b, facilitating efficient system purging and ensuring that no fuel remains in the lower portion of the lines, no fuel is switched between lines, or no switching occurs during maintenance.

[0051] During the first stage of purging, the first quick-release valve 34 and the second quick-release valve 35 are closed to purge the fuel valves 49 one by one (typically there are two or three fuel valves 49 in each cylinder head 22, and each engine typically has four to twelve cylinders). During this stage, the first control valve 40 and the second control valve 41 associated with a given fuel valve 49 are opened, and all fuel valves 49 are purged sequentially. After the fuel valves 49 have been purged, the first control valve 40 and the second control valve 41 are both closed, and the second quick-release valve 35 is opened to purge the fuel supply line 32 and the fuel return line 36 by blowing purge gas through the fuel supply line 35 and the fuel return line 36. This will remove most of the liquid second fuel, but in the vertical extension of the second supply line section 32, there is a risk that the purge gas may bubble as it passes through the liquid second fuel column against the influence of gravity, and therefore there is a risk that not all liquid fuel in the second supply line section 32c will be removed. Therefore, in the subsequent stage, both the first quick-release valve 34 and the second quick-release valve 35 are opened, allowing purge gas to flow from the lowest supply line section 32b to the lowest return line section 36b. Any liquid fuel in the second supply line section 36c flows towards the lower supply line section 32b by gravity. At the lower supply line section 32b, the liquid fuel encounters the purge gas flowing from the lowest supply line section 32b into the first quick-release valve 34. Thus, the second liquid fuel is dragged through the first quick-release valve 34 by the purge gas and upwards from the first quick-release valve 34 to the discharge tank 52. Therefore, any second fuel remaining from the previous purging stage is effectively removed. During this purging stage, the second quick-release valve 35 is opened to equalize the pressure between the fuel supply line 32 and the fuel return line 36, thereby allowing any second fuel in the second supply line section 32c to flow towards the lowest supply line section 32b under the influence of gravity. Preferably, the flow restriction imposed by the first bypass valve 34 when it is open is less than the flow restriction imposed by the second bypass valve 35 when it is open, so as to ensure that the purge gas will take the path of least resistance and flow through the first quick valve 34 when it is open.

[0052] In one embodiment, 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 can be less than 50% of the cross-sectional area of ​​the second supply line section, and even less than 25% of the cross-sectional area of ​​the second supply line section. In this embodiment, the diameter of the pipe forming the second supply line section is 1 / 2 inch. The cross-sectional area of ​​the supply line must be large to allow sufficient fuel flow to the engine during operation. However, the return line can be smaller because only a portion of the fuel is returned during operation. Therefore, the return line, particularly the second return line section, can have a significantly smaller cross-sectional area, which prevents bubbling of fuel through the purge gas in the second return line, thereby ensuring that the purge gas pushes the fuel towards the exhaust canister.

[0053] This document has described various aspects and implementations in conjunction with various embodiments. However, those skilled in the art, when practicing the claimed subject matter, can understand and implement other variations of the disclosed embodiments based on a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "the" do not exclude a plurality. The fact that certain measures are referenced in mutually different dependent claims does not indicate that a combination of these measures cannot be utilized to obtain benefits.

[0054] The reference numerals used in the claims should not be construed as limiting the scope. Unless otherwise stated, the drawings are intended to be read in conjunction with the description (e.g., crosshairs, arrangement of parts, scale, degrees, etc.) and are considered part of the entire written specification of this disclosure. As used in the description, the terms “horizontal,” “vertical,” “left,” “right,” “up,” and “down,” and their adjective and adverbial derivatives (e.g., “horizontally,” “to the right,” “upward,” etc.) refer only to the orientation of the structure shown when the particular drawing is facing the reader. Similarly, the terms “inward” and “outward” generally refer to the orientation of a surface relative to its axis of extension or axis of rotation, depending on the circumstances.

Claims

1. A dual-fuel system for a large two-stroke turbocharged single-flow internal combustion crosshead engine, the engine being capable of operating using a first fuel and a different second fuel, the first fuel being fuel oil and the second fuel being a liquid fuel, the dual-fuel system comprising: In at least one cylinder of cylinder liner (1), The reciprocating piston (10) in the cylinder liner (1) and the cylinder head (22) covering the cylinder (1). A combustion chamber, formed within the cylinder liner (1) between the reciprocating piston and the cylinder head (22), A first fuel system for supplying the first fuel; A second fuel system (30) for supplying the second fuel, the second fuel system including a fuel supply line (32) and a fuel return line (36), the fuel supply line (32) for supplying the second fuel to at least one fuel valve (49) disposed in the cylinder head (22) or the cylinder liner (1), and the fuel return line (36) for returning the second fuel from the at least one fuel valve (49). The fuel supply pipeline (32) is characterized in that it includes a first supply pipeline section (32a) and a second supply pipeline section (32c) having a vertical extension, and a lowest supply pipeline section (32b) located between the first supply pipeline section (32a) and the second supply pipeline section (32b), wherein the first supply pipeline section (32a) is located upstream of the lowest supply pipeline section (32b), and the second supply pipeline section (32c) is located downstream of the lowest supply pipeline section (32b). The fuel return line (36) includes a first return line section (36a) and a second return line section (36c) having vertical extensions, and a lowest return line section (36b) of the fuel supply line (36) located between the first return line section (36a) and the second return line section (36c), wherein 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). The lowest supply line section (36b) is located below the at least one fuel valve (49). A purging system for discharging the second fuel from the at least one fuel valve (49), the fuel supply line (32), and the fuel return line (36) to a discharge tank (52), the discharge tank (52) being located at a height above the lowest supply line section (32b). The purging system is characterized by comprising: A first bypass valve (34) connects the lowest supply line section (32b) to the fuel return line (36). The second bypass valve (35) connects a portion of the fuel supply line (32) downstream of the second supply line section (32c) to the fuel return line (36), and A purge gas system, wherein the purge gas system is configured to: When the first bypass valve (34) is closed and the second bypass valve (35) is open, the second fuel is pushed from the fuel supply line (32) and the fuel return line (36) to the discharge tank (52) to empty the fuel supply line (32) and the fuel return line (36), and Subsequently, when both the first bypass valve (34) and the second bypass valve (35) are open, any remaining second fuel is dragged from the lowest supply line section (32b) and the second supply line section (36c) toward the discharge tank (52) by purge gas.

2. The fuel system of claim 1, wherein, The second fuel is selected from methanol, ammonia, and liquefied petroleum gas.

3. The fuel system of claim 1 or 2, wherein, The purging gas system includes a purging gas supply unit (51).

4. The fuel system of any one of claims 1-3, wherein, The purging gas is an inert gas.

5. The fuel system of any one of claims 1 to 4, wherein, The first bypass valve (34) imposes a smaller flow restriction when it is open than the second bypass valve (35) when it is open.

6. The fuel system of any one of claims 1 to 5, wherein, When the second bypass valve (35) is open, it balances the pressure between the fuel supply line (32) and the fuel return line (36).

7. The fuel system of any one of claims 1 to 6, wherein, The engine is mounted in a structure, and wherein the at least one fuel valve (49) moves relative to the structure during engine operation due to engine vibration, and wherein the first supply line portion, the second supply line portion, the first return line portion, and the second return line portion reduce the stress in the fuel supply line (32) and the fuel return line (36) caused by the movement of the at least one fuel valve (49) relative to the portion of the second fuel supply system (30) carried by the structure.

8. The fuel system of any one of claims 1-7, wherein, The first bypass valve (34) and the second bypass valve (35) are normally closed valves.

9. The fuel system according to any one of claims 1 to 8, the fuel system comprising a liquid detection sensor (43) for detecting the presence of liquid in the lowest supply line section or the lowest return line section.

10. The fuel system of any one of claims 1 to 9, wherein, The at least one fuel valve (49) is connected to the fuel supply line (32) via a first control valve (40) and to the fuel return line (36) via a second control valve (41), wherein the first control valve (40) and the second control valve (41) are open during purging of the at least one fuel valve (49), and wherein the first control valve (40) and the second control valve (41) are closed during purging of the fuel supply line (32) and the fuel return line (36).

11. The fuel system according to any one of claims 1 to 10, wherein, The cross-sectional area of ​​the second return pipeline section (36c) is smaller than the cross-sectional area of ​​the second supply pipeline section (32c).

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

13. A marine vessel comprising the engine according to claim 12.

14. The marine vessel according to claim 13, wherein, The engine is located in an engine room below the deck, wherein the exhaust tank (52) and a portion of the second fuel supply system (30) are located above the deck, and wherein the fuel supply line (32) connects the portion of the second fuel supply system (30) above the deck to the at least one fuel valve (49), and wherein the fuel return line (36) connects the at least one fuel valve (49) to the exhaust tank (52) above the deck.

15. A method of operating a fuel system for a large two-stroke turbocharged single-flow internal combustion crosshead engine, the engine being capable of operating using a first fuel and a different second fuel, the first fuel being fuel oil and the second fuel being a liquid fuel, the engine comprising: In at least one cylinder of cylinder liner (1), The reciprocating piston (10) in the cylinder liner (1) and the cylinder head (22) that covers the cylinder. A combustion chamber, formed within the cylinder liner (1) between the reciprocating piston (10) and the cylinder head (22), A first fuel system for supplying the first fuel. A second fuel system (30) for supplying the second fuel, the second fuel system including a fuel supply line (32) and a fuel return line (36), the fuel supply line (32) for supplying pressurized second fuel to at least one fuel valve (49) disposed in the cylinder head (22) or the cylinder liner (1), and the fuel return line (36) for returning the pressurized second fuel from the at least one fuel valve (49). Its features are, The fuel supply pipeline includes a first supply pipeline section (32a) and a second supply pipeline section (32c) having vertical extensions, and a lowest supply pipeline section (32b) located between the first supply pipeline section (32a) and the second supply pipeline section (32b), wherein the first supply pipeline section (32a) is located upstream of the lowest supply pipeline section (32b), and the second supply pipeline section (32c) is located downstream of the lowest supply pipeline section (32b). The fuel return line (36) includes a first return line section (36a) and a second return line section (36c) having vertical extensions, and a lowest return line section (36b) of the fuel supply line (36) located between the first return line section (36a) and the second return line section (36c), wherein 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). The lowest supply line section (36b) is located below the at least one fuel valve (49). A purging system for discharging the second fuel from the at least one fuel valve (49), the fuel supply line (32), and the fuel return line (36) to a discharge tank (52), the discharge tank (52) being located at a height above the lowest supply line section (32b). The purging system is characterized by comprising: A first bypass valve (34) connects the lowest supply line section (32b) to the fuel return line (36). The second bypass valve (35) connects the portion of the fuel supply line (32) downstream of the second supply line section (32c) to a fuel return line. purge air system (51). The method includes: Close the first bypass valve (34), open the second bypass valve (35), and push the second fuel from the fuel supply line (32) and the fuel return line (36) to the discharge tank (52). Subsequently, both the first bypass valve (34) and the second bypass valve (35) are opened, and the purge gas drags any remaining second fuel in the minimum supply line section (32b) and the second supply line section (36c) toward the discharge tank (52) through the first bypass valve (34).

16. The method of claim 15, comprising: The presence of liquid in the lowest supply line section (32b) or the lowest return line section (36b) is detected using a liquid detection sensor (43).

17. The method according to claim 15 or 16, wherein, The at least one fuel valve (49) is connected to the fuel supply line (32) via a first control valve (40) and to the fuel return line (36) via a second control valve (41). The method includes: opening the first control valve (40) and the second control valve (41) when purging the at least one fuel valve (49), and closing the first control valve (40) and the second control valve (41) when purging the fuel supply line (32) and the fuel return line (36).

18. The method according to any one of claims 15 to 17, wherein, The cross-sectional area of ​​the second return pipeline section (36c) is smaller than the cross-sectional area of ​​the second supply pipeline section (32c).

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