Large turbocharged two-stroke dual-fuel uniflow crosshead internal combustion engine and method for purging the fuel system of said engine

Abstract

A method of purging the fuel system (30) of a large turbocharged, two-stroke, dual-fuel, uniflow crosshead internal combustion engine is disclosed, the fuel system having a conventional fuel system supplying a conventional fuel and a second fuel system (30) supplying a liquid second fuel such as ammonia or LPG. The second fuel system includes a second fuel tank (31), a second fuel supply line (32) supplying pressurized second fuel to a fuel valve (49), and a second fuel return line (36) returning the pressurized second fuel from the fuel valve. The engine has a purge gas system that purges the second fuel from a fuel valve, a second fuel supply line, and a second fuel return line to a drain tank (52), and the method is characterized in that after purging stops, a space including at least a portion of the fuel valve and the second fuel supply and return lines is isolated from the rest of the second fuel system by closing a plurality of valves (32d, 36d, 35, 40, 41), and measuring and using an internal pressure and temperature of the space to determine whether the internal pressure of the space corresponds to a saturation pressure on a pressure / temperature saturation curve of the second fuel, and continuing purging if the pressure in the space corresponds to the saturation pressure.

Description

[Technical Field]

[0001] The present invention relates to a method of purging the fuel system of a large turbocharged, two-stroke, dual-fuel, uniflow crosshead internal combustion engine, said engine comprising: at least one cylinder within a cylinder liner; a reciprocating piston disposed in the cylinder liner and a cylinder cover covering the cylinder; a combustion chamber formed in the cylinder liner between the reciprocating piston and the cylinder cover; a conventional fuel system supplying a conventional fuel and a secondary fuel system supplying a secondary fuel such as ammonia or LPG; the second fuel system includes a second fuel tank, a second 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 second fuel return line for returning the pressurized second fuel from the at least one fuel valve, and the engine further includes: The fuel supply system further includes a purge gas system for purging the second fuel from the at least one fuel valve, the second fuel supply line, and the second fuel return line to a drain tank.

[0002] Large turbocharged two-stroke uniflow crosshead internal combustion engines are typically used as prime movers in large ocean-going vessels such as container ships and in power plants. This type of engine is most often run on heavy fuel oil or other fuels such as diesel.

[0003] In recent years, there has been a demand for large two-stroke diesel engines to be able to run on other types of secondary fuels, such as ammonia and LPG. Engines that can operate in both a fuel oil mode, where they run on fuel oil only, and a secondary fuel mode, where they run on a secondary fuel and pilot fuel, are often referred to as dual-fuel engines.

[0004] Dual-fuel engines are required to be able to run on both conventional fuels, such as heavy fuel oil or diesel, and the potentially environmentally friendly second fuel mentioned above. This requires a dedicated fuel supply and injection system for each type of fuel used. The requirement for two fuel supply and injection systems significantly increases the initial cost of manufacturing the engine and increases its complexity and maintenance costs. However, some equipment, such as a hydraulic pump, can be used in conjunction with both the fuel supply system and the injection system to provide hydraulic power to the fuel pump, which pressurizes the fuel.

[0005] Thus, a dual-fuel engine includes a conventional fuel system for a conventional fuel and a second fuel system for a second fuel. Conventional fuel systems are well known in the art and will not be described in further detail. The second fuel system includes elements, such as a second fuel tank, installed on the deck of the vessel on which the engine is installed. The second fuel system must connect the second fuel tank to the engine's fuel valve, which is typically installed in the engine's cylinder cover or cylinder liner. Because this type of engine experiences relatively large vibrations during engine operation, the fuel valve is constantly moving during engine operation. However, the second fuel tank on deck does not move. Therefore, the second fuel system must be able to accommodate the movement of the fuel valve relative to the second fuel tank. This is difficult. If a straight connection is made between the second fuel tank and the fuel valve, the stresses induced in the second fuel supply line and the second fuel return line can become unmanageable, potentially resulting in leaks or ruptures, especially at the connections between sections of the fuel supply and return lines. Providing an elbow large enough to accommodate relative movement without placing undue stress on the pipes forming the supply and return lines is known in the art. The larger the elbow, the greater the stress relief. Because the fuel valve is located near the top of the engine and the secondary fuel tank is located on deck, i.e., higher than the fuel valve, the most effective way to create a large enough elbow is to provide an elbow that extends downward from the fuel valve and secondary fuel tank. However, such an elbow has a bottom section where the two downwardly extending portions of the supply and return lines join. This presents a problem when purging the secondary fuel system with inert gas. Purging is required, for example, when the secondary fuel system is not in use, especially before maintenance work on the secondary fuel system. The problem is that it is difficult to push the liquid secondary fuel out of the upward-facing portion downstream of the bottom section of the supply line because the inert gas may bubble rather than remove the liquid secondary fuel as it passes through the layer of liquid secondary fuel in the upward-facing portion.Additionally, liquid secondary fuel may become trapped elsewhere in the secondary fuel system, leaving engine operators uncertain whether the secondary fuel system has been completely emptied after purging and unable to safely perform maintenance work because secondary fuel may still be present.

[0006] WO 2024 / 032900 A1 describes a method for purging the fuel system of an engine as mentioned at the outset, but this method is not a reliable way to completely empty the fuel system. Summary of the Invention

[0007] The object of the present invention is to provide a method for purging the fuel system of a large turbocharged, two-stroke, dual-fuel, uniflow crosshead internal combustion engine of the type mentioned in the introduction, in which the above-mentioned problems related to completely emptying the second fuel system are at least significantly reduced.

[0008] These and other problems are solved by the features of the independent claims. More specific implementations will become apparent from the dependent claims, the description and the drawings.

[0009] According to a first aspect, a method of purging a fuel system of a large turbocharged two-stroke dual fuel uniflow crosshead internal combustion engine is provided. However, the said institution: at least one cylinder within a cylinder liner; a reciprocating piston disposed in the cylinder liner and a cylinder cover covering the cylinder; a combustion chamber formed in the cylinder liner between the reciprocating piston and the cylinder cover; a conventional fuel system supplying a conventional fuel and a secondary fuel system supplying a secondary fuel such as ammonia or LPG; the second fuel system includes a second fuel tank, a second 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 second fuel return line for returning the pressurized second fuel from the at least one fuel valve; the engine further comprising a purge gas system for purging the second fuel from the at least one fuel valve, the second fuel supply line, and the second fuel return line to a drain tank; and the method further comprises: At least one space including at least a portion of the at least one fuel valve disposed in the cylinder cover or cylinder liner and the second fuel supply line and return line is isolated from the rest of the second fuel system by closing a plurality of valves after purging is stopped; the pressure and temperature within the at least one volume are measured and used to determine whether the pressure within the at least one volume corresponds to a saturation pressure on a pressure / temperature saturation curve of a respective second fuel; If the pressure in said at least one space corresponds to said saturation pressure, purging is continued.

[0010] Therefore, the operator can obtain clear information whether the secondary fuel system has been completely emptied after the purge operation. When the pressure in the isolated space falls below the saturation pressure at the prevailing temperature in the space (the saturation pressure according to the pressure / temperature saturation curve of the secondary fuel), it indicates that the space has been completely emptied and there is no need to further purge the space to enable maintenance work. This is because the pressure in the secondary fuel system increases until it reaches the saturation pressure while the secondary fuel remaining in the fuel system vaporizes in the isolated space. This therefore provides information whether the secondary fuel remains in the space after purging.

[0011] In one embodiment of the present invention, all fuel valves arranged on the cylinder cover or cylinder liner and the second fuel supply line and return line are separated into one space. However, it is also possible to divide the one space into at least two sub-spaces. In this way, the operator can know where the remaining second fuel is present in the at least two sub-spaces.

[0012] Preferably, if any of the at least two sub-volumes indicates the presence of residual second fuel, purging continues only in that volume.

[0013] In some embodiments, it may be preferable to measure the temperature at different locations in said at least one space in order to assess what the saturation pressure should be if the presence of remaining second fuel is indicated, thereby providing an additional indication of whether said at least one space is empty and therefore safe for maintenance work to be performed.

[0014] According to one embodiment of the first aspect, the purge gas system comprises a purge gas supply.

[0015] According to a preferred embodiment of said first aspect, the purge gas is an inert gas, for example nitrogen.

[0016] According to a second aspect, there is provided a large turbocharged two-stroke dual fuel uniflow crosshead internal combustion engine, the engine comprising: at least one cylinder within a cylinder liner; a reciprocating piston disposed in the cylinder liner and a cylinder cover covering the cylinder; a combustion chamber formed in the cylinder liner between the reciprocating piston and the cylinder cover; a conventional fuel system that supplies a conventional fuel; and a secondary fuel system that supplies a liquid secondary fuel, such as ammonia or LPG; the second fuel system includes a second fuel tank, a second 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 second fuel return line for returning the pressurized second fuel from the at least one fuel valve, and the engine further includes: a purge gas system for purging the second fuel from the at least one fuel valve, the second fuel supply line, and the second fuel return line to a drain tank; And the said institution: a plurality of valves disposed in the cylinder cover or cylinder liner for isolating at least one space including at least a portion of the at least one fuel valve and the second fuel supply line and return line from the remainder of the second fuel system; means for measuring the pressure and temperature within said at least one space; means for using the measured pressure and temperature to determine whether the pressure within the at least one volume corresponds to a saturation pressure on a pressure / temperature saturation curve of the respective second fuel; means for continuing purging when the pressure in said at least one space corresponds to said saturation pressure; The present invention is characterized by having the following. [Brief explanation of the drawings]

[0017] The invention will now be explained in more detail with reference to exemplary embodiments shown in the drawings. [Figure 1] 1 shows a front view of a large two-stroke diesel engine according to an exemplary embodiment; FIG. [Figure 2] Figure 1 shows an overview of the large two-stroke engine as seen from the rear. [Figure 3] 3 is a schematic representation of a first embodiment of the large two-stroke engine of FIGS. 1 and 2, together with its intake and exhaust systems; [Figure 4] 4 is a schematic representation of a second fuel system of the large two-stroke engine of FIGS. 1 to 3. [Figure 5] 1 shows the temperature versus pressure saturation curve for ammonia. Detailed explanation

[0018] In the following detailed description, an internal combustion engine, a vessel including such an engine, a method of operating such an engine, and a dual fuel system for such an engine are described with reference to an exemplary embodiment of a large turbocharged, two-stroke, dual fuel, uniflow crosshead internal combustion engine. The exemplary large turbocharged, two-stroke, dual fuel, uniflow crosshead internal combustion engine is of the high-pressure type, i.e., compression ignition type, with fuel injected at or near top dead center of the piston.

[0019] The present disclosure provides a large, two-stroke, uniflow-scavenged, turbocharged internal combustion engine. Figures 1 and 2 depict a large, low-speed, turbocharged, two-stroke internal combustion engine. The engine has a crankshaft 8 and a crosshead 9. Figure 3 is a schematic representation of a large, low-speed, turbocharged, two-stroke diesel engine, along with its intake and exhaust systems. The engine has six in-line cylinders. Large, low-speed, turbocharged, two-stroke internal combustion engines typically have four to fourteen in-line cylinders. The cylinders are supported on a cylinder frame 23. The cylinder frame 23 is supported on an engine frame 11. Such an engine can be used, for example, as a main engine on a ship or as a stationary engine for driving a generator in a power plant. The total engine power output can be in the range of 1,000 to 110,000 kW, for example.

[0020] In the following embodiment, the engine is a two-stroke uniflow compression ignition engine, and a scavenging port 18 is provided in the lower region of each cylinder liner 1, and an exhaust valve is arranged in the top center of the cylinder liner 1. The cylinder of the engine is formed by the cylinder liner 1.

[0021] The engine is a dual-fuel engine that can operate by switching between a first fuel, which is a conventional fuel, and a second fuel (e.g., ammonia or LPG). That is, it has an operating mode using the first fuel and another operating mode using the second fuel. The first fuel, which is a conventional fuel, is typically fuel oil, such as marine diesel or heavy fuel oil.

[0022] During engine operation, scavenging air is guided through the scavenging air 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 arranged in the cylinder cover 22. Following fuel injection, combustion occurs and exhaust gas is produced. Two or more fuel valves 49 are provided in each cylinder cover 22. The fuel valves 49 are arranged in the cylinder cover 22 around the exhaust valve 4 arranged in the center of the cylinder cover 22. The fuel valves 49 receive fuel from the fuel supply system 30.

[0023] When the exhaust valves 4 open, the exhaust gases flow through exhaust ducts provided on 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 gases pass through the second exhaust pipe 25 and are released into the atmosphere through the exhaust outlet 21.

[0024] The turbine 6 drives the compressor 7 via a shaft. Outside air is supplied to the compressor 9 through an air intake 12. The compressor 7 sends compressed scavenging air into a scavenging pipe 13 connected to the scavenging air receiver 2. The scavenging air in the scavenging pipe 13 passes through an intercooler 14 to cool the scavenging air.

[0025] The cooled scavenging air passes through an auxiliary blower 16 driven by an electric motor 17. The auxiliary blower 16 compresses the scavenging air flow when the compressor 7 of the turbocharger 5 cannot provide sufficient pressure for the scavenging air receiver 2, i.e. when the engine is at low or partial load. When the engine load is high, the turbocharger compressor 7 can provide sufficiently compressed scavenging air, so the auxiliary blower 16 is bypassed by the check valve 15 and the electric motor 17 is switched off.

[0026] For each engine cycle, the exact amount of fuel to be dosed is injected into cylinder 1 through fuel valve 49. In some embodiments, electronic control unit 50 is configured to calculate engine load as a function of the amount of fuel dosed.

[0027] The engine fuel system includes a first fuel system for a first fuel, which may be a conventional fuel such as fuel oil. The first fuel system is well known and will not be described in further detail.

[0028] Figure 4 is a schematic representation of a secondary fuel system 30 for a vessel fitted with a large two-stroke engine. The secondary fuel system 30 is divided into two main sections: an above-deck section and an engine room section.

[0029] The second fuel system 30 includes a second fuel tank 31 in the deck section for storing a second fuel. The second fuel tank 31 is connected to a fuel supply line 32. A fuel return line 36 is connected to a drain tank 52 from which the second fuel may be returned to the second fuel tank 31 by means not shown. These lines 32 and 36 extend from the deck section to the engine room section.

[0030] In the engine room section, the fuel supply line 32 is composed of multiple sections, including a first supply line section 32a having a vertically extending portion, a bottom supply line section 32b, and a second supply line section 32c having a vertically extending portion. The fuel return line 36 may similarly be composed of multiple sections, including a first return line section 36a, a bottom 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 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.

[0031] The illustrated system further includes a first bypass valve 34 connecting the most downstream supply line section 32b with a fuel return line 36. A second bypass valve 35 may connect a portion of the fuel supply line 32 downstream of the second supply line section 32c to the fuel return line 36.

[0032] 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. The most downstream 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 most downstream supply line section 32b, and the second supply line section 32c is located downstream of the most downstream 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 37c having a portion running in the vertical direction. 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.

[0033] The purge gas system comprises an inert gas supply device 61 connected to the fuel supply line 32 through an inert gas supply line 37. The inert gas supply line 37 is preferably equipped with a valve 37a or similar element for controlling the flow of purge gas into 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 purging operations. This is necessary, for example, when the engine is running on the first fuel and the second fuel system 30 is not in use, and is particularly necessary when maintenance needs to be performed on the second fuel system 30.

[0034] The drain tank 52 is disposed at a position higher than the lowermost supply line section 32b. The drain tank 52 is used to recover the second fuel during the purging operation. The purged mixture of the second fuel and the purge gas may be processed in a system (not shown), and the second fuel may be returned to the second fuel tank 31.

[0035] The system may also include a liquid sensor 43 configured to detect the presence of liquid second fuel in the lowermost supply line section 32b or the lowermost return line section 36b.

[0036] Additional components include an actuation fluid control valve 45, a one-way valve 46, an actuation fluid supply line 47, and an actuation fluid return line 48, which are part of a fuel valve actuation system configured to timely actuate a fuel valve 49 to perform a fuel injection event with a precise dosage of the second fuel.

[0037] This configuration of the secondary fuel system 30 allows for efficient secondary fuel supply during normal operation and effective system purging when required. The vertically running portions of the supply and return line sections help accommodate relative movement between the engine and deck components due to engine vibration, while bypass valves, if implemented, facilitate complete drainage of the secondary fuel during purging operations. All or some of the valves 34, 35, 40, and 41 of the secondary fuel system, as well as valves 32d, 37a, and 36d of the fuel supply line 32, inert gas supply line 37, and fuel return line 36, can be controlled by an electronic control unit 50.

[0038] Although the purge gas system described above should have completely purged all of the second fuel from the fuel valves and the second fuel supply and return lines of the second fuel system, some residual second fuel may remain in the second fuel system.

[0039] Therefore, after purging is stopped, the second fuel valve 49 and the second fuel supply and return lines 32, 36 are isolated from the rest of the second fuel system by closing valves 32d, 37a, 36d in accordance with the present invention. Then, immediately after the valves 32a, 37a, 36a are closed, the pressure and temperature within the at least one volume are measured by at least one pressure sensor 51 and temperature sensor 52. The embodiment of FIG. 4 uses multiple pressure sensors 51, each positioned to measure the pressure within the second fuel valve 49, the second fuel supply line 32, and the second fuel return line 36, respectively. The pressure and temperature measurements are used to determine whether the pressure within the at least one volume corresponds to the saturation pressure on the pressure / temperature saturation curve for the respective second fuel. See the pressure / temperature saturation curve for ammonia in FIG. 5. If the pressure within the at least one volume corresponds to the saturation pressure shown on the pressure / temperature saturation curve at that temperature, purging is continued. This indicates that the second fuel is still present in the second fuel valve 49 and the second fuel supply / return lines 32, 36, and as this remaining second fuel evaporates, the pressure inside the second fuel valve 49 and the second fuel supply / return lines 32, 36 rises to the saturation pressure of the second fuel at that temperature.

[0040] According to the invention, this procedure is continued until the pressure in the space comprising the second fuel valve 49 and the second fuel supply and return lines 32, 36 falls below the saturation pressure, which indicates that the space is completely emptied and that no further purging of this space is required to allow maintenance work.

[0041] The space containing all fuel valves 49 and second fuel supply and return lines 32, 36 can be divided into, for example, three sub-spaces by further closing, for example, valves 35, 40, 41. In this way, the system is divided into a space containing the fuel supply line 32, a space containing the fuel valve supply line 38, fuel valves 49 and fuel valve return line 39, and a space containing the fuel return line 36. In this way, the operator will have information about where the remaining second fuel is located among the three sub-spaces.

Claims

1. 1. A method of purging a fuel system of a large turbocharged two-stroke dual fuel uniflow crosshead internal combustion engine, comprising: However, the said institution: at least one cylinder within a cylinder liner; a reciprocating piston disposed in the cylinder liner and a cylinder cover covering the cylinder; a combustion chamber formed in the cylinder liner between the reciprocating piston and the cylinder cover; a conventional fuel system supplying a conventional fuel; and a secondary fuel system supplying a liquid secondary fuel such as ammonia or LPG; the second fuel system includes a second fuel tank, a second 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 second fuel return line for returning the pressurized second fuel from the at least one fuel valve; the engine further includes a purge gas system for purging the second fuel from the at least one fuel valve, the second fuel supply line, and the second fuel return line to a drain tank; and the method further comprises: At least one space including at least a portion of the at least one fuel valve disposed in the cylinder cover or cylinder liner and the second fuel supply line and return line is isolated from the rest of the second fuel system by closing a plurality of valves after purging is stopped; the pressure and temperature within the at least one volume are measured and used to determine whether the pressure within the at least one volume corresponds to a saturation pressure on a pressure / temperature saturation curve of a respective second fuel; purging is continued if the pressure in the at least one space corresponds to the saturation pressure; A method characterized by:

2. 2. The method of claim 1, wherein the at least one space is divided into at least two subspaces.

3. 3. The method of claim 2, wherein if any of the at least two sub-volumes indicates the presence of residual second fuel, purging continues only in that sub-volume.

4. 2. The method of claim 1, wherein temperatures are measured at different locations in the at least one space to estimate what the saturation pressure should be if the presence of remaining second fuel is indicated.

5. 10. The method of claim 1, wherein the purge gas system comprises a purge gas supply.

6. 6. The method of claim 5, wherein the purge gas is an inert gas such as nitrogen.

7. A large turbocharged two-stroke dual-fuel uniflow crosshead internal combustion engine, said engine comprising: at least one cylinder within a cylinder liner; a reciprocating piston disposed in the cylinder liner and a cylinder cover covering the cylinder; a combustion chamber formed in the cylinder liner between the reciprocating piston and the cylinder cover; a conventional fuel system supplying a conventional fuel; and a secondary fuel system supplying a liquid secondary fuel such as ammonia or LPG; the second fuel system includes a second fuel tank, a second 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 second fuel return line for returning the pressurized second fuel from the at least one fuel valve; the engine further includes a purge gas system for purging the second fuel from the at least one fuel valve, the second fuel supply line, and the second fuel return line to a drain tank; And the said institution: a plurality of valves disposed in the cylinder cover or cylinder liner for isolating at least one volume including at least a portion of the at least one fuel valve and the second fuel supply line and return line from the remainder of the second fuel system; means for measuring the pressure and temperature within said at least one space; means for using the measured pressure and temperature to determine whether the pressure within the at least one volume corresponds to a saturation pressure on a pressure / temperature saturation curve of a respective second fuel; means for continuing purging when the pressure in said at least one space corresponds to said saturation pressure; An institution characterized by having:

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