Fuel supply system for large two-stroke compression ignition high-pressure gas injection internal combustion engines

Abstract

The Company provides fuel supply systems that supply high-pressure gas to large two-stroke compression-ignition internal combustion engines. The fuel supply system includes a feed pipe (9) connecting the outlet of a liquefied gas storage tank (8) to the inlet (40) of a high-pressure pump, a transfer pipe (50) connecting the outlet of the high-pressure pump to the inlet of a high-pressure vaporizer (14), and a supply pipe (18) connecting the outlet of the high-pressure vaporizer to the inlet of an engine's fuel injection system. The high-pressure pump includes two or more independently operating cryogenic pump units (41, 42, 43). Each pump unit includes a pump piston (62) slidably disposed in a pump cylinder (61) and a drive cylinder (45) having a hydraulic drive piston (46) that drives the pump piston.

Description

Technical Field

[0001] The present disclosure relates to a fuel supply system for a large slow-speed two-stroke uniflow compression ignition internal combustion engine, and more particularly to a fuel supply system for a large slow-speed two-stroke compression ignition internal combustion engine that injects and supplies high-pressure gas to the internal combustion chamber of the engine at high pressure.

Background Art

[0002] Generally, a large two-stroke uniflow turbocharged compression ignition internal combustion crosshead engine is used as a propulsion system for a large ship or a prime mover for a power plant. Due to its overwhelming size, weight, and output, which are completely different from those of a general internal combustion engine, a large two-stroke turbocharged compression ignition internal combustion engine is classified as a unique type.

[0003] Conventionally, large two-stroke compression ignition internal combustion engines operate on liquid fuels such as fuel oil, i.e., heavy oil. However, due to the increasing environmental concerns, developments have been made towards the use of alternative fuels such as gas, methanol, coal slurry, petroleum coke, etc. One group of fuels for which the demand is increasing is liquefied gas, particularly liquefied natural gas (LNG). Natural gas is converted into a liquid state at cryogenic temperature in a liquefaction plant. LNG is transported over long distances to the destination by specially designed cryogenic ships (LNG carriers).

[0004] An LNG carrier is equipped with one or more LNG storage tanks. These tanks have the capacity to store LNG at extremely low temperatures of -162°C (-260°F). Generally, LNG storage tanks have a double-walled design, with the LNG placed inside and the outer container containing insulation. The most common type of tank is the full-containment tank. Tank sizes vary considerably depending on the application. Although substantially insulated, heat is continuously transferred from the outside to the LNG inside the storage tank, causing vaporization of the LNG. If this LNG vapor is not released from the storage tank, the pressure and temperature inside the tank will continue to rise, which is unacceptable and dangerous. LNG is a refrigerant and remains liquid at extremely low temperatures. By releasing the vaporized gas from the storage tank to maintain a constant pressure, the temperature inside the tank can be kept constant. This process is known as automatic refrigeration. Therefore, during the transport of LNG by LNG carriers, LNG continuously vaporizes, generating boil-off gas in the LNG storage tanks.

[0005] Boil-off gas generated in LNG storage tanks is used for ship propulsion engines or burned in gas combustors.

[0006] When high-pressure gas injection engines, such as large two-stroke compression-ignition internal combustion engines, are used as propulsion engines for LNG carriers, high-pressure cryogenic pumps are used to pump high-pressure liquefied natural gas from LNG storage tanks to high-pressure vaporizers. Typically, cryogenic pumps have two or more pump cylinders in which pump pistons are slidably arranged. Cryogenic pumps are known that use a crankshaft to drive the pump pistons. This crankshaft is driven by an electrically driven motor via belt drive.

[0007] The pressure of LNG delivered to the vaporizer by a high-pressure cryogenic pump is regulated by the operation of an electric motor and the use of control valves. However, this known control system is relatively slow and has difficulty controlling transient operations, particularly those involving relatively abrupt changes in fuel demand from large two-stroke diesel engines.

[0008] LNG is a gaseous fuel at ambient temperature and pressure, which in this application is 20 degrees Celsius (°C) and 1 atmosphere (atm). Generally, LNG is stored in vacuum-insulated containers at or near its boiling point, approximately -160°C. Cryogenic temperatures are typically any temperature below -150°C.

[0009] Patent Document 1 discloses a fuel gas supply system comprising a reciprocating piston cryogenic pump driven by a rotary hydraulic motor. The inertia of the rotary hydraulic motor, combined with the inertia of the components of the reciprocating piston cryogenic pump, such as the crankshaft and piston, results in a large combined inertia for the cryogenic pump assembly. As a result, changes in the supply pressure to the rotary hydraulic motor will not be immediately transmitted to changes in the pressure at the outlet of the reciprocating piston cryogenic pump. This is because it takes time for the energy stored in the moving mass to be converted into energy at the pump outlet. Therefore, dynamic control of the pressure delivered by the reciprocating piston cryogenic pump will be hindered by this delay and will therefore be inaccurate in situations where the delivered pressure needs to be dynamically adjusted.

[0010] Therefore, it is necessary to provide an improved fuel supply system for supplying high-pressure gas to a large two-stroke compression-ignition internal combustion engine. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] EP2832972 [Overview of the project] [Problems that the invention aims to solve]

[0012] The object of the present invention is to provide a fuel supply system that overcomes or at least mitigates the above-mentioned problems. [Means for solving the problem]

[0013] The above and other objectives are achieved by the features of the independent claim. Further implementations will become apparent from the dependent claims, specification, and drawings.

[0014] According to a first embodiment, a fuel supply system is provided for supplying high-pressure gas to a large two-stroke compression-ignition internal combustion engine. The engine is equipped with a fuel injection system for injecting the supplied high-pressure gas into the engine's combustion chamber. The fuel supply system comprises a feed pipe connecting the outlet of a liquefied gas storage tank to the inlet of a high-pressure pump for transferring liquefied gas from a liquefied gas storage tank to a high-pressure pump; a transfer pipe connecting the outlet of the high-pressure pump to the inlet of a high-pressure vaporizer for transferring high-pressure liquefied gas from the high-pressure pump to a high-pressure vaporizer; and a supply pipe connecting the outlet of the high-pressure vaporizer to the inlet of the engine's fuel injection system for transferring high-pressure vaporized gas to the engine's fuel injection system. The high-pressure pump comprises two or more independently operating pump units, each pump unit comprising a pump piston slidably disposed in a pump cylinder and a hydraulic drive piston slidably disposed in a drive cylinder, the drive piston being coupled to the pump piston to drive the pump piston.

[0015] By providing a fuel supply system having a high-pressure pump in which each pump piston is actuated by a linear hydraulic actuator, the pressure of the high-pressure liquefied gas delivered to the vaporizer can be precisely controlled by controlling the pressure of the working fluid supplied to the linear actuator. This is possible because drive systems based on hydraulic linear actuators have virtually no inertia compared to other types of drives, and such drive systems respond immediately to changes in the pressure of the working fluid delivered to the hydraulic linear actuator. Therefore, changes in the pressure of the working fluid delivered to the linear actuator are immediately reflected in the pressure of the liquefied gas supplied to the vaporizer. Controlling the hydraulic supply pressure is relatively easy and straightforward. Thus, the gas pressure can be controlled with significantly faster response times and less over-pressure.

[0016] According to a first possible embodiment of the first aspect, the fuel supply system further comprises a high-pressure hydraulic fluid source and at least one hydraulic control valve connected to a tank for controlling the flow of hydraulic fluid to and from the drive cylinders of one or more pump units, wherein the high-pressure hydraulic fluid source is preferably a variable and controllable pressure level source.

[0017] According to a second possible embodiment of the first aspect, the drive cylinder comprises a drive chamber and a return chamber.

[0018] According to a third possible embodiment of the first aspect, the drive chamber is connected to a hydraulic control valve, and the return chamber is preferably always connected to a hydraulic fluid source at a pressure lower than the pressure of the high-pressure hydraulic fluid source.

[0019] According to a fourth possible embodiment of the first aspect, the drive cylinder is provided with a position sensor for sensing the position of the drive piston in the drive cylinder concerned.

[0020] According to a fifth possible embodiment of the first aspect, the fuel supply system further comprises an electronic control unit that receives a signal from a position sensor, and at least one hydraulic control valve is an electronic control valve coupled to the electronic control unit.

[0021] According to a sixth possible embodiment of the first aspect, the electronic control unit is configured to selectively connect the drive chamber of the pump unit to a source or tank of high-pressure hydraulic fluid.

[0022] According to a seventh possible embodiment of the first aspect, the electronic control unit is configured to start the pump stroke of a drive piston when the pump stroke of another drive piston approaches the end point and there is a small overlap between the ending pump stroke and the starting pump stroke. Thus, a substantially stable flow of LNG to the vaporizer can be achieved without large pressure fluctuations.

[0023] According to an eighth possible embodiment of the first aspect, the electronic control unit is configured to take into account the power at the end of the pump stroke and the power at the start of the pump stroke in order to obtain a substantially constant flow of high-pressure liquefied gas from the high-pressure pump to the high-pressure vaporizer.

[0024] According to a ninth possible embodiment of the first aspect, the electronic control unit is configured to determine when to start one pump stroke within a drive cylinder / unit and when to end any pump stroke within a drive cylinder. Thus, the point at which the pump stroke starts and, in particular, where the pump stroke ends can be accurately controlled.

[0025] According to a tenth possible embodiment of the first aspect, the electronic control unit is configured to operate each drive cylinder substantially continuously, preferably with a small overlap.

[0026] According to the 11th possible embodiment of the first aspect, when one of the pump units fails, the electronic control unit is configured to operate the drive pistons of the remaining functioning pump units. Thus, redundancy is obtained and the pumping action can continue even if one of the pump units fails.

[0027] According to the 12th possible embodiment of the first aspect, the electronic control unit is configured to operate the drive pistons of the remaining functioning pump units such that the drive cylinders of the remaining functioning pump units are operated substantially continuously, preferably with a small overlap.

[0028] According to the 13th possible embodiment of the first aspect, the electronic control unit is configured to adjust the position of the drive piston where the drive chamber is disconnected from the source of the high-pressure operating fluid in relation to the magnitude of the liquefied gas flow from the high-pressure pump to the high-pressure vaporizer. Thus, regardless of the speed of the pump piston and the drive piston and the inertia generated, the position where the pump stroke reverses can be kept at the same position.

[0029] According to the 14th possible embodiment of the first aspect, when the liquefied gas flow from the high-pressure pump to the high-pressure vaporizer increases, the electronic control unit is configured to adjust the position of the drive piston where the drive chamber of the relevant drive piston is disconnected from the source of the high-pressure liquid in the direction opposite to the direction of the drive stroke.

[0030] According to the 15th possible embodiment of the first aspect, when the liquefied gas flow from the high-pressure pump to the high-pressure vaporizer decreases, the electronic control unit is configured to adjust the position of the drive piston where the drive chamber of the relevant drive piston is disconnected from the source of the high-pressure liquid in the direction of the drive stroke.

[0031] According to a 16th possible embodiment of the first aspect, the electronic control unit is configured to adjust, by algorithm, plan, or randomly, the position of the drive piston in which the drive chamber of the drive piston in question is disconnected from the source of the high-pressure fluid, in order to distribute the positions in which the pump piston reverses over the stroke range of the pump piston in order to reduce wear of the pump cylinder.

[0032] According to a 17th possible embodiment of the first aspect, the electronic control unit is configured to control the pressure of the liquefied gas in the transfer pipe by controlling the pressure of the working fluid supplied to the drive chamber. Thus, effective and immediate control of the pressure of the liquefied gas in the transfer pipe is achieved.

[0033] According to a 18th possible embodiment of the first aspect, the electronic control unit is configured to use a desired pressure of liquefied gas in a transfer pipe in a feedforward function for controlling the pressure of the working fluid supplied to the drive chamber. By using feedforward control of the liquefied gas pressure via hydraulic pressure, more rapid and stable control of the liquefied gas pressure can be achieved.

[0034] According to a 19th possible embodiment of the first aspect, the electronic control unit is configured to use the measured pressure of the liquefied gas in the transfer pipe in a feedback function for controlling the pressure of the working fluid supplied to the drive chamber. Thus, nonlinearity and transient fluctuations can be adapted by the control system.

[0035] According to a 20th possible embodiment of the first aspect, the electronic control unit is configured to control the operation and deactivation of each drive piston independently of controlling the pressure of the working fluid supplied to the drive chamber. Therefore, the control method for the operation of the drive pistons can be optimized by the electronic control unit independently of the pressure control.

[0036] According to a 21st possible embodiment of the first aspect, the electronic control unit is configured to use signals representing the position of the drive piston to control the operation and deactivation of the drive piston.

[0037] According to a second aspect, a large two-stroke turbocharged compression-ignition internal combustion engine is provided, having a high-pressure gas injection system and a fuel supply system according to the first aspect and any possible embodiment thereof.

[0038] According to a third embodiment, an LNG carrier or a cargo ship having a liquefied gas tank is provided, equipped with an engine according to a second embodiment.

[0039] According to a fourth aspect, a method is provided for supplying a high-pressure vaporized gas to an internal combustion engine in order to inject a high-pressure gas into the engine. This method is Storing liquefied gas in a liquefied gas storage tank, Using a high-pressure pump to deliver liquefied gas to a high-pressure vaporizer, The process involves vaporizing the high-pressure liquefied gas inside the high-pressure vaporizer, It includes supplying vaporized high-pressure gas to the engine, The high-pressure pump comprises two or more independently operating pump units, each pump unit comprising a pump piston slidably positioned in a pump cylinder, and a hydraulically driven piston coupled to the pump piston to drive the pump piston, and the method further comprises To drive the drive pistons individually, high-pressure hydraulic fluid is supplied to each drive cylinder, The system includes controlling the pressure of the liquefied gas leaving the high-pressure pump by individually controlling the pressure of the working fluid supplied to the drive cylinders.

[0040] According to a first possible embodiment of the fourth aspect, the method further comprises acting one of the drive pistons for a drive stroke and then deacting that drive piston for a return stroke.

[0041] According to a second possible embodiment of the fourth aspect, the pump piston and the drive piston are connected to each other and move simultaneously.

[0042] According to a third possible embodiment of the fourth aspect, the method further comprises starting the pump stroke of a drive piston when the pump stroke of another drive piston is approaching its endpoint and there is a small overlap between the ending pump stroke and the beginning pump stroke.

[0043] According to a fourth possible embodiment of the fourth aspect, the method further comprises taking into account the power at the end of the pump stroke and the power at the start of the pump stroke in order to obtain a substantially constant flow of high-pressure liquefied gas from the high-pressure pump to the high-pressure vaporizer.

[0044] According to a fifth possible embodiment of the fourth aspect, the method further comprises operating each drive cylinder substantially continuously, preferably with a small overlap.

[0045] These and other aspects of the present invention will become apparent from the embodiments described below.

[0046] In the following detailed portions of this disclosure, the present invention will be described in further detail with reference to exemplary embodiments shown in the drawings. [Brief explanation of the drawing]

[0047] [Figure 1] Upright view of a large two-stroke diesel engine according to an exemplary embodiment. [Figure 2] This diagram illustrates a fuel supply system that delivers high-pressure natural gas from an LNG storage tank to the large two-stroke diesel engine shown in Figure 1. [Figure 3] Elevation view of the high-pressure pump of the fuel injection system shown in Figure 2. [Figure 4] Figure 3 shows a diagram representing a high-pressure pump. [Figure 5]Detailed cross-sectional view of the high-pressure pump unit shown in Figure 3. [Figure 6] Graph illustrating the operation of the high-pressure pump in Figure 3. [Figure 7] Graph illustrating the operation of the high-pressure pump in Figure 3. [Figure 8] Graph illustrating the operation of the high-pressure pump in Figure 3. [Figure 9] Figure 3 shows a control system for controlling a high-pressure pump. [Figure 10] A graph illustrating the movement of the piston of the high-pressure pump in Figure 3 at various speeds. [Figure 11] A graph illustrating the movement of the piston of the high-pressure pump in Figure 3 at various speeds. [Modes for carrying out the invention]

[0048] In the following detailed description, a fuel supply system for a large two-stroke low-speed turbocharged compression-ignition internal combustion engine with a crosshead is described with reference to exemplary embodiments, but this internal combustion engine may also be of other types, such as a two-stroke Otto, a four-stroke Otto, or a diesel, with or without a turbocharger, with or without exhaust gas recirculation or selective catalytic reduction.

[0049] Figure 1 shows a large, low-speed turbocharged two-stroke diesel engine with a rotating wheel and a crosshead. In this exemplary embodiment, the engine is a six-cylinder in-line configuration. Large, low-speed turbocharged two-stroke diesel engines typically have four to fourteen cylinders in line and are supported by a cylinder frame supported by an engine frame 6. This engine can be used, for example, as a main engine for a ship or a stationary engine to power a generator in a power plant. The total output of this engine may range, for example, from 1,000 to 110,000 kW.

[0050] In this exemplary embodiment, the engine is a two-stroke, uniflow, compression-ignition engine having scavenging ports in the lower region of cylinder 1 and a central exhaust valve 4 at the top of cylinder liner 1. Scavenging is delivered from scavenging receiver 2 to the scavenging ports of individual cylinders 1. The piston of cylinder liner 1 compresses the scavenging, and the high-pressure gaseous fuel is injected through the fuel valve in the cylinder cover, combustion occurs, and exhaust gases are produced.

[0051] When the exhaust valve 4 opens, the exhaust gas flows through the exhaust duct associated with the cylinder 1 to the exhaust gas receiver 3, then to the turbine of the turbocharger 5, from where the exhaust gas flows out into the atmosphere through the exhaust pipe. The turbine of the turbocharger 5 drives a compressor supplied with outside air through an air inlet. The compressor delivers compressed scavenging gas to a scavenging pipe that leads to the scavenging receiver 2. The scavenging gas in the scavenging pipe passes through the intercooler 7 and is cooled.

[0052] Figure 2 is a simplified diagram of the engine's fuel supply system. The fuel supply system can be installed on a vessel such as an LNG carrier or a cargo ship having a liquefied gas tank, such as a container ship with a liquefied gas tank.

[0053] The fuel supply system includes an LNG storage tank 8 in which natural gas is stored at cryogenic temperatures. The pressure inside the LNG storage tank 8 is kept relatively low and constant so that boil-off gas can be released from the tank for use in low-pressure gas injection engines, such as boilers or auxiliary engines on ships. The boil-off process also keeps the LNG inside the storage tank at a low temperature. The liquefied gas in the storage tank 8 may be of a different type than natural gas, such as ethane or methane.

[0054] A feed pipe 9 connects the outlet of the LNG storage tank 8 to the inlet of the high-pressure pump 40. A low-pressure feed pump 10 assists in transferring liquefied gas from the LNG storage tank 8 to the inlet of the high-pressure pump 40. Alternatively, the LNG storage tank 8 can be pressurized to omit the low-pressure supply pump 10. A transfer pipe 50 connects the outlet of the high-pressure pump 40 to the inlet of the high-pressure vaporizer 14 in order to transfer high-pressure liquefied gas from the high-pressure pump 40 to the high-pressure vaporizer 14. The high-pressure pump 40 pressurizes the liquefied gas to the high-pressure vaporizer 14 via the transfer pipe 50. The high-pressure vaporizer 14 receives the high-pressure liquefied gas and vaporizes the gas using the heat exchanger of the high-pressure vaporizer 14. The high-pressure vaporizer 14 exchanges heat between the liquefied gas and a heat exchange medium, such as glycol, which circulates through a circulation circuit 15. The circulation circuit 15 includes a circulation pump 16 and a heater 17. The high-pressure vaporized gas leaves the high-pressure vaporizer 14 through the outlet of the high-pressure vaporizer 14, which is connected to the supply pipe 18.

[0055] The supply pipe 18 connects the outlet of the high-pressure vaporizer 14 to the inlet of the engine's fuel injection system, allowing the high-pressure vaporized gas to be transferred to the engine's fuel injection system. The valve device 19 controls the connection between the fuel supply system and the large two-stroke diesel engine.

[0056] The high-pressure pump 40 is provided with two or more pump units 41, 42, 43 (in this embodiment, three pump units are shown). Each pump unit 41, 42, 43 includes a pump piston 62 slidably disposed in a pump cylinder 61 and a hydraulic drive piston 46 slidably disposed in a drive cylinder 45 having a drive piston 46 coupled to the pump piston 62 to drive the pump piston 62.

[0057] The pump piston 62 and the pump cylinder 61 form a cryogenic positive displacement pump. The pump piston 62 and the pump cylinder 61 form the so-called cold end of the pump unit having a pump chamber 63. The cold end is kept at a low temperature by a circulation circuit including a liquefied gas circulation supply pipe 11 and a liquefied gas circulation return pipe 12. The circulating liquefied gas plays a role in cooling the cold ends of the pump units 41, 42, and 43.

[0058] The pump cylinder 61 is connected to the drive pistons of the related pump units 41, 42, and 43 via piston rods 49. The drive piston 46 divides the inside of the drive cylinder 45 into a drive chamber 48 and a return chamber 47.

[0059] The drive cylinder 45 is connected to a source of high-pressure hydraulic fluid 20, for example, a pump or pump station via a high-pressure hydraulic fluid supply pipe 23. In the shown embodiment, the source of high-pressure hydraulic fluid 20 includes an electric drive motor 21 that drives a high-pressure pump 22. The high-pressure pump 22 can be, for example, a positive displacement pump, preferably a variable displacement positive displacement pump. In one embodiment, for redundancy purposes, the source of high-pressure hydraulic fluid includes two high-pressure hydraulic pumps 22, each driven by its own electric drive motor 21.

[0060] Figure 3 is an elevation view showing a high-pressure pump 40, which has three pump units 41, 42, and 43, each having a pump cylinder 61, supported by a frame 35, along with a drive cylinder 45 and a control valve 24, and an accumulator 53 for equalizing the high pressure of the high-pressure pump 40 and the low pressure of the return chamber. The pump units 41, 42, and 43 are compactly arranged on the frame 35, and the components on the frame 35 have only ATEX-approved electrical components that do not generate sparks, so the unit can be installed without problems in an ATEX environment.

[0061] Figure 4 shows a high-pressure pump 40 together with its pump units 41, 42, and 43. Each pump unit 41, 42, and 43 is connected to a tank via a hydraulic fluid return line 26 and to a source of high-pressure hydraulic fluid, which includes a variable displacement positive displacement pump 22 connected to each pump unit 41, 42, and 43 via a hydraulic fluid supply pipe 23. Each pump unit 41, 42, and 43 is connected to a transfer pipe 50.

[0062] Each pump unit 41, 42, and 43 is equipped with a hydraulic control valve 24 configured to selectively connect its respective drive chamber 48 to a source or tank of high-pressure working fluid via a control pipe 25.

[0063] Each pump unit 41, 42, 43 comprises a drive unit 44 in the form of a linear hydraulic actuator, formed by a drive cylinder 45 in which a drive piston 46 is slidably positioned. Thus, the pump units are mechanically independent of each other. The return chamber 47 is permanently connected to a hydraulic supply source. The hydraulic supply source includes a hydraulic pump 30, for example, a variable displacement positive displacement pump, via a return chamber supply line 31, which preferably includes a flow limiter 33 and is coupled to an accumulator 32 to ensure a stable supply of pressurized hydraulic fluid to the return chamber 47. Alternatively, a low-pressure supply source is obtained from a high-pressure hydraulic system via a pressure-reducing valve. In one embodiment, the pressure of the hydraulic fluid supplied to the return chamber is significantly lower than the pressure of the hydraulic fluid supplied to the drive chamber 48. Alternatively, the effective pressure surface of the side of the drive piston 46 facing the return chamber 47 may be positioned to be significantly smaller than the effective pressure surface of the drive piston facing the drive chamber 48. In the latter case, the pressure of the hydraulic fluid in the return chamber 47 can be made substantially equal to the pressure of the hydraulic fluid supplied to the drive chamber.

[0064] Each pump unit 41, 42, and 43 comprises a pump 60 of the type of linear positive displacement pump, formed by a pump cylinder 61 that receives a pump piston 62 therein to form a pump chamber 63. The pump chamber 63 is connected to a feed pipe 9 via a first one-way valve 51 that allows flow only into the pressure chamber 63. The pump chamber 63 is connected to a transfer pipe 50 via a second one-way valve 52 that allows flow only out of the pressure chamber 63.

[0065] Figure 5 is a detailed cross-sectional view of the pump units 41, 42, and 43 of the high-pressure pump 40. The pump units 41, 42, and 43 each include a hydraulic linear actuator 44 which contains a cylinder 45 in which a drive piston 46 is housed. The drive piston 46 is preferably connected integrally to a piston shaft 47. The piston rod 49 and the drive piston 46 are provided with holes 58 for receiving the rod 57 of a position sensor 56. The signal from the position sensor 56 is sent to an electronic control unit 70. The drive piston 46 divides the inside of the drive cylinder 45 into a drive chamber 48 and a return chamber 47. In Figure 5, the return chamber is not visible because the drive piston 46 has reached the end of its drive stroke. The drive chamber 48 is connected to a hydraulic control valve 24 via a hole 25. The return chamber 47 is permanently connected to a hydraulic supply source via a hole 31.

[0066] The piston rod 49 of the linear hydraulic actuator 44 is connected to the piston rod 62 of the cryogenic pump 60. The connection between the piston rod 49 and the piston rod 62 is established by a connector piece 54 so that the piston rod 49 and the piston rod 62 move together. The drive cylinder 45 is connected to the pump cylinder 61 by a bolted connection 55. The cryogenic pump 60 is provided with an outlet that connects the pump chamber 63 to the transfer pipe 50.

[0067] Figure 9 shows a control system in the form of an electronic control unit 70 for controlling the operation of the high-pressure pump 40.

[0068] The electronic control unit 70 receives the gas pressure setpoint 71. The gas pressure setpoint 71 is sent to the addition point 72. The gas pressure measured at the first addition point 72 is subtracted, and the difference between the setpoint and the measured gas pressure is sent to the PI controller 74, which is part of the feedback control loop.

[0069] The gas pressure setpoint is sent to the feedforward piston ratio gain unit 78. The signal from the feedforward piston ratio gain unit 78 is compared with the signal from the PI controller 74 at the second summing point 76.

[0070] The measured gas pressure sent to the first addition point 72 is based on the gas pressure measurement within the engine's pipe volume 85, i.e., downstream of the valve device 19. The valve device 19 is a bleed valve device in the two-wheel block that receives the flow of vaporized gas from the supply pipe 18. The measured gas pressure is filtered by the filter 86.

[0071] The results of the comparison at the second addition point 76 are sent to the high-pressure hydraulic fluid supply source 20. Based on this signal, the high-pressure hydraulic fluid supply source 20 delivers hydraulic fluid with the corrected pressure to the high-pressure pump unit 40.

[0072] The electronic control unit 70 receives a signal representing the position of the drive piston, and the piston control unit 92 processes this position signal. The piston control unit 92 is coupled to the piston actuation method unit 90. The operation of the piston control unit 92 and the piston actuation method unit 90 is described in more detail below. The signal from the piston actuation method unit 90 is sent to the control valve 24 of the high-pressure pump 40 to actuate the drive piston 46.

[0073] The drive piston 46 operates, causing the liquefied high-pressure gas to be pumped through the high-pressure vaporizer 14 to the supply pipe 18.

[0074] The main pressure control of the electronic control unit 70 is feedforward. The PI (proportional-integral) controller compensates for nonlinearity and provides assistance for transient fluctuations.

[0075] The gas pressure is automatically controlled by setting the hydraulic pressure of the hydraulic feed to pump units 41, 42, and 43. Pressure control is performed on the hydraulic side and does not need to be done on the gas side. If the hydraulic pressure is properly controlled, the gas pressure in this system will not become too high.

[0076] The drive piston 46 is controlled via a control method that does not involve pressure control active parts.

[0077] Each pump unit 41, 42, and 43 can be controlled individually. Therefore, it is possible to operate them with different piston methods and various operating conditions. Furthermore, since it is possible to change from three pump units 41, 42, and 43 to two pump units during two strokes, the possibility of operating pump units 41, 42, and 43 individually provides redundancy.

[0078] The return speed can be faster than the forward (pump) speed, making it possible for the two pump units to overlap when operating only two units. The overlap between pump units 41, 42, and 43 can be adjusted according to the need to reduce pressure spikes.

[0079] In contrast to the high wear occurring at the fixed position of the cylinder, the final position of the pump stroke can change over time in order to distribute the wear across the area of ​​the pump cylinder 61.

[0080] The system generates little to no excessive pressure, even in the event of a sudden shutdown (piston stop). This is due to very low inertia and other factors that negatively affect the dynamic response.

[0081] The control valve 24 may be a hydraulic control valve or an electronic control valve. In this embodiment, where the control valve 24 is a hydraulic control valve, an electronically controlled solenoid valve (not shown) is provided to control the hydraulic control signal to the control valve 24. The electronically controlled solenoid valve receives an electronic control signal from the electronic control unit 70.

[0082] The electronic control unit 70, more specifically the piston operating method unit 90, is configured to selectively connect the drive chambers 48 of the pump units 41, 42, and 43 to a high-pressure hydraulic fluid supply source 20 or a tank.

[0083] The electronic control unit 70, more specifically the piston operating method unit 90, is configured to start the pump stroke of one drive piston 47 when the pump stroke of another drive piston 47 is approaching its end and there is a small overlap between the ending pump stroke and the beginning pump stroke. In one embodiment, the electronic control unit 70 is configured to operate each drive cylinder substantially continuously, preferably with a small overlap. Thus, a substantially stable flow of LNG to the high-pressure vaporizer 14 can be achieved without large pressure fluctuations, as illustrated in the examples of Figures 6 and 7.

[0084] Figures 6, 7, and 8 illustrate the normal operation of the high-pressure pump 40. Thin continuous lines represent pump unit 41, thick continuous lines represent pump unit 42, and dotted lines represent pump unit 43. Figure 6 is a graph showing the movement of the drive piston 46 / pump piston 62. As can be seen from the graph, the pump stroke of the next pump unit begins just before the pump stroke of the currently operating pump unit ends. Figure 7 shows the pressure obtained by the pressure output from the transfer pipe 50 of the three pump units 41, 42, and 43. The obtained pressure is substantially constant and does not fluctuate.

[0085] Figure 8 shows the speed characteristics of the pump unit. Here, it is clear that the return stroke speed is significantly faster than the pump stroke speed, which allows for overlap between pump units even when using only two out of three or more pump units.

[0086] In one embodiment, the electronic control unit 70, more specifically the piston operating method unit 90, is configured to take into account the power at the end of the pump stroke and the power at the start of the pump stroke in order to obtain a substantially constant flow of high-pressure liquefied gas from the high-pressure pump to the high-pressure vaporizer 14.

[0087] In one embodiment, the electronic control unit 70, more specifically the piston actuation method unit 90, is configured to determine when one of the pump units 41, 42, or 43 should start a pump stroke, and when any of the drive units 41, 42, or 43 should end a pump stroke. Thus, the starting point of a pump stroke, and more specifically the ending point of a pump stroke, can be precisely controlled by the piston actuation method unit 90, preferably together with the piston control unit 92.

[0088] In one embodiment, the electronic control unit 70 is configured to operate the remaining functional drive pistons of the pump units 41, 42, and 43 if one of the pump units 41, 42, and 43 fails. Thus, redundancy is achieved, and the pumping operation can continue even if one of the pump units 41, 42, and 43 fails.

[0089] In one embodiment, the electronic control unit 70 is configured to adjust the position of the drive piston 46 at which the drive chamber 48 is disconnected from the source of the high-pressure working fluid, in relation to the magnitude of the flow of liquefied gas from the high-pressure pump 40 to the high-pressure vaporizer. Thus, the position at which the pump stroke reverses can be controlled regardless of the speed of the drive piston 46 and the pump piston 62 and the resulting inertia.

[0090] According to one embodiment, when the flow of liquefied gas from the high-pressure pump to the high-pressure vaporizer increases, the electronic control unit 70 is configured to adjust the position of the drive piston 46 in the opposite direction to the drive stroke at a position where the drive chamber 48 of the drive piston 46 is disconnected from the high-pressure liquid supply source 20. Also, when the flow of liquefied gas from the high-pressure pump to the high-pressure vaporizer decreases, the electronic control unit 70 is configured to adjust the position of the drive piston 46 in the direction of the drive stroke at a position where the drive chamber 48 of the drive piston 46 is disconnected from the high-pressure liquid supply source 20. This is shown in Figures 10 and 11.

[0091] Figure 10 shows the effect of the increased speed of the drive piston 46 and pump piston 62 at the final position of the drive stroke / pump stroke. The thin continuous line represents the pump unit 41, the thick continuous line represents the pump unit 42, and the dotted line represents the pump unit 43. The electronic control unit 70 signals the hydraulic control valve 24 to connect the drive chamber 48 to the tank, regardless of the load / magnitude of the flow of liquefied gas delivered by the high-pressure pump 40, when the drive piston reaches a stroke of 80 mm. Due to inertia and the faster speed, the stop / reverse position of the drive piston 46 changes from 85 mm at 25% load to 89 mm at 50% load and 98 mm at 100 percent load.

[0092] Figure 11 is a graph showing the effect of the electronic control unit 70 in compensating for the increased speed of the drive piston 46 / pump piston 62 by connecting the drive chamber 48 to the tank, with a shorter stroke when the load is heavy and a longer stroke when the load is light. As can be seen in the graph, the electronic control unit 70 can thus precisely control the final position of the drive / pump stroke.

[0093] In the example graph, the signal to connect the drive chamber 48 to the tank for 25% load (i.e., 25% of the maximum capacity of the high-pressure pump 40) for the next drive cylinder is issued when the previous cylinder is 75 mm into the drive chamber. The drive chamber of the "previous" drive cylinder is connected to the tank when that cylinder is 93 mm into the drive chamber. The "signal ON" for connecting the next drive cylinder to the high-pressure supply source and the "signal OFF" for connecting the "previous" cylinder to the tank are shown in Table 1 below.

[0094] [Table 1]

[0095] Naturally, it is also possible to program the electronic control unit 70 to intentionally change the starting position in order to reduce wear on the pump cylinder 61.

[0096] In one embodiment, the electronic control unit 70 is configured, by algorithm, plan, or randomly, to adjust the position of the drive piston 46 in which the drive chamber 48 of the drive piston 46 is disconnected from the high-pressure fluid supply source 20, in order to distribute the positions in which the pump piston 62 reverses over the stroke range of the pump piston 62 in order to reduce wear on the pump cylinder 61. Wear on the pump cylinder 61 is known to be most severe at the end position of the pump stroke. By changing the end position of the pump stroke, wear on the pump cylinder 61 can be diffused over a larger area, so the life of the pump cylinder 61 can be greatly increased.

[0097] In one embodiment, the electronic control unit 70 is configured to control the operation and deactivation of each drive piston 46 independently of the control pressure of the working fluid supplied to the drive chamber 48. Therefore, the control method for the operation of the drive pistons can be optimized by the electronic control unit 70 independently of pressure control.

[0098] The present invention has been described in conjunction with various embodiments herein. However, a person skilled in the art who practices the claimed invention can understand and implement other variations of the disclosed embodiments by examining the drawings, this disclosure, and the appended claims. In the claims, the word “equips” does not exclude other elements or steps, nor does it exclude that configurations that are not explicitly stated to be multiple may be multiple. An electronic control unit may be formed by a combination of individual electronic control units. The mere fact that certain measurements are listed in different dependent claims does not indicate that combinations of these measurements cannot be used as an advantage. Reference numerals used in the claims should not be construed as limiting the range.

Claims

1. A fuel supply system for supplying high-pressure gas to a large two-stroke compression-ignition internal combustion engine, wherein the engine is provided with a fuel injection system for injecting the supplied high-pressure gas into the combustion chamber of the engine. The fuel supply system is A single feed pipe is provided to connect the outlet of the liquefied gas storage tank to the inlet of the high-pressure pump in order to transfer liquefied gas from the liquefied gas storage tank to the high-pressure pump, A single transfer pipe is provided to connect the outlet of the high-pressure pump to the inlet of the high-pressure vaporizer in order to transfer high-pressure liquefied gas from the high-pressure pump to a single high-pressure vaporizer, A supply pipe is provided to connect the outlet of the high-pressure vaporizer to the inlet of the fuel injection system of the engine in order to transfer the high-pressure vaporized gas to the fuel injection system of the engine, Electronic control unit and Equipped with, The high-pressure pump comprises two or more individual, independently operating cryogenic pump units. Each of the cryogenic pump units comprises a single pump piston slidably disposed within a pump cylinder, and a single hydraulic drive piston coupled to the single pump piston by a single piston rod for driving the pump piston, and slidably disposed within a drive cylinder. A fuel supply system in which each of the cryogenic pump units is mechanically independent of the others and is individually controlled and operated by the electronic control unit.

2. The fuel supply system according to claim 1, further comprising a source of high-pressure hydraulic fluid and at least one control valve connected to a tank for controlling the flow of hydraulic fluid to and from the drive cylinders of a plurality of pump units.

3. The fuel supply system according to claim 2, wherein the source of the high-pressure working fluid is a source having a variable and controllable pressure level.

4. The fuel supply system according to claim 2 or 3, wherein the drive cylinder comprises a drive chamber and a return chamber.

5. The fuel supply system according to claim 4, wherein the drive chamber is connected to the control valve.

6. The drive cylinder is equipped with a return chamber, The fuel supply system according to claim 2, wherein the return chamber is connected to a hydraulic fluid supply source having a pressure lower than the pressure of the high-pressure hydraulic fluid supply source.

7. The fuel supply system according to claim 2, 3, or 6, wherein the drive cylinder is provided with a position sensor for sensing the position of the drive piston in the drive cylinder.

8. The fuel supply system according to claim 7, wherein the electronic control unit receives a signal from the position sensor, and the at least one control valve is an electronically controlled valve coupled to the electronic control unit.

9. The aforementioned drive cylinder is equipped with a drive chamber, The fuel supply system according to claim 8, wherein the electronic control unit is configured to selectively connect the drive chamber of the pump unit to the source or tank of the high-pressure working fluid.

10. The fuel supply system according to claim 9, wherein the electronic control unit is configured to start the pump stroke of a drive piston when the pump stroke of another drive piston is approaching its end and there is a small overlap between the ending pump stroke and the beginning pump stroke.

11. The fuel supply system according to claim 10, wherein the electronic control unit is configured to take into account the power at the end of the pump stroke and the power at the start of the pump stroke in order to obtain a substantially constant flow of high-pressure liquefied gas from the high-pressure pump to the high-pressure vaporizer.

12. The fuel supply system according to any one of claims 9 to 11, wherein the electronic control unit is configured to adjust the position of the drive piston at which the drive chamber is disconnected from the source of the high-pressure working fluid, in relation to the magnitude of the flow of liquefied gas from the high-pressure pump to the high-pressure vaporizer.

13. The fuel supply system according to claim 12, wherein the electronic control unit is configured to adjust the position of the drive piston in the opposite direction to the drive stroke when the flow of liquefied gas from the high-pressure pump to the high-pressure vaporizer increases, such that the drive chamber of the drive piston is disconnected from the source of the high-pressure working fluid.

14. The fuel supply system according to claim 12 or 13, wherein the electronic control unit is configured to adjust the position of the drive piston in the direction of the drive stroke so that the drive chamber of the drive piston is disconnected from the supply source of the high-pressure working fluid when the flow of liquefied gas from the high-pressure pump to the high-pressure vaporizer decreases.

15. The fuel supply system according to any one of claims 9 to 14, wherein the electronic control unit is configured to adjust, by algorithm, plan, or randomly, the position in which the drive chamber of the drive piston in question is disconnected from the source of the high-pressure working fluid in order to distribute the positions in which the pump piston reverses over the stroke range of the pump piston in order to reduce wear of the pump cylinder.

16. The fuel supply system according to any one of claims 9 to 15, wherein the electronic control unit is configured to control the pressure of the liquefied gas in the transfer pipe by controlling the pressure of the working fluid supplied to the drive chamber.

17. The fuel supply system according to claim 16, wherein the electronic control unit is configured to use a desired pressure of the liquefied gas in the transfer pipe in a feedforward function for controlling the pressure of the working fluid supplied to the drive chamber.

18. The fuel supply system according to claim 16 or 17, wherein the electronic control unit is configured to use the measured pressure of liquefied or vaporized gas in a feedback function for controlling the pressure of the working fluid supplied to the drive chamber.

19. The fuel supply system according to any one of claims 16 to 18, wherein the electronic control unit is configured to control the operation and deactivation of each of the drive pistons independently of the control of the pressure of the working fluid supplied to the drive chamber.

20. A large two-stroke turbocharged compression-ignition internal combustion engine having a high-pressure gas injection system and a fuel supply system according to any one of claims 1 to 19.

21. An LNG carrier or cargo ship having a liquefied gas tank, comprising the engine described in claim 20.

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