Direct injection gaseous fuel supply system for a two-stroke internal combustion piston engine, two-stroke internal combustion piston engine and method of operating a two-stroke internal combustion piston engine

Abstract

The present invention relates to a direct injection gaseous fuel supply system (10) for an internal combustion piston engine (1), the fuel supply system (10) comprising: a liquefied gas storage tank (14) configured to store liquefied gas under cryogenic conditions; a fuel supply pipeline (16) extending from the tank to a fuel injector in the engine (1), the fuel supply pipeline (16) comprising at least the following components: a liquefied gas high-pressure pump unit (18); a heat exchanger unit (22) for evaporating the liquefied gas and heating the gaseous gas; and a gaseous gas accumulator (24) located between the heat exchanger unit (22) and the fuel injector; and at least two gaseous gas fuel injectors fluidically connected to the gaseous gas accumulator (24). The liquefied gas high-pressure pump unit (18) comprises a reciprocating piston having a pumping portion (32) and a driving portion (34), and a hydraulic drive assembly (36) arranged to cause hydraulic power fluid from a hydraulic power fluid source (102) to act on the driving portion (34) of the reciprocating piston so as to drive the piston in a reciprocating manner.

Description

Technical Field

[0001] The invention relates to a direct injection gaseous fuel supply system for a two-stroke internal combustion piston engine. The invention also relates to a two-stroke internal combustion piston engine provided with a direct injection gaseous fuel supply system and a method of operating a two-stroke internal combustion engine. Background Art

[0002] Internal combustion piston engines are widely used to provide mechanical power in land power plants and marine vessels to generate electricity and / or propulsion power.

[0003] Dual fuel engines use a low pressure gaseous fuel such as natural gas that is mixed at a relatively low pressure with the intake air admitted into the engine cylinders. The air / gaseous fuel mixture provided to the cylinders is compressed under certain operating conditions and then ignited using a spark or using a compression ignition pilot fuel such as diesel that is injected into the air / gaseous fuel mixture present in the cylinders.

[0004] Direct injection gas engines are also known in which a gaseous fuel such as liquefied natural gas (LNG) is injected under high pressure into the cylinders while combustion is already taking place in the cylinders due to diesel pilot. Direct injection gas engines operate on gaseous fuel and the diesel pilot provides ignition of the gaseous fuel.

[0005] DK179056B1 discloses a fuel supply system for supplying high-pressure gas to a large two-stroke compression ignition internal combustion engine. 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 includes: a supply pipeline, which connects the outlet of the liquefied gas storage tank to the inlet of the high-pressure pump to deliver the liquefied gas from the liquefied gas storage tank to the high-pressure pump; a delivery pipeline, which connects the outlet of the high-pressure pump to the inlet of the high-pressure vaporizer to deliver the high-pressure liquefied gas from the high-pressure pump to the high-pressure vaporizer; a supply pipeline, which connects the outlet of the high-pressure vaporizer to the inlet of the fuel injection system of the engine to deliver the high-pressure vaporized gas to the fuel injection system of the engine. The high-pressure pump includes two or more pump units. Each pump unit includes a pump piston slidably arranged in a pump cylinder and a hydraulically powered drive piston slidably arranged in a drive cylinder, wherein the drive piston is connected to the pump piston to drive the pump piston.

[0006] US9188069 B2 discloses an engine fuel system having liquid and gaseous fuel systems each injecting fuel directly into the engine cylinder. The gaseous fuel system is a direct injection gas system comprising a liquefied gas reservoir, a liquefied gas pump, a liquefied gas vaporizer and a gaseous gas fuel rail connected to the fuel injector.

[0007] Both of the above-mentioned prior art documents propose to control the operation of the gaseous fuel pump by operating the control fluid of the high-pressure piston pump. The variable control of the high-pressure pump requires a variable high-pressure pump to control the fluid system. The common problem of the prior art solutions is the complex structure of the liquefied gas pump and its controllability.

[0008] It is an object of the present invention to provide a direct injection gaseous fuel supply system for a two-stroke internal combustion piston engine which is significantly improved compared to prior art solutions.

[0009] The object of the present invention is to provide a two-stroke internal combustion piston engine with a direct injection gaseous fuel supply system and a method of operating a two-stroke internal combustion piston engine which is significantly improved compared to prior art solutions for large two-stroke internal combustion piston engines. Summary of the invention

[0010] The object of the present invention can be achieved through the embodiments described below.

[0011] According to an embodiment of the present invention, there is provided a direct injection gaseous fuel supply system for a two-stroke internal combustion piston engine, the fuel supply system comprising:

[0012] - a fuel supply line extending from a liquefied gas source to a fuel injector in the engine, the fuel supply line comprising at least the following components:

[0013] -Liquefied gas high pressure pump unit;

[0014] - a heat exchanger unit for evaporating the liquefied gas and heating the gaseous gas; and

[0015] - a gaseous gas accumulator located between the heat exchanger unit and the fuel injector; and

[0016] - at least one gaseous gas fuel injector in fluid communication with the gaseous gas accumulator, wherein the liquefied gas high-pressure pump unit comprises a reciprocating piston having a pumping portion and a driving portion, and a hydraulic drive assembly arranged so that a hydraulic power fluid at a constant pressure from a hydraulic power fluid source acts on the driving portion of the reciprocating piston so as to drive the piston in a reciprocating manner.

[0017] According to one embodiment of the invention, the reciprocating piston is a double-acting piston and the hydraulic drive assembly is arranged to controllably cause hydraulic power fluid at a constant pressure from the hydraulic power fluid source to act on the drive portion of the double-acting piston.

[0018] According to one embodiment of the invention, the engine is a large two-stroke marine crosshead engine.

[0019] According to one embodiment of the invention, the gaseous fuel supply system is configured to supply fuel to one cylinder of a large two-stroke crosshead engine, the gaseous fuel supply system being connected to a common liquefied gas reservoir for the cylinders of the engine.

[0020] Since each of the engine's cylinders is provided with a dedicated gaseous fuel supply system, individual cylinders can be isolated from the fuel system, for example for maintenance, and the engine operation can still be maintained using the other cylinders of the engine, and liquid fuel can be burned in such cylinders where the gaseous fuel supply is cut off.

[0021] According to one embodiment of the invention, the hydraulic drive assembly is arranged to controllably cause hydraulic power fluid to act on the drive portion of the reciprocating piston by controllably driving a directional valve of the hydraulic drive assembly back and forth between a first position and a second position.

[0022] According to one embodiment of the present invention, the hydraulic drive assembly of the liquefied gas high-pressure pump unit includes a three-position four-way directional valve, which is configured to alternately supply pressurized power fluid to the first side or the second side of the driving part of the double-acting piston, or to lock the position of the piston and stop and / or lock the position of the piston at a desired position.

[0023] According to one embodiment of the invention, the hydraulic drive assembly of the liquefied gas high-pressure pump unit comprises a 2-position 4-way directional valve configured to alternately supply pressurized power fluid to a first side or a second side of a drive portion of the double-acting piston.

[0024] According to one embodiment of the present invention, the hydraulic drive assembly is configured as follows:

[0025] - reciprocating the piston in full strokes, each of which increases the pressure by a predetermined amount, until the injection pressure is at a level from which a single full stroke will increase the pressure above a set value; and

[0026] - moving the piston with a partial stroke from the bottom dead center to a position between its extreme positions and stopping the movement of the piston.

[0027] According to one embodiment of the present invention, the hydraulic drive assembly is configured as follows:

[0028] - reciprocating the piston in full strokes, each of which increases the pressure by a predetermined amount, until the injection pressure is at a level from which a single full stroke will increase the pressure above a set value; and

[0029] - moving the piston to a position between its extreme positions with a partial intake stroke and moving the piston to the piston top dead center position.

[0030] According to one embodiment of the present invention, the pumping section and the driving section of the liquefied gas high-pressure pump unit are configured so that the maximum pressure of the liquefied gas obtainable from the pumping section using the hydraulic power fluid at a predetermined pressure corresponds to a set injection pressure.

[0031] According to one embodiment of the present invention, the hydraulic drive assembly is configured to cause the piston to reciprocate at a frequency of 0.5-6 times per second, preferably 3-6 times per second.

[0032] According to one embodiment of the present invention, the hydraulic drive assembly is configured to cause the piston to reciprocate in an intermittent manner.

[0033] According to one embodiment of the present invention, the liquefied gas high-pressure pump unit is configured to increase the pressure of the liquefied gas to a pressure about 0.5 times the pressure of the hydraulic power fluid, wherein the pressure of the fluid is in the range of 12-15 MPa.

[0034] A two-stroke internal combustion piston engine according to the invention comprises more than one cylinder, wherein each cylinder is provided with a direct injection gaseous fuel supply system as described above.

[0035] According to one embodiment of the invention, each cylinder of the engine comprises two gaseous fuel injectors and three liquid fuel injectors.

[0036] A method of operating a two-stroke internal combustion piston engine comprising a plurality of cylinders, a common rail liquid fuel injection system and a direct injection gaseous fuel supply system, the method comprising the steps of operating the engine so that at least one of the cylinders operates by injecting only liquid fuel into the at least one cylinder, while the remaining cylinders operate by injecting both gaseous fuel and liquid fuel into each of the remaining cylinders.

[0037] The exemplary embodiments of the invention presented in this patent application shall not be interpreted as limiting the applicability of the appended claims. The verb "comprise" is used as an open limitation in this patent application and does not exclude the presence of unlisted features. Unless otherwise expressly stated, the features set forth in the dependent claims can be freely combined with each other. The novel features that are considered to be characteristic of the invention are specifically set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In the following, the present invention will be described with reference to the attached exemplary schematic drawings, in which:

[0039] Figure 1 A direct injection gaseous fuel supply system according to an embodiment of the present invention is illustrated;

[0040] Figures 2 to 4 The operating steps of the high pressure pump unit and the hydraulic drive assembly according to the embodiment of the present invention are illustrated;

[0041] Figure 5 illustrates a two-stroke internal combustion engine according to another embodiment of the present invention; and

[0042] Figure 6 to Figure 7 Operation steps in a high-pressure pump unit and a hydraulic drive assembly according to another embodiment of the present invention are illustrated. DETAILED DESCRIPTION

[0043] Figure 1 A direct injection gaseous fuel supply system 10 for a large two-stroke internal combustion piston engine is schematically depicted, showing the fuel supply system 10 for a portion of one cylinder 12 of the engine. The engine has at least one cylinder forming a variable volume between a reciprocating piston, a cylinder bore and a cylinder head or the like. Figure 1 Only cylinder 12 of the engine is illustrated very schematically, since the construction and operation of a generally large two-stroke crosshead internal combustion piston engine is well known to a person skilled in the art. The liquid fuel system comprises a common rail with one or several liquid fuel injectors adapted to inject liquid fuel directly into the variable volume as an ignition source. The gaseous fuel system is in fluid connection with a tank as a reservoir or source of liquefied gas, a high-pressure pump unit, a drive assembly of the pump unit and the gaseous fuel injectors. In the engine, the compressed gaseous fuel is ignited by a separate liquid fuel injection system.

[0044] The fuel supply system 10 includes a liquefied gas source, which is here a liquefied gas storage tank 14 configured to store liquefied gas under cryogenic conditions. In practice, the gas is usually stored in the tank at a temperature of -160 to -150°C and a pressure of 200 to 300 kPa. A fuel supply line 16 extending from the storage tank 14 to a fuel injector 19 in the engine 1 is provided in the system.

[0045] The fuel supply line 16 includes a liquefied gas high-pressure pump unit 18 connected to the fuel supply line 16. There is also a liquefied gas low-pressure pump unit 20 arranged to the fuel supply line 16 between the high-pressure pump unit 18 and the tank 14. The low-pressure pump unit 20 is configured to increase the pressure of the liquefied gas to about 900 kPa. The low-pressure pump unit acts as a transfer pump, and it improves the operation of the system so that the risk of excessive pressure drop at the high-pressure pump unit 18 during the suction stroke can be at least minimized, preferably completely avoided. In the high-pressure pump unit 18, if the liquid pressure drops below the vapor pressure, liquid boiling will occur, and may cause cavitation and priming loss in the pump. Vapor bubbles may reduce or stop the flow of liquid, reduce pump efficiency, reduce the quality of the compressed liquid, and may damage the system. All of these can be avoided or at least minimized according to aspects of the present invention by a combination of a high-pressure pump unit 18 and a suitably sized low-pressure pump unit 20. The high-pressure pump unit 18 is configured to increase the pressure of the liquefied gas from about 900 kPa to 15 MPa.

[0046] The fuel supply system 10 also includes a heat exchanger unit 22 located downstream of the high-pressure pump unit 18 in the direction of gas flow. The heat exchanger unit 22 is arranged to the fuel supply pipeline 16 downstream of the high-pressure pump unit 18. The heat exchanger unit 22 is configured to maintain a pressure of at least 15MPa, which is also advantageously a set value for the gaseous gas injection pressure. When the high-pressure pump unit 18 is configured to operate with liquefied gas under low temperature conditions, the heat exchanger unit 22 evaporates the pressurized liquid gas into a gaseous form and heats the gaseous gas to a high temperature compared to the temperature prevailing in the tank 14. The heat required to evaporate the liquefied gas into a gaseous gas can be obtained completely or partially from the engine 1. Auxiliary heat sources such as electric heaters or boilers can also be provided. In this regard, the gas is referred to as a liquefied gas and a gaseous gas in order to distinguish the current phase of the gas. Therefore, even if it is in a liquid phase or a supercritical phase, the gas is also referred to as a gas.

[0047] The fuel supply system 10 further includes a gaseous gas accumulator 24. The accumulator is configured to store gaseous gas at a temperature of about -50°C to -20°C and a pressure of about 12 MPa to 15 MPa. The accumulator is arranged between the heat exchanger unit 22 and the fuel injector 19. Figure 1As can be seen in the diagram, each cylinder of the engine comprises two gaseous fuel injectors 19, both of which are in flow communication with a common gaseous gas accumulator 24. The gaseous gas accumulator 24 is provided with a temperature sensor 28 and a pressure sensor 26, whose measurement signals are advantageously used to control the operation of the fuel supply system 10. The gaseous gas accumulator comprises an inlet 25 for gaseous gas to which the fuel supply line 16 is connected, and an outlet 27 for connecting the fuel supply line 16 connecting each of the at least two fuel injectors 19 to the accumulator 24. The gaseous gas accumulator 24 is also provided with an additional outlet 23. A gaseous gas return conduit 60 is arranged in the system, extending from the additional outlet 23 of the gaseous gas accumulator 24 to the tank 14. The gaseous gas return conduit 60 is provided with a start and safety valve 62 controlled by a two-position three-way directional valve 64. There is also a three-way valve 66 connected to the return line 60, by means of which the start-up and safety valve 64 and the tank 14 can be selectively connected to each other and / or to the fuel for further processing. The start-up and safety valve 62 is directly connected to the control oil supply line 106 and is connected to the control oil return line 108 via a two-position three-way directional valve.

[0048] The liquefied gas high-pressure pump unit 18 includes a reciprocating piston 30 having a pumping portion 32 and a driving portion 34, and a hydraulic drive assembly 36 arranged to controllably subject the hydraulic power fluid to the driving portion of the reciprocating piston 30. The pumping portion 32 includes a cylinder 38 in which the piston 30 is arranged to reciprocate. The cylinder 38 and the piston 30 define a pumping chamber 40 on one side of the piston, the volume of which increases or decreases depending on the position of the piston 30, the volume being the smallest at the top dead center of the piston 30 and the volume being the largest at the bottom dead center of the piston 30. The fuel supply line 16 connecting the pump unit 18 to the tank 14 is in flow communication with the pumping chamber 40. There is a first one-way valve 42 connected to the pumping chamber so as to allow only liquefied gas to flow into the pumping chamber 40. And, the fuel supply line 16 connecting the pump unit 18 to the heat exchanger unit 22 is also in flow communication with the pumping chamber 40. And, there is also a second one-way valve 44 connected to the pumping chamber so as to allow the flow of liquefied gas to flow out only from the pumping chamber 40. These one-way valves may be integrated into the high pressure pump unit 18.

[0049] The fuel supply system is also provided with a fuel return line 16' for returning possible leaking fuel from the pump unit to the tank 14. Both the fuel return line 16' and the fuel supply line 16 are provided with a valve 13, which makes it possible to isolate the fuel supply system from a single cylinder while keeping the other cylinders normally using the gaseous fuel supply system. In this way, some of the cylinders can be operated in diesel mode by burning liquid fuel by compression ignition, while some of the cylinders can be operated by igniting the gaseous fuel with liquid fuel, wherein the liquid fuel is ignited by compression ignition and the gaseous fuel is ignited by the combustion of the liquid fuel. A throttle valve 15 is arranged on the return line 16', just upstream or before the tank 14, to keep the pressure in the return line substantially at the level to which the low-pressure pump 20 raises the pressure of the liquefied gas.

[0050] exist Figure 1 In the embodiment, the hydraulic drive assembly 36 of the liquefied gas high pressure pump unit includes a three-position four-way directional valve 46, which is configured to alternately supply pressurized power fluid to the first side or the second side of the double-acting piston of the drive part or to lock the position of the piston in a desired position. In this regard, the wording 4 / 3 means that the valve has 4 ports and the number of positions is 3.

[0051] The gaseous fuel supply system 10 includes a control fluid system 100 for operating the hydraulic drive assembly, which preferably uses oil as its working medium and can therefore also be referred to as a control oil hydraulic system 100. The control oil system includes a tank 102 as a reservoir or source of hydraulic power fluid (i.e., control oil). The control fluid system 100 also includes a high-pressure pump 104 that appropriately pressurizes the control oil (preferably up to 30 MPa) to operate the hydraulic drive assembly 36. The control oil system also includes a control oil supply pipeline 106, which is configured to deliver the pressurized control fluid to any desired device in the fuel supply system 10 at a substantially constant pressure, but in particular to the hydraulic drive assembly 36. There is also a control oil return pipeline 108 in the system for returning the control oil to the tank 102. The control oil supply pipeline 106 and the control oil return pipeline 108 are flow-connected to the corresponding ports of the directional valve 46 of each cylinder of the engine. In this way, the piston 30 of the pump unit 18 is actively driven to its two optional directions by the pressure of the control oil in the control oil system 100.

[0052] The injector is advantageously substantially as disclosed in International Publication No. WO 2017 / 162902 A1, particularly relating to the first fuel supply portion described therein. In addition, the injector comprises a sealing system as described in that disclosure using the term "sealed fluid chamber" corresponding to the sealing system, the description of which is incorporated herein by reference. A control fluid system 100 is fluidly connected to each of the injectors so that pressurized control oil is supplied to the sealing system 17 of the injector through a control oil supply conduit 106 and returned to the tank through an oil return conduit 108.

[0053] exist Figure 2 , Figure 3 and Figure 4 In more detail, Figure 1 The operation of the high pressure pump unit 18 and the hydraulic drive assembly 36. First, refer to Figure 2 , the piston 30 of the high pressure pump unit 18 is shown at the end of its suction stroke, i.e. at its bottom dead center. That is, when the piston 30 in the pumping section 32 is in its extreme position ( Figure 2 4 (left side in the figure), the pumping chamber 40 has its maximum volume. Accordingly, the piston 30 in the drive part 34 moves to the extreme position of its suction stroke. The high-pressure control oil has flowed from the pressure port 46.1 through the directional valve 46 to the port 46.2 connected to the chamber flow in the drive part 34, which causes the suction stroke movement. During the movement of the piston 30 toward the end of its suction stroke position, liquefied gas enters the chamber 40 from the fuel supply line 16 allowed by the non-return valve 42, as shown by the arrow in the chamber 40. As previously discussed, since the low-pressure pump unit 20 increases the pressure in the fuel supply line, the risk of abnormalities such as cavitation due to the suction movement of the piston can be minimized, and the speed of the piston can be maximized.

[0054] The directional valve 46 of the hydraulic drive assembly 36 has four ports 46.1, 46.2, 46.3, 46.4, of which port 46.1 is a pressure port and port 46.3 is a tank port. The tank port 46.3 is provided with a first controllable throttle 48. In addition, a second controllable throttle 50 is provided in the pipeline between the fourth port 46.4 and the drive part 34 of the piston 30 on the side behind the piston (i.e. the side that increases the volume during the pumping stroke action, i.e. the compression stroke). Figure 2 In the embodiment of the present invention, the directional valve 46 is arranged in a first position in which the pressure port 46.1 is connected to the side of the drive side piston that pushes the piston 30 to the direction in which the pumping chamber 40 has its maximum volume. The return flow of the control oil flowing through the first throttle 48 and the second throttle 50 by means of the speed of the piston 30 is kept low enough to avoid any cavitation in the pumping chamber 40.

[0055] exist Figure 3 In FIG. 4 , the second position of the directional valve 46 of the hydraulic drive assembly 36 is shown. Figure 2 The first position shown in Figure 4 , in which all ports are blocked and the position of the piston 30 is locked in the pump unit 18.

[0056] exist Figure 4 , the directional valve 46 is set in the third position. In the third position, the pressure port 46.1 is connected to both sides of the drive side 34 of the piston 30. At this time, due to the pressure, on both sides of the piston on the drive side, the effective area that causes the combined force to the piston makes the area ratio of about 1:3-1:5, preferably, about 1:4. In this way, the force allowed to be applied to the piston during the compression stroke is 4 times the force allowed to be applied to the piston during the suction stroke, which pushes the piston 30 to the direction in which the pumping chamber 40 has its minimum volume, that is, to the top dead center position of the piston 30. When the pump unit 18 is controlled to operate, the directional valve of the hydraulic drive assembly 36 is controlled to be in the first position ( Figure 2 ) and the third position ( Figure 4 ), wherein the same power fluid and thus the same and constant pressure in the control fluid system is used to obtain the reciprocating movement of the piston 30 during the pumping sequence. The pressurized control oil supply is selectively connected to both sides of the piston 30 from the pressure port 46.1 at the drive part 34. In this way, the hydraulic drive assembly 36 is configured to control the pump unit 18 to perform a pumping sequence, during which the piston 30 is arranged to reciprocate in the pump unit 18. This is achieved by activating the directional valve 46 to move between the first position and the third position.

[0057] More advantageously, the hydraulic drive assembly 36 is configured to first reciprocate the piston 30 between the top dead center and the bottom dead center with a full stroke, each stroke of the stroke increasing the pressure of the liquefied gas stepwise or stroke by stroke by a predetermined amount. This is referred to as a full stroke pumping sequence. This will be done until the liquefied gas pressure, preferably corresponding to the injection pressure, is at a level where a complete single stroke of the piston 30 will increase the pressure above the set value. The typical state of the liquefied gas after the high pressure pump unit 18 is such that the pressure is 12 MPa to 15 MPa and the temperature is -145°C to -135°C.

[0058] According to an embodiment of the present invention, at this stage of the pumping sequence, that is, after the last full stroke of the piston 30, the hydraulic drive assembly 36 is configured to return the piston 30 from its top dead center to the bottom dead center, and only move the piston to cause the next part of the pumping stroke to cause the pressure of the liquefied gas to rise to the set target pressure, that is, to execute a partial stroke of the piston to a position between its extreme positions. Then, the piston stops moving until the next pumping sequence is started. The three-position four-way directional valve can be a proportional control valve with position feedback that can be used to determine the stop position of the piston.

[0059] The length of the partial stroke can be determined by calculation based on measured variables available from the system (liquefied gas pressure, temperature, piston and chamber dimensions, piston position). For example, the piston can be moved until a set target pressure is achieved and verified by pressure measurement, or the piston can be moved to a position where the pressure verified by a position sensor is calculated as the target pressure.

[0060] According to another embodiment of the present invention, at this stage of the pumping sequence, i.e., after the last full stroke of the piston 30, the hydraulic drive assembly 36 is configured to return the piston 30 from its top dead center toward the bottom dead center by only a distance, which causes the next partial pumping stroke to return to the top dead center, thereby causing the pressure of the liquefied gas to rise to the set target pressure, i.e., executing a partial stroke of the piston 30 from a position between its extreme positions back to the top dead center position. Then, the piston stops moving until the next pumping sequence is started.

[0061] The length of the partial stroke can be determined by calculation based on measured variables available from the system (liquefied gas pressure, temperature, piston and chamber dimensions, piston position).

[0062] The electronic control unit ECU (i.e., control computer) of the fuel supply system comprises a computer program which, when executed, controls the operation of the fuel supply system, in particular the high pressure pump unit 18 as described above. The ECU and the computer program are arranged to configure the system and / or its parts to operate in the manner described herein.

[0063] During a full stroke pumping sequence, the position of the directional valve is changed and the piston 30 is advantageously arranged to reciprocate between its top and bottom dead centers at a frequency of 3-6 times per second. The hydraulic drive assembly is configured to reciprocate the piston in an intermittent manner so that its operation is based on the pressure measurement 28 in the accumulator 24 and is independent of the activation of the injector 19. Advantageously, the output of the pump unit 18 during one pumping sequence substantially corresponds to the amount of fuel injected through the injector 19 in the cylinder for one engine cycle.

[0064] Now refer back to Figure 1, the gaseous gas pressure in the accumulator 24 of the gaseous fuel injector 19 in one cylinder of the engine is maintained at a desired pressure, which is advantageously 12MPa-15MPa and can also be expressed as an injection pressure. The pressure in the accumulator 24 is measured by a sensor 28, which value is used in the control process to control the operation of the liquefied gas high-pressure pump unit 18 as described above. The desired minimum injection pressure and maximum injection pressure are set. The measured pressure in the accumulator 24 is compared with the minimum injection pressure and the maximum injection pressure. If the measured pressure is lower than the minimum target pressure, the pump unit 18 is started and operated until the measured pressure in the accumulator is at least the maximum injection pressure. In this way, the injection pressure is controlled by means of the pressure measurement 28 in the high-pressure pump unit 18 and the accumulator 24.

[0065] In addition, the gaseous gas in the accumulator is maintained at a desired temperature of -50°C to -20°C. The temperature in the accumulator is measured by a sensor 26, which value is used in the control process to control the operation of the heat exchanger unit 22. A desired minimum temperature and a maximum temperature are set. The measured temperature in the accumulator 24 is compared with the minimum set temperature and the maximum set temperature. If the measured temperature is below the minimum target temperature, the heat exchanger unit heating power is maintained as is or increased until the measured temperature in the accumulator is at least the maximum set temperature. In this way, the gaseous fuel temperature is controlled by means of the temperature measurement 26 in the heat exchanger unit 22 and the accumulator 24.

[0066] The volume of the accumulator 24 depends on the required injection quantity and the total volume of the fuel supply system between the high-pressure pump unit 18 and the gas injectors 19. During full-load operation, the volume of the accumulator is advantageously 3 to 10 times the volume of the fuel injected by the two injectors of one cylinder. This volume is typically 2.5 to 10 liters.

[0067] Figure 5The cylinder head 200 of a large two-stroke crosshead piston engine 1 as seen from inside the cylinder 204 is schematically disclosed. The large two-stroke engine specifically desired by the gaseous fuel supply system according to the present invention is a low-speed crosshead engine having a cylinder diameter greater than about 50 cm to 1 m and a stroke length of about 2.5 meters. An exhaust valve 202 at the center of each cylinder and an injector 19, 201 of the engine 1 in the cylinder are shown. According to an embodiment of the present invention, the two-stroke internal combustion piston engine comprises at least two cylinders, wherein each cylinder is provided with a direct injection gaseous fuel supply system having two injectors 19 in the cylinder and three additional liquid fuel injectors 201 connected to a common rail fuel injection system 206. For those skilled in the art of large two-stroke engines, it is known that the number of liquid fuel injectors can vary. The liquid fuel injector 201 and the common rail liquid fuel injection system 206 are configured to inject, for example, heavy fuel oil, light fuel oil and / or marine fuel oil. In this way, any one of the cylinders of the two-stroke engine can be operated in dual-fuel mode with a gaseous fuel as its main fuel ignited with liquid fuel, and, if desired, also in diesel mode with liquid fuel exclusively as a diesel engine. In dual-fuel mode, the cylinders are fueled by a combination of gaseous gas and liquid fuel. Advantageously, according to the invention, the engine is operated, at least in special cases, so that at least one of the cylinders is operated by injecting only liquid fuel into this cylinder, while the remaining cylinders are operated by injecting both gaseous fuel and liquid fuel into each of the remaining cylinders. Advantageously, in at least one of the cylinders that is operated by injecting only liquid fuel into the cylinder, a direct injection gaseous fuel supply system is maintained during the operation of the engine.

[0068] exist Figure 6 and Figure 7 , the operations of the high-pressure pump unit 18 and the hydraulic drive assembly 36 according to another embodiment of the present invention are described in a more detailed manner. Figure 6 and Figure 7 The high pressure pump unit 18 and the hydraulic drive assembly 36 are intended to be used with Figure 1 The gaseous fuel supply system in the embodiment of the present invention is used in combination to replace the high pressure pump unit 18 and the hydraulic drive assembly 36 shown here. Figure 6 , the piston 30 of the high pressure pump unit 18 is shown at the end of its suction stroke, i.e., at its bottom dead center position. That is, when the piston 30 in the pumping section 32 is in its extreme position ( Figure 64 (left side in the figure), the pumping chamber 40 has its maximum volume. Accordingly, the piston 30 in the drive part 34 moves to the extreme position of its suction stroke. High-pressure control oil flows from the pressure port 46.1 through the directional valve 46 to the port 46.2 connected to the chamber flow in the drive part 34, which causes the suction stroke movement. During the movement of the piston 30 toward the end of its suction stroke position, liquefied gas is sucked into the chamber 40 from the fuel supply line 16 allowed by the one-way valve 42, as shown by the arrow. As discussed previously, since the low-pressure pump unit 20 increases the pressure in the fuel supply line, the risk of abnormalities due to the suction movement of the piston can be minimized and the speed of the piston can be maximized.

[0069] The directional valve 46 of the hydraulic drive assembly 36 is a 4 / 2-way directional valve and has four ports 46.1, 46.2, 46.3, 46.4, of which port 46.1 is a pressure port and port 46.3 is a tank port. The tank port 46.3 is provided with a first controllable throttle 48. In addition, the pipeline between the fourth port 46.4 and the drive part 34 of the piston 30, which is located on the rear side of the piston (i.e., the side of the increased volume during the pumping stroke action), is provided with a second controllable throttle 50. Figure 6 In the embodiment of the present invention, the directional valve 46 is set in the first position, in which the pressure port 46.1 is connected to the side of the drive side piston that pushes the piston 30 to the direction in which the pumping chamber 40 has its maximum volume. The return flow of the control oil flows through the fourth port 46.4 and the tank port 46.3, and then, as can be seen in the figure, flows through the first throttle 48 and the second throttle 50, by means of which the speed of the piston 30 is kept low enough to avoid any cavitation in the pumping chamber 40.

[0070] exist Figure 7 In the embodiment of the present invention, the 4 / 2-way directional valve 46 is set in the second position. In the second position, the pressure port 46.1 is connected to the ports 46.2 and 46.4, and in this way, it is also connected to both sides of the drive side piston. Due to the difference in effective piston area between the piston side on the drive side of the piston, the pressure of the controlled fluid pushes the piston 30 in the direction in which the pumping chamber 40 has its minimum volume. The effective area that causes the combined force on the piston is such that the ratio of the area is about 1:3 to 1:5, preferably about 1:4.

[0071] When based on Figure 6 and Figure 7 When the pump unit 18 is controlled to operate, the directional valve of the hydraulic drive assembly 36 is controlled to be in the first position ( Figure 6 ) and the third position ( Figure 7), wherein the same power fluid and fluid pressure in the control fluid system are used to obtain reciprocating movement of the piston 30 in both directions. At this time, the hydraulic drive assembly 36 is configured to control the pump unit 18 to perform a pumping sequence, during which the piston 30 is arranged to reciprocate in the pump unit 18. This is achieved by activating the directional valve 46 to move between the first position and the third position. The typical state of the liquefied gas after the high-pressure pump unit 18 is such that the pressure is 12Mpa to 15MPa and the temperature is -145°C to -135°C.

[0072] according to Figure 6 and Figure 7 In the embodiment shown in FIG. 1 , the hydraulic drive assembly 36 is advantageously configured to reciprocate the piston 30 with a full stroke, with each stroke in the stroke increasing the pressure of the liquefied gas stepwise or stroke by stroke by a predetermined amount. This is done until the liquefied gas pressure, preferably the injection pressure, is so high that the pump stops moving. The pumping section 32 and the drive section 34 of the liquefied gas high-pressure pump unit 18 are configured so that the maximum pressure of the liquefied gas (preferably or for example 15 MPa) that can be obtained from the pumping section using a hydraulic power fluid at a predetermined pressure (preferably or for example 900 kPa) corresponds to the set injection pressure (preferably or for example 15 MPa). In other words, the pump unit 18 is configured to increase the pressure of the liquefied gas to a pressure of about 0.5 times the pressure of the control oil. When the reciprocating movement of the piston stops, the pumping sequence stops. Thereafter, at least two optional procedures follow. First, the pressure of the control fluid can be retained to push the piston 30 to squeeze the liquefied gas, in which case the piston 30 can move to its top dead center position as the pressure in the accumulator 24 decreases. Secondly, the intake stroke of the piston 30 may start immediately.

[0073] The electronic control unit ECU (ie control computer) of the fuel supply system comprises a computer program which, when executed, controls the operation of the fuel supply system, in particular the high pressure pump unit 18 as described above.

[0074] During a pumping sequence, the position of the directional valve is changed and the piston 30 is advantageously arranged to reciprocate at a frequency of 3-6 times per second. The hydraulic drive assembly is configured to reciprocate the piston in an intermittent manner so that its operation is based on the pressure measurement 28 in the accumulator 24 and is independent of the activation of the injectors 19. Advantageously, the output of the pump unit 18 during one pumping sequence substantially corresponds to the amount of fuel injected through the two injectors 19 for one engine cycle.

[0075] The invention can be applied to Figures 2 to 4 and Figure 6 to Figure 7According to the embodiment of the set of and the operation associated with these figures, after the last full stroke of the piston 30, the hydraulic drive assembly 36 is configured to return the piston 30 from its top dead center only a distance (partial suction stroke) that causes the next partial pumping stroke until the top dead center to cause the liquefied gas pressure to rise to the set target pressure. The piston then stops moving until the next pumping sequence is started. The piston 30 is advantageously returned to its top dead center position after each pumping sequence before the next pumping sequence.

[0076] Although the present invention is described herein by way of example in conjunction with what is currently considered to be the most preferred embodiment, it is to be understood that the present invention is not limited to the disclosed embodiments, but is intended to cover various combinations or variations of the features of the present invention as defined in the appended claims and several other applications included within the scope of the present invention. When the details mentioned in conjunction with any of the above embodiments are technically feasible in combination with another embodiment, these details may be used in conjunction with another embodiment.

[0077] Numbered list of implementations

[0078] The following embodiments describe alternative advantageous implementations of the invention.

[0079] 1. A direct injection gaseous fuel supply system for a two-stroke internal combustion piston engine, the fuel supply system comprising:

[0080] - a fuel supply line extending from a liquefied gas source to a fuel injector in the engine, the fuel supply line comprising at least the following components:

[0081] -Liquefied gas high pressure pump unit;

[0082] - a heat exchanger unit for evaporating the liquefied gas and heating the gaseous gas; and

[0083] - a gaseous gas accumulator located between the heat exchanger unit and the fuel injector; and

[0084] - at least one gaseous gas fuel injector in fluid communication with the gaseous gas accumulator, wherein the liquefied gas high-pressure pump unit comprises a reciprocating piston having a pumping portion and a driving portion, and a hydraulic drive assembly arranged so that a hydraulic power fluid at a constant pressure from a hydraulic power fluid source acts on the driving portion of the reciprocating piston so as to drive the piston in a reciprocating manner.

[0085] 2. A direct injection gaseous fuel supply system according to embodiment 1, wherein the hydraulic drive assembly is arranged to cause hydraulic power fluid at a constant pressure from the hydraulic power fluid source to act on the drive portion of the reciprocating piston in a controllable manner.

[0086] 3. A direct injection gaseous fuel supply system according to embodiment 1 or 2, wherein the reciprocating piston is a double-acting piston.

[0087] 4. A direct injection gaseous fuel supply system according to embodiment 1 or 2, wherein the hydraulic drive assembly is arranged to cause the hydraulic power fluid to act on the drive portion of the reciprocating piston in a controllable manner by driving a directional valve of the hydraulic drive assembly back and forth between a first position and a second position in a controllable manner.

[0088] 5. A direct injection gaseous fuel supply system according to embodiment 1 or 2, wherein the hydraulic drive assembly of the liquefied gas high-pressure pump unit includes a three-position four-way (4 / 3-way) directional valve, which is configured to alternately supply pressurized power fluid to the first side or the second side of the drive part of the double-acting piston, and stop and / or lock the position of the piston at a desired position.

[0089] 6. A direct injection gaseous fuel supply system according to embodiment 1 or 2, wherein the hydraulic drive assembly of the liquefied gas high-pressure pump unit includes a two-position four-way directional valve, and the two-position four-way directional valve is configured to alternately supply pressurized power fluid to the first side or the second side of the drive part of the reciprocating piston.

[0090] 7. A direct injection gaseous fuel supply system according to embodiment 1 or 2, wherein the gaseous gas accumulator includes an inlet for the gaseous gas and an outlet for each of the at least one fuel injector.

[0091] 8. A direct injection gaseous fuel supply system according to embodiment 1 or 2, wherein the fuel supply system includes at least two fuel injectors.

[0092] 9. The direct injection gaseous fuel delivery system of embodiment 5, wherein the hydraulic drive assembly is configured to:

[0093] - reciprocating the piston in full strokes, each of which increases the pressure by a predetermined amount, until the injection pressure is at a level from which a single full stroke will increase the pressure above a set value; and

[0094] - moving the piston with a partial stroke from the bottom dead center to a position between its extreme positions and stopping the movement of the piston.

[0095] 10. The direct injection gaseous fuel supply system according to embodiment 5 or 6, wherein the hydraulic drive assembly is configured to:

[0096] - reciprocating the piston in full strokes, each of which increases the pressure by a predetermined amount, until the injection pressure is at a level from which a single full stroke will increase the pressure above a set value; and

[0097] - moving the piston to a position between its extreme positions with a partial intake stroke and moving the piston to its top dead center position.

[0098] 11. A direct injection gaseous fuel supply system according to embodiment 6, wherein the pumping section and the driving section of the liquefied gas high-pressure pump unit are configured so that the maximum pressure of the liquefied gas that can be obtained from the pumping section using the hydraulic power fluid at a predetermined pressure corresponds to a set injection pressure.

[0099] 12. A direct injection gaseous fuel supply system according to embodiment 5 or 6, wherein the hydraulic drive assembly is configured to cause the piston to reciprocate at a frequency of 0.5-6 times per second.

[0100] 13. A direct injection gaseous fuel supply system according to embodiment 11, wherein the hydraulic drive assembly is configured to cause the piston to reciprocate at a frequency of 3-6 times per second.

[0101] 14. A direct injection gaseous fuel supply system according to embodiment 12 or 13, wherein the hydraulic drive assembly is configured to cause the piston to reciprocate in an intermittent manner.

[0102] 15. A direct injection gaseous fuel supply system according to embodiment 11, wherein the hydraulic drive assembly is configured to first cause the piston to reciprocate with a full stroke and then reciprocate with a partial stroke after the full stroke until a predetermined injection pressure is reached in the gaseous gas accumulator.

[0103] 16. A direct injection gaseous fuel supply system according to embodiment 5 or 6, wherein the hydraulic drive assembly is configured to pump with a full stroke and then operate the pump unit with a partial stroke of the piston to a position between the extreme positions of the piston.

[0104] 17. A direct injection gaseous fuel supply system according to embodiment 5 or 6, wherein the hydraulic drive assembly is configured to operate the pump unit in a full-stroke pumping sequence, and after the last full stroke of the piston (30), the hydraulic drive assembly (36) is configured to return the piston (30) only a distance from its top dead center, which distance causes the next partial pumping stroke until the top dead center to cause the pressure of the liquefied gas to rise to the set target pressure.

[0105] 18. A direct injection gaseous fuel supply system according to embodiment 110, wherein the liquefied gas high-pressure pump unit is configured to increase the pressure of the liquefied gas to a pressure approximately 0.5 times the pressure of the hydraulic power fluid when the pressure of the hydraulic power fluid is in the range of 12-15 MPa.

[0106] 19. A direct injection gaseous fuel supply system according to embodiment 1, wherein the liquefied gas high-pressure pump unit is configured to increase the pressure of the liquefied gas to a pressure approximately 0.5 times the pressure of the hydraulic power fluid, wherein the pressure of the fluid is in the range of 12-15 MPa.

[0107] 20. A direct injection gaseous fuel supply system according to embodiment 2 or 19, wherein the fuel supply system includes a high-pressure pump unit for hydraulic power fluid pressure, and the high-pressure pump unit is configured to deliver pressurized control fluid at a substantially constant pressure.

[0108] 21. A direct injection gaseous fuel supply system according to any one of the preceding embodiments, wherein the fuel supply system comprises at least two fuel injectors for each cylinder of the two-stroke internal combustion piston engine.

[0109] 22. A direct injection gaseous fuel supply system according to any one of the aforementioned embodiments 1 to 19, wherein the fuel supply pipeline includes a liquefied gas high-pressure pump unit connected to the fuel supply pipeline and a liquefied gas low-pressure pump unit arranged between the high-pressure pump unit and the storage tank.

[0110] 23. A direct injection gaseous fuel supply system according to any one of the preceding embodiments, wherein the fuel supply system is provided with a fuel supply line and a fuel return line each provided with a shut-off valve.

[0111] 24. A direct injection gaseous fuel supply system according to embodiments 22 and 18, wherein the valve in the fuel supply line is arranged between the low-pressure pump and the high-pressure pump unit.

[0112] 25. A direct injection gaseous fuel supply system according to embodiment 9 or 14, wherein the hydraulic drive assembly is configured to move the piston in a partial stroke, so that the partial stroke starts after a previous full stroke at the top dead center position of the piston, and the piston returns to the top dead center position through a partial suction stroke and a pumping stroke.

[0113] 26. A two-stroke internal combustion piston engine, the engine comprising more than one cylinder, wherein each cylinder of the engine is provided with a direct injection gaseous fuel supply system according to any one of the preceding embodiments, the direct injection gaseous fuel supply system having a common liquefied gas storage tank.

[0114] 27. A two-stroke internal combustion piston engine according to embodiment 24, wherein each cylinder of the engine comprises two gaseous gas injectors and three liquid fuel injectors.

[0115] 28. A two-stroke crosshead internal combustion piston engine according to embodiment 26 or 27.

[0116] 29. A two-stroke crosshead internal combustion piston engine according to embodiment 26 or 27, the engine comprising a control computer, the control computer comprising a computer program which, when executed, controls the operation of the fuel supply system in the manner described in embodiments 30 to 31.

[0117] 30. A method for operating a two-stroke internal combustion piston engine, the two-stroke internal combustion piston engine comprising a plurality of cylinders, a common rail liquid fuel injection system and a direct injection gaseous fuel supply system according to any one of the aforementioned embodiments 1 to 25, the method comprising the following steps: operating the engine so that at least one of the cylinders operates by injecting only liquid fuel into the at least one cylinder, while the remaining cylinders operate by injecting both gaseous fuel and liquid fuel into each of the remaining cylinders.

[0118] 31. A method for operating a two-stroke internal combustion piston engine according to embodiment 30, the method comprising: allowing hydraulic power fluid under constant pressure from a hydraulic power fluid source to act on the driving part of the reciprocating piston and drive the piston in a reciprocating manner and operate the pump unit in a full-stroke pumping sequence, and after the last full stroke of the piston, causing the piston to return only a distance from its top dead center, which distance causes the next partial pumping stroke until the top dead center to cause the pressure of the liquefied gas to rise to the set target pressure.

[0119] 32. A method of operating a two-stroke internal combustion piston engine according to embodiment 30, wherein the direct injection gaseous fuel supply system is maintained in at least one of the cylinders that operates by injecting only liquid fuel into the cylinder.

Claims

1. A direct injection gaseous fuel supply system (10) for a two-stroke internal combustion piston engine (1), the fuel supply system (10) comprising: - a fuel supply line (16) extending from a liquefied gas source (14) to a gaseous fuel injector (19) in the engine (1), the fuel supply line (16) comprising at least the following components: - liquefied gas high pressure pump unit (18); - a heat exchanger unit (22) for evaporating the liquefied gas and heating the gaseous gas; and - a gaseous gas accumulator (24) located between the heat exchanger unit (22) and the gaseous gas fuel injector (19); and - at least one gaseous gas fuel injector (19) in fluid communication with said gaseous gas accumulator (24), The liquefied gas high-pressure pump unit (18) comprises a reciprocating piston (30) having a pumping portion (32) and a driving portion (34), and a hydraulic drive assembly (36), wherein the hydraulic drive assembly is arranged to allow a hydraulic power fluid under a constant pressure from a hydraulic power fluid source (102) to act on the driving portion (34) of the reciprocating piston (30) so as to drive the piston in a reciprocating manner, and is characterized in that the hydraulic drive assembly (36) comprises a directional valve (46) having four ports, wherein the four ports The directional valve (46) includes a pressure port (46.1), and the directional valve (46) includes a pumping position. In this pumping position, the pressure port (46.1) of the directional valve (46) is connected to both sides of the piston (30) located at the drive part (34) of the liquefied gas high-pressure pump unit (18), thereby causing a pumping stroke action in the liquefied gas high-pressure pump unit (18), and there is a difference in effective piston area between the two sides of the piston (30) located at the drive part (34) of the piston (30).

2. The direct injection gaseous fuel supply system (10) according to claim 1, characterized in that The hydraulic drive assembly (36) is arranged to controllably cause hydraulic power fluid at a constant pressure from the hydraulic power fluid source (102) to act on the drive portion (34) of the double-acting reciprocating piston.

3. The direct injection gaseous fuel supply system (10) according to claim 1 or 2, characterized in that: The hydraulic drive assembly (36) is arranged to controllably cause hydraulic power fluid to act on the drive portion (34) of the reciprocating piston (30) by controllably driving the directional valve (46) of the hydraulic drive assembly (36) back and forth between a first position and a second position.

4. The direct injection gaseous fuel supply system (10) according to claim 1, characterized in that The hydraulic drive assembly (36) is configured to: - reciprocating the piston (30) in full strokes, each of which increases the pressure by a predetermined amount, until the injection pressure is at a level from which a single full stroke will increase the pressure above a set value; and - moving the piston (30) to a position between its extreme positions with a partial suction stroke and moving the piston (30) to its top dead center position.

5. The direct injection gaseous fuel supply system (10) according to claim 1, characterized in that The pumping section (32) and the driving section (34) of the liquefied gas high-pressure pump unit (18) are configured so that the maximum pressure of the liquefied gas obtainable from the pumping section (32) using the hydraulic power fluid at a predetermined pressure corresponds to a set injection pressure.

6. The direct injection gaseous fuel supply system (10) according to claim 1, characterized in that The hydraulic drive assembly (36) is configured to cause the piston to reciprocate at a frequency of 3-5 times per second.

7. The direct injection gaseous fuel supply system (10) according to claim 6, characterized in that The hydraulic drive assembly (36) is configured to cause the piston to reciprocate in an intermittent manner.

8. The direct injection gaseous fuel supply system (10) according to claim 1, characterized in that The liquefied gas high-pressure pump unit (18) is configured to increase the pressure of the liquefied gas to a pressure 0.5 times the pressure of the hydraulic power fluid.

9. The direct injection gaseous fuel supply system (10) according to claim 1, characterized in that The fuel supply system (10) comprises at least two gaseous fuel injectors (19) for each cylinder of the two-stroke internal combustion piston engine (1).

10. The direct injection gaseous fuel supply system (10) according to claim 1, characterized in that The liquefied gas high-pressure pump unit (18) is coupled to the fuel supply line, and the fuel supply line (16) includes a liquefied gas low-pressure pump unit (20) arranged between the liquefied gas high-pressure pump unit (18) and a liquefied gas source (14).

11. The direct injection gaseous fuel supply system (10) according to claim 1, characterized in that The difference in effective piston area between the two sides of the drive portion (34) of the piston (30) is such that the ratio of the areas is 1:3-1:

5.

12. A two-stroke internal combustion piston engine (1), comprising more than one cylinder, wherein: Each cylinder is provided with a direct injection gaseous fuel supply system (10) according to any one of claims 1 to 11.

13. A two-stroke internal combustion piston engine (1) according to claim 12, wherein: Each cylinder of the engine (1) comprises two gaseous fuel injectors (19) and two liquid fuel injectors (201).

14. A method for operating a two-stroke internal combustion piston engine (1), the two-stroke internal combustion piston engine comprising a plurality of cylinders (204), a common rail liquid fuel injection system (206) and a direct injection gaseous fuel supply system (10) according to any one of the preceding claims 1 to 11, the method comprising the following steps: operating the engine so that at least one of the cylinders (204) is operated by injecting only liquid fuel into the at least one cylinder, while the remaining cylinders (204) are operated by injecting both gaseous fuel and liquid fuel into each of the remaining cylinders.

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