Fuel supply system for supplying liquid fuel into two or more cylinders of an internal combustion piston engine, internal combustion piston engine and method of operating an internal combustion engine

Abstract

The invention relates to a fuel supply system (8) for supplying liquid fuel into two or more cylinders (12) of an internal combustion piston engine, comprising: i. a first fuel source (16), at least one first fuel high-pressure pump (18) connected to the first fuel source (16), and a first pressure rail (24) connected to the high-pressure side of the at least one first fuel high-pressure pump (18); ii. a first fuel injection valve (100) for each cylinder of the engine, connected to the first pressure rail (24); iii. a second fuel source (20), at least one second fuel high-pressure pump (22) connected to the second fuel source (20), and a second pressure rail (28) connected to the high-pressure side of the at least one second fuel high-pressure pump (22); iv. a control valve unit (34) arranged between the first pressure rail (24) and the second pressure rail (28) and configured to control the flow connection between the first pressure rail (24) and the second pressure rail (28).

Description

Technical Field

[0001] The present invention relates to a fuel supply system for supplying liquid fuel to two or more cylinders of an internal combustion piston engine according to claim 1.

[0002] This invention relates to an internal combustion piston engine and a method of operating an internal combustion engine. Background Technology

[0003] There is a strong market demand for reducing emissions from internal combustion engines, particularly decarbonization. An effective solution for reducing emissions and lowering operating costs from large internal combustion engines in ships and power plants is the so-called dual-fuel or tri-fuel engine, which can operate on fuels that are carbon-free or contain less carbon than conventionally used fossil fuels. These multi-fuel engines offer the flexibility to select the most suitable fuel based on availability and price of different fuels and / or emission restrictions in a particular place or at a particular time. For example, a ship's engine can operate on non-carbon fuels in areas with strict emission restrictions and on fossil fuel oils elsewhere.

[0004] EP20036427B1 discloses a fuel injection system for a piston engine, having a first fuel circuit for injecting liquid fuel and a second fuel circuit for injecting liquid ignition fuel into the cylinders of the engine. The first fuel circuit includes at least one fuel injection pump and at least one fuel injector for each cylinder, and the second fuel circuit is provided with at least one high-pressure pump and includes at least one ignition fuel injector for each cylinder of the engine. The fuel injection system includes means for introducing liquid ignition fuel from the second fuel circuit into the first fuel circuit between the fuel injection pump and the fuel injector. When residual fuel has been used, the engine's fuel injection pump and fuel injector can be flushed with higher quality fuel before a planned transition from liquid fuel mode to gas mode.

[0005] DE102015203607B4 discloses a fuel supply system for an internal combustion engine, which is configured to inject two different fuels as a fuel mixture into the engine via a common injector and a high-pressure fuel system.

[0006] US115852003B2 discloses a dual-fuel internal combustion engine and a fuel injection system having a main injection system and a pilot injection system. In the main injection system, a common fuel injector is alternatively connected to two fuel lines for different fuels. The pilot injection system has a separate pilot injector. Fuel from the pilot injection system can be supplied to the main injector as a working fluid or a blocking fluid.

[0007] The fuel supply system still needs improvement.

[0008] The object of this invention is to provide a fuel supply system that enables the operation of an engine using different fuels with a single injection valve. Another object of this invention is to provide an internal combustion piston engine capable of operating with different fuels in an improved manner. Yet another object of this invention is to provide a method for operating an internal combustion engine using different fuels in an improved manner. Summary of the Invention

[0009] The objectives of the invention can be substantially satisfied as disclosed in the independent claims and in other claims that describe various embodiments of the invention in more detail.

[0010] A fuel supply system for supplying liquid fuel to two or more cylinders of an internal combustion piston engine, comprising: i. A first fuel source, at least one first high-pressure fuel pump connected to the first fuel source, and a first pressure rail connected to the high-pressure side of the at least one first high-pressure fuel pump. ii. A first fuel injection valve for each cylinder of the engine, which is connected to a first pressure rail. iii. A second fuel source, at least one second high-pressure fuel pump connected to the second fuel source, and a second pressure rail connected to the high-pressure side of the at least one second high-pressure fuel pump. iv. A control valve unit disposed between the first pressure rail and the second pressure rail, and configured to control the flow connection between the first pressure rail and the second pressure rail.

[0011] In this way, both the first liquid fuel and the second liquid fuel can be effectively injected into the cylinder of the internal combustion engine using a single fuel injection valve. As a preferred embodiment of the invention, the first fuel has a low calorific value of less than 33 MJ / kg, and the second fuel has a low calorific value of ≥33 MJ / kg.

[0012] According to one aspect of the invention, the system further includes a second fuel injection valve for each cylinder of the engine, which is connected to a second pressure rail.

[0013] In addition to fuel injection via the first fuel injection valve, the second fuel injection valve can be effectively used to inject additional fuel, such as ignition fuel or ignition auxiliary fuel.

[0014] According to one aspect of the invention, the system includes a fuel injector body for each cylinder of an engine, the injector body including a first fuel injection valve and a second fuel injection valve.

[0015] This results in a simpler cylinder head design, reducing the number of orifices required for several injectors.

[0016] According to one aspect of the invention, at least one of the first fuel injection valve and the second fuel injection valve, preferably both the first fuel injection valve and the second fuel injection valve are provided with valve-specific fuel accumulators.

[0017] In this way, hydraulic fluctuations are suppressed, thereby providing more stable injection and injection accuracy.

[0018] According to one aspect of the invention, a first pressure rail is connected to a first high-pressure fuel pump at its first end, and a control valve unit is connected to the first end of the first pressure rail.

[0019] According to one aspect of the invention, a first high-pressure fuel pump and a control valve unit are connected to different locations on a first pressure rail, advantageously connected to opposite ends of the first pressure rail.

[0020] By selecting the location of the control valve unit, certain additional functions can be obtained. For example, when the control valve unit is at the second end of the first pressure rail, reverse flow can be achieved, and the first pressure rail can be flushed using a second fuel.

[0021] According to one aspect of the invention, a first high-pressure fuel pump is arranged in an adjustable flow connection with both a first fuel source and a second fuel source at the pump inlet side.

[0022] This provides redundancy in pumping possibilities, allowing the second fuel to be supplied to the first pressure rail if the first fuel is unavailable or if the second fuel high pressure is not working and the second fuel is desired to be supplied to the first high pressure rail.

[0023] According to one aspect of the invention, the system includes a sealing oil supply system arranged to supply sealing oil to each of the first fuel injection valves for sealing the fuel section and valve control section of the injector. Leakage of the first fuel is prevented by using the sealing oil.

[0024] According to one aspect of the invention, the sealing oil supply system is connected to a second fuel source.

[0025] This simplifies the fuel supply system and avoids the need for an additional fluid as a sealing oil.

[0026] According to one aspect of the invention, a first fuel injection valve in a fuel supply system includes

[0027] i. Fuel inlet, ii. A fuel passage, arranged to flow in communication with the fuel inlet. iii. A fuel outlet in the fuel passage, the outlet comprising one or more injection orifices, iv. A valve needle arranged to close or open the fuel outlet; wherein v. The injection valve is configured to inject liquid fuel with a low calorific value <33MJ / kg, and the total cross-sectional area of ​​the fuel outlet is less than 8.5mm. 2 / MW, where MW is the nominal maximum power output per cylinder.

[0028] According to one aspect of the invention, the fuel injection valve includes a computer-controlled injection valve.

[0029] The electronic control system provides excellent flexibility in the control and operation of the injection valve.

[0030] According to one aspect of the invention, a first check valve is arranged in the system to prevent fuel from flowing back from the first pressure rail toward the first high-pressure fuel pump.

[0031] According to one aspect of the invention, a second check valve is arranged in the fuel supply system to prevent backflow of fuel from the first pressure rail to the control valve unit. The first fuel may typically be toxic and requires special materials, and preventing backflow avoids such toxic fuel from entering the control valve and components of the system on the other side of the control valve unit.

[0032] According to one aspect of the invention, the second check valve is arranged to connect with the control valve unit. This makes the arrangement more compact.

[0033] An internal combustion piston engine includes a fuel supply system according to any one of claims 1 to 15 for supplying liquid fuel to its cylinder, wherein a first fuel injection valve is configured for compression ignition of fuel in the combustion chamber of the engine.

[0034] A method of operating an internal combustion engine, the internal combustion engine including a fuel supply system for supplying liquid fuel into its cylinders, wherein the fuel supply system includes

[0035] i. A first fuel source, comprising at least one first high-pressure fuel pump and a first pressure rail connected to said at least one first high-pressure fuel pump. ii. A first fuel injection valve for each cylinder of the engine, which is connected to a first pressure rail. iii. A second fuel source, comprising at least one second high-pressure fuel pump and a second pressure rail connected to the high-pressure side of the at least one second high-pressure fuel pump. iv. A control valve unit between the first pressure rail and the second pressure rail, configured to control the flow connection between the first pressure rail and the second pressure rail, and in this method a. Operate the second high-pressure fuel pump. b. Open the control valve unit to allow the second fuel to flow from the second fuel high-pressure pump to the first pressure rail. c. The first pressure rail is filled with a second fuel, which is pressurized to a predetermined minimum operating pressure. d. The pressure in the first pressure rail is determined by the second fuel high-pressure pump. e. The engine is started and operated by injecting a second fuel into the cylinder of the engine using a first fuel injection valve.

[0036] According to one aspect of the invention, a first check valve arranged in the system prevents fuel from flowing back from the first pressure rail to the first high-pressure fuel pump.

[0037] According to one aspect of the invention, the system further includes a sealing oil supply system arranged to supply sealing oil to each of the first fuel injection valves, and in the method, when the engine is operated by injecting a second fuel into the cylinders of the engine via the first fuel injection valves, switching the engine operation to burn the second fuel in the engine includes the following steps:

[0038] f. Activate the sealing oil supply system and supply sealing oil to the sealing chamber of the first fuel injector. g. Start the first high-pressure fuel pump. h. The control valve unit closes the flow connection via the flow path between the first and second pressure rails, thereby stopping the second fuel flow from the second pressure rail to the first pressure rail, and the pressure in the first pressure rail is determined by the first high-pressure fuel pump. i. Fuel in the first pressure rail is injected by the first fuel injection valve, and the fuel composition in the first pressure rail changes from the second fuel to the first fuel. Afterward, the first fuel is injected only by the first fuel injection valve. j. The fuel is ignited by compression ignition.

[0039] According to one aspect of the invention, the fuel supply system further includes a second fuel injection valve for each cylinder of the engine, which is connected to a second pressure rail, and in the method, a second fuel injected through the second fuel injection valve assists in the compression ignition of the first fuel.

[0040] According to one aspect of the invention, after performing steps a to j, changing the operation of the engine includes the following steps: k. The control valve unit opens the flow connection via the flow path between the first and second pressure rails, allowing the second fuel flow from the second pressure rail to the first pressure rail to begin. 1. The pressure of the first fuel in the first fuel source decreases to a level that causes the first check valve to close. m. Fuel in the first pressure rail is injected by the first fuel injection valve, and the fuel composition in the first pressure rail changes from the first fuel to the second fuel, after which the second fuel is injected only by the first fuel injection valve.

[0041] According to one aspect of the invention, after performing steps a to m, changing the operation of the engine includes the following steps: n. Recording engine stop command o. Stop the operation of the second fuel injection valve. p. Stop the operation of the first fuel injection valve.

[0042] The exemplary aspects of the invention presented in this patent application should not be construed as limiting the applicability of the appended claims. The verb "comprising" is used in this patent application as an open limitation that does not exclude the presence of features not yet described. Unless otherwise expressly stated, the foregoing aspects may be freely combined with each other. Novel features considered to be characteristic of the invention are specifically set forth in the appended claims. Attached Figure Description

[0043] In the following description, the invention will be illustrated with reference to the accompanying exemplary schematic diagrams, wherein...

[0044] Figure 1 A fuel supply system according to an embodiment of the present invention is shown for supplying liquid fuel to two or more cylinders of an internal combustion piston engine. Figure 2 A fuel injector according to another embodiment of the present invention is shown. Figure 3 A fuel supply system according to another embodiment of the present invention is shown. Figure 4 A fuel injector according to another embodiment of the present invention is shown. Figure 5 A fuel supply system according to yet another embodiment of the present invention is shown. Figure 6 A fuel supply system according to yet another embodiment of the present invention is shown, and Figure 7 A fuel supply system according to yet another embodiment of the present invention is shown. Detailed Implementation

[0045] Figure 1A fuel supply system 8 for supplying liquid fuel to two or more cylinders 12 of an internal combustion piston engine 100 is schematically depicted. The fuel supply system is suitable for engines with different cylinder configurations, such as inline or V-type engines, and multiple cylinders. The fuel supply system 8 is advantageous for use with liquid fuels, one of which is a low-viscosity, low-calorific-value fuel, and the other is a high-viscosity, high-calorific-value fuel. In this regard, the low-viscosity fuel has a viscosity of <1 mm. 2 The viscosity is / s, and the low calorific value fuel has a low calorific value of <33MJ / kg. The fuel supply system 8 is particularly advantageous for use with liquid ammonia or methanol as low viscosity and low calorific value fuels, as well as light fuel oil, marine diesel or diesel as high viscosity and high calorific value fuels.

[0046] The fuel supply system 8 includes a first pressure rail 24 in which fuel is maintained at a predetermined injection pressure during operation. The first pressure rail 24 is connected to a first fuel source 16, which may include a fuel storage device and a desired fuel processing device. At least one first high-pressure fuel pump 18 is present and connected to the first fuel source and the first pressure rail 24, pressurizing the fuel to the desired pressure. The first high-pressure fuel pump 18 is preferably a piston pump configured to pump methanol, ammonia, LFO, or any mixture thereof. A plurality of first fuel injection valves 100 are arranged in the system 8, namely, first fuel injection valves 100 for each cylinder of the engine, connected to the first pressure rail 24. The first fuel injection valves 100 are preferably configured for compression ignition of fuel in the combustion chamber of the engine.

[0047] Each of the first fuel injection valves 100 is connected to a first pressure rail 24 such that the injection pressure in each cylinder is substantially equal to that of the others. The first high-pressure fuel pump 18 is preferably a common rail piston pump, capable of operating with so-called alternative fuels including methanol and ammonia, and also with LFO and mixtures of alternative fuels and LFO. The first pressure rail 24 serves as a common rail, i.e., a common fuel accumulator for all the first fuel injection valves that share a rail volume and therefore share the same pressure. In the first pressure rail, when in use, there is fuel pressurized substantially at a pressure corresponding to the injection pressure of the injection valve. The injection valves are electronically controlled valves, such that their opening timing and duration are controlled by a forced controller. The valve needle is hydraulically controlled by a control fluid, the behavior of which is controlled by an electronically controlled solenoid valve. Therefore, the timing and duration of injection are independent of the fuel pressure and the operation of the first high-pressure fuel pump 18. The first high-pressure fuel pump 18 is preferably located outside the engine, at a distance from the engine, and the conduit between the pump 18 and the engine is a double-walled high-pressure conduit designed to operate with alternative fuels, LFO, and mixtures of LFO and alternative fuels.

[0048] The fuel supply system 8 includes a second pressure rail 28 connected to a second fuel source 20. At least one second high-pressure fuel pump 22 is present, connected to the second pressure rail 28 and the second fuel source 20 arranged in the fuel supply system 8, to deliver fuel from the second fuel source and pressurize the second fuel to a desired pressure, which substantially corresponds to the injection pressure. According to the invention, fuel can be delivered from either the first fuel source 16 or the second fuel source 20 to the first fuel injection valve 100. To achieve this function, the fuel supply system 8 provides a flow path 32 between the first pressure rail 24 and the second pressure rail 28. The fuel supply system 8 also includes a control valve unit 34 arranged between the first pressure rail 24 and the second pressure rail 28 and configured to control the flow connection between the first pressure rail 24 and the second rail 28. By controlling the valve unit 34, when the valve unit 34 is open and the pressure in the second pressure rail 28 is higher than the pressure in the first pressure rail 24, the supply of second fuel from the second fuel source 20 to the first pressure rail 24 can be permitted. Accordingly, when valve unit 34 is closed, control valve unit 34 prevents the supply of second fuel from the second pressure rail 28 to the first pressure rail 24. Figure 1 In this configuration, a first pressure rail 24 is connected to a first fuel high-pressure pump 18 at its first end 24.1, and a control valve unit 34 is connected to the second end 24.2 of the pressure rail. Depicted by dashed lines, alternatively or additionally, the control valve unit 34'' may be connected to the first end 24.1 of the first pressure rail 24. The control valve unit includes a switching valve 34''. The actual storage tanks for the first and second fuels may be located in different locations and will have conditions and safety levels based on their characteristics.

[0049] According to one aspect of the invention, based on Figure 1 The fuel supply system 8 can be the only fuel injection system in the engine. In this case, the engine is operated and the fuel supply system 8 is controlled so that the fuel is ignited in the cylinder without any auxiliary fuel to promote ignition, such as ignition injection. In this embodiment, the second pressure rail 28 can also be considered as a fuel delivery pipe, because... Figure 1 There is no injector connected to the second pressure rail 28.

[0050] According to another aspect of the invention, Figure 1 The fuel supply system 8 can be composed of an auxiliary fuel injection system ( Figure 1 (Not shown) A supplemental fuel injection system in the engine. This means that the engine is operated and the fuel supply system 8 is controlled such that fuel in the cylinder is ignited with the assistance of an auxiliary fuel injection system, which is arranged to ignite so-called ignition fuel supplied to the engine cylinder. This auxiliary fuel injection system is configured to inject fuel that is more ignitable than the fuel injected via the fuel supply system 8 according to the invention.

[0051] As an optional feature, Figure 1 A third pressure rail 28' associated with a third fuel source 20' is shown. At least one third fuel high-pressure pump 22' is connected to the third pressure rail 28' and the third fuel source 20', and is arranged to pressurize the third fuel to a desired pressure. The fuel supply system 8 also includes a second control valve unit 34', which is arranged between the first pressure rail 24 and the third pressure rail 28' and configured to control the flow connection between the first pressure rail 24 and the third rail 28'. This feature enables the use of at least three different fuels in the engine by injecting any fuel into the engine via the first fuel injection valve 100.

[0052] A first check valve 36 is arranged in the system at the first end of the first pressure rail 24.1 to prevent fuel from flowing back from the first pressure rail 24 toward the first high-pressure fuel pump 18. Thus, when second fuel is introduced from the second pressure rail 28 into the first pressure rail 24, the second fuel will not flow out of the first pressure rail 24 to the first fuel source 16, nor to the first high-pressure fuel pump 18. A second check valve 38 is also present at the second end of the first pressure rail 24.2 between the last of the first fuel injection valves 100 and the control valve unit 34. The second check valve is arranged in the fuel supply system 8 to prevent fuel from flowing back from the first pressure rail 24 to the control valve unit 34 and the second pressure rail 28 when the control valve unit 34 is open. When the pressure in the second pressure rail 28 is higher than the pressure in the first pressure rail 24 and valve 34' is open, the second check valve 38 allows fuel to flow from the second pressure rail 28 to the first pressure rail 24. Therefore, regardless of whether the control valve is located at the first end or the second end of the first pressure rail, the check valves 36 and 38 can be arranged to connect with the control valve units 34' and 34 integrated into the main body of the control valve. Pressure rails 24, 28, and 28' are preferably equipped with a safety valve 42. The safety valve is arranged to prevent overpressure in the rail. It is located between the high-pressure fuel pump and the control valve unit. Its purpose is to protect the system from high-pressure pump failure and pressure relief in the event of undesirable pressure rise.

[0053] exist Figure 1 In this configuration, a first pressure rail 24 is connected to a first high-pressure fuel pump 18 at its first end 24.1, and a control valve unit 34 is connected to the second end 24.2 of the pressure rail. Depicted by dashed lines, alternatively or additionally, the control valve unit 34''' may be connected to the first end 24.1 of the first pressure rail 24. The control valve unit includes a switching valve 34''.

[0054] It should be noted that the injection valve 100 can be controlled by a computer controller, which in... Figure 1 Not shown in the image.

[0055] Figure 1 Optional features related to the invention are also disclosed. Specifically, according to one aspect of the invention, for the second pressure rail 28, there is a bypass passage 44 arranged to bypass the second fuel high-pressure pump 22. The flow direction of fluid in the bypass passage 44 is only permitted in one direction. For this purpose, the bypass passage 44 is provided with a one-way valve 46, arranged to allow flow in the direction from the high-pressure side to the low-pressure side of the pump 22. The bypass passage 44 and the one-way valve 46 can be inside or outside the high-pressure pump 22. The purpose of the bypass passage 44 is to allow flushing of the second pressure rail 28 and the first pressure rail 24 with a second fuel available from the second fuel source 20. In practice, the second fuel source 20 provides a low-pressure delivery pump 48 between the second fuel high-pressure pump 22 and the fuel tank. When the engine is stopped and it is typically necessary to flush the fuel passages in the second pressure rail 28 and the first pressure rail 24 with the second fuel before, for example, maintenance work, the second fuel may be less toxic than the first fuel. Flushing can be accomplished by opening a safety valve 42, which may have the function of opening the safety valve 42 via a solenoid (not shown). When safety valve 42 and control valve unit 34 are open, low-pressure delivery pump 48 operates, and second fuel flows into second pressure rail 28 through bypass channel 44 and check valve 46, and further flows to first pressure rail 24 via control valve unit 34, and then to tank return line (not shown) via safety valve. (This is combined with...) Figure 1 This has been disclosed, but it also applies to other embodiments.

[0056] Figure 2 An embodiment of a fuel injector 10 including a first fuel injection valve 100 arranged in a body 16 is disclosed. The injector 10 can be applied to... Figure 1 The fuel supply system shown. Body 16 includes a first injection valve 100 as the only injection valve in the body, which can be used as the only injector in the engine cylinder or as one or more injectors.

[0057] Figure 2 A direct injection valve 100 is shown. The valve 100 includes a fuel inlet 102 and a fuel passage 104, the fuel passage 104 being arranged in flow communication with the fuel inlet 102 via a flow path 106 disposed to the injector body 16. The flow path 106 is preferably provided with a so-called flow fuse 108, which prevents excessive fuel flow in the event of a valve 100 malfunction. As a preferred feature, the flow path 106 is provided with an accumulator 110 disposed within the body of the injector 10.

[0058] In a preferred embodiment, an accumulator 110 is arranged between the fuel passage 104 and the fuel inlet 102. The accumulator 110 is also arranged between the fuel inlet 102 and the flow fuse 108, such that the volume of the flow passage downstream of the flowing fuel (in the normal operating fuel flow direction) is small, and therefore the amount of fuel leakage that may occur in the event of a failure is small. The accumulator is used for only one valve, thus ensuring fuel delivery during injection. The inlet 102 of the direct injection valve 100 is arranged to be controllably flow-connected to the first fuel source 16 and the second fuel source 20, which only... Figure 2 This is illustrated schematically. Thus, the fuel injected by the direct injection valve 100 can be selected between the first fuel and the second fuel, or even a mixture of the first fuel and the second fuel can be used.

[0059] Valve 100 is provided with a valve needle 114, which is arranged to close or open fuel outlet 112 by its axial movement. Valve needle 114 is controlled by a hydraulic system 116. The hydraulic system can be implemented in various ways, utilizing the principle of generating a biasing force on the needle against the force generated by the fuel injection pressure. Figure 2 In this embodiment, the hydraulic system is provided with an inlet 118 for pressurized working fluid, which is guided through the inlet 118 to the needle housing at the end of the needle opposite the fuel outlet 112. A pressure chamber 124 is present, defined by the end of the needle 114, such that the pressure of the working fluid exerts a force on the needle 114. An outlet flow passage 122 of the hydraulic system 116 is provided with a valve 120, which, when open, releases pressure from the chamber 124, causing the needle to move upwards as shown in the figure, thereby opening the fuel outlet 112. When the valve 120 is closed, pressure builds up in the chamber 124, forcing the needle 114 back to the closed position. The valve is a solenoid valve that can be electronically operated by a computer controller. The working fluid also fills a sealed fluid chamber 126 surrounding the upper part of the needle 114 at a pressure higher than the fuel injection pressure to prevent the first fuel from flowing into the hydraulic system 116 and mixing with the working fluid.

[0060] The valve also includes a fuel outlet 112 arranged to lead to a fuel passage 104, which may include one or more injection orifices 112.1, 112.2. As clearly seen in the enlarged cross-section of the valve, the orifice may have a circular cross-section with a diameter defining the geometric cross-sectional area of ​​the orifice. In the presence of multiple orifices, the area A of the outlet 112 is the sum of the areas Ao of each orifice, i.e. .

[0061] The dimensions of the total area A of the fuel outlet are preferably set such that it is less than 8.5 mm. 2 / MW, where MW is the nominal maximum power output per cylinder, determined based on the engine specification for which the fuel injection valve is intended. The valve is a multi-fuel injection device, sized to produce substantially equal nominal maximum power per cylinder of the engine by burning either of the fuels used in practice. In practice, engines typically operate on two different liquid fuels. According to the invention, the area of ​​the fuel outlet 112 is designed based on the cylinder-specific nominal maximum power output when used with a fuel having the lowest calorific value among the various fuels. More specifically, when used with a fuel having a calorific value <33 MJ / kg, the area A of the fuel outlet 112 is less than 8.5 mm. 2 / MW, where MW is the cylinder-specific nominal maximum power. The size of area A is determined by considering fuel pressure, resulting in an injection pressure of 600-2500 bar. This pressure range covers the possible variations in fuel viscosity, and when in use, the appropriate amount of fuel in each fill can be fine-tuned by the total injection duration. In multi-fuel engines, the fuel pressures of different fuels can be selected to be close to each other, allowing different fuels to be more easily directed to the same direct injection valve operating as a multi-fuel injection valve. The fuel pressure of one of the fuels, such as the second fuel (e.g., light fuel oil, LFO), can be selected to be slightly higher than the fuel pressure of the first fuel (a fuel with a low calorific value), allowing the second fuel to be used to displace or flush portions of the fuel system shared by both fuels during fuel switching. This can be important from a safety and maintenance perspective, as some fuels with low calorific values ​​(e.g., ammonia or methanol) have toxic properties.

[0062] For example, the engine is designed to operate with at least two fuels, one of which has a lower calorific value than the other, and the direct injection valve is designed based on the fuel having the lowest calorific value of the first and second fuels. When applied to engines with smaller cylinder bores (e.g., 200 mm), in this case, determining a cylinder-specific nominal maximum power of 150 kW, the area A will be less than 1275 mm². 2 Accordingly, when applied to large-bore engines (such as 640mm), in this case, determining the cylinder-specific nominal maximum power to be 1300kW, the area A will be less than 1105mm². 2 Preferably, the area is designed to be close to the value A of the area thus obtained in order to avoid an unnecessarily long injection period; however, some compromises may be acceptable in practice as long as they do not lead to degradation of the combustion process.

[0063] Using this embodiment, an engine can be operated such that liquid fuel, a first fuel (lower calorific value), or a second fuel (higher calorific value) is injected into the engine cylinders as needed via a first fuel injection valve and ignited by compression ignition. Ignition occurs when the pressure, temperature, fuel-air mixture, and the presence of chemically active substances (free radicals) are suitable for ignition.

[0064] Figure 3 A fuel supply system 8 according to an embodiment of the present invention is disclosed. The fuel supply system 8 includes two pressure rails 24, 28 for supplying fuel for injection: a first pressure rail 24 and a second pressure rail 28. The pressure rails suppress the desired injection pressure of used fuel, and fuel injectors are connected to the pressure rails in a parallel configuration, the injectors being arranged to the cylinder head of the engine 300. The pressure rails as a whole include a first accumulator volume outside the injectors (serving as a common rail for injection valves) and a second accumulator volume inside the injectors (serving as injector-specific or injector-dedicated pressure accumulators 110), such as, for example... Figure 2 As shown.

[0065] The fuel supply system 8 for the first pressure rail 24 includes a first fuel source 16 and at least one first high-pressure fuel pump 18, the first high-pressure fuel pump 18 being arranged to pressurize the first fuel delivered from the first fuel source 16 in the first pressure rail 24 to a desired injection pressure. The first high-pressure pump 18 is located outside the engine, and the conduit from the pump 18 to the engine is a double-walled high-pressure pipe designed to operate with low-calorific-value fuels, LFO, and mixtures of LFO and low-calorific-value fuels (see [link to relevant documentation]). Figure 7 ).

[0066] The fuel supply system 8 accordingly includes a second fuel source 20 connected to a second pressure rail 28 and at least one second high-pressure fuel pump 22, the second high-pressure fuel pump 22 being arranged to pressurize the second fuel delivered from the second fuel source 20 in the second pressure rail 28 to a desired injection pressure. The fuel supply system includes a first fuel injection valve 100 and a second fuel injection valve 200 for each cylinder of the engine 100. The first fuel injection valve 100 is arranged to be connected to the first pressure rail 24 such that the first fuel injection valve 100 shares a common fuel accumulator space in the first pressure rail 24. The second fuel injection valve 200 is arranged to be connected to the second pressure rail 28 such that the second fuel injection valve 200 shares a common fuel accumulator space in the second pressure rail 28.

[0067] In the fuel supply system 8, a first fuel injection valve 100 is configured to inject main fuel into the cylinder 12, which carries most of the heat to the cylinder. The main fuel can be one of a first fuel and a second fuel; therefore, according to the invention, the main fuel can be supplied to the first fuel injection valve 100 from either a first fuel source 16 or a second fuel source 20. To achieve this function, the fuel supply system 8 provides a flow path 32 between a first pressure rail 24 and a second pressure rail 28. The dimensions of this flow path are designed to achieve the flow rate of the second fuel required when used as the main fuel. The fuel supply system is provided with a control valve unit 34, which is configured to control the flow connection between the first pressure rail 24 and the second pressure rail 28 via the flow path 32. Figure 3 In this configuration, flow path 24 includes a conduit located between a first pressure rail 24 and a second pressure rail 28. A control valve unit 34 allows the supply of second fuel from the second fuel source 20 to the first pressure rail 24 when the valve unit 34 is open and the pressure in the second pressure rail 28 is higher than the pressure in the first pressure rail 24. Conversely, when the valve unit 34 is closed, the control valve unit 34 prevents the supply of second fuel from the second pressure rail 28 to the first pressure rail 24.

[0068] The second check valve 38 allows fuel to flow from the second pressure rail 28 to the first pressure rail 24, but prevents flow in the opposite direction. When the second check valve 38 is integrated into the control valve unit 34', it can be said that the control valve unit allows fuel to flow from the second pressure rail 28 to the first pressure rail 24, but prevents flow in the opposite direction.

[0069] exist Figure 3 In the illustrated embodiment, a first high-pressure fuel pump 18 and a control valve unit are connected to opposite ends 24.1, 24.2 of a first pressure rail 24. System 8 also includes a second fuel injection valve 200 for each cylinder of the engine, connected to the second pressure rail 28. Thus, the second fuel can be used as primary fuel when injected at least via the first fuel injection valve 100, and the second fuel can be used as auxiliary fuel to facilitate ignition, such as ignition injection, when fuel from the first fuel source 16 (i.e., the first fuel) is injected via the first fuel injection valve 100 as primary fuel. Figure 3 In this configuration, the first fuel injection valve 100 and the second fuel injection valve 200 are arranged to separate the injector body into physically distinct injectors.

[0070] The fuel supply system 8 includes a sealing oil supply system 40, which is arranged to supply sealing oil to each of the first fuel injection valves 100 for sealing the fuel injection section and valve control section of the valve. In this embodiment, the sealing oil supply system connected to the second fuel source 20 and therefore to the system 8 uses a second fuel as the sealing oil. A sealing oil supply pump 21 is present, which pressurizes the sealing oil to a suitable pressure, which may differ from the pressure in the first pressure rail 24 and the second pressure rail 28.

[0071] Figure 4 An alternative embodiment of the fuel injector is disclosed, wherein a first fuel injection valve 100 and a second fuel injection valve 200 are arranged in a common fuel injector body 16. Figure 4 The illustrated embodiments are applicable to Figure 3 , Figure 5 and Figure 7 The fuel supply system 8 shown is suitable for a fuel supply system that includes two fuel sources and a pressure rail. The system then includes a fuel injector body 16 for each cylinder of the engine, and the injector body includes a first fuel injection valve 100 and a second fuel injection valve 200.

[0072] Figure 4 Fuel injector 10 is disclosed, wherein the common body 16 includes, for example, Figure 2 The diagram shows a first injection valve 100 and a second liquid fuel injection valve 200, the second liquid fuel injection valve 200 being configured to inject so-called pilot fuel into the engine, at least during normal operation using the first fuel. Typically, the amount of pilot fuel is such that it promotes and ensures compression ignition of the main fuel by influencing the environment within the main combustion chamber. It should be understood that the timing of injection and ignition can be set in many ways. The second fuel injection can occur as a single injection period or as a shorter sequential injection period, overlapping or not overlapping between the first and second fuels. Accordingly, the first fuel injection can also occur once or multiple times for a single combustion cycle. The actual onset of combustion depends largely on the timing of both the first and second fuel injections, but does not necessarily correspond directly to the start of either injection moment. Ignition occurs when pressure, temperature, fuel mixture, and the presence of chemically active substances (free radicals) are suitable for ignition and support premixed and / or diffusion combustion. Figure 4In one embodiment, the second fuel injection valve 200 includes a needle 204 for supplying a second fuel to the combustion chamber of the engine. A second fuel passage 206 is flowably connected to a second fuel inlet 201 via a second fuel supply passage 212. The second fuel supply passage 212 has a second accumulator space 214 disposed in the injector body 16 between the second fuel passage and the second fuel inlet 201. Therefore, the second fuel passage 206 is flowably connected to the second fuel inlet 201 via the second accumulator space 214. The fuel injector unit 10 also includes a hydraulically operated and electrically controlled second valve control section 210 disposed at the end of the second fuel injection valve needle 204 opposite to the needle tip. The second fuel supply section can be designed to deliver fuel to the engine's combustion chamber in an amount representing even up to 70-100% of the energy to enable the engine to operate at its design load. However, the most important function of the second fuel is to facilitate or provide ignition of the first fuel, in which case it typically represents less than 10% of the total fuel energy entering the cylinder.

[0073] from Figure 4 It is clear that the control fluid return lines from both valves are combined to a single outlet 122. This means that in this embodiment, the pressurized working fluid and sealing fluid in the direct injection valve 100 are a second fuel; however, the second fuel is supplied to the first fuel injection valve 100 through a dedicated inlet 118. Thus, the working fluid leading to the first valve can be at a different pressure than the second fuel. This also provides independent pressure control. The sealing fluid chamber 126 in the first fuel injection valve is in continuous flow connection to inlet 118. This ensures that the pressure in the sealing fluid chamber is substantially at a sufficient level and substantially free of pulsations.

[0074] When designing and / or manufacturing a fuel injection valve according to an embodiment of the invention, an injector body 16, a fuel inlet 102, and a fuel passage 114 are disposed on the injector body, which is preferably an assembly of multiple components. In the body, the fuel passage 114 is arranged in flow communication with the fuel inlet 102. A fuel outlet 112 is formed at an end of the body 16, through which fuel is injected as a spray. The fuel outlet is disposed to the fuel passage, and the outlet may be provided with one or more injection holes 112.1, 112.2. A valve needle 114 is axially movable within the body to close or open the fuel outlet 112. The desired cylinder-specific nominal maximum power for a cylinder intended to use the fuel injection valve is determined, and the fuel outlet 112 is provided with a diameter of less than 8.5 mm. 2 / MW is the area where MW is the cylinder-specific nominal maximum power when used with a fuel with the lowest calorific value expected and / or designed for use in the engine. Specifically, MW is the cylinder-specific nominal maximum power when used with a liquid fuel having a low calorific value <33MJ / kg. It should be understood that in some practical applications, the second injection valve can be implemented as an injector operated by an accelerator pump, wherein the valve needle is opened by fuel pressure and a force against the spring force provided by a dedicated accelerator pump for the injector.

[0075] Figure 5 Embodiments of the present invention have been disclosed, wherein the fuel supply system 8 is otherwise similar to Figure 3 The fuel supply system shown includes a control valve unit 34''' connected to the first end 24.1 of the first pressure rail 24 where the high-pressure pumps 18 and 22 are located. The control valve unit includes a valve that provides a continuous and controllable mixture of the second fuel and the first fuel. The control valve unit is configured to open flow communication from the second pressure rail 28 to the first pressure rail in response to a pressure difference between the second pressure rail 28 and the first pressure rail. Thus, the rate of introduction of the second fuel from the second pressure rail can be controlled by the pressure difference between the control rails.

[0076] Figure 6 Embodiments of the present invention have been disclosed, wherein the fuel supply system 8 is otherwise similar to Figure 3 The fuel supply system shown includes, except for the second pressure rail connected to the pressurized working fluid of the second fuel injection valve 200 and the first injection valve 200 (see [link]). Figure 2 and Figure 4 The first fuel injection valve 100 supplies fuel to each of the second fuel injection valves 200 at injection pressure through the inlet 118. Thus, the second fuel serves as both a sealing fluid and a control fluid, i.e., the working fluid in the first fuel injection valve 100.

[0077] Figure 6 Optional features related to the invention are also disclosed. Specifically, according to one aspect of the invention, for the first pressure rail 24, between the first check valve 36 and the first high-pressure pump 18, and upstream of the first check valve 36, a flexible portion 50, preferably a flexible tube portion, is provided in the fuel line. Since the first high-pressure fuel pump 18 is preferably a common rail piston pump capable of operating with alternative fuels, it is preferably located outside the engine. When the pump is away from the engine, it does not occupy nearby space. The flexible portion 50 isolates engine vibrations from the high-pressure pump 18. (This is combined with...) Figure 6 This feature has been disclosed, but it also applies to other embodiments.

[0078] Figure 7Various embodiments of the invention are disclosed, demonstrating an effective and versatile solution for altering the fuel source supplied to the first fuel injection valve 100. The figures show a fuel supply system 8 comprising two pressure rails 24, 28 for delivering fuel for injection: a first pressure rail 24 and a second pressure rail 28. The pressure rails suppress the desired injection pressure of spent fuel, and fuel injectors are connected to these pressure rails in a parallel configuration, the injectors being arranged to the cylinder head of the engine 300. Both pressure rails include a first accumulator volume outside the injector as a common rail for the injection valve and a second accumulator volume inside the injector as an injector-specific or injector-dedicated pressure accumulator 110, such as, for example... Figure 2 As shown. The fuel supply system 8 includes a first fuel source 16 and at least one first high-pressure fuel pump 18, which is arranged to pressurize the first fuel in the first pressure rail 24 to a desired injection pressure. Accordingly, the fuel supply system 8 includes a second fuel source 20 connected to a second pressure rail 28 and at least one second high-pressure fuel pump 22, which is arranged to pressurize the second fuel in the second pressure rail 28 to a desired injection pressure. The fuel supply system includes a first fuel injection valve 100 and a second fuel injection valve 200 for each cylinder of the engine 100. The fuel supply system 8 also includes a sealing oil supply system 40, which is arranged to supply sealing oil to each of the first fuel injection valves 100 for sealing the fuel injection section and valve control section of the valve. In this embodiment, the sealing oil supply system connected to the second fuel source 20 and thus to the system 8 uses the second fuel as the sealing oil. There is a sealing oil supply pump 21 that pressurizes the sealing oil to a suitable pressure, which may be different from the pressure in the first pressure rail 24 and the second pressure rail 28. Therefore, in this respect, the fuel supply system is similar to Figure 3 The fuel supply system shown.

[0079] When changing fuels, and during engine operation using a mixture of the first and second fuels in different ways, the fuel mixing may be significantly affected. In the figure, the fuel supply system includes a control valve unit 34, which is arranged at the second end 24.2 of the pressure rail between the first pressure rail 24 and the second pressure rail 28, with the control valve unit positioned at the second end 24.2 of the first pressure rail 24. Between the first pressure rail 24 and the second pressure rail 28, there is also a control valve unit 34''' connected to the first end 24.1 of the first pressure rail 24, with high-pressure pumps 18 and 22 located at the aforementioned end. As an alternative or supplement to one or both of the control valve units 34 and 34'', the fuel supply system 8 provides a low-pressure mixing device 19 for the first and second fuels on the low-pressure side of the first high-pressure pump 18. The mixing device 19 includes a mixing valve 16.1 at the inlet side of the first high-pressure pump 18, and the mixing valve 16.2 is connected to the first fuel source 16 and the second fuel source 20 via a first inlet passage 16.2 and a second inlet passage 16.3. The mixing device 19 is located a considerable distance from the engine, so the fuel mixing is effective, but the change in fuel composition takes a considerable amount of time to reach the engine. Therefore, there is a significant hysteresis in the system.

[0080] The control valve unit 34 at the second end 24.2 of the pressure rail is actually located at the engine, so the response to changes in the setting is quite rapid. When the control valve unit 34 is at the end of the rail opposite to the fuel inlet (high-pressure pump side), the fuel conversion occurs in reverse flow, that is, when the control valve unit 34 is open, the supply of second fuel begins from the second end of the first rail.

[0081] The control valve unit 34''' at the first end 24.1 of the pressure rail is located at the engine, so the response to setting changes is quite rapid. When the control valve unit 34''' is located at the same end of the rail as the fuel inlet (high-pressure pump side), fuel switching occurs when the control valve unit 34''' opens from the first end 24.1 of the first rail.

[0082] The appropriate combination of means to achieve fuel modification and / or the production of fuel mixtures can be selected according to the actual application needs of the fuel supply system 8 and the engine 300.

[0083] An internal combustion engine includes a fuel supply system 8 for supplying liquid fuel to its cylinders, the fuel supply system comprising: i. A first fuel source 16, comprising at least one first high-pressure fuel pump 18 and a first pressure rail 24 connected to the at least one first high-pressure fuel pump 18. ii. A first fuel injection valve 100 for each cylinder of the engine, which is connected to a first pressure rail 24. iii. A second fuel source 20, comprising at least one second high-pressure fuel pump 22 and a second pressure rail 28 connected to the high-pressure side of the at least one second high-pressure fuel pump 22. iv. A control valve unit 34 between the first pressure rail 24 and the second pressure rail 28, configured to control the flow connection between the first pressure rail 24 and the second pressure rail 28. Operate by the following steps: a. Operate the second high-pressure fuel pump 22. b. Open the control valve unit 34 to allow the second fuel to flow from the second fuel high-pressure pump 22 to the first pressure rail 24. c. The first pressure rail 24 is filled with a second fuel, which is pressurized to a predetermined minimum operating pressure. d. The pressure in the first pressure rail 24 is determined by the second high-pressure fuel pump 22. e. The engine 300 is started and operated by injecting second fuel into the cylinder of the engine using the first fuel injection valve 100.

[0084] The above method is used to start an engine using a second fuel-preferred LFO. This can be applied to systems equipped with... Figure 1 , Figure 3 , Figure 5 , Figure 6 or Figure 7 The fuel supply system of the engine.

[0085] The engine operation can be converted to operation via the combustion of the first fuel in the engine. The system 8 also includes a sealing oil supply system 40 (see...). Figure 3 , Figure 5 and Figure 7 The sealing oil supply system 40 is arranged to supply sealing oil to each of the first fuel injection valves 100, wherein when the engine 300 is operated by injecting second fuel into the cylinders of the engine via the first fuel injection valves 100, the operation of the engine 300 is switched to burning the first fuel in the engine, including the following steps: f. Activate the sealing oil supply system 40 and supply sealing oil to the sealing chamber of the first fuel injector 100. g. Start the first high-pressure fuel pump 18. h. Control valve unit 34 closes the flow connection via flow path 32 between the first pressure rail 24 and the second pressure rail 28, thereby stopping the second fuel flow from the second pressure rail 28 to the first pressure rail 24, and the pressure in the first pressure rail 24 is determined by the first high-pressure fuel pump 18. i. Fuel in the first pressure rail 24 is injected by the first fuel injection valve 100, and the fuel composition in the first pressure rail 24 changes from the second fuel to the first fuel, thereafter the first fuel is injected only by the first fuel injection valve 100, and j. The fuel is ignited by compression ignition.

[0086] When the fuel supply system 8 also includes a second fuel injection valve 200, such as Figure 3 , Figure 5 , Figure 6 and Figure 7 As disclosed herein, for each cylinder of an engine connected to a second pressure rail 28, in this method, the compression ignition of the first fuel is assisted by the second fuel injected by the second fuel injection valve 200.

[0087] After the engine 300 is started and operated by injecting the second fuel into the engine cylinders via the first fuel injection valve 100, i.e., after steps a to e are performed, the operation of the engine is switched to burning the second fuel in the engine, including the following steps.

[0088] k. Control valve unit 34 opens the flow connection via flow path 32 between the first pressure rail 24 and the second pressure rail 28, so that the second fuel flow from the second pressure rail 28 to the first pressure rail 24 begins. 1. The pressure of the first fuel in the first fuel source 16 is reduced to a level that causes the first check valve 36 to close.

[0089] m. The fuel in the first pressure rail 24 is injected by the first fuel injection valve 100, and the fuel composition in the first pressure rail 24 changes from the first fuel to the second fuel, after which the second fuel is injected only by the first fuel injection valve 100.

[0090] When the second fuel is used, the engine can be stopped, such that after steps a to m are performed, the changes in engine operation, including the engine stop command, are recorded, the operation of the second fuel injection valve is stopped, and the operation of the first fuel injection valve is stopped.

[0091] Control valve unit 34 can be configured to reduce the pressure of the second fuel when fuel flows through the control valve unit, such as Figure 5 As shown.

[0092] The fuel supply system according to the invention enables the engine to be operated in various ways. (Reference) Figure 3 When the first fuel used is methanol (MeOH) and the second fuel used is light fuel oil (LFO), an exemplary operating mode of the fuel supply system 8 is described below: Start the engine using LFO i. Opened control valve unit 34 ii. The first pressure rail 24 and the second pressure rail 28 are filled with LFO from the second fuel source 20 under high pressure.

[0093] iii. The first fuel high-pressure pump 18 is not running.

[0094] iv. Use LFO as the primary fuel to start the engine.

[0095] v. Operate only the second fuel injection valve 200 to avoid nozzle clogging and / or provide valve cooling, for example, during an injection duration of 2° crank angle.

[0096] Start the engine using an LFO to reach 20% load, then switch to MeOH.

[0097] i. Open control valve unit 34

[0098] ii. Using LFO from the second fuel source 20, fill the first pressure rail 24 and the second pressure rail 28 under high pressure.

[0099] iii. First fuel high-pressure pump 18 is not in operation.

[0100] iv. Use LFO as the main fuel to start the engine

[0101] v. To achieve a stable condition, for example, at 20% load.

[0102] vi. Start the first fuel high-pressure pump 18 and raise the pressure of the first fuel to a level that barely opens the first one-way valve 36, corresponding to the "standby state".

[0103] vii. Fuel Change Command Triggered

[0104] viii. Start the sealing oil supply pump 21. The sealing oil supply pump 21 pressurizes the sealing oil to a suitable pressure and supplies the sealing oil to the first injection valve 100.

[0105] ix. The second fuel injection valve 200 is activated to utilize LFO operation.

[0106] x. Operate the first fuel high-pressure pump 18 to raise the pressure of the first fuel to the level that opens the first check valve 36.

[0107] xi. Control valve unit 34 is closed and the first and second pressure rails are fluidly separated.

[0108] xii. The first fuel injection valve 100 injects a mixture of LFO and MeOH until only MeOH remains in the first pressure rail.

[0109] xiii. Operating the engine solely by burning MeOH

[0110] xiv. Engine load can be modified by individually controlling the injection of LFO and / or MeOH.

[0111] The engine was shut off in MeOH and the fuel system was subsequently flushed with LFO.

[0112] i. Operate the sealing oil supply pump 21, which pressurizes the sealing oil to a suitable pressure and supplies the sealing oil to the first injection valve 100.

[0113] ii. Operate the second fuel injection valve 200 using LFO.

[0114] iii. Operate the first fuel high-pressure pump 18 to bring the pressure of the first fuel to a level that opens the first check valve 36.

[0115] iv. Control valve unit 34 closes and fluidly separates the first pressure rail and the second pressure rail.

[0116] v. First fuel injection valve 100 injects only MeOH

[0117] vi. To start and receive commands to stop the engine.

[0118] vii. Combine the first and second pressure rails to open control valve unit 34

[0119] viii. Operate or shut down the first fuel high-pressure pump 18, causing the pressure of the first fuel to drop to a level that closes the first check valve 36, which in turn causes the second check valve 36 to open.

[0120] ix.MeOH burns in the engine, and the fuel in the first pressure rail becomes LFO.

[0121] x. Use LFO to stop the operation of the second fuel injection valve 200.

[0122] xi. Use LFO to stop the operation of the first fuel injection valve 100

[0123] xii. Engine stopped

[0124] While the invention has been described by way of example with reference to embodiments currently considered to be the most preferred, it will be apparent to those skilled in the art that the basic idea of ​​the invention can be implemented in many ways, along with technological advancements. Therefore, the invention and its embodiments are not limited to the examples and samples described above, but can be varied within the scope of the patent claims and their legal equivalents. When such a combination is technically feasible, the details mentioned in any of the foregoing embodiments can be used in conjunction with another embodiment.

Claims

1. A fuel supply system (8) for supplying liquid fuel to two or more cylinders (12) of an internal combustion piston engine, comprising: i. A first fuel source (16), at least one first high-pressure fuel pump (18) connected to the first fuel source (16), and a first pressure rail (24) connected to the high-pressure side of the at least one first high-pressure fuel pump (18). ii. A first fuel injection valve (100) for each cylinder of the engine, the first fuel injection valve being connected to the first pressure rail (24). iii. A second fuel source (20), at least one second high-pressure fuel pump (22) connected to the second fuel source (20), and a second pressure rail (28) connected to the high-pressure side of the at least one second high-pressure fuel pump (22). Its features iv. A control valve unit (34) is arranged between the first pressure rail (24) and the second pressure rail (28) and is configured to control the flow connection between the first pressure rail (24) and the second pressure rail (28).

2. The fuel supply system according to claim 1, characterized in that, The system also includes a second fuel injection valve (200) for each cylinder of the engine, the second fuel injection valve being connected to the second pressure rail (28).

3. The fuel supply system according to claim 2, characterized in that, The system includes a fuel injector body (38) for each cylinder of the engine, the injector body including a first fuel injection valve (100) and a second fuel injection valve (200).

4. The fuel supply system according to claim 2 or 3, characterized in that, At least one of the first fuel injection valve (100) and the second fuel injection valve (200), preferably both the first fuel injection valve (100) and the second fuel injection valve (200) are provided with a valve-specific fuel accumulator (110).

5. The fuel supply system according to any one of claims 1 to 4, characterized in that, The first pressure rail (24) is connected to the first fuel high-pressure pump (18) at its first end (24.1), and the control valve unit (34) is connected to the first end of the first pressure rail (24).

6. The fuel supply system according to any one of claims 1 to 4, characterized in that, The first fuel high-pressure pump (18) and the control valve unit (34) are connected to different locations, advantageously connected to opposite ends (24.1, 24.2) of the first pressure rail (24).

7. The fuel supply system according to any one of claims 1 to 4, characterized in that, The first high-pressure fuel pump (18) is arranged to be in an adjustable flow connection with both the first fuel source (16) and the second fuel source (20) at the inlet side of the pump (18).

8. The fuel supply system according to any one of the preceding claims, characterized in that, The system includes a sealing oil supply system (40) arranged to supply sealing oil to each of the first fuel injection valves (100) to seal the valve control section and the fuel section of the injector.

9. The fuel supply system according to claim 8, characterized in that, The sealing oil supply system (40) is connected to the second fuel source (20).

10. The fuel supply system according to any one of the preceding claims, characterized in that, The first fuel injection valve (100) includes i. Fuel inlet (102). ii. A fuel passage (104) arranged in flow communication with the fuel inlet (102), iii. A fuel outlet (112) in the fuel passage (104), the outlet (112) comprising one or more injection orifices (112.1, 112.2). iv. Valve needle (114), which is arranged to close or open the fuel outlet (112). in v. The injection valve is configured to inject liquid fuel with a low calorific value <33 MJ / kg, and the total cross-sectional area of ​​the fuel outlet (112) is less than 8.5 mm. 2 / MW, where MW is the nominal maximum power output per cylinder.

11. The fuel supply system according to claim 1 or 2, characterized in that, Fuel injection valves (100, 200) include computer-controlled injection valves.

12. The fuel supply system according to claim 1, characterized in that, The system is equipped with a first check valve (36) to prevent fuel from flowing back from the first pressure rail (24) toward the first fuel high-pressure pump (18).

13. The fuel supply system according to claim 1, 3, or 4, characterized in that, The fuel supply system (8) is equipped with a second check valve (38) to prevent fuel from flowing back from the first pressure rail (24) to the control valve unit (34).

14. The fuel supply system according to claim 1, 3, or 5, characterized in that, The second check valve (38) is arranged to be connected to the control valve unit (34).

15. The fuel supply system according to claims 2 and 4, characterized in that, The first check valve (38) is arranged to be connected to the control valve unit (34).

16. An internal combustion piston engine comprising a fuel supply system (8) according to any one of the preceding claims, the fuel supply system being configured to supply liquid fuel to a cylinder of the internal combustion piston engine, wherein a first fuel injection valve (100) is configured for compression ignition of fuel in the combustion chamber of the engine.

17. A method of operating an internal combustion engine (300), said internal combustion engine comprising a fuel supply system for supplying liquid fuel to its cylinders, wherein The fuel supply system includes i. A first fuel source (16), the first fuel source comprising at least one first high-pressure fuel pump (18) and a first pressure rail (24) connected to the at least one first high-pressure fuel pump (18). ii. A first fuel injection valve (100) for each cylinder of the engine, the first fuel injection valve being connected to the first pressure rail (24). iii. A second fuel source (20), the second fuel source comprising at least one second high-pressure fuel pump (22) and a second pressure rail (28) connected to the high-pressure side of the at least one second high-pressure fuel pump (22). iv. A control valve unit (34) between the first pressure rail (24) and the second pressure rail (28), the control valve unit being configured to control the flow connection between the first pressure rail (24) and the second pressure rail (28), and In the method a. Operate the second high-pressure fuel pump (22). b. Open the control valve unit (34) to allow the second fuel to flow from the second fuel high-pressure pump (22) to the first pressure rail (24). c. The first pressure rail (24) is filled with a second fuel, which is pressurized to a predetermined minimum operating pressure. d. The pressure in the first pressure rail (24) is determined by the second high-pressure fuel pump (22). e. The engine (300) is started and operated by injecting the second fuel into the cylinder of the engine by means of the first fuel injection valve (100).

18. The method of operating an internal combustion engine according to claim 17, wherein, A first check valve (36) arranged in the system (8) prevents fuel from flowing back from the first pressure rail (24) toward the first fuel high-pressure pump (18).

19. The method of operating an internal combustion engine according to claim 17, wherein, The system (8) further includes a sealing oil supply system (40) arranged to supply sealing oil to each of the first fuel injection valves (100), and In the method When the engine (300) is operated by injecting the second fuel into the cylinder of the engine via the first fuel injection valve (100), switching the operation of the engine (300) to burn the second fuel in the engine includes the following steps: f. Activate the sealing oil supply system (40) and supply sealing oil to the sealing chamber of the first fuel injector (100). g. Start the first high-pressure fuel pump (18). h. The control valve unit (34) closes the flow connection via the flow path (32) between the first pressure rail (24) and the second pressure rail (28), thereby stopping the second fuel flow from the second pressure rail (28) to the first pressure rail (24), and the pressure in the first pressure rail (24) is determined by the first high-pressure fuel pump (18). i. Fuel in the first pressure rail (24) is injected by the first fuel injection valve (100), and the fuel composition in the first pressure rail (24) changes from the second fuel to the first fuel, thereafter the first fuel is injected only by the first fuel injection valve (100), and j. The fuel is ignited by compression ignition.

20. The method of operating an internal combustion engine according to claim 17, wherein, The fuel supply system (8) also includes a second fuel injection valve (200) for each cylinder of the engine, the second fuel injection valve being connected to the second pressure rail (28), and in the method, the compression ignition of the first fuel is assisted by the second fuel injected by the second fuel injection valve (200).

21. The method of operating an internal combustion engine according to claim 16, wherein, After performing steps a through j, the operation of changing the engine includes the following steps: k. The control valve unit (34) opens the flow connection via the flow path (32) between the first pressure rail (24) and the second pressure rail (28), so that a second fuel flow from the second pressure rail (28) to the first pressure rail (24) begins. l. The pressure of the first fuel in the first fuel source (16) decreases to a level that causes the first check valve (36) to close. m. Fuel in the first pressure rail (24) is injected by the first fuel injection valve (100), and the fuel composition in the first pressure rail (24) changes from the first fuel to the second fuel, after which the second fuel is injected only by the first fuel injection valve (100).

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