Fuel injector, use of a fuel injector, piston engine and method of operating a piston engine

Abstract

The fuel injector (1) for direct injection of fuel into a main combustion chamber (14) of a piston engine comprises nozzle holes (2, 3, 5) for introducing fuel into the main combustion chamber (14), and a fuel injector needle (4, 6) for controlling fuel injection via the nozzle holes (2, 3, 5), the nozzle holes (2, 3, 5) comprising at least one non-axial nozzle hole (3, 5) configured to inject fuel to a direction that deviates, when projected onto a plane that is perpendicular to the axial direction of the fuel injector needle (4, 6), from the radial direction of the fuel injector needle (4, 6).

Description

[0001] Fuel injector, use of a fuel injector, piston engine and method of operating a piston engine

[0002] Technical field of the invention

[0003] The present invention concerns a fuel injector, as defined in claim 1 , and a use of such a fuel injector. The invention also concerns a piston engine and a method of operating a piston engine.

[0004] Background of the invention

[0005] Many large piston engines, such as ship and power plant engines, are operated utilizing pilot fuel injection. Main fuel is introduced into the cylinders either via the inlet channel or by means of direct injection into the cylinders. The main fuel typically forms a lean air-fuel mixture. The pilot fuel is liquid fuel, such as light fuel oil. The liquid pilot fuel is injected by means of pilot fuel injectors into the cylinders. The pilot fuel is self-ignited, and the ignition of the pilot fuel triggers or promotes combustion of the main fuel. The main fuel may be a fuel with lower reactivity and also with lower energy density and the pilot fuel may be a fuel with higher reactivity and also typically with higher energy density.

[0006] Pilot fuel injection has conventionally been used in engines that are operated using natural gas as the main fuel. However, pilot fuel injection may also be used in engines that are operated using new types of fuel, such as ammonia, methanol or hydrogen, or mixtures of different fuels.

[0007] Conventionally, the pilot fuel has been injected into the cylinder during the compression stroke close to top dead center. However, if the engine is operated with particularly low reactivity fuel and / or using very lean mixtures, a single pilot fuel injection event close to top dead center may not be sufficient for achieving reliable ignition and desired combustion phasing and speed. Such problems may be encountered, for instance, if the engine is operated using ammonia. Similar problems may also be encountered with other fuels, such as hydrogen. Although hydrogen has a high auto-ignition temperature and high octane number, its low ignition energy makes it sensitive to the formation of spontaneous self-ignition regions, which causes abnormal combustion, for example knocking. The risk of auto-ignition and other abnormal combustion can be to certain extent reduced by using leaner air-fuel mixtures, but the lean mixtures involve the risk of emissions from incomplete combustion and difficulties in the ignition.

[0008] To address the problems mentioned above and other challenges creating abnormal or incorrectly phased combustion of the main fuel, the amount of the pilot fuel may be increased and / or introduction of the pilot can be timed differently. Often the pilot fuel is introduced into the cylinder by means of multiple injection events, and some of these pilot injection events may take place very early. Although the early pilot fuel injection and the increased amount of the pilot fuel increase the reactivity of the charge, they also may lead to increased interaction between the fuel spray and the walls of the combustion chamber. This wall wetting when taking place on the cylinder liner can affect the lubrication film properties on the liner surface and may lead to contamination of the lubrication oil, which further can reduce drastically the lubrication oil lifetime. If the oil change interval is not shortened correspondingly, the lubrication oil contamination may lead to a severe damage of engine components.

[0009] Similar wall wetting problems may be encountered with direct injection of main fuel.

[0010] Summary of the invention

[0011] An object of the invention is to provide an improved fuel injector for direct injection of fuel into a main combustion chamber of a cylinder of a piston engine. Other objects of the invention are to provide a use of such a fuel injector, an improved piston engine and a method of operating a piston engine.

[0012] The fuel injector according to the invention comprises one or more nozzle holes for introducing fuel into the main combustion chamber, and at least one moveable fuel injector needle for controlling fuel injection via said one or more nozzle holes. Said one or more nozzle holes comprise at least one non-axial nozzle hole that is configured to inject fuel to a direction that deviates, when projected onto a plane that is perpendicular to the axial direction of the respective fuel injector needle, from the radial direction of said fuel injector needle.

[0013] The nozzle holes that are configured to inject fuel to a direction deviating from the radial direction of the fuel injector reduce the penetration of the fuel jet in the combustion chamber. The interaction between the fuel spray and the wall of the main combustion chamber is thus reduced and problems caused by wall wetting can be avoided.

[0014] According to an embodiment of the invention, the angle between the center axis of said at least one non-axial nozzle hole, when projected onto said plane that is perpendicular to the axial direction of the respective fuel injector needle, and the radius of said fuel injector needle intersecting with said center axis at the inner end of said non-axial nozzle hole is 10-50 degrees. The angle in the above-mentioned range keeps the penetration depth in a suitable range and helps creating a suitable swirl in the main combustion chamber.

[0015] According to an embodiment of the invention, the outer end of said at least one non-axial nozzle hole is provided with a portion having a larger diameter than the inner end of said non-axial nozzle hole. Together with the non-radial direction, the enlarged outer portion helps reducing the penetration of the fuel jet in the main combustion chamber.

[0016] According to an embodiment of the invention, the diameter of the outer end of said at least one non-axial nozzle hole is 200-400 percent of the diameter of the inner end of said non-axial nozzle hole. According to an embodiment of the invention, the diameter of the outer end of said at least one non-axial nozzle hole is 10-30 percent of the length of said non-axial nozzle hole. According to an embodiment of the invention, the length of said portion having a larger diameter is 30-70 percent of the whole length of said non-axial nozzle hole. Each of the above-mentioned parameters helps achieving a suitable jet penetration in the main combustion chamber.

[0017] According to an embodiment of the invention, the angle between the axial direction of said at least one non-axial nozzle hole and the axial direction of the respective injector needle is 30-90 degrees. This helps avoiding interaction between the fuel jet and both the cylinder wall and the piston.

[0018] According to an embodiment of the invention, said at least one non-axial nozzle hole opens inside the fuel injector into a sac volume in the uppermost third of said sac volume or into the area of the needle valve seat. Also this helps in reducing the fuel jet penetration in the main combustion chamber.

[0019] According to an embodiment of the invention, the one or more nozzle holes comprise one or more pilot fuel nozzle holes including one or more non-axial pilot fuel nozzle holes, said one or more pilot fuel nozzle holes being configured to inject liquid pilot fuel into the main combustion chamber, and said at least one fuel injector needle comprises a pilot fuel injector needle for controlling fuel injection via said one or more pilot fuel nozzle holes.

[0020] Especially when part of the pilot fuel is injected into the combustion chamber early, the pilot fuel does not ignite immediately. Therefore, it is important to avoid wall interaction. The fuel injector according to the invention is thus advantageous especially when used for pilot fuel injection, and in particular when at least part of the pilot fuel is injected very early. Also, as the pilot fuel injection duration is much shorter than the main fuel injection duration, dynamic effects play a greater role in the pilot fuel injection. This allows the behavior of the fuel jet to be adjusted by small changers in the orientation and dimensioning of the nozzle holes.

[0021] According to an embodiment of the invention, said one or more pilot fuel nozzle holes comprise an axial nozzle hole that is configured to inject fuel in the axial direction of said pilot fuel injector needle. With the axial pilot fuel hole part of the pilot fuel can be injected towards the piston, and the risk of wall wetting can be reduced further.

[0022] According to an embodiment of the invention, the fuel injector is configured so that the pilot fuel injector needle has a closed state, a fully lifted state and at least one partially lifted state, and in said at least one partially lifted state a greater portion of the pilot fuel is injected through the axial nozzle hole than in the fully lifted state. The partially lifted state can be used for early pilot fuel injection to avoid wall wetting. In the fully lifted state more fuel is injected via the non-axial pilot fuel nozzle holes to facilitate ignition of the main fuel.

[0023] According to an embodiment of the invention, the pilot fuel injector needle has at least one partially lifted state, in which pilot fuel is injected fully or mainly through the axial nozzle hole. This prevents effectively wall wetting and can be used, in particular, for very early pilot fuel injection.

[0024] According to an embodiment of the invention, the fuel injector is configured so that in the fully lifted state of the pilot fuel injector needle pilot fuel is injected fully or mainly through said one or more non-axial pilot fuel nozzle holes. This facilitates the ignition and helps avoiding contact between the pilot fuel jet and the piston.

[0025] According to an embodiment of the invention, the pilot fuel injector needle is configured to protrude into said axial nozzle hole in the closed state of the pilot fuel injector needle. The pilot fuel injector can thus have a pintle-type design. This allows, for example, to control the flow pattern through the axial nozzle hole according to the injector needle lift.

[0026] According to an embodiment of the invention, the pilot fuel injector needle is configured to protrude in the closed state out of said axial nozzle hole and the diameter of the part protruding out of said axial nozzle hole increases towards the outer end of the pilot fuel injector needle. This shape allows decreasing the flow through the axial nozzle hole at full lift of the injector needle or even fully closing the axial nozzle hole. However, even many other shapes of the protruding part could be used to achieve a desired spray pattern.

[0027] According to an embodiment of the invention, the axial nozzle hole has a larger flow area than said one or more non-axial pilot fuel nozzle holes. A relatively large amount of fuel can thus be injected through a single axial nozzle hole.

[0028] According to an embodiment of the invention, the fuel injector is configured to be positioned so that the pilot fuel injector needle is offset from the center axis of the cylinder and said one or more non-axial pilot fuel nozzle holes are positioned so that more pilot fuel is directed to the side locating farther from the wall of the cylinder. This allows to further reduce the contact between the fuel spray and the wall of the cylinder.

[0029] According to an embodiment of the invention, the fuel injector comprises a plurality of non-axial pilot fuel nozzle holes, and on the side configured to be located closer to the wall of the cylinder, the angular distance between two consecutive non-axial pilot fuel nozzle holes is greater than on the side configured to be located farther from the wall of the cylinder. More pilot fuel nozzle holes can thus be arranged on the side located farther from the wall of the cylinder and less fuel is injected close to the wall.

[0030] According to an embodiment of the invention, the fuel injector is a dual-fuel injector comprising one or more main fuel nozzle holes, one or more pilot fuel nozzle holes, a main fuel injector needle for controlling injection of main fuel via the main fuel nozzle holes, and a pilot fuel injector needle for controlling injection of pilot fuel via the pilot fuel nozzle holes.

[0031] In dual-fuel injectors at least one of the injector needles is typically offset from the center axis of the cylinder, and the nozzle holes are arranged unsymmet- rically about the center axis of the cylinder. With the nozzle hole configuration according to the invention, wall wetting can be prevented even in cases where some of the nozzle holes are located closer to the wall of the cylinder.

[0032] According to the invention, the fuel injector defined above can be used for injecting liquid pilot fuel into a main combustion chamber of a cylinder of a piston engine that uses ammonia or other gaseous fuel, ethanol or methanol as the main fuel. Ammonia, many other gaseous fuels, ethanol and methanol are fuels that may need large amounts of pilot fuel and / or very early pilot fuel injection. By using the fuel injector according to the invention for injecting the pilot fuel, interaction between the fuel and the wall of the cylinder can be reduced.

[0033] The piston engine according to the invention comprises a plurality of cylinders, a cylinder head for each cylinder of the engine, and a fuel injector defined above mounted in each cylinder head for direct fuel injection into the main combustion chamber of the cylinder.

[0034] According to an embodiment of the invention, the engine is configured to be operable using ammonia or other gaseous fuel, ethanol or methanol as main fuel.

[0035] The method according to the invention comprises the step of injecting fuel directly into a main combustion chamber of the engine using a fuel injector defined above.

[0036] According to an embodiment of the invention, the method comprises the step of introducing main fuel into a cylinder of the engine, and in said step of injecting fuel directly into the main combustion chamber, liquid pilot fuel is injected using said fuel injector into the main combustion chamber of said cylinder to facilitate the ignition and / or combustion of the main fuel. The main fuel can be ammonia or other gaseous fuel, ethanol or methanol. Brief of the

[0037] Embodiments of the invention are described below in more detail with reference to the accompanying drawings, in which

[0038] Fig. 1 shows schematically a cylinder head and a part of a cylinder of a piston engine,

[0039] Fig. 2 shows a front view of a fuel injector according to an embodiment of the invention,

[0040] Fig. 3 shows a bottom view of the fuel injector of figure 2,

[0041] Fig. 4 shows a cross-sectional view taken along line B-B of figure 3,

[0042] Fig. 5 shows an enlarged view of detail A of figure 4,

[0043] Fig. 6 shows nozzle holes of a fuel injector according to an embodiment of the invention,

[0044] Fig. 7 shows nozzle holes of a fuel injector according to another embodiment of the invention,

[0045] Fig. 8 shows a cross-sectional view of a fuel injector according to a further embodiment of the invention,

[0046] Fig. 9 shows a detail of the fuel injector of figure 8,

[0047] Fig. 10 shows a nozzle hole configuration according to an embodiment of the invention,

[0048] Fig. 11 shows an illustration of the spray pattern of fuel injected via a radial nozzle hole,

[0049] Fig. 12 shows an illustration of the spray pattern of fuel injected via a nonradial nozzle hole, and

[0050] Figs. 13A-13D show different shapes of pintle-type fuel injector needles. Detailed description of embodiments of the invention

[0051] Figure 1 shows schematically part of a cylinder 10 of a piston engine. The engine is a large piston engine. The expression “large piston engine” refers here to an engine having a cylinder diameter of at least 150 mm. The engine can be, for instance, an engine that is used as a main or an auxiliary engine in a ship or an engine that is used at a power plant for driving a generator for producing electricity. The engine is a four-stroke engine. The engine can comprise a plurality of cylinders 10. The cylinders 10 can be arranged, for instance, in-line or in a V-configuration.

[0052] The cylinder 10 can be formed by a cylinder liner 11 inserted into an engine block. Each cylinder 10 is provided with a piston 12, which is configured to move in a reciprocating manner within the cylinder 10. The piston 12 moves between top dead center (TDC) and bottom dead center (BDC). The piston 12 is connected to a crankshaft (not shown).

[0053] The upper end of each cylinder 10 is closed by a cylinder head 13. The expression “upper end” refers here to the end that is closer to top dead center. The cylinder 10 does not need to be in a vertical position, but it can be inclined from the vertical direction, such as in a V-engine.

[0054] The piston 12, the cylinder head 13 and the wall of the cylinder 10 delimit a main combustion chamber 14.

[0055] The cylinder head 13 is provided with an intake channel 15 and with an exhaust channel 16. The intake channel 15 is configured to introduce intake air into the main combustion chamber 14. Also part of the fuel used in the engine can be introduced into the main combustion chamber 14 via the intake channel 15. The intake air of the engine can be pressurized by means of one or more turbochargers. The exhaust channel 16 is configured to discharge exhaust gas from the main combustion chamber 14.

[0056] Each cylinder 10 is provided with one or more intake valves 17 and with one or more exhaust valves 18. The intake valves 17 are configured to control the supply of intake air (and possibly fuel) from the intake channel 15 into the main combustion chamber 14. The exhaust valves 18 are configured to control discharging of exhaust gas from the main combustion chamber 14. The number of intake valves 17 could be in the range of 1 to 3. Also the number of exhaust valves 18 could be in the range of 1 to 3. Each cylinder 10 can be provided, for instance, with two intake valves 17 and two exhaust valves 18. Alternatively, each cylinder 10 could be provided with three intake valves 17 and two exhaust valves 18. The opening and closing of the intake valves 17 and the exhaust valves 18 could be controlled mechanically, hydraulically, electrically, pneumatically or by means of a combination of two or more of the above mentioned means. The valve timing could be fixed or variable.

[0057] The engine further comprises at least one fuel injector 1 for each cylinder 10 of the engine. The fuel injector 1 is mounted to the cylinder head 13. The fuel injector 1 is configured to inject fuel directly into the main combustion chamber 14.

[0058] In the example of figure 1 , the fuel injector 1 is a dual-fuel injector. The dualfuel injector 1 is configured to inject both main fuel and pilot fuel into the main combustion chamber 14. The fuel injector comprises a pilot fuel nozzle 8 and a main fuel nozzle 9. The pilot fuel is liquid fuel, which refers here to a fuel that is liquid in atmospheric pressure and at a temperature of 20 °C. The pilot fuel can be, for instance, light fuel oil.

[0059] The main fuel can be liquid fuel or gaseous fuel, the term “gaseous fuel” referring here to a fuel that is gaseous in atmospheric pressure and at a temperature of 20 °C. Even if the main fuel is gaseous, it can be introduced into the fuel injector 1 in liquid phase. The main fuel can be, for instance, ammonia, ethanol or methanol. However, the main fuel could also be some other fuel requiring pilot fuel injection or benefiting from pilot fuel injection, in particular a gaseous fuel. The engine can be configured to be operable using two or more different main fuels. The engine can thus be a dual-fuel or multi-fuel engine. The engine could have different operating modes, and the pilot fuel injection could be used only in some of the operating modes. For instance, the pilot fuel injection could be used only when a certain main fuel is used.

[0060] The engine can be configured to be operable using lean mixtures, i.e. mixtures containing more air than is needed for complete combustion of the fuel. A stoichiometric mixture has just enough air for complete combustion of the fuel and an air-fuel equivalence ratio A = 1.0. The engine could be operated, for instance, using mixtures having an air-fuel equivalence ratio of at least 1.5. Figure 2 shows a fuel injector 1 according to an embodiment of the invention. Figures 3 to 6 show different views of the fuel injector 1 of figure 2. Figure 7 shows an alternative nozzle hole configuration for the fuel injector of figures 2 to 6. Figure 8 shows a fuel injector 1 according to a further embodiment of the invention. Details of fuel injectors according to embodiments of the invention are shown in figures 9 and 10. All the features of the different embodiments are not essential features of the invention. Also, features of the different embodiments can be combined and / or replaced by features of other embodiments.

[0061] The fuel injectors 1 of figures 2 and 8 are dual-fuel injectors. Each of the fuel injectors 1 is thus configured to inject two different fuels into the main combustion chamber 14. The fuel injector 1 is configured to inject into the main combustion chamber 14 main fuel and pilot fuel. The combustion of the main fuel forms a major part of the heat release in the cylinder 10, preferably at least 85 percent. The pilot fuel is injected into the main combustion chamber 14 to facilitate ignition and / or combustion of the main fuel.

[0062] In the embodiments of the figures, the fuel injector 1 comprises a main fuel injection portion and a pilot fuel injection portion. The pilot fuel injection portion comprises a plurality of pilot fuel nozzle holes 2, 3 for introducing pilot fuel into the main combustion chamber 14. The pilot fuel injection portion further comprises a moveable pilot fuel injector needle 4 (shown in figures 8-10) for controlling fuel injection via the pilot fuel nozzle holes 2, 3. The pilot fuel nozzle holes 2, 3 are arranged in a pilot fuel nozzle 8, which is configured to protrude into the main combustion chamber 14.

[0063] The main fuel injection portion comprises a plurality of main fuel nozzle holes 5 for introducing main fuel into the main combustion chamber 14. The main fuel injection portion further comprises a moveable main fuel injector needle 6 (shown only in figure 8) for controlling fuel injection via the main fuel nozzle holes 5. The main fuel nozzle holes 5 are arranged in a main fuel nozzle 9, which is configured to protrude into the main combustion chamber 14.

[0064] The fuel injector needles 4, 6 can be electrically controlled. Each fuel injector needle 4, 6 is moveable in the axial direction of the fuel injector needle 4, 6 and has at least a closed state and a lifted, open state, in which flow into a sac volume 20 and further through the respective nozzle holes 2, 3, 5 is allowed. Figure 9 shows the pilot fuel injector needle 4 in the closed state and figure 10 shows the pilot fuel injector needle 4 in a lifted state. In the closed state of the injector needle 4, 6 it rests against a needle valve seat 21 .

[0065] In a mounted state of the fuel injector 1 , the axial directions of the fuel injector needles 4, 6 can be parallel to the axial direction of the cylinder 10.

[0066] The pilot fuel nozzle holes 2, 3 comprise non-axial nozzle holes 3. The axial directions of the non-axial pilot fuel nozzle holes 3 differ from the axial direction of the pilot fuel injector needle 4. In addition, the axial direction of each of the non-axial pilot fuel nozzle hole 3 deviates, when projected onto a plane that is perpendicular to the axial direction of the pilot fuel injector needle 4, from the radial direction of the pilot fuel injector needle 4. The center axis C of the non- axial pilot fuel nozzle hole 3 does thus not intersect with the center axis of the pilot fuel injector needle 4. As the axial directions of the non-axial pilot fuel nozzle holes 3 differ from the radial direction of the pilot fuel injector needle 4, the non-axial pilot fuel nozzle holes 3 are configured to inject fuel to a direction that deviates, when projected onto a plane that is perpendicular to the axial direction of the pilot fuel injector needle 4, from the radial direction of the pilot fuel injector needle 4. Due to the alignment of the non-axial pilot fuel nozzle holes 3, wall wetting caused by the pilot fuel injection can be reduced.

[0067] The main fuel nozzle holes 5 are non-axial nozzle holes. Also the main fuel nozzle holes 5 can be configured such that the axial direction of each of the non-axial main fuel nozzle hole 5 deviates, when projected onto a plane that is perpendicular to the axial direction of the main fuel injector needle 6, from the radial direction of the main fuel injector needle 6. The non-axial main fuel nozzle holes 5 can thus be configured to inject fuel to a direction that deviates, when projected onto a plane that is perpendicular to the axial direction of the main fuel injector needle 6, from the radial direction of the main fuel injector needle 6.

[0068] In the embodiment of figures 2 to 6, the angle 0 between the center axis C of each non-axial pilot fuel nozzle hole 3, when projected onto the plane that is perpendicular to the axial direction of the pilot fuel injector needle 4, and the radius R of the pilot fuel injector needle 4 intersecting with the center axis C at the inner end 3a of the non-axial pilot fuel nozzle hole 3 is approximately 30 degrees. The angle 0 could be, for instance, in the range of 10-50 degrees. The main fuel nozzle holes 5 could be configured in a similar way. The center axis C of the non-axial pilot fuel nozzle hole 3 is offset from the center axis of the pilot fuel injector needle 4 by a distance L3 that depends on angle 0. The alignment of the non-axial pilot fuel nozzle holes 3 could thus also be described by said offset L3.

[0069] The effects of the non-radial alignment of the pilot fuel nozzle holes 3 are illustrated by figures 11 and 12. Figure 11 shows a prior art configuration, where the pilot fuel nozzle holes are arranged radially. Figure 12 shows a pilot fuel injector according to an embodiment of the invention. With the nozzle hole configuration according to the invention, the fuel jet spreads more effectively when exiting the fuel injector, which reduces the jet penetration in the main combustion chamber 14. The lines through the nozzle holes depict streamlines. The non-radial alignment of the nozzle holes 3 creates controlled cavitation in the nozzle hole 3 on the side where the wall of the nozzle hole 3 and the inner side of the pilot fuel nozzle form an acute angle. The spreading of the fuel jet is caused at least partly by the cavitation occurring in the nozzle hole 3. The spreading of the fuel jet is achieved with a nozzle hole 3 having a constant diameter. However, the effect could be further improved by providing the outer end of the nozzle hole 3 with a portion having a larger diameter than the inner end.

[0070] In the embodiments of figures 2 to 7, the outer end of each of the non-axial pilot fuel nozzle holes 3 is provided with a portion 3B having a larger diameter than the inner end 3A of the non-axial pilot fuel nozzle hole 3. The larger diameter in the outer end of the non-axial pilot fuel nozzle hole 3 reduces the penetration of the pilot fuel jet in the main combustion chamber 14.

[0071] In the embodiments of figures 2 to 7, the diameter D2 of the outer end of the non-axial pilot fuel nozzle hole 3 is approximately 300 percent of the diameter D1 of the inner end 3a of the non-axial pilot fuel nozzle hole. The diameter D2 of the outer end of the non-axial pilot fuel nozzle hole 3 could be in the range of 200-400 percent of the diameter D1 of the inner end of the non-axial pilot fuel nozzle hole 3.

[0072] In the embodiments of figures 2 to 7, the length L2 of the portion 3B having a larger diameter is approximately half of the whole length L1 of the non-axial pilot fuel nozzle hole 3. The length L2 could be 30-70 percent of the whole length L1 of the non-axial pilot fuel nozzle hole 3.

[0073] In the embodiments of figures 2 to 7, the diameter D2 of the outer end of the non-axial pilot fuel nozzle hole 3 is approximately 20 percent of the length L1 of the non-axial pilot fuel nozzle hole 3. The diameter D2 of the outer end of the non-axial pilot fuel nozzle hole 3 could be in the range of 10-30 percent of the length L1 of the non-axial pilot fuel nozzle hole 3.

[0074] In the embodiments of figures 2 to 7, each non-axial pilot fuel nozzle hole 3 is formed by an outer portion 3B and an inner portion 3A. Each of the outer portion 3B and the inner portion 3A has a constant diameter.

[0075] The outer end of each of the non-axial main fuel nozzle holes 5 could be provided in a similar way with a portion having a larger diameter than the inner end of the non-axial main fuel nozzle hole 5.

[0076] In the embodiments of figures 2 to 7, the angle y (gamma) between the axial direction C of the non-axial pilot fuel nozzle hole 3 and the axial direction of the pilot fuel injector needle 4 is 60 degrees. The angle could be, for instance, in the range of 30-90 degrees. The angle between the axial direction of the main fuel nozzle hole 5 and the axial direction of the main fuel injector needle 6 is 75 degrees. However, the angle could be in the same range as that of the non-axial pilot fuel nozzle holes 3.

[0077] The dual-fuel injectors 1 of the figures are positioned such that the center axis of the fuel injector 1 is aligned with the center axis of the cylinder 10. The pilot fuel nozzle 8 and the pilot fuel injector needle 4 are thus offset from the center axis of the cylinder 10. In the embodiment of figures 2 to 6, the non-axial pilot fuel nozzle holes 3 are positioned so that more pilot fuel is directed to the side locating farther from the wall of the cylinder 10. In figure 6, the left hand side of the fuel injector is located closer to the wall of the cylinder 10. On the left hand side, the angular distance between two consecutive non-axial pilot fuel nozzle holes 3 is greater than on the right hand side, which is located farther from the wall of the cylinder 10. The angular distance a between two consecutive non-axial pilot fuel nozzle holes 3 is 45 degrees on the side that is located farther from the wall of the cylinder 10. On the side located closer to the wall of the cylinder 10, there is an angle of 135 degrees between two consecutive non-axial pilot fuel nozzle holes 3.

[0078] Figure 7 shows an alternative embodiment, where the non-axial pilot fuel nozzle holes 3 are distributed evenly along the perimeter of the pilot fuel nozzle 8. The fuel injector 1 comprises six non-axial pilot fuel nozzle holes 3 and the angular distance a between two consecutive non-axial pilot fuel nozzle holes is thus 60 degrees.

[0079] In the embodiment of figure 8, the pilot fuel injection portion additionally comprises an axial pilot fuel nozzle hole 2 that is configured to inject fuel in the axial direction of pilot fuel injector needle 4. The pilot fuel injector needle 4 has a closed state and a fully lifted state. Between the closed state and the fully lifted state the pilot fuel injector needle 4 has partially lifted states. In at least one of the partially lifted states a greater portion of the pilot fuel is injected through the axial nozzle hole 2 than in the fully lifted state. The pilot fuel injection portion may be configured such that in at least one partially lifted state pilot fuel is injected fully or mainly through the axial pilot fuel nozzle hole 2. The pilot fuel injection portion may be further configured such that in the fully lifted state of the pilot fuel injector needle 4 pilot fuel is injected fully or mainly through the non-axial pilot fuel nozzle holes 3. The axial pilot fuel nozzle hole 2 allows directing more fuel towards the piston 12 during early pilot fuel injection events. This reduces further the wall wetting problems. In the fully lifted state of the pilot fuel injector needle 4, the pilot fuel can be directed to the upper part of the cylinder 10 to better facilitate the ignition of the main fuel.

[0080] In the embodiment of figure 8, the pilot fuel injector needle 4 is a pintle-type needle. The pilot fuel injector needle 4 is thus configured to protrude into the axial pilot fuel nozzle hole 2 in the closed state of the pilot fuel injector needle 4, as can be best seen in the enlarged view of figure 9. The axial nozzle hole 2 has a larger diameter and flow area than the non-axial pilot fuel nozzle holes

[0081] 3. This allows a sufficiently large portion of the pilot fuel to be injected via the axial nozzle hole 2. By means of a suitable shape of a pintle-type pilot fuel injector needle 4 and the axial nozzle hole 2, the fuel injector 1 can be configured to inject a different portion of the pilot fuel through the axial nozzle hole 2 and the non-axial nozzle holes 3 at different lifts of the pilot fuel injector needle

[0082] 4. Figures 13A to 13D show examples of different shapes of a protruding part 4A of the pilot fuel injector needle 4. In the embodiment of figure 13A, the protruding part 4A has a frustoconical shape and it tapers towards the outer end of the pilot fuel injector needle 4. With this shape, the flow area through the axial nozzle hole 2 increases as the lift of the pilot fuel injector needle 4 increases. A greater portion of the fuel is thus injected through the axial nozzle hole at the full lift than at partial lifts of the pilot fuel injector needle 4. Also in the embodiments of figures 13B and 13C the protruding part 4A tapers towards the outer end of the pilot fuel injector needle 4. However, in the embodiments of figures 13B and 13C the protruding part 4A does not taper continuously as in the embodiment of figure 13A but in steps. In figure 13B the protruding part 4A comprises two portions with different diameters. An outer portion of the protruding part 4A has a smaller diameter than an inner portion. In figure 13C the protruding part 4A comprises three portions with different diameters. The outermost part has the smallest diameter and the innermost portion has the largest diameter. With the pilot fuel injector needles of figures 13B and 13C the injection through the axial nozzle hole 2 changes as the function of the lift of the pilot fuel injector needle 4 in a similar way as with the pilot fuel injector needle 4 of figure 13A.

[0083] In the embodiment of figure 13D, the diameter of the protruding part 4A increases towards the outer end of the pilot fuel injector needle 4. The protruding part 4A is configured to protrude out of the axial nozzle hole 2 at least in the closed state of the pilot fuel injector needle 4. As the lift of the pilot fuel injector needle 4 increases, the flow area through the axial nozzle hole 2 decreases. A greater portion of the fuel is thus injected through the axial nozzle hole 2 at partial lifts than at the full lift of the pilot fuel injector needle 4. The protruding part 4A can be configured to even close the axial nozzle hole 2 at the full lift.

[0084] Even many other shapes of the protruding part 4A could be used to achieve the desired spray pattern at different lifts. The axial nozzle hole 2 does not need to have a constant diameter, but it can have a special shape adapted to cooperate with the protruding part 4A of the pilot fuel injector needle 4 to produce the desired spay patterns.

[0085] In the embodiment of figures 8 and 9, the non-axial pilot fuel nozzle holes 3 have a constant diameter. However, also with the pintle-type pilot fuel injector needle 4, the outer ends of the non-axial pilot fuel nozzle holes 3 could be provided with a portion having a larger diameter.

[0086] Figure 10 shows part of a fuel injector 1 according to a further embodiment of the invention. The non-axial pilot fuel nozzle holes 3 open inside the fuel injector 1 into a sac volume 20. The term “sac volume” refers to the space that is located below the needle valve seat 21 , i.e. downstream from the needle valve seat 21 . In the closed state of the pilot fuel injector needle 4, the sac volume 20 is thus in fluid communication with the main combustion chamber 14. In the embodiment of figure 10, the non-axial pilot fuel nozzle holes 3 open into the sac volume 20 close to the needle valve seat 21 . The non-axial pilot fuel nozzle holes 3 open into the uppermost fourth of the sac volume 20. The positioning of the inner ends of the non-axial pilot fuel nozzle holes 3 affects the flow from the sac volume 20 into the main combustion chamber 14 and reduces the jet penetration in the main combustion chamber 14. The non-axial pilot fuel nozzle holes 3 could open even into the area of the needle valve seat 21. Figure 10 shows nozzle holes 3 with a constant diameter, but also in the embodiment of figure 10 the nozzle holes 3 could be provided with an outer end having a larger diameter.

[0087] Although a dual-fuel injector has been described above, the fuel injector according to the invention could be a main fuel injector configured to inject main fuel, or a pilot fuel injector configured to inject pilot fuel. In case the fuel injector is a pilot fuel injector, the main fuel could be introduced into the main combustion chamber 14 by means of a separate fuel injector configured to inject the fuel directly into the main combustion chamber 14. Alternatively, the main fuel, or part of the main fuel, could be introduced into the main combustion chamber 14 via the intake channel 15.

Claims

Claims:

1. A fuel injector (1 ) for direct injection of fuel into a main combustion chamber (14) of a cylinder (10) of a piston engine, the fuel injector (1 ) comprising- one or more nozzle holes (2, 3, 5) for introducing fuel into the main combustion chamber (14), and- at least one moveable fuel injector needle (4, 6) for controlling fuel injection via said one or more nozzle holes (2, 3, 5), wherein- said one or more nozzle holes (2, 3, 5) comprise at least one non-axial nozzle hole (3, 5) that is configured to inject fuel to a direction that deviates, when projected onto a plane that is perpendicular to the axial direction of the respective fuel injector needle (4, 6), from the radial direction (R) of said fuel injector needle (4, 6).

2. The fuel injector (1 ) according to claim 1 , wherein the angle (0) between the center axis (C) of said at least one non-axial nozzle hole (3, 5), when projected onto said plane that is perpendicular to the axial direction of the respective fuel injector needle (4, 6), and the radius (R) of said fuel injector needle (4, 6) intersecting with said center axis (C) at the inner end of said non-axial nozzle hole (3, 5) is 10-50 degrees.

3. The fuel injector (1 ) according to claim 1 or 2, wherein the outer end of said at least one non-axial nozzle hole (3, 5) is provided with a portion (3B) having a larger diameter than the inner end of said non-axial nozzle hole (3, 5).

4. The fuel injector (1 ) according to claim 3, wherein the diameter (D2) of the outer end of said at least one non-axial nozzle hole (3, 5) is 200-400 percent of the diameter (D1 ) of the inner end of said non-axial nozzle hole (3, 5).

5. The fuel injector (1 ) according to claim 3 or 4, wherein the diameter (D2) of the outer end of said at least one non-axial nozzle hole (3, 5) is 10-30 percent of the length (L1 ) of said non-axial nozzle hole (3, 5).

6. The fuel injector (1 ) according to any of claims 3 to 5, wherein the length (L2) of said portion (3B) having a larger diameter is 30-70 percent of the whole length (L1 ) of said non-axial nozzle hole (3, 5).

7. The fuel injector (1 ) according to any of the preceding claims, wherein the angle (y) between the axial direction of said at least one non-axial nozzle hole (3, 5) and the axial direction of the respective injector needle (4, 6) is 30-90 degrees.

8. The fuel injector (1 ) according to any of the preceding claims, wherein said at least one non-axial nozzle hole (3, 5) opens inside the fuel injector (1 ) into a sac volume (20) in the uppermost third of said sac volume (20) or into the area of the needle valve seat (21 ).

9. The fuel injector (1 ) according to any of the preceding claims, wherein the one or more nozzle holes (2, 3, 5) comprise one or more pilot fuel nozzle holes (2, 3) including one or more non-axial pilot fuel nozzle holes(3), said one or more pilot fuel nozzle holes (2, 3) being configured to inject liquid pilot fuel into the main combustion chamber (14), and said at least one fuel injector needle (4, 6) comprises a pilot fuel injector needle(4) for controlling fuel injection via said one or more pilot fuel nozzle holes (2, 3).

10. The fuel injector (1 ) according to claim 9, wherein said one or more pilot fuel nozzle holes (2, 3) comprise an axial nozzle hole (2) that is configured to inject fuel in the axial direction of said pilot fuel injector needle (4).11 . The fuel injector (1 ) according to claim 10, wherein the fuel injector (1 ) is configured so that the pilot fuel injector needle (4) has a closed state, a fully lifted state and at least one partially lifted state, and in said at least one partially lifted state a greater portion of the pilot fuel is injected through the axial nozzle hole (2) than in the fully lifted state.

12. The fuel injector (1 ) according to claim 11 , wherein the pilot fuel injector needle (4) has at least one partially lifted state, in which pilot fuel is injected fully or mainly through the axial nozzle hole (2).

13. The fuel injector (1 ) according to claim 11 or 12, wherein the fuel injector(1 ) is configured so that in the fully lifted state of the pilot fuel injector needle (4) pilot fuel is injected fully or mainly through said one or more non-axial pilot fuel nozzle holes (3).

14. The fuel injector (1 ) according to any of claims 10 to 13, wherein the pilot fuel injector needle (4) is configured to protrude into said axial nozzle hole(2) in the closed state of the pilot fuel injector needle (4).

15. The fuel injector (1 ) according to claim 14, wherein the pilot fuel injector needle (4) is configured to protrude in the closed state out of said axial nozzle hole (2) and the diameter of the part (4A) protruding out of said axial nozzle hole (2) increases towards the outer end of the pilot fuel injector needle (4).

16. The fuel injector (1 ) according to any of claims 10 to 15, wherein the axial nozzle hole (2) has a larger flow area than said one or more non-axial pilot fuel nozzle holes (3).

17. The fuel injector (1 ) according to any of claims 9 to 16, wherein the fuel injector (1 ) is configured to be positioned so that the pilot fuel injector needle (4) is offset from the center axis of the cylinder (10) and said one or more non-axial pilot fuel nozzle holes (3) are positioned so that more pilot fuel is directed to the side locating farther from the wall of the cylinder (10).

18. The fuel injector (1 ) according to claim 17, wherein the fuel injector (1 ) comprises a plurality of non-axial pilot fuel nozzle holes (3), and on the side configured to be located closer to the wall of the cylinder (10), the angular distance (a) between two consecutive non-axial pilot fuel nozzle holes (3) is greater than on the side configured to be located farther from the wall of the cylinder (10).

19. The fuel injector (1 ) according to any of the preceding claims, wherein the fuel injector (1 ) is a dual-fuel injector comprising one or more main fuel nozzle holes (5), one or more pilot fuel nozzle holes (2, 3), a main fuel injector needle (6) for controlling injection of main fuel via the main fuel nozzle holes (5), and a pilot fuel injector needle (4) for controlling injection of pilot fuel via the pilot fuel nozzle holes (2, 3).

20. The use of a fuel injector (1 ) according to any of the preceding claims for injecting liquid pilot fuel into a main combustion chamber (14) of a cylinder (10) of a piston engine that uses ammonia or other gaseous fuel, ethanol or methanol as the main fuel.

21. A piston engine comprising a plurality of cylinders (10), a cylinder head (13) for each cylinder (10) of the engine, and a fuel injector (1 ) according to any of claims 1 to 19 mounted in each cylinder head (13) for direct fuel injection into the main combustion chamber (14) of the cylinder (10).

22. The piston engine according to claim 21 , wherein the engine is configured to be operable using ammonia or other gaseous fuel, ethanol or methanol as main fuel.

23. A method of operating a piston engine, the method comprising the step of injecting fuel directly into a main combustion chamber (14) of the engine using a fuel injector (1 ) according to any of claims 1 to 19.

24. The method of claim 23, wherein the method comprises the step of introducing main fuel into a cylinder (10) of the engine, and in said step of injecting fuel directly into the main combustion chamber (14), liquid pilot fuel is injected using said fuel injector (1 ) into the main combustion chamber (14) of said cylinder (10) to facilitate the ignition and / or combustion of the main fuel.

25. The method of claim 24, wherein the main fuel is ammonia or other gaseous fuel, ethanol or methanol.

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