A fuel valve for a large turbocharged two-stroke uniflow crosshead internal combustion engine

Abstract

Described is a fuel valve (30) for injection of fuel into a combustion chamber (14) of a large turbocharged two-stoke uniflow crosshead internal combustion engine, said fuel valve (30) comprising an elongated fuel valve housing (32) with a longitudinal axis (X), a rear end (31) and a front end (33), an elongated nozzle (40) having a bore (50) and a closed end (44), which bore (50) opens into at least one through-going opening (45), said nozzle (40) being arranged at the front end of said housing (32), an axially displaceable valve needle (35) with a hollow cut-off shaft (37) received axially displaceable between a open position and a closed position in said bore (50) in the nozzle (40) for opening and closing access to said at least one opening (45), said cut-off shaft (37) is provided with a plurality of holes (49) so as to connect said at least one opening (45) in the nozzle (40) to the interior of the hollow cut-off shaft (37) in said open position of the hollow cut-off shaft (37) and to disconnect said at least one opening (45) in the nozzle from the interior of the hollow cut-off shaft (37) in said closed position of the hollow cut-off shaft (37). The fuel valve (30) is peculiar in that said plurality of holes (49) in said cut-off shaft (37) have a total cross sectional area that is smaller than a total cross sectional area of said at least one opening (45). Hence, by providing the opening or openings (45) in the nozzle (40) with a larger total cross sectional area than the holes (49) in the cut-off shaft (37), said holes in the cut-off shaft are made to actual nozzle holes and the problems relating to development of cracks in the nozzle (40) are reduced.

Description

TECHNICAL FIELD

[0001] The present invention relates to a fuel valve for injection of fuel into a combustion chamber of a large turbocharged two-stroke uniflow crosshead internal combustion engine, said fuel valve comprising an elongated fuel valve housing with a longitudinal axis, a rear end and a front end, an elongated nozzle having a bore and a closed end, which bore opens into at least one through-going opening in said nozzle, said nozzle being arranged at the front end of said housing, an axially displaceable valve needle with a hollow cut-off shaft received axially displaceable between an open position and a closed position in said bore in the nozzle for opening and closing access to said at least one opening, said cut-off shaft is provided with a plurality of holes so as to connect said at least one opening in the nozzle to the interior of the hollow cut-off shaft in said open position of the hollow cut-off shaft and to disconnect said at least one opening in the nozzle from the interior of the hollow cut-off shaft in said closed position of the hollow cut-off shaft.

[0002] The invention also relates to a large two-stroke turbocharged uniflow scavenged internal combustion engine with crossheads comprising such a fuel valve.BACKGROUND OF THE INVENTION

[0003] A fuel valve of the kind described in the introduction is known from EP 2378109 A1. The invention differs from this known fuel valve by the feature mentioned in the characterizing part of claim 1.

[0004] Large turbocharged two-stroke uniflow crosshead internal combustion engines are typically used as prime movers in large ocean going ships, such as container ships or in power plants. Very often, these engines are operated with heavy fuel oil or with fuel oil.

[0005] The cylinders of these engines are provided with a single exhaust valve centrally placed in the cylinder cover i.e. at the top of the cylinder and with a ring of scavenge air ports at the lower region of the cylinder liner, which ports are controlled by the movement of the piston. Accordingly, the direction of transport of gas through the cylinder is always from bottom to top, hence the designation uniflow scavenged. Typically, the scavenge ports are slanted to create a swirl in the gases in the combustion chamber.

[0006] Two or three fuel valves are disposed in the cylinder cover around the centrally placed exhaust valve, with their nozzles projecting into the combustion chamber. The fuel valves are peripherally disposed (i.e. not central) in the cylinder cover with the nozzle bores of the nozzles substantially directed with the swirl, away from the cylinder wall and into the combustion chamber. Occasionally, a single nozzle hole of a nozzle is directed against the swirl in the combustion chamber.

[0007] The fuel valve comprises an elongated housing with the rear end protruding from the upper surface of the cylinder cover and with the elongated fuel valve housing extending through the cylinder cover. Attached to the front end of the elongated fuel valve housing projecting into the combustion chamber the fuel valve comprises a nozzle.

[0008] Known nozzles for large two-stroke diesel engines of the crosshead type typically have an elongated nozzle body comprising a cylindrical section with a straight main bore leading from the base of the nozzle at a rear end of the nozzle body to nozzle bores that are located near the tip or front end of the nozzle body. The tip can be round or flat but is closed since the nozzle bores must not be directed downwardly towards the piston (when the piston is at top dead center, i.e. the moment of fuel injection for a compression igniting engine, the upper surface of the piston is very close to the tip of the nozzle). Thus, the nozzle bores are mainly laterally directed relative to the center axis of the nozzle / fuel valve and typically approximately at a right angle to the center axis of the engine cylinder. Typically, each nozzle is provided with three to seven nozzle bores that are all connected to the main bore.

[0009] Typically, the known fuel valves for injecting liquid fuel are provided with an axially displaceable valve needle that cooperates with a conical valve seat for controlling the flow of fuel to the nozzle. In addition, the forward section of the valve needle comprises a cut-off shaft that is tightly received in the main bore and acts as a slide valve for closing off the nozzle bores when the valve needle is in the closed position to thereby significantly reduce the so-called sac volume, i.e. the residual volume of fuel in the space formed by the main bore in the nozzle. Without such a slide valve arrangement, the volume of residual fuel in the main bore (and in the nozzle bores) would drip into the combustion chamber after a finished fuel injection event, which has detrimental effects on fuel consumption, reliability, and emissions.

[0010] Since the nozzle body projects into the combustion chamber it is exposed to the hot combustion gases of the combustion chamber and parts of the nozzle body will therefore reach relatively high temperatures. Recently, there has been a demand for large two-stroke diesel engines to be able to handle alternative types of fuel, for example, methanol, LPG, ammonia and / or other similar fuels. Such alternative fuels are relatively clean fuels that result in significantly lower levels of sulfurous components, NOx and CO2 in the exhaust gas when used as fuel for a large low-speed uniflow turbocharged two-stroke internal combustion engine when compared with e.g. using Heavy Fuel Oil as fuel.

[0011] When such alternative fuels are injected into the combustion chamber of the cylinder through the nozzle bores evaporation of the fuel occurs resulting in a dramatic reduction of temperature due to the required evaporation heat. Thus, the incoming fuel in the main bore leaving the nozzle through the nozzle bores has a significantly lower temperature than the combustion gas surrounding the outer surface of the nozzle body. Therefore, the material of the nozzle body is exposed to a substantial temperature gradient, causing stresses in the material of the nozzle. Thus, there exists a high risk that cracks are developed in the area of the nozzle where the nozzle holes are located when exposed to high operating temperature gas in the combustion chamber and the high cooling effect of the injected fuel.

[0012] Currently, ammonia enjoys very high interest as alternative fuel for internal combustion engines mainly because it may be produced in an environmental friendly way by use of electricity from renewable energy sources, such as sun, wind and wave energy and because the combustion of ammonia per se takes place without formation of carbon containing greenhouse gases, such as carbon dioxide.

[0013] The invention also relates to a large turbocharged two-stroke uniflow crosshead internal combustion engine comprising a fuel valve as described above and claimed in the attached claims.SUMMARY OF THE INVENTION

[0014] It is an object of the present invention to provide a fuel valve of the kind mentioned in the introduction, where the above mentioned challenges relating to development of cracks in the nozzle are at least significantly reduced.

[0015] The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the figures.

[0016] According to a first aspect, there is provided a fuel valve for injection of fuel into a combustion chamber of a large turbocharged two-stroke uniflow crosshead internal combustion engine, said fuel valve comprising an elongated fuel valve housing with a longitudinal axis, a rear end and a front end, an elongated nozzle having a bore and a closed end, which bore opens into at least one through-going opening in said nozzle, said nozzle being arranged at the front end of said housing, an axially displaceable valve needle with a hollow cut-off shaft received axially displaceable between an open position and a closed position in said bore in the nozzle for opening and closing access to said at least one opening, said cut-off shaft is provided with a plurality of holes so as to connect said at least one opening in the nozzle to the interior of the hollow cut-off shaft in said open position of the hollow cut-off shaft and to disconnect said at least one opening in the nozzle from the interior of the hollow cut-off shaft in said closed position of the hollow cut-off shaft, and being characterized in that said plurality of holes in said cut-off shaft have a total cross sectional area that is smaller than a total cross sectional area of said at least one opening.

[0017] Hence, by providing the opening or openings in the nozzle with a larger total cross sectional area than the holes in the cut-off shaft, said holes in the cut-off shaft are made to actual nozzle holes and the problems relating to development of cracks in the nozzle are reduced. This is due to the fact that the cooling effect of the evaporated fuel on the material of the nozzle close to the opening(s) is hereby smaller and hence the material is exposed to a substantial smaller temperature gradient, resulting in lower stresses in the material of the nozzle and lower risk that cracks are developed in the area of the opening(s) in the nozzle.

[0018] It is preferred that said plurality of holes in said cut-off shaft are provided within the circumference(s) of said at least one opening in said open position of the hollow cut-off shaft.

[0019] In one embodiment of the invention, the at least one opening in the nozzle may be constituted of one opening having form of an elongated slot, which in the open position of the hollow cut-off shaft encircle all the holes in the cut-off shaft.

[0020] In another embodiment of the invention, the at least one opening in the nozzle may be constituted of more openings. Such openings may be elongated slots encircling two or more holes in the hollow cut-off shaft or bores each encircling one hole in the hollow cut-off shaft, when the hollow cut-off shaft is in its open position. In this way, partition walls between the openings in the nozzle are provided, hence strengthen the construction of the nozzle.

[0021] Fuel being injected through nozzle holes, which in the fuel valve according to the invention are constituted of the holes in the hollow cut-off shaft, typically diverge taking form of a conus when leaving the respective nozzle hole. The conus angle is typically larger than 10° and often about 20° or even more. Hence, in order to reduce the negative impact of the cooling effect of the injected fuel on the material of the nozzle surrounding the at least one opening in the nozzle, it is preferred that the size of the at least one opening is dimensioned so the injected fuel will not get in contact with an inner surface of the respective opening in the nozzle. In order to obtain this, the at least one opening should be provided in such a way that its inner surface is positioned outside an imaginary conus having its base at a hole in the hollow cut-off shaft and a conus angle of at least 10°, preferable at least 15° and most preferably at least 20°. The imaginary conus is preferably concentric to the respective hole in the hollow cut-off shaft.

[0022] In case the inner surface of the at least one opening only comprises generatrices that are perpendicular to the longitudinal axis of the fuel valve housing, the most critical points are the points of the edge of the at least one opening being positioned farthest away from the holes in the hollow cut-off shaft. In such case, it is preferred that this edge is positioned outside an imaginary conus having its base at a hole in the hollow cut-off shaft and a conus angle of at least 10°, preferably at least 15° and most preferably at least 20°. The imaginary conus is preferably concentric to the respective hole in the hollow cut-off shaft.

[0023] The at least one opening may in another embodiment of the invention be provided with inclined inner surface, where the cross section area increases from an end close to the hollow cut-off shaft in direction to the other end. In such an embodiment the inner surface is preferably inclined with an angle of at least 5°, preferable at least 7° and most preferably at least 10° relative to a centerline through to the respective hole in the hollow cut-off shaft. The centerline through to the respective hole in the hollow cut-off shaft is typically inclined a few degrees relative to the longitudinal axis of the fuel valve housing.

[0024] The nozzle holes in the nozzle may be distributed radially and preferably also axially over the nozzle. The nozzle holes may axially be positioned near a tip of the nozzle, which tip preferably is closed. The nozzle holes may preferably be positioned over a relatively narrow range of the perimeter of the nozzle, such as between approximately 50° to 120°. The radial orientation of the nozzle holes may further be directed away from a wall of the combustion chamber defined by a cylinder liner. Further, the nozzle holes may be directed such that they are roughly in the same direction as a direction of a swirl of scavenge air in the combustion chamber caused by the configuration of scavenge ports.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention will be explained in more details with reference to the example embodiments shown in the drawings, in which: Fig. 1 is an elevated view showing the fore end and one lateral side of a large two-stroke unit flow scavenged turbocharged engine according to an example embodiment, Fig. 2 is an elevated view showing the aft end and the other lateral side of the engine of Fig. 1, Fig. 3 is a diagrammatic representation of the engine according to Fig. 1 with its intake and exhaust systems, Fig. 4 is a sectional view of an embodiment of a fuel valve for use in the engine of Figs. 1 to 3, Fig. 5 is a sectional view of another embodiment of a fuel valve for use in the engine of Figs. 1 to 3, Fig. 6 is a sectional view a nozzle of the fuel valve of Fig. 4 or 5, Fig. 7 is a sectional view of the nozzle of Fig. 6 showing a fuel jet conus, Fig. 8, is a sectional view of the tip of the nozzle of Fig. 6 with the distal cylindrical portion of the valve needle in the closed position, Fig. 9 is a view of Fig. 8 with the distal cylindrical portion of the valve needle in the open position, and Fig. 10 is a diagrammatic representation of the position of the nozzles of the fuel valves of Fig. 5 in the cylinder cover, as seen from the side of the piston and illustrating the orientation of the nozzle bores and the resulting fuel jets. DETAILED DESCRIPTION

[0026] In the following detailed description, a fuel valve 30, and a large two-stroke engine in which the fuel valve is used will be described by the example embodiments. Figs. 1 to 3 show a large low speed turbocharged two-stroke internal combustion engine with a crankshaft 22 and crossheads 23. Fig. 3 shows a diagrammatic representation of a large low speed turbocharged two-stroke internal combustion engine with its intake and exhaust systems. In this example embodiment, the engine has six cylinders (that are formed by cylinder liners 1) in line. Large turbocharged two-stroke internal combustion engines have typically between five and sixteen cylinders in line, carried by an engine frame 24. The engine may e.g. be used as the main engine in an ocean-going vessel or as a stationary engine for operating a generator in a power station. The total output of the engine may, for example, range from 5,000 to 110,000 kW.

[0027] The engine can be a diesel (compression-igniting) engine of the two-stroke uniflow type with scavenge ports 19 in the form of a ring of piston-controlled ports at the lower region of the cylinder liners 1 and an exhaust valve 4 at the top of the cylinder liners 1. Thus, the flow in the combustion chamber 14 is always from the bottom to the top and thus the engine is of the so-called uniflow type. The scavenging air is passed from the scavenging air receiver 2 to the scavenging air ports 19 of the individual cylinders that are formed by the cylinder liners 1. A reciprocating piston 21 in the cylinder liner 1 compresses the scavenging air, fuel is injected via the nozzles of two or three fuel valves 30 that are arranged in the cylinder cover 26. Combustion follows and exhaust gas is generated. When an exhaust valve 4 is opened, the exhaust gas flows through an exhaust duct 20 associated with the cylinder 1 concerned into an exhaust gas receiver 3 and onwards through a first exhaust conduit 18 to a turbine 6 of the turbocharger 5, from which the exhaust gas flows away through a second exhaust conduit 7. Through a shaft 8, the turbine 6 drives a compressor 9 supplied via an air inlet 10.

[0028] The compressor 9 delivers pressurized charging air to a charging air conduit 11 leading to the charging air receiver 2. The scavenging air in the conduit 11 passes through an intercooler 12 for cooling the charging air. The cooled charging air passes via an auxiliary blower 16 driven by an electric motor 17 that pressurizes the charging air flow in low or partial load conditions to the charging air receiver 2. At higher loads the turbocharger compressor 9 delivers sufficient compressed scavenging air and then the auxiliary blower 16 is bypassed via a non-return valve 15.

[0029] The cylinders are formed in a cylinder liner 1. The cylinder liners 1 are carried by a cylinder frame 25 that is supported by the engine frame 24.

[0030] Fig. 4 illustrates an embodiment of the one of the two or three fuel valves 30 that are mounted in a through-going bore in the cylinder cover 26 of each cylinder with the rear end 31 of the fuel valve 30 protruding from the upper side of the cylinder cover 26 and with the front end of the nozzle 40 marginally protruding into the combustion chamber 14. The fuel valve 30 comprises an elongated fuel valve housing 32 with a nozzle holder at its forward end 33. The nozzle holder connects the nozzle 40 to the elongated fuel valve body 32. Liquid fuel (e.g. methanol, LPG, ammonia and / or other similar fuels) is delivered in a controlled and timed manner by the fuel valve 30 to the combustion chamber 14 via the nozzle 40. The fuel valve 30 illustrated in Fig. 4 has an elongated fuel valve housing 32 which at its rear end 31 has a head by which the fuel valve 30 in a known manner may be mounted in the cylinder cover 26 and be connected with a fuel pump (not shown) of the internal combustion engine.

[0031] The head at the rear end 31 includes a fuel inlet 81 which is in flow connection with a duct extending through the valve body 32. An axially displaceable valve needle 35 is journaled in the elongated fuel valve housing 32 and has an open position in which the valve needle 35 has lift from a preferably conical valve seat 36 and a closed position in which a matching section of the valve needle 35 rests in a sealing fashion on the valve seat 36. The valve needle is resiliently biased towards the closed position by resilient means, in the present embodiment formed by a helical spring 83. Lift of the valve needle 35 against the bias of the helical spring 83 is caused by the pressure of the fuel supplied to the fuel valve 30 acting on a surface of the valve needle 35 or of a piston or plunger operably connected to the valve needle 35. The elongated fuel valve housing 32 of the fuel valve 30 carries at its forward end 33 a nozzle 40. The nozzle 40 is configured to project into the combustion chamber 14 of the engine cylinder liner 1, when the fuel valve 30 is mounted on the cylinder cover 26.

[0032] The fuel valve according to the invention may also be of the hydraulic controlled type or part of a common rail fuel valve system.

[0033] In the present embodiment, the fuel valve comprises an axially movable valve needle 35 that comprises a conical section that cooperates with a conical seat 36 in the elongated fuel valve housing 32 of the fuel valve 30.

[0034] Fig. 5 illustrates a fuel valve 30 according to another embodiment, that is similar to the embodiment of Fig. 4, except for comprising a booster pump to amplify the pressure of the fuel that is supplied to the fuel valve 30. The main component of the booster pump is a booster plunger 80. The other components of the fuel valve 30 according to this embodiment and the nozzle 40 are in concept identical to the fuel valve of Fig. 4.

[0035] Fig. 10 illustrates how the nozzles 40 are peripherally positioned in the cylinder cover 26 and illustrates the direction of the fuel jets which corresponds to the direction of the axes I,II,II,IV, and V. The direction of the swirl of the gases in the combustion chamber 14 is illustrated by the curved interrupted arrow 66.

[0036] Figs. 6 to 9 illustrate the nozzle 40 and the distal section of the valve needle 35 in greater detail.

[0037] The nozzle 40 has a nozzle body that extends from a base 42 at a proximal end to a closed distal end 44 that forms the tip of the nozzle 40. A cylindrical portion 43 of the nozzle body extends from the base to the distal end 44. The nozzle body is made from a suitable material, e.g. a suitable alloy as is well known in the art.

[0038] An inlet 48 opens to the base 42 for receiving liquid fuel from the elongated fuel valve housing 32 of the fuel valve 30 when the valve needle 35 is in the open position. A single straight main bore 50 extends longitudinally from the inlet 48 into said nozzle body.

[0039] The closed distal end (tip) 44 comprises a substantially planar end surface 47 with a circular or elliptical outline. The end surface 47 connects to the cylindrical portion via a curved or rounded transition surface 46.

[0040] The axially displaceable valve needle 35 comprises a hollow cut-off shaft 37, which comprises a cylindrical end section 39 carried by a shank 38 moving in unison with the valve needle 35. The cylindrical end section 39 is received with tight fit in the straight main bore 50 and axially displaceable between a open position and a closed position in the bore 50. The hollow cut-off shaft 37 is provided with a plurality of holes 49, which are provided close to the distal end of the cylindrical end section 39. The hollow cut-off shaft 37 is rotationally positioned in the straight main bore 50 and retained in proper position e.g. by means of a pin, not shown.

[0041] The nozzle 40 according to the invention is provided with a through-going opening 45 having form of an elongated slot, which in the open position of the hollow cut-off shaft 37 encircles all the holes 49 in the cut-off shaft, see Fig. 9. In this way, the opening 45 in the nozzle 40 is connected to the interior of the hollow cut-off shaft 37 in the open position of the hollow cut-off shaft 37 and disconnected from the interior of the hollow cut-off shaft 37 in the closed position of the hollow cut-off shaft 37, see Fig. 8.

[0042] In other not shown embodiments of the invention, the nozzle may comprise more openings 45. Such openings 45 may be elongated slots encircling two or more holes 49 in the hollow cut-off shaft 37 or bores each encircling one hole 49 in the hollow cut-off shaft 37, when the hollow cut-off shaft 37 is in its open position. In this way, partition walls between the openings 45 in the nozzle 40 are provided, hence strengthen the construction of the nozzle 40.

[0043] Thus, in the fuel valve 30 according to the invention the holes 49 in the cut-off shaft 37 constitute the nozzle holes through which the fuel is injected and from the outlet which the injected fuel will diverge and enter into the combustion chamber 14 via the opening 45 in the nozzle 40. Fig. 7 shows a fuel jet from a hole 49, which enters the combustion chamber 14 in the form of a conus having a conus angle of 20°.

[0044] In Fig. 7 it is seen that the hollow cut-off shaft 37 comprises a longitudinally extending hole 34 through which the fuel flows in direction to the holes 49. In the shown embodiment, the hole 34 is drilled eccentrically relative to the longitudinal axis X of the fuel valve housing 32. In this way, the thickness of the wall of the hollow cut-off shaft 37 may be made larger in the area of the holes 49, hence the length of these holes 49, which act as nozzle holes, is made longer and thus more optimal for proper injection of the fuel. A further advantage of the larger material thickness in the area of the holes 49 is that the material may better withstand the impact of the high temperature in the combustion chamber 14. However, the hole 34 in the hollow cut-off shaft 37 may also be drilled concentric relative to the longitudinal axis X of the fuel valve housing 32. In Fig. 8 the axially displaceable valve needle 35 is shown in its closed position, where the holes 49 in the hollow cut-off shaft 37 are covered by an inner wall of the nozzle 40, thus disconnecting the opening 45 in the nozzle 40 to the interior of the hollow cut-off shaft 37.

[0045] In Fig. 9 the axially displaceable valve needle 35 is shown in its open position, where the holes 49 in the hollow cut-off shaft 37 opens into the opening 45 in the nozzle 40, thus connecting the opening 45 in the nozzle 40 to the interior of the hollow cut-off shaft 37 allowing fuel to be injected into the combustion chamber 14.

[0046] As the injected fuel evaporates and cools down dramatically with the above mentioned problems associated with stresses and possible cracks in the nozzle, it is of great importance that the injected fuel does not get into contact with the material of the nozzle or at least that the contact is reduced. Thus, according to the invention the holes 49 in the cut-off shaft 37 are provided within the circumference of the opening 45 in the open position of the hollow cut-off shaft 37, as most clearly shown in Fig. 9, and in addition the holes 49 in the cut-off shaft 37 have a total cross sectional area that is smaller than the total cross sectional area of the opening 45.

[0047] Hence, in order to reduce the negative impact of the cooling effect of the injected fuel on the material of the nozzle surrounding the opening 45 in the nozzle 40, the size of the opening 45 is dimensioned so the injected fuel will not get in contact with an inner surface of the opening 45 in the nozzle 40. As fuel being injected through the holes 49 typically diverge taking form of a conus 27 having an angle of typically larger than 10° and often larger than 20°, the opening 45 should preferably be provided in such a way that its inner surface is positioned outside an imaginary conus 27 having its base at a hole 49 in the hollow cut-off shaft 37 and a conus angle of at least 10°, preferable at least 15° and most preferably at least 20°. The imaginary conus 27 is preferably concentric to the respective hole 49 in the hollow cut-off shaft 37.

[0048] Typically, the inner upper and lower surfaces 28, 29 of the opening 45 comprise generatrices that are parallel and slightly inclined relative to the longitudinal axis X of the fuel valve housing 32. Thus, the most critical points of the opening 45 are the points of the edge 52 of the opening 45 being positioned farthest away from the holes 49 in the hollow cut-off shaft 37. In such case, it is preferred that these point are positioned outside an imaginary conus having its base at a hole 49 in the hollow cut-off shaft 37 and a conus angle of at least 10°, preferably at least 15° and most preferably at least 20°. The imaginary conus is preferably concentric to the respective hole 49 in the hollow cut-off shaft 37.

[0049] The opening 45 may, in another embodiment of the invention be provided with inclined inner surfaces, where the cross section area increases from an end close to the hollow cut-off shaft 37 in direction to the other end. In such an embodiment, not shown, the inner upper and lower surfaces of the opening 45 is preferably inclined with an angle of at least 5°, preferable at least 7° and most preferably at least 10° relative to a centerline through to the respective hole 49 in the hollow cut-off shaft 37.

Examples

Embodiment Construction

[0026]In the following detailed description, a fuel valve 30, and a large two-stroke engine in which the fuel valve is used will be described by the example embodiments. Figs. 1 to 3 show a large low speed turbocharged two-stroke internal combustion engine with a crankshaft 22 and crossheads 23. Fig. 3 shows a diagrammatic representation of a large low speed turbocharged two-stroke internal combustion engine with its intake and exhaust systems. In this example embodiment, the engine has six cylinders (that are formed by cylinder liners 1) in line. Large turbocharged two-stroke internal combustion engines have typically between five and sixteen cylinders in line, carried by an engine frame 24. The engine may e.g. be used as the main engine in an ocean-going vessel or as a stationary engine for operating a generator in a power station. The total output of the engine may, for example, range from 5,000 to 110,000 kW.

[0027]The engine can be a diesel (compression-igniting) engine of the t...

TECHNICAL FIELD

[0001] The present invention relates to a fuel valve for injection of fuel into a combustion chamber of a large turbocharged two-stroke uniflow crosshead internal combustion engine, said fuel valve comprising an elongated fuel valve housing with a longitudinal axis, a rear end and a front end, an elongated nozzle having a bore and a closed end, which bore opens into at least one through-going opening in said nozzle, said nozzle being arranged at the front end of said housing, an axially displaceable valve needle with a hollow cut-off shaft received axially displaceable between an open position and a closed position in said bore in the nozzle for opening and closing access to said at least one opening, said cut-off shaft is provided with a plurality of holes so as to connect said at least one opening in the nozzle to the interior of the hollow cut-off shaft in said open position of the hollow cut-off shaft and to disconnect said at least one opening in the nozzle from the interior of the hollow cut-off shaft in said closed position of the hollow cut-off shaft.

[0002] The invention also relates to a large two-stroke turbocharged uniflow scavenged internal combustion engine with crossheads comprising such a fuel valve.BACKGROUND OF THE INVENTION

[0003] A fuel valve of the kind described in the introduction is known from EP 2378109 A1. The invention differs from this known fuel valve by the feature mentioned in the characterizing part of claim 1.

[0004] Large turbocharged two-stroke uniflow crosshead internal combustion engines are typically used as prime movers in large ocean going ships, such as container ships or in power plants. Very often, these engines are operated with heavy fuel oil or with fuel oil.

[0005] The cylinders of these engines are provided with a single exhaust valve centrally placed in the cylinder cover i.e. at the top of the cylinder and with a ring of scavenge air ports at the lower region of the cylinder liner, which ports are controlled by the movement of the piston. Accordingly, the direction of transport of gas through the cylinder is always from bottom to top, hence the designation uniflow scavenged. Typically, the scavenge ports are slanted to create a swirl in the gases in the combustion chamber.

[0006] Two or three fuel valves are disposed in the cylinder cover around the centrally placed exhaust valve, with their nozzles projecting into the combustion chamber. The fuel valves are peripherally disposed (i.e. not central) in the cylinder cover with the nozzle bores of the nozzles substantially directed with the swirl, away from the cylinder wall and into the combustion chamber. Occasionally, a single nozzle hole of a nozzle is directed against the swirl in the combustion chamber.

[0007] The fuel valve comprises an elongated housing with the rear end protruding from the upper surface of the cylinder cover and with the elongated fuel valve housing extending through the cylinder cover. Attached to the front end of the elongated fuel valve housing projecting into the combustion chamber the fuel valve comprises a nozzle.

[0008] Known nozzles for large two-stroke diesel engines of the crosshead type typically have an elongated nozzle body comprising a cylindrical section with a straight main bore leading from the base of the nozzle at a rear end of the nozzle body to nozzle bores that are located near the tip or front end of the nozzle body. The tip can be round or flat but is closed since the nozzle bores must not be directed downwardly towards the piston (when the piston is at top dead center, i.e. the moment of fuel injection for a compression igniting engine, the upper surface of the piston is very close to the tip of the nozzle). Thus, the nozzle bores are mainly laterally directed relative to the center axis of the nozzle / fuel valve and typically approximately at a right angle to the center axis of the engine cylinder. Typically, each nozzle is provided with three to seven nozzle bores that are all connected to the main bore.

[0009] Typically, the known fuel valves for injecting liquid fuel are provided with an axially displaceable valve needle that cooperates with a conical valve seat for controlling the flow of fuel to the nozzle. In addition, the forward section of the valve needle comprises a cut-off shaft that is tightly received in the main bore and acts as a slide valve for closing off the nozzle bores when the valve needle is in the closed position to thereby significantly reduce the so-called sac volume, i.e. the residual volume of fuel in the space formed by the main bore in the nozzle. Without such a slide valve arrangement, the volume of residual fuel in the main bore (and in the nozzle bores) would drip into the combustion chamber after a finished fuel injection event, which has detrimental effects on fuel consumption, reliability, and emissions.

[0010] Since the nozzle body projects into the combustion chamber it is exposed to the hot combustion gases of the combustion chamber and parts of the nozzle body will therefore reach relatively high temperatures. Recently, there has been a demand for large two-stroke diesel engines to be able to handle alternative types of fuel, for example, methanol, LPG, ammonia and / or other similar fuels. Such alternative fuels are relatively clean fuels that result in significantly lower levels of sulfurous components, NOx and CO2 in the exhaust gas when used as fuel for a large low-speed uniflow turbocharged two-stroke internal combustion engine when compared with e.g. using Heavy Fuel Oil as fuel.

[0011] When such alternative fuels are injected into the combustion chamber of the cylinder through the nozzle bores evaporation of the fuel occurs resulting in a dramatic reduction of temperature due to the required evaporation heat. Thus, the incoming fuel in the main bore leaving the nozzle through the nozzle bores has a significantly lower temperature than the combustion gas surrounding the outer surface of the nozzle body. Therefore, the material of the nozzle body is exposed to a substantial temperature gradient, causing stresses in the material of the nozzle. Thus, there exists a high risk that cracks are developed in the area of the nozzle where the nozzle holes are located when exposed to high operating temperature gas in the combustion chamber and the high cooling effect of the injected fuel.

[0012] Currently, ammonia enjoys very high interest as alternative fuel for internal combustion engines mainly because it may be produced in an environmental friendly way by use of electricity from renewable energy sources, such as sun, wind and wave energy and because the combustion of ammonia per se takes place without formation of carbon containing greenhouse gases, such as carbon dioxide.

[0013] The invention also relates to a large turbocharged two-stroke uniflow crosshead internal combustion engine comprising a fuel valve as described above and claimed in the attached claims.SUMMARY OF THE INVENTION

[0014] It is an object of the present invention to provide a fuel valve of the kind mentioned in the introduction, where the above mentioned challenges relating to development of cracks in the nozzle are at least significantly reduced.

[0015] The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the figures.

[0016] According to a first aspect, there is provided a fuel valve for injection of fuel into a combustion chamber of a large turbocharged two-stroke uniflow crosshead internal combustion engine, said fuel valve comprising an elongated fuel valve housing with a longitudinal axis, a rear end and a front end, an elongated nozzle having a bore and a closed end, which bore opens into at least one through-going opening in said nozzle, said nozzle being arranged at the front end of said housing, an axially displaceable valve needle with a hollow cut-off shaft received axially displaceable between an open position and a closed position in said bore in the nozzle for opening and closing access to said at least one opening, said cut-off shaft is provided with a plurality of holes so as to connect said at least one opening in the nozzle to the interior of the hollow cut-off shaft in said open position of the hollow cut-off shaft and to disconnect said at least one opening in the nozzle from the interior of the hollow cut-off shaft in said closed position of the hollow cut-off shaft, and being characterized in that said plurality of holes in said cut-off shaft have a total cross sectional area that is smaller than a total cross sectional area of said at least one opening.

[0017] Hence, by providing the opening or openings in the nozzle with a larger total cross sectional area than the holes in the cut-off shaft, said holes in the cut-off shaft are made to actual nozzle holes and the problems relating to development of cracks in the nozzle are reduced. This is due to the fact that the cooling effect of the evaporated fuel on the material of the nozzle close to the opening(s) is hereby smaller and hence the material is exposed to a substantial smaller temperature gradient, resulting in lower stresses in the material of the nozzle and lower risk that cracks are developed in the area of the opening(s) in the nozzle.

[0018] It is preferred that said plurality of holes in said cut-off shaft are provided within the circumference(s) of said at least one opening in said open position of the hollow cut-off shaft.

[0019] In one embodiment of the invention, the at least one opening in the nozzle may be constituted of one opening having form of an elongated slot, which in the open position of the hollow cut-off shaft encircle all the holes in the cut-off shaft.

[0020] In another embodiment of the invention, the at least one opening in the nozzle may be constituted of more openings. Such openings may be elongated slots encircling two or more holes in the hollow cut-off shaft or bores each encircling one hole in the hollow cut-off shaft, when the hollow cut-off shaft is in its open position. In this way, partition walls between the openings in the nozzle are provided, hence strengthen the construction of the nozzle.

[0021] Fuel being injected through nozzle holes, which in the fuel valve according to the invention are constituted of the holes in the hollow cut-off shaft, typically diverge taking form of a conus when leaving the respective nozzle hole. The conus angle is typically larger than 10° and often about 20° or even more. Hence, in order to reduce the negative impact of the cooling effect of the injected fuel on the material of the nozzle surrounding the at least one opening in the nozzle, it is preferred that the size of the at least one opening is dimensioned so the injected fuel will not get in contact with an inner surface of the respective opening in the nozzle. In order to obtain this, the at least one opening should be provided in such a way that its inner surface is positioned outside an imaginary conus having its base at a hole in the hollow cut-off shaft and a conus angle of at least 10°, preferable at least 15° and most preferably at least 20°. The imaginary conus is preferably concentric to the respective hole in the hollow cut-off shaft.

[0022] In case the inner surface of the at least one opening only comprises generatrices that are perpendicular to the longitudinal axis of the fuel valve housing, the most critical points are the points of the edge of the at least one opening being positioned farthest away from the holes in the hollow cut-off shaft. In such case, it is preferred that this edge is positioned outside an imaginary conus having its base at a hole in the hollow cut-off shaft and a conus angle of at least 10°, preferably at least 15° and most preferably at least 20°. The imaginary conus is preferably concentric to the respective hole in the hollow cut-off shaft.

[0023] The at least one opening may in another embodiment of the invention be provided with inclined inner surface, where the cross section area increases from an end close to the hollow cut-off shaft in direction to the other end. In such an embodiment the inner surface is preferably inclined with an angle of at least 5°, preferable at least 7° and most preferably at least 10° relative to a centerline through to the respective hole in the hollow cut-off shaft. The centerline through to the respective hole in the hollow cut-off shaft is typically inclined a few degrees relative to the longitudinal axis of the fuel valve housing.

[0024] The nozzle holes in the nozzle may be distributed radially and preferably also axially over the nozzle. The nozzle holes may axially be positioned near a tip of the nozzle, which tip preferably is closed. The nozzle holes may preferably be positioned over a relatively narrow range of the perimeter of the nozzle, such as between approximately 50° to 120°. The radial orientation of the nozzle holes may further be directed away from a wall of the combustion chamber defined by a cylinder liner. Further, the nozzle holes may be directed such that they are roughly in the same direction as a direction of a swirl of scavenge air in the combustion chamber caused by the configuration of scavenge ports.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention will be explained in more details with reference to the example embodiments shown in the drawings, in which: Fig. 1 is an elevated view showing the fore end and one lateral side of a large two-stroke unit flow scavenged turbocharged engine according to an example embodiment, Fig. 2 is an elevated view showing the aft end and the other lateral side of the engine of Fig. 1, Fig. 3 is a diagrammatic representation of the engine according to Fig. 1 with its intake and exhaust systems, Fig. 4 is a sectional view of an embodiment of a fuel valve for use in the engine of Figs. 1 to 3, Fig. 5 is a sectional view of another embodiment of a fuel valve for use in the engine of Figs. 1 to 3, Fig. 6 is a sectional view a nozzle of the fuel valve of Fig. 4 or 5, Fig. 7 is a sectional view of the nozzle of Fig. 6 showing a fuel jet conus, Fig. 8, is a sectional view of the tip of the nozzle of Fig. 6 with the distal cylindrical portion of the valve needle in the closed position, Fig. 9 is a view of Fig. 8 with the distal cylindrical portion of the valve needle in the open position, and Fig. 10 is a diagrammatic representation of the position of the nozzles of the fuel valves of Fig. 5 in the cylinder cover, as seen from the side of the piston and illustrating the orientation of the nozzle bores and the resulting fuel jets. DETAILED DESCRIPTION

[0026] In the following detailed description, a fuel valve 30, and a large two-stroke engine in which the fuel valve is used will be described by the example embodiments. Figs. 1 to 3 show a large low speed turbocharged two-stroke internal combustion engine with a crankshaft 22 and crossheads 23. Fig. 3 shows a diagrammatic representation of a large low speed turbocharged two-stroke internal combustion engine with its intake and exhaust systems. In this example embodiment, the engine has six cylinders (that are formed by cylinder liners 1) in line. Large turbocharged two-stroke internal combustion engines have typically between five and sixteen cylinders in line, carried by an engine frame 24. The engine may e.g. be used as the main engine in an ocean-going vessel or as a stationary engine for operating a generator in a power station. The total output of the engine may, for example, range from 5,000 to 110,000 kW.

[0027] The engine can be a diesel (compression-igniting) engine of the two-stroke uniflow type with scavenge ports 19 in the form of a ring of piston-controlled ports at the lower region of the cylinder liners 1 and an exhaust valve 4 at the top of the cylinder liners 1. Thus, the flow in the combustion chamber 14 is always from the bottom to the top and thus the engine is of the so-called uniflow type. The scavenging air is passed from the scavenging air receiver 2 to the scavenging air ports 19 of the individual cylinders that are formed by the cylinder liners 1. A reciprocating piston 21 in the cylinder liner 1 compresses the scavenging air, fuel is injected via the nozzles of two or three fuel valves 30 that are arranged in the cylinder cover 26. Combustion follows and exhaust gas is generated. When an exhaust valve 4 is opened, the exhaust gas flows through an exhaust duct 20 associated with the cylinder 1 concerned into an exhaust gas receiver 3 and onwards through a first exhaust conduit 18 to a turbine 6 of the turbocharger 5, from which the exhaust gas flows away through a second exhaust conduit 7. Through a shaft 8, the turbine 6 drives a compressor 9 supplied via an air inlet 10.

[0028] The compressor 9 delivers pressurized charging air to a charging air conduit 11 leading to the charging air receiver 2. The scavenging air in the conduit 11 passes through an intercooler 12 for cooling the charging air. The cooled charging air passes via an auxiliary blower 16 driven by an electric motor 17 that pressurizes the charging air flow in low or partial load conditions to the charging air receiver 2. At higher loads the turbocharger compressor 9 delivers sufficient compressed scavenging air and then the auxiliary blower 16 is bypassed via a non-return valve 15.

[0029] The cylinders are formed in a cylinder liner 1. The cylinder liners 1 are carried by a cylinder frame 25 that is supported by the engine frame 24.

[0030] Fig. 4 illustrates an embodiment of the one of the two or three fuel valves 30 that are mounted in a through-going bore in the cylinder cover 26 of each cylinder with the rear end 31 of the fuel valve 30 protruding from the upper side of the cylinder cover 26 and with the front end of the nozzle 40 marginally protruding into the combustion chamber 14. The fuel valve 30 comprises an elongated fuel valve housing 32 with a nozzle holder at its forward end 33. The nozzle holder connects the nozzle 40 to the elongated fuel valve body 32. Liquid fuel (e.g. methanol, LPG, ammonia and / or other similar fuels) is delivered in a controlled and timed manner by the fuel valve 30 to the combustion chamber 14 via the nozzle 40. The fuel valve 30 illustrated in Fig. 4 has an elongated fuel valve housing 32 which at its rear end 31 has a head by which the fuel valve 30 in a known manner may be mounted in the cylinder cover 26 and be connected with a fuel pump (not shown) of the internal combustion engine.

[0031] The head at the rear end 31 includes a fuel inlet 81 which is in flow connection with a duct extending through the valve body 32. An axially displaceable valve needle 35 is journaled in the elongated fuel valve housing 32 and has an open position in which the valve needle 35 has lift from a preferably conical valve seat 36 and a closed position in which a matching section of the valve needle 35 rests in a sealing fashion on the valve seat 36. The valve needle is resiliently biased towards the closed position by resilient means, in the present embodiment formed by a helical spring 83. Lift of the valve needle 35 against the bias of the helical spring 83 is caused by the pressure of the fuel supplied to the fuel valve 30 acting on a surface of the valve needle 35 or of a piston or plunger operably connected to the valve needle 35. The elongated fuel valve housing 32 of the fuel valve 30 carries at its forward end 33 a nozzle 40. The nozzle 40 is configured to project into the combustion chamber 14 of the engine cylinder liner 1, when the fuel valve 30 is mounted on the cylinder cover 26.

[0032] The fuel valve according to the invention may also be of the hydraulic controlled type or part of a common rail fuel valve system.

[0033] In the present embodiment, the fuel valve comprises an axially movable valve needle 35 that comprises a conical section that cooperates with a conical seat 36 in the elongated fuel valve housing 32 of the fuel valve 30.

[0034] Fig. 5 illustrates a fuel valve 30 according to another embodiment, that is similar to the embodiment of Fig. 4, except for comprising a booster pump to amplify the pressure of the fuel that is supplied to the fuel valve 30. The main component of the booster pump is a booster plunger 80. The other components of the fuel valve 30 according to this embodiment and the nozzle 40 are in concept identical to the fuel valve of Fig. 4.

[0035] Fig. 10 illustrates how the nozzles 40 are peripherally positioned in the cylinder cover 26 and illustrates the direction of the fuel jets which corresponds to the direction of the axes I,II,II,IV, and V. The direction of the swirl of the gases in the combustion chamber 14 is illustrated by the curved interrupted arrow 66.

[0036] Figs. 6 to 9 illustrate the nozzle 40 and the distal section of the valve needle 35 in greater detail.

[0037] The nozzle 40 has a nozzle body that extends from a base 42 at a proximal end to a closed distal end 44 that forms the tip of the nozzle 40. A cylindrical portion 43 of the nozzle body extends from the base to the distal end 44. The nozzle body is made from a suitable material, e.g. a suitable alloy as is well known in the art.

[0038] An inlet 48 opens to the base 42 for receiving liquid fuel from the elongated fuel valve housing 32 of the fuel valve 30 when the valve needle 35 is in the open position. A single straight main bore 50 extends longitudinally from the inlet 48 into said nozzle body.

[0039] The closed distal end (tip) 44 comprises a substantially planar end surface 47 with a circular or elliptical outline. The end surface 47 connects to the cylindrical portion via a curved or rounded transition surface 46.

[0040] The axially displaceable valve needle 35 comprises a hollow cut-off shaft 37, which comprises a cylindrical end section 39 carried by a shank 38 moving in unison with the valve needle 35. The cylindrical end section 39 is received with tight fit in the straight main bore 50 and axially displaceable between a open position and a closed position in the bore 50. The hollow cut-off shaft 37 is provided with a plurality of holes 49, which are provided close to the distal end of the cylindrical end section 39. The hollow cut-off shaft 37 is rotationally positioned in the straight main bore 50 and retained in proper position e.g. by means of a pin, not shown.

[0041] The nozzle 40 according to the invention is provided with a through-going opening 45 having form of an elongated slot, which in the open position of the hollow cut-off shaft 37 encircles all the holes 49 in the cut-off shaft, see Fig. 9. In this way, the opening 45 in the nozzle 40 is connected to the interior of the hollow cut-off shaft 37 in the open position of the hollow cut-off shaft 37 and disconnected from the interior of the hollow cut-off shaft 37 in the closed position of the hollow cut-off shaft 37, see Fig. 8.

[0042] In other not shown embodiments of the invention, the nozzle may comprise more openings 45. Such openings 45 may be elongated slots encircling two or more holes 49 in the hollow cut-off shaft 37 or bores each encircling one hole 49 in the hollow cut-off shaft 37, when the hollow cut-off shaft 37 is in its open position. In this way, partition walls between the openings 45 in the nozzle 40 are provided, hence strengthen the construction of the nozzle 40.

[0043] Thus, in the fuel valve 30 according to the invention the holes 49 in the cut-off shaft 37 constitute the nozzle holes through which the fuel is injected and from the outlet which the injected fuel will diverge and enter into the combustion chamber 14 via the opening 45 in the nozzle 40. Fig. 7 shows a fuel jet from a hole 49, which enters the combustion chamber 14 in the form of a conus having a conus angle of 20°.

[0044] In Fig. 7 it is seen that the hollow cut-off shaft 37 comprises a longitudinally extending hole 34 through which the fuel flows in direction to the holes 49. In the shown embodiment, the hole 34 is drilled eccentrically relative to the longitudinal axis X of the fuel valve housing 32. In this way, the thickness of the wall of the hollow cut-off shaft 37 may be made larger in the area of the holes 49, hence the length of these holes 49, which act as nozzle holes, is made longer and thus more optimal for proper injection of the fuel. A further advantage of the larger material thickness in the area of the holes 49 is that the material may better withstand the impact of the high temperature in the combustion chamber 14. However, the hole 34 in the hollow cut-off shaft 37 may also be drilled concentric relative to the longitudinal axis X of the fuel valve housing 32. In Fig. 8 the axially displaceable valve needle 35 is shown in its closed position, where the holes 49 in the hollow cut-off shaft 37 are covered by an inner wall of the nozzle 40, thus disconnecting the opening 45 in the nozzle 40 to the interior of the hollow cut-off shaft 37.

[0045] In Fig. 9 the axially displaceable valve needle 35 is shown in its open position, where the holes 49 in the hollow cut-off shaft 37 opens into the opening 45 in the nozzle 40, thus connecting the opening 45 in the nozzle 40 to the interior of the hollow cut-off shaft 37 allowing fuel to be injected into the combustion chamber 14.

[0046] As the injected fuel evaporates and cools down dramatically with the above mentioned problems associated with stresses and possible cracks in the nozzle, it is of great importance that the injected fuel does not get into contact with the material of the nozzle or at least that the contact is reduced. Thus, according to the invention the holes 49 in the cut-off shaft 37 are provided within the circumference of the opening 45 in the open position of the hollow cut-off shaft 37, as most clearly shown in Fig. 9, and in addition the holes 49 in the cut-off shaft 37 have a total cross sectional area that is smaller than the total cross sectional area of the opening 45.

[0047] Hence, in order to reduce the negative impact of the cooling effect of the injected fuel on the material of the nozzle surrounding the opening 45 in the nozzle 40, the size of the opening 45 is dimensioned so the injected fuel will not get in contact with an inner surface of the opening 45 in the nozzle 40. As fuel being injected through the holes 49 typically diverge taking form of a conus 27 having an angle of typically larger than 10° and often larger than 20°, the opening 45 should preferably be provided in such a way that its inner surface is positioned outside an imaginary conus 27 having its base at a hole 49 in the hollow cut-off shaft 37 and a conus angle of at least 10°, preferable at least 15° and most preferably at least 20°. The imaginary conus 27 is preferably concentric to the respective hole 49 in the hollow cut-off shaft 37.

[0048] Typically, the inner upper and lower surfaces 28, 29 of the opening 45 comprise generatrices that are parallel and slightly inclined relative to the longitudinal axis X of the fuel valve housing 32. Thus, the most critical points of the opening 45 are the points of the edge 52 of the opening 45 being positioned farthest away from the holes 49 in the hollow cut-off shaft 37. In such case, it is preferred that these point are positioned outside an imaginary conus having its base at a hole 49 in the hollow cut-off shaft 37 and a conus angle of at least 10°, preferably at least 15° and most preferably at least 20°. The imaginary conus is preferably concentric to the respective hole 49 in the hollow cut-off shaft 37.

[0049] The opening 45 may, in another embodiment of the invention be provided with inclined inner surfaces, where the cross section area increases from an end close to the hollow cut-off shaft 37 in direction to the other end. In such an embodiment, not shown, the inner upper and lower surfaces of the opening 45 is preferably inclined with an angle of at least 5°, preferable at least 7° and most preferably at least 10° relative to a centerline through to the respective hole 49 in the hollow cut-off shaft 37.

Examples

Embodiment Construction

[0026]In the following detailed description, a fuel valve 30, and a large two-stroke engine in which the fuel valve is used will be described by the example embodiments. Figs. 1 to 3 show a large low speed turbocharged two-stroke internal combustion engine with a crankshaft 22 and crossheads 23. Fig. 3 shows a diagrammatic representation of a large low speed turbocharged two-stroke internal combustion engine with its intake and exhaust systems. In this example embodiment, the engine has six cylinders (that are formed by cylinder liners 1) in line. Large turbocharged two-stroke internal combustion engines have typically between five and sixteen cylinders in line, carried by an engine frame 24. The engine may e.g. be used as the main engine in an ocean-going vessel or as a stationary engine for operating a generator in a power station. The total output of the engine may, for example, range from 5,000 to 110,000 kW.

[0027]The engine can be a diesel (compression-igniting) engine of the t...

Claims

1. A fuel valve (30) for injection of fuel into a combustion chamber (14) of a large turbocharged two-stroke uniflow crosshead internal combustion engine, said fuel valve (30) comprising an elongated fuel valve housing (32) with a longitudinal axis (X), a rear end (31) and a front end (33), an elongated nozzle (40) having a bore (50) and a closed end (44), which bore (50) opens into at least one through-going opening (45) in said nozzle, said nozzle (40) being arranged at the front end of said housing (32), an axially displaceable valve needle (35) with a hollow cut-off shaft (37) received axially displaceable between an open position and a closed position in said bore (50) in the nozzle (40) for opening and closing access to said at least one opening (45), said cut-off shaft (37) is provided with a plurality of holes (49) so as to connect said at least one opening (45) in the nozzle (40) to the interior of the hollow cut-off shaft (37) in said open position of the hollow cut-off shaft (37) and to disconnect said at least one opening (45) in the nozzle from the interior of the hollow cut-off shaft (37) in said closed position of the hollow cut-off shaft (37), characterized in that said plurality of holes (49) in said cut-off shaft (37) have a total cross sectional area that is smaller than a total cross sectional area of said at least one opening (45).

2. A fuel valve (30) according to claim 1, characterized in that said plurality of holes (49) in said cut-off shaft (37) are provided within the circumference(s) of said at least one opening (45) in said open position of the hollow cut-off shaft (37).

3. A fuel valve (30) according to claim 1 or 2, characterized in that the at least one opening (45) in the nozzle (40) is constituted of one opening having form of an elongated slot, which in the open position of the hollow cut-off shaft (37) encircles all the holes (49) in the cut-off shaft (37).

4. A fuel valve (30) according to claim 1, 2 or 3, characterized in that the at least one opening (45) in the nozzle (40) is constituted of more openings.

5. A fuel valve (30) according to claim 4, characterized in that such openings (45) are elongated slots encircling two or more holes (49) in the hollow cut-off shaft (37), when the hollow cut-off shaft (37) is in its open position.

6. A fuel valve (30) according to claim 4, characterized in that such openings (45) are bores each encircling one hole (49) in the hollow cut-off shaft (37), when the hollow cut-off shaft (37) is in its open position.

7. A fuel valve (30) according to any one of claims 1 to 3, characterized in that an edge (52) of the at least one opening (45) being positioned farthest away from the holes (49) in the hollow cut-off shaft (37) is positioned outside an imaginary conus having its base at a hole (49) in the hollow cut-off shaft (37) and a conus angle of at least 10°, preferably at least 15° and most preferably at least 20°, where the imaginary conus preferably is concentric to the respective hole (49) in the hollow cut-off shaft (37).

8. A fuel valve (30) according to any one of claims 1 to 7, characterized in that the at least one opening (45) is provided with inclined inner surface, where the cross section area increases from an end close to the hollow cut-off shaft (37) in direction to the other end.

9. A fuel valve (30) according to claim 8, characterized in that the inner surface is inclined with an angle of at least 5°, preferable at least 7° and most preferably at least 10° relative to a centerline through to the respective hole (49) in the hollow cut-off shaft (37).

10. A large turbocharged two-stroke uniflow crosshead internal combustion engine comprising a fuel valve (30) as defined in any of the preceding claims.

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