Fuel injector in a combustion engine with prechamber

Abstract

An engine system (40), comprising a compression-ignition engine (20) with at least one cylinder and a cylinder head (23) defining one prechamber (24) in communication with the cylinder, and a fuel injector (1) for injecting liquid fuel therein, the engine system further comprising a high-pressure liquid fuel source configured to supply fuel at pressures above 60 bar to the fuel injector, the fuel injector (1) comprising: - a housing (2) extending axially along an injector axis (A) from a proximal end (2.1) to a distal end (2.2) and having a nozzle portion (3) at the distal end (2.2) with a plurality of spray holes (5), each spray hole (5) being aligned to a spray-hole axis (C) of the respective spray hole (5) and extending from an inlet (5.1) inside the housing (2) to an outlet (5.2), and - a pintle (8) being axially movable between an open position and a closed position in which it closes the spray holes (5), wherein a plurality of spray holes (5) are co-aligned spray holes (5) having spray-hole axes (C) that are inclined by less than 10°, preferably less than 6°, with respect to a common alignment axis (B).

Description

FUEL INJECTOR IN A COMBUSTION ENGINE WITH PRECHAMBERTechnical Field

[0001] The invention relates to a fuel injector for injecting fuel into a prechamber of an engine.Background Art

[0002] Fuel injectors are used in combustion engines to inject fuel e.g., into a runner of an air intake manifold ahead of a cylinder intake valve or directly into the combustion chamber of an engine cylinder. It is also known to inject fuel into a prechamber located in a cylinder head outside of the cylinder. The prechamber communicates with the cylinder so that fuel can also pass from the prechamber to the cylinder. In the prechamber, a fuel-air mixture is formed which can be ignited by a glow plug or a spark plug.

[0003] According to one known injector design, a pintle is disposed within an injector housing and is movable between a closed position, in which it (or a ball that is fixed to the pintle) closes a nozzle at one end of the injector housing, and an open position, in which it is moved away from the nozzle, thereby enabling fuel injection. The nozzle has at least one, often a plurality of injector holes or spray holes that traverse the wall of the injector housing. For each spray hole, a spray-hole axis can be defined which characterizes the general direction of the spray hole and may be a symmetry axis thereof. During operation, fuel traverses the spray hole and forms a plume of fuel droplets outside of the injector housing. In order to achieve an optimum fuel distribution, various spray holes are directed to significantly different directions, i.e., their respective spray-hole axes are pairwise separated by relatively large angles. Also, in order to avoid unburnt fuel wetting e.g., the cylinder wall, the spray holes may be designed to limit the effective length of the individual plumes.Technical Problem

[0004] It is thus an object of the present invention to provide an improved fuel injector for injection into a prechamber.

[0005] This problem is solved by a fuel injector according to claim 1 and by an engine system according to claim 15.General Description of the Invention

[0006] The invention provides an engine system comprising a compressionignition engine with at least one engine cylinder, generally a plurality of engine cylinders, and a cylinder head defining a prechamber (one per engine cylinder), and each prechamber comprising a respective fuel injector for injecting fuel therein, the engine system further comprising a high-pressure liquid fuel source configured to supply fuel at pressures above 60 bar, preferably above 100 bar, to the fuel injectors.

[0007] It will be understood that the prechamber is located in a cylinder head of the engine and is in communication with a respective engine cylinder. Fuel is injected into the prechamber, where it mixes with air. The fuel-air mixture can be ignited inside the prechamber and / or inside the cylinder (more likely).

[0008] The fuel injector comprises a housing extending axially along an injector axis from a proximal end to a distal end and having a nozzle portion at the distal end with a plurality of spray holes, each spray hole being aligned to a spray-hole axis of the respective spray hole and extending from an inlet inside the nozzle housing to an outlet. The housing may comprise a plurality of interconnected pieces. It may define an inner cavity for containing and guiding liquid fuel. It extends along an injector axis, which may be a symmetry axis of at least some parts of the injector. With respect to the injector axis, one can define a proximal end and a distal end. During operation of the fuel injector, fuel flows towards the distal end at which a nozzle portion is disposed. The nozzle portion, which may be formed by a dedicated element that can be referred to as a nozzle housing, is adapted for ejecting fuel from the injector. For this purpose, it comprises a plurality of spray holes. The spray holes could also be referred to as orifices, ejection holes, or the like. Each spray hole is aligned to a spray-hole axis of the respective spray hole. The spray-hole axis is preferably a symmetry axis of the spray hole. It should be noted that the spray hole axes of different spray holes are not identical, although they may be parallel to each other. The spray-hole axis corresponds to a general direction of motion of the fuel from the inside to the outside, although the precise motion of the fuel may be more complicated. Each spray hole extends from an inlet inside of the housing to an outlet. The inlet is in direct communication with the inside of the housing, e.g., with the abovementioned inner cavity. During an injection, fuel traverses the spray hole from the inlet to the outlet, thereby exiting the housing. As will be apparent from the following discussion, the invention provides an improved approach of fuel injection in a prechamber engine, where the injector has a simple design but allows high pressure operation and forming a straight plume of pulverized fuel.

[0009] The fuel injector further comprises a pintle being axially movable between an open position and a closed position in which it closes the spray holes. The pintle may have an axially extending pintle shaft that is normally cylindrical and elongate, with a length of the pintle shaft corresponding to e.g., more than 10 times its diameter. In some embodiments, a ball is provided at a distal end of the pintle. The ball may be fixed to the pintle distal end, whereby it may also be considered as a part of the pintle. In the closed position, the pintle (or the ball, respectively) closes the spray holes and prevents fuel from being ejected. In a typical embodiment, the pintle / ball engages a nozzle seat at the distal end of the housing, thereby closing the nozzle. The spray holes are then formed within the nozzle seat, which is part of the nozzle portion, e.g., the nozzle housing. The pintle can be moved axially to an open position in which the nozzle is open, and fuel can be ejected. Specifically, the fuel injector is an inward opening injector, so that the open position is a proximal position, and the closed position is a distal position. In embodiments, the nozzle seat comprises a dome portion that extends distally, and in which the spray holes are arranged. An annular sealing surface is provided at the basis of the dome, surrounding all of the spray holes (and upstream thereof). Accordingly, the ball resting on the annular sealing surface in closed position prevents fuel flow towards the spray holes. The internal volume defined by the dome is conventionally referred to as sac.

[0010] A plurality of spray holes are co-aligned spray holes having spray-hole axes that are inclined by less than 10°, preferably less than 6°, with respect to a common alignment axis. These co-aligned spray holes are aligned to the alignment axis in the sense that their spray-hole axes are almost or exactly parallel to the alignment axis. In other words, the alignment axis characterizes the alignment of the co-aligned spray holes. During operation, fuel is ejected from these spray holes at least approximately in the same direction. In an injector according to prior art, in which the spray-hole axes differ significantly, every spray hole generates a plume of fuel droplets, and the plumes of different spray holes are usually well separated. The co-aligned spray holes of the inventive injector, on the other hand, may collectively generate a quasi-singular plume. While the fuel is ejected individually through each spray hole and individual plumes are generated close to the outlets, the individual plumes then merge to effectively form a single plume. This plume comprises fuel originating from each of the co-aligned spray holes. With this configuration, it is possible to generate a comparatively long plume that comprises a high amount of fuel. However, the individual spray hole can be relatively small, e.g., compared to a single spray hole that can eject the same amount of fuel during the same time. Without limiting the invention to this effect, the atomization of the liquid fuel may be better with a plurality of smaller spray holes than with a single larger spray hole.

[0011] In a preferred embodiment, the fuel injector further comprises an armature that is axially movable from a passive position to an active position, thereby moving the pintle to the open position, and a magnetic coil for magnetically attracting the armature towards the active position. The armature is movable along the injector axis between the passive position and the active position. Here and the following, "along the injector axis" particularly, but not exclusively, means "parallel to the injector axis". More generally, it means "at least partially in the direction of the injector axis". The armature, like the pintle, is disposed inside the housing. The armature is configured to cooperate with the pintle with to move it by mechanical coupling. As the armature moves towards the active position, it moves the pintle towards the open position. As it moves towards the passive position, the pintle can move or is moved to the closed position. Since the injector is inward opening, the active position is a proximal position, and the passive position is a distal position. Preferably, the armature is moved to the passive position by the force of a return spring. The magnetic coil is adapted for magnetically attracting the armature towards the active position. Preferably, the magnetic coil magnetizes a pole piece which enhances the magnetic field to attract the armature. In such a configuration, the pole piece is disposed in the direction of the active position, i.e. , proximal of the armature. The magnetic coil can be activated by a coil current, which gives rise to a magnetic field.

[0012] Generally, the number of co-aligned spray holes is not limited within the scope of the invention. However, according to a typical embodiment, the injector comprises between three and seven spray holes. It is difficult to form a stable, coherent plume with only two spray holes. On the other hand, more than seven co-aligned spray holes are difficult to provide in the limited space of a typical nozzle portion. This could complicate the production of the fuel injector and lead to increased costs. More specifically, the fuel injector may comprise between four and six co-aligned spray holes. A particularly preferred embodiment provides a total of five co-aligned spray holes.

[0013] Preferably, the outlet of at least one co-aligned spray hole communicates with a counterbore, which counterbore has a larger cross-section than the spray hole at the outlet. More preferably, this applies to every co-aligned spray hole. At its outlet, the spray hole communicates with a counterbore. One could also say that the spray hole is connected to the counterbore through the outlet. The counterbore is disposed at the outer end of the spray hole and could alternatively also be regarded as part of the spray hole, or the spray hole and the counterbore can be regarded as portions of an ejector duct through which fuel is ejected. If the cross-section of the counterbore is not constant, a minimum cross-section of the counterbore is larger than the cross-section of the spray hole at the outlet. The shape of the counterbore is preferably cylindrical so that the counterbore canbe characterized by a radius and a diameter. The cross-section of the counterbore is greater than the cross-section of the spray hole at the outlet, i.e., the cross-section available for the fuel as it is ejected from the injector increases when it passes from the spray hole through the outlet into the counterbore. This may have different advantages. In particular, it may improve the atomization of the fuel during ejection. It may also positively influence the shape of the plume. It should be appreciated that the term “counterbore” is not to be construed in a limiting way as to the manufacturing method, i.e., that the counterbore has to be mechanically bored from the outside of the nozzle housing.

[0014] One preferred embodiment provides that at least one co-aligned spray hole has a cross-section that decreases from the inlet to the outlet. In particular, this may apply to every co-aligned spray hole. One could also say that the respective spray hole generally tapers from the inlet to the outlet. Without being limited to this explanation, the tapering shape of the spray hole may beneficially influence the shape of the plume that is ejected from the spray hole. Preferably, the cross-section of at least one co-aligned spray hole decreases continuously from the inlet to the outlet. For example, the cross-section may decrease linearly or quadratically. In case of a linear decrease, the spray hole may be described as frusto-conical. However, the cone angle may be comparatively small, e.g., between 2° and 10° or between 3° and 8°.

[0015] In some embodiments, the alignment axis could be significantly tilted against the injector axis. This would also result in a plume that deviates significantly from the injector axis. Such an embodiment could be advantageous if the injector can only be installed in a certain position in which the intended direction of the plume does not nearly coincide with the injector axis. However, in another preferred embodiment, the alignment axis is inclined by less than 10°, preferably less than 6°, with respect to the injector axis. It may be inclined by less than 7°, less than 5° or less than 2° with respect to the injector axis. Preferably, it is parallel to the injector axis. In this case, one could also say that the injector axis is the alignment axis.

[0016] Also, the spray-hole axes of the co-aligned spray holes may be inclined by less than 7°, preferably less than 5°, more preferably less than 2° with respect to the alignment axis. This generally promotes the formation of a singular plume because the individual spray holes are even better aligned to a common direction. Specifically, the spray-hole axes of the co-aligned spray holes may be parallel to the alignment axis. In combination with the abovementioned embodiment this may define an injector in which the spray-hole axes of all co-aligned spray holes are parallel to the injector axis.

[0017] While it is within the scope of the invention that at least one spray hole may have a spray-hole axis that is inclined by more than 10°, resp. 6°, with respect to the alignment axis, it is preferred that every spray hole of the fuel injector is a co-aligned spray hole. Thus, the entire nozzle portion is adapted for creating a plume that is directed (and somewhat focused) in the direction of the alignment axis.

[0018] According to one embodiment at least one spray hole has a length along its spray-hole axis between 150 pm and 500 pm, preferably between 250 pm and 350 pm. This may in particular pertain to at least one co-aligned spray hole, preferably a plurality of co-aligned spray holes, more preferably to all co-aligned spray holes. The length is measured from the inlet to the outlet, the latter being either located at the outer boundary of the nozzle portion or at the transition to the counterbore.

[0019] The creation of a quasi-unitary plume by a plurality of co-aligned spray holes allows to keep the diameter of the individual spray hole comparatively small while still being able to inject a sufficiently large amount of fuel. One embodiment provides that at least one co-aligned spray hole has a maximum diameter of 200 pm, or possibly less than 180°pm, less than 150 pm or less than 100 pm. Strictly speaking, this refers to a spray hole with a circular cross-section. In case of a non-circular cross-section, the term “diameter” refers to the maximum dimension of the spray hole perpendicular to the sprayhole axis. In case of an elliptical cross-section, this would refer to the major axis of the ellipse. Preferably, the diameter of every co-aligned spray hole may be in the range specified above.

[0020] There are various possibilities how the co-aligned spray holes can be disposed with respect to the alignment axis. One embodiment provides that radial positions of a plurality of co-aligned spray holes with respect to the alignment axis differ by less than 10%, preferably less than 5%. More specifically, the radial positions of these coaligned spray holes can be identical. In other words, the respective co-aligned spray holes are approximately or exactly disposed on a circle around the alignment axis. The radial position can be defined by the (radial) distance between the spray-hole axis at the inlet and the alignment axis. The absolute value of the radial position may depend on various factors, like the radius of the individual co-aligned spray hole and the number of coaligned spray holes. In a typical embodiment, it may be between 400 pm and 900 pm. Preferably, at least 3 co-aligned spray holes are (approximately or exactly) disposed on a circle around the alignment axis. It is also preferred that every co-aligned spray hole is disposed on the circle, although it is possible that some co-aligned spray holes are otherwise distributed.

[0021] The formation of a largely symmetric and stable plume is promoted by a symmetric arrangement of the spray holes. In other words, co-aligned spray holes may be more or less evenly distributed along the tangential direction. According to such an embodiment, the tangential offsets between neighboring pairs of co-aligned spray holes differ by less than 10%, preferably less than 5%. That is to say, if the tangential offset between each co-aligned spray hole and the one next to it are considered, these tangential offsets differ by less than 10%. E.g., if the first and second spray hole are tangentially offset by 72°, the second and third spray hole are tangentially offset by between approx. 65° and 79° (or between approx. 69° and 75°). The tangential offset is defined as the angle between the intersection of the spray-hole axes with a tangential- radial plane (i.e. , a plane perpendicular to the alignment axis).

[0022] On the one hand, formation of a quasi-singular plume is promoted by a small distance between the individual spray holes, on the other hand the spray holes and in particular their respective counterbores (if present) still needs to be separated by a certain distance to avoid negative effects like incomplete atomization of the fuel. Under these considerations, it is preferred that a distance between neighboring counterbores corresponds to between 20% and 60% of a maximum diameter of a counterbore. Preferably, this pertains to the counterbores of all co-aligned spray holes. In most embodiments, every counterbore has the same diameter. If not, the counterbore with the largest diameter is considered. If a counterbore as a non-circular cross-section, the term “diameter” refers to the maximum dimension of the counterbore perpendicular to the spray-hole axis. The distance between the counterbores is measured perpendicular to the spray-hole axis of one of the counterbores.

[0023] Irrespective of whether a counterbore is present or not, the distance between two co-aligned spray holes should neither be too small nor too great. A too small distance could e.g., result in unwanted interference and impairment of the atomization process. A too great distance could impair the formation of a quasi-unitary plume. One embodiment provides that a distance between neighboring co-aligned spray holes corresponds to between 40% and 200% of a maximum diameter of a co-aligned spray hole. Again, the diameter is measured perpendicular to the spray-hole axis and corresponds to the largest dimension in case of a non-circular cross-section. The distance between the spray holes is measured perpendicular to the spray hole axis of one of the spray holes.

[0024] It is understood that the engine is a compression ignition internal combustion engine, i.e. of the type where fuel ignites due to the high temperatureachieved by compressing air in the cylinder. The fuel may typically be diesel. The cylinder head is disposed on top of an engine block that defines at least one cylinder, typically a plurality. The prechambers - one per cylinder - are disposed inside the cylinder head and communicate with a respective cylinder. Each fuel injector is disposed to inject liquid fuel into the respective prechamber. A glow plug may be disposed in the prechamber.

[0025] The high pressure liquid fuel source may conventionally comprise a fuel tank and a fuel rail to which the fuel injectors are connected directly or indirectly, and pumping means configured to supply fuel at pressure higher than 60 bar to the fuel rail, in particular at pressures between 100 and 250 bar, and even pressures up to 350 bar and hiher.Brief Description of the Drawings

[0026] Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:Fig. 1 is a partial cross-sectional view of a part of an inventive engine system with an inventive fuel injector;Fig. 2 is a cross-sectional view of the fuel injector from fig.1 ;Fig. 3 is a perspective view of a nozzle portion of the fuel injector from fig.1 ;Fig. 4 is a side view of the nozzle portion from fig.3;Fig. 5 is a sectional view along the line V-V in fig. 4; andFig. 6 is view in the direction VI in fig.5.Description of Preferred Embodiments

[0027] Fig.1 schematically shows a partial cross-sectional view of a part of an inventive engine system 40 with a compression ignition engine 20, e.g., a diesel engine for an offroad vehicle like an excavator. The engine 20 comprises an engine block 21 with a cylinder 22 in which a piston 25 is reciprocatingly movable. A cylinder head 23 is mounted on top of the engine block 21. It defines a prechamber 24 that communicates with the cylinder 22. An inventive fuel injector 1, which will be described in detail further below, is mounted to the cylinder head 23. It comprises a housing 2 that extends along an injector axis A from a proximal end 2.1 outside the cylinder head 23 to a distal end 2.2 inside the prechamber 24. At the distal end 2.2, a nozzle portion 3 is disposed through which liquid fuel, here diesel, can be selectively injected into the prechamber 24 by actuating the injector. A glow plug 30may be mounted to the cylinder head 23 adjacent theprechamber 24 for preheating purposes, in particular at cold start. The engine may comprise more than one engine cylinder, in which case each cylinder has a respective prechamber 24 and fuel injector 1.

[0028] Although not shown, the fuel injector 1 is part of a high-pressure fuel delivery system that may conventionally comprise a fuel tank and a fuel rail to which the fuel injectors are connected directly or indirectly, and pumping means configured to supply fuel at pressure higher than 60 bar to the fuel rail, in particular at pressures between 100 and 250 bar, and optionally up to 350 bar or even higher. In practice, the fuel tank holds the liquid fuel and includes a low-pressure pump (generally in-tank), that directs fuel to a high pressure pumps configured to deliver pressurized fuel to the fuel rail, at a predetermined high pressure, here within the mentioned range.

[0029] Fig.2 shows a sectional view of the fuel injector 1. It can be seen that the housing 2 comprises several interconnected components, which will not be discussed here, and defines an inner cavity 7 for containing and guiding liquid fuel. A pintle 8 is disposed within the cavity 7 of the housing 2 and is movable between a closed position, as shown in fig. 2, and an open position which is not shown here. In the closed position, a ball 9, which is fixed to the pintle 8, rests against the nozzle portion 3 and closes a plurality of ejector ducts 4 that traverse the nozzle portion 3. The pintle 8 is biased towards the closed position by a first spring 13. Furthermore, an armature 10 is axially movable within the housing 2 between a passive position, which is shown in fig. 2, and an active position, which is not shown in the figures. The armature 10 is biased towards the passive position by a second spring 14. When the armature 10 moves towards the active position, it engages the pintle 8 and moves it towards the open position. Therefore, the pintle 8 comprises a radially protruding annular collar (or perch) located proximally from the armature 10. Hence, for opening the injector, when the armature moves proximally, the armature engages the collar and moves toward the active position while displacing the pintle. Hence there is a mechanical coupling in the opening direction. The armature 10 can be moved by a magnetic field that is generated by a magnetic coil 12 disposed inside the housing 2. When the coil 12 is activated, it magnetizes a pole piece 11, which attracts the armature 10 to its active position. This configuration of pintle I armature / solenoid is well known in the art.

[0030] Figs. 3 to 6 show the nozzle portion 3 in detail, which nozzle portion 3 is formed by a nozzle housing or body that is premanufactured before it is connected with other parts of the housing 2. An inner surface of the nozzle portion 3 forms a nozzle seat 3.1 against which the ball 9 rests in the closed position of the pintle 8. A total of five co-aligned spray holes 5 traverse the wall of the nozzle portion 3. Each co-aligned spray 5 is aligned to a spray-hole axis C. All spray-hole axes C are parallel to an alignment axis B, which in this case is identical to the injector axis A.

[0031] A can be noticed, the nozzle portion 3 (body) is cup-shaped and the bottom thereof has a dome shaped wall portion 3.2 (extending distally). The spray holes 5 are arranged in the dome portion. The nozzle seat 3.1 is formed as an annular sealing surface that surrounds the dome portion, hence located upstream of the spray holes 5. In the closed position the ball 9 rests on the annular sealing surface and blocks current flow toward the spray holes. The volume defined by the inner surface of the dome (and codefined by ball 9) is referred to as sac.

[0032] The respective co-aligned spray hole 5 extends from an inlet 5.1 that communicates with the inner cavity 7 to an outlet 5.2, which communicates with a counterbore 6. The cross-section of the spray hole 5 and the cross-section of the counterbore 6 are both circular. The spray hole has a cross-section that tapers from the inlet 5.1 towards the outlet 5.2, resulting in a frusto-conical shape. The cross-section of the counterbore 6 is constant, apart from a small region near the outlet 5.1 , where it tapers due to its manufacturing process. Both the spray hole 5 and the counterbore 6 are symmetric with respect to the spray-hole axis C.

[0033] In this example, every co-aligned spray hole 5 has a length along its sprayhole axis C of 300 pm, which could however be different in other embodiments, e.g., between 150 pm and 500 pm, preferably between 250 pm and 350 pm. The diameter of each co-aligned spray hole 5 at the outlet 5.2 in this example is 174 pm, but could be different in other embodiments. In general, the spray holes may have a maximum diameter of 200 pm. In practice spray hole diameters between 60 and 200 pm can be envisaged, and even lower diameters if technically feasible. As can best be seen in fig. 6, which represents a view in the direction of the injector axis A, all five spray holes 5 are located at the same radial position r with respect to the alignment axis B, i.e., their respective spray-hole axes C are at the same radial distance from the alignment axis B. Also, they are equally offset from each other in the tangential direction, i.e., the tangential offsets a between neighboring pairs of co-aligned spray holes 5 are identical, namely 72°. It will be understood, though, that the radial positions r as well as the tangential offsets a could differ by e.g., less than 10% or less than 5% without changing the performance of the fuel injector 1 significantly. Also, arranging individual spray holes 5 or the entire group of co-aligned spray holes 5 in a slightly non-parallel position relative to the injector axis A (e.g., tilted by less than 10°), would not significantly change the performance.

[0034] In this embodiment, each counterbore 6 has a diameter of 350 pm. The distance ai between the neighboring counterbores 6 is chosen so that these counterbores 6 are somewhat spaced from each other. In this example, the distance ai corresponds to about 30% of the diameter d2 of the counterbore 5, but could be different, e.g., between 20% and 60%. Accordingly, although the counterbores 5, and the ejector ducts 4 as a whole, are comparatively close together while avoiding unwanted interference between them. Correspondingly, a distance a2 between neighboring co-aligned spray holes 5 corresponds to about 150% of a maximum diameter di of each co-aligned spray hole 5. In other embodiments, though, this ratio could be different, e.g., corresponding to between 40% and 200%.

[0035] When the pintle 8 is moved to the open position, liquid fuel is ejected through the spray holes 5. The fuel is atomized when it exits the outlet 5.2, a process that is facilitated by the counterbore 6. Initially, each spray hole 5 gives rise to an individual plume of fuel droplets. However, at a relatively short distance from the outlet, e.g., several millimeters or a few centimeters, the plumes form a quasi-singular plume 35 that extends over a major part of the prechamber, as schematically shown in fig.1. Since the plume 35 is formed by a plurality of comparatively small spray holes 5, it consists of finer droplets than in case of a single spray hole having a cross-section that corresponds to the combined cross-section of the five co-aligned spray holes 5.Legend of Reference Numbers:1 fuel injector 20 engine2 housing 21 motor block2.1 proximal end 22 cylinder2.2 distal end 23 cylinder head3 nozzle portion 24 prechamber3.1 nozzle seat 25 piston4 ejector duct 30 glow plug5 spray hole 35 plume5.1 inlet 40 engine system5.2 outlet A injector axis6 counterbore a1, a2 distance7 inner cavity B alignment axis8 pintle C spray-hole axis9 ball d1, d2 diameter10 armature r radial position11 pole piece a tangential offset12 magnetic coil13, 14 spring

Claims

Claims1. An engine system (40), comprising a compression-ignition engine (20) with at least one cylinder and a cylinder head (23) defining one prechamber (24) in communication with the cylinder, and a fuel injector (1) for injecting fuel therein, the engine system further comprising a high-pressure liquid fuel source configured to supply fuel at pressures above 60 bar to the fuel injector, the fuel injector (1) comprising: a housing (2) extending axially along an injector axis (A) from a proximal end (2.1) to a distal end (2.2) and having a nozzle portion (3) at the distal end (2.2) with a plurality of spray holes (5), each spray hole (5) being aligned to a spray-hole axis (C) of the respective spray hole (5) and extending from an inlet (5.1) inside the housing (2) to an outlet (5.2), and a pintle (8) being axially movable between an open position and a closed position in which it closes the spray holes (5), wherein a plurality of spray holes (5) are co-aligned spray holes (5) having spray-hole axes (C) that are inclined by less than 10°, preferably less than 6°, with respect to a common alignment axis (B).

2. The engine system according to claim 1 , comprising: an armature (11) being axially movable from a passive position to an active position, thereby moving the pintle (8) to the open position, and a magnetic coil (12) for magnetically attracting the armature (11) towards the active position.

3. The engine system according to any of the preceding claims, comprising between three and seven, preferably between four and six, more preferably five co-aligned spray holes (5).

4. The engine system according to any of the preceding claims, wherein the outlet (5.2) of at least one co-aligned spray hole (5) communicates with a counterbore (6), which counterbore (6) has a larger cross-section than the spray hole (5) at the outlet (5.2).

5. The engine system according to any of the preceding claims, wherein at least one coaligned spray hole (5) has a cross-section that decreases from the inlet (5.1) to the outlet (5.2).

6. The engine system according to any of the preceding claims, wherein the alignment axis (B) is inclined by less than 10°, preferably less than 6°, with respect to the injector axis (A) and is preferably parallel to the injector axis (A).

7. The engine system according to any of the preceding claims, wherein the spray-hole axes (C) of the co-aligned spray holes (5) are inclined by less than 7°, preferably less than 5°, more preferably less than 2° with respect to the alignment axis (B).

8. The engine system according to any of the preceding claims, wherein every spray hole (5) of the fuel injector (1) is a co-aligned spray hole (5).

9. The engine system according to any of the preceding claims, wherein at least one spray hole (5) has a length along its spray-hole axis (C) between 150 pm and 500 pm, preferably between 250 pm and 350 pm.

10. The engine system according to any of the preceding claims, wherein at least one coaligned spray hole (5) has a diameter (di) of maximum 200 pm.

11. The engine system according to any of the preceding claims, wherein radial positions (r) of a plurality of co-aligned spray holes (5) with respect to the alignment axis (B) differ by less than 10%, preferably less than 5%.

12. The engine system according to any of the preceding claims, wherein tangential offsets (a) between neighboring pairs of co-aligned spray holes (5) differ by less than 10%, preferably less than 5%.

13. The engine system according to any of the preceding claims, wherein a distance (ai) between neighboring counterbores (6) corresponds to between 20% and 60% of a maximum diameter (d2) of a counterbore (6).

14. The engine system according to any of the preceding claims, wherein a distance (a2) between neighboring co-aligned spray holes (5) corresponds to between 40% and 200% of a maximum diameter (di) of a co-aligned spray hole (5).

15. The engine system according to any of the preceding claims, comprising a plurality of engine cylinders, whereby the cylinder head defines one prechamber per enginecylinder, and each prechamber comprises a respective fuel injector for injecting fuel therein.

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