Dual-fuel injector

Abstract

According to the present invention there is provided a dual-fuel injector (10) for directly injecting two separate fuels into a combustion chamber (12) of an internal combustion engine, the dual-fuel injector (10) comprising: an injector body assembly (14) housing a dual needle valve arrangement (16) comprising a first needle valve (18) and a second needle valve (20), the second needle valve (20) defining an internal bore (22) in which the first needle valve (18) is slidably received; a first biasing means (84) configured to bias the first needle valve (18) into engagement with a first valve seat portion (70); a first control chamber (28) defined at least in part by an upper end (30) of the first needle valve (18) such that varying a first pressure in the first control chamber (28) varies the force on the upper end (30) of the first needle valve (18); and a second control chamber (32) defined at least in part by an upper end (34) of the second needle valve (20) such that varying a second pressure in the second control chamber (32) varies the force on the upper end (34) of the second needle valve (20); wherein at least a part of the first control chamber (28) is external to the second needle valve (20) and at least part of the first biasing means (84) is disposed within the first control chamber (28).

Description

[0001] Dual-fuel injector

[0002] Technical field

[0003] The present invention relates generally to fuel injectors and more specifically to a dual-fuel injector for direct injection into a combustion chamber of an internal combustion engine.

[0004] Background

[0005] Internal combustion (IC) engines are typically powered by combusting a fuel, such as petrol (gasoline) or diesel, in a combustion chamber. New technologies have been developed to increase fuel efficiency, reduce emissions of IC engines, and enable the use of carbon neutral renewable fuels (such as alcohol fuels produced from renewable organic materials). One such development involves the combustion of two separate fuels within the combustion chamber of a dual-fuel engine. For example, a limited amount of a first fuel or ‘auxiliary fuel’, such as diesel, may be supplied to the combustion chamber to initiate or facilitate combustion, and a second fuel or ‘main fuel’, such as an alcohol fuel e.g., methanol, may be supplied to the combustion chamber due to its advantageous combustion or emissions characteristics.

[0006] In a dual-fuel engine, the first and second fuels may be supplied to the combustion chamber in a number of different ways. Some examples include: mixing the two fuels together with air in an inlet manifold before supplying the fuel / air mixture to the combustion chamber through an inlet valve (referred to as port fuel injection); supplying the second fuel by port fuel injection (with injection into an inlet manifold) but directly injecting the first fuel into the combustion chamber for ignition; or directly injecting each fuel to the combustion chamber using separate direct fuel injectors. However, each of these methods has drawbacks in terms of efficiency and / or packaging of the engine components.

[0007] The dual-fuel direct injector, that are configured to inject (both) first and second fuels directly into the combustion chamber in use, has been developed in an attempt to overcome these drawbacks. However, significant manufacturing challenges remain.

[0008] For example, dual-fuel injectors typically require a concentric arrangement of needle valves, as well as separate control chambers for controlling each of the needle valves to control injection of the first and second fuels. To allow this arrangement, up to now, the outer needle has had to be made of two parts, which are then joined together thereafter, e.g., using a press fitting or threaded arrangement. This has therefore added complexityto the manufacturing process, e.g., requiring additional grinding operations or increases in clearances, which have compromised the hydraulic performances of these injectors.

[0009] It is against this background that the present invention has been devised.

[0010] Summary

[0011] According to the present invention there is provided a dual-fuel injector for directly injecting two separate fuels into a combustion chamber of an internal combustion engine, the dualfuel injector comprising: an injector body assembly housing a dual needle valve arrangement comprising a first needle valve and a second needle valve, the second needle valve defining an internal bore in which the first needle valve is slidably received; a first biasing means configured to bias the first needle valve into engagement with a first valve seat portion; a first control chamber defined at least in part by an upper end of the first needle valve such that varying a first pressure in the first control chamber varies the force on the upper end of the first needle valve; and a second control chamber defined at least in part by an upper end of the second needle valve such that varying a second pressure in the second control chamber varies the force on the upper end of the second needle valve; wherein at least a part of the first control chamber is external to the second needle valve and at least part of the first biasing means is disposed within the first control chamber.

[0012] This arrangement advantageously simplifies the manufacture of the fuel injector, particularly because it obviates the need to arrange the first control chamber and the first biasing means within the second needle valve, and yet only increases the first needle valve control volume minimally.

[0013] The first control chamber may be entirely external to the second needle valve. The first biasing means may be entirely disposed within the first control chamber.

[0014] The upper end of the first or second needle valves may be provided by e.g., a cap arranged over the upper end thereof.

[0015] In an embodiment, the second needle valve is integrally formed as a unitary part.

[0016] In an embodiment, the first control chamber is partially static.In an embodiment, the first control chamber is defined at least in part by the injector body assembly.

[0017] In an embodiment, the injector body assembly comprises a nozzle control valve (NCV) housing. An upper surface of the first control chamber may be defined by the NCV housing, optionally the lower end of the NCV housing.

[0018] In an embodiment, a lower surface of the first control chamber is defined by the first needle valve, optionally the upper end of the first needle valve.

[0019] The outer surface of the first control chamber may be defined by an intermediate housing between the NCV housing and a nozzle body, optionally the inner wall thereof.

[0020] In an embodiment, the first biasing means is disposed around at least a part of the first needle valve, optionally around at least a part of the upper end of the first needle valve.

[0021] In an embodiment, the first needle valve is movable between a closed configuration in which a first fuel path to the combustion chamber is closed and an open configuration in which the first fuel path to the combustion chamber is open. A first gap (G 1 ) may be defined between the first needle valve and a first valve stop when the first needle valve is arranged in the closed configuration, and the first needle valve may abut the first valve stop when the first needle valve is arranged at a full lift position in the open configuration.

[0022] In an embodiment, the second needle valve is movable between a closed configuration in which a second fuel path to the combustion chamber is closed and an open configuration in which the second fuel path to the combustion chamber is open. A second gap (G2) may be defined between the second needle valve and a second valve stop when the second needle valve is arranged in the closed configuration and the second needle valve may abut the second valve stop when the second needle valve is arranged at a full lift position in the open configuration

[0023] The first gap (G1) is preferably larger than the second gap (G2).

[0024] The first needle valve may abut the first valve seat portion when the first needle valve is arranged in the closed configuration. The second needle valve may abut a second valve seat portion when the second needle valve is arranged in the closed configuration.In an embodiment, the first gap (Gi) is around twice the length of the second gap (G2).

[0025] In an embodiment, the second control chamber is defined at least in part by the injector body assembly.

[0026] The upper surface and outer surface of the second control chamber may be defined by the intermediate housing. The lower surface of the second control chamber may be defined by the second needle valve, optionally the upper end of the second needle valve. The inner surface of the second control chamber may be defined by the first needle valve, optionally the outer surface thereof.

[0027] In an embodiment, the dual-fuel injector further comprises a second biasing means configured to bias the second needle valve into engagement with a second valve seat portion. Optionally, the second biasing means is disposed around the second needle valve.

[0028] The dual-fuel injector arrangement beneficially allows the second biasing means to be located remotely from the second control chamber, and hence the second control chamber to have a very small control volume. This ensures precise timing of the opening and closing of the second needle valve.

[0029] In an embodiment, the dual-fuel injector further comprises a second accumulator volume in the second flow path to one or more second fuel injection outlets. The second biasing means may be disposed within the second accumulator volume.

[0030] In an embodiment, the dual-fuel injector further comprises a collar coupled to the second needle valve. The second biasing means may engage the collar and a portion of the injector body assembly to bias the second needle valve into engagement with the second valve seat portion.

[0031] Optionally, the second biasing means may engage, or extend between, the collar and the intermediate housing, preferably the lower end thereof, to bias the second needle valve into engagement with the second valve seat portion.

[0032] In an embodiment, the first needle valve is co-axial and / or concentric with the second needle valve.The first needle valve may define a first needle valve axis. The second needle valve may define a second needle valve axis. The first control chamber may comprise a first control chamber axis that is coaxial with the first needle valve axis and / or the second needle valve axis. Additionally or alternatively, the second control chamber may comprise a second control chamber axis that is coaxial with the first needle valve axis and / or the second needle valve axis. In a preferred embodiment, the first control chamber axis, the second control chamber axis, first needle valve axis and the second needle valve axis are all coaxial.

[0033] In a preferred embodiment, the first fuel is diesel and / or the second fuel is methanol.

[0034] Brief description of the drawings

[0035] Examples of the present invention will now be described by way of non-limiting examples only, with reference to the accompanying figures, in which:

[0036] Figure 1 is a schematic cross-sectional view of a dual-fuel injector comprising first and second control chambers;

[0037] Figure 2 is an expanded schematic cross-sectional view of the first and second control chambers of the dual-fuel injector of Figure 1 ; and

[0038] Figure 3 is a flow chart depicting a method of operation of the dual-fuel injector of Figure 1.

[0039] Detailed description

[0040] Figure 1 shows a schematic cross-sectional view of a dual-fuel injector 10 for directly injecting two separate fuels into a combustion chamber 12 of an internal combustion engine. For example, the injector 10 may be configured to directly inject a first fuel such as diesel, and a second fuel such as an alcohol fuel e.g., methanol. As explained previously by way of background, the second fuel (as the ‘main fuel’) may be selected for its advantageous combustion or emissions characteristics, and the first fuel (as the ‘auxiliary fuel’) may be selected to assist with combustion of the second fuel.

[0041] The dual-fuel injector 10 is for direct injection into the combustion chamber 12 of an internal combustion engine, meaning that the fuel is injected directly into the combustion chamber12. This contrasts with other types of injection, such as port fuel injection where fuel(s) are injected into an intake manifold for mixing with air before entering a combustion chamber.

[0042] The dual-fuel injector 10 comprises an injector body assembly 14 housing a dual needle valve arrangement 16 for regulating the separate supply of the first and second fuels to the combustion chamber 12. To this end, the dual needle valve arrangement 16 comprises a first needle valve 18 and a second needle valve 20. The second needle valve 20 defines an internal bore 22 and the first needle valve 18 is slidably received within the internal bore 22 as shown in Figure 1. As such, the first needle valve 18 may be understood as the inner needle valve, while the second needle valve 20 may be understood as the outer needle valve. The injector 10 comprises a first biasing means 84 configured to bias the first needle valve 18 into engagement with a first valve seat portion 70.

[0043] The dual-fuel injector 10 also includes a first control chamber 28 for controlling the movement of the first needle valve 18 and a second control chamber 32 for controlling the movement of the second needle valve 20. To this end, the first control chamber 28 is at least partly defined by an upper end 30 of the first needle valve 18. Accordingly, varying a first pressure in the first control chamber 28 varies the force on the upper end 30 of the first needle valve 18, facilitating control of the movement of the first needle valve 18. On the other hand, the second control chamber 32 is at least partly defined by an upper end 34 of the second needle valve 20. Accordingly, varying a second pressure in the second control chamber 32 varies the force on the upper end 34 of the second needle valve 20, and the movement of the second needle valve 20 can therefore be controlled by controlling the pressure in the second control chamber 32.

[0044] At least a part of the first control chamber 28 is external to the second needle valve 20 and at least part of the first biasing means 84 is disposed within the first control chamber 28.

[0045] This arrangement advantageously simplifies the manufacture of the fuel injector 10, particularly because it obviates the need to arrange the first control chamber 28 and the first biasing means 84 within the second needle valve 20, and yet only increases the first needle valve control volume minimally. Additionally, this arrangement allows the second needle valve 20 to be integrally formed. In other words, the second valve needle 20 is formed as a unitary piece (e.g., as opposed to being made up of two or more separate parts). This further simplifies manufacture of the fuel injector 10, by removing the need to join two separate parts of the second needle valve 20 around the first control chamber 28 and the first biasing means 84, e.g., using a press fitting or threaded arrangement, andhence avoids compromising the hydraulic performance of the injector 10 associated with the two-part second needle valve 20 of the prior art.

[0046] The first control chamber 28 may be entirely external to the second needle valve 20, such that no part of the first control chamber 28 is arranged within the second needle valve 20. Likewise, the first biasing means 84 may be entirely disposed within the first control chamber 28.

[0047] Now further details on the dual-fuel injector 10 will be provided, starting with the first and second needle valves 18, 20.

[0048] As shown in Figure 1, the first and second needle valves 18, 20 are co-axial, so that the first needle valve 18 defines a first needle valve axis 24, and the second needle valve 20 defines a second needle valve axis 26, and the first needle valve axis 24 is the same as / aligns with the first needle valve axis 24. Moreover, since the first needle valve 18 is arranged within the second needle valve 20, the first and second needle valves 18, 20 are concentric. Such arrangements are advantageous for balancing loads and reducing wear in use. In other embodiments, the first and second needle valves 18, 20 may have other arrangements.

[0049] As stated above, the first and second needle valves 18, 20 are controlled by the first and second control chambers 28, 32 respectively. In particular, when the pressure in a control chamber 28, 32 is decreased, the corresponding needle valve 18, 20 is moved axially upwards, and when the pressure is increased, the corresponding needle valve 18, 20 is moved axially downward. The pressure in each control chamber 30, 32 may be varied / controlled by a respective nozzle control valve (not shown).

[0050] However, the concentric arrangement of the first and second needle valves 18, 20 of Figure 1 means that when the second needle valve 20 is moved up (or down), the first needle valve 18 (arranged within the second needle valve 20) moves with it. On the other hand, if only the first needle valve 18 is moved up (or down), the second needle valve 20 will remain stationary.

[0051] Now turning to the injector body assembly 14, the injector body assembly 14 provides the housing for the fuel injector 10. The injector body assembly 14 comprises a nozzle body 40 at the lower end of the dual-fuel injector 10, a nozzle control valve (NCV) housing 42 at the upper end of the dual-fuel injector 10, and an intermediate housing 44 extending between the nozzle body 40 and the NCV housing 42.The nozzle body 40 at the lower end of the dual-fuel injector 10 defines a second valve seat portion 72 for the second needle valve 20, whereas the second needle valve 20 defines the first valve seat portion 70 for the first needle valve 18.

[0052] The first needle valve 18 is arranged to engage with the first valve seat portion 70 to control injection of the first fuel into the combustion chamber 12. In a closed (or non-injecting) configuration, the first needle valve 18 is arranged against the first valve seat portion 70, while in an open (or injecting) configuration, the first needle valve 18 is arranged away from the first valve seat portion 70 (axially upward therefrom). In the open configuration, one or more first fuel injection outlets 74 defined in the second needle valve 20 allow fluid communication between a first accumulator volume 78 within the second needle valve 20 and the combustion chamber 12. The first needle valve 18 is arranged in a full lift position in the open configuration when it is arranged at its most distal position from the first valve seat portion 70.

[0053] On the other hand, the second needle valve 20 is arranged to engage with the second valve seat portion 72 to control injection of the second fuel into the combustion chamber 12. In a closed (or non-injecting) configuration, the second needle valve 20 is arranged against the second valve seat portion 72, while in an open (or injecting) configuration, the second needle valve 20 is arranged away from the second valve seat portion 72 (axially upward therefrom). In the open configuration, one or more second fuel injection outlets 76 defined in the nozzle body 40 allow fluid communication between a second accumulator volume 80 within the nozzle body 40 and the combustion chamber 12. The second needle valve 20 is arranged in a full lift position in the open configuration when it is arranged at its most distal position from the second valve seat portion 72.

[0054] To feed the first fuel to the first accumulator volume 78, the dual-fuel injector 10 includes a first fuel feed 60, which extends down from a first fuel store (not shown) through the NCV housing 42, then through the intermediate housing 44, and finally through the second needle valve 20 to the first accumulator volume 78 within the second needle valve 20. The first fuel feed 60 takes the form of channels (also referred to as bores) extending through each of the NCV housing 42, the intermediate housing 44 and the second needle valve 20.Likewise, to feed the second fuel to the second accumulator volume 80, the dual-fuel injector 10 also includes a second fuel feed 62, which extends down from a second fuel store (not shown) through the NCV housing 42 and then through the intermediate housing 44 into the second accumulator volume 80 within the nozzle body 40. The second fuel feed 62 also takes the form of channels (also referred to as bores) extending through each of the NCV housing 42 and the intermediate housing 44.

[0055] The NCV housing 42 is provided at the upper end of the dual-fuel injector 10 for housing the nozzle control valves (not shown), which control the pressures of the control chambers 30, 32, and hence the axial movement of the first and second needle valves 18, 20.

[0056] The intermediate housing 44 extends between the nozzle body 40 and the NCV housing 42. The intermediate housing 44 defines a through bore therein comprising an upper region 48 and a lower region 50. The upper region 48 has a narrower diameter than the lower region 50, such that the through bore is stepped. An upper portion of the first valve needle 18 extends through the upper region 48 of the through bore, while the second needle valve 20 extends through the lower region 50 of the through bore.

[0057] The intermediate housing 44 around the upper region 48 of the through bore defines a first guide portion 88 for guiding the axial movement of the first needle valve 18, while the intermediate housing 44 around the lower region 50 of the through bore defines a second guide portion 90 for guiding the axial movement of the second needle valve 20. Furthermore, the second needle valve 20 defines a third guide portion 92 therein for guiding the axial movement of the first needle valve 18 within the internal bore 22 of the second needle valve 20.

[0058] The second needle valve 20 preferably interfaces the second guide portion 90 of the intermediate housing 44 with a matched clearance fit, such that a small clearance may exist between the intermediate housing 44 and the second needle valve 20 to enable a slidable relation. In more detail, the second guide portion 90 may include an upper second guide portion 90a and a lower second guide portion 90b, wherein the upper and lower second guide portions 90a, 90b are arranged on opposing sides of the first fuel feed 60 within the second needle valve 20 (with the upper second guide portion 90a arranged above the lower second guide portion 90b).

[0059] A matched clearance fit between the upper second guide portion 90a and the second needle valve 20 may advantageously ensure fluid separation between the first fuel feed60 and the second control chamber 32 (thereby preventing the fluids therein from mixing), whereas a matched clearance fit between the lower second guide portion 90b and the second needle valve 20 may advantageously ensure fluid separation between the first fuel feed 60 and the second fuel feed 62 / the second accumulator volume 80 (thereby preventing the fuels therein from mixing).

[0060] Likewise, the first needle valve 18 preferably interfaces the first and third guide portions 88, 92 with a matched clearance fit, such that a small clearance may exist between each of the first and third guide portions 88, 92 and the first needle valve 18 to enable a slidable relation.

[0061] A matched clearance fit between the first guide portion 88 of the intermediate housing 44 and the first needle valve 18 may advantageously ensure fluid separation between the first control chamber 28 and the second control chamber 32 (thereby preventing the fluids therein from mixing), whereas a matched clearance fit between the third guide portion 92 of the second needle valve 20 and the first needle valve 18 may advantageously ensure fluid separation between the second control chamber 32 and the second fuel feed 62 / the second accumulator volume 80 (thereby preventing the fluids therein from mixing).

[0062] Now the first and second control chambers 28, 32 will be overviewed, with reference to Figure 2 which provides an expanded view of the first and second control chambers 28, 32.

[0063] The first control chamber 28 is provided within the upper region 48 of the through bore, and is axially above (and outside or external to) the second needle valve 20.

[0064] The first control chamber 28 is defined between the injector body assembly 14 and the first needle valve 18. In particular, the upper surface of the first control chamber 28 is defined by the lower end 46 of the NCV housing 42 (e.g., the downward-facing surface thereof), the outer surface of the first control chamber 28 is defined by a portion of the intermediate housing 44 (e.g., the inward-facing surface thereof), and the lower surface of the first control chamber 28 is defined by the upper end 30 of the first needle valve 18 (e.g., the upward-facing surface thereof).

[0065] The lower end 46 of the NCV housing 42 defines a first valve stop 52 for the first needle valve 18, the first needle valve 18 abutting the first valve stop 52 when the first needle valve 18 is arranged at the full lift position in the open configuration. When the first needlevalve 18 is arranged in the closed configuration, a first gap Gi is defined between the first needle valve 18 (e.g., the uppermost end thereof) and the first valve stop 52.

[0066] On the other hand, the second control chamber 32 is provided within the lower region 50 of the through bore. In more detail, the second control chamber 32 is defined between the injector body assembly 14 and the second needle valve 20. In particular, the upper surface of the second control chamber is defined by a portion of the intermediate housing 44 (e.g., the downward-facing surface thereof) , the outer surface of the second control chamber is defined by another portion of the intermediate housing 44 (e.g., the inward-facing surface thereof), and the lower surface of the first control chamber 28 is defined by the upper end 34 of the second needle valve 20 (e.g., the upward-facing surface thereof).

[0067] Furthermore, because the first needle valve 18 extends through the second control chamber 32, the first needle valve 18 (e.g., the outward-facing surface thereof) further defines the inner surface of the second control chamber 32, and means that the second control chamber 32 is annular.

[0068] The intermediate housing 44 defines a second valve stop 54 for the second needle valve 20, the second needle valve 20 abutting the second valve stop 54 when the second needle valve 20 is arranged at the full lift position in the open configuration. When the second needle valve 20 is arranged in the closed configuration, a second gap G2 is defined between the second needle valve 20 (e.g., the uppermost end thereof) and the second valve stop 54.

[0069] This configuration of the second control chamber 32 allows the control volume of the second needle valve 20 to be reduced, and hence ensures precise timing of the opening and closing of the second needle valve and hence improves combustion performance.

[0070] The first and second control chambers 28, 32 are arranged co-axially with the first and second needle valves 18, 20. In other words, the first control chamber 28 has a first control chamber axis 64 and the second control chamber 32 has a second control chamber axis 66, and the first and second control chamber axes 64, 66 are the same as the first and second needle valve axes 24, 26. Such a configuration is advantageous for manufacturing the injector 10 and also helps to balance and align forces applied to the first and second needle valves 18, 20 in use, thereby reducing wear.In the embodiment of Figure 1, the dual-fuel injector 10 further comprises a second biasing means 86 in addition to the first biasing means 84. Each of the first and second biasing means 84, 86 are provided in the form of springs, although other arrangements are conceived.

[0071] The first biasing means 84 is arranged to bias the first needle valve 18 into the closed configuration. In other words, the first biasing means 84 is arranged to bias the first needle valve 18 into engagement with the first valve seat portion 70. Biasing the first needle valve 18 against the first valve seat portion 70 covers or blocks the first fuel injection outlets 74 of the second needle valve 20, thereby interrupting the flow path of the first fuel (the first flow path) between the first accumulator volume 78 and the combustion chamber 12.

[0072] In some preferred examples, the first biasing means 84 is disposed around the first needle valve 18 within the first control chamber 28. To this end, the first needle valve 18 may be narrower at the upper end 30 thereof so that the first biasing means 84 can be disposed therearound and yet still within the upper region 48 of the through bore. The first biasing means 84 engages / extends between the upper portion of the first needle valve 18 and the lower end of the NCV housing 42 to bias the first needle valve 18.

[0073] On the other hand, the second biasing means 86 is arranged to bias the second needle valve 20 into the closed configuration - that is, into engagement with the second valve seat portion 72. Biasing the second needle valve 20 against the second valve seat portion 72 covers or blocks the second fuel injection outlets 76, thereby interrupting the flow path of the second fuel (the second flow path) between the second accumulator volume 80 and the combustion chamber 12.

[0074] In some preferred examples the second biasing means 86 is disposed around the second needle valve 20 within the second accumulator volume 80 in the nozzle body 40. It will be appreciated that the second biasing means 86 is therefore located in an entirely separate volume of the dual-fuel injector 10 compared to the second control chamber 32. Accordingly, the second control chamber 32 does not need to be dimensioned to accommodate the second biasing means 86, which helps to facilitate a reduction in the second fuel control volume, and hence ensures precise timing of the opening and closing of the second needle valve 20.In some examples the second biasing means 86 may engage both a collar 82 coupled to the second needle valve 20 and a downward-facing portion of the intermediate housing 44 of the injector body assembly 14 to bias the second needle valve 20. The provision of an engagement collar 82 facilitates simpler assembly of the dual-fuel injector 10. Furthermore, the provision of the engagement collar 82 beneficially allows the second needle valve 20 to have a smaller overall outer needle diameter and hence reduces the excess needle material needed for the second needle valve 20.

[0075] In addition to the second biasing means 86, due to the above-described concentric configuration of the fuel injector 10 (that is, with the first needle valve 18 arranged within the second needle valve 20), the first biasing means 84 also acts to bias the second needle valve 20 (via the first needle valve 18 therein) into the closed configuration - that is, into engagement with the second valve seat portion 72.

[0076] In opposition to the first and second control chambers 28,32 and the first and second biasing means 84, 86 applying downward forces on the first and second needle valves 18, 20, the first and second fuels are directed through the fuel injector 10 in such a way that they continuously apply upwardly directed forces against the first and second needle valves 18, 20. In the closed configurations of the first and second needle valves 18, 20, these forces are balanced, but when the downward forces provided by the first and second control chambers 28,32 are reduced (by de-pressurising the control fluid therein), the upwardly directed forces of the first and second fuels overcome the downward forces of the first and second control chambers 28,32 and the first and second biasing means 84, 86 and the first and second needle valves 18, 20 are lifted away from the first and second valve seat portions 70, 72 into the open configurations.

[0077] Now a method of operating the fuel injector 10 will be described with reference to Figure 3.

[0078] In the first step 102 of the method, the first and second needle valves 18, 20 are arranged in their respective closed configurations, as shown in Figure 1.

[0079] In the second step 104, the first control chamber 28 is depressurised with no control fluid supplied to the first control chamber 28. As such, the upwardly directed force of the first fuel on the first needle valve 18 can overcome the downward force of the first biasing means 84 and the first needle valve 18 is drawn up, thereby compressing the first biasing means 84 and moving the first needle valve 18 away from the first valve seat portion 70and into the open configuration. As a result, the first fuel in the first accumulator volume 78 is directed into the combustion chamber 12 through the one or more first fuel injection outlets 74 for combustion in the combustion chamber 12.

[0080] In the third step 106, the first control chamber28 is re-pressurised, and the pressure in the first control chamber 28, along with the first biasing means 84, exerts enough downward force on the first needle valve 18 to overcome the upwardly directed force of the first fuel and to move the first needle valve 18 back down until it again abuts the first valve seat portion 70 in the closed configuration. As such, the first fuel in the first accumulator volume 78 can no longer pass into the combustion chamber 12 through the one or more first fuel injection outlets 74, and combustion of the first fuel in the combustion chamber 12 ceases.

[0081] In the fourth step 108, the second control chamber 32 is depressurised with no control fluid supplied to the second control chamber 32. As such, the upwardly directed force of the second fuel on the second needle valve 20 can overcome the downward force of the second biasing means 86 and the second needle valve 20 is drawn up (along with the first needle valve 18 arranged within the second needle valve 20). This therefore compresses the second (and first) biasing means 86, 84 and moves the second (and first) needle valves 20, 18 away from the second (and first) valve seat portions 72, 70 and into the open configurations. As a result, the second (and first) fuels in the second (and first) accumulator volumes 80, 78 are directed into the combustion chamber 12 through the second (and first) fuel injection outlets 76, 74 for combustion in the combustion chamber 12.

[0082] In the fifth step 110, the second control chamber 32 is re-pressurised, and the pressure in the second control chamber 32, along with the second (and first) biasing means 86, 84 exerts enough downward force on the second (and first) needle valves 20, 18 to overcome the upwardly directed force of the second fuel and to move the second (and first) needle valves 20, 18 back down until they again abut the second (and first) valve seat portion 72, 70 in the closed configuration. As such, the second (and first) fuel in the second (and first) accumulator volume 80, 78 can no longer pass into the combustion chamber 12 through the second (and first) fuel injection outlets 76, 74, and combustion of the second (and first) fuels in the combustion chamber 12 ceases.

[0083] The method 100 may then begin again at the second step 104 or else come to an end, depending on the needs of the internal combustion engine.Advantageously, the third step 106 may not be performed, such that it is skipped over, within one or some cycles of the method 100 - or throughout the entire method 100 - as needed. This beneficially avoids any interruption or delay in the injection of fuels into the combustion chamber 12.

[0084] To this end, the first gap Gi between the first needle valve 18 and the first valve stop 52 when the first needle valve 18 is arranged in the closed configuration may be larger than the second gap G2 between the second needle valve 20 and the second valve stop 54 when the second needle valve 20 is arranged in the closed configuration.

[0085] For example, the first gap G1 may be between around 0.4mm and 0.8mm, or between around 0.5mm and 0.7mm, or around 0.6 mm, while the second gap G2 may be between around 0.1mm and 0.5mm, or between around 0.2mm and 0.4mm, or around 0.3 mm. In other words, the first gap G1 may be around 0.1 to 0.5mm larger than the second gap G2, around 0.2 to 0.4mm larger than the second gap G2, optionally around 0.3mm larger than the second gap G2. The first gap G1 may be around twice the length of the second gap G2.

[0086] Because the first gap G1 is larger than the second gap G2, even when the first needle valve 18 is already arranged upward after the second step 104, it is still possible to move the second needle valve 20 up via the fourth step 108, which in turn brings the first needle valve 18 even further up. In other words, this arrangement obviates the need to move the first needle valve 18 back down into its closed configuration via the third step 106 before the fourth step 108 can begin, and helps to obviate any interruption or delay in the injection of fuels into the combustion chamber 12.

[0087] Finally, the fuel injector 10 is configured such that the injector body assembly 14 remains static or stationary (or unmoving or immobile), while the first and second needle valves 18, 20 move or are mobile within the fuel injector 10. Each of the first and second control chambers 28, 32 is therefore partially static / stationary (because of the parts defined by the injector body assembly 14) and partially moving / mobile (because of the parts defined by the first and second needle valves 18, 20).

[0088] It will be appreciated that the description provided above serves to demonstrate possible examples of the present invention. Features described in relation to any of the examples above may be readily combined with any other features described with reference todifferent examples without departing from the scope of the invention as defined in the appended claims.

Claims

Claims1. A dual-fuel injector (10) for directly injecting two separate fuels into a combustion chamber (12) of an internal combustion engine, the dual-fuel injector (10) comprising: an injector body assembly (14) housing a dual needle valve arrangement (16) comprising a first needle valve (18) and a second needle valve (20), the second needle valve (20) defining an internal bore (22) in which the first needle valve (18) is slidably received;a first biasing means (84) configured to bias the first needle valve (18) into engagement with a first valve seat portion (70);a first control chamber (28) defined at least in part by an upper end (30) of the first needle valve (18) such that varying a first pressure in the first control chamber (28) varies the force on the upper end (30) of the first needle valve (18); anda second control chamber (32) defined at least in part by an upper end (34) of the second needle valve (20) such that varying a second pressure in the second control chamber (32) varies the force on the upper end (34) of the second needle valve (20); wherein at least a part of the first control chamber (28) is external to the second needle valve (20) and at least part of the first biasing means (84) is disposed within the first control chamber (28).

2. The dual-fuel injector (10) of Claim 1, wherein the second needle valve (20) is integrally formed as a unitary part.

3. The dual-fuel injector (10) of Claim 1 or Claim 2, wherein the first control chamber (28) is partially static.

4. The dual-fuel injector (10) of any preceding claim, wherein the first control chamber (28) is defined at least in part by the injector body assembly (14).

5. The dual-fuel injector (10) of any preceding claim, wherein the injector body assembly (14) comprises a nozzle control valve (NCV) housing (42), and wherein an upper surface of the first control chamber (28) is defined by the NCV housing (42), optionally the lower end (46) of the NCV housing (42).

6. The dual-fuel injector (10) of any preceding claim, wherein a lower surface of the first control chamber (28) is defined by the first needle valve (18), optionally the upper end (34) of the first needle valve (18).

7. The dual-fuel injector (10) of any preceding claim, wherein the first biasing means (84) is disposed around at least a part of the first needle valve (18), optionally around at least a part of the upper end (30) of the first needle valve (18).

8. The dual-fuel injector (10) of any preceding claim, wherein:the first needle valve (18) is movable between a closed configuration in which a first fuel path to the combustion chamber (12) is closed and an open configuration in which the first fuel path to the combustion chamber (12) is open, wherein a first gap (Gi) is defined between the first needle valve (18) and a first valve stop (52) when the first needle valve (18) is arranged in the closed configuration, and the first needle valve (18) abuts the first valve stop (52) when the first needle valve (18) is arranged at a full lift position in the open configuration; andthe second needle valve (20) is movable between a closed configuration in which a second fuel path to the combustion chamber (12) is closed and an open configuration in which the second fuel path to the combustion chamber (12) is open, wherein a second gap (G2) is defined between the second needle valve (20) and a second valve stop (54) when the second needle valve (20) is arranged in the closed configuration and the second needle valve (20) abuts the second valve stop (54) when the second needle valve (20) is arranged at a full lift position in the open configuration; andthe first gap (G1) is larger than the second gap (G2).

9. The dual-fuel injector (10) of Claim 8, wherein the first gap (G1) is around twice the length of the second gap (G2).

10. The dual-fuel injector (10) of any preceding claim, wherein the second control chamber (32) is defined at least in part by the injector body assembly (14).

11. The dual-fuel injector (10) of any preceding claim, wherein the dual-fuel injector (10) further comprises a second biasing means (86) configured to bias the second needle valve (20) into engagement with a second valve seat portion (72), optionally wherein the second biasing means (86) is disposed around the second needle valve (20).

12. The dual-fuel injector (10) of Claim 11, wherein the dual-fuel injector (10) further comprises a second accumulator volume (80) in the second flow path to one or moresecond fuel injection outlets (76), and wherein the second biasing means (86) is disposed within the second accumulator volume (80).

13. The dual-fuel injector of Claim 11 or Claim 12, wherein the dual-fuel injector further comprises a collar (82) coupled to the second needle valve (20), and wherein the second biasing means (86) engages the collar (82) and a portion of the injector body assembly (14) to bias the second needle valve (20) into engagement with the second valve seat portion (72).

14. The dual-fuel injector (10) of any preceding claim, wherein the first needle valve (18) is co-axial and / or concentric with the second needle valve (20).

15. The dual-fuel injector (10) of any preceding claim, wherein the first fuel is diesel and / or the second fuel is methanol.

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