FIELD OF THE INVENTION

[0001 ] The present invention relates to fuel injection systems, such as those used with air-cooled unmanned aerial vehicles (UAV) or snowmobile engines.

[0002] In particular the present invention relates to single or dual fluid injection systems, and preferably direct injection systems, and more preferably those systems used for delivering heavy fuel.

BACKGROUND TO THE INVENTION

[0001 ] UAVs and snowmobiles have certain space/packaging limitations around the engine. Both vehicles need the engine to be powerful yet compact. This is particularly relevant for UAVs where the engine typically needs to have a low profile in order to minimise wind resistance and/or maximise streamlining.

[0002] Whilst the following discussion makes particular reference to and exemplifies UAV engines and associated fuel delivery systems and problems relating thereto, it will be appreciated that similar cold conditions and packaging limitations associated with UAVs may also apply to snowmobiles.

[0003] UAV and snowmobile engines, like other engines, require a fuel system to deliver fuel into the combustion chamber(s) of the engine. The weight of mechanical and electrical components, as well as the airframe and control surfaces, contribute to the overall weight of a UAV.

[0004] By their very nature, it is important to keep down the weight of all components on a UAV where possible in order to maximise the performance characteristics of the engine and the propulsion system, typically a propeller for a UAV (or tracks and associated drivetrain for a snowmobile), as well as to maximise vehicle endurance for a given amount of on-board fuel. Hence, it is beneficial to be able to reduce the overall weight of mechanical and electrical components, including components in the fuel delivery system, for the engine.

[0005] Likewise, UAVs and snowmobiles have limited space for the packaging of certain components. UAVs in particular need a low frontal profile to minimise wind resistance. This places packaging limitations on the overall height and width across the engine and engine components. Maintaining a low profile is preferred in order to improve speed through the air and/or maximise fuel efficiency and UAV performance.

[0006] In respect of fuel systems for UAV engines, known UAV engines predominantly use naturally aspirated engines that rely on the airflow drawn into the combustion chambers to entrain fuel from a carburettor. Such engines are predominantly suitable for gasoline/petrol as the fuel, and have severe

performance limitations, particularly at high altitudes or high engine speeds/loads.

[0007] Some alternative types of fuel systems are also known which use fuel injection relying on a single fuel injector to inject fuel into an inlet manifold to entrain with the air, or single/multiple fuel injectors with each one injecting fuel into a respective inlet duct for a corresponding combustion chamber. Such injection systems again, are more so suitable where gasoline/petrol is the fuel used by the engine.

[0008] Heavy fuels can sometimes be injected by such systems, but these typically need to be kept warm in order to avoid issues with poor vaporisation (and hence combustion) when delivered by the fuel system due in the main to high viscosity properties. That is, heavy fuels, such as diesel and kerosene based fuels, require the fuel to be kept sufficiently warm in order to efficiently be delivered to the engine by the fuel injector(s). If the fuel gets too cold, this may lead to unsatisfactory vaporisation of the fuel within the combustion chamber(s) due to the high viscosity of the fuel in turn leading to poor engine performance, stability problems (e.g. increased vibration and thereby problems with camera payloads, for example) or potentially stalling of the engine and hence UAV operation.

[0009] Heating the fuel in the combustion chambers using glow plugs is common practice in diesel engines. However, diesel engines tend to be heavy in order to cope with the compression ignition pressures within the combustion chamber(s). Also, glow plugs would represent an additional piece of equipment on a UAV engine that would also need an additional electrical power supply. Such electrical heating is power hungry, in turn adding to the cost and complexity of equipment required for an overall aircraft.

[0010] It would nonetheless be beneficial to be able to run a UAV engine on a 'heavy fuel'. This is partly due to the fact that heavy fuels are becoming standard fuels for many users, and partly because of their low volatility and, thereby, safety. However, heavy fuel characteristics include low octane rating as well as low volatility, and consequently engines running on heavy fuel are prone to knock (pre-ignition), particularly at leaner than stoichiometric air-fuel ratios and under engine load. Such instability caused in the UAV as a result of such knock could for example lead to unwanted problems with camera operation for surveillance or surveying applications.

[001 1 ] Known direct injection systems optimised for gasoline use, such as those used in motorcycle applications in recent times, have weight and frontal area as a low priority. Consequently, there has been no real need or demand to modify the single or axially arranged dual injector arrangements of known Dl fuel systems. In the cases of dual fluid injection systems, axial arrangements of the fuel and delivery injectors are also considered to represent a more efficient and technically better solution. Direct injection (Dl) fuel systems, particularly air assisted (dual fluid) Dl fuel systems are well suited to inject heavy fuel into the combustion chamber(s) of an engine. [0012] Dual fluid Dl is known to better atomise the heavy fuel and deliver as much of a metered amount of fuel as possible. Such Dl fuel systems can hence provide for better combustion conditions within the engine combustion

chamber(s) as, once atomised, the fuel is more able to vaporize as a greater effective surface area is exposed for combustion per unit volume of injected fuel.

[0013] As alluded to hereinbefore, such dual fluid Dl systems, predominantly used on engines for road vehicles, typically utilise a fuel injector piggybacked on top of a delivery injector in an inline or axial arrangement. The fuel injector outputs an amount of fuel which is entrained in pressurised air and the combined charge of fuel and air is delivered into the combustion space by the delivery injector.

[0014] However, whilst this axial arrangement of the fuel injector on top of the delivery injector is acceptable for many applications, a UAV needs to be lightweight and streamlined. Having a fuel injector projecting upwards on top of a delivery injector would create significant packaging and engine performance problems for the UAV engine.

[0015] Furthermore, any benefits which may ensue from some degree of heat being transferred from the warmer engine cylinder head to the fuel system by virtue of its proximity to the cylinder head (i.e. and contributing to some degree of warming of the fuel) are effectively reduced by the fuel injector being further away from this warmer part of the engine. Similar problems also exist for snowmobile applications.

[0016] However, having a fuel injection path through a fuel rail other than directly axially between the fuel injector(s) and the entry into the combustion chamber creates a fuel delivery path that is also not directly axial. This can present a problem for correctly delivering fuel to the combustion chambers in that the injected fuel may cause 'wall wetting' in the fuel delivery path, may not fully atomise or otherwise not be fully delivered into the combustion chamber. [0017] It will be appreciated that the present invention providing an interface in a low fuel rail arrangement is specifically advantageous for UAV and

snowmobile applications. The lower profile arrangement brings the injector(s) closer to the engine for additional warmth - which improves one or more of reliability, longevity, fuel economy and smooth running of the engine.

[0018] Cost, size, space and weight advantages desirably resulting from the present invention are considered particularly beneficial for small UAV and snowmobile engine applications where low ambient and low wind chill

temperatures will be experienced.

[0019] Furthermore, one or more desirable applications of the present invention enable(s) the overall height of the fuel system (and hence the engine cowl covering the top of the engine and the fuel system injectors and fuel rail) to be reduced to in turn reduce weight and drag, and also vulnerability to damage.

[0020] Beneficially, reducing the overall height of the engine and fuel injection system enables production costs to be kept to a minimum so that the UAV engine and cowling can remain cost competitive in the market.

[0021 ] It is therefore desirable of the present invention to provide a fuel rail for a fuel injection system that allows for non-axial alignment of an injector relative to an entry to a combustion chamber of an engine and yet reduces the risk of poor fuel delivery.

[0022] It is also desirable of the present invention to provide a fuel rail interface in a dual fluid fuel system that facilitates satisfactory transportation of a metered quantity of fuel from a fuel metering injector to a corresponding fuel delivery injector.

SUMMARY OF THE INVENTION [0023] With the aforementioned in mind, the present invention provides in one aspect a fuel injection system injector interface including an inlet to receive a nozzle of a fuel injector, an outlet, and a passage connecting the inlet and the outlet, wherein the inlet and the outlet have different axial alignments.

[0024] Preferably the passage includes a first portion inclined towards the outlet.

[0025] A further aspect of the present invention provides a fuel injection system injector interface including an inlet to receive a nozzle of a fuel injector, an outlet for delivery of fuel to an entry to a combustion chamber of the engine, and a passage connecting the inlet and the outlet, wherein the passage varies in width between the inlet and the outlet.

[0026] Another aspect of the present invention provides a fuel injection system injector interface including an inlet to receive a nozzle of a fuel injector, an outlet, and a passage connecting the inlet and the outlet, the passage having a side wall arranged to guide fuel between the inlet and outlet, wherein the inlet and the outlet are not axially aligned with each other.

[0027] Thus, the injector interface of the present invention is a device that provides an improved interface between the fuel injector and the cylinder head/combustion chamber, and more particularly, a delivery injector arranged with respect the cylinder head/combustion chamber.

[0028] The passage may be an internal passage within the injector interface. The passage may be integral to the injector interface. Thus, the passage may be cast or machined in a body of the injector interface, or formed by combining interface components together. The injector interface may be a fuel rail. The passage is thus not a separate interface piece outside or inside of the fuel rail between the inlet and outlet. [0029] Another aspect of the present invention provides a fuel injection system injector interface including an inlet to receive a nozzle of a fuel injector, an outlet, and a passage connecting the inlet and the outlet, wherein fuel injected by the fuel injector into the passage is incident at an angle onto a surface of the passage.

[0030] Preferably the fuel incident onto the surface is reflected or directed towards the outlet.

[0031 ] Thus, the present invention is applicable to angled spray injectors or injectors aligned to spray towards an interior side wall of the passage.

[0032] Preferably the passage is generally circular and the width varies in diameter between the inlet and the outlet. The width or diameter may vary along substantially all of the passage's length or along a portion of the passage.

[0033] The passage first portion may be inclined at an angle Ψ between 0.0° and 45° with respect to a central axis passing through a centre of the inlet that leads to the passage. Thus, at Ψ = 0.0° alignment, the first portion may extend in axial alignment with the inlet. Preferably the first portion is inclined at an angle Ψ of between 5.0° and 20°, and more preferably between 5.0° and 10°. A preferred alignment for such an angled passage arrangement is at around 7.5° ± 0.5°.

[0034] The inlet may include a hollow to accommodate the nozzle or plume from the injector. The hollow is preferably circular. The hollow may have a side wall that tapers to a base portion of the hollow. The side wall may alternatively be stepped or have a smooth, continuous taper. The side wall may taper at an angle a between 5° and 80° with respect to the base portion, and more preferably taper at an angle a of 45°.

[0035] The passage may include a narrowing aperture from the inlet, which preferably tapers for fluid connection to the passage portion. That narrowing aperture may also be inclined, such that an outlet of that aperture to the passage portion is angled to meet the passage portion.

[0036] When the fuel injector is received in a first opening of the inlet, the nozzle of the fuel injector is not in axial alignment with the inclined first portion of the passage.

[0037] The passage may include the inclined first portion in fluid connection with a second portion. Preferably the second portion is in fluid connection between the first portion and the outlet.

[0038] The outlet of the injector interface may include an opening to receive an inlet end of a delivery injector. The second portion may be shorter than the first portion.

[0039] The first and second portions may be connected at a corner or elbow of the passage. The corner or elbow may include a radiused portion to assist flow of fuel changing direction at the corner or elbow through the passage. The radius may be provided at an outside portion of the corner or elbow with respect to fuel flow through the passage at that point. The radius may be between 0.5mm and 10.0mm, preferably between 0.5mm and 5.0mm, and more preferably around 1.0mm.

[0040] The system may be a dual fluid direct injection system with a fuel injector and a delivery injector.

[0041 ] A dual fluid direct injection system may have the passage leading from the inlet to the outlet, wherein a delivery injector is received, in use, in the outlet. The delivery injector is arranged to receive the fuel under pressure and additionally pressurised air from an air supply, and to inject the fuel and air into the combustion chamber of the engine, with the fuel injector arranged to inject fuel into a hollow in a base of the inlet, the hollow leading to the passage. [0042] Advantages and benefits of forms of the present invention include reducing fuel delivery problems that may be associated with an injector interface having a fuel passage therethrough that is not axially inline between a fuel injector and an entry to a combustion chamber.

[0043] Preferably the injector interface is arranged within a lateral fuel rail. Lateral entry of the fuel injector into the fuel rail reduces the overall height of the fuel system by having the fuel injector on its side injecting into the fuel rail relative to the engine rather than axially arranged with an engine cylinder and injecting directly towards the engine. This brings the fuel injector closer to the engine and reduces the overall packaging envelope of the fuel rail and fuel system . This also helps to warm the fuel delivered to and injected by the fuel injector because of the shorter heat conduction and convection paths to the injector and associated connections.

[0044] For a lateral fuel rail, the inclined passage, and preferably together with the radiused corner, helps to maintain accurate fuel delivery given that the fuel has to effectively transit around a corner to a corresponding delivery injector. However, reflecting fuel injected at high pressure, and preferably a mix of fuel and air in a dual fluid injection system, off a side wall of the inclined passage could be considered counter intuitive. Nevertheless, it has been found beneficial to reflect injected fuel off the side wall of the inclined passage portion at an angle such that the reflected portion is directed towards where the first and second portions meet.

[0045] This improves the ability to inject heavy fuel, particularly under extreme cold conditions, and improves combustion, fuel economy, engine efficiency and stability.

[0046] A further aspect of the present invention provides a fuel injection system injector interface assembly including a fuel injector having an outlet end and an inlet end, an injector interface having an inlet body arranged to receive at least a nozzle of the fuel injector, a rear housing to receive the inlet end of the fuel injector, and at least one seal arranged to seal the fuel injector inlet and outlet ends in the respective inlet body and rear housing to prevent fuel leakage from around the fuel injector, and retaining means to retain the fuel injector inlet and outlet ends in the respective inlet body and rear housing.

[0047] The injector interface assembly thereby provides a 'floating' fuel injector that is readily replaceable when required.

[0048] The fuel injector may have restricted longitudinal movement bounded rearward by the rear housing and forward by the inlet body being in fixed positions, preferably the inlet body and rear housing being held in position by the retaining means.

[0049] The retaining means may be removable or releasable, or both. Thus, the injector interface assembly provides a multi component assembly wherein the fuel injector is readily removable, such as for replacement or refurbishment, by removing or releasing the retaining means. The retaining means may include one or more clips, such as wire or plastic clips.

[0050] The rear housing may include connection for a fuel delivery conduit, and optionally a fuel return conduit. The inlet body and rear housing may also retain a fuel pressure regulator therebetween.

[0051 ] The inlet body may include an outlet arranged to receive an inlet of a delivery injector. The delivery injector may be for a dual fluid direct injection system arranged to deliver a fuel-air mixture directly into a combustion chamber of the engine.

[0052] It will be appreciated that one or more forms of the present invention address(es) cooling and wind resistance issues for UAV and snowmobile engines that operate in very cold environments (e.g. -10°C and below). [0053] The lateral fuel rail arrangement of the present invention can

accommodate different fuel injector types, including top-feed (fuel) injectors.

These are typically commercially available in high volume and hence are desirable for use for cost and ease of sourcing benefits. Such top-feed fuel injectors can be made to work with the lateral fuel rail despite being arranged laterally with respect to the engine cylinder. The top-feed fuel injector may be provided with suitable attachments at its inlet or outlet to facilitate the use thereof in a lateral orientation.

[0054] Furthermore, one or more forms of the present invention is

advantageous in isolating the lateral fuel rail by way of a separator that divides the engine housing into two spaces to help keep the fuel system and hence injectors warm whilst also containing airflow across the engine.

[0055] The present invention may include embodiments of a fuel interface manufactured as a single piece item. Manufacturing may be by initial casting of an interface body and subsequent machining to form the passage(s), whether angled or lateral with respect to the engine cylinder, through the body.

[0056] Machining the fuel interface directly into the fuel rail means the final rail is much simpler to make than previous lateral fuel rail systems and can be kept smaller and lighter as a result.

[0057] With the aforementioned in mind, the present invention may provide a UAV or snowmobile engine fuel injection system fuel rail including a first opening to receive a nozzle of a fuel injector, and a first passage having an inlet leading from the first opening to an outlet for delivery of fuel via a cylinder head passage into a combustion chamber of the engine, wherein the first opening and the outlet have different axial alignments.

[0058] When the fuel injector is received in the first opening, the nozzle of the fuel injector is also not in axial alignment with the outlet. [0059] The system may be a dual fluid direct injection system with a fuel injector and a delivery injector.

[0060] A dual fluid direct injection system may have the first passage leading from the first opening to a second opening in which, in use, is received an inlet of a delivery injector, the delivery injector arranged to receive the fuel under pressure and additionally pressurised air from an air supply, and inject the fuel and air into the combustion chamber of the engine, the fuel injector and the delivery injector arranged to inject the fuel in different directions relative to each other due to differing axial alignment of the first opening and nozzle of the delivery injector.

[0061 ] Advantages and benefits of forms of the present invention include reducing the weight and frontal area of the fuel system , and improving heat retention of the fuel and fuel rail to maintain or enhance fuel vaporisation and the combustion characteristics, particularly of a heavy fuel engine.

[0062] Lateral entry of the fuel injector into the fuel rail reduces overall height of the fuel system by having the fuel injector on its side injecting into the fuel rail relative to the engine rather than injecting directly towards the engine. This brings the fuel injector closer to the engine. This also helps to warm the fuel delivered to and injected by the fuel injector because of the shorter heat conduction and convection paths to the injector and associated connections.

[0063] According to one or more embodiments of the present invention, the fuel injector and the delivery injector of a dual fluid direct injection fuel system are not axially aligned. That is, their nozzles inject in different directions rather than one injecting directly toward the other in axial alignment.

[0064] The fuel injector may be arranged at an angle relative to the delivery injector such that a fuel plume from the fuel injector is directed towards the delivery injector but not axially inline with a corresponding plume from the delivery injector.

[0065] The fuel injector and the delivery injector may each have a longitudinal central axis. According to one or more embodiments of the present invention, the fuel injector longitudinal central axis is not in axial alignment with the delivery injector longitudinal central axis.

[0066] The first opening in the fuel rail, and therefore the fuel injector, may be orientated at an angle between 10° and 90° relative to the second opening in the fuel rail to receive the delivery injector. Preferably at an angle between 45° and 90°, and more preferably between 80° and 90°.

[0067] It will be appreciated that, as the difference in this angle of alignment increases such that the fuel injector is arranged more and more on its side and increasingly out of axial alignment relative to the delivery injector, there is a corresponding reduction in overall height of the fuel injection system, thereby enhancing packaging of the fuel injection system, particularly relevant to UAV and snowmobile engines where packaging space is limited.

[0068] Preferably, the first opening of the fuel rail is substantially at a right angle with respect to its outlet or the second opening to receive the delivery injector. Thus, the fuel injector and delivery injector can be at right angles with respect to each other. With the delivery injector typically aligned pointing into the combustion chamber of the engine, it will be understood that the first opening of the fuel rail to receive the fuel injector, and therefore the fuel injector itself when installed, may be aligned laterally (sideways) with its nozzle directed into the first opening.

[0069] Particularly in the case of UAVs, this reduction in overall height also brings streamlining benefits, as well as reducing the height of any cowling and/or engine covers, and thereby decreasing overall weight of the UAV, for additional weight reduction benefits.

[0070] Forms of the present invention beneficially provide a more compact arrangement than axially aligned fuel injectors (and for dual fluid systems, delivery injectors), and also provide shorter heat paths between the cylinder head interface and the fuel injectors to preheat the fuel for improved fuel delivery.

[0071 ] For heavy fuel Dl operated engines, bringing the fuel injector closer to the cylinder head shortens the conduction and convection heat paths to warm the fuel in the injectors and the fuel supply lines to the injectors. This improves ability to inject heavy fuel, particularly under extreme cold conditions, and improves combustion, fuel economy, engine efficiency and stability.

[0072] A further aspect of the present invention provides a fuel injection system injector interface including an inlet to receive fuel injected from a nozzle of a fuel injector, an outlet, and a passage connecting the inlet and the outlet, the passage including a passage first portion leading into the interface from the inlet, wherein the fuel injected by the fuel injector impinges at an acute angle on a surface of the initial passage portion.

[0073] It has beneficially been found that directing the spray from the fuel injector onto the lead in surface into the passage of the interface at an acute angle allows the fuel to deflect or be directed from that surface into the main portion of the passageway. This helps guide the fuel through the passageway to the outlet. It will be appreciated that the fuel may entrain in an airflow passing into the passageway and be helped to mix with and travel with the airflow by impinging onto and deflecting off of the surface.

[0074] Preferably the fuel deflects from the surface at or about the impinging angle i.e. an acute angle, and more preferably the opening into the interface from the inlet is positioned in a deflection path of the fuel when the fuel deflects from the surface.

[0075] The fuel injector may provide a fuel spray pattern as a cone or multiple streams behaving like a conical spray or some other spray pattern behaving like a conical spray pattern into the inlet, with at least a portion of the fuel spray pattern impinging on the surface at the acute angle.

[0076] Alternatively, the fuel injector may provide a fuel spray pattern as a single stream, whether lateral or angled as it leaves the fuel injector, which impinges on the surface at the acute angle.

[0077] A peripheral portion of the fuel spray pattern may be sprayed at the surface at the acute angle. Thus, the outer portion of the fuel spray may impinge on the surface whilst any central or core portion of spray may be directed more towards an opening into the passage.

[0078] The passage first portion may include a first portion surface narrowing from the inlet and leading into the remaining passage of the interface.

[0079] The first portion surface may be tapered, conical or a curved lumen narrowing from the inlet into the rest of the passage. This opening from the inlet may be machined into the material of the interface or may be an insert received in an opening at the inlet.

[0080] The acute angle is preferably greater than zero degrees (0°) and no greater than forty degrees (40°), more preferably between 20° and 36°, and yet more preferably substantially 32°. The cone (plume) angle of the spray from the fuel injector may be about 20° and a spray pattern included angle of about 24°, though other angles are considered to fall within the scope of the present invention provided the impinging angle remains an acute angle. [0081 ] The fuel injector may include a multi hole orifice to create the fuel pattern for delivery into the passage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0082] The present invention may be more fully understood from the following description of preferred embodiments thereof made with reference to the accompanying drawings in which:

[0083] Figure 1 shows a section through a fuel rail of a dual fluid direct injection system wherein a passage first portion is angled with respect to the orientation of the fuel injector according to an embodiment of the present invention;

[0084] Figure 2 shows an exploded view of a fuel rail assembly according to an embodiment of the present invention;

[0085] Figures 3A to 3E show alternative embodiments of the present invention incorporating a fuel spray impinging at an acute angle onto a surface of a passage first portion; and

[0086] Figure 4 shows a section through a fuel rail of a dual fluid direct injection system wherein a passage first portion is inline or axial with respect to the orientation of the fuel injector according to an embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT

[0087] Figure 1 shows a fuel injector interface in the form of a fuel rail 10 providing an interface between a fuel injector (not shown) and a delivery injector (not shown) to deliver dual fluids (fuel and air) directly into a combustion chamber of an engine. Figure 1 includes an ellipse E highlighting the passage and its features.

[0088] The fuel rail 10 includes an inlet 12 to receive a nozzle end of the fuel injector and an outlet 14 to receive the inlet end of a delivery injector.

[0089] A passage 16 connects the inlet to the outlet. The passage may be between 2.0mm and 10.0mm long, preferably around 6.0mm-7.00mm long. The passage has a portion 18 inclined with respect to the inlet. The inclined portion has a side wall arranged to reflect a plume of fuel (and in the case of a dual fluid injection system, fuel and air) at an angle from an angle of incidence of preferably around 7.5°±0.5°. The reflected fuel plume is thereby directed towards the juncture between the first and second portions of the passage. The inclined portion leads to a corner or elbow 20 connected to a shorter second portion 22 leading to the outlet. The corner or elbow has a radius Ri of approximately 2.0mm. The radiused corner advantageously assists smooth transit of the fuel (or fuel and air) from the first portion to the second portion.

[0090] The passage may have an internal diameter Di of between 1 .0mm and 5mm, preferably substantially 2.0mm. The bore of the passage may taper or vary in diameter along the length of the passage. For example, the inclined first portion may taper to the corner or elbow. Also, the second portion may taper. The second portion may have a diameter D ₂ between 1 .00mm and 5.0mm, preferably substantially 2.0mm.

[0091 ] The inlet 12 can include a shoulder 24 arranged to act as a stop for a portion of the fuel injector (not shown).

[0092] A space created between a nozzle end of the fuel injector and the base 28 of the hollow 26 by the fuel injector abutting the shoulder 24 provides sufficient room for the fuel plume from the fuel injector to be entrained in air entering the space via an air inlet fed by an air supply (such as a compressor). [0093] Fuel injected by the fuel injector can efficiently and effectively mix with air from the air supply at the space formed by the hollow. That fuel-air mix is under pressure and transits the inclined passage to the delivery injector inlet by which the fuel-air mix is directly injected into the combustion chamber.

[0094] Figure 2 shows a fuel rail assembly 40 for use with a dual fluid direct injection system.

[0095] The fuel rail assembly has a fuel injector 42 having an outlet end 44 and an inlet end 46, a fuel rail inlet body 48 arranged to receive at least a nozzle 50 of the fuel injector, a rear housing 52 to receive the inlet end of the fuel injector, and at least one seal 54 arranged to seal the fuel injector inlet and outlet ends in the respective inlet body and rear housing to prevent fuel leakage from around the fuel injector, and retaining means (not shown) to retain the fuel injector inlet and outlet ends in the respective inlet body and rear housing.

[0096] The fuel injector may have restricted longitudinal movement bounded rearward by the rear housing and forward by the inlet body being in fixed positions, and preferably the inlet body and rear housing are held in position by the retaining means.

[0097] The retaining means may be removable or releasable, or both. Thus, the fuel rail assembly provides a multi component assembly wherein the fuel injector is readily removable, such as for replacement or refurbishment, by removing or releasing the retaining means. The retaining means may include one or more clips, such as wire or plastic clips.

[0098] The rear housing may include connection for a fuel delivery conduit 56a, and optionally a fuel return conduit 56b. The inlet body and rear housing may also retain fuel pressure regulator 58 therebetween. [0099] The inlet body 48 may include an outlet 60 arranged to receive an inlet 62 of a delivery injector 64. The delivery injector may be for a dual fluid direct injection system arranged to deliver a fuel-air mixture directly into a combustion chamber of the engine. 0 ring seals 66 may be provided between components.

[00100] In use, the fuel rail assembly is connected to the cylinder head of an engine to allow the fuel injector and delivery injector to deliver fuel and air to the engine.

[00101 ] According to one or more embodiments of the present invention, the interface can receive a range of different fuel sprays from the fuel injector for transportation to the delivery injector. For example, the fuel spray from the fuel injector may be delivered as a broadening spray, such as from a multi hole spray or as a cone, or as a pencil stream, angled or bent stream.

[00102] In the case of a multi hole spray, the outlet holes from the fuel injector serve to create a spray which approximates a conical spray, and the interface is preferably arranged so that the fuel streams impinge on the wall of the connecting passage at an acute angle. As a result, the axis of the first portion of the connecting passage of the interface can preferably be on the same axis as the injector. The same would apply to a fuel injector arranged to deliver an angled pencil stream spray which impinges on the wall of the connecting passage at an acute angle.

[00103] However, whilst such a coaxial arrangement may be beneficial from a manufacturing stand-point, as evidenced from the previous discussion in respect of Figure 1 , it is not essential that the fuel injector and connecting passage are arranged coaxially. What is more relevant is that, whatever the arrangement of fuel injector with respect to the connecting passage, part of the fuel spray issuing from the fuel injector is able to impinge at an acute angle on the surface(s) of the connecting passage. [00104] Referring more generally to Figures 1 and 2, the fuel injection system depicted in these figures includes a delivery injector 64 supplied with air and fuel under pressure from a respective fuel injector 42 and an air passage (not shown).

[00105] The delivery injector 64 is mounted to deliver a metered quantity of fuel entrained in air directly into a combustion chamber of an engine (such as a UAV or snowmobile engine). The delivery injector 64 is supplied with the fuel assisted by air pressure within the system via a passage 22. Unlike conventional dual fluid Dl injection systems, the fuel injector 42 is not mounted axially inline with and above the delivery injector 64; rather, the fuel injector 42 enters the fuel rail 10 laterally (from the side). The height of the overall fuel injection system is thereby reduced. This also brings the fuel injector 42 closer to the engine, which helps improve fuel injector warming, and therefore fuel warming. That is, the lateral rail arrangement is more able to utilise heat from the engine due to the geometry and reduced length of the heat path between it and the cylinder head. Distance between the fuel injector 42 and delivery injector 64 is also shortened compared with axially aligned injectors.

[00106] The fuel injector 42 has a nozzle 50 received in a first opening or inlet 12 of the fuel rail 10. The fuel injector 42 has a central longitudinal axis which is angled with respect to the central longitudinal axis of the delivery injector 64. The delivery injector 64 has its inlet 62 received in an outlet 14 of the fuel rail 10. The delivery injector of the dual fluid direct injection system is arranged to deliver the dual fluids via a delivery injector nozzle into the combustion chamber of the engine.

[00107] The lateral (side) entry of the fuel injector 42 into the fuel rail 10 reduces overall height (thereby reducing frontal area and reducing overall packaging space as well as, importantly, wind resistance for a UAV). Heat conducted through the metal of the fuel rail 10 and also convected within the heated space above helps to heat the fuel injector 42 and associated fuel lines to and from the injector, helping to keep heavy fuel less viscous than would otherwise be the case with an axially or inline setup. Also, bringing the entry for the fuel injector 42 to a lateral position on the fuel rail 10 shortens the fuel path between the fuel injector nozzle 50 and the delivery injector inlet 62, thereby improving the metering of fuel to the delivery injector 64 and overall dual fluid delivery into the combustion chamber.

[00108] Figures 3A to 3E show a fuel injector 100 spraying fuel 102,

104, 106, 108, 109 into a passage first portion 1 10 of a fuel rail interface 1 12.

Each interface has a passage 1 14 therethrough between an inlet 1 16 and an outlet 1 18.

[00109] In Figure 3A, a pencil or linear stream of fuel is sprayed into the first passage portion to impinge at an acute angle a on the surface 120 of the side wall 122 in the first passage portion. The first passage portion 122 is inclined with respect to the direction of the fuel spray i.e. the fuel spray is directed straight from the injector into the passage inlet and impinges the side wall of the passage first portion at an acute angle due to the inclination of that passage portion from the axis of the fuel stream.

[001 10] It will be appreciated that the passage first wall portion is preferably between the inlet and a change in axial direction of the passage first portion along the passage, such as prior to an elbow or corner 124 or other change of direction in the passage.

[001 1 1 ] Figure 3B shows an embodiment wherein the fuel spray is an angled spray or a cone pattern or multi-hole spray, and the peripheral portion of the cone spray impinges the surface at the acute angle. In this embodiment, the passage first portion forms a conical surface. However, other shapes are considered to fall within the scope of the present invention.

[001 12] For all of the embodiments referenced with respect to Figures 3A to 3E, preferably the angle of deflection of the spray rebounding from the surface is at an acute angle equal to or substantially the same as or somewhat shallower than the acute angle of impingement, such that the spray deflected from the surface is directed into an opening leading to the remainder of the passage.

[001 13] As shown in Figures 3B and 3C, the passage first portion is axially aligned with the fuel injector, such that, if a linear or pencil fuel plume was injected into the inlet, the fuel would be directed straight down the passage to the elbow 124. However, with a broadening spray, such as a cone or multi jet cone 106, the spray pattern spreads out and impinges (at least the peripheral portion impinges) onto the side wall of the first passage portion. The first passage portion then narrows or tapers leading into the remainder of the passage. This narrowing or tapering provides a suitable angle of reflection for the fuel from the surface and directs the fuel into the opening to the passage.

[001 14] Figure 3D shows an inclined passage from the inlet to the elbow with respect to the axial alignment of the injector. Thus, a conical or multi stream conical fuel spray 108 all impinges on the surface at an acute angle, and thereafter is guided down the remainder of the passage.

[001 15] Preferably the angle a is greater than zero degrees but no greater than 40°. The actual acute angle of impingement onto the surface of the passage first portion is determined by the alignment of the injector relative to the opening into the passage, the shape or arrangement of the passage first portion, and the shape of the fuel spray pattern.

[001 16] Figure 3E shows an embodiment wherein the fuel spray is an angled or bent spray which impinges the surface 120 at an acute angle. This embodiment is similar to that shown in Figure 3B, wherein the passage first portion forms a conical surface. The embodiment of Figure 3E shows the fuel injector 100 and first portion 1 10 in axial alignment, but with the fuel spray issuing from the fuel injector 100 as an angled or bent stream such that it impinges the surface 120 at an acute angle, with the fuel spray then being deflected from the surface and directed into an opening leading to the remainder of the passage.

[001 17] Figure 4 shows a fuel injector interface similar to that described with reference to Figure 1 (with similar reference numerals used to depict similar elements), but includes a connecting passage of the fuel interface that is not angled with respect to a fuel injector (not shown). Rather in this embodiment the connecting passage and fuel injector are axially arranged with respect to each other.

[001 18] The fuel rail 210 again includes an inlet 212 to receive a nozzle end of the fuel injector and an outlet 214 to receive the inlet end of a delivery injector. A passage 216 connects the inlet to the outlet. The passage 216 in this instance however is not inclined with respect the inlet and rather is arranged axially with respect to the inlet. The passage 216 similarly leads to a corner or elbow 220 connected to a shorter second portion 222 leading to the outlet. The corner or elbow is radiused (R-i ) to advantageously assist smooth transit of the fuel (or fuel and air) from the first portion to the second portion

[001 19] The fuel interface arrangement depicted in greater detail in Figure 4 is one that would correlate to the lateral fuel rail arrangements shown in Figures 3B, 3C and 3E.

[00120] Application of the present invention facilitates a fuel rail for a fuel injection system that allows for non-axial alignment of an injector relative to an entry to a combustion chamber of an engine to enable realisation of beneficial packaging arrangements without sacrificing fuel delivery quality.