Fuel injector assembly

Abstract

A fuel injector assembly delivering gaseous fuel comprising a fuel injector 21. The fuel injector comprises a main injector housing 32, an electromagnetic actuator 24 mounted on the injector housing.

Description

FIELD OF THE INVENTION This invention relates to a fuel injector assembly for gaseous fuel. In particular, but not exclusively, the invention relates to a fuel injector assembly for use in a fuel system of an internal combustion engine or fuel cell for a gaseous fuel such as hydrogen. BACKGROUND Gaseous fuels, such as hydrogen, are promising alternative fuels to fossil fuels, such as gasoline and diesel, due to their potential for low or zero emissions and there has been considerable interest in developing traditional internal combustion engines to run on ecologically produced hydrogen. High pressure injection of gaseous fuels into the combustion chamber of an internal combustion engine offers benefits, including reduced compression work, reduced susceptibility to uncontrolled auto-ignition, and greater flexibility in combustion strategies resulting in improved efficiency. A relatively low flow fuel injector for hydrogen fuel is already known, particularly for use with internal combustion engines, but there remains a need fora relatively high flow injector to satisfy the demands of engines with fuel cells. Injectors capable of delivering the requisite high flows for gaseous fuel delivery typically include a large flow area which requires a significant force from an actuator of the injector. For example, an electromagnetic actuator requires a significant magnetic force to open an inwardly opening injector valve needle. In addition, the injector must open against a large gaseous fuel pressure difference between the injector inlet and the injector outlet. In order to generate the necessary force from the electromagnetic actuator, it is necessary to apply a large electrical current to the solenoid coil of the actuator, which can consequently lead to a large increase in temperature within the solenoid coil and the surrounding components. In some injector applications, it is sufficient to rely on the short ‘off time’ between injections to allow the dissipation of thermal energy. It is also known to manage the thermal energy within the injector using active cooling means, including the use of a fuel flow through the injector during injection. One of the problems with fuel cell applications, however, is that the duration of injection is much longer than in internal combustion engine applications, which means the associated thermal loading is higher. Such injectors tend to be sidefeed injectors so that fuel enters the injector much lower along the axial length of the injector and cannot easily be routed past the actuator for cooling purposes. The mounting of an injector in a fuel cell engine also requires the injector to be positioned or mounted on one or more O-rings, and so conductive thermal dissipation does not provide adequate cooling. It is against this background that the invention has been devised. SUMMARY OF THE INVENTION According to a first aspect, there is provided a fuel injector assembly of a fuel injection system for delivering gaseous fuel. The fuel injector assembly comprises a fuel injector having a longitudinal injector axis. The fuel injector comprises a main injector housing, an electromagnetic actuator, and a cooling device. The electromagnetic actuator is mounted on the main injector housing and comprises a solenoid assembly comprising a solenoid tube housing a solenoid coil to which current is applied, in use, to actuate the electromagnetic actuator. The cooling device comprises a cooling chamber configured to receive a cooling fluid, the cooling chamber being defined at least in part by an internal wall portion, separate from the main injector housing, and an external wall portion. The internal wall portion forms a part of a thermal path between the solenoid coil and the cooling chamber. The external wall portion may form a part of an external surface of the fuel injector assembly. The fuel injector assembly may be a gaseous fuel injector for delivering hydrogen, for example. The cooling device on the fuel injector provides an effective means for dissipating heat from the fuel injector. Importantly, the configuration of the cooling device, with the external wall forming an external wall of the fuel injector assembly, meaning it can be readily be mounted on the injector. Equally, however, the injector configuration does not need to be modified to mount the cooling device so that for applications which do not require cooling, the injector arrangement remains the same, providing a manufacturing advantage. For example, in applications for which heating of the injector may be a more significant problem, such as in hydrogen fuel cell applications, the cooling device can be included, but can be easily left off if not required. The internal wall of the cooling device forms a part of the direct thermal path between the actuator and external heat sink to which heat can be dissipated through the cooling device. In embodiments, an overmould may be provided to at least partially encapsulate the electromagnetic actuator. In embodiments, the overmould may define an upwardly-facing surface that extends radially from the longitudinal injector axis and a downwardly-facing surface that extends radially from the injector axis. The upwardly and downwardly-facing surfaces enable the overmould to effectively engage the cooling device for mounting. In some embodiments, the cooling device may be mounted, at least in part, axially above the upwardly-facing surface of the overmould. The cooling device thus acts to encapsulate an upper portion of the fuel injector assembly. In embodiments, the cooling device may define a downward-facing surface which engages with the upwardly-facing surface of the overmould. This enables the cooling device to effectively engage with the overmould when mounting. In other embodiments, the cooling device may be mounted, at least in part, axially below the downwardly-facing surface of the overmould. This enables the cooling device to annular surround the fuel injector to provide effective heat dissipation. The cooling device can also be easily slid onto the fuel injector from the side, if required. In embodiments, the cooling device may comprise an upper surface which engages with the downwardly-facing surface of the overmould. This enables the cooling device to effectively engage with the overmould when mounting. In some embodiments, the internal wall portion of the cooling device may be engaged with an outer surface of the solenoid tube. This provides effective thermal contact between the cooling device and the solenoid tube. In some embodiments, the internal wall portion of the cooling device and the external wall portion of the cooling device may be brazed or welded together to form a modular component. The cooling device may be readily assembled onto the injector, or not, depending on the cooling requirements for the particular injector application. In some embodiments, the gaseous fuel may be hydrogen. According to a second aspect, there is provided a method of assembling a fuel injector assembly of a fuel injection system for delivering gaseous fuel to an internal combustion engine. The method comprises mounting an electromagnetic actuator on a main injector housing, whereby the electromagnetic actuator comprises a solenoid coil mounted within a solenoid tube; applying an overmould to at least a part of the electromagnetic actuator; and mounting a cooling device, having a cooling chamber, an external wall portion, and an internal wall portion, on the main injector housing so that the internal wall forms a part of a thermal path between the solenoid coil and the cooling chamber, and so that the external wall portion forms an external surface of the fuel injector assembly. For example, the method may comprise applying an overmould to at least a part of the electromagnetic actuator prior to mounting the cooling device. The method may further comprise press-fitting the cooling device to the overmould. It will be appreciated that the fuel injector assembly is appropriate for use with an internal combustion engine or a fuel cell application. Preferred and / or optional features of the first aspect are applicable to the second aspect also, alone or in appropriate combination. BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more readily understood, preferred non-limiting embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a mounting portion of a known fuel injector assembly for gaseous fuel; Figure 2 is a cross section of a mounting portion of a fuel injector of an embodiment; Figure 3 is a perspective view of the fuel injector of Figure 2 in one embodiment; Figure 4 is a perspective view of the fuel injector of Figure 2 in another embodiment; Figure 5 is a cross section of a mounting portion of a fuel injector of another embodiment; and Figure 6 is a perspective view of the fuel injector of Figure 5. DETAILED DESCRIPTION OF THE INVENTION Throughout this description, terms such as ‘upper’ and ‘lower’, and other directional references, are used with reference to the orientation of the injector as shown in the accompanying drawings. However, it will be appreciated that such references are not limiting and that injectors according to the invention can be used in any orientation. By way of background to the invention, an upper portion of a known fuel injector assembly 1 comprising a fuel injector 2 is shown in Figure 1. Internally the injector 2 comprises an injection nozzle (not shown) having an injector valve needle that is inwardly-opening within the injection nozzle and is controlled by means of a servovalve mechanism. Externally, the injector assembly 1 can be seen to include several housing parts, including an actuator housing or overmould 4 and a main injector housing or fuel tube 6 that houses the valve needle. The injector assembly 1 is arranged to inject gaseous fuel into a combustion chamber of an associated internal combustion engine, or to a fuel cell, by moving the valve needle towards and away from a valve needle seating to control the gaseous fuel flow through one or more injector outlets. An electromagnetic actuator (not shown in Figure 1) is positioned towards the upper end of the injector 2, within the actuator housing 4. The electromagnetic actuator comprises a solenoid coil to which a current is supplied to generate an electromagnetic force that acts on the injector valve needle, directly or indirectly. Operation of the actuator therefore controls movement of the valve needle to control the injection of gaseous fuel. Gaseous fuel is introduced to the injector 2 via inlet fuel ports 8. The actuator housing 4 is formed from an overmould that is typically formed from plastic. The injector assembly 1 is clamped to an associated engine head through the overmould 4. Also, being positioned on multiple O-rings 10, which contact the associated engine head when the injector 2 is clamped to it, there is no direct metal-to-metal contact between the injector 2 and the engine head. It is important to control and manage the temperature of electromagnetic or solenoid actuators for fuel injectors as temperature changes can affect the performance of the fuel injectors in operation. Heating of the solenoid coil through operation presents a number of problems for the injector. For example, an increase in the temperature of the solenoid coil can cause the resistance of the coil to increase. An increase in resistance causes further heating for a given current supplied to the solenoid coil, which again causes a rise in the resistance. An increasing temperature therefore drives a cyclical heating problem if heat is not effectively dissipated from the solenoid coil. Excessive heating to the solenoid coil can result, for example, in thermal damage to the actuator and / or the resistance of the solenoid coil reaching a threshold whereby given voltages are unable to meet corresponding current targets, thus preventing the injector from operating as desired. Further, an increase in the temperature of the solenoid coil can cause thermal dissipation to other components within the fuel injector, causing them to expand despite the components being at least partially radially and / or axially constrained. For example, elastomer dampers (not shown) retained within the fuel injector may increase in length axially when heated above a standard operating temperature range. This increase in length can result in a shorter needle lift for the valve in the fuel injector, thus causing a reduction in flow. When the injector cools, and thus when the elastomer dampers cool, this effect is reversed and normal operating conditions can resume. This variation in flow and performance is not desirable and may not be acceptable for certain customer applications. It is therefore necessary identify a more reliable means of managing the temperature within the fuel injector for delivering gaseous fuel. The invention addresses this problem by equipping the fuel injector assembly with a cooling device that provides a direct heat transfer path between the actuator and the cooling device to allow heat to dissipate from the solenoid coil. Referring to Figure 2, an injector assembly 20 comprises a fuel injector 21 having a main injector housing comprising a fuel tube 32 with several sections of varying diameter, including an upper region 34 of relatively narrower diameter and a lower region 36 of relatively large diameter. High pressure gaseous fuel is introduced to the injector 21 via inlet fuel ports 65 in the lower region 36. A step 38 defines a supporting ledge between the upper and lower regions 34, 36 of the fuel tube 32. A moveable armature (not shown) of an injector actuator 24 is coupled to an injector valve needle 22 and is configured to control the injection of gaseous fuel into an associated engine or engine head. The actuator 24 comprises a solenoid coil 26 that is wound on a bobbin 28, the bobbin 28 being supported by the step 38. A solenoid tube 30 annularly surrounds the actuator 24 and is spaced from the solenoid coil 26. The fuel tube 32 extends through the bobbin 28 and the actuator 24. When current is applied to the solenoid coil 26, an electromagnetic force is generated that acts on the armature to control the movement of the injector valve needle 22 along a main axis A-A of the fuel injector 21. An overmould 40 is applied to the upper region 34 of the fuel tube 32 and fills any open gaps, for example including the space between the solenoid coil 26 and the solenoid tube 30, forming an internal wall 41 of the overmould 40. The overmould 40 is configured to cover the components of the actuator 24 of the fuel injector 21, including the majority of the solenoid tube 30 while leaving a small lower section of the solenoid tube 30 exposed to abut partially with the step 38 and partially with an outer surface of the fuel tube 32, for example as illustrated in Figure 2. The overmould 40 defines an upwardly-facing upper surface 44 that extends radially from the longitudinal injector axis A-A. The overmould 40 further defines a downwardly-facing lower surface 48 that extends radially from the longitudinal injector axis A-A. The overmould 40 includes a side projection 45 that extends, at an angle, axially above the upper surface 44. An O-ring (not shown) may be retained within the overmould 40 to provide a seal against the fuel tube 32 to prevent contamination from the external environment outside of the injector assembly 20, but is not essential. An end cap 46 covers the upper region 34 of the fuel tube 32 and defines an internal abutment surface for a valve needle spring (not shown) that serves to bias the valve needle 22 closed. The end cap 46 and the overmould 40 together provide an upper enclosure for the components of the injector 21 that extend beyond a pocket in the engine housing component in which the injector assembly 20 is received. The side projection 45 of the overmould 40 houses an electrical connector 64 for the actuator 24. An externally mounted, modular cooling device 50 comprising an annular waterjacket is assembled onto the overmould 40 on the upper region 34 of the fuel tube 32. The cooling device 50 is mounted on top of the overmould 40 so that a lower surface 51 of the cooling device 50 abuts against, and covers at least in part, the upper radially-extending surface 44 of the overmould 40. The cooling device 50 is configured to provide heat dissipation via thermal transfer from the solenoid coil 26 to a circulating cooling medium or liquid, such as water or other suitable fluid, to prevent the components of the actuator 24, and thus the injector 21, from reaching undesirable high temperatures during operation. The cooling device 50 comprises a cooling chamber, tank, or cavity 52 defined by an external annular sidewall 54, an internal annular sidewall 53, and a lid 56, which defines an upper surface of the cooling device 50. The cooling chamber 52 is configured to retain the cooling fluid. As can be seen most clearly in Figures 3 and 4, an inlet 60 and an outlet 62 to the cooling chamber 52 are disposed on the lid 56 to provide flow paths for cooling fluid to enter and exit the cooling chamber 52, respectively, during operation of the cooling device 50. The external sidewall 54, the internal sidewall 53, the lid 56, the inlet 60, and the outlet 62 are connected together, for example by welding or brazing, to form the modular cooling device 50, which can be readily assembled onto the injector 21, or not, depending on the cooling requirements for the particular injector application. An outer surface of the external sidewall 54 of the cooling device 50 defines an external surface of the injector assembly 20 around the upper region 34 of the fuel tube 32. The cooling chamber 52 is not symmetric about the injector axis A-A and extends to a lower axial position on one side, terminating in a lower section 52a. The internal annular sidewall 53 of the cooling chamber 52 is aligned with a portion of the upper region 34 of the fuel tube 32 and abuts with the solenoid tube 30, for example as illustrated in Figure 2. The inlet 60 and the outlet 62 may be positioned on substantially opposite sides of the lid 56, for example as illustrated in Figures 3 and 4. A pump (not shown) is configured to deliver the cooling fluid into the cooling chamber 52 via the inlet 60 which then exits the cooling chamber 52 via the outlet 62. Other configurations may be equally applicable. The abutment of the internal annular sidewall 53 and the solenoid tube 30 forms a conductive thermal bridge or path for thermally connecting the solenoid coil 26 to the cooling chamber 52. The thermal path is effectively comprised of the internal overmould wall 41, the solenoid tube 30, and the internal annular sidewall 53 such that heat is able to transfer from the solenoid coil 26 to circulating cooling fluid within the cooling chamber 52. The internal overmould wall 41, the solenoid tube 30, and the internal annular sidewall 53 may be constructed from a conductive material, such as a metal or alloy. The internal overmould wall 41 may be constructed from the same material as the overmould 40, such as a plastic or polymer material. In such cases, the thickness of the internal overmould wall 41 is selected to enable effective heat transfer through it. In operation, current is supplied to the solenoid coil 26, which causes the solenoid coil 26 to generate heat that is conducted via the abovementioned thermal path to cooling fluid within the cooling chamber 52. The cooling fluid absorbs the transferred heat, thus allowing the cooling device 50 to act as a heat sink for the solenoid coil 26. Due to the positions of the inlet 60 and the outlet 62 on the lid 56, the cooling fluid circulates around a significant proportion of the cooling chamber 52 before exiting, thus enabling the cooling fluid to absorb a large amount of heat from the solenoid coil 26. Cooling fluid is delivered through the inlet 60 to the cooling chamber 52 at a relatively low temperature compared to the temperature of the solenoid coil 26 during operation. Heat generated by the solenoid coil 26 during operation thus can be advantageously absorbed due to the relatively large temperature differential between the heated solenoid coil 26 and the low temperature cooling fluid within the cooling chamber 52. Cooling fluid that has been circulated around the cooling chamber 52 then exits the cooling chamber 52 and is replaced by additional relatively low temperature cooling fluid through the inlet 60. Advantageously, the temperature differential between the solenoid coil 26 and the relatively low temperature cooling fluid can be maintained to provide effective heat transfer and dissipation. Once installed or assembled onto the fuel injector 21, the cooling device 50 is fixedly secured to the fuel injector 21. For example, the cooling device 50 may be spot welded or brazed to the end cap 46 at the upper end 34 of the injector 21, as illustrated in Figure 3. In another example, a threaded pin or bolt 68 may be embedded in the end cap 46 of the injector 21. Once the cooling device 50 is slid into position, a corresponding nut 66 passes over the threaded pin 68 on top of the lid 56, thus securing the cooling device 50 to the injector 21, as illustrated in Figure 4. It is an important feature of the arrangement that the abutment of the internal annular sidewall 53 of the cooling device 50 and the solenoid tube 30 provides a direct thermal path between the solenoid coil 26 and the cooling device 50. In order to assemble the injector assembly 20 in Figures 2 to 4, the following assembly steps are followed. Initially, the internal components of the injector 21, including the valve needle 22 and the armature, are assembled within the fuel tube 32. Separately, the components of the actuator 24, including the solenoid coil 26, the bobbin 28, the solenoid tube 30, and other components, are assembled onto the overmould 40. The end cap 46 is applied to the upper end of the injector 21 and the overmould 40 is applied to the upper region 34 of the fuel tube 32, defining an upwardly-facing, upper surface 44 of the overmould 40. In this manner, the end cap 46 and the overmould 40 encapsulate the upper region 34 except for a small portion of the solenoid tube 30, which is left exposed to engage with the step 38 and with an outer surface of the fuel tube 32, for example as illustrated in Figure 2. Separately, the components of the cooling device 50 are assembled. The internal annular sidewall 53, the external annular sidewall 54, and the lid 56 are welded or brazed together to form the cooling chamber 52, and the inlet 60 and the outlet 62 are welded or brazed to the lid 56. The assembled cooling device 50 is then placed over the assembled fuel injector 21, including the overmould 40, so that the lower surface 51 of cooling device 50 abuts against the upper surface 44 of the overmould 40. The cooling device 50 is secured as discussed previously so that the external annular sidewall 54 of the cooling chamber 52 defines the external wall of the overall injector assembly 20. Advantageously, the modular nature of the cooling device 50 enables the cooling device 50 to be utilised with different injectors and injector assemblies and in different applications depending on the requirements. For example, where higher actuator currents and actuation speeds might be required, the cooling device 50 can be applied to an injector assembly 20, but in other applications there may be no cooling requirement. The cooling device 50 thus advantageously provides an externally mounted heat sink capable of maintaining optimal operating conditions of an injector assembly 20 where necessary, but being readily left off the injector 21 if not needed and without requiring other modifications to the associated injector assembly 20. Figures 5 and 6 show a fuel injector assembly 70 of an alternative embodiment in which the cooling device 50 is configured differently so that it sits beneath or below an upper section 71 of the overmould 40, rather than being located entirely on top of the overmould 40. Like parts to those shown in Figure 2 are denoted with like reference numbers and will not necessarily be described in further detail. The cooling device 50 annularly surrounds a lower section 72 of the overmould 40. The lower section 72 of the overmould 40 is comprised of the internal overmould wall 41, which resides between the solenoid coil 26 and the solenoid tube 30. The upper section 71 of the overmould 40 defines a radially-extending, downwardly-facing surface 49 that engages with an upper surface 78 of the cooling device 50. As before, an external wall of the cooling chamber 52 defines an external surface of the fuel injector assembly 70. In this embodiment, the cooling chamber 52 is defined within an internal wall portion 76 and an external wall portion 74 of the cooling device 50. A radially-extending portion 76a of the internal wall portion 76 that extends radially from the injector axis A-A interfaces with an axially-extending portion 74b of the external wall portion 74, and a radially-extending portion 74a of the external wall portion 74 interfaces with an axially-extending portion 76b of the internal wall portion 76. The external wall portion 74 and the internal wall portion 76 are welded or brazed together at their respective interfaces to form the cooling chamber 52. The cooling device 50 is mounted beneath the upper section of the overmould 40 to annularly surround, and abut against, the axially-extending portion 76b of the inner wall portion 76. The upper surface 78 of the cooling device 50 abuts against the downwardly-facing, radially-extending surface 49 of the upper section 71 of the overmould 40. The axially-extending portion 76b of the inner wall portion 76 abuts against an outer surface of the solenoid tube 30 to form a thermal path between the solenoid coil 26 and the cooling device 50. The inlet and outlet 60, 62 are welded or brazed to the upper surface 78 of the radially-extending portion 76a of the inner wall 76, for example as best seen in Figure 6. To one side of the injector assembly 70 (the right hand side in the view shown in Figure 5), the upper surface 78 of the cooling device 50 is exposed and the overmould 40 does not cover the cooling device 50 in this section. In order to assemble the injector assembly 70 in Figures 5 and 6, initially the internal components of the injector 21, including the valve needle 22 and the actuator 24, are assembled. Separately, the components of the actuator 24 are assembled onto the injector 21 and the overmould 40 is assembled onto the actuator / injector assembly 70. The cooling device 50 is then press-fitted axially beneath the upper section 71 of the overmould 40 so that the axially-extending portion 76b of the inner wall portion 76 surrounds and abuts with the outer surface of the solenoid tube 30, and the upper surface 78 of the cooling device 50 abuts against the lower surface 49 of the upper section 71 of the overmould 40. The abutment between the internal wall portion 76 of the cooling device 50 and the solenoid tube 30 allows heat generated by the solenoid coil 26 in operation to be dissipated via the thermal path formed between the solenoid coil 26, the internal overmould wall 41, the solenoid tube 30, and the cooling chamber 52. 5 Advantageously, the axially-extending portion 76b of the inner wall portion 76 of the cooling device 50 abuts the majority of the external annular surface of the solenoid tube 30 to provide optimal and effective heat dissipation. It will be appreciated that the cooling devices may have other arrangements and / or 10 configurations that are equally applicable with the embodiments. Other modifications and variations will be apparent to the skilled person without deviating from the scope of the appended claims. 15

Claims

1. A fuel injector assembly (20; 70) of a fuel injection system for delivering gaseous fuel, the fuel injector assembly (20; 70) comprising:a fuel injector (21), having a longitudinal injector axis (A-A), the fuel injector (21) comprising a main injector housing (32);an electromagnetic actuator (24) mounted on the main injector housing (32) and comprising a solenoid assembly comprising a solenoid tube (30) housing a solenoid coil (26); anda cooling device (50) comprising a cooling chamber (52) configured to receive a cooling fluid, the cooling chamber (52) being defined at least in part by an internal wall portion (53, 76), separate from the main injector housing (32), and an external wall portion (54, 74);wherein the internal wall portion (53, 76) forms a part of a thermal path between the solenoid coil (26) and the cooling chamber (52).

2. The fuel injector assembly (20; 70) as claimed in claim 1, wherein the external wall portion (54, 74) forms a part of an external surface of the fuel injector assembly (20, 70).

3. The fuel injector assembly (20; 70) as claimed in claim 1 or claim 2, comprising an overmould (40) at least partially encapsulating the electromagnetic actuator (24).

4. The fuel injector assembly (20; 70) as claimed in claim 3, wherein the overmould (40) defines an upwardly-facing surface (44) that extends radially from the longitudinal injector axis (A-A) and a downwardly-facing surface (48, 49) that extends radially from the longitudinal injector axis (A-A).

5. The fuel injector assembly (20; 70) as claimed in claim 4, wherein the cooling device (50) is mounted, at least in part, axially above the upwardly-facing surface (44) of the overmould (40).

6. The fuel injector assembly (20; 70) as claimed in claim 5, wherein the cooling device defines a lower surface (51) that engages with the upwardly-facing surface (44) of the overmould (40).

7. The fuel injector assembly (20; 70) as claimed in claim 4, wherein the cooling device (50) is mounted, at least in part, axially below the downwardly-facing surface (49) of the overmould (40).

8. The fuel injector assembly (70) as claimed in claim 7, wherein the cooling device (50) comprises an upper surface (78) that engages with the downwardly-facing surface (49) of the overmould (40).

9. The fuel injector assembly (20; 70) as claimed in any preceding claim, wherein the internal wall portion (53, 76) of the cooling device (50) is engaged with an outer surface of the solenoid tube (30).

10. The fuel injector assembly (20; 70) as claimed in any preceding claim, wherein the internal wall portion (53, 76) of the cooling device (50) and the external wall portion (54, 74) of the cooling device (50) are brazed or welded together to form a modular component.

11. The fuel injector assembly (20; 70) as claimed in any preceding claim, wherein the gaseous fuel is hydrogen.

12. A method of assembling a fuel injector assembly (20; 70) of a fuel injection system for delivering gaseous fuel to an internal combustion engine, the method comprising;mounting an electromagnetic actuator (24) on a main injector housing (32), the electromagnetic actuator (24) comprising a solenoid coil (26) mounted within a solenoid tube (30);applying an overmould (40) to at least a part of the electromagnetic actuator (24); andmounting a cooling device (50), having a cooling chamber (52), an external wall portion (54, 74), and an internal wall portion (53, 76), on the main injector housing (32) so that the internal wall (53, 76) forms a part of a thermal path between the solenoid coil (26) and the cooling chamber (52).

13. The method as claimed in claim 12, comprising applying an overmould (40) to at least a part of the electromagnetic actuator (24) prior to mounting the cooling device (50).5 14. The method as claimed in claim 12 or claim 13, comprising press-fitting thecooling device (50) to the overmould (40).

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