Coolant jacket

Abstract

A coolant jacket (50, Fig. 5) of an internal combustion engine powered by hydrogen fuel, the engine comprising at least one cylinder assembly (23, Fig. 3) having a combustion chamber (24, Fig. 3) comp

Description

FIELD The present teachings relate to a coolant jacket of an internal combustion engine suitable for use with a hydrogen-based fuel. The present teachings also relate to an internal combustion engine comprising said coolant jacket and suitable for use with a hydrogenbased fuel, and a working machine comprising said coolant jacket and / or said engine. BACKGROUND There is increasing concern relating to the contribution carbon dioxide emissions make to global warming and, as a way of minimising such emissions, legislation is planned to ban or restrict internal combustion powered vehicles and machines that utilise fossil fuels. As a result many industries are seeking alternative means for powering vehicles and machines that reduce or eliminate the use of fossil fuels such as gasoline (petrol) or diesel. For light vehicles, such as passenger cars, batteries charged using electricity from renewable energy sources appears to be the favoured approach. The duty cycles of light vehicles are less impaired by the reduced energy density of batteries and can accommodate the longer charging time as compared to traditional refuelling time of gasoline and diesel. In addition, the mass of the batteries needed to have a reasonable range does not appreciably restrict the ability of these vehicle to carry the required payload of people and their belongings. However, heavy vehicles may operate for a full working day or over successive shifts with limited downtime, and may be required to carry a heavy payload over a significant distance, such as line haul / freight trucks, or carry out a working operation, such as construction or agricultural machinery. For these use cases, the low energy density, cost and recharging time of batteries means they represent a less attractive option because their required mass may restrict the available payload in the case of trucks and in all cases the cost and recharging time may make their use uneconomic and impractical. Hydrogen based fuel has been proposed as a solution to these issues as it can be produced in a renewable manner, has a greater energy density than lithium ion batteries, and refuelling can be carried out as quickly as for gasoline and diesel. Commonly, fuel cells are proposed as a means of "cleanly" converting hydrogen to electricity on a vehicle. The electricity is used in powering electric motors for traction and / or to drive hydraulic pumps that in turn power working arms of working machines such as excavators, materials handlers or the like. However fuel cells are currently expensive and fragile, so their implementation faces practical challenges. It is also known to use hydrogen as a fuel in internal combustion engines. This is attractive as supply chains and maintenance expertise already exists for internal combustion engines, even though adaptation is required for them to run on hydrogen. Difficulties arise in using hydrogen as a fuel in a traditional diesel combustion engine for heavy machinery. Firstly, hydrogen fuel requires the use of a spark plug for ignition of the hydrogen, which diesel engines do not possess. Further diesel engines are configured to mix diesel fuel with air in a way that is optimised for high efficiency and low emissions with compression ignition. Gasoline internal combustion engines do comprise a spark plug and mix fuel and air in a way that is optimised for spark ignition. However gasoline engines do not have characteristics required for operation of heavy machines, such as high torque outputs at a low rpm. Beyond this, it is also desirable for existing manufacturers of engines for heavy duty applications to be able carry over their existing engine designs with minimal adaptations for efficient combustion of hydrogen fuel. The present invention seeks to overcome or at least mitigate the problems which may arise when using hydrogen as a fuel in an internal combustion engine. SUMMARY The present teachings provide a coolant jacket of claim 1 according to the appended claims. An aspect of the teachings provides a coolant jacket of an internal combustion engine powered by hydrogen fuel, wherein said engine may comprise at least one cylinder assembly which may have: a combustion chamber which may comprise a cylinder defining a cylinder longitudinal axis, and / or a hydrogen fuel injector which may be configured for direct fuel injection into said combustion chamber. The coolant jacket may comprise a void through which a coolant fluid can flow. The void may comprise an injector cooling portion arranged to extend at least partially around said hydrogen fuel injector to effect cooling of the injector. By extending around at least a portion of the fuel injector, coolant flowing through the injector cooling portion is provided in close proximity to a greater surface area of the fuel injector, as compared to a coolant jacket which does not extend around the fuel injector in this way. Thereby cooling is facilitated. Consequently, when coolant fluid is flowing through the void of the coolant jacket, more effective cooling of said hydrogen fuel injector can be achieved. Effective cooling of the hydrogen fuel injector is of particular importance for internal combustion engines powered by hydrogen fuel since hydrogen gas has a much higher energy density than diesel, and so is more sensitive to temperature than diesel. Therefore, there is a greater risk of hazardous pre-ignition events occurring, which is a very prevalent characteristic of hydrogen internal combustion engines. Consequently, it is important when using hydrogen fuel that the fuel injector is effectively cooled. Optionally, the hydrogen fuel injector is inclined at a non-zero angle to said cylinder longitudinal axis. Optionally said injector cooling portion is configured to extend only partially around said fuel injector. Hydrogen combustion has been found to be particularly sensitive to injector position and it is preferred to position the injector at a non-zero angle to the cylinder longitudinal axis. Providing an injector cooling portion which extends only partially around a fuel injector provided at a non-zero angle to the cylinder longitudinal axis permits the use of less complex moulds during manufacture of the engine, as compared to an injector cooling portion that completely encircles the fuel injector. In this way, the complexity and cost of manufacturing the engine is reduced, whilst ensuring effective cooling of the fuel injector when the engine is in use. Accordingly, a coolant jacket is provided which is specifically configured to effectively cool the hydrogen fuel injector, whilst enabling the injector to be positioned at a location that is desirable for optimal combustion and enabling simplified construction of the coolant jacket to be achieved. Optionally the injector cooling portion is configured to circumscribe a barrier region configured to form a barrier to a notional coolant flow path, wherein said notional coolant flow path completely encircles said fuel injector. In other words, the void does not completely encircle the fuel injector. This permits the use of less complex moulds during manufacture of the engine, as compared to an injector cooling portion that completely encircles the fuel injector. Optionally said fuel injector comprises a length and the injector cooling portion extends in a direction substantially along said length to effect cooling of the injector. In this way, when in use, cooling along the length of the fuel injector is facilitated, thereby enhancing cooling of the fuel injector. In some embodiments, said fuel injector defines an injector longitudinal axis and the injector cooling portion is configured to extend in a direction substantially axially with respect to said injector longitudinal axis. In other words, wherein the injector cooling portion of the coolant jacket extends in a direction which is transverse to the cylinder longitudinal axis. Optionally the injector cooling portion comprises a curved portion configured to extend at least partially around the fuel injector. In this way, the injector cooling portion more closely conforms to the external profile of the fuel injector, thereby enhancing the effectiveness of the coolant jacket to cool the injector. Optionally the curved portion comprises a cross-section which is shaped to form a sector of an annulus. In some embodiments, the curved portion comprises a sector of a cylinder, such that the cooling portion extends in a direction substantially along the or a length of the fuel injector. In other words, the injector cooling portion of the coolant jacket has a length extending in a direction which is substantially transverse to the cylinder longitudinal axis. In this way, cooling along the length of the fuel injector is facilitated, thereby enhancing cooling of the fuel injector. Optionally the curved portion comprises a first end and a second end. Optionally the injector cooling portion comprises a first leg extending from the first end and a second leg extending from the second end, for example such that the injector cooling portion comprises a substantially U-shaped portion. An injector cooling portion having a curved portion with first and second legs can be more easily manufactured, compared to an injector cooling portion that completely encircles the fuel injector. In this way, the complexity and cost of manufacturing the engine is reduced. In some embodiments, the barrier region is provided in the space defined between the first leg, the curved portion and the second leg. In some embodiments, the fuel injector is located in the space defined between the first leg, the curved portion and the second leg. Optionally said fuel injector defines an injector longitudinal axis and the injector cooling portion is configured to extend substantially circumferentially with respect to a notional circle having its centre at said injector longitudinal axis. Optionally said fuel injector defines an injector longitudinal axis and the injector cooling portion is configured to extend substantially axially with respect to said injector longitudinal axis. Optionally the injector cooling portion is defined by a boundary, wherein the boundary defines a region in which the fuel injector is located. In some embodiments, the boundary extends partially around the region in which the fuel injector is located. In some embodiments, the boundary defines a region in which the barrier region is located. Optionally the boundary of the injector cooling portion is shaped to conform to at least a portion of an external profile of said injector. In this way, when coolant fluid is flowing through the void of the coolant jacket, improved cooling of the injector can be achieved because the coolant is able to flow in closer proximity to an external surface of the injector. Optionally said fuel injector comprises a nozzle and the injector cooling portion is positioned proximal said nozzle. Optionally said fuel injector is provided proximal a perimeter of said cylinder, e.g. adjacent said perimeter. In other words, the fuel injector is spaced apart from the cylinder longitudinal axis, for example such that the injector is proximal a side wall of the combustion chamber. Put another way, the fuel injector is provided such that it is not central to the combustion chamber, but is offset to a side of the combustion chamber with respect to the cylinder longitudinal axis. Optionally said injector is inclined to said cylinder longitudinal axis at an angle of greater than about 45°, for example at an angle in the range of from about 67° to about 71°, for example about 69°. It has been found that inclining the fuel injector in this manner provides improved combustion when using hydrogen fuel. Optionally said cylinder assembly comprises a spark plug and the void of the coolant jacket further comprises a spark plug cooling portion. Optionally the spark plug cooling portion is configured to extend around said spark plug to effect cooling of said spark plug. In this way, effective cooling of the spark plug can be achieved when the coolant is flowing through the void of the coolant jacket. Optionally the spark plug cooling portion is configured to encircle said spark plug. Optionally the spark plug cooling portion comprises an annulus, optionally the annulus is arranged to be substantially coaxial with a longitudinal axis of said spark plug. In this way, coolant flowing through the spark plug cooling portion is in close proximity to an external surface of the spark plug, thereby enabling effective cooling of the spark plug to be achieved. Optionally the spark plug cooling portion is separate and / or spaced apart from the injector cooling portion. By providing separate spark plug and injector cooling portions, each of the spark plug and fuel injector can be provided with dedicated cooling portions that optimise the cooling function of the coolant jacket. Providing a separate injector cooling portion, which is separate from the spark plug cooling portion, enables the fuel injector to be located at a position which is optimal for combustion of the hydrogen fuel, whilst enabling effective cooling of both the fuel injector and the spark plug. Optionally the spark plug cooling portion is downstream of the injector cooling portion. In this way, priority is given to cooling the hydrogen fuel injector, thereby reducing the risk of pre-ignition events occurring. Optionally the coolant jacket comprises at least one coolant exit through which coolant can flow out of the coolant jacket, such that coolant that enters the spark plug coolant portion subsequently flows to the coolant exit. In this way, effective cooling of the spark plug is achieved before the coolant flows to the coolant exit. In other words, the amount of coolant bypassing the spark plug coolant portion as it flows to the coolant exit is reduced. In some embodiments, the coolant jacket has at least one coolant inlet, which is designed to permit coupling of said jacket with a coolant supply, and at least one coolant exit, designed to permit coupling of said jacket with a coolant discharge. Optionally the spark plug cooling portion comprises an entry port configured such that coolant flowing from the injector cooling portion can enter the spark plug cooling portion via the entry port. Optionally the coolant exit(s) is (are) angularly offset from the entry port with respect to a longitudinal axis of said spark plug. In this way, coolant flowing via the entry port is prevented from flowing straight to the coolant exit, bypassing the spark plug cooling portion. This facilitates effective cooling of the spark plug. In some embodiments, the coolant exit is provided proximal a perimeter of the spark plug coolant portion. Optionally the coolant jacket comprises a pair of coolant exits arranged diametrically opposite each other with respect to the spark plug cooling portion. Optionally the coolant jacket comprises a lower coolant jacket located proximal the cylinder assembly. Optionally the lower coolant jacket is configured to be in fluid communication with an upper coolant jacket located distal the cylinder assembly, optionally via the coolant exit(s). Optionally the void of the coolant jacket comprises one or more of a central arm, a first side arm and a second side arm through which coolant can flow. Optionally at least one of the or each arm is arranged to extend downstream from the injector cooling portion. Optionally one or more of the central arm, first side arm and second side arm comprises a region of restricted flow. In some embodiments, the region of restricted flow is provided by an area of the void having a reduced cross-sectional area, i.e. the cross-sectional area is in a plane transverse to the direction of flow of the coolant. In the regions of restricted flow, the velocity of coolant flowing through the respective arm is increased. In other words, the flow speed of the coolant is increased in the regions of restricted flow. In this way, a temperature difference between the coolant and the surrounding area is maximised, and heat transfer to the coolant enhanced. The regions of restricted flow also serve to reduce the volume of the void, thereby providing additional space for the placement of other elements of the engine. Where the void of the coolant jacket is formed by sand casting, the flow dynamics created by the regions of restricted flow enables more effective cleaning out of sand from the void after manufacture. Furthermore, the regions of restricted flow and associated flow dynamics reduces the occurrence of areas of stagnant flow in the coolant jacket as a whole. In some embodiments, the central arm, first side arm and / or second side arm comprise fluid channels providing fluid communication between the injector cooling portion and the spark plug cooling portion. In some embodiments, the coolant jacket is configured to cool only a single cylinder assembly of the internal combustion engine. In this way, more effective cooling of a respective cylinder assembly of the internal combustion engine can be achieved. The present teachings provide an engine of claim 24 according to the appended claims. An aspect of the teachings provides an engine for use with a working vehicle, wherein the engine comprises an internal combustion engine powered by hydrogen fuel. The engine may comprise at least one cylinder assembly, which may have: a combustion chamber, which may comprise a cylinder defining a cylinder longitudinal axis, and / or a hydrogen fuel injector which may be configured for direct fuel injection into the combustion chamber. The engine may further comprise a coolant jacket as disclosed herein. In some embodiments, a separate coolant jacket is provided for each cylinder assembly of the engine. Optionally the engine comprises a plurality of cylinder assemblies and a series of coolant jackets are provided. Optionally each of the series of coolant jackets is associated with a single cylinder assembly. In other words, only one coolant jacket is provided per cylinder assembly. In this way, cooling of each cylinder assembly can be optimised. It has been found that this enables more effective cooling of all cylinder assemblies to be achieved. For example, for an engine with four cylinder assemblies, each cylinder assembly has a dedicated coolant jacket, such that the engine comprises four separate coolant jackets. Similarly, for an engine with six cylinder assemblies, each cylinder assembly has a dedicated coolant jacket, such that the engine comprises six separate coolant jackets. Furthermore, where the void of the coolant jacket is formed by sand casting, more effective cleaning out of sand from the void can be achieved, as compared to the case where the coolant jacket is arranged to cool more than one cylinder assembly. Optionally the coolant jackets are arranged such that coolant fluid can flow from a coolant supply, through each of the coolant jackets in parallel, to a coolant discharge. In this way, dedicated cooling of each cylinder assembly can be achieved enabling more even cooling across all cylinder assemblies to be achieved. Furthermore, where the void of the coolant jacket is formed by sand casting, more effective cleaning out of sand from the void can be achieved, as compared to the case where two or more coolant jackets are coupled together to enable fluid communication in series, i.e. from one jacket to the next. The present teachings provide a working machine of claim T1 according to the appended claims. An aspect of the teachings provides a working machine comprising a coolant jacket as disclosed herein, and / or the engine as disclosed herein. It will be appreciated that the optional features described may apply to any aspect disclosed herein. All combinations contemplated are not recited explicitly for the sake of brevity. BRIEF DESCRIPTION OF DRAWINGS Embodiments will now be described by way of example only with reference to the accompanying figures, in which: Figure 1 is a cross-sectional view of an internal combustion engine in accordance with the present disclosure; Figure 2 is an underside isometric view of the cylinder head of the internal combustion engine of Figure 1; Figure 3 is an enlarged cross-sectional view of a cylinder, cylinder head and piston on the same plane as Figure 1, with the piston in a bottom dead centre position; Figure 4 is a partial plan view of the cylinder head of Figure 2, illustrating the position of one of the fuel injectors; Figure 5 is an enlarged cross-sectional view of the cylinder head and fuel injector along the plane D-D of Figure 4; Figures 6a and 6b are respectively perspective and side views of a mould configured to form the (lower) coolant jacket of the engine of Figure 1; Figure 7 shows a perspective view of a mould configured to form an upper coolant jacket, coupled to a series of the moulds shown in Figures 6a and 6b, showing an upper side of the moulds; Figure 8 shows a perspective view of a mould configured to form an upper coolant jacket, coupled to a series of the moulds shown in Figures 6a and 6b, showing an under side of the moulds; and Figure 9 shows a working machine comprising the engine of Figure 1. DETAILED DESCRIPTION In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of various embodiments and the teachings. However, those skilled in the art will understand that: the present teachings may be practiced without these specific details or with known equivalents of these specific details; that the present teachings are not limited to the described embodiments; and, that the present teachings may be practiced in a variety of alternative embodiments. It will also be appreciated that well known methods, procedures, components, and systems may not have been described in detail. With reference to Figures 1 to 4, an embodiment of the present teaching provides an internal combustion engine powered by hydrogen fuel, generally indicated at 10. The engine 10 is a four-stroke IC engine configured to be powered by hydrogen, hereafter referred to as a hydrogen fuelled IC engine. The engine 10 may be suitable for use as the prime mover in a working machine 100 -see Figure 9 which depicts a backhoe loader - but may also be a telescopic handler, a forklift truck, a wheeled loading shovel, a dumper, an excavator or a tractor, for example. Such working machines 100 are suitable for use in off-highway applications such as agriculture, forestry and construction. In these industries they are generally configured to perform tasks such as excavation, load handling, harvesting or planting crops. The engine 10 may also be utilised in a genset - a self-contained unit to provide electrical power at off-grid locations. The internal combustion engine 10 has a cylinder block 12 and a cylinder head 14. The cylinder block 12 and the cylinder head 14 comprises a series of cylinders 16. Each cylinder 16 defines a cylinder longitudinal axis A, as shown in Figure 3. As the engine may be classed as medium / heavy duty, each cylinder 16 has a bore diameter of 106mm in order to provide the desired torque characteristics, but in other embodiments, the diameter may be greater than or equal to 100mm, e.g. in a range of 100 to 150mm. Each cylinder 16 forms part of a cylinder assembly 23. Each cylinder assembly 23 comprises a piston assembly 20. Figure 3 shows a cross sectional view through a single cylinder assembly 23. The remaining cylinder assemblies (not shown) of the internal combustion engine 10 are substantially identical to the cylinder assembly 23 shown. In this embodiment, the internal combustion engine 10 is a straight four cylinder engine, with four cylinders 16 arranged with axes A parallel to one another in a linear formation, and four piston assemblies 20 along a common crankshaft 18 (Figure 1). In alternative embodiments, the internal combustion engine has some other known cylinder arrangement, e.g. a straight six or V6. A piston head 28 of the piston assembly 20 is arranged to move in a reciprocating manner along axis A and generate rotating drive to the crankshaft 18 as is well known per se in internal combustion engines. In this embodiment the engine 10 is fuelled solely by hydrogen. In other embodiments, the engine 10 may be fuelled by hydrogen in combination with other fuels, such as natural gas. With reference to Figure 2, the cylinder head 14 comprises two inlet ports (i.e. a first inlet port 32a and a second inlet port 32b) for air to be introduced into each combustion chamber 24 and two exhaust ports (i.e. a first exhaust port 32a and a second exhaust port 34b) for exhaust gases to be expelled per cylinder. Each cylinder assembly 23 includes a combustion chamber 24 (Figure 3). Each combustion chamber 24 is defined by the cylinder 16, a corresponding roof 15 of the cylinder head, and piston assembly 20. The engine 10 further comprises an inlet runner 46 (Figure 1) per cylinder assembly 23 arranged to feed into the inlet ports 32a,b of each cylinder head 14 from an inlet manifold (not shown). The inlet runner 46 bifurcates to connect to the inlet ports 32a,b. In this way, the inlet runner 46 leaves more space available to locate components such at the spark plug 36 and fuel injector 22. With reference to Figure 3 in particular, it can be seen that the inlet runner 46 is inclined with respect to a lower face of the cylinder head 14 at a relatively steep angle, which in this embodiment is approximately 36°, but may be in the range of 32° to 36°. Similarly, an outlet runner 47 per cylinder assembly 23 connects the exhaust ports 34a,b of each cylinder 16 with an exhaust manifold (not shown) and is bifurcated where they connect to each port, and merge before connecting to the manifold. In this embodiment, the engine 10 includes a hydrogen fuel delivery system by which hydrogen fuel may be directly injected into each cylinder 16 from a pressurised fuel tank 102 (Figure 9) via a fuel injector 22. The rated pressure of the fuel tank 12 is typically in excess of 35MPa and the hydrogen pressure may be stepped down before being introduced into the cylinders 16. As shown in Figures 1 and 3, the internal combustion engine 10 is of the direct injection type. The cylinder assembly 23 includes the fuel injector 22 mounted to a fuel injection port 30 for injecting fuel directly into the combustion chamber 24. The fuel injector 22 has an injector longitudinal axis B. The fuel injector 22 is supported within the cylinder head 14. In this embodiment, as best seen in Figures 2 and 3, the fuel injector 22 is arranged so that the injection port 30 is located intermediate the two inlet ports 32a,b such that axis B of the fuel injector 22 is at an angle of 69° with respect to the longitudinal axis A. This positioning of the fuel injector 22 has been found to optimise combustion in hydrogen fuelled engines. Variants of this embodiment in which the fuel injector is at other angles to the axis A, in the range of 67° to 71°, are also envisioned, in order to take into account thickness constraints of the cylinder head 14 and to package the fuel injector 22 around the proximate components, in particular the inlet runner 46. The fuel injector 22 is located between a bottom face of the cylinder head 14 and a lower wall of the inlet runner 46, such that a nozzle 22a of the fuel injector 22 is positioned proximal the cylinder wall, which defines a side wall 27 of the combustion chamber 24. The side wall 27 defines a perimeter of the cylinder 16. In this embodiment, with the required power output, a relatively large diameter injector 22 is utilised to supply a sufficient amount of fuel, e.g. around 11mm diameter. To package the injector in the above described location, a relatively high roof 15 is required. Through each roof 15 is arranged a spark plug 36 to ignite the hydrogen-air mixture. In this embodiment, the spark plug 36 is centrally mounted in the roof 15. The spark plug has a longitudinal axis C (as shown in Figure 3). In the illustrated embodiment, the longitudinal axis C of the spark plug 36 is coaxial with the cylinder axis A. In some embodiments, the longitudinal axis of the spark plug 36 may be parallel to the cylinder axis A, for example not coaxial. For example, the longitudinal axis of the spark plug 36 may be offset from the cylinder axis A by about 10mm or less, for example by about 5mm or less, for example by about 2mm. With reference to Figure 5, the engine 10 further comprises a coolant jacket 50, for example a water jacket. The coolant jacket 50 is formed of a void 52 through which coolant can flow in order to cool desired parts of the engine 10. In particular, the coolant jacket 50 is shaped to focus the cooling action of the coolant on specific components of the engine 10 that are vulnerable to heating and / or sensitive to higher temperatures. The coolant jacket 50 is formed in the cylinder head 14 of the engine 10. With reference to Figure 5, a cross-section through the engine 10 along line D-D of Figure 4 is illustrated. Various sections of the void 52 of the coolant jacket 50 are visible in Figure 5. The void 52 that forms the coolant jacket 50 is formed in the cylinder head 14 of the engine during casting of the cylinder head 14, for example by using a mould to create the void. Such a mould is shown in Figure 4 and generally indicated by reference numeral 54. In other words, the mould 54 can be thought of as the inverse of the void 52. For clarity, features of the void 52 will be described below in relation to the mould 54. With reference to Figures 6a and 6b, the coolant jacket 50 includes an injector cooling portion 56. As shown in Figures 7 and 8, the injector cooling portion 56 is shaped to partially extend around the fuel injector 22, at a region 60 proximal the nozzle 22a of the fuel injector 22. The fuel injector 22 has a length extending along the axis B and the injector cooling portion 56 extends in a direction substantially along the length of the fuel injector 22 (i.e. in the direction of axis B), thereby effecting cooling of the injector 22 along a portion of its length. As can be seen most clearly in Figures 6b, the injector cooling portion 56 includes a curved portion 58 arranged to extend partially around the injector 22. In the illustrated embodiment, the injector 22 has a substantially cylindrical profile in the region 60 proximal the nozzle 22a (Figure 8) and the curved portion 58 of the injector cooling portion 58 is shaped to conform to the external profile of the cylindrical region 60 of the injector 22. The curved portion 58 of the injector cooling portion 56 can be thought of as having the form of a sector of a cylinder, having a length which extends in a direction substantially along the length of the fuel injector. In other words, the sector of the cylinder has a length which extends substantially along axis B. The cross-section of the curved portion is consequently shaped to form a sector of an annulus, said notional annulus encircling the region 60 of the injector 22. Put another way, the injector cooling portion 56, specifically the curved portion 58, is configured to extend substantially circumferentially with respect to a notional circle 64 having its centre at the injector longitudinal axis B. As described above, the injector cooling portion 56 is configured to extend substantially axially with respect to the injector longitudinal axis B. As can be seen from Figure 6b, the injector cooling portion 56 is substantially U-shaped. The curved portion 58 extends from a first end 58a to a second end 58b, which are located diametrically opposite each other with respect to the notional circle 64. A first leg 60a extends from the first end 58a and a second leg 60b extends from the second end 58b. The first leg 60a and the second leg 60b are substantially parallel to one another. As can be seen, for example from Figure 6b, the injector cooling portion 56 circumscribes a barrier region 62 configured to form a barrier to the flow of coolant. In other words, the barrier region prevents coolant following a flow path which would completely encircle the fuel injector 22. Put another way, the barrier region 62 forms a barrier to a notional coolant flow path (e.g. around the notional circle 64), wherein said notional coolant flow path completely encircles said fuel injector 22. In this way, the fuel injector 22 is not completely encircled by the injector cooling portion 56. This enables a simpler mould design to be used when casting the cylinder head 14. In the illustrated embodiment, the curved portion 58 and the first and second legs 60a,b extending therefrom define the barrier region 62. The fuel injector 22 is positioned within this barrier region 62. The first and second legs 60a,b form coolant inlets through which coolant can enter the void 52 of the coolant jacket 50. It will be appreciated that the void 52 of the coolant jacket 50 is defined by a boundary 66 formed by the material of the cylinder head 14. In other words, the shape of the void, including the injector cooling portion 56, as well as the other features of the coolant jacket 50 described below, is defined by this boundary 66. The boundary 66 also delineates the barrier region 62 in which the injector 22 is located. The void 52 of the coolant jacket 50 includes a spark plug cooling portion 68 configured to effect cooling of the spark plug 36 located in the roof 15 of the combustion chamber 24. The spark plug cooling portion 68 is configured to extend around the spark plug 36 such that it encircles the spark plug 36. The spark plug cooling portion 68 is formed of an annulus arranged to be substantially coaxial with the longitudinal axis C of the spark plug 36. In this way, in the illustrated embodiment, the annulus of the spark plug cooling portion 68 is also substantially coaxial with the cylinder axis A. The spark plug cooling portion 68 is separate and spaced apart from the injector cooling portion 56, corresponding to the position of the spark plug 36 and injector 22 in the cylinder assembly 23. Furthermore, the spark plug cooling portion 68 is provided downstream of the injector cooling portion 56, such that priority is given to cooling the injector 22, thereby reducing the risk of preignition events occurring. The coolant jacket 50 includes a pair of coolant exits 70a,b through which coolant can flow out of the coolant jacket 50. The pair of coolant exit ports 70a,b are provided proximal a perimeter 72 of the spark plug cooling portion 68 and diametrically opposite each other with respect to the spark plug cooling portion 68. The coolant jacket 50 is configured to effect cooling of a single cylinder assembly 23. As such, the coolant jacket is arranged to extend around the inlet ports 32a,b and the outlet ports 34a,b (i.e. exhaust ports) of the cylinder assembly 23. As shown in Figure 6a in particular, the void 52 of the coolant jacket 50 includes a first inlet side arm 74, a central inlet arm 76 and a second inlet side arm 78 through which coolant can flow. Each arm 74,76,78 extends downstream from the injector cooling portion 56. The first inlet side arm 74 extends from the injector cooling portion 56, around a first region 80a corresponding to the location of the first inlet port 32a of the cylinder assembly 23, and towards the first coolant exit 70a and the spark plug cooling portion 68. The central inlet arm 76 extends from the injector cooling portion 56, between the first regions 80a and a second region 80b, each corresponding to the location of an inlet port 32a,b of the cylinder assembly 23, and towards the spark plug cooling portion 68. The second inlet side arm 78 extends from the injector cooling portion 56, around the second region 80b corresponding to the location of the second inlet port 32b of the cylinder assembly 23, and towards the second coolant exit 70b and the spark plug cooling portion 68. In use, coolant flows from the injector cooling portion 56 to one of the first inlet side arm 72, the central inlet side arm 74 and the second inlet side arm 76. The coolant jacket 50 includes a central exhaust coolant inlet 88 located diametrically opposite the injector coolant portion 56 with respect to the spark plug cooling portion 68. The void 52 of the coolant jacket 50 includes a first exhaust side arm 90, a central exhaust arm 92 and a second exhaust side arm 94 through which coolant can flow. Each arm 90,92,94 extends downstream from the central exhaust coolant inlet 88. The first exhaust side arm 90 extends from the central exhaust coolant inlet 88, around a first region 81a corresponding to the location of the first exhaust port 34a of the cylinder assembly 23, and towards the first coolant exit 70a and the spark plug cooling portion 68. The central exhaust arm 92 extends from the central exhaust coolant inlet 88, between the first region 81a and a second region 81b, each corresponding to the location of an exhaust port 34a,b of the cylinder assembly 23, and towards the spark plug cooling portion 68. The second exhaust side arm 94 extends from the central exhaust coolant inlet 88, around the second region 81b corresponding to the location of the second exhaust port 34b of the cylinder assembly 23, and towards the second coolant exit 70b and the spark plug cooling portion 68. In use, coolant flows from the central exhaust coolant inlet 88 to one of the first exhaust side arm 90, the central exhaust side arm 92 and the second exhaust side arm 94. Each of the first inlet side arm 74, central inlet arm 76, second inlet side arm 78 and central exhaust arm 92 includes a region of restricted flow. In other words, the volume of the void in the region of restricted flow is reduced. Put another way, the cross-sectional area of the void in a plane transverse to the direction of flow of the coolant is reduced. The first inlet side arm 74 includes a restricted region 82 proximal the injector cooling portion 56. The central inlet arm 76 includes a restricted region 84 proximal the injector cooling portion 56. The second inlet side arm 78 includes a restricted region 86 proximal the injector cooling portion 56. The central exhaust arm 92 includes a restricted region 87 proximal the spark plug cooling portion 68. When in use, the flow speed of the coolant through each of the restricted regions 82,84,86,87 is increased. In this way, a temperature difference between the coolant and the surrounding area is maximised, and heat transfer to the coolant enhanced. Where the void of the coolant jacket is formed by sand casting, the flow dynamics created by the restricted regions 82,84,86,87 results in more effective cleaning out of sand from the void after manufacture. Furthermore, the regions of restricted flow 82,84,86,87 and associated flow dynamics reduces the occurrence of areas of stagnant flow in the coolant jacket 50 as a whole. The spark plug cooling portion 68 includes a pair of entry ports 71a,b through which coolant fluid can enter the spark plug cooling portion 68. The entry points 71a,b are diametrically opposite each other with respect to the longitudinal axis of the spark plug C. Coolant fluid from the injector cooling portion 56 can travel along the inlet central arm 76, through the first entry port 71a and into the spark plug cooling portion 68. Similarly, coolant fluid from the central exhaust inlet 88 can travel along the exhaust central arm 92, through the second entry port 71b and into the spark plug cooling portion 68. The coolant exits 70a,b are angularly offset from the entry ports 71a,b with respect to the longitudinal axis C of the spark plug 36. In the illustrated embodiment, the coolant exits 70a,b are angularly offset from the entry ports 71a,b by 90° with respect to the longitudinal axis C of the spark plug 36. In this way, coolant that passes through the entry ports 71a,b does not bypass the spark plug cooling portion 68, but instead flows through the spark plug cooling portion 68 to one or other of the coolant exits 70a,b. As can be seen from Figure 6a, the first inlet arm 74, second inlet arm 78, first exhaust arm 90 and second exhaust arm 94 are shaped such that the coolant jacket 50 is substantially rectangular in shape. In addition to the first and second legs 60a,b of the injector cooling portion 56, coolant inlets 96 are provided at each corner of the coolant jacket 50. Having multiple coolant inlets 60a,b,96 enables improved cleaning of the void 50 to be achieved when the void 52 is formed by sand casting. The coolant jacket 50 forms a lower coolant jacket arranged such that coolant from a coolant supply (not shown) enters the coolant jacket via the inlets 60a,b,96. Coolant flows through the lower coolant jacket 50 to an upper coolant jacket 98 (Figures 7 and 8) via the coolant exits 70a,b. The lower coolant jacket 50 is located proximal the cylinder assembly 23 and the upper coolant jacket 98 is located distal the cylinder assembly 23. The upper coolant jacket 98 is also formed of a void 100 (see Figure 5) formed in the cylinder head 14 of the engine during casting of the cylinder head 14, for example by using a mould to create the void. Such a mould is shown in Figures 7 and 8 and generally indicated by reference numeral 102. In other words, the mould 102 can be thought of as the inverse of the void 100. With reference to Figure 5, a cross-section through the engine 10 along line D-D of Figure 4 is illustrated. Various sections of the void 100 of the coolant jacket 98 are visible in Figure 5. As described above, the coolant jacket 50 is configured to effect cooling of a single cylinder assembly 23. Accordingly, a separate coolant jacket 50 is provided for each cylinder assembly 23 of the engine 10. In this way, coolant will flow through each of the coolant jackets 50 in parallel, from the coolant supply to the upper coolant jacket 98 and on to the coolant discharge (not shown). In other words, the coolant jackets 50 are not arranged in series, so coolant will not flow from one to the other. In this way, dedicated cooling of each assembly 23 can be achieved. Furthermore, where a sand mould is used to form the void 52 of the coolant jacket 50, more effective cleaning out of sand from the void 52 can be achieved, as compared to the case where two or more coolant jackets 50 are coupled together to enable fluid communication in series, i.e. from one jacket to the next. With reference to Figures 7 and 8, in the illustrated embodiment, four lower water jackets 50 are provided, one for each cylinder assembly 23 of the engine 10. Each of which is arranged to receive coolant from a coolant supply (not shown) and coolant flows out of the coolant exits 70a,b of the respective coolant jacket 50 to the upper coolant jacket 98. Coolant from the upper coolant jacket 98 then flows to the coolant discharge (not shown). The one or more embodiments are described above by way of example only and it will be appreciated that the variations are possible without departing from the scope of protection afforded by the appended claims.

Claims

1. A coolant jacket of an internal combustion engine powered by hydrogen fuel, wherein said engine comprises at least one cylinder assembly having:a combustion chamber comprising a cylinder defining a cylinder longitudinal axis, anda hydrogen fuel injector configured for direct fuel injection into said combustion chamber, wherein the coolant jacket comprises a void through which a coolant fluid can flow, and wherein the void comprises an injector cooling portion arranged to extend at least partially around said hydrogen fuel injector to effect cooling of the injector.

2. A coolant jacket according to claim 1, wherein the hydrogen fuel injector is inclined at a non-zero angle to said cylinder longitudinal axis and wherein said injector cooling portion is configured to extend only partially around said fuel injector.

3. A coolant jacket according to claim 1 or 2, wherein the hydrogen fuel injector is inclined at a non-zero angle to said cylinder longitudinal axis, and wherein the injector cooling portion is configured to circumscribe a barrier region configured to form a barrier to a notional coolant flow path, wherein said notional coolant flow path completely encircles said fuel injector.

4. A coolant jacket according to any preceding claim, wherein said fuel injector comprises a length and the injector cooling portion extends in a direction substantially along said length to effect cooling of the injector.

5. A coolant jacket according to any preceding claim, wherein the injector cooling portion comprises a curved portion configured to extend at least partially around the fuel injector.

6. A coolant jacket according to claim 5, wherein the curved portion comprises a cross-section which is shaped to form a sector of an annulus.

7. A coolant jacket according to claim 5 or 6, wherein the curved portion comprises a first end and a second end, and wherein the injector cooling portion comprises a first leg extending from the first end and a second leg extending from thesecond end, for example such that the injector cooling portion comprises a substantially U-shaped portion.

8. A coolant jacket according to any of claims 5 to 7, wherein said fuel injector defines an injector longitudinal axis and the injector cooling portion is configured to extend substantially circumferentially with respect to a notional circle having its centre at said injector longitudinal axis and / or wherein the injector cooling portion is configured to extend substantially axially with respect to said injector longitudinal axis.

9. A coolant jacket according to any preceding claim, wherein the injector cooling portion is defined by a boundary, wherein the boundary defines a region in which the fuel injector is located.

10. A coolant jacket according to claim 9, wherein the boundary of the injector cooling portion is shaped to conform to at least a portion of an external profile of said injector.

11. A coolant jacket according to any preceding claim, wherein said fuel injector comprises a nozzle and wherein the injector cooling portion is positioned proximal said nozzle.

12. A coolant jacket according to any preceding claim, wherein said fuel injector is provided proximal a perimeter of said cylinder, e.g. adjacent said perimeter.

13. A coolant jacket according to any preceding claim, wherein said injector is inclined to said cylinder longitudinal axis at an angle of greater than about 45°, for example at an angle in the range of from about 67° to about 71°, for example about 69°.

14. A coolant jacket according to any preceding claim, wherein said cylinder assembly comprises a spark plug and the void of the coolant jacket further comprises a spark plug cooling portion, wherein the spark plug cooling portion is configured to extend around said spark plug to effect cooling of said spark plug.

15. A coolant jacket according to claim 14, wherein the spark plug cooling portion is configured to encircle said spark plug.

16. A coolant jacket according to claim 14 or 15, wherein the spark plug cooling portion comprises an annulus, optionally wherein the annulus is arranged to be substantially coaxial with a longitudinal axis of said spark plug.

17. A coolant jacket according to any of claims 14 to 16, wherein the spark plug cooling portion is separate and / or spaced apart from the injector cooling portion.

18. A coolant jacket according to any of claims 14 to 17, wherein the spark plug cooling portion is downstream of the injector cooling portion.

19. A coolant jacket according to any of claims 14 to 18, wherein the coolant jacket comprises at least one coolant exit through which coolant can flow out of the coolant jacket, such that coolant that enters the spark plug coolant portion subsequently flows to the coolant exit.

20. A coolant jacket according to claim 19, wherein the spark plug cooling portion comprises an entry port configured such that coolant flowing from the injector cooling portion can enter the spark plug cooling portion via the entry port, and wherein the coolant exit(s) is (are) angularly offset from the entry port with respect to a longitudinal axis of said spark plug.

21. A coolant jacket according to claim 19 or 20, wherein the coolant jacket comprises a pair of coolant exits arranged diametrically opposite each other with respect to the spark plug cooling portion.

22. A coolant jacket according to any preceding claim, wherein the coolant jacket comprises a lower coolant jacket located proximal the cylinder assembly, and wherein the lower coolant jacket is configured to be in fluid communication with an upper coolant jacket located distal the cylinder assembly, optionally via the coolant exit(s).

23. A coolant jacket according to any preceding claim, wherein the void of the coolant jacket comprises one or more of a central arm, a first side arm and a second side arm through which coolant can flow, the or each arm being arranged to extend downstream from the injector cooling portion, and wherein one or more of the central arm, first side arm and second side arm comprises a region of restricted flow.

24. An engine for use with a working vehicle, wherein the engine comprises an internal combustion engine powered by hydrogen fuel, wherein the engine comprises at least one cylinder assembly having:a combustion chamber, comprising a cylinder defining a cylinder longitudinal axis, anda hydrogen fuel injector configured for direct fuel injection into the combustion chamber, wherein the engine further comprises a coolant jacket according to any of claims 1 to 23.

25. An engine in accordance with claim 24, wherein the engine comprises a plurality of cylinder assemblies and a series of coolant jackets are provided, wherein each of the series of coolant jackets is associated with a single cylinder assembly.

26. An engine in accordance with claim 25, wherein the coolant jackets are arranged such that coolant fluid can flow from a coolant supply, through each of the coolant jackets in parallel, to a coolant discharge.

27. A working machine comprising a coolant jacket according to any of claims 1 to 23, and / or the engine according to claim 24, 25 or 26.

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