Internal combustion engine

Abstract

A hydrogen fuelled internal combustion engine comprising at least one cylinder assembly including: a combustion chamber comprising a cylinder, a cylinder head defining a roof, and a reciprocating piston assembly; two inlet ports within the cylinder head, selectively closable by a corresponding inlet valve and being inclined at a non-zero angle to an axis defined by the cylinder; an inlet runner to supply air to the inlet ports; a fuel injector to inject fuel through the cylinder head at an injection point, arranged below the inlet runner; at least one outlet port within the cylinder head selectively closable by a corresponding outlet valve; and a spark plug. A crown of the piston comprises a curved bowl recessed into the piston and located remote from the injection point. A flow directing feature downstream of the injector injects fuel at a narrower angle into the combustion chamber than the injector itself.

Description

[0001] INTERNAL COMBUSTION ENGINE

[0002] FIELD

[0003] The present teachings relate to an internal combustion engine suitable for use with a hydrogen-based fuel.

[0004] BACKGROUND

[0005] There is increasing concern relating to the contribution carbon dioxide emissions make to climate change 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.

[0006] 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.

[0007] 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.

[0008] 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 in a similar timeframe 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.

[0009] Difficulties arise in using of 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.

[0010] The present invention seeks to overcome or at least mitigate the problems described above. However, that is not to say it is limited to these situations, and more generally seeks to provide an internal combustion engine suitable for use with a hydrogen-based fuel, regardless of its intended application.

[0011] SUMMARY

[0012] The present teachings provide an internal combustion engine, working machine and method according to the appended claims.

[0013] An aspect of the present teachings provides a hydrogen fuelled internal combustion engine, The engine may comprise at least one cylinder assembly. The or each cylinder assembly may comprise a combustion chamber comprising a cylinder, a cylinder head defining a roof, and a reciprocating piston assembly. The or each cylinder assembly may comprise two inlet ports within the cylinder head, the inlet ports being selectively closable by a corresponding inlet valve and being inclined at a non-zero angle to an axis defined by the cylinder. The or each cylinder assembly may comprise an inlet runner to supply air to the inlet ports. The or each cylinder assembly may comprise a fuel injector to inject fuel through the cylinder head at an injection point, and being arranged below the inlet runner. The or each cylinder assembly may comprise at least one outlet port within the cylinder head, the at least one outlet port being selectively closable by a corresponding outlet valve. The or each cylinder assembly may comprise a spark plug mounted to the cylinder head. The roof may define a void above a top dead centre position of the piston. A crown of the piston may comprise a curved bowl recessed into the piston, the bowl being located remote from the injection point.

[0014] Advantageously, such an arrangement generates a tumbling motion of the fuel air mixture prior to ignition thereof and may assist in generating a pressure depression drawing hydrogen from the injection point during an intake stroke, thereby promoting a more homogenous fuel-air mixture prior to ignition.

[0015] The crown of the piston may comprise an intruder projecting out of the piston. The intruder may be proximate the injection point.

[0016] This arrangement assists in maintaining a desired compression ratio of the engine, thereby enhancing its efficiency.

[0017] The spark plug may be located intermediate the inlet ports and the at least one outlet port.

[0018] Advantageously this allows the intruder to promote movement of the fuel-air mixture into closer proximity with the spark plug, enabling a faster burn of the fuel-air mixture, once ignited by the spark plug.

[0019] The curved bowl may has a smaller radius of curvature in a plane defined by the cylinder axis and an axis of fuel injected by the injector than in a plane normal thereto.

[0020] Advantageously, this enables the bowl to occupy a large area of the crown, to promote tumble, whilst allowing space for the intruder proximate to the injector.

[0021] The bowl may comprise between 60% and 85% of the surface of the crown, optionally between 70% and 80%, e.g. around 75%.

[0022] Advantageously, this provides a suitable size of bowl for directing the fuel and air in a tumble motion.

[0023] A depth of the bowl may be between 10% and 40% of the width of the bowl transverse to the direction of injection of fuel from the injector, optionally between 20 and 30%, e.g. around 25%.

[0024] Advantageously, this provides a suitable depth of bowl for directing the fuel and air in a tumble motion

[0025] The intruder may have a curved, e.g. substantially crescent shape in plan view. Advantageously, this maximises the potential volume of the intruder, to promote squish at TDC and the depression during the inlet stroke.

[0026] A flow directing feature may be provided downstream of the injector, the flow directing feature being configured to inject fuel at a narrower angle into the combustion chamber than the injector itself.

[0027] Advantageously this maximises the velocity of a plume of fuel entering the combustion chamber and therefore enhances the tumble motion. It may further minimise the fuel fouling the roof which may further slow its motion.

[0028] Thee flow directing feature may comprise a wall downstream and spaced from the fuel injector having a single aperture therein of smaller cross-sectional area than a nozzle of the injector, optionally wherein the aperture is axially aligned with the injector.

[0029] Advantageously, this is a simple structure for achieving a plume with a high velocity and narrow angle. The depression generated by the intruder may help in drawing hydrogen out of the space between the injector and the wall, thereby promoting a more homogeneous fuel-air mixture.

[0030] The wall may be part of a flow cap mounted to the injector.

[0031] Advantageously, this is a simple way of providing a wall and aperture at a suitable distance downstream of the injector.

[0032] The void may comprise walls which are inset from a perimeter of the piston projected onto the roof.

[0033] Advantageously, this may further increase the compression ratio, to maintain the efficiency of the engine.

[0034] The inset walls may be transversely offset from a plane defined by the cylinder axis and an axis of fuel injected by the injector.

[0035] Advantageously, in this location the walls do not appreciably affect the tumble motion. And may assist in bringing the fuel air mixture closer to the spark plug prior to ignition, thereby enabling a faster burn. The roof further may comprise a channel located thereon, the channel extending in a radial orientation, and wherein the channel is aligned with a longitudinal axis of the fuel injector.

[0036] Advantageously, this may reduce the risk of the fuel contacting the roof, which may inhibit the generation of the tumble motion.

[0037] The roof may comprises a first face and a second face inclined relative to one another and meeting at an apex and defining the void, optionally wherein the two inlet ports being located within the first face and the or each outlet port being located within the second face.

[0038] Advantageously, this arrangement may match the inclined geometry of the inlet and outlet ports and their respective valves, and also promotes the tumble motion.

[0039] The cylinder head may be secured by six fasteners, such as six bolts, to a cylinder block defining the cylinder.

[0040] The inlet runner may extend intermediate two of the six bolts.

[0041] The piston assembly may comprises a crankshaft and the bolts may be arranged symmetrically about a plane defined by an axis of the crank shaft and an axis of the piston.

[0042] The apex of the cylinder head may be non-parallel to a plane passing through an axis of the crank shaft and an axis of the piston, optionally the angle between said apex and plane may be in the range of 20° to 40°, optionally 25° to 35°, for example 30°.

[0043] Each inlet port may have a centre; and further wherein a line extending between the centres of the inlet ports may be non-parallel to a plane passing through an axis of a crank shaft of the reciprocating piston assembly and an axis of the piston, optionally the angle between said line and plane may be in the range of 20° to 40°, optionally 25° to 35°, for example 30°.

[0044] Each inlet port may have a centre; and further wherein a line extending between the centres of the inlet ports may be substantially normal, in a plan view, to a longitudinal axis of the inlet runner.

[0045] The inlet runner may bifurcates into a first section and a second section, the two sections each being connected to different inlet ports. The internal combustion engine may comprise two outlet ports, wherein each inlet port has a centre and each outlet port has a centre and the centre of each inlet port may be arranged in a symmetrical fashion with respect to the centre of each outlet port, and the line of symmetry may be a diameter bisecting the cylinder head.

[0046] The first face may be angled at an angle with respect to a plane transverse an axis of the cylinder in the range of 12.5° to 14.5°, e.g. 13.5°, and / or wherein the second face may be angled at an angle with respect to a plane transverse an axis of the cylinder in the range of 10.5° to 12.5°, e.g. 11.5°.

[0047] The cylinder may have a diameter of at least 100mm.

[0048] Advantageously, a cylinder having a diameter greater than this typically produces operating characteristics, such as torque outputs, that are suitable for medium to heavy duty operation, e.g. working machines and heavy goods vehicles.

[0049] The cylinder has a displacement of between 0.75 and 1.5 litres.

[0050] Advantageously, a cylinder having displacement in this range typically produces operating characteristics, such as torque outputs, that are suitable for medium to heavy duty operation, e.g. working machines and heavy goods vehicles.

[0051] A further aspect of the present teachings provides a working machine or genset comprising an internal combustion engine according to the first aspect.

[0052] A further aspect of the present teachings provides a piston head comprising a crown. The crown may comprise a curved bowl recessed into the piston and an intruder projecting out of the piston.

[0053] A further aspect of the present teachings provides a method of operating an internal combustion engine, the method comprising steps of:

[0054] (a) drawing air into the cylinder of an internal combustion engine according to the first aspect by opening the inlet ports and moving the piston to expand the combustion chamber volume;

[0055] (b) injecting fuel comprising hydrogen into the combustion chamber volume via the fuel injector to form an air-fuel mixture within the combustion chamber volume;

[0056] (c) closing the at least one inlet port; (d) compressing the air-fuel mixture being moving the piston to reduce the combustion chamber volume;

[0057] (e) operating the spark plug to ignite the air-fuel mixture to expand the combustion chamber volume by exerting force on the piston; and

[0058] (f) repeating steps (b) to (e).

[0059] It is understood that the aspects and embodiments of the invention can be combined in any way, to take advantage of synergistic effects thereof.

[0060] BRIEF DESCRIPTION OF DRAWINGS

[0061] Embodiments will now be described by way of example only with reference to the accompanying figures, in which:

[0062] Figure 1 is a plan view of an internal combustion engine of the present teachings with a rocker cover removed;

[0063] Figure 2 is a vertical cross-section on the plane 2-2 of Figure 1;

[0064] Figure 3 is vertical cross-section on the plane 3-3 of Figure 1;

[0065] Figure 4 is vertical cross-section on the plane 4-4 of Figure 1;

[0066] Figures 5A and 5B are enlarged cross-sectional views of a cylinder, cylinder head and piston on the same plane as Figure 4 with the piston in a top dead centre and bottom dead centre respectively;

[0067] Figure 5C is a further enlarged view of part of a fuel injector and cylinder head;

[0068] Figure 6 is an underside isometric view of the cylinder head of the internal combustion engine of Figure 1;

[0069] Figure 7 is an enlarged isometric view of a portion of the cylinder head of Figure 6 showing a roof of one cylinder;

[0070] Figure 8 plan view of the roof of the roof of Figure 7;

[0071] Figures 9 and 10 are a plan view and isometric views respectively of a piston of the internal combustion engine of Figure 1; Figures 11 and 12 are cross-sectional views through the piston of Figure 9 on the planes D-D and C-C respectively; and

[0072] Figure 13 is a side view of the piston of Figure 9 when viewed from the direction indicated by arrow E.

[0073] Figure 14 is a side view of a working machine incorporating an internal combustion engine of an embodiment of the present teachings.

[0074] DETAILED DESCRIPTION

[0075] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of various embodiments and the inventive concept. 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.

[0076] 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.

[0077] The engine 10 may be suitable for use as the prime mover in a working machine 100 - see Figure 14 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.

[0078] 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 2. Each cylinder 16 forms part of a cylinder assembly 23. Each cylinder assembly 23 comprises a piston assembly 20. Figure 2 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.

[0079] 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 4). In alternative embodiments, the internal combustion engine has some other known cylinder arrangement, e.g. a straight six or V6.

[0080] 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.

[0081] The cylinder head 14 is secured by six bolts 38 (not all visible) for each cylinder 16 to the cylinder block 12, as best seen in Figures 1 and 2. The bolts 38 are arranged symmetrically about a plane defined by a rotating axis F of the crankshaft 18 and the axis A of the cylinder 16. The angle between an adjacent two of the six bolts 38 is 46°. In this embodiment two sets of three bolts 38 are provided either side of the crank axis with an angle of 88° between the outermost bolts 38 of each set. Other angles in the range of 36° to 60° are also envisaged between bolts 38 on each side of the crank axis, which are set by the constraints of the cylinder head 14.

[0082] So called "six bolt heads" are commonly found in compression ignition internal combustion engines - e.g. diesel engines - which operate at higher compression ratios and pressures than spark ignition engines - e.g. gasoline engines. Six bolts per cylinder are typically required to maintain the integrity of the sealing between the engine block 12 and cylinder head 14 under these higher pressures, whereas gasoline engines typically utilise four bolts per cylinder. The six bolts 38 restrict the space available to supply the combustion chamber 24 with the required air, hydrogen fuel and spark, and allow exhaust gases to be outlet, whilst ensuring the engine 10 runs efficiently and is compact.

[0083] Compression ignition engines are commonly used in heavy duty applications where their high torque output at low rpm is beneficial for the hauling of heavy loads, providing power to hydraulic pumps driving actuators of working arms of excavators or materials handling vehicles, or driving power take-offs to working implements such as agricultural machinery. When utilising hydrogen as a fuel in such applications, it is also desirable to maintain similar torque characteristics despite the change in fuel to hydrogen and the need to ignite the fuel using a spark.

[0084] 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.

[0085] As configured the engine has a maximum power output of around 129kW, although it will be appreciated that the present teachings are applicable to engines with a wide range of power outputs. In the present embodiment the engine has a total displacement of 4.8 litres (i.e. 1.2 litres per cylinder). In engines used in medium / heavy duty off-highway applications each cylinder may typically have a displacement of between 0.75 and 1.5 litres. Such a displacement is relatively high by comparison with passenger vehicle engines, but is suited to providing the operating characteristics described above. The rated maximum operating speed of such engines is also typically lower than for passenger vehicles, e.g. being up to 2500rpm.

[0086] In this embodiment the engine 100 is fuelled solely by hydrogen. In other embodiments, the engine 100 may be fuelled by hydrogen in combination with other fuels, such as natural gas.

[0087] The cylinder head 14 comprises two inlet ports 32 for air to be introduced into each combustion chamber 24 and two outlet ports 34 for exhaust gases to be expelled per cylinder (Figure 6). Each combustion chamber 24 is defined by the cylinder 16, a corresponding roof 15 of the cylinder head, and piston assembly 20.

[0088] 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.

[0089] 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 14) 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.

[0090] As shown in Figures 4, 5A and 5B, the internal combustion engine 10 is of the direct injection type in this embodiment. The cylinder assembly 23 includes the fuel injector 22 mounted to a fuel injection port 54 for injecting fuel directly into the combustion chamber 24. The fuel injector 22 has a longitudinal axis B. The fuel injector is supported within the cylinder head 14.

[0091] With particular reference to Fig 5C, a flow directing feature in the form of a flow cap 25 may be mounted downstream of the end of the fuel injector 22. In this embodiment, the flow cap 25 comprises a cylindrical skirt 26 and an end wall 27 remote from the injector 22. The end wall has a single aperture 29 axially aligned with the injector, but with a smaller cross-sectional area than a poppet valve 22a at the nozzle of the injector 22. In this way, the flow cap 25 can ensure that hydrogen ejected from the poppet valve 22a with a wide spread is directed with a narrower plume (i.e. a narrower angle) as it enters the combustion chamber 24. In turn, this inhibits the likelihood of the hydrogen impinging on the roof 15, where it may lose kinetic energy and generate less effective tumble mixing and / or contact hot locations within the combustion chamber 24, such as the spark plug 26 and self-ignite.

[0092] In this embodiment, the flow cap 25 is welded to the tip of the injector 22, but in other embodiments, may be mounted in other suitable ways.

[0093] Each inlet port 32 is selectably closable by a corresponding inlet valve 42, whilst each outlet port 34 is closable via a corresponding outlet valve 44. These inlet valves 42 and outlet valves 44 are part of a valve train 40. The inlet and outlet valves 42, 44 are located, when closed, in the corresponding port 32, 34 in a recessed position from an inner surface 64 of the cylinder head 14. The inlet ports 32 have a larger diameter than that of the outlet ports 34 in order to optimise the airflow into the combustion chamber and achieve an optimised air-hydrogen mixture for lean combustion.

[0094] The engine 10 further comprises an inlet runner 46 per cylinder assembly 23 arranged to feed into the inlet ports 32 of each cylinder head 14 from an inlet manifold (not shown). The inlet runner 46 bifurcates to connect to the inlet ports 32. The inlet runners 46 extends between two of the six bolts 38. In this way, the inlet runner 46 leaves more space available to locate components such at the spark plug 36 and fuel injector 22.

[0095] Similarly, an outlet runner 47 per cylinder assembly 23 connects the outlet ports 34 of each cylinder 16 with an exhaust manifold (not shown) and is bifurcated where they connect to each port, merge before connecting to the manifold, and extend between two of the six bolts 38 on the opposite side of the cylinder head 14. In this embodiment, as best seen in Figure 8, imaginary lines I and O passing through centres of the inlet ports 32 and outlet ports 34 respectively are arranged at a non-zero, non-right angle to the axis of rotation F of the crankshaft 18. This angle is 30°, which is substantially the same angle formed by a line projecting from the centres of adjacent pairs of bolts 38 intersecting with axis F. Other angles in the range of 20° to 40° e.g. 25° to 35° are also envisioned. This is referred to as the ports 32, 34 being "skewed". This allows the inlet runner 46 to extend between the bolts 38 normal to this line, and for the bifurcated portion being of identical length and shaped as identical mirror images.

[0096] This can be contrasted with conventional gasoline engines where the four bolt pattern enables two inlet ports to be arranged on one side of the cylinder head 14 with an imaginary line extending between their centres being parallel to axis F, and outlet ports on the opposite side in a similar arrangement to generate a tumbling motion within the cylinder 16 (a so-called cross flow configuration). It can also be contrasted with known diesel engines where the inlet ports are arranged with an imaginary line between their centres being arranged transverse axis F and the outlet ports being arranged in a similar configuration in an opposite sector of the cylinder head 14 (a so-called tandem configuration). This tandem configuration in conjunction with a particular arrangement of inlet and outlet runners can achieve a swirling motion that is desirable for an efficient and low emission compression ignition combustion.

[0097] In this embodiment, as best seen in Figures 7 and 8, the inlet ports 32 and outlet ports 34 have centres that are arranged in a symmetrical fashion with respect to one another. The centre of each inlet port 32 is arranged in a symmetrical fashion with respect to the centre of a corresponding outlet port 34. The line of symmetry is a diameter bisecting the cylinder head 14.

[0098] 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° . This angle generates the tumble motion, with the upper end of the range being constrained by the packaging of other components such as the spark plug 28, and minimising the height of the cylinder head.

[0099] In this embodiment the spark plug 36 is also vertically located in the centre of the cylinder head 14 intermediate the inlet and outlet ports 32, 34 to promote even combustion in the combustion chamber 24. The engine 10 of the first embodiment therefore enables a compression ignition cylinder block 12 of a configuration typically used for generating high torque at low engine speeds to achieve similar characteristics with spark ignition of hydrogen based fuels, whilst ensuring low emissions

[0100] With reference to Figures 5A, 5B, 6, and 7 in particular, each roof of the cylinder head comprises a first face 58 and a second face 60 which define the roof 15. The first face 58 and the second face 60 are generally planar and inclined relative to one another and meet at an apex 62. This is commonly referred to as a "pent roof".

[0101] The first face 158 is angled with respect to a plane transverse axis A by 13.5°, however, other angles in the range of 12.5° to 14.5° are also envisaged. Likewise, the second face 160 is angled with respect to plane transverse axis A by 11.5°, however, angles in the range of 10.5° to 12.5° are also envisaged. These ranges of angles optimise the tumble motion of the inlet and exhaust mixtures (see curved arrow of Figure 5B), whilst being suitable for the required packaging of components around the cylinder head 14. Any total angle greater than the range of 23° to 27° would result in problems with excessive recesses on roof, impacting air-fuel mixture motion. In this embodiment the angle of the faces with respect to the plane transverse axis A differ, such that the apex 62 is offset from a centre of the roof and the first face 58 has a smaller projected area than the second face 60. The apex 62 has a curved transition from the first face 58 to the second face 60.

[0102] The two inlet ports 32 are located within the first face 58 and the two outlet ports 34 are located within the second face 60. The inlet ports 32 are larger than the outlet ports 34, such that in this embodiment the inlet ports 32 extend into the apex 62.

[0103] The apex 62 is arranged at a non-zero, non-right angle to the axis of rotation F of the crankshaft 18, at the same angle as that of the imaginary lines I and O.

[0104] In this embodiment, an axis of movement of the inlet valves 42 and outlet valves 44 are arranged substantially perpendicularly to the first face 58 and second face 60 respectively. So as to further enhance the tumble motion at least the inlet valves 42 are recessed into their respective ports 32.

[0105] In variants of this embodiment, the axis of operation of the inlet valves 42 are arranged perpendicularly to the first face 58, however angles in the range of 12° to 13.5° with respect to a plane transverse axis A are also envisioned. Likewise, in this variant, the axis of operation of the outlet valves 44 are arranged perpendicularly to the second face 60. However, angles in the range of 10° to 11.5° with respect to a plane transverse axis A are also envisaged. These angles minimise the likelihood of the inlet and outlet mixture flows soiling the inner surface 64 of the roof 15.

[0106] The angle of inlet and exhaust of combustion components though inlet and outlet ports 32, 34 provided by the pent roof, the straight path and equal length bifurcations described above in combination with the inclined entry angle of the inlet runner allows a purer tumble motion of the air to be created across a full width of the combustion chamber 24 during the inlet stroke. This promotes homogenisation of the combustion mixture.

[0107] In this embodiment, as best seen in Figures 7 and 8 each roof 15 further comprises a channel 66 located thereon. The channel 66 extends along the first face in a radial orientation and is aligned with axis B of the fuel injector 22. This channel 66 reduces the risk of fuel soiling the roof 15 that would occur due to the angle of the fuel injector 22, and allows the hydrogen based fuel to mix effectively with the air during the inlet and compression stroke. This promotes a cleaner and more efficient combustion cycle. Further, the channel 66 also reduces the opportunity for the fuel to enter the intake ports if the timing of the intake valves permits.

[0108] In this embodiment, as best seen in Figures 5A and 5B, the fuel injector 22 is arranged so that the injection port 54 is located intermediate the two inlet ports 32 such that axis B of the fuel injector 22 is at an angle of 21° with respect to the plane of axis F. However, variants of this embodiment with other angles in the range of 19° to 23° are also envisioned, in order to take into account thickness constraints of the cylinder head 14 and water jacket, and to package the fuel injector 22 around the proximate components, in particular the inlet runner 46. The body 56 of the fuel injector 22 is located between a bottom face of the cylinder head 14 and a lower wall of the inlet runner 46.

[0109] 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.

[0110] Referring to Figures 7 and 8, it can be seen that the roof 15 is not circular and therefore does not match the wall of the cylinder 16. Rather, perimeter walls 70 between corresponding inlet and outlet ports 32, 34 are inset from the cylinder wall (shown in dashed lines in Figure 8), and are straight. Similarly, a perimeter wall 72 between the outlet ports 34 and opposite the fuel injection port 54 is inset and straight. This reduces the volume of the combustion chamber and thus maintains a desired compression ratio of each cylinder, despite the raised pent roof configuration thereof.

[0111] Further, this configuration tends to bring the fuel-air mixture closer to the spark plug 36, thereby promoting a faster burn of the fuel, which reduces the opportunity of pre-ignition, a very prevalent characteristic of hydrogen internal combustion engines. At the same time, this shape does not interrupt the desired tumble motion of the fuel-air mixture. In other embodiments, it will be appreciated that the shape of these inset portions maybe non-linear, e.g. curved inwards or outwards.

[0112] Turning now to Figures 9 to 13, an embodiment of the piston head 28 is described in more detail.

[0113] To further improve the fuel-air mixing and therefore combustion of the hydrogen fuel, a crown (upper face) 80 of the piston head 28 is provided with specific contours. More particularly, the crown 80 is provided with a bowl or depression 82 below a datum level P which substantially aligns with an interface between the cylinder block 12 and the cylinder head 14 when in its top dead centre (TDC) position, as seen in Figure 5A, and an intruder 84 which extends above the datum P.

[0114] The bowl 82 has a dished shape whose radius of curvature along plane D-D is greater than the radius of curvature along the plane C-C, but where the lowermost point of these curves is at the same depth. This results in the bowl being wider on plane D-D than plane C-C. In addition, the midpoint M of the bowl is offset from the longitudinal axis of the piston 28 and the axis A of the cylinder.

[0115] As can be seen in Figures 5A and 5B, the bowl is oriented such the bowl 82 is remote from the injector 22. This position, coupled with the angle of the injector and shape of the bowl promotes a greater tumbling motion of the fuel-air mixture during an inlet and compression stroke of the piston 28, during operation of the engine 10. In turn, this further improves the homogeneity of the fuel-air mix. This motion is indicated in simplified form by the curling arrow in Figure 5B.

[0116] The bowl 82 is positioned such that a flat rim 86 is provided around its perimeter at the level of datum P, to avoid a thin strip of material that may be of insufficient strength.

[0117] In this embodiment, the bowl comprises between 60% and 85% of the surface of the crown, optionally between 70% and 80%, e.g. around 75%. A depth of the bowl below the datum level P is between 10% and 40% of the width of the bowl transverse to the direction of injection of fuel from the injector, optionally between 20 and 30%, e.g. around 25%.

[0118] The intruder 84 is, in this embodiment, a curved - e.g. crescent shape in plan view, and is positioned between the bowl 82 and the rim 86 on one side. Specifically, the intruder is positioned proximate to the injector 22 as can be seen in Figures 5A and 5B. From Figures 11 and 12, in particular, a slope 88 rising from the rim 86 remote from the bowl 82 which terminates in a flat top 90, can be seen. The curve of the bowl 82 rises to meet the flat top 90. Sides 92 of the intruder 84, where the crescent shape come to a point are also sloped inwardly. This arrangement avoids the presence of sharply angled edges that may be insufficiently strong, and may also become excessively hot, increasing the risk of selfignition of the hydrogen fuel.

[0119] The intruder 84 maintains, to a certain extent, the compression ratio of the cylinder by reducing the volume of the combustion chamber, compensating for the greater volume created by the bowl 82. In addition, during the inlet stroke of the piston 28, the intruder 84 creates a low pressure area adjacent the injector 22, which may help draw out hydrogen fuel from the flow cap 25, further promoting a homogeneous fuel-air mix. Further, the shape thereof may promote the tumble motion. In addition, as the piston moves to TDC the intruder promotes the movement of the fuel-air mix closer to the spark plug 36 at the centre of the roof 15 (referred to commonly as "squish"), promoting faster combustion which reduces the opportunity of pre-ignition.

[0120] In operation, during an intake stroke, the piston moves from the TDC position of Figure 5A downwardly to the bottom dead centre (BDC) position of Figure 5B. During this motion the inlet valves 42 are opened along with the poppet valve 22a of the fuel injector 22. The motion of the piston, coupled with the pressure of the fuel being injected, causes the tumble motion where the fuel and air rotates about a horizontal axis and mixes. This motion continues as the piston starts its compression stroke and the volume of the combustion chamber 24 reduces. When the spark plug 36 sparks at or around the end of the compression stroke, a generally homogeneous fuel-air mix is achieved, which by virtue of the intruder 84 and the inset perimeter walls 70, 72 is centred around the spark plug.

[0121] 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. For example, the engine may be a pure cross-flow engine with no skewing of the ports. The roof / roof of the combustion chamber may have a different shape rather than being a pent roof, for example it may have hemispherical ("hemi") shape.

Claims

CLAIMS1. A hydrogen fuelled internal combustion engine, the engine comprising at least one cylinder assembly, the or each cylinder assembly comprising: a combustion chamber comprising a cylinder, a cylinder head defining a roof, and a reciprocating piston assembly; two inlet ports within the cylinder head, the inlet ports being selectively closable by a corresponding inlet valve and being inclined at a non-zero angle to an axis defined by the cylinder; an inlet runner to supply air to the inlet ports; a fuel injector to inject fuel through the cylinder head at an injection point, and being arranged below the inlet runner; at least one outlet port within the cylinder head, the at least one outlet port being selectively closable by a corresponding outlet valve; and a spark plug mounted to the cylinder head; wherein the roof defines a void above a top dead centre position of the piston; wherein a crown of the piston comprises a curved bowl recessed into the piston, the bowl being located remote from the injection point; and wherein a flow directing feature is provided downstream of the injector, the flow directing feature being configured to inject fuel at a narrower angle into the combustion chamber than the injector itself.

2. The internal combustion engine of claim 1, wherein the spark plug is located intermediate the inlet ports and the at least one outlet port.

3. The internal combustion engine of claim 1 or claim 2, wherein the curved bowl has a smaller radius of curvature in a plane defined by the cylinder axis and an axis of fuel injected by the injector than in a plane normal thereto.

4. The internal combustion engine of any preceding claim, wherein the bowl comprises between 60% and 85% of the surface of the crown, optionally between 70% and 80%, e.g. around 75%.

5. The internal combustion engine of any preceding claim, wherein a depth of the bowl is between 10% and 40% of the width of the bowl transverse to the direction of injection of fuel from the injector, optionally between 20 and 30%, e.g. around 25%.

6. The internal combustion engine of any preceding claim, wherein the crown of the piston comprises an intruder projecting out of the piston, the intruder being proximate the injection point.

7. The internal combustion engine of claim 6, wherein the intruder has a curved, e.g. substantially crescent shape in plan view.

8. The internal combustion engine of any preceding claim, wherein the flow directing feature comprises a wall downstream and spaced from the fuel injector having a single aperture therein of smaller cross-sectional area than a nozzle of the injector, optionally wherein the aperture is axially aligned with the injector.

9. The internal combustion engine of claim 8, wherein the wall is part of a flow cap mounted to the injector.

10. The internal combustion engine of any preceding claim, wherein the void comprises walls which are inset from a perimeter of the piston projected onto the roof.

11. The internal combustion engine of claim 10, wherein the inset walls are transversely offset from a plane defined by the cylinder axis and an axis of fuel injected by the injector.

12. The internal combustion engine of any preceding claim, wherein the roof further comprises a channel located thereon, the channel extending in a radial orientation, and wherein the channel is aligned with a longitudinal axis of the fuel injector.

13. The internal combustion engine of any preceding claim, wherein the roof comprises a first face and a second face inclined relative to one another and meeting at an apex and defining the void, optionally wherein the two inlet ports being located within the first face and the or each outlet port being located within the second face.

14. The internal combustion engine of claim 13, wherein the first face is angled at an angle with respect to a plane transverse an axis of the cylinder in the range of 12.5° to 14.5°, e.g. 13.5°, and / or wherein the second face is angled at an angle with respect to a plane transverse an axis of the cylinder in the range of 10.5° to 12.5°, e.g. 11.5°.

15. The internal combustion engine of any preceding claim, wherein the cylinder head is secured by six fasteners, such as six bolts to a cylinder block defining the cylinder.

16. The internal combustion engine of claim 15, wherein the inlet runner extends intermediate two of the six bolts.

17. The internal combustion engine of claim 15 or claim 16, wherein the piston assembly comprises a crankshaft and the bolts are arranged symmetrically about a plane defined by an axis of the crank shaft and an axis of the piston.

18. The internal combustion engine of any one of claims 13 to 17, wherein the apex of the cylinder head is non-parallel to a plane passing through an axis of the crank shaft and an axis of the piston, optionally the angle between said apex and plane being in the range of 20° to 40°, optionally 25° to 35°, for example 30°.

19. The internal combustion engine of any one of claims 13 to 18, wherein each inlet port has a centre; and further wherein a line extending between the centres of the inlet ports is non-parallel to a plane passing through an axis of a crank shaft of the reciprocating piston assembly and an axis of the piston, optionally the angle between said line and plane being in the range of 20° to 40°, optionally 25° to 35°, for example 30°.

20. The internal combustion engine of any preceding claim, wherein each inlet port has a centre; and further wherein a line extending between the centres of the inlet ports is substantially normal, in a plan view, to a longitudinal axis of the inlet runner.

21. The internal combustion engine of any preceding claim, wherein the inlet runner bifurcates into a first section and a second section, the two sections each being connected to different inlet ports.

22. The internal combustion engine of any preceding claim, comprising two outlet ports, wherein each inlet port has a centre and each outlet port has a centre and the centre of each inlet port is arranged in a symmetrical fashion with respect to the centre of each outlet port, the line of symmetry being a diameter bisecting the cylinder head.

23. The internal combustion engine of any preceding claim, wherein the cylinder has a diameter of at least 100mm.

24. The internal combustion engine of any preceding claim, wherein the cylinder has a displacement of between 0.75 and 1.5 litres.

25. A working machine or genset comprising an internal combustion engine according to any preceding claim.

26. A method of operating an internal combustion engine, the method comprising steps of:(a) drawing air into the cylinder of an internal combustion engine according to any of claims 1 to 24 by opening the inlet ports and moving the piston to expand the combustion chamber volume;(b) injecting fuel comprising hydrogen into the combustion chamber volume via the fuel injector to form an air-fuel mixture within the combustion chamber volume;(c) closing the at least one inlet port;(d) compressing the air-fuel mixture being moving the piston to reduce the combustion chamber volume;(e) operating the spark plug to ignite the air-fuel mixture to expand the combustion chamber volume by exerting force on the piston; and(f) repeating steps (b) to (e).

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