An internal combustion engine

Abstract

A hydrogen fuel internal combustion engine comprising a cylinder head and one or more cylinder assemblies. The or each cylinder assembly comprises: a combustion chamber at least partially defined by a roof of the cylinder head; and a spark plug extending through the roof, the spark plug comprising a first electrode separated from a second electrode via a gap. At least one of the first and second electrodes protrudes from the roof such that the gap is within the combustion chamber. Each cylinder assembly comprises a barrier on or adjacent the spark plug configured to inhibit a liquid flowing on the roof reaching the gap.

Description

FIELD

[0001] The present teachings relate to an internal combustion engine, and in particular to a hydrogen fuel internal combustion engine.BACKGROUND

[0002] In modern spark-ignition internal combustion (IC) engines, a mixture of fuel and air is ignited in a combustion chamber via a spark plug. Typically, a combustion chamber is defined by at least a roof of a cylinder head of the engine, and a reciprocating piston. The spark plug commonly extends through the roof.

[0003] In order to reduce emissions from internal combustion (IC) engines, as well as potentially to reduce greenhouse gases, hydrogen is being proposed as an alternative to diesel or gasoline as a fuel for such engines.

[0004] The primary product of hydrogen combustion in an IC engine is water vapour. Gasoline combustion also produces water vapour but less relative to hydrogen combustion. Such water vapour tends to condense on the roof of the combustion chamber after the engine has shut down and began to cool. The quantity of condensed water tends to be higher when air humidity is high, ambient temperature is low, and the engine is operated for a short period so as to prevent the engine from reaching its full operating temperature.

[0005] The presence of condensed water in the combustion chamber can be problematic when condensed water adhered to a wall of the combustion chamber flows into contact with the spark plug (e.g. when the engine is inclined relative to the horizontal). If water contacts the spark plug, the spark plug may be prevented from producing a spark (e.g. via the water bridging the gap between the spark plug's electrodes, and / or via fouling of the spark plug), thus preventing combustion of the hydrogen in the combustion chamber. This may prevent the engine operating entirely, or only running on a reduced number of cylinders. In the latter case, this may result in undesirable hydrogen emissions, compromised engine power output, and / or damage to engine components.

[0006] The present teachings seek to overcome or at least mitigate the problems of the prior art.SUMMARY

[0007] The present teachings provide a hydrogen fuel internal combustion engine, a working machine, a sleeve for mounting a spark plug to a roof of a combustion chamber of an internal combustion engine, and a spark plug for igniting a fuel-air mixture in a combustion chamber of an internal combustion engine, according to the appended claims.

[0008] A first aspect of the teachings provides a hydrogen fuel internal combustion engine. The engine may comprise a cylinder head. The engine may comprise one or more cylinder assemblies. The or each cylinder assembly may comprise a combustion chamber at least partially defined by a roof of the cylinder head. The or each cylinder assembly may comprise a spark plug extending through the roof. The spark plug may comprise a first electrode separated from a second electrode via a gap. At least one of the first and second electrodes may protrude from the roof such that the gap is within the combustion chamber. Each cylinder assembly may comprise a barrier on or adjacent the spark plug configured to inhibit a liquid flowing on the roof reaching the gap.

[0009] Advantageously, the barrier helps prevent liquid, such as condensed water, in the combustion chamber from reaching and bridging the gap between the electrodes, and so helps prevent engine misfire. Moreover, reducing the exposure of the gap to liquids such as water can help reduce fouling of one or both electrodes, helping to prolong the service life of the spark plug.

[0010] The barrier may be configured to inhibit the liquid reaching the first or second electrodes.

[0011] Advantageously, such a configuration helps prevent liquid contacting the electrodes to prevent fouling thereof.

[0012] The barrier may have a profile comprising a drip feature arranged to disrupt a flow path of liquid from the roof towards the gap.

[0013] The drip feature may disrupt a possible flow path from the roof onto the spark plug and / or gap and / or first or second electrodes under the force of gravity in normal working conditions. Advantageously, such a configuration helps prevent the liquid from reaching the gap.

[0014] The drip feature may comprise one or more of a projection and / or recess.

[0015] The projection and / or recess may comprise at least one vertex arranged to provide a discontinuity in the flow path of liquid.

[0016] Advantageously, the vertex helps promote detachment of the liquid from the barrier, and so helps prevent the liquid from reaching the gap.

[0017] The drip feature may be V-shaped or trapezoidal-shaped in cross-section. The drip feature may be arranged such that the liquid drips from a vertex or side of the drip feature, in use.

[0018] Advantageously, such a configuration helps inhibit the liquid reaching the gap by promoting detachment of the liquid from the barrier.

[0019] The drip feature may be a projection extending into the combustion chamber.

[0020] Advantageously, such a configuration may be simpler to implement and more effective than a recess or other form of barrier. The projection may extend into the combustion chamber relative to the first or second electrode or an intermediate portion thereof, such as a base of the electrode or the surrounding structure of the spark plug. The projection may be separated from the spark plug or first and second electrodes via a recess or upwardly inclined surface.

[0021] The barrier may fully surround the gap.

[0022] Advantageously, such a configuration helps inhibit liquid from reaching the gap regardless of the inclination of the engine in normal use.

[0023] The barrier may fully surround the first and second electrodes.

[0024] Advantageously, such a configuration helps inhibit liquid from contacting the spark plug regardless of the inclination of the engine.

[0025] The barrier and the spark plug may be concentrically aligned.

[0026] Advantageously, such a configuration may help to minimise the size of the barrier.

[0027] The barrier may be annular.

[0028] Advantageously, such a configuration helps inhibit liquid from reaching the gap regardless of the inclination of the engine, whilst helping to minimise the length of the barrier.

[0029] The or each cylinder assembly may further comprise a sleeve arranged to receive the spark plug therein. The spark plug may be mounted to the cylinder head via the sleeve. The sleeve may comprise the barrier.

[0030] Advantageously, such a configuration may make it easier to retrofit the barrier to an engine, as well as simplify repair and replacement of the barrier.

[0031] The cylinder head may comprise the barrier.

[0032] Advantageously, such a configuration may help to simplify assembly of the engine and / or minimise part-count.

[0033] The spark plug may comprise the barrier.

[0034] Advantageously, such a configuration may make it easier to retrofit the barrier to an engine, as well as simplify replacement of the barrier if required.

[0035] The first and second electrodes may be separated transversely with respect to a longitudinal axis of the spark plug to form the gap.

[0036] Advantageously, such a configuration may help to minimise protrusion of the spark plug into the combustion chamber, which helps to reduce the risk of liquid flowing or dripping onto the electrodes.

[0037] The first electrode may surround the second electrode such that the gap is annular.

[0038] The spark plug may protrude into the combustion chamber a distance from the roof in the range of 2.5 to 4.5mm; optionally, 2.5 to 3.5mm.

[0039] Advantageously, such distances help to minimise protrusion of the spark plug into the combustion chamber, which thus helps to reduce the risk of liquid flowing or dripping onto the electrodes.

[0040] A width of the gap between the first and second electrodes may be in the range of 0.2 to 0.7mm; optionally, 0.2 to 0.5mm.

[0041] Such gap widths are especially beneficial for hydrogen fuelled engines, which require relatively less ignition energy from the spark plug to ignite a fuel-air mixture in the combustion chamber (e.g. relative to gasoline engines).

[0042] The roof may be substantially flat.

[0043] The roof may be a pent roof comprising two faces meeting at an apex. The spark plug and the barrier may intersect the apex.

[0044] The barrier may be a first barrier. Each cylinder assembly may further comprise a second barrier intersecting the apex on an opposite side of the gap to the first barrier.

[0045] The first and second electrodes may be positioned substantially centrally with respect to the roof.

[0046] Advantageously, such a configuration may help to improve combustion of a fuel-air mixture in the combustion chamber.

[0047] A longitudinal axis of the spark plug may be substantially parallel to an axis of reciprocating motion of the piston.

[0048] Advantageously, such a configuration may help to improve packaging of the spark plug in the engine.

[0049] The or each cylinder assembly may comprise two or more of the barriers.

[0050] A second aspect of the teachings provides a working machine comprising an engine according to the first aspect.

[0051] A third aspect of the teachings provides a genset comprising an engine according to the first aspect.

[0052] A fourth aspect provides for the use of a barrier on or adjacent the spark plug of an engine according to the first aspect to inhibit water flowing on the roof reaching the gap.

[0053] Advantageously, the use of barrier helps prevent condensed water formed as a combustion product of hydrogen in the combustion chamber from reaching and bridging the gap between the electrodes, and so helps prevent engine misfire. Moreover, reducing the exposure of the gap to water can help reduce fouling of one or both electrodes, helping to prolong the service life of the spark plug.

[0054] A fifth aspect of the teachings provides a sleeve for mounting a spark plug to a roof of a combustion chamber of an internal combustion engine. The sleeve may be configured to receive the spark plug therein such that a first end of the sleeve is adjacent first and second electrodes of the spark plug. The sleeve may be configured such that the first end protrudes from the roof into the combustion chamber when the sleeve is mounted to the combustion chamber. The first end may comprise a barrier configured to inhibit a liquid flowing on the roof reaching the first and / or second electrodes of the received spark plug, in use.

[0055] A sixth aspect of the teachings provides a spark plug for igniting a fuel-air mixture in a combustion chamber of an internal combustion engine. The spark plug may comprise a first electrode separated from a second electrode via a gap. The spark plug may comprise a barrier configured to inhibit a liquid flowing on a roof of the combustion chamber reaching the gap, when the spark plug protrudes from said roof into the combustion chamber, in use.BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Embodiments are now disclosed by way of example only with reference to the drawings, in which: Figure 1 is a plan view of an internal combustion engine according to an embodiment; Figure 2 is a view along section X-X shown in Figure 1; Figure 3 is a side view of a working machine including the engine of Figure 1; Figure 4 is an upper isometric view of a combustion chamber of the engine of Figure 1; Figure 5 is a detailed view of the combustion chamber of Figure 4; Figure 6 is a view along section A-A in Figure 2; Figure 7 is a detailed view along section A-A in Figure 2 where the engine is inclined from horizontal; Figure 8 is a side view of a combustion chamber of the engine of Figure 1 according to an embodiment; and Figure 9 is an upper plan view of the combustion chamber of Figure 8. DETAILED DESCRIPTION OF EMBODIMENT(S)

[0057] 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.

[0058] Figures 1 and 2 show an internal combustion engine 1 according to an embodiment. Figure 1 shows a plan view of the engine 1, and Figure 2 shows a cross-sectional view of the engine 1 along section X-X shown in Figure 1.

[0059] In the illustrated embodiment, the engine 1 is a gaseous fuel engine configured to be exclusively powered by hydrogen fuel. In alternative embodiments, the engine 1 may instead be configured to be (e.g. exclusively) powered by an alternative gaseous fuel, e.g. such as natural gas, or a liquid fuel, such as gasoline. In some embodiments, the engine 1 may be powered via two or more different fuels; e.g. a blend of hydrogen and another gaseous fuel.

[0060] The engine 1 may be suitable for use as the prime mover in a working machine 200 (see Figure 3 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 are suitable for use in off-highway industries such as agriculture and construction. In these industries they are generally configured to perform tasks such as excavation, load handling, harvesting or planting crops. The engine may also be utilised in a genset - a self-contained unit to provide electrical power at off-grid locations. As such the engine 1 is typically required to have certain characteristics such as a high torque output over a wide engine speed band, with peak torque occurring at a relatively low engine speed, which differ from light passenger vehicles, for example. In off-highway applications, this provides "torque backup" that enables working machines to continue to carry out working operations when encountering increased loads, or resistance to a working operation - e.g. an excavator encountering a particularly solid piece of earth to be excavated. Figure 2 shows the orientation of the engine 1 when installed in the working machine 200, and the working machine 200 is stood on horizontal ground in a non-working condition.

[0061] In this embodiment, the engine 1 has four cylinder assemblies indicated generally at 19. As configured, the engine has a maximum power output of around 55kW, although it will be appreciated that the present teachings are applicable to engines with a wide range of power outputs.

[0062] With further reference to Figure 4, each cylinder assembly 19 includes a cylinder 15 including two inlets 6 and two outlets 9, a reciprocating piston 20 translationally movable within the cylinder 15 along an axis X1, an intake port 4 leading to the two inlets 6, and an exhaust port 5 leading away from the two outlets 9. Each inlet 6 is selectively opened and closed by an intake valve 7i, such that there are two intake valves 7i. Each outlet 9 is selectively opened and closed by an exhaust valve 7e such that there are two exhaust valves 7e.

[0063] The engine 1 includes a cylinder block 2, a cylinder head 3, and an intake system 10. The cylinder head 3 is mounted to the cylinder block 2. The intake system 10 is mounted to the cylinder head 3. The cylinder block 2 includes the cylinders 5. The cylinder head 3 includes the intake port 4 and the exhaust port 5 of each cylinder assembly 19.

[0064] Each cylinder assembly 19 includes a combustion chamber 100 defined by a roof 102 of the cylinder head 3, the piston 20, and the cylinder 15. The roof 102 defines a ceiling of the combustion chamber 100 when the engine 1 is in a normal orientation during operation.

[0065] In the illustrated embodiment, the roof 102 is substantially flat and substantially normal to the piston axis X1. In alternative embodiments (not shown), the roof may be a pent-roof or hemispherical roof.

[0066] As shown in Figure 4, the two inlets 6 and two outlets 9 pass through the roof 102.

[0067] In the illustrated embodiment, the intake system 10 is configured to supply hydrogen fuel and air to the combustion chamber 100 for combustion. The intake system 10 is configured to supply fuel to the intake port 4 of each cylinder assembly 19 via a corresponding fuel injector 22. A mixture of air and fuel is then supplied from the intake port 4 to the combustion chamber 100 via the inlets 6. As such, the engine 1 is a port fuel injection (PFI) engine.

[0068] Additionally or alternatively, the engine 1 may be configured to supply hydrogen fuel to each combustion chamber 100 via direct fuel injection into the combustion chamber 100 (e.g. via a fuel injector 25 in or adjacent to the cylinder 15, illustrated schematically in broken lines in Figure 2).

[0069] In the illustrated embodiment, each fuel injector 22, 25 is supplied with gaseous hydrogen fuel from a pressurised fuel tank 202 (see Figure 3). The rated pressure of the fuel tank 202 is typically in excess of 35MPa and the hydrogen pressure may be stepped down before being introduced into the cylinders 15.

[0070] As the engine 1 utilises hydrogen as a fuel, a spark is required to initiate combustion. Thus, each cylinder assembly 19 includes a spark plug 101 (illustrated schematically in Figure 2). The spark plug 101 is in the cylinder head 3 and extends through the roof 102.

[0071] With further reference to Figure 5, which shows a detailed view of an end of the spark plug 101, and Figure 6, which shows a cross-sectional view along section A-A in Figure 2, the spark plug 101 includes a first electrode 104 separated from a second electrode 106 via a gap 108. The spark plug 101 is configured to generate a spark between the first and second electrodes 104, 106 across the gap 108 to ignite a fuel-air mixture in the combustion chamber 100 during a combustion cycle of the engine 1. The spark plug 101 is connected to a coil 103 which generates a high tension current to initiate the spark in the spark plug 101, as required.

[0072] The spark plug 101 extends through the roof 102. The first and second electrodes 104, 106 protrude from the roof 102 such that the gap 108 is within the combustion chamber 100; i.e. the portions of the first and second electrodes 104, 106 defining the gap 108 protrude out into the combustion chamber 100 with respect to the roof 102. In alternative embodiments, only one of the electrodes 104, 106 may protrude from the roof 102.

[0073] The first and second electrodes 104, 106 are separated transversely with respect to a longitudinal axis X2 of the spark plug 101 to form the gap 108. This helps to minimise protrusion of the spark plug 101 into the combustion chamber 100, which helps to reduce the risk of liquid flowing or dripping onto the electrodes 104, 106 from the walls of the combustion chamber 100. Additionally or alternatively, the first and second electrodes 104, 106 may be separated longitudinally with respect to the longitudinal axis X2.

[0074] In some embodiments, a distance D between a distal end (lowest point) of the spark plug 101 and the portion of the roof 102 through which the spark plug 101 extends is in the range of 2.5 to 4.5mm, e.g. in the range of 2.5 to 3.5mm. Such distances D help to minimise protrusion of the spark plug 101 into the combustion chamber 100 from the roof 102.

[0075] In the illustrated embodiment, the spark plug 101 is a surface-discharge spark plug. The first electrode 104 surrounds the second electrode 106 such that the gap 108 is substantially annular. In alternative embodiments, the spark plug 101 may be any suitable spark plug, such as a J-type spark plug (i.e. in which one of the electrodes has a substantially J-shaped profile).

[0076] In the illustrated embodiment, the spark plug 101 is interposed between the two inlets 6 and two outlets 9. The first and second electrodes 104, 106 are positioned substantially centrally with respect to the roof 102, but may be offset from the centre in alternative embodiments.

[0077] As will be appreciated from Figures 2 and 6, the spark plug 101 is arranged in the cylinder head 3 such that the longitudinal axis X2 of the spark plug 101 is substantially parallel to the axis of reciprocating motion X1 of the piston 20. In alternative embodiments, the spark plug 101 may be oriented at a non-zero angle to said axis X1.

[0078] In the illustrated embodiment, the spark plug 101 is mounted to the cylinder head 3 via a sleeve 112 in which the spark plug 101 is received. The sleeve 112 may be formed from metal such as steel.

[0079] The engine 1 includes an engine cooling system including a water jacket 113 in the cylinder head 3, part of which is shown in Figure 6. The sleeve 112 extends through the water jacket 113 so as to seal the spark plug 101 from a coolant in the water jacket 113. The sleeve 112 also provides a seal with the cylinder head 3 for inhibiting the coolant leaking from the water jacket 113 (e.g. into the combustion chamber 100 or to the outside of the engine 1). The sleeve 112 also provides a seal between the spark plug 101 and the cylinder head 3 to inhibit oil and other contaminants from fouling the spark plug 101 or from entering the combustion chamber 3, as well as inhibiting combustion gas from the combustion chamber 100 passing between the spark plug 101 and cylinder head 3. The sleeve 112 includes a number of sealing features, such as O-rings 115, to aid the sealing in this embodiment.

[0080] The sleeve 112 is mounted to a bore 404 of the cylinder head 3 via engagement between male screw threads 400 on the sleeve 112 and female screw threads 402 on the surface of the cylinder head 3 defining the bore 404. The sleeve 112 includes a shoulder 406 which abuts against a step 408 of the cylinder head 3 to set the depth of protrusion of the sleeve 112 into the combustion chamber 100.

[0081] The spark plug 101 is mounted to the sleeve 112 via engagement between male screw threads 410 on the spark plug 101 and female screw threads 412 on the sleeve 112. The spark plug 101 includes a shoulder 414 which abuts against a step 416 of the sleeve 112 to set the depth of protrusion of the spark plug 101 relative to the sleeve 112, and thus the protrusion distance D into the combustion chamber 100. A sealing member 420 is arranged between the shoulder 414 of the spark plug 101 and the shoulder 416 of the sleeve 112 to provide a seal therebetween.

[0082] In alternative embodiments, the spark plug 101 may be (e.g. directly) mounted to the cylinder head 3 without the sleeve 112.

[0083] It is known that hydrogen-air mixtures require less ignition energy to ignite relative to gasoline-air mixtures, for example. As such, the width of the gap 108 between the electrodes 104, 106 of the spark plug 101, which is a factor that determines the ignition energy of the spark, can be made smaller compared to spark plugs for gasoline engines for example. For example, the width of the gap 108 may be in the range of 0.2 to 0.7mm, e.g. in the range of 0.2 to 0.5mm. Whereas, in gasoline engines, the gap between a spark plug's electrodes tends to be higher, e.g. in the range of 0.8 to 1.8 mm. Since the spark plug 101 has a relatively smaller width gap 108, water can more easily bridge the gap so as to prevent the spark plug 101 generating a spark. As such, the spark plug 101 is more susceptible to problems resulting from spark plug wetting (i.e. water contacting the spark plug 101).

[0084] Since the electrodes 104, 106 protrude from the roof 102, condensed water, or any other liquid (e.g. lubricating oil), adhered to the roof 102 may flow along the roof 102, e.g. under the force of gravity, and into contact with the gap 108. The risk of this occurring is higher when the engine 102 is inclined relative to the horizontal as shown in Figure 7, in which condensed water adhered to and flowing along the roof 102 is indicated via a dashed arrow denoted W. If the water W reaches and bridges the gap 108, the spark plug 101 may be unable to produce a spark resulting in engine misfire.

[0085] To inhibit this, the cylinder assembly 19 includes a barrier 110 configured to inhibit a liquid adhered to the roof 102 and flowing therealong, such as the water W, from reaching the gap 108.

[0086] In the illustrated embodiment, the barrier 110 is configured to inhibit a liquid adhered to the roof 102 from reaching the first or second electrodes 104, 106. The barrier 110 extends circumferentially around and fully surrounds the first and second electrodes 104, 106 so as to shield them from the water W as shown in Figure 7. Advantageously, this helps prevent water contacting the spark plug 101, inhibiting fouling of the electrodes 104, 106.

[0087] As shown in Figure 5, the barrier 110 is substantially annular about a central axis X2 of the barrier 110, which is aligned with the longitudinal axis X2 of the spark plug 101 in this embodiment such that the barrier 110 and spark plug 101 are concentrically aligned.

[0088] In alternative embodiments, the barrier 110 may have any suitable non-annular closed shape (e.g. rectangular), or open shape.

[0089] In the illustrated embodiment, the barrier 110 projects from the roof 102 into the combustion chamber 100, but may be at least partially recessed with respect to (e.g. into) the roof 102 in other embodiments.

[0090] In the illustrated embodiment, the barrier 110 has a profile including a drip feature 111 configured to detach liquid flowing over the barrier 110 therefrom. Advantageously, the drip feature 111 promotes the shedding of water from the barrier (i.e. dripping from it) rather than reaching the electrodes 104, 106.

[0091] In the illustrated embodiment, the drip feature 111 includes a projection 111 arranged to disrupt the flow path of liquid W from the roof 102 towards the gap 108. In alternative embodiments, the drip feature 111 may include more than one of such projection.

[0092] In the illustrated embodiment, the projection 111 includes an inner surface 110a, proximal the gap 108, an outer surface 110b, distal to the gap 108, and a rim 114 interposed between the inner and outer surfaces 110a, 110b. The rim 114 is joined to each of the inner and outer surfaces 110a, 110b via a respective vertex. In use, the water W drips from a lowermost of the vertices or a side (e.g. the rim 114) of the projection 111.

[0093] Additionally or alternatively, the drip feature 111 may include one or more recesses arranged to disrupt the flow path of liquid W. The or each recess may be defined via a vertex arranged to provide a discontinuity in the flow path of liquid W.

[0094] In the illustrated embodiment, the inner and outer surfaces 110a, 110b are inclined relative to the piston axis X1. The inner surface 110a is inclined upwardly (i.e. away from the combustion chamber 100) in a direction from the roof 102 towards the gap 108. The outer surface 110b is inclined downwardly (i.e. into the combustion chamber 100) in the direction from the roof 102 towards the gap 108. As such, the inner and outer surfaces 110a, 110b converge to join the rim 114. This helps to promote water shedding from the rim 114.

[0095] The projection 111 extends from the roof 102 into the combustion chamber 100. The rim 104 includes the lowest portion of the projection 111. The rim 104 is separated from the spark plug 101 via the inner surface 110a, but may be separated via a recess in other embodiments, to inhibit liquid flowing from the rim 104 to the spark plug 101.

[0096] In the illustrated embodiment, the rim 114 is a substantially planar surface but may be a sharp edge where the inner and outer surfaces 110a, 110b join in other embodiments, for example. It may however be preferable for the barrier 110 to avoid terminating in a sharp point at the rim 114 for manufacturability and / or durability reasons. The rim 114 joins to the inner and outer surfaces 110,a 110b via the vertices such that the projections 111 has a trapezoidal profile. In alternative embodiments, the projection 111 may have a V-shaped profile. In some embodiments, the rim 114 may join without discontinuity (i.e. smoothly) to at least one the inner and outer surfaces 110a, 110b of the drip feature 111.

[0097] In the illustrated embedment, the gradient of the outer surface 110b with respect to the roof 102 is steeper relative to the inner surface 110a. This helps to ensure that liquid flowing over the barrier 110 from the roof 102 has sufficient momentum to detach from the barrier 110 at the rim 114. In alternative embodiments, the inner face 110a may be steeper, or the faces 110a, 110b may have substantially the same gradient.

[0098] In alternative embodiments, the barrier 110 may have any suitable profile (e.g. a saw tooth shaped profile, or a steep sided hump shaped profile) which is configured to detach liquid flowing over the barrier therefrom.

[0099] In the illustrated embodiment, an end of the sleeve 112 adjacent the combustion chamber 100 includes the barrier 110. The barrier 110 is thus adjacent to the spark plug 101. Advantageously, providing the barrier 110 on the sleeve 112 simplifies retrofitting the barrier 110 to existing engines, as well as simplifying repair and replacement of the barrier 110.

[0100] In an alternative embodiment (not shown), the cylinder head 3 may instead include the barrier 110. For example, the barrier 110 may be on (e.g. cast on or machined into) the roof 102, e.g. such that the barrier is adjacent to the spark plug 101. Advantageously, such embodiments may not include the sleeve 112, which may help to simplify manufacture of the engine 1.

[0101] In yet a further alternative embodiment (not shown), the spark plug 101 may include the barrier 110. For example, the barrier 110 may be on (e.g. machined into) the first electrode 104. In such embodiments, the barrier may fully surround the gap 108 and the second electrode 106. Advantageously, providing the barrier 110 on the spark plug 101 simplifies retrofitting the barrier 110 to existing engines, as well as simplifying repair and replacement of the barrier 110. Moreover, this may help to minimise the size of the barrier 110.

[0102] An alternative embodiment of a cylinder assembly 19' for the engine 1 is described with reference to Figures 8 and 9. Features in common with the cylinder assembly 19 described above share common reference numerals and a description of which shall not be repeated for brevity. The cylinder assembly 19' may share any features described in relation to the cylinder assembly 19 described above, and vice versa. Figure 8 shows the orientation of the cylinder assembly 19' when the engine 1 is installed in the working machine 200, and the working machine 200 is stood on horizontal ground in a non-working condition.

[0103] The cylinder assembly 19' includes a combustion chamber 100' defined by the piston 20 and a pent-type roof 102'. The roof 102' includes a first face 102a' and a second face 102b' inclined relative to one another and meeting at an apex 300 (represented by a dashed line in Figure 9). The first face 102a' includes the two outlets 9 and the second face 102b' includes the two inlets 6. The spark plug 101 intersects the apex 300 as shown in Figure 9.

[0104] It will be appreciated from Figure 8 that the first and second faces 102a', 102'b are oriented such that condensed water adhered to them will flow away from the spark plug 101 across the normal orientation range of the engine 1 in use. As such, there is less of a need for a barrier to shield the spark plug 101 from water adhered to the first and second faces 102a', 102'b of the roof 102'.

[0105] The apex 300 is substantially perpendicular to the axis X1 of piston motion, and so is substantially parallel to the flat roof 102 of the first embodiment. As such, condensed water adhered to the apex 300 can potentially flow therealong and into contact with the sparkplug 101 in a similar manner to water adhered to the flat roof 102 of the first embodiment.

[0106] As shown in Figure 9, the cylinder assembly 19' includes two barriers 110' on or adjacent the spark plug 101 configured to inhibit a liquid adhered to the apex 300 and flowing therealong from contacting at least the gap 108 of the spark plug 101. The barriers 110' intersect the apex 300 and are located on or adjacent to opposite sides of the spark plug 101.

[0107] In the illustrated embodiment, the barriers 110' are shown as having rectangular profiles in plan view, but may have any suitable profiles in other embodiments (e.g. partially annular or crescent shaped). In some embodiments, the two barriers 110' may be joined to form a single barrier.

[0108] In the illustrated embodiment, the barriers 110' are formed on the roof 102', but one or both of the barriers 110' may be formed on the sleeve 112 in alternative embodiments.

[0109] 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 hydrogen fuel internal combustion engine comprising a cylinder head and one or more cylinder assemblies, the or each cylinder assembly comprising: a combustion chamber at least partially defined by a roof of the cylinder head; and a spark plug extending through the roof, the spark plug comprising a first electrode separated from a second electrode via a gap, wherein at least one of the first and second electrodes protrudes from the roof such that the gap is within the combustion chamber, and wherein each cylinder assembly comprises a barrier on or adjacent the spark plug configured to inhibit a liquid flowing on the roof reaching the gap.

2. The engine of claim 1, wherein the barrier is configured to inhibit the liquid reaching the first or second electrodes, optionally wherein the liquid is water.

3. The engine of claims 1 or 2, wherein the barrier has a profile comprising a drip feature arranged to disrupt a flow path of liquid from the roof towards the gap; optionally wherein the drip feature comprises one or more of a projection and / or recess; optionally wherein the projection and / or recess comprises at least one vertex arranged to provide a discontinuity in the flow path of liquid; optionally wherein the drip feature is V-shaped or trapezoidal-shaped in cross-section, and arranged such that the liquid drips from a vertex or side of the drip feature, in use; and optionally wherein the drip feature is a projection extending into the combustion chamber.

4. The engine of any preceding claim, wherein the barrier fully surrounds the gap; optionally wherein the barrier fully surrounds the first and second electrodes; optionally wherein the barrier and the spark plug are concentrically aligned; and optionally wherein the barrier is annular.

5. The engine of any preceding claim, wherein the or each cylinder assembly further comprises a sleeve arranged to receive the spark plug therein, wherein the spark plug is mounted to the cylinder head via the sleeve, and wherein the sleeve comprises the barrier.

6. The engine of any one of claims 1 to 4, wherein the cylinder head comprises the barrier; and / or wherein the spark plug comprises the barrier.

7. The engine of any preceding claim, wherein the first and second electrodes are separated transversely with respect to a longitudinal axis of the spark plug to form the gap; optionally, wherein the first electrode surrounds the second electrode such that the gap is annular; and optionally wherein a width of the gap between the first and second electrodes is in the range of 0.2 to 0.7mm; optionally, 0.2 to 0.5mm.

8. The engine of any preceding claim, wherein the spark plug protrudes into the combustion chamber a distance from the roof in the range of 2.5 to 4.5mm; optionally, 2.5 to 3.5mm.

9. The engine of any preceding claim, wherein the roof is substantially flat.

10. The engine of any one of claims 1 to 8, wherein the roof is a pent roof comprising two faces meeting at an apex, and wherein the spark plug and the barrier intersect the apex; optionally wherein the barrier is a first barrier, and wherein each cylinder assembly further comprises a second barrier intersecting the apex on an opposite side of the gap to the first barrier.

11. The engine of any preceding claim, wherein the first and second electrodes are positioned substantially centrally with respect to the roof and / or, wherein a longitudinal axis of the spark plug is substantially parallel to an axis of reciprocating motion of the piston.

12. A working machine or a genset comprising the engine of any previous claim.

13. The use of a barrier on or adjacent the spark plug of an engine according to any one of claims 1 to 12 to inhibit water flowing on the roof reaching the gap.

14. A sleeve for mounting a spark plug to a roof of a combustion chamber of an internal combustion engine, wherein the sleeve is configured to receive the spark plug therein such that a first end of the sleeve is adjacent first and second electrodes of the spark plug, wherein the sleeve is configured such that the first end protrudes from the roof into the combustion chamber when the sleeve is mounted to the combustion chamber, and wherein the first end comprises a barrier configured to inhibit a liquid flowing on the roof reaching the first and / or second electrodes of the received spark plug, in use.

15. A spark plug for igniting a fuel-air mixture in a combustion chamber of an internal combustion engine, the spark plug comprising a first electrode separated from a second electrode via a gap, wherein the spark plug comprises a barrier configured to inhibit a liquid flowing on a roof of the combustion chamber reaching the gap, when the spark plug protrudes from said roof into the combustion chamber, in use.

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