Inlet port of a gaseous hydrogen internal combustion engine

Abstract

A gaseous hydrogen internal combustion engine (100,fig.2A) comprising an inlet port (106,fig.2A) comprising a runner 110 and a valve seat 148, and an inlet valve 162 having a valve head 166. The runne

Description

TECHNICAL FIELD The present disclosure relates to an inlet port of a gaseous hydrogen internal combustion engine. Aspects of the invention relate to a gaseous hydrogen internal combustion engine, and to a vehicle. BACKGROUND Gaseous fuels such as hydrogen can be combusted with a significantly higher aicfuel ratio compared to liquid gasoline. Running at such a lean ratio requires a large volume of airto be injected into the combustion chamber of the engine in a short time to increase engine power density at high load conditions. Therefore, achieving a high flow rate (flow coefficient) is a design constraint. A high flow coefficient requires streamlined airflow entering the combustion chamber, with the effect of low air tumble in the combustion chamber. Therefore, a compromise of high flow coefficient is a less homogeneous air-fuel mixture in the combustion chamber. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a gaseous hydrogen internal combustion engine, and a vehicle as claimed in the appended claims. According to an aspect of the present invention there is provided a gaseous hydrogen internal combustion engine comprising: an inlet port comprising a runner and a valve seat; and an inlet valve, wherein the runner comprises an elongate section having a roof, sides, and floor; wherein the runner further comprises a curved section connected to a downstream end of the elongate section, the curved section being shorter than the elongate section and curved relative to the elongate section, and comprising a proximal section connected to the floor and a distal section connected to the roof; and wherein the valve seat is connected to a downstream end of the curved section, wherein the inlet valve comprises a valve head configured to seal a downstream end of the valve seat when in a closed position, wherein the diameter of the valve head defines a reference area, wherein the elongate section of the runner has an average cross-sectional area along its length of between 40% to 65% of the reference area, wherein the elongate section of the runner defines an equivalent circle of equal cross-sectional area to the runner, wherein the roof is recessed relative to the equivalent circle along most or all the length of the elongate section, wherein the valve seat is angled relative to the elongate section so that a perimeter of the valve head presents a proximal side and a distal side relative to the elongate section, and wherein the floor comprises a longitudinal curve proximal to and upstream of the proximal section, configured to steer airflow away from the proximal side of the perimeter of the valve head. An advantage is a significant improvement in tumble ratio with a limited reduction of the flow coefficient. The benefit of the higher tumble ratio outweighs the penalty of the reduced flow coefficient. A first factor is the small cross-sectional area of the inlet port, which creates more boundary layer turbulence than a large-area port, to promote tumble. A second factor is the recessed roof, resulting in a straighter roof which improves the flow rate towards the distal side of the valve head, such that the flow rate entering the combustion chamber past the distal side of the valve head is greater than that entering past the proximal side of the valve head, to promote tumble. A third factor is the longitudinal upwards curve towards the end of the floor, which biases separating floor airflow away from the proximal side of the valve head and towards the distal side of the valve head, to further promote tumble. Optionally, the proximal side of the valve head is proximal to the proximal section of the curved section of the runner, and the distal side of the valve head is proximal to the distal section of the curved section of the runner. Optionally, the average cross-sectional area reduces from an upstream end of the runner to a downstream end of the runner, and optionally from the upstream end of the runner to the downstream end of the elongate section of the runner. An advantage is an improvement in flow coefficient, because the area reduction creates a region of reduced static pressure just upstream of the valve seat, creating pressure recovery. Optionally, an average deviation of the roof from the equivalent circle is greater than an average deviation of the sides from the equivalent circle. Optionally, the floor is recessed relative to the equivalent circle. Optionally, the sides and floor have a different average radius of curvature than the roof. Optionally, the roof comprises a relatively flat portion, relative to the sides, and wherein the relatively flat portion of the roof is recessed relative to the equivalent circle. An advantage is that the recessed roof and floor create a wide aspect ratio, which can increase airflow speed. Optionally, the roof comprises a valve stem aperture, and wherein the roof defines a flow attachment surface extending up to the valve stem aperture. An advantage is that the geometry of the roof minimises pressure loss and avoids a reduction in flow coefficient. Optionally, the elongate section of the runner has a height between the floor and roof, and a width between the sides, and wherein an aspect ratio defined by the heightwidth is other than 1:1, and optionally increases towards the downstream end of the elongate section. An advantage is that the wide aspect ratio towards the upstream end increases airflow speed, and the taller aspect ratio towards the downstream end can increase the flow coefficient while maintaining high tumble. Optionally, the longitudinal curve is a second curve of a longitudinal reversed curve section of the floor, wherein the longitudinal reversed curve section comprises a first curve proximal to the downstream end of the elongate section, to lower the floor relative to the roof, and wherein the second curve is downstream of the first curve and has opposite curvature than the first curve to steerthe airflow away from the proximal side of the perimeter of the valve head. An advantage is that the curves create a turning effect on the floor airflow, which turns the airflow away from the proximal side of the valve head as the airflow separates from the downstream end of the elongate section. By separating the floor airflow and biasing it towards the distal side of the valve head, tumble motion is promoted. Optionally, the second curve has a smaller radius than the first curve. An advantage is that the second curve turns the airflow away from the proximal side of the valve head, to promote tumble motion. Optionally, the first curve and / or the second curve of the floor is recessed relative to the equivalent circle. Optionally, the engine comprises a masking structure to recess the valve seat and valve head relative to a main surface ofa chamber roof of a combustion chamber ofthe gaseous hydrogen internal combustion engine, wherein the masking structure has a height of several millimetres at a side of the masking structure corresponding to the proximal side ofthe valve head. An advantage is reducing the amount of relief that needs to be cut into the piston crown ofthe piston, allowing a high compression ratio to be maintained. The masking structure also helps to direct more airflow over the distal side ofthe valve head, to promote high tumble. Optionally, an inner diameter ofthe valve seat comprises a first section defined by a first slope angle, a second section above the first section and defined by a second slope angle, and an optional third section above the second section and defined by a third slope angle, wherein the slope angles are defined relative to an axis of a valve stem ofthe inlet valve, wherein the first slope angle defines a sealing face for the valve head and is selected from the range 40 to 50 degrees, wherein the second slope angle is selected from the range 20 to 40 degrees, and wherein the optional third slope angle is selected from the range 5 to 20 degrees. Optionally, each section comprises a straight slope. An advantage is that the slope angles define contoured surfaces, to improve flow coefficient. The multi-angled cut is also more machinable than a curved transition. Optionally, a lower edge ofthe first section ofthe valve seat is connected to an upper surface ofthe masking structure. Optionally, the gaseous hydrogen internal combustion engine further comprises an exhaust valve, wherein an inner angle between the intake valve and the exhaust valve is selected from the range 25 to 35 degrees, and wherein a compression ratio of the gaseous hydrogen internal combustion engine is at least 12:1. An advantage of the angle is allowing a higher compression ratio. This is because a small angle reduces the top dead centre volume of the combustion chamber, because the depth of any relief cutouts on the piston crown can be minimised due to the valve heads being less inclined relative to the piston crown. Optionally, the elongate section is generally straight. Optionally, the elongate section is generally straight relative to the curved section. Optionally, the elongate section is generally straight and extends at an angle selected from the range 40 to 50 degrees relative to a valve stem angle, and wherein the proximal section of the curved section defines a separation edge at an end of the floor of the elongate section. An advantage is improved tumble because the airflow will encounter a sheer drop at the end of the straight elongate section of the runner, causing the floor airflow to separate and create a jet whose momentum is directed away from the proximal side of the valve head. Therefore, more airflow is biased towards the distal side of the valve head, to promote tumble motion as the valve opens. Optionally, the inlet port comprises a distribution chamber and a pair of the runners fluidly coupled to the distribution chamber, each runner extending to a different one of a pair of valve seats and inlet valves for a same combustion chamber of the gaseous hydrogen internal combustion engine. According to another aspect of the present invention, there is provided a vehicle comprising the gaseous hydrogen internal combustion engine. According to a further aspect of the present invention there is provided a gaseous hydrogen internal combustion engine comprising: an inlet port comprising a runner and a valve seat; and an inlet valve, wherein the runner comprises an elongate section, wherein the inlet valve comprises a valve head, wherein the diameter of the valve head defines a reference area, and wherein the elongate section of the runner has an average cross-sectional area along its length of between 40% to 65% of the reference area. According to a further aspect of the present invention there is provided a gaseous hydrogen internal combustion engine comprising: an inlet port comprising a runner and a valve seat; and an inlet valve, wherein the runner comprises an elongate section having a roof, and wherein the elongate section of the runner defines an equivalent circle of equal cross-sectional area to the runner, wherein the roof is recessed relative to the equivalent circle along most or all the length of the elongate section. According to a further aspect of the present invention there is provided a gaseous hydrogen internal combustion engine comprising: an inlet port comprising a runner and a valve seat; and an inlet valve, wherein the runner comprises an elongate section having a roof, sides, and floor, wherein the runner further comprises a curved section connected to a downstream end ofthe elongate section, the curved section being shorter than the elongate section and curved relative to the elongate section, and comprising a proximal section connected to the floor and a distal section connected to the roof, wherein the valve seat is connected to a downstream end ofthe curved section, wherein the inlet valve comprises a valve head configured to seal a downstream end ofthe valve seat when in a closed position, wherein the valve seat is angled relative to the elongate section so that a perimeter ofthe valve head presents a proximal side and a distal side relative to the elongate section, and wherein the floor comprises a longitudinal curve proximal to and upstream ofthe proximal section, configured to steer airflow away from the proximal side ofthe perimeter of the valve head. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination that falls within the scope ofthe appended claims. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination that falls within the scope ofthe appended claims, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments ofthe invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 illustrates a perspective view illustrating an example of a vehicle; FIG. 2A illustrates a schematic top view illustrating an example of a gaseous hydrogen internal combustion engine; FIG 2B illustrates a schematic side cross-section view illustrating an example of a gaseous hydrogen internal combustion engine; FIG. 3 illustrates a perspective view illustrating an example of an inlet port; FIG. 4 illustrates a side cross-section view illustrating an example of an inlet port; FIG. 5 illustrates a cross-section view along an example runner of an inlet port; FIG. 6 illustrates a side view illustrating an example of a valve seat; FIG. 7 illustrates a side view illustrating an example of a valve seat and masking structure; FIG. 8 illustrates a side view illustrating an example of a longitudinal reversed curve section in a floor of a runner; FIG. 9 illustrates a graph illustrating flow coefficient relative to valve lift for two example inlet ports; and FIG. 10 illustrates a graph illustrating tumble ratio relative to valve lift for two example inlet ports. DETAILED DESCRIPTION A vehicle 1 in accordance with an embodiment of the present invention is described herein with reference to the accompanying FIG. 1. In some, but not necessarily all examples, the vehicle 1 is a passenger vehicle, also referred to as a passenger car or as an automobile. In other examples, embodiments of the invention can be implemented for other applications, such as commercial vehicles. FIG. 2A illustrates a schematic top view illustrating an example of a gaseous hydrogen internal combustion engine 100 (“engine” / “hydrogen engine"). The engine 100 may be a four-stroke or two-stroke engine, with one or more combustion chambers 102 (optionally cylinders), each containing a reciprocating piston 103. The engine 100 comprises air inlet and exhaust ports 176, fuel injectors, and igniters (e.g., spark plugs), for each combustion chamber 102. The engine 100 may be split into an engine block and a cylinder head. Unlike a traditional gasoline or diesel engine, the engine 100 is fuelled by gaseous hydrogen rather than by liquid hydrocarbons. A gaseous hydrogen internal combustion engine physically differs from a liquid-fuelled engine (e.g., gasoline or diesel) in several ways. The engine 100 can include, among other things: hardened and stronger moving parts and head gaskets; and gas fuel injectors rather than liquid fuel injectors. Gas fuel injectors may have different nozzle designs than gasoline fuel injectors, and may be configured for direct and / or indirect injection. Furthermore, a control system (not shown) of the hydrogen engine 100 may have a different control range of air-fuel ratio than a liquid hydrocarbon engine. An air-gasoline ratio, by mass, will start to become lean when it exceeds approximately 14 to 14 8. By contrast, an air-hydrogen ratio, by mass, will start to become lean when it exceeds approximately 34.3. The control range of air-hydrogen ratio may exceed 100:1 or may exceed 150:1, during lean running. This is much leaner than a hydrocarbon fuelled engine, for which the control range of air-fuel ratio may be less than 20:1 (gasoline) or less than 80:1 (diesel). The geometric compression ratio of the hydrogen engine 100 may be within the range 9:1 to 16:1. Advantageously, the compression ratio may be greater than 12:1 or greater than 12.5:1, which would be a very high compression ratio fora spark ignition engine. FIG. 2A illustrates four combustion chambers 102 formed within an engine block, and four air inlet ports 106 formed within a cylinder head. The inlet ports 106 are fluidly connected to an external inlet manifold 105. Each inlet port 106 splits into two runners 110, supplying air to a pair of inlet valves 162 (FIG. 2B) of each combustion 6 chamber 102. Each inlet port 106 can be regarded as having a distribution chamber 108 towards its upstream end, and a plurality of runners 110 extending from the distribution chamber 108 to the combustion chamber 102. In other embodiments, the combustion chamber 102 has one inlet valve 162 per combustion chamber 102, therefore each inlet port 106 has only one runner 110. In still further embodiments, the combustion chamber 102 has more than two inlet valves 162 per combustion chamber 102, therefore each inlet port 106 has more than two runners 110. FIG. 2A also illustrates four exhaust ports 176 fluidly coupled to an external exhaust manifold 180. The design of the exhaust ports 176 is outside the scope of this disclosure. The primary exhaust gas of a hydrogen engine 100 is water vapour. FIG 2B illustrates a schematic side cross-section view illustrating an example of a hydrogen engine 100. The side cross-section refers to the plane extending on the vertical axis along which the piston 103 travels, and extending from the intake valve side to the exhaust valve side of the combustion chamber 102. The inlet port 106 is fluidly connected to the combustion chamber 102 by an inlet valve 162. The exhaust port 176 is fluidly connected to the combustion chamber 102 by an exhaust valve 178. The inlet valves 162 and exhaust valves 178 may be poppet valves. They are shown in a seated position, and move down into the combustion chamber 102 when opened. The combustion chamber 102 contains a reciprocating piston 103 movable between top dead centre (TDC) and bottom dead centre (BDC) positions. The compression ratio of the combustion chamber 102 is defined based on the volume when the piston 103 is at TDC. The engine 100 may be an interference engine, to promote a high compression ratio. Optionally (not shown), a crown of the piston 103 comprises shallow valve reliefs (machined cutouts) to prevent interference with the inlet and exhaust valves 162,178. The crown may also comprise a central machined bowl, to promote fuel-air mixing. The chamber roof 104 defining the upper boundary of the combustion chamber 102 comprises the inlet ports 106 and exhaust ports 176. The chamber roof 104 may be non-flat. As shown in FIGS. 2B and 3, the chamber roof 104 may be domed, being highest in the centre. Therefore, the inlet ports 106 and exhaust ports 176 are inclined relative to the centrelines of the combustion chamber 102 and piston 103. The inclination of the inlet port 106 and exhaust port 176 means that the inlet valves 162 and exhaust valves 178 are correspondingly inclined, to seal against the inlet port 106 and exhaust port 176. The valve inner angle a (“included valve angle”) between an inlet valve 162 and an exhaust valve 178 is selected from the range 20 to 40, or 25 to 35 degrees. The valve inner angle a reduces the TDC volume of the combustion chamber 102 compared to a higher valve inner angle, for a given valve relief on the piston crown. Therefore, a low valve inner angle a of approximately 30 degrees facilitates a high compression ratio, without needing deep valve reliefs on the piston crown. Although a high compression ratio improves various attributes of combustion, it may limit the inlet air's ability to “tumble” effectively. Air tumble relates to the anti-clockwise swirling / vortical motion in the side cross-section plane of FIGS. 2B and 3. High tumble improves mixing of air and fuel. Tumble motion is induced if the momentum of the inlet air entering the combustion chamber 102 past the higher / distal side 170 of the inlet valve 162 (right side in FIG. 4) is greater than the momentum of the inlet air entering the combustion chamber 102 through the lower / proximal side 168 of the inlet valve 162 (left side in FIG. 4). This asymmetry promotes the anti-clockwise swirling motion. However, if the inlet port geometry improves tumble, this would be at the expense of flow coefficient. The flow coefficient is a parameter indicating the flow capacity of the inlet port 106 and inlet valves 162. If the flow coefficient is too low, then the pressure loss in the intake port is high which reduces the amount of air that can be injected within a valve opening window, therefore limiting the maximum possible air-fuel ratio. It was initially thought that a high flow coefficient would be the most important parameter for a hydrogen engine 100, such that sacrifices in tumble ratio (dimensionless amount of tumble) would need to be made. However, the inventors found that a high-tumble inlet port design (shown in FIGS. 3-8) yielded a significant improvement in tumble ratio without a significant loss of flow coefficient. The gains regarding tumble ratio may outweigh the losses in flow coefficient. Furthermore, the inlet port 106 can be used with a high compression ratio engine 100 (>12:1), along with a shallow valve inner angle a (~30 degrees), and minimal machining of the piston crown. FIG. 3 illustrates a perspective view illustrating an example of an inlet port 106 and chamber roof 104 For clarity, FIGS. 3-8 are void models, such that the visible external surfaces represent the internal surfaces of the inlet port 106 and combustion chamber 102. The runners 110 of the inlet port 106 extend diagonally inwardly and downwardly from the distribution chamber 108 to the chamber roof 104. The directions ‘inward’ and ‘downward’ referto a local engine coordinate system, and do not suggest a particular orientation of the engine 100. FIGS. 3-5 show that each runner 110 comprises a roof 114, left and right sides 120, and a floor 122. The roof 114, sides 120 and floor 122 define the top side, left and right sides, and bottom side of the rounded crosssection. The roof 114, sides 120, and floor 122 define a rounded cross-section of tubular form. FIGS. 3-4 show that the runner 110 has an elongate section 112 and a curved section 136 downstream of the elongate section 112. The curved section 136 leads to the valve seat 148. The valve seat 148 may be a separate part than the runner 110, such as a press-fit part. As best shown in FIG. 4, the curved section 136 means that airflow along the floor 122 of the runner 110 does not flow directly onto the back of the valve head 166 while remaining attached to the floor 122. The curved section 136 represents a sudden drop in the floor 122, creating flow separation from the floor 122 at the interface between the elongate section 112 and the curved section 136. This will increase the asymmetry of flow momentum passing through the proximal and distal sides 168, 170 of the valve head 166, to promote tumble motion in the combustion chamber 102. The distribution chamber 108 of the inlet port 106 has an upstream end and a downstream end. The upstream end of the distribution chamber 108 may also be a port entrance hole of the cylinder head, to interface with the inlet manifold 105. The downstream end of the distribution chamber 108 is where split between the two runners 110 of the inlet port 106 begins. As shown in FIG. 4, each runner 110 has an upstream end 130, which may also be the downstream end of the distribution chamber 108. Each runner 110 also has a downstream end 146, opposite the upstream end 130 and connected to the separate valve seat 148. Within the runner 110, the elongate section 112 of the runner 110 has an upstream end 130, which may also be the upstream end 130 of the runner 110, and a downstream end 132. The curved section 136 of the runner 110 has an upstream end 132, which may also be the downstream end 132 of the elongate section 112, and a downstream end 146, which may also be the downstream end 146 of the runner 110. The curved section 136 is located in a throat region of the runner 110. The upstream end 132 of the curved section 136 represents the beginning of a curve transitioning from a first drop angle to a second drop angle. As shown in FIG. 6, the valve seat 148 has an upstream end 150, which may also be the downstream end 146 (FIG. 4) of the curved section 136 of the runner 110. The valve seat 148 also has a downstream end 152 where the valve head 166 is seated / sealed when in a closed position. The elongate section 112 of each runner 110 is generally straight when viewed in the side view / side crosssection. In top view, the runners 110 diverge from each other in a Y shape, their separation increasing with distance from the distribution chamber 108. The runner centreline along the elongate section 112 may extend at an average first drop angle selected from the range 20 to 40 degrees relative to a horizontal plane. The horizontal plane runs parallel to a mating surface of the cylinder head for mating with an engine block. As shown in FIG. 6, the runner centreline along the curved section 136 is curved, transitioning to a second steeper drop angle p which may be selected from the range p = 70 to 80 degrees, or 72.5 to 77.5 degrees relative to the horizontal plane. The valve seat 148 may be orientated at this second drop angle, as well as the 9 inlet valve 162. The valve inner angle a depends on the drop angle of the inlet and exhaust valves 162, 178. For example, a valve inner angle a of 30 degrees may correspond to a drop angle of 75 degrees. The illustrated inlet valve 162 is a poppet valve having a valve stem 164 and a valve head 166. The inner angle between the elongate section 112 of the runner 110 and the valve stem 164 may be approximately equal to the difference between the first and second drop angles, e.g., 40 to 50 degrees. It can also be said that the valve head 166 and valve seat 148 are angled relative to the elongate section 112 by this angle. The curved section 136 is shorter than the elongate section 112. The elongate section 112 may have an average length two or more times longer than that of the curved section 136. The elongate section 112 may have a length of several centimetres, whereas the curved section 136 may have an average length of less than one centimetre. These lengths add up to the overall length of the runner 110 FIG. 4 illustrates the interior of the inlet port 106 in side cross-section. The valve seat 148, inlet valve 162, and chamber roof 104 are also shown. The side cross-section is aligned with the centreline of the runner 110 and the centreline of the valve stem 164. As shown in FIG. 4, the inclination of the inlet port 106 means that the distal side 170 of the valve head 166 is higher than the proximal side 168 of the valve head 166. The proximal side 168 of the valve head 166 is proximal to the perimeter of the combustion chamber 102, whereas the opposite distal side 170 of the valve head 166 is proximal to the centreline of the combustion chamber 102. The distal side 170 of the valve head 166 is proximal to the roof 114 of the runner 110, while the proximal side 168 of the valve head 166 is proximal to the floor 122 of the runner 110. The curved section 136 of the runner 110 defines a proximal section 138 (short side radius) connected to the floor 122, and a distal section 142 (long side radius) connected to the roof 114 The proximal and distal sections 138,142 transition from the first drop angle to the second drop angle. The angle change of the proximal section 138 may be similar, or approximately the same as the angle change of the distal section. The proximal section 138 of the curved section 136 of the runner 110 has a tighter radius than the distal section 142 of the curved section 136. The proximal section 138 may have a tighter radius less than half or less than a third of the radius of the distal section 142. The radius at the floor 122 may define a sharp edge. The tight radius of the proximal section 138 at the floor 122 defines a separation edge (138) to promote flow separation from the floor 122 of the runner 110 at the downstream end 132 of the elongate section 112. The separated flow defines a jet whose momentum is directed more towards the distal side 170 of the valve head 166. Therefore, the airflow is biased more towards the distal side 170 of the valve head 166, whereas the proximal side 168 of the valve head 166 is relatively masked from the separated flow. This asymmetry of the flow passing through the inlet valve 162 opening induces a tumble motion in the combustion chamber 102. FIG. 4 further illustrates the roof 114 of the runner 110 comprising a valve stem aperture 116 and a valve guide 161. The valve guide 161 is a tubular section connected to the roof 114 of the runner 110 along the elongate 10 section 112. The valve stem 164 of the inlet valve 162 extends within the valve guide 161. The valve guide 161 extends parallel or coaxially with the valve stem 164 of the inlet valve 162. The valve stem aperture 116 represents the hole in the roof 114 where the valve guide 161 meets the roof 114 of the runner 110. The valve stem 164 passes through the valve guide 161, through the valve stem aperture 116, along a downstream portion of the elongate section 112 of the runner 110, through the curved section 136 of the runner 110, and to the valve head 166. FIG. 4 further illustrates that the roof 114 of the elongate section 112 of the runner 110 may be smooth. The roof 114 of the elongate section 112 of the runner 110 defines a flow attachment surface 118 extending between the upstream end 130 of the runner 110 / elongate section 112 of the runner 110 and the valve stem aperture 116. The flow attachment surface 118 may extend from said upstream end to the upstream end of the valve stem aperture 116. This contrasts from other inlet port designs which comprise an intruding bulge just upstream of the valve guide 161 and valve stem aperture 116. This smoothness of the flow attachment surface 118 of the roof 114 minimises pressure loss and avoids a reduction in flow coefficient. The flow attachment surface 118 of the roof 114 of the runner 110 may be substantially flat or contoured. The flow attachment surface 118 of the roof 114 may be defined as a surface that is flatter than the floor 122 of the runner 110 taken in the same cross-section plane. The flow attachment surface 118 of the roof 114 may be defined as a surface that is sufficiently flat to promote attached airflow, and / or substantially flat (notwithstanding any highly smoothed contours). Furthermore, the flow attachment surface 118 of the roof 114 of the runner 110 may continue from the downstream edge of the valve stem aperture 116 to the distal section 142 of the curved section 136. Furthermore, the distal section 142 of the curved section 136 may be regarded as a continuation of the flow attachment surface 118. Therefore, the flow attachment surface 118 may continue all the way to the valve seat 148. FIG. 4 also illustrates that the roof 114 of the runner 110 may be configured to promote flow attachment, while the floor 122 of the runner 110 may be configured to promote flow separation. These can be described as a ‘low roof and ‘high floor’. FIG. 4 illustrates that the roof 114 may be low. If a straight line is drawn along the roof 114 of the runner 110 from the upstream end 130 of the elongate section 112 to the downstream end 132 of the elongate section 112, and is extruded downstream, then the line may intersect the combustion chamber 102 and / or a portion of the chamber roof 104 and / or the exhaust valve seat 148. The low roof 114 means that the bend radius of the distal section 142 of the curved section 136 is minimised, therefore minimising pressure loss of the airflow along the roof 114 through the curved section 136. This further promotes tumble due to the higher momentum of the roof airflow passing the distal side 170 of the valve head 166. If a similar straight line is drawn along the floor 122 between the upstream and downstream ends 130, 132 of the elongate section 112 ofthe runner 110 and extruded, the extruded line may intersect the proximal side 168 of the valve head 166 ofthe inlet valve 162. The extruded line may intersect the valve head 166 closer to the centreline ofthe valve head 166 than the perimeter ofthe valve head 166. The floor 122 could therefore be described as a raised floor 122. The raised floor 122 combined with the earlier-described separation edge (138) ofthe proximal section 138 ofthe floor 122 masks the inlet valve’s perimeter at the proximal side 168 from the separated floor airflow. This further promotes tumble due to the momentum ofthe floor airflow passing the proximal side 168 ofthe valve head 166 being substantially different (lower) than the roof airflow passing the distal side 170 ofthe valve head 166. FIG. 5 illustrates a cross-section view along a runner 110 of an inlet port 106, about halfway along the runner 110 and upstream ofthe valve stem aperture 116. The cross-section plane is perpendicular to the centreline of the runner 110. This highlights the rounded tubular form of the runner 110 As shown in FIG. 5, the elongate section 112 of the has a width W_E between the left and right sides 120, and a height H_E between the floor 122 and roof 114 These may individually vary along the length ofthe elongate section 112, while preserving a generally constant cross-sectional area. An aspect ratio defined by the heightwidth (H_E:W_E) maybe otherthan 1:1, and optionally increases towards the downstream end 132 of the elongate section 112. Proximal to the upstream end 130 ofthe elongate section 112 ofthe runner 110, the width W_E may be greater than the height H_E, to increase airflow speed. Proximal to the downstream end 132 ofthe elongate section 112 ofthe runner 110, the height H_E may be closer to the width W_E, or may be equal to or greater than the width W_E. This is because a slightly taller aspect ratio can ‘buy back’ a degree of flow coefficient (which depends largely on cross-sectional area) while maintaining high tumble. FIG. 5 also visually illustrates the low roof 114 and raised floor 122, by overlaying an equivalent circle which shows the roof 114 and floor 122 to be recessed and flattened relative to the sides 120 ofthe runner 110. An equivalent circle is a true circle of equal cross-sectional area to the runner 110, with its centre aligned with the centreline of the runner 110. As shown, roof 114 and / or floor 122 ofthe runner 110 along the elongate section 112 are recessed relative to the equivalent circle. Furthermore, the roof 114 and / or floor 122 may be similarly recessed along the curved section 136 ofthe runner 110. The roof 114 may be recessed relative to the equivalent circle to a greater degree than the floor 122. As shown, one or both sides 120 of the runner 110 may extend generally along the circumference of the equivalent circle. In the cross-section of FIG. 5, the runner 110 has a rounded square form (mostly round, slightly square), such that the corners of the runner 110 protrude relative to the equivalent circle, whereas the central portions of the roof 114 and floor 122 are recessed. The roof 114 and floor 122 may be relatively square compared to the sides 120. In FIG. 5, the runner 110 has a small cross-sectional area relative to the cross-sectional area of the valve head 166 which is visible in the background. For example, the elongate section 112 of the runner 110 has an average cross-sectional area along its length of between 40% to 65% of the area of the valve head 166 (reference area), or between 50% to 60%, or between 55% to 60%. This may be true of both the elongate section 112 and the curved section 136 of the runner 110. The small cross-sectional area of the runner 110 creates more turbulence in the runner 110 than a large cross-sectional area, due to boundary layer growth. This further promotes tumble. By contrast, a larger area would increase the flow coefficient but may not promote tumble. In some examples, the average cross-sectional area reduces from the upstream end 130 of the runner 110 to the downstream end 146 of the runner 110, and optionally from the upstream end 130 of the runner 110 to the downstream end 132 of the elongate section 112 of the runner 110 (upstream of the throat defined by the curved section 136). This is to create a region of reduced static pressure just upstream of the valve seat 148, creating pressure recovery which improves the flow coefficient. FIG. 6 illustrates a detailed side view of the inner / interior surface of the valve seat 148. A centreline is also shown, which represents the centreline of the valve seat 148, the inlet valve 162, and the downstream end 146 of the runner 110. The innersurface ofthe annular valve seat 148, facing the centreline, comprises a plurality of conical sections 154, 156, 158 to transition from the cross-sectional area ofthe throat area / curved section 136 ofthe runner 110 to the larger cross-sectional area of the valve head 166 of the inlet valve 162. The plurality of conical sections comprise a first section 154 defined by a first slope angle 6_1, a second section 156 above the first section 154 and defined by a second slope angle 5_2, and an optional third section 158 above the second section 156 and defined by a third slope angle 6_3. The slope angles are defined relative to the centreline. Each section may represent a cut ofthe valve seat 148, in the sense that conical sections are machined (ground or cut) into the inner faces ofthe valve seat 148 that will mate with corresponding conical sections of the corresponding inlet valve 162. Therefore, each slope angle 6_1, 0_2, 0_3 represents a cut angle. The first section 154 has the largest diameter and its lower edge 159 represents the downstream end 152 of the valve seat 148 The second section 156 has a smaller diameter than the first section 154. The third section 13 158 has a smaller diameter than the second section 156. The upper edge of the third section 158 represents the upstream end 150 of the valve seat 148, which may be the downstream end 146 of the runner 110. The upper edge of the third section 158 may have a diameter substantially equal to that of the downstream end 146 of the runner 110. The first slope angle 6_1 defines a sealing face for the valve head 166 and is selected from the range 40 to 50 degrees. The second slope angle 6_2 is selected from the range 20 to 40 degrees. The third slope angle 0_3 is selected from the range 5 to 20 degrees. The slope angles are configured to provide a contoured transition to improve flow rate. A multi-angled cut is also easier to machine than a curved transition, and provides a good seal with the valve head 166. The valve head 166 may seal against the first section 154 of the valve seat 148 when in a closed position. Therefore, the first section 154 of the valve seat 148 may define a sealing face of the valve seat 148 The second and third sections 154, 156, 158 of the valve seat 148 may represent transitional surfaces which progressively increase the cross-sectional area from that of the runner 110 to that of the valve head 166. FIG. 7 illustrates a side view illustrating another view of the valve seat 148, and an underlying masking structure 172 formed in / connected to the chamber roof 104. The masking structure 172 is configured to recess the valve seat 148 and the valve head 166 relative to the piston crown at TDC. Furthermore, the masking structure 172 recesses the valve seat 148 and valve head 166 from a surrounding main surface 173 of the chamber roof 104. The masking structure 172 reduces the amount of relief which needs to be cut into the piston crown of the piston 103, due to the recessing of the valve head 166. If the masking structure 172 is too tall, the compression ratio may be reduced. The masking structure 172 also helps to get more airflow over the upper / distal side 170 of the valve head 166. The masking structure 172 is in the form of an angled circular tubular plinth, protruding in an inclined direction parallel to the centreline shown in FIG. 6. The upper surface 174 of the masking structure 172 is connected to the valve seat 148 Specifically, the top surface of the plinth may be connected to the lower edge of the first section 154 of the valve seat 148. The upper surface 174 of the masking structure 172 may extend perpendicularly to the centreline. Therefore, the first slope angle 6_1 may be at an angle of 40 to 50 degrees relative to the horizontal plane of the upper surface 174 of the masking structure 172. The masking structure has a height M_H of several millimetres, in the side cross-section, and measured at a proximal side of the masking structure 172 corresponding to the proximal side 168 of the valve head 166. In other words, the height M_H is measured at a proximal side of the masking structure 172 closest to the floor 122 of the runner 110 The height M_H of the masking structure 172 may be less than half the valve stroke length of the inlet valve 162. The height M_H of the masking structure 172 may be in the order of 2-5 millimetres. The surrounding main surface 173 of the chamber roof 104 may comprise lower and upper portions, such as flat and / or domed portions, and interconnects the intake and exhaust valve seats. The illustrated masking structure 172 is stepped relative to the main surface 173. The proximal side of the masking structure 172 where M_H is measured is connected to a lower portion / generally flat portion of the main surface 173 of the chamber roof 104, whereas the distal side of the masking structure 172 (corresponding to the distal side 170 of the valve head 166) is connected to an upper portion / domed portion of the main surface 173 of the chamber roof 104, such that the height of the distal side of the masking structure 172 is less than the height of the proximal side of the masking structure 172. FIG. 8 illustrates a geometric feature which may be implemented in the floor 122 of the runner 110, to promote tumble FIG. 8 is a side cross-section view illustrating a longitudinal reversed curved section 136 of the floor 122 of the elongate section 112 of the runner 110. The longitudinal reversed section comprises a first longitudinal curve 126 and a second longitudinal curve 128. Both curves are located in a downstream half of the elongate section 112 (proximal to the downstream end 132). Throughout the first and second curves 128, the floor 122 of the inlet port 106 remains sloped in a downwards direction. The first curve 126 is in a downwards direction to lower the floor 122 relative to the roof 114. The second curve 128 is in an opposite direction to the first curve 126, to at least partially cancel out the divergence of the floor 122 from the roof 114. The second curve 128 is proximal to and upstream of the proximal section 138, and is configured to steer airflow away from the proximal side 168 of the perimeter of the valve head 166 The second curve 128 is connected to the downstream end of the first curve 126 so the curves form a gentle ramp / S-curve, upstream of the separation edge (138). The downstream end of the second curve 128 is proximal to, or meets, the separation edge (138) of the floor 122 (i.e. the proximal section 138 of the curved section 136 of the runner 110). The curves create a turning effect on the floor airflow, which turns the airflow away from the proximal side 168 of the valve head 166 as the airflow separates from the proximal section 138 (separation edge) of the floor 122. By separating the floor airflow and biasing it towards the distal side 170 of the valve head 166, tumble motion is promoted. The first curve 126 has a first radius r_1, and the second curve 128 has a second radius r_1. The radius r_1 may be selected from the range 60 to 70 mm, and the radius r_2 may be selected from the range 45 to 65 mm. The second curve 128 may have a tighter radius than the first radius, which when combined with the separation edge (138) ‘flicks’ the airflow away from the proximal side 168 of the valve head 166. FIGS. 9 and 10 are graphs illustrating flow coefficient (FIG. 9, y-axis) and tumble ratio (FIG. 10, y-axis) relative to inlet valve lift (x-axis) for two example inlet port designs. Each one incorporates aspects of the present invention. The line with square markers represents a first, ‘higher flow, lower tumble’ design. The line with circular markers represents a second, ‘higher tumble, lower flow’ design, depicted in FIGS. 3-8. The first inlet port design is similar to the second inlet port design, except it has a larger cross-sectional area. The first design has an average runner cross-sectional area of approximately 70-75% of the valve head area. The second design has an average runner cross-sectional area of approximately 50-60%% of the valve head area. Furthermore, the second design has a low roof 114 (illustrated) whereas the first design has a higher roof 114. Their floor positions are similar. Both designs provide a good tumble ratio and a good flow coefficient. The second design (FIGS. 3-8) provides a significant increase in tumble ratio, with only a moderate flow coefficient penalty. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application. For example, one or more of at least the following features may be omitted: raised floor 122; low roof 114; longitudinal reversed curve section 124; multi-angled cuts 154, 156, 158; masking structure 172; etc. Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Claims

1. A gaseous hydrogen internal combustion engine comprising:an inlet port comprising a runner and a valve seat; andan inlet valve,wherein the runner comprises an elongate section having a roof, sides, and floor;wherein the runner further comprises a curved section connected to a downstream end ofthe elongate section, the curved section being shorter than the elongate section and curved relative to the elongate section, and comprising a proximal section connected to the floor and a distal section connected to the roof; and wherein the valve seat is connected to a downstream end ofthe curved section,wherein the inlet valve comprises a valve head configured to seal a downstream end ofthe valve seat when in a closed position, wherein the diameter ofthe valve head defines a reference area, wherein the elongate section of the runner has an average cross-sectional area along its length of between 40% to 65% of the reference area, wherein the elongate section ofthe runner defines an equivalent circle of equal cross-sectional area to the runner, wherein the roof is recessed relative to the equivalent circle along most or all the length of the elongate section, wherein the valve seat is angled relative to the elongate section so that a perimeter of the valve head presents a proximal side and a distal side relative to the elongate section, and wherein the floor comprises a longitudinal curve proximal to and upstream ofthe proximal section, configured to steer airflow away from the proximal side ofthe perimeter ofthe valve head.

2. The gaseous hydrogen internal combustion engine of claim 1, wherein the average cross-sectional area reduces from an upstream end ofthe runner to a downstream end ofthe runner, and optionally from the upstream end ofthe runner to the downstream end ofthe elongate section ofthe runner.

3. The gaseous hydrogen internal combustion engine of claim 1 or 2, wherein an average deviation of the roof from the equivalent circle is greater than an average deviation ofthe sides from the equivalent circle.4 The gaseous hydrogen internal combustion engine of claim 1, 2, or 3, wherein the floor is recessed relative to the equivalent circle.

5. The gaseous hydrogen internal combustion engine of any preceding claim, wherein the roof 114 comprises a valve stem aperture 116, and wherein the roof 114 defines a flow attachment surface extending up to the valve stem aperture 116.

6. The gaseous hydrogen internal combustion engine of any preceding claim, wherein the elongate section ofthe runner has a height between the floor and roof, and a width between the sides, and wherein an aspect ratio defined by the heightwidth is other than 1:1, and optionally increases towards the downstream end ofthe elongate section.

7. The gaseous hydrogen internal combustion engine of any preceding claim, wherein the longitudinal curve is a second curve of a longitudinal reversed curve section ofthe floor, wherein the longitudinal reversed17curve section comprises a first curve proximal to the downstream end of the elongate section, to lower the floor relative to the roof, and wherein the second curve is downstream of the first curve and has opposite curvature than the first curve to steer the airflow away from the proximal side of the perimeter of the valve head.

8. The gaseous hydrogen internal combustion engine of claim 7, wherein the second curve has a smaller radius than the first curve.

9. The gaseous hydrogen internal combustion engine of any preceding claim, comprising a masking structure to recess the valve seat and valve head relative to a main surface of a chamber roof of a combustion chamber of the gaseous hydrogen internal combustion engine, wherein the masking structure has a height of several millimetres at a side of the masking structure corresponding to the proximal side of the valve head.10 The gaseous hydrogen internal combustion engine of any preceding claim, wherein an inner diameter of the valve seat comprises a first section defined by a first slope angle, a second section above the first section and defined by a second slope angle, and an optional third section above the second section and defined by a third slope angle, wherein the slope angles are defined relative to an axis of a valve stem of the inlet valve, wherein the first slope angle defines a sealing face for the valve head and is selected from the range 40 to 50 degrees, wherein the second slope angle is selected from the range 20 to 40 degrees, and wherein the optional third slope angle is selected from the range 5 to 20 degrees.

11. The gaseous hydrogen internal combustion engine of claims 9 and 10, wherein a lower edge of the first section of the valve seat is connected to an upper surface of the masking structure.

12. The gaseous hydrogen internal combustion engine of any preceding claim, further comprising an exhaust valve, wherein an inner angle between the intake valve and the exhaust valve is selected from the range 25 to 35 degrees, and wherein a compression ratio of the gaseous hydrogen internal combustion engine is at least 12:1.

13. The gaseous hydrogen internal combustion engine of any preceding claim, wherein the elongate section is generally straight and extends at an angle selected from the range 40 to 50 degrees relative to a valve stem angle, and wherein the proximal section of the curved section defines a separation edge at an end of the floor of the elongate section.

14. The gaseous hydrogen internal combustion engine of any preceding claim, wherein the inlet port comprises a distribution chamber and a pair of the runners fluidly coupled to the distribution chamber, each runner extending to a different one of a pair of valve seats and inlet valves for a same combustion chamber of the gaseous hydrogen internal combustion engine.

15. A vehicle 1 comprising the gaseous hydrogen internal combustion engine of any one of the preceding claims.

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