Internal combustion engine

Abstract

A gaseous fuel internal combustion engine comprising: an engine structure comprising: a crankcase; and a gearcase; and a ventilation system comprising a gas pressure source and a ventilation path. The gas pressure source is configured to transport ventilation gas along the ventilation path from a gas inlet to a first portion of the gearcase and then to the crankcase, and to transport a combination of the ventilation gas and a blow-by gas including the gaseous fuel from the crankcase via a separate outlet as an expelled gas.

Description

[0001] INTERNAL COMBUSTION ENGINE

[0002] FIELD

[0003] The present teachings relate to an internal combustion engine, in particular to a gaseous fuel internal combustion engine.

[0004] BACKGROUND

[0005] In internal combustion engines, it is common for air and fuel in the combustion chamber of a cylinder, as well as combustion gases formed in the combustion chamber, to leak to a degree from the combustion chamber past the piston and into the engine's crankcase. The leaking gases are commonly known as blow-by gases.

[0006] In engines powered by a gaseous fuel such as hydrogen, accumulation of the gaseous fuel component of the blow-by gases in the crankcase can pose a problem if not adequately ventilated. This is due to the relatively high flammable range of some gaseous fuels (e.g. hydrogen is flammable in air in concentrations of between 4 and 75%). Unless the blowby gases are ventilated such that the concentration of gaseous fuel in the crankcase is below its lower flammability limit, there is a risk that the gaseous fuel in the crankcase could ignite, potentially damaging the engine and its surroundings. It is also possible for the gaseous fuel to then ignite the lubricating oil in the crankcase, causing further combustion to occur.

[0007] Crankcase ventilation systems are known to be configured to ventilate blow-by gases from the crankcase of gaseous fuel internal combustion engines. Typically, such systems introduce a ventilation gas, such as air, directly into the crankcase to dilute the blow-by gas therein.

[0008] Problems can arise due to the shape of the crankcase and passages within the engine causing blow-by gas to accumulate in pockets thereof and exceed a lower flammability limit, despite ventilation of the crankcase. Further, problems may arise if locations where ventilation gas and expelled gas are introduced to and removed from the engine respectively mean that the flow of such gas does not adequately ventilate all of the interior space of the engine, also allowing blow-by gases to accumulate in certain "dead-spots" and risk exceeding lower flammability limits.

[0009] Moreover, when the gaseous fuel is hydrogen, exposing components in the gearcase formed from metal, such as steel, to high concentrations of the blow-by gases may leave them susceptible to damage via hydrogen embrittlement. The present teachings seek to overcome or at least mitigate one or more problems associated with the prior art.

[0010] SUMMARY

[0011] The present teachings provide a gaseous fuel internal combustion engine according to the appended claims.

[0012] A first aspect of the present teachings provides a gaseous fuel internal combustion engine comprising: a crankcase; and a ventilation system configured to expel blow-by gas contained within the crankcase.

[0013] The engine may comprise an engine structure. The engine structure may comprise: the crankcase; and a gearcase. The ventilation system may comprise a gas pressure source and a ventilation path. The gas pressure source may be configured to transport ventilation gas along the ventilation path from a gas inlet to a first portion of the gearcase and then to the crankcase. The gas pressure source may be configured to transport a combination of the ventilation gas and a blow-by gas including the gaseous fuel from the crankcase via a separate outlet as an expelled gas.

[0014] Advantageously, transporting the ventilation gas from the gas inlet to the gearcase and then to the crankcase helps to reduce the concentration of blow-by gas in the gearcase, and thus reduces the risk of combustion of the blow-by gas in the gearcase, as well as reducing the exposure of components in the gearcase to the blow-by gas. By reducing the exposure of the components in the gearcase to the blow-by gas, the risk of exposure- related damage to these components (e.g. via hydrogen embrittlement) is reduced.

[0015] Moreover, such a configuration of the ventilation system may help to improve the packaging of an inflow portion of the ventilation path.

[0016] The outlet may comprise an outflow portion of the ventilation path. A section of the outflow portion may be arranged in the engine structure.

[0017] Advantageously, such a configuration of the outflow portion may help to inhibit the blowby gas from freezing due to the increased temperature of the engine structure during operation. This is especially beneficial when the gaseous fuel is hydrogen, since the blowby gas is likely to include a higher concentration of water vapour as a by-product of hydrogen combustion.

[0018] The engine structure may further comprise a cylinder block, a cylinder head and / or a rocker cover. The outflow portion may pass through one or more of the cylinder block, the cylinder head, the rocker cover and a second portion of the gearcase. The second portion of the gearcase may be separate from the first portion of the gearcase.

[0019] Advantageously, such a configuration may help to improve the packaging of the outflow portion and may avoid the need for pipework external of the engine that may be prone to damage.

[0020] The outflow portion may pass in series through at least the cylinder block, the cylinder head and the rocker cover.

[0021] Advantageously, such a configuration may help to improve the packaging of the outflow portion.

[0022] The outflow portion may pass through a second portion of the gearcase. The second portion of the gearcase may be separate from the first portion of the gearcase.

[0023] Advantageously, such a configuration may help to improve the packaging of the outflow portion.

[0024] The gas pressure source may be configured to transport the ventilation gas along an inflow portion of the ventilation path from the gas inlet to the crankcase. The outlet may comprise an outflow portion of the ventilation path.

[0025] The ventilation system may comprise a routing unit mounted adjacent to the engine structure. The routing unit may comprise: a housing; an inflow conduit in the inflow portion of the ventilation path; and an outflow conduit in the outflow portion of the ventilation path. The inflow conduit and the outflow conduit may be at least partially housed within the housing.

[0026] Advantageously, combining the inflow and outflow conduits in the single routing unit may help to improve the packaging of the ventilation system, and help simplify assembly of the engine.

[0027] The outflow conduit may comprise an oil pre-separator configured to reduce a concentration of oil in the expelled gas.

[0028] Advantageously, such a configuration may help to improve the packaging of the ventilation system.

[0029] The oil pre-separator may be a passive oil pre-separator. The gas pressure source may be downstream of the crankcase. The outflow conduit may be upstream of the gas pressure source.

[0030] Advantageously, the oil pre-separator may help to reduce the amount of oil in the expelled gas flowing through gas pressure source, which may help to increase the efficiency of, and / or reduce damage to, the gas pressure source.

[0031] The routing unit may be mounted adjacent to the gearcase.

[0032] The inflow portion of the ventilation path may enter the first portion of the gearcase via an aperture in the gearcase. The gearcase aperture may be downstream of the inflow conduit. The routing unit may be mounted to the gearcase adjacent to the gearcase aperture.

[0033] Advantageously, such a configuration may help to improve the packaging of the ventilation system.

[0034] The routing unit may overlie the gearcase aperture.

[0035] The inflow conduit and the first portion of the gearcase may be contiguous.

[0036] The gearcase aperture may be in a forward facing wall of the gearcase.

[0037] In liquid fuelled engines, an aperture is typically provided in this location for taking a drive from the gearcase to a fuel injection pump, so it is possible to re-purpose the aperture without a needing to reconfigure the engine.

[0038] The gearcase aperture may be above a cam gear mounted to an engine camshaft.

[0039] This location may minimise the amount of lubrication oil splashed towards the aperture.

[0040] The outflow portion of the ventilation path may enter the engine structure (e.g. a second portion of the gearcase separate to the first portion) via an outflow aperture in the engine structure. The outflow aperture may be downstream of the outflow conduit.

[0041] The routing unit may be mounted to the engine structure adjacent to the outflow aperture.

[0042] Advantageously, such a configuration may help to improve the packaging of the ventilation

[0043] The gearcase may comprise the outflow aperture.

[0044] The separate outlet may comprise an outflow portion of the ventilation path passing within the engine structure from the crankcase to an engine structure outlet. The outflow portion may be configured to promote flow of the ventilation gas across an axial extent of the engine structure with respect to a crankshaft axis of the engine, so as to inhibit stagnation of the blow-by gas in the engine structure.

[0045] Advantageously, such a configuration of the outflow portion may help to improve ventilation of the blow-by gas across the engine structure.

[0046] The gas pressure source may be downstream of the crankcase. The ventilation system may comprise an oil pre-separator upstream of the gas pressure source. The oil preseparator may be configured to reduce a concentration of oil in the expelled gas transported from the crankcase to the gas pressure source.

[0047] Advantageously, the oil pre-separator may help to reduce the amount of oil in the expelled gas flowing through gas pressure source, which may help to increase the efficiency of, and / or reduce damage to, the gas pressure source.

[0048] The oil pre-separator may be a passive oil pre-separator.

[0049] The gas pressure source may be a pump.

[0050] Advantageously, using a pump as the gas pressure source may enable greater control of the flowrate of the expelled gas. Moreover, providing the gas pressure source as a pump may enable greater flexibility for where the pump can be located in the engine.

[0051] The pump may comprise an impeller rotatable about a rotation axis. The rotation axis may be arranged to be substantially vertical in a normal operating orientation of the engine. For example, the rotation axis of the impeller may be substantially parallel to an axis of one or more cylinders of the engine.

[0052] Advantageously, such an arrangement of the impeller may help to drain oil and other liquids, which are deposited from the expelled gas from the pump.

[0053] The gas pressure source may be configured to induce a below-atmospheric pressure in the crankcase; optionally, in the range of -100 to -10 mbar relative to atmospheric pressure; for example, -80 to -20 mbar relative to atmospheric pressure.

[0054] Advantageously, inducing a below-atmospheric pressure in the crankcase helps to inhibit the blow-by gas from flowing from the crankcase to other parts of the engine via routes separate to the outlet.

[0055] The gas pressure source may be downstream of the crankcase. The ventilation system may comprise an oil separator configured to reduce a concentration of oil in the expelled gas transported from the crankcase.

[0056] Advantageously, the oil separator may help to remove oil in the expelled gas prior to it being exhausted to atmosphere, or supplied to the one or more cylinders of the engine. This may, have environmental and / or emissions benefits, and also may reduce the amount of oil consumed by the engine, saving costs in replacement.

[0057] The engine may further comprise an oil passage arranged to transport oil removed from the expelled gas by the oil separator to the crankcase.

[0058] The oil separator may be a passive oil separator (e.g. a cyclonic oil separator).

[0059] Advantageously, such an oil separator may help to reduce the parasitic losses of the engine.

[0060] The oil separator may be arranged downstream of the gas pressure source.

[0061] Advantageously, such an arrangement of the oil separator and gas pressure source may aid oil removed from the expelled gas by the oil separator to be returned to the crankcase.

[0062] The oil separator may be mounted to the gas pressure source.

[0063] The engine structure may comprise one or more cylinders. The engine may further comprise an intake system configured to supply air to the one or more cylinders. The ventilation system may be configured to transport the expelled gas to the intake system for supply to the one or more cylinders via the outlet, e.g. via an outflow portion of the ventilation path.

[0064] Advantageously, such a configuration of the intake system and ventilation system may help to improve the fuel efficiency of the engine and / or reduce emissions.

[0065] The gas inlet may be in fluid communication with a supply of air. The intake system may comprise an intake passage arranged to transport air from the gas inlet to the one or more cylinders. The ventilation system may be configured to draw air as the ventilation gas into the ventilation path from the intake passage at a first location.

[0066] Advantageously, such a configuration of the intake system and ventilation system negates the need for a separate dedicated gas inlet for the ventilation system.

[0067] The engine may further comprise a compressor along the intake passage. The first location may be upstream of the compressor. Advantageously, such a configuration of the compressor and the ventilation system may help to reduce the pressure of ventilation air flowing along the ventilation path towards the crankcase, and thus may help the gas pressure source to induce a below-atmospheric pressure in the crankcase.

[0068] The compressor may be a turbocharger or a supercharger.

[0069] The gas pressure source may be configured to induce a lower pressure in the crankcase relative to a pressure at an inlet to the compressor.

[0070] Advantageously, such a configuration of the intake system and ventilation system may be beneficial for reduced oil consumption and lower emissions.

[0071] The compressor may be configured to induce a pressure at the inlet to the compressor of -60 to 0 mbar relative to atmospheric pressure.

[0072] The ventilation system may be configured to exhaust the expelled gas from the separate outlet, e.g. via an outflow portion of the ventilation path, to a second location of the intake passage. The second location may be downstream of the first location with respect to the intake passage.

[0073] Advantageously, such a configuration of the intake system and ventilation system inhibits expelled gas exhausted into the intake passage from flowing along the ventilation path to the crankcase.

[0074] The second location may be upstream of the compressor.

[0075] The gas inlet may comprise a filter.

[0076] Advantageously, the filter helps to prevent dust, debris and the like from entering the gearcase and the crankcase.

[0077] The gaseous fuel may be hydrogen.

[0078] Advantageously, hydrogen produces fewer harmful emissions compared to some other gaseous fuels, and can be produced via renewable energy sources.

[0079] The engine may comprise an engine structure comprising the crankcase. The ventilation system may comprise a gas pressure source and a ventilation path. The gas pressure source may be configured to transport ventilation gas along an inflow portion of the ventilation path from a gas inlet to the crankcase. The gas pressure source may be configured to transport a combination of the ventilation gas and a blow-by gas including the gaseous fuel from the crankcase along an outflow portion of the ventilation path as an expelled gas. The ventilation system may comprise a routing unit mounted adjacent to the engine structure. The routing unit may comprise: a housing; an inflow conduit in the inflow portion of the ventilation path; and an outflow conduit in the outflow portion of the ventilation path. The inflow conduit and the outflow conduit may be at least partially housed within the housing.

[0080] Advantageously, combining the inflow and outflow conduits in the single routing unit may help to improve the packaging of the ventilation system, and help simplify assembly of the engine.

[0081] The outflow conduit may comprise an oil separator configured to reduce a concentration of oil in the expelled gas in the ventilation path.

[0082] Advantageously, such a configuration of the outflow conduit may help to remove oil in the expelled gas prior to it being exhausted to atmosphere, or supplied to the one or more cylinders of the engine.

[0083] The oil separator may be a passive oil separator.

[0084] Advantageously, such an oil separator may help to reduce the parasitic losses of the engine.

[0085] The oil separator may be configured to change a flow direction of the expelled gas travelling along the ventilation path at least once (e.g. at least twice).

[0086] Advantageously, such a configuration of the outflow conduit may help to reduce the amount of oil in the expelled gas flowing along the outflow conduit.

[0087] The oil separator may comprise a wall arranged so as to divert expelled gas travelling along the ventilation path.

[0088] Advantageously, such a configuration of the outflow conduit may help to reduce the amount of oil in the expelled gas flowing along the outflow conduit.

[0089] The wall may be arranged substantially normal to a flow direction of the expelled gas immediately upstream of the wall.

[0090] The oil separator may comprise a textured surface arranged for contact with the expelled gas. Advantageously, such a configuration of the outflow conduit may help to increase the surface area of the outflow conduit contacted by the expelled gas, which may help increase the deposition of oil and other liquids.

[0091] The oil separator may comprise a wall arranged so as to divert expelled gas travelling along the ventilation path. The wall may comprise the textured surface.

[0092] Advantageously, such a configuration of the outflow conduit may help to increase the surface area of the wall contacted by the expelled gas, which may help increase the deposition of oil and other liquids.

[0093] The wall may be arranged substantially normal to a flow direction of the expelled gas immediately upstream of the wall.

[0094] The oil separator may be configured to reduce a speed of the expelled gas travelling along the ventilation path.

[0095] Advantageously, such a configuration of the outflow conduit may help to reduce the amount of oil in the expelled gas flowing along the outflow conduit.

[0096] The outflow conduit may comprise a first portion upstream of a second portion. A cross- sectional area of the second portion normal to the flow direction may be greater than the first portion so as to reduce a speed of the expelled gas in the second portion relative to the first portion.

[0097] The outflow conduit may comprise an oil drainage outlet for draining oil separated from the expelled gas by the oil separator.

[0098] The outflow conduit may be upstream of the gas pressure source.

[0099] Advantageously, the outflow conduit may help to reduce the amount of oil in the expelled gas flowing through gas pressure source, which may help to increase the efficiency of, and / or reduce damage to, the gas pressure source.

[0100] The inflow portion of the ventilation path may enter the engine structure via an inflow aperture in the engine structure. The inflow aperture may be downstream of the inflow conduit. The routing unit may be mounted to the engine structure adjacent to said inflow aperture.

[0101] Advantageously, such a configuration may help to improve the packaging of the ventilation system. The engine structure may comprise a gearcase comprising the inflow aperture.

[0102] Advantageously, such a configuration may help to improve the packaging of the ventilation system.

[0103] The inflow aperture may be in a forward facing wall of the gearcase.

[0104] In liquid fuelled engines, an aperture is typically provided in this location for taking a drive from the gearcase to a fuel injection pump, so it is possible to re-purpose the aperture without a needing to reconfigure the engine.

[0105] The inflow aperture may be above a cam gear mounted to engine camshaft.

[0106] This location helps flush buoyant blow-by gas such as hydrogen from an upper part of the gearcase that may otherwise become a trap for high concentrations of the blow-by gas. In addition it may minimise the amount of lubrication oil splashed towards the aperture.

[0107] The routing unit may overlie the inflow aperture.

[0108] Advantageously, such a configuration may help to improve the packaging of the ventilation system.

[0109] The outflow portion of the ventilation path may enter the engine structure via an outflow aperture in the engine structure. The outflow aperture may be downstream of the outflow conduit. The routing unit may be mounted to the engine structure adjacent to said outflow aperture.

[0110] Advantageously, such a configuration may help to improve the packaging of the ventilation system.

[0111] The engine structure may comprise a gearcase comprising the outflow aperture.

[0112] Advantageously, such a configuration may help to improve the packaging of the ventilation system.

[0113] The inflow and outflow conduits may be integrally formed.

[0114] Advantageously, integrally forming the first and second conduits may help to minimise the volume occupied by the routing unit, helping to improve the packaging of the ventilation system.

[0115] The engine may comprise an engine structure comprising the crankcase. The ventilation system may comprise a gas pressure source and a ventilation path. The gas pressure source may be configured to transport ventilation gas along the ventilation path from a gas inlet to the crankcase via a crankcase inlet. The gas pressure source may be configured to transport a combination of the ventilation gas and a blow-by gas including the gaseous fuel along an outflow portion of the ventilation path as an expelled gas. The outflow portion may pass within the engine structure from the crankcase to an engine structure outlet. The outflow portion may be configured to promote flow of the ventilation gas across an axial extent of the engine structure with respect to a crankshaft axis of the engine, so as to inhibit stagnation of the blow-by gas in the engine structure.

[0116] Advantageously, such a configuration of the outflow portion may help to improve ventilation of the blow-by gas across the engine structure.

[0117] The crankcase inlet and the engine structure outlet may be at or towards a first axial end of the engine structure. The outflow portion may be configured to promote flow of the ventilation gas towards an opposite second axial end of the engine structure.

[0118] The crankcase inlet may be at or towards a first axial end of the engine structure. The engine structure outlet may be at or towards an opposite second axial end of the engine structure. The outflow portion may be configured to promote flow of the ventilation gas towards the second axial end of the engine structure. Advantageously, such a configuration of the engine structure outlet may help to improve ventilation of the blowby gas across the engine structure.

[0119] The engine structure may comprise a chamber protruding from a body of the engine structure. The outflow portion may pass from the body to the chamber. The chamber may comprise the engine structure outlet.

[0120] Advantageously, such a configuration has been found to reduce the local flow speed of the ventilation gas and so promote the deposition of oil and other liquids entrained by the ventilation gas. This reduces the concentration of liquid in the ventilation gas downstream of the engine structure outlet.

[0121] The chamber may have a greater flow cross-sectional area relative to the engine structure outlet.

[0122] Advantageously, such a configuration has been found to reduce the local flow speed of the ventilation gas and so promote the deposition of oil and other liquids entrained by the ventilation gas. This reduces the concentration of liquid in the ventilation gas downstream of the engine structure outlet. The flow cross-sectional area of the chamber upstream and / or adjacent the engine structure outlet may be greater than the flow cross-sectional area of the engine structure outlet.

[0123] In a normal operating orientation of the engine, the chamber may be configured such that the expelled gas travels generally upwards before passing through the engine structure outlet.

[0124] Advantageously, such a configuration has been found to promote the deposition of oil and other liquids entrained by the ventilation gas. This reduces the concentration of liquid in the ventilation gas downstream of the engine structure outlet.

[0125] The chamber may protrude substantially upwardly from the body of the engine structure.

[0126] The engine structure outlet may comprise an outlet conduit passing through a peripheral wall defining the chamber. The outlet conduit may have first and second open ends in fluid communication with each other. The first open end may be within the chamber and spaced from the peripheral wall.

[0127] Advantageously, such a configuration has been found to promote the deposition of oil and other liquids entrained by the ventilation gas. This reduces the concentration of liquid in the ventilation gas downstream of the engine structure outlet.

[0128] The second open end may be external to the chamber and spaced from the peripheral wall.

[0129] A length of the outlet conduit between the first open end and the peripheral wall may be more than 20%, e.g. more than 30 %, e.g. more than 40%, e.g. more than 50%, of a corresponding width of the chamber.

[0130] Advantageously, such a configuration has been found to promote the deposition of oil and other liquids entrained by the ventilation gas. This reduces the concentration of liquid in the ventilation gas downstream of the engine structure outlet.

[0131] The engine structure may comprise an oil fill conduit for receiving oil for replenishing the engine therewith. The oil fill conduit may comprise the chamber.

[0132] The oil fill conduit may have a relatively large flow cross-sectional area, helping to reduce the flow speed of the ventilation gas passing therethrough. The engine structure may further comprise a rocker cover. The outflow portion may pass from the crankcase to the rocker cover. The rocker cover may be configured to promote flow of the ventilation gas across the axial extent of the engine structure.

[0133] The oil fill conduit may protrude from a body of the rocker cover.

[0134] The oil fill conduit may be on a top side of the rocker cover.

[0135] The oil fill conduit may protrude (e.g. upwardly) from a (e.g. top) surface of a body of the engine structure (e.g. the rocker cover).

[0136] The rocker cover may comprise a cavity for receiving one or more rocker arms, and a channel. The outflow portion may pass sequentially from the crankcase through at least the cavity, the channel, and then the engine structure outlet. The channel may be configured to promote flow of the ventilation gas across the axial extent of the engine structure.

[0137] Advantageously, such a configuration helps to promote cross-flow of gases throughout the engine structure without the need for moving parts.

[0138] The rocker cover may comprise the engine structure outlet.

[0139] The channel may comprise a downstream portion at or towards a first axial end of the engine structure. The channel may comprise an upstream portion closer to an opposite second axial end of the engine structure relative to the downstream portion. The upstream portion may be more open to the cavity relative to the downstream portion.

[0140] Advantageously, such a configuration helps to promote cross-flow of gases throughout the engine structure without the need for moving parts.

[0141] The upstream portion may comprise a plurality of openings. Each opening may provide a passage for the expelled gas from the cavity to the channel.

[0142] The downstream portion may comprise one or more openings. Each opening may provide a passage for the expelled gas from the cavity to the channel.

[0143] Advantageously, providing the downstream portion with one or more openings may help to inhibit stagnant regions forming in the expelled gas towards the first axial end.

[0144] The upstream portion may extend 5 to 50% of a width of the cavity between the first and second axial ends; optionally, 10 to 50% of the width; optionally, 20 to 50% of the width.

[0145] The channel may extend generally parallel to the axis of the crankshaft. The channel may be adjacent an internal top side of the rocker cover.

[0146] Advantageously, such a configuration may help to inhibit oil in the rocker cover entering the channel, and thus being transported along the ventilation path.

[0147] The rocker cover may comprise a main body and a member, such as a plate. The member may be mounted to an internal top side of the main body. The channel may be formed between said internal top side of the main body and the member.

[0148] Advantageously, such a configuration may help to simplify assembly of the engine.

[0149] The main body may be formed as a single monolithic piece of material (e.g. via a casting or pressing process).

[0150] The engine structure may further comprise a cylinder block and / or a cylinder head. The outflow portion may pass within the cylinder block and / or cylinder head. The outflow portion may be configured to promote flow of the ventilation gas across the axial extent of the cylinder block and / or cylinder head, so as to inhibit stagnation of the blow-by gas therein.

[0151] The outflow portion may be wholly within the engine structure.

[0152] The engine may comprise an engine structure comprising the crankcase; and an oil reservoir below the crankcase. The ventilation system may comprise a gas pressure source configured to transport a blow-by gas including the gaseous fuel from the crankcase as an expelled gas. The ventilation system may comprise a first oil separator configured to reduce a concentration of oil in the expelled gas. The ventilation system may be configured such that a gas pressure in the crankcase is higher than a gas pressure in the first oil separator, in use. The engine may comprise a first drainage conduit arranged to transport oil removed from the expelled gas by the first oil separator to the oil reservoir. The first drainage conduit may be configured to hold a head of oil exerting a hydrostatic pressure on oil in the oil reservoir, for inhibiting gas in the crankcase being transported to the oil separator via the first drainage conduit, in use.

[0153] Advantageously, such a configuration of the drainage conduit enables the oil removed from the expelled gas by the first oil separator to constantly drain to the oil reservoir despite the pressure differential between the crankcase and oil separator. As such, there is no need to alter the operation of the ventilation system (e.g. to equalise the pressures in the crankcase and oil separator) to enable the removed oil to be drained to the oil reservoir. A first end of the first drainage conduit may be connected to the first oil separator. A second end of the first drainage conduit may be connected to the oil reservoir. The first drainage conduit may be configured such that oil flows from the first end to the second end unimpeded by moving parts.

[0154] Advantageously, such a configuration of the first drainage conduit helps to reduce the maintenance requirements of the engine.

[0155] A first end of the first drainage conduit may be connected to the first oil separator. A second end of the first drainage conduit may be connected to the oil reservoir. The first end may be at the level of, or above, the crankcase.

[0156] Advantageously, such a location of the first end may help to ensure that a height of oil that can be held in the first drainage conduit provides a sufficient hydrostatic head to balance the pressure differential between the crankcase and oil separator.

[0157] The engine structure may comprise a cylinder block above the crankcase. The first end may be at the level of, or above, the cylinder block.

[0158] Advantageously, such a mounting location of the first oil separator may help to ensure that a height of oil that can be held in the first drainage conduit provides a sufficient hydrostatic head to balance the pressure differential between the crankcase and oil separator.

[0159] The engine structure may comprise a gearcase. The first oil separator may be mounted adjacent to the gearcase.

[0160] Advantageously, such a configuration may help to improve the packaging of the ventilation system.

[0161] The first drainage conduit may be arranged to transport the oil adjacent to a bottom of the oil reservoir.

[0162] Advantageously, such a configuration may help to reduce the risk of an oil level in the oil reservoir dropping below an outlet of the first drainage conduit, which could result in gas bypassing the oil and travelling from the crankcase along the first drainage conduit to the first oil separator.

[0163] The first drainage conduit may be arranged outside of the engine structure.

[0164] Advantageously, such a configuration may help to simplify assembly and maintenance of the engine. The gas pressure source may be downstream of the crankcase. The first oil separator may be upstream of the gas pressure source.

[0165] Advantageously, arranging the gas pressure source downstream of the crankcase may help to induce a below-atmospheric pressure in the crankcase, which helps to inhibit the blow-by gas from flowing from the crankcase to other parts of the engine separate to the ventilation system.

[0166] Moreover, the first oil separator may help to reduce the amount of oil in the expelled gas flowing through gas pressure source, which may help to increase the efficiency of, and / or reduce damage to, the gas pressure source.

[0167] The ventilation system may comprise a second oil separator configured to reduce a concentration of oil in the expelled gas. The ventilation system may be configured such that a gas pressure in the crankcase is lower than a gas pressure in the second oil separator, in use. The engine may comprise a second drainage conduit, separate to the first drainage conduit, arranged to transport oil removed from the expelled gas by the second oil separator to a portion of the engine structure leading to the oil reservoir.

[0168] The second oil separator may be a passive (e.g. cyclonic) oil separator.

[0169] The gas pressure source may be downstream of the crankcase. The second oil separator may be downstream of the gas pressure source.

[0170] The first oil separator may be a passive oil separator.

[0171] Advantageously, such an oil separator may help to reduce the parasitic losses of the engine.

[0172] The gas pressure source may be a pump.

[0173] Advantageously, using a pump as the gas pressure source may enable greater control of the flowrate of the expelled gas. Moreover, providing the gas pressure source as a pump may enable greater flexibility for where the pump can be located in the engine.

[0174] The gaseous fuel may be hydrogen.

[0175] Advantageously, hydrogen produces fewer harmful emissions compared to some other gaseous fuels, and can be produced via renewable energy sources.

[0176] The engine may comprise an engine structure comprising a crankcase. The ventilation system may be configured to transport a blow-by gas including the gaseous fuel from the crankcase as an expelled gas. The ventilation system may comprise an oil separator configured to reduce a concentration of oil in the expelled gas. The oil separator may comprise: a separator portion configured to separate oil from the expelled gas; and an outlet portion mounted to the separator portion. The outlet portion may comprise an oil outlet in fluid communication with the separator portion for draining the separated oil from the oil separator. The engine structure may comprise an inlet portion comprising an oil inlet. The outlet portion may be mounted to the inlet portion such that oil exiting the oil outlet enters the oil inlet, and such that the separator portion is mounted to the engine structure.

[0177] Advantageously, mounting the outlet portion of the oil separator to the inlet portion of the engine structure such that oil exiting the oil outlet enters the oil inlet, and such that the separator portion is mounted to the engine structure may help to improve the packaging of the ventilation system and simplify assembly of the engine, since no separate drainage hose between the oil separator and engine structure is needed.

[0178] One of the outlet portion and the inlet portion may comprise a male portion comprising the respective oil outlet or oil inlet. The other of the outlet portion and the inlet portion may comprise a corresponding female portion comprising the respective oil outlet or oil inlet. The male portion may be received in the female portion.

[0179] Advantageously, the male and female portions may provide a locating feature for helping to simplify assembly of the engine.

[0180] The male portion may comprise male screw threads and the female portion may comprise corresponding female screw threads. The outlet portion may be mounted to the inlet portion via engagement of the male and female screw threads.

[0181] Advantageously, such a configuration of the male and female portions may help to reduce the space envelope of the outlet and inlet portions since space for additional fixing means may not be required.

[0182] The outlet portion may comprise the male portion and the inlet portion may comprise the female portion. The male portion may be rotatable relative to the separator portion about a screw axis of the male portion so as to engage the male and female screw threads.

[0183] Advantageously, such a configuration of the male and female portions may help to simplify assembly of the engine.

[0184] The outlet portion may comprise a recess engageable with a tool, such as a screwdriver or Allen key, for rotating the male portion about the screw axis thereof. Advantageously, provision of the recess may help to simplify assembly of the engine.

[0185] The recess may be opposite to the oil outlet.

[0186] At least part of the separator portion and at least part of the outlet portion may be formed as a single monolithic piece of material such that the outlet portion is mounted to the separator portion.

[0187] Advantageously, such a configuration of the oil separator helps to simplify assembly of the engine.

[0188] The separator portion may comprise a truncated cone portion. The at least part of the outlet portion and (e.g. an apex of) the truncated portion may be formed as a single monolithic piece of material.

[0189] The separator portion may be adjacent the inlet portion.

[0190] Advantageously, such a configuration of the engine may reduce the space envelope of the oil separator, and thus help to improve the packaging of the ventilation system.

[0191] The outlet portion may be arranged substantially below the separator portion.

[0192] Advantageously, arranging the outlet portion below the separator portion enables the separated oil to flow from the separator portion to the oil outlet under gravity, and thus without requiring an external power source.

[0193] The separator portion may be elongate. A longitudinal axis of the separator portion may be substantially perpendicular to an axis of the oil outlet.

[0194] Advantageously, such a configuration may help to improve the packaging of the ventilation system.

[0195] A maximum length of the outlet portion may be less than a maximum length of the separator portion.

[0196] Advantageously, such a configuration may help to improve the packaging of the ventilation system.

[0197] A volume of the outlet portion may be less than a volume of the separator portion.

[0198] Advantageously, such a configuration may help to improve the packaging of the ventilation system. The engine may further comprise a sealing arrangement between the outlet portion and the inlet portion. The sealing arrangement may be configured to inhibit leakage of oil travelling from the oil outlet towards the oil inlet.

[0199] The sealing arrangement may comprise a sealing member, such as an O-ring.

[0200] The oil separator may be a passive oil separator.

[0201] Advantageously, such an oil separator may help to reduce the parasitic losses of the engine.

[0202] The oil separator may be a cyclonic oil separator configured to form a vortex in the expelled gas so as to separate the oil therefrom.

[0203] The separator portion may comprise a truncated cone portion having an apex. The outlet portion may be mounted to said apex.

[0204] The crankcase may comprise the oil inlet.

[0205] Advantageously, such a configuration may help to improve the packaging of the ventilation system.

[0206] The ventilation system may be configured such that a gas pressure in the crankcase is less than a gas pressure in the oil separator.

[0207] Advantageously, such a pressure differential may help to transport the separated oil from the separator portion to the oil inlet.

[0208] The ventilation system may comprise a gas pressure source configured to transport the expelled gas from the crankcase. The oil separator may be downstream of the gas pressure source.

[0209] The gas pressure source may be a pump.

[0210] The gaseous fuel may be hydrogen.

[0211] The engine may comprise an engine structure comprising the crankcase. The ventilation system may comprise an outflow ventilation path and a gas pressure source configured to transport a blow-by gas including the gaseous fuel from the crankcase along the outflow ventilation path as an expelled gas. The outflow ventilation path may comprise an external conduit external to the engine structure. The engine may comprise a heat transfer arrangement configured to transfer combustion generated heat from the engine structure to at least part of the external conduit for heating the expelled gas transported therein. Advantageously, transferring heat to the external conduit may help to prevent water vapour in the expelled gas from freezing, which could block the external conduit, and damage components of the ventilation system. Moreover, by employing combustiongenerated heat, parasitic losses of the engine may be reduced.

[0212] The heat transfer arrangement may comprise a heat transfer path and a fluid pressure source, such as a pump. The fluid pressure source may be configured to transport a heat transfer fluid along the heat transfer path from the engine structure to said at least part of the external conduit for transferring the combustion generated heat thereto.

[0213] Advantageously, such a configuration of the heat transfer arrangement helps transfer combustion generated heat from engine structure to the external conduit more efficiently.

[0214] The heat transfer arrangement may further comprise a heat exchanger, such as a radiator, for cooling the engine structure. The heat exchanger may be in the heat transfer path.

[0215] Advantageously, such a configuration of the heat transfer arrangement negates the need for separate plumbing for the engine cooling system and the external conduit heating system.

[0216] The heat transfer path may be a closed path. The heat transfer path may exit the engine structure via a first aperture therein. The heat transfer path may pass along the at least part of the external conduit. The heat transfer path may then enter the engine structure via a second aperture therein.

[0217] Advantageously, such a configuration of the heat transfer arrangement helps transfer combustion generated heat from engine structure to the external conduit more efficiently.

[0218] The engine structure may comprise a cylinder block and a cylinder head. The at least part of the external conduit may be adjacent one or both of the cylinder head and the cylinder block. Each of the first aperture and the second aperture may be in the cylinder head or the cylinder block.

[0219] Advantageously, such a configuration of the heat transfer arrangement helps to reduce the length of the heat transfer path outside of the engine structure, and thus helps to improve the packaging of the heat transfer arrangement.

[0220] The heat transfer path may comprise a duct at least partially surrounding the at least part of the external conduit, for transferring the combustion generated heat from heat transfer fluid in the duct to the at least part of the conduit. Advantageously, such a configuration of the heat transfer arrangement helps transfer combustion generated heat from engine structure to the external conduit more efficiently.

[0221] The duct may be an annular duct substantially surrounding said at least part of the external conduit.

[0222] Advantageously, such a configuration of the heat transfer arrangement helps transfer combustion generated heat from the engine structure to the external conduit more efficiently.

[0223] The heat transfer arrangement may comprise a passive heat transfer device configured to transfer the combustion generated heat from the engine structure to said at least part of the external conduit.

[0224] Advantageously, such a configuration of the heat transfer arrangement helps to transfer combustion generated heat from the engine structure to the external conduit more efficiently whilst minimising the parasitic losses of the engine.

[0225] The passive heat transfer device may comprise one or more heat pipes.

[0226] Advantageously, such a configuration of the heat transfer arrangement helps to transfer combustion generated heat from the engine structure to the external conduit more efficiently.

[0227] The passive heat transfer device may comprise a heat transfer member connected to a portion of the engine structure and to the at least part of the external conduit. The heat transfer member may be configured to transfer the combustion generated heat from the portion of the engine structure to the at least part of the external conduit.

[0228] The portion of the engine structure may be formed from a first material. The heat transfer member may be formed from a second material having a thermal conductivity greater than or equal to the first material.

[0229] Advantageously, such a configuration of the heat transfer arrangement helps transfer combustion generated heat from the engine structure to the external conduit more efficiently.

[0230] The passive heat transfer device may at least partially surround the at least part of the external conduit. Advantageously, such a configuration of the heat transfer arrangement helps transfer combustion generated heat from the engine structure to the external conduit more efficiently.

[0231] The passive heat transfer device may comprise an annular portion substantially surrounding said at least part of the conduit.

[0232] Advantageously, such a configuration of the heat transfer arrangement helps transfer combustion generated heat from the engine structure to the external conduit more efficiently.

[0233] A portion of the outflow ventilation path extending between the crankcase and the external conduit may be within the engine structure.

[0234] Advantageously, such a configuration of the outflow ventilation path helps to prevent water and water vapour in the expelled gas from freezing.

[0235] The gas pressure source may be external to the engine structure. The external conduit may lead to the gas pressure source.

[0236] A portion of the outflow ventilation path downstream of the external conduit may pass within the engine structure.

[0237] Advantageously, such a configuration of the outflow ventilation path helps to prevent water and water vapour in the expelled gas from freezing.

[0238] The engine may further comprise a thermally insulative material at least partially covering the external conduit for increasing the thermal insulation thereof.

[0239] The gaseous fuel may be hydrogen.

[0240] A second aspect of the present teachings provides an oil separator for a crankcase ventilation system configured to expel blow-by gas contained within a crankcase therefrom. The oil separator is configured to reduce a concentration of oil in the expelled gas. The oil separator comprises: a separator portion configured to separate oil from the expelled gas; and an outlet portion mounted to the separator portion. The outlet portion comprises an oil outlet in fluid communication with the separator portion for draining the separated oil from the oil separator. The outlet portion is configured to be mounted to an inlet portion of an engine structure such that oil exiting the oil outlet enters the inlet portion, and such that the separator portion is mounted to the engine structure. One of the outlet portion and the inlet portion may comprise a male portion comprising the respective oil outlet or oil inlet. The other of the outlet portion and the inlet portion may comprise a corresponding female portion comprising the respective oil outlet or oil inlet. The male portion may be received in the female portion.

[0241] Advantageously, the male and female portions may provide a locating feature for helping to simplify assembly of the engine.

[0242] The male portion may comprise male screw threads and the female portion may comprise corresponding female screw threads. The outlet portion may be mounted to the inlet portion via engagement of the male and female screw threads.

[0243] Advantageously, such a configuration of the male and female portions may help to reduce the space envelope of the outlet and inlet portions since space for additional fixing means may not be required.

[0244] The outlet portion may comprise the male portion and the inlet portion may comprise the female portion. The male portion may be rotatable relative to the separator portion about a screw axis of the male portion so as to engage the male and female screw threads.

[0245] Advantageously, such a configuration of the male and female portions may help to simplify assembly of the engine.

[0246] The outlet portion may comprise a recess engageable with a tool, such as a screwdriver or Allen key, for rotating the male portion about the screw axis thereof.

[0247] Advantageously, provision of the recess may help to simplify assembly of the engine.

[0248] The recess may be opposite to the oil outlet.

[0249] At least part of the separator portion and at least part of the outlet portion may be formed as a single monolithic piece of material such that the outlet portion is mounted to the separator portion.

[0250] Advantageously, such a configuration of the oil separator helps to simplify assembly of the engine.

[0251] The separator portion may comprise a truncated cone portion. The at least part of the outlet portion and (e.g. an apex of) the truncated portion may be formed as a single monolithic piece of material.

[0252] The separator portion may be adjacent the inlet portion. Advantageously, such a configuration of the engine may reduce the space envelope of the oil separator, and thus help to improve the packaging of the ventilation system.

[0253] The outlet portion may be arranged substantially below the separator portion.

[0254] Advantageously, arranging the outlet portion below the separator portion enables the separated oil to flow from the separator portion to the oil outlet under gravity, and thus without requiring an external power source.

[0255] The separator portion may be elongate. A longitudinal axis of the separator portion may be substantially perpendicular to an axis of the oil outlet.

[0256] Advantageously, such a configuration may help to improve the packaging of the ventilation system.

[0257] A maximum length of the outlet portion may be less than a maximum length of the separator portion.

[0258] Advantageously, such a configuration may help to improve the packaging of the ventilation system.

[0259] A volume of the outlet portion may be less than a volume of the separator portion.

[0260] Advantageously, such a configuration may help to improve the packaging of the ventilation system.

[0261] The oil separator may further comprise a sealing arrangement between the outlet portion and the inlet portion. The sealing arrangement may be configured to inhibit leakage of oil travelling from the oil outlet towards the oil inlet.

[0262] The sealing arrangement may comprise a sealing member, such as an O-ring.

[0263] The oil separator may be a passive oil separator.

[0264] Advantageously, such an oil separator may help to reduce the parasitic losses of the engine.

[0265] The oil separator may be a cyclonic oil separator configured to form a vortex in the expelled gas so as to separate the oil therefrom.

[0266] The separator portion may comprise a truncated cone portion having an apex. The outlet portion may be mounted to said apex. It will be appreciated that features of the first and second aspects may be combined with each other.

[0267] BRIEF DESCRIPTION OF THE DRAWINGS

[0268] Embodiments are now disclosed by way of example only with reference to the drawings, in which:

[0269] Figure 1 shows an isometric view of an internal combustion engine according to an embodiment;

[0270] Figure 2 shows a side view of an exemplary working machine incorporating the internal combustion engine of Figure 1;

[0271] Figure 3 shows a simplified block diagram of an internal combustion engine crankcase ventilation system;

[0272] Figure 4 shows an isometric view of a pump, an oil separator and a routing unit of the crankcase ventilation system of the internal combustion engine of Figure 1;

[0273] Figure 5 shows an isometric view of the pump and the routing unit of Figure 4 isolated from other components of the internal combustion engine of Figure 1;

[0274] Figure 6 shows a cross-sectional view of the routing unit through section X6-X6 shown in Figure 5;

[0275] Figure 7 shows a cross-sectional view of the routing unit through section X7-X7 shown in Figure 5;

[0276] Figure 8 shows a cross-sectional view of the routing unit through section X8-X8 shown in Figure 5;

[0277] Figure 9 shows a cross-sectional view of the internal combustion engine through section X4-X4 shown in Figure 1;

[0278] Figure 10 shows a cross-sectional view of the internal combustion engine through section Xl-Xl shown in Figure 1;

[0279] Figure 11 shows a cross-sectional view of the internal combustion engine through section X2-X2 shown in Figure 1;

[0280] Figure 12 shows a cross-sectional view of a rocker cover of the internal combustion engine through section Xl-Xl shown in Figure 1;

[0281] Figure 13 shows a cross-sectional view of the rocker cover of the internal combustion engine through section X5-X5 shown in Figure 1; Figure 14 shows a cross-sectional view of the rocker cover through section X9-X9 shown in Figure 13;

[0282] Figure 15 shows a rear isometric view of the oil separator of the internal combustion engine of Figure 1;

[0283] Figure 16 shows a cross-sectional view of the internal combustion engine through section X3-X3 shown in Figure 1;

[0284] Figure 17 shows a side view of a drainage conduit and an oil reservoir of the internal combustion engine of Figure 1;

[0285] Figure 18 shows a simplified schematic representation of the drainage conduit and the oil reservoir of Figure 17;

[0286] Figure 19 shows a front isometric view of the oil separator of the internal combustion engine of Figure 1;

[0287] Figure 20a shows a cross-sectional view of the oil separator and an engine structure of the internal combustion engine through section X10-X10 shown in Figure 4;

[0288] Figure 20b shows a cross-sectional view of a further embodiment of the oil separator and an engine structure of the internal combustion engine through a section equivalent to the section X10-X10 shown in Figure 4;

[0289] Figure 21 shows an isometric view of an embodiment of a heat transfer arrangement of the internal combustion engine of Figure 1;

[0290] Figure 22 shows a simplified block diagram of the heat transfer arrangement of Figure 21;

[0291] Figure 23 shows an exemplary heat transfer path of the heat transfer arrangement of Figure 21;

[0292] Figure 24 shows a simplified schematic representation of an embodiment of a heat transfer arrangement of the internal combustion engine of Figure 1;

[0293] Figure 25 shows a cross-sectional view of a rocker cover according to a further embodiment, which is a corresponding view to that shown in Figure 12;

[0294] Figure 26 is a view along section X12-X12 shown in Figure 25; and

[0295] Figure 27 is an upper isometric view of the rocker cover of Figure 25.

[0296] DETAILED DESCRIPTION OF EMBODIMENT(S)

[0297] 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.

[0298] Figure 1 shows an internal combustion engine 100 according to an embodiment. The engine 100 is a gaseous fuel engine configured to be powered by a gaseous fuel, such as hydrogen, compressed natural gas (CNG), biogas or the like. In the illustrated embodiment, the engine 100 is powered by hydrogen.

[0299] The engine 100 may be suitable for use as the prime mover in a working machine 10 (see Figure 2 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 10 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 100 may also be utilised in a genset - a self-contained unit to provide electrical power at off-grid locations. As such the engine 100 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 10 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.

[0300] The engine 100 includes an engine structure 102 including a crankcase 104, an oil reservoir 105, a cylinder head 106, a rocker cover 107, a cylinder block 108, and a gearcase 109.

[0301] The cylinder block 108 includes one or more cylinders 112; four in the present embodiment (see Figure 10). The cylinder head 106 is mounted to the cylinder block 108 so as to be coupled to the one or more cylinders 112. The cylinder head 106 includes one or more inlet ports (not shown) for supplying air to each cylinder 112, and one or more exhaust ports (not shown) for exhausting combustion gases from each cylinder 112. Each inlet port is selectively opened and closed by an inlet valve (not shown), and each exhaust port is selectively opened and closed by an exhaust valve (not shown).

[0302] In the present embodiment, the engine 100 includes a hydrogen fuel delivery system by which hydrogen fuel may be directly injected into each cylinder 112 from a pressurised fuel tank 12 (Figure 2). The rated pressure of the fuel tank 12 is typically in excess of 35MPa and the hydrogen pressure may be stepped down before being introduced into the cylinders 112. In other embodiments, the engine 100 is a port fuel injection (PFI) engine, and the one or more inlet ports also supply hydrogen fuel to each cylinder 112.

[0303] In alternative embodiments (not shown), the engine 100 may have more or fewer cylinder assemblies, e.g. 2, 3, 6, or 8. In addition, in other embodiments the cylinders 112 may be oriented in a "V" or boxer configuration rather than inline as in the disclosed embodiment.

[0304] With reference to Figure 11, the engine 100 includes a valvetrain 200 including a camshaft 202 and rocker arms 204 arranged to open and close each inlet valve and each exhaust valve via rotation of the camshaft 202. The camshaft 202 is mounted to the cylinder block 108. The rocker arms 204 are mounted to the cylinder head 106. Motion of the camshaft 202 is transferred to the rocker arms 204 via pushrods 206 extending between the cylinder block 108 and the cylinder head 106. The rocker cover 107 is mounted to the cylinder head 106 and houses the rocker arms 204.

[0305] As shown in Figure 10, each cylinder 112 receives a piston 113 which is translationally movable within the cylinder 112. During operation of the engine 100, translational movement of each piston 113 is converted into rotational movement of a crankshaft 111. The crankshaft 111 rotates about a crankshaft axis A. The crankcase 104 houses the crankshaft 111.

[0306] In the illustrated embodiment, the cylinder block 108 and the crankcase 104 are partially integrated. Specifically, the engine 100 is of the bedplate type in which an upper portion 104a of the crankcase 104 is cast integrally and monolithically with the cylinder block 108. A lower portion 104b is manufactured as a separate casting, with the joint between the upper and lower portions 104a, 104b being at the midpoint of the crankshaft bearing journals. In alternative embodiments, the cylinder block 108 and the crankcase 104 may be a wholly single casting (not shown), i.e. as a single integral and monolithic material, or as two or more wholly separate castings (not shown). In these cases, separate bearing caps may be used to mount the crankshaft to the crankcase 104.

[0307] The oil reservoir 105 (also commonly known as an oil sump) stores oil for use in the engine's lubrication system. The oil reservoir 105 is mounted to the crankcase 104, below the crankcase 104. The oil reservoir 105 is open to the crankcase 104, and is arranged so as to collect lubrication oil drained from the remainder of the engine 100.

[0308] In the present embodiment the engine 100 has a total displacement of 4.4 litres (i.e. 1.1 litres per cylinder. In engines used in off-highway applications each cylinder may typically have a displacement of between 0.75 and 1.5 litres. Such a displacement is relatively high by comparison with passenger vehicle engines, but is suited to providing the operating characteristics described above.

[0309] The gearcase 109 is mounted to one or both of the cylinder block 108 and the crankcase 104. The gearcase 109 projects laterally from said one or both of the cylinder block 108 and the crankcase 104. The gearcase 109 houses a gear assembly 339 (shown in Figure 9) configured to transmit rotary motion of the crankshaft 111 to the camshaft 202 for operation of the rocker arms 204. The gearcase 109 is in fluid communication with the crankcase 104.

[0310] With further reference to Figure 3, the engine 100 includes an intake system 115 configured to supply air to the one or more cylinders 112 for combustion. The intake system 115 has been omitted from Figure 1 for clarity. In the illustrated embodiment, the intake system 115 is configured to supply air to the cylinder head 106 for delivery to the cylinders 112 via the respective inlet ports.

[0311] The intake system 115 includes an intake passage 140 (represented by a solid double line in Figure 3) arranged to transport air from an air inlet 118 upstream to the cylinders 112 downstream. The air inlet 118 may include an air filter. The intake passage 140 is configured to supply air to the cylinders 112 via the cylinder head 106 for combustion.

[0312] During operation of the engine 100, some gaseous fuel and air introduced into each cylinder 112, as well as combustion gases formed within the cylinder 112, flow out of the combustion chamber past the piston 113 and into the crankcase 104 following the path indicated by arrow 205 as "blow-by" gas. The blow-by gas may also accumulate in the gearcase 109, which is in fluid communication with the crankcase 104. For example, if the gaseous fuel, and thus the blow-by gas, is more buoyant than air (e.g. hydrogen), then high concentrations of the blow-by gas may accumulate at the top of the gearcase 109, which is inherently shaped to act as a trap.

[0313] The engine 100 includes a ventilation system 110 configured to ventilate the blow-by gas from the crankcase 104 and the gearcase 109.

[0314] Figure 3 shows a simplified diagram of the ventilation system 110 according to an embodiment. The ventilation system 110 includes a ventilation path 116 (indicated by a dash-dot line in Figure 3) to transport ventilation gas (air in this embodiment) from a ventilation path inlet from the air intake system 115 to the crankcase 104 so as to dilute the concentration of blow-by gas in the crankcase 104. This portion of the ventilation path 116 is referred to as an inflow portion 125, being upstream of the crankcase 104. The wording "ventilation gas" is used to differentiate from air supplied to the one or more cylinders 112 for combustion. The ventilation system 110 is configured to draw air as the ventilation gas into the ventilation path 116 from the intake passage 140 at a first location 140a which defines the ventilation path inlet.

[0315] The ventilation system 110 is further configured to transport the diluted blow-by gas from the crankcase 104 (hereinafter "expelled gas") via the ventilation path 116 to an outlet. This portion of the ventilation path 116 is referred to as the outflow portion 126, being downstream of the crankcase 104.

[0316] The ventilation system 110 is configured to exhaust the expelled gas from the crankcase 104 to a second location 140b of the intake passage 140 which defines a ventilation path outlet. The second location 140b is downstream of the first location 140a with respect to the intake passage 140.

[0317] The ventilation system 110 further includes a gas pressure source 114 within the ventilation path 116. The gas pressure source 114 is configured to transport ventilation gas along the inflow portion 125 of the ventilation path 116 from the first location 140a to the gearcase 109, and then to the crankcase 104. As will be discussed more in the following, in the illustrated embodiment, the gas pressure source 114 transports the ventilation gas from the first location 140a to a first portion 109a of the gearcase 109, and then to the crankcase 104.

[0318] The gas pressure source 114 is further configured to transport a combination of the ventilation gas and the blow-by gas, which includes the gaseous fuel, from the crankcase 104 and gearcase 109 along the outflow portion 126 of the ventilation path 116 to the second location 140b as expelled gas.

[0319] Advantageously, transporting ventilation gas from the first location 140a to the crankcase 104 via the gearcase 109 helps to flush blow-by gas out of and away from the gearcase

[0320] 109. As such, the risk of combustion of the blow-by gas in the gearcase 109 is reduced. Moreover, exposure of components in the gearcase 109 (e.g. the gear assembly 339) to the blow-by gas is reduced, which may reduce damage to said components caused by exposure to the blow-by gas containing hydrogen (e.g. via hydrogen embrittlement).

[0321] In the illustrated embodiment, the gas pressure source 114 is a pump 114 or blower. In alternative embodiments (not shown), any suitable gas pressure source may be used. For example, in some embodiments, the gas pressure source 114 may be provided by a compressor or turbine (e.g. a compressor or turbine stage of a turbocharger) in the intake system 115 / exhaust system, which is in fluid communication with the ventilation system

[0322] 110. The pump 114 is configured to induce a below-atmospheric pressure in the crankcase 104 in the range of -100 to -10 mbar relative to atmospheric pressure; for example, -80 to -20 mbar relative to atmospheric pressure. In the illustrated embodiment, the pump 114 is arranged downstream of the crankcase 104 in the outflow portion 126 of the ventilation path 116.

[0323] In alternative embodiments (not shown), the pump 114 may be configured to induce any suitable below-atmospheric pressure in the crankcase 104. In other embodiments, the pump 114 may be configured to induce an above-atmospheric pressure in the crankcase 104. For example, the pump 114 may be arranged upstream of the crankcase 104 in the inflow portion 125 of the ventilation path 116.

[0324] The ventilation system 110 includes a first oil separator 304, which will also be referred to as "the oil pre-separator 304", upstream of the pump 114. The oil pre-separator 304 is configured to reduce a concentration of oil in the expelled gas transported from the crankcase 104 to the pump 114. The oil pre-separator 304 is in the outflow portion 126.

[0325] With further reference to Figures 4 and 5, the ventilation system 110 includes a routing unit 300 mounted adjacent to the engine structure 102. As will be discussed in more detail in the following, the routing unit 300 includes an inflow conduit 302 in the inflow portion 125 of the ventilation path 116, an outflow conduit 304 in the outflow portion 126 of the ventilation path 116, and a housing 306. The inflow conduit 302 and the outflow conduit 304 are at least partially housed within the housing 306. Advantageously, combining the inflow and outflow conduits 302, 304 in the single routing unit 300 helps to improve the packaging of the ventilation system 110, and helps simplify assembly of the engine 100.

[0326] In the illustrated embodiment, the outflow conduit 304 is the oil pre-separator 304. In alternative embodiments (not shown), the outflow conduit 304 may additionally or alternatively include a separate oil pre-separator.

[0327] As discussed more in the following, the oil pre-separator 304 of this embodiment is a passive oil separator. A 'passive oil separator' is defined as an oil separator that requires no external power source to reduce a concentration of oil in the expelled gas flowing through the oil separator. In alternative embodiments, the ventilation system 110 may include any suitable active or passive oil pre-separator.

[0328] In the illustrated embodiment, the routing unit 300 is mounted adjacent to the gearcase 109. With reference to Figures 4 and 5, the routing unit 300 is mounted to the gearcase 109 such that a major face 305 of the housing 306 is in contact with a wall 318 of the gearcase 109. Such contact increases heat transfer from the engine structure 102 to the routing unit 300, which as discussed more in the following, helps to inhibit freezing of water vapour in the expelled gas in the outflow conduit 304. Moreover, such mounting of the routing unit 300 to the gearcase 109 helps to improve the packaging of the ventilation system 110.

[0329] In alternative embodiments (not shown), the routing unit 300 may be mounted adjacent any suitable portion of the engine structure 102 (e.g. the crankcase 104 or the cylinder block 108).

[0330] Referring back to Figure 3, the ventilation system 110 includes a second oil separator 130, which will also be referred to "the oil separator 130", configured to reduce a concentration of oil in the expelled gas transported from the crankcase 104. The oil separator 130 is a passive oil separator. In the illustrated embodiment, the oil separator 130 is a cyclonic oil separator, discussed more in the following. In alternative embodiments (not shown), the oil separator 130 may be any suitable active or passive oil separator. The oil separator 130 is in the outflow portion 126. The oil separator 130 is arranged downstream of the pump 114.

[0331] In the illustrated embodiment, the ventilation system 110 is configured to transport the expelled gas to the intake system 115 for supply to the one or more cylinders 112 via the outflow portion 126. As such, the ventilation system 110 may be considered a closed-loop system. In the illustrated embodiment, expelled gas is transported from the crankcase 104 to the intake system 115 via the outflow portion 126.

[0332] In alternative embodiments (not shown), the ventilation system 110 may not be configured transport the expelled gas to the intake system 115. In such embodiments, the ventilation system 110 may be configured to exhaust the expelled gas to the atmosphere (e.g. downstream of the pump 114), and may be considered an open-loop system.

[0333] In alternative embodiments (not shown), the ventilation system 110 is configured to draw any suitable gas into the ventilation path 116 (e.g. exhaust gas from combustion in the one or more cylinders 112).

[0334] The intake passage 140 in the cylinder head 106 is separate and sealed from the ventilation path 116 in the cylinder head 106.

[0335] The intake system 115 includes a compressor 142 along the intake passage 140. The first location 140a is upstream of the compressor 142. The second location 140b is upstream of the compressor 142. The compressor 142 may be a turbocharger, a supercharger, or any device suitable for compressing engine intake air.

[0336] The pump 114 is configured to induce a lower pressure in the crankcase 104 relative to a pressure at an inlet 144 to the compressor 142, which may be beneficial for reduced oil consumption and lower emissions. In the illustrated embodiment, the compressor 142 induces a pressure at the inlet 144 of -60 to 0 mbar relative to atmospheric pressure.

[0337] The outflow portion 126 terminates above a footprint of the cylinder block 108. In the illustrated embodiment, the outflow portion 126 terminates at the second location 140b of the intake passage 140. The second location 140b in this embodiment is arranged above the rocker cover 107. Advantageously, terminating the outflow portion 126 above the footprint of the cylinder block 108 may help ensure that at least a section of the outflow portion 126 is heated from the combustion within the one or more cylinders 112, in use, helping to inhibit freezing of the expelled gas in the outflow portion 126.

[0338] In the following, the ventilation path 116 will be described in further detail with further reference to Figures 4 to 16.

[0339] As shown in Figures 1, 4 and 5, the inflow portion 125 of the ventilation path 116 includes a first section 125a extending between the first location 140a and the inflow conduit 302 of the routing unit 300. In the illustrated embodiment, the first section 125a is a pipe external to the engine structure 102, but may be at least partially within the engine structure 102 in alternative embodiments.

[0340] As shown in Figures 6 and 8, the inflow portion 125 of the ventilation path 116 (represented by arrows formed from two dashed lines in Figures 6 to 10) passes through the inflow conduit 302 of the routing unit 300 from an inlet 308 to an outlet 310 of the inflow conduit 302. The inflow conduit 302 is separate from the outflow conduit 304, which will be discussed more in the following.

[0341] With further reference to Figure 9, which shows a view along section X4-X4 in Figure 1, the inflow portion 125 of the ventilation path 116 enters the first portion 109a of the gearcase 109 via an inflow aperture 312 in the gearcase 109. The inflow aperture 312 is downstream of the inflow conduit 302. In the illustrated embodiment, the routing unit 300 is mounted to the gearcase 109 adjacent to the inflow aperture 312. In particular, the routing unit 300 is mounted to the gearcase 109 so as to overlie the aperture 312. In the illustrated embodiment, the outlet 310 of the inflow conduit 302 is adjacent the aperture 312 such that the inflow conduit 302 and the first portion 109a of the gearcase 109 are aligned.

[0342] As shown in Figure 8, the housing 306 of the routing unit 300 includes a collar 314 defining the outlet 310. The collar 314 is received in, and engages, the inflow aperture 312. A seal 316, which in the illustrated embodiment is an O-ring, is secured to the collar 314 and engages the perimeter of the aperture 312, to seal the ventilation path 116 between the inflow conduit 302 and the gearcase 109. In the illustrated embodiment, the inflow aperture 312 is in a forward facing wall 318 of the gearcase 109. In embodiments where the engine 100 is derived from a liquid fuelled engine, an aperture is typically provided in this location for taking a driveshaft from the gearcase 109 to a fuel injection pump, so it may be possible to re-purpose this aperture without the need to reconfigure the engine.

[0343] In the illustrated embodiment, the inflow aperture 312 is above a cam gear 339a mounted to the camshaft 202. This location may minimise the amount of lubrication oil splashed towards the aperture 312 and therefore towards the routing unit 300, which may at least partially obstruct the inflow conduit 302.

[0344] In alternative embodiments (not shown), the inflow aperture 312 may be in any suitable portion of the engine structure 102, such as the crankcase 104.

[0345] With reference to Figure 10, which shows a view along section Xl-Xl in Figure 1, the inflow portion 125 passes from the first portion 109a of the gearcase 109 to the crankcase 104, via one or more (e.g. a plurality of) crankcase inlets 127 in a wall dividing the gearcase 109 and the crankcase 104. The one or more crankcase inlets 127 are located at or towards a first axial end Al of the engine structure 102 with respect to the crankshaft axis A.

[0346] In the illustrated embodiment, a section of the outflow portion 126 of the ventilation path 116 is arranged in the engine structure 102. The outflow portion 126 passes through one or more of the cylinder block 108, the cylinder head 106, the rocker cover 107 and a second portion 109b of the gearcase 109 which is separate from the first portion 109a.

[0347] As outlined in the following, the outflow portion 126 passes in series through at least the cylinder block 108, the cylinder head 106 and the rocker cover 107.

[0348] With reference to Figure 11, which shows a view along section X2-X2 in Figure 1, the outflow portion 126 of the ventilation path 116 (represented by arrows formed from two solid lines in Figures 11 to 13 and 16) includes one or more gas flow passages 120 in the engine structure 102 for transporting the expelled gas from the crankcase 104 to the rocker cover 107. In the illustrated embodiment, the outflow portion 126 includes a plurality of the gas flow passages 120 distributed across and along the crankcase 104. By 'distributed across and along the crankcase' it is intended to mean that locations of at least two inlets of the gas flow passages 120 in the crankcase 104 are longitudinally offset, and at least two are transversely offset.

[0349] In the illustrated embodiment, the gas flow passages 120 include a plurality of pushrod passages 131 that are longitudinally spaced, each arranged to receive at least one of the pushrods 206 of the valvetrain 200. Each pushrod passage 131 extends through the cylinder block 108 and the cylinder head 106, and is in fluid communication with the crankcase 104 and the rocker cover 107. Advantageously, using the pushrod passages 131 negates the need to provide separate dedicated gas flow passages between the cylinder head 106 and the crankcase 104 for the expelled gas, instead using pre-existing passages in the engine structure 102.

[0350] In some embodiments, the gas flow passages 120 may additionally or alternatively include one or more (e.g. a plurality of) oil drain passages for draining oil from the cylinder head 106 to the crankcase 104 which are at least laterally spaced. For example, the gas flow passages 120 may include all of the oil drain passages in the cylinder head 106. During operation of the engine 100, oil sprayed onto components of the valvetrain 200 (e.g. the rocker arms 204) housed in the rocker cover 107 for lubrication is transported to the oil reservoir 105 via the oil drain passages. The oil drain passages may pass from the rocker cover 107, through the cylinder head 106, the cylinder block 108, and the crankcase 104 to the oil reservoir 105. The gas flow passages 120 may include the oil drain passages of the cylinder block 108 downstream of the cylinder head 106 and upstream of the crankcase 104. The oil drain passages may form a network of oil drain passages including one or more inlets in the cylinder head 106 and one or more outlets in the crankcase 104. The number of inlets in the cylinder head 106 may be more than, less than or equal to the number of outlets in the crankcase 104.

[0351] With reference to Figure 12, which shows a view of the rocker cover 107 along section XI- XI in Figure 1 with components of the valvetrain 200 omitted, the gas flow passages 120 terminate in the rocker cover 107. The expelled gas in the outflow portion 126 then exits the rocker cover 107 via an outlet 320 in the rocker cover 107. Like the one or more crankcase inlets 127 previously discussed, the rocker cover outlet 320 is located at or towards the first axial end Al of the engine structure 102. In alternative embodiments (not shown) the rocker cover outlet 320 and the one or more crankcase inlets 127 may be located at or towards different axial ends of the engine structure 102.

[0352] Since the one or more crankcase inlets 127 and the rocker cover outlet 320 are located on a common end of the engine structure 102, there is a potential for the flow of ventilation gas within the engine structure 102 to predominantly flow along the gas flow passages 120 closest to the first axial end Al, resulting in relatively less ventilation of the crankcase 104 towards an opposed second axial end A2 of the engine structure 102. This may lead to the blow-by gas stagnating in some regions of the engine structure 102. Such stagnation of the blow-by gas may lead to concentrations of the blow-by gas in these regions exceeding the lower flammability limit of the gaseous fuel, and thus increase the risk of ignition of the blow-by gas. As will be outlined in the following, to mitigate this problem, the outflow portion 126 is configured to promote flow of the ventilation gas across an axial extent of the engine structure 102 with respect to the crankshaft axis A, so as to inhibit stagnation of the blowby gas in the engine structure 102. In the illustrated embodiment, the outflow portion 126 is configured to promote flow of the ventilation gas towards the second axial end A2 of the engine structure 102.

[0353] In the illustrated embodiment, the rocker cover 107 is configured to promote flow of the ventilation gas across the axial extent of the engine structure 102. Put another way, the rocker cover 107 is configured to increase the flow of the ventilation gas towards the second axial end A2 of the engine structure 102, and thus increase the flow of the expelled gas along the outflow portion 126 from the second axial end A2 of the crankcase 104 to the rocker cover 107. Advantageously, such directing of the ventilation gas may help to improve ventilation of the blow-by gas across the axial extent of the crankcase 104 and avoid stagnant regions in the engine structure 102 where the concentration of blow-by gas is high and may exceed the lower flammability limit.

[0354] The rocker cover 107 includes a cavity 322 and a channel 324. The cavity 322 receives the rocker arms 204. The channel 324 is in fluid communication with the cavity 322, and terminates at the rocker cover outlet 320. The outflow portion 126 passes sequentially through the cavity 322, the channel 324, and then the rocker cover outlet 320. In the illustrated embodiment, the channel 324 is configured to increase the flow of ventilation gas towards the second axial end A2 of the crankcase 104.

[0355] In the illustrated embodiment, the channel 324 extends generally parallel to the crankshaft axis A. This helps to increase the flow of expelled gas from the second axial end A2 of the crankcase 104 to the rocker cover 107.

[0356] Figure 13 is a view of the rocker cover 107 along section X5-X5 in Figure 1 with components of the valvetrain 200 omitted. Figure 14 is a view of the rocker cover 107 along section X9-X9 in Figure 13. Figure 13 also shows section Xl-Xl, which is viewed in Figure 12, for reference.

[0357] With further reference to Figures 13 and 14, the channel 324 is adjacent an internal top side 330a of the rocker cover 107. In the illustrated embodiment, the rocker cover 107 includes a main body 330 and a member 332, which in the illustrated embodiment is in the form of a plate, mounted to an internal top side 330a of the main body 330. The channel 324 is formed between the internal top side 330a of the main body 330 and the member 332. The member 332 is identified generally via hatching in Figure 13. The main body 330 may be formed as a single monolithic piece of material (e.g. via a casting or pressing process). The channel 324 includes a downstream portion 324a at or towards the first axial end Al, and an upstream portion 324b closer to the second axial end A2 relative to the downstream portion 324a. The upstream portion 324b of the channel 324 is more open to the cavity 322 relative to the downstream portion 324a. As such, since the pump 114 is downstream of the channel 324, the suction from the cavity 322 to the channel 324 is higher closer to the second axial end A2, which increase the flow of expelled gas along the outflow portion 126 from the second axial end A2 of the crankcase 104 to the rocker cover 107. By 'more open to the cavity 322', it is intended to mean that that the total area of the flow passage(s) of the expelled gas from the cavity 322 to the upstream portion 324b of channel 324 is greater relative to the downstream portion 324a.

[0358] The upstream portion 324b includes a plurality of upstream openings 326, each providing a passage for the expelled gas from the cavity 322 to the channel 324. The upstream openings 326 include a first upstream opening 326a formed between the member 332 and the internal top side 330a. The first upstream opening 326a is closest to the second axial end A2 of the rocker cover 107, and has the greatest area, relative to the remaining openings 326, which helps to increase suction of the expelled gas towards the second axial end A2. The upstream openings 326 further includes a plurality of axially extending second upstream openings 326b each in the form of a gap between a first lateral end 332a of the member 332 and the internal top side 330a. The upstream openings 326 further includes a plurality of third upstream openings 326c, each in the form of a gap between the member 332 and a portion of the internal top side 330a surrounding a countersunk bore 328 for receiving a portion of a spark plug (not shown). In alternative embodiment (not shown), the upstream portion 324b may include one or more upstream openings 326 having any suitable configuration.

[0359] In the illustrated embodiment, the downstream portion 324a includes a plurality of downstream openings 340, which include a plurality of axially extending first downstream openings 340a each in the form of a gap between the first lateral end of the member 332 and the internal top side 330a. The downstream openings 340 further includes a plurality of second downstream openings 340b, each in the form of a gap between the member 332 and a portion of the internal top side 330a surrounding one of the countersunk bores 328. As shown in Figure 14, the area of the second upstream openings 326b is greater than the area of the first downstream openings 340a. Moreover, the area of the third upstream openings 326c is greater than the area of the second downstream openings 340b. Providing the downstream portion 324a with one or more openings helps to inhibit stagnant regions forming in the expelled gas towards the first axial end Al. In alternative embodiment (not shown), the downstream portion 324b may include no downstream openings 340, or one or more downstream openings 340 having any suitable configuration. In the illustrated embodiment, there are no openings between a second lateral end 332b of the member 332, opposite to the first lateral end 332a, and the internal top side 330a, but there may be such openings in alternative embodiments.

[0360] In alternative embodiments (not shown), the member 332 may include one or more (e.g. a plurality of) holes in addition to those for receiving the sparkplugs, such holes providing passages between the cavity 322 and the channel 324.

[0361] In some embodiments, the upstream portion 324b extends 5 to 50% of a width of the cavity 322 between the first and second axial ends Al, A2; optionally, 10 to 50% of the width; optionally, 20 to 50% of the width.

[0362] In alternative embodiments (not shown), the rocker cover 107 may have any suitable configuration so as to increase the flow of the ventilation gas towards the second axial end A2 of the engine structure 102. For example, the rocker cover 107 may include one or more suitably arranged baffles.

[0363] Figures 25 to 27 show an alternative embodiment of the rocker cover, which is denoted by reference 107'. Features in common with the rocker cover 107 of the previous embodiment share common reference numerals and a description of these features will not be repeated for brevity. The rocker cover 107' may share any features described in relation to the rocker cover 107 and vice versa.

[0364] Figure 25 shows a cross-sectional view of the rocker cover 107' similar to the view of the rocker cover 107 in Figure 12. In contrast to the previous embodiment, the rocker cover 107' does not include the channel 324 or the member 332.

[0365] The rocker cover 107' includes an oil fill conduit 600 for receiving oil or another lubricant for replenishing the engine 100 therewith. The oil fill conduit 600 includes an oil inlet 602 closed via a removable closure 604, such as an oil filler cap. When the closure 604 is removed, oil poured into the oil inlet 602 flows to the oil reservoir 105 via the cavity 322 in the rocker cover 107, and passages in the cylinder head 106, cylinder block 108 and crankcase 104. The rocker cover 107 of the previous embodiment includes a similar oil fill conduit 600. In alternative embodiments (not shown), a different part of the engine structure 102 may include the oil fill conduit 600.

[0366] In the illustrated embodiment, the oil fill conduit 600 is located at or towards the second axial end A2 of the engine structure 102.

[0367] As shown in Figure 25, the oil fill conduit 600 includes the rocker cover outlet, which is denoted by reference 320' in this embodiment. As such, the rocker cover outlet 320' is located at or towards the second axial end A2 of the engine structure 102, which promotes flow of the ventilation gas across the axial extent of the engine structure 102 from the first axial end Al to the second axial end A2.

[0368] With reference to Figure 26, which shows a view along section X12-X12 in Figure 25, the oil filler conduit 600 includes a chamber 620 protruding from the main body 330 of the rocker cover 107'. The outflow portion 126 of the ventilation path passes from the cavity 332 in the main body 330 to the chamber 620. The chamber 620 includes the rocker cover outlet 320'. In alternative embodiments (not shown), another portion of the engine structure 102 other than the oil filler conduit 600 may include the chamber 600 and outlet.

[0369] In the illustrated embodiment, the chamber 620 has a greater flow cross-sectional area (i.e. normal to the mean flow direction) relative to the rocker cover outlet 320'. For example, the flow cross-sectional area of the chamber 620 upstream and / or adjacent the rocker cover outlet 320' may be greater than the flow cross-sectional area of the rocker cover outlet 320'. This helps to reduce the flow speed of the expelled gas passing through the chamber 620. Reducing the flow speed of the expelled gas promotes the deposition of oil and other liquids entrained by the expelled gas, and so reduces the concentration of oil in the expelled gas downstream of the rocker cover outlet 320'.

[0370] In the illustrated embodiment, in a normal operating orientation of the engine 100, the chamber 620 is configured such that the expelled gas travels generally upwards before passing through the rocker cover outlet 320'. For example, the chamber 620 may protrude substantially upwardly from the main body 330 of the rocker cover 107'. As such, the expelled gas is forced to flow counter to the force of gravity, which helps to promote deposition of oil and other liquids entrained by the expelled gas.

[0371] In the illustrated embodiment, the chamber 620 is defined by a peripheral wall 624. The rocker cover outlet 320' includes an outlet conduit 606 passing through the peripheral wall 624. The outlet conduit 606 has a first open end 606a and a second open end 606b. The first and second open ends 606a, 606b are in fluid communication with each other. The first open end 606a is within the chamber 620 and spaced from the peripheral wall 624. It has been found that locating the first open end 606a within the chamber 620 and spacing it from the peripheral wall 624 helps to promote the deposition of oil and other liquids entrained by the expelled gas. The second open end 606b is external to the chamber 620 and spaced from the peripheral wall 624.

[0372] The outlet conduit 606 has a longitudinal axis 608. A length of the outlet conduit 606 along the longitudinal axis 608 between the first open end 606a and the peripheral wall 624 may be more than 20%, e.g. more than 30 %, e.g. more than 40%, e.g. more than 50%, of a corresponding width of the chamber 620. In the illustrated embodiment, the oil inlet 602 of the oil fill conduit 600 is above the rocker cover outlet 320'. The rocker cover outlet 320' is configured to inhibit oil received in the oil inlet 602 passing through the rocker cover outlet 320'. In the illustrated embodiment, the first open end 606a of the outlet conduit 606 is oriented to face away from the oil inlet 602, e.g. generally downwards. As such, oil received in the oil inlet 602 is prevented from travelling directly into the outlet conduit 606 via the first open end 606a.

[0373] In the illustrated embodiment, in a normal operating orientation of the engine 100, the first open end 606a is below the second open end of the outlet conduit 606 so as to inhibit oil that has entered the first end 606a of the outlet conduit 606 from flowing to the second open end 606b under the action of gravity.

[0374] In the illustrated embodiment, in a normal operating orientation of the engine 100, the longitudinal axis 608 of the outlet conduit 606 slopes downwardly in a direction from the second open end 606b to the first open end 606a. This helps ensure that oil within the outlet conduit 606 exits the outlet conduit 606 via its first open end 606a under the action of gravity, so that the oil is returned to within the engine structure 102.

[0375] In alternative embodiments (not shown), the rocker cover outlet 320' may have any suitable configuration. With further reference to Figure 27 , in this embodiment, the section 126a of the outflow portion 126 (represented as dashed lines in Figure 27) is modified relative to the previous embodiment, to extend from the rocker cover outlet 320' proximate the second axial end A2 to the routing unit 300 proximate the first axial end Al. The oil fill conduit 600 is on a top side of the rocker cover 107', and protrudes (e.g. upwardly) from a top external surface 601 of the rocker cover 107'. This helps reduce the length of the section 126a of the outflow portion 126 between the rocker cover outlet 320' and the routing unit 300, simplifies assembly and inspection of the outflow portion 126, and helps ensure that the expelled gas travels generally upwards before passing through the rocker cover outlet 320' as discussed above.

[0376] With reference to Figures 1 and 3-6, the outflow portion 126 includes a section 126a extending between the rocker cover outlet 320 and the outflow conduit 304 of the routing unit 300. In the illustrated embodiment, said section 126a is an external pipe 126a, which is external to the engine structure 102, and will be discussed more in the following.

[0377] As shown in Figures 6 and 7, the outflow portion 126 of the ventilation path 116 passes through the outflow conduit 304 from an inlet 350 to a pair of outlets 352 of the outflow conduit 304. The outflow conduit 304 is separate from the inflow conduit 302 described above. In alternative embodiments (not shown), the outflow conduit 304 may include only one, or more than two outlets 352. The outflow conduit 304 is configured to reduce a concentration of oil in the expelled gas at the outlets 352 relative to the inlet 350, and thus, as previously discussed, acts as an oil separator.

[0378] In the illustrated embodiment, the outflow conduit 304 is configured such that the expelled gas travelling from the inlet 350 to the outlets 352 changes flow direction a plurality of times, and the flow cross-section and hence flow velocity changes. Advantageously, this results in deposition of oil and other liquids (e.g. water generated as a by-product of hydrogen combustion) entrained with the expelled gas in the outflow conduit 304.

[0379] The outflow conduit 304 includes a wall 354 arranged so as to divert expelled gas travelling from the inlet 350 to the outlets 352. In the illustrated embodiment, the wall 354 faces the inlet 350 so as to enforce a first change in flow direction. The wall 354 is arranged substantially normal to a flow direction of the expelled gas immediately upstream of the wall 354, which helps increase the deposition of oil and other liquids. In alternative embodiments (not shown), the wall 354 may have any suitable configuration. For example, the outflow conduit 304 may additionally or alternatively include one or more walls in the form of baffles within the outflow conduit 304.

[0380] The wall 354 includes a textured (i.e. non-smooth) surface 354a. This increases the surface area of the wall 354 contacted by the expelled gas, which helps increase the deposition of oil and other liquids. In the illustrated embodiment, a portion of the texture surface 354a is arranged opposite to the inlet 350, such that the expelled gas contacts the textured surface 354a after flowing into the outflow conduit 304 through the inlet 350. In alternative embodiments (not shown), one or more other portions of the outflow conduit 304 may alternatively or additionally include a textured surface arranged for contact with the expelled gas.

[0381] In the illustrated embodiment, the outflow conduit 304 includes a dog-leg portion 356, which includes the outlets 352. The dog-leg portion 356 enforces a second change in flow direction of the expelled gas before it reaches the outlet 352. In alternative embodiments (not shown), the expelled gas travelling from the inlet 350 to the outlets 352 may change flow direction one or more (e.g. two or more) times. For example, the outflow conduit 304 may force the expelled gas to travel along a tortuous path between the inlet 350 and the outlets 352.

[0382] The outflow conduit 304 is configured to reduce a speed of the expelled gas travelling from the inlet 350 to the outlets 352, which aids deposition of oil and other liquids. In the illustrated embodiment, the outflow conduit 304 includes a first portion 304a upstream of a second portion 304b. A cross-sectional area of the second portion 304b normal to the flow direction of the expelled gas is greater than the first portion 304a. As such, a speed of the expelled gas in the second portion 304b is less than in the first portion 304a. In alternative embodiments (not shown), the outflow conduit 304 may have any suitable configuration for reducing the speed of the expelled gas travelling from the inlet 350 to the outlets 352 (e.g. the outflow conduit 304 may include one or more baffles).

[0383] As shown in Figure 6, the outflow conduit 304 includes a drainage outlet 358 for draining oil and other liquids from the outflow conduit 304.

[0384] As will be outlined in the following, the outflow portion 126 of the ventilation path 116 transports the expelled gas from the outflow conduit 304, in sequence, to the pump 114, the oil separator 130, and then to an outflow aperture 360 in the gearcase 109.

[0385] As shown in Figures 4 and 5, each of the two outlets 352 of the outflow conduit 304 is fluidly connected to a corresponding inlet 114i of the pump 114 via a connecting passage 362 of the outflow portion 126. In the illustrated embodiment, the pump 114 is a side channel pump (also known as a side channel blower) having the two inlets 114i. The pump 114 includes an impeller (not shown) rotatable within a housing about a rotation axis so as to move fluid at the two inlets 114i to an outlet (not shown). The two inlets 114i are arranged either side of a rotation plane of the impeller.

[0386] In the illustrated embodiment, the pump 114 is arranged such that the rotation axis of the impeller is substantially vertical in a normal operating orientation of the engine 100. For example, the rotation axis of the impeller may be substantially parallel to an axis of the cylinders 112. Such an arrangement of the impeller has been found to help drain oil and other liquids, which are deposited from the expelled gas within the pump 114, from at least the lowermost inlet 114i. Each of the two connecting passages 362 slopes downwards from the corresponding pump inlet 114i towards the corresponding outlet 352 of the outflow conduit 304. Advantageously, this helps to drain the oil and other liquids from the pump 114 to the outflow conduit 304, from where it can be drained via the drainage outlet 358. In alternative embodiments (not shown), the pump 114 may include only one inlet 114i, and / or more than one outlet 114o (e.g. two outlets 114o).

[0387] With reference to Figure 15, the outlet of the pump 114 is fluidly connected to an inlet 130i of the oil separator 130 via a connecting passage 364 of the outflow portion 126. As stated above, in this embodiment, the oil separator 130 is a cyclonic oil separator. The oil separator 130 being cyclonic causes the flow of expelled gas through it to form a vortex. The expelled gas enters the separator 130 through the inlet 130i, and forms a vortex. The expelled gas then exits the oil separator 130 via a gas outlet 130o. As will be discussed more in the following, the separated oil exits the separator 130 via an oil outlet 412. With reference to Figures 5, 9 and 15, the gas outlet 130o of the separator 130 is fluidly connected to the outflow aperture 360 in the gearcase 109 via a connecting passage 368 of the outflow portion 126. The outflow aperture 360 leads to the second portion 109b of the gearcase 109 such that the outflow portion 126 passes through said second portion 109b. The second portion 109b is separate from the first portion 109a of the gearcase 109, such that ventilation gas travelling through the first portion 109a cannot mix with expelled gas travelling through the second portion 109b.

[0388] In alternative embodiments (not shown), the outflow aperture 360 may be in any suitable portion of the engine structure 102 (e.g. the cylinder block 108 or the cylinder head 106).

[0389] With reference to Figures 1, 9 and 16, the expelled gas exits the second portion 109b of the gearcase 109 via a passage 380 in the engine structure 102. The outflow portion 126 passes from the second portion 109b of the gearcase 109 within the engine structure 102 in series through the cylinder block 108, the cylinder head 108, and the rocker cover 107, to an outlet 370 in the rocker cover 107. This section of the outflow portion 126 passing through the rocker cover 107 is separate and sealed from the cavity 322 and the channel 324. As such, expelled gas passing through the rocker cover 107 upstream of the oil separator 130 cannot mix with expelled gas passing through the rocker cover 107 downstream of the oil separator 130. The outlet 370 is fluidly connected to the second location 140b of the intake passage 140 (see Figure 3) via a connecting passage of the outflow portion 126.

[0390] As will be understood from Figures 4 and 9, in the illustrated embodiment, the routing unit 300 is mounted to the gearcase 109 adjacent to the outflow aperture 360, which helps improve the packaging of the ventilation system 110. In alternative embodiments (not shown), the routing unit 300 may have any suitable mounting location on the engine structure 102.

[0391] As shown in Figures 6 to 8, the inflow conduit 302 crosses and extends over the outflow conduit 304. This helps to improve the packaging of, and simplify the assembly of, the ventilation system 110.

[0392] In the illustrated embodiment, the inflow and outflow conduits 302, 304 are integrally formed (i.e. they share at least one common wall). This helps to reduce the size of the routing unit 300, and thus helps to improve the packaging of the ventilation system 110. Moreover, the inflow and outflow conduits 302, 304 are integrally formed with the housing 306, helping to further reduce the size of the routing unit 300. The inflow and outflow conduits 302, 304 and the housing 306 are formed from a suitable plastic which is nonreactive to water and oil, but may be formed any suitable material(s) (e.g. a metal such as aluminium or stainless steel) in alternative embodiments. In the illustrated embodiment, the routing unit 300 is formed from a plurality of connected parts, where each part is formed as a single monolithic piece of material (e.g. via a casting, moulding or additive manufacturing process). In alternative embodiments, the routing unit 300 may be formed as a single monolithic piece of material, for example, via an additive manufacturing process.

[0393] The ventilation system 110 is configured such that a gas pressure in the crankcase 104, and thus the oil reservoir 105, is higher than a gas pressure in the oil pre-separator 304 (i.e. the outflow conduit 304 in the illustrated embodiment) in use. This is due to the pump 114 being immediately downstream of the oil pre-separator 304, and thus the pressure in the crankcase 104 will be relatively higher due to pressure losses. Faced with this pressure difference, there is a potential problem that oil and other liquids collected by the oil preseparator 304 would be unable to drain to the oil reservoir 105 whilst the engine 100 is running.

[0394] Prior art solutions to this problem include controlling the flow of drainage of oil from such an oil separator to an oil reservoir using a valve, which opens only when the pressures in the oil separator and oil reservoir have equalised (e.g. when the engine is not running). However, the use of a valve adds to the number of moving parts of the engine, and the associated maintenance requirements. Moreover, some engines, such as those used in gensets, are required to run for long periods without stopping, and therefore, a large amount of oil may need to be stored before it can be returned to the oil reservoir for such engines.

[0395] With reference to Figures 4, 5 and 17, to mitigate the foregoing problem, the engine 100 includes a first drainage conduit 400 arranged to transport oil removed from the expelled gas by the oil pre-separator 304 to the oil reservoir 105. As outlined in the following, the first drainage conduit 400 is configured to hold a head of oil for exerting a hydrostatic pressure on oil in the oil reservoir 105, for inhibiting gas in the crankcase 104 being transported to the oil pre-separator 304 via the first drainage conduit 400, in use. As such, oil removed from the expelled gas by the oil pre-separator 304 can constantly drain to the oil reservoir 105 despite the pressure differential between the crankcase 104 and oil preseparator 304 as long as said head of oil is maintained. Therefore, there is no need to alter the operation of the ventilation system 110 (e.g. to equalise the pressures in the crankcase 104 and oil pre-separator 304) to enable the removed oil to be drained to the oil reservoir 105.

[0396] In the illustrated embodiment, the first drainage conduit 400 is arranged outside of the engine structure 102, which helps to simplify assembly and maintenance of the engine 102. In alternative embodiments (not shown), at least part of the first drainage conduit 400 may be arranged within the engine structure 102. Arranging at least part of the first drainage conduit 400 within the engine structure 102 may reduce a requirement for parts of the engine structure 102, e.g. an oil sump, to be customised for engines with a CCV system as described herein.

[0397] As shown in Figure 17, a first end 400a of the first drainage conduit 400 is fluidly connected to the drainage outlet 358 of the oil pre-separator 304. A second end 400b of the first drainage conduit 400 is fluidly connected to the oil reservoir 105. In the illustrated embodiment, the first drainage conduit 400 is configured such that oil flows from the first end 400a to the second end 400b unimpeded by moving parts, such as valves. As such, the maintenance requirements of the engine 100 are reduced.

[0398] Figure 18 shows a schematic representation of the crankcase 104, the oil reservoir 105 and the first drainage conduit 400. In the following, 'pl' shall denote the gas pressure in the crankcase 104, 'p2' the gas pressure in the oil pre-separator 304, 'hl' the head of oil in the oil reservoir 105 with respect to a horizontal reference plane 402, and 'h2' the head of oil in the first drainage conduit 400 with respect to the reference plane 402. As outlined above, when the engine 100 is running, the gas pressure in the crankcase 104 pl is greater than the gas pressure in the oil pre-separator p2 (i.e. pl>p2). It will be appreciated that to balance the hydrostatic pressures of the oil in the oil reservoir 105 and the first drainage conduit 400, the following equation must be satisfied: pl + pghl = p2 + pgh2, where g is acceleration due to gravity and p is the density of the oil.

[0399] Hence, to inhibit gas in the crankcase 104 being transported to the oil pre-separator 304 via the first drainage conduit 400, the first drainage conduit 400 must hold a head:

[0400] Put another way, the first drainage conduit 400 must hold an additional head of oil relative to the oil reservoir 105 corresponding to:

[0401] . , pl - p2

[0402] Uh = - , pg where h = h2 - hl.

[0403] In the illustrated embodiment, during operation of the engine 100, the difference between the gas pressure pl in the crankcase 104 and the gas pressure p2 in the oil pre-separator 304 (i.e. pl-p2) is approximately 0.6 Pa, which corresponds to an additional head of oil in the first drainage conduit 400 relative to the oil reservoir 105 (A / i) of approximately 80mm. To ensure that a sufficient head of oil h2 can be held in the first drainage conduit 400, the first end 400a of the first drainage conduit 400 is connected to the oil pre-separator 304 so as to be at the level of, or above, the crankcase 104. In the illustrated embodiment, the first end 400a of the first drainage conduit 400 is at the level of the cylinder block 108, but may be higher in alternative embodiments (e.g. at the level of the cylinder head 106).

[0404] In the illustrated embodiment, the first drainage conduit 400 is arranged to transport the oil adjacent to a bottom 105a of the oil reservoir 105, as shown in Figure 17. This helps to mitigate the risk of the oil level in the oil reservoir 105 dropping below the second end 400b of the first drainage conduit 400, which could result in gas in the crankcase 104 bypassing the oil and travelling along the first drainage conduit 400 to the oil pre-separator 304.

[0405] In the illustrated embodiment, the gas pressure in the crankcase 104, which is upstream of the pump 114, is lower than a gas pressure in the oil separator 130, which is downstream of the pump 114. As such, this pressure difference is favourable for enabling oil to be drained from the oil separator 130 to the oil reservoir 105 under gravity. As outlined in the following, the engine 100 includes a second drainage conduit, separate to the first drainage conduit 400, arranged to transport oil removed from the expelled gas by the oil separator 130 to an inlet portion 416 of the engine structure 102 leading to the oil reservoir 105.

[0406] With reference to Figures 19 and 20, the oil separator 130 includes a separator portion 130a configured to separate oil from the expelled gas, and an outlet portion 130b mounted to the separator portion 130a. The separator portion 130a includes the oil separator inlet 130i and the gas outlet 130o. The outlet portion 130b includes an oil outlet 412 in fluid communication with the separator portion 130a for draining the separated oil from the oil separator 130.

[0407] In the illustrated embodiment, the separator portion 130a causes the flow of expelled gas entering therein via the oil separator inlet 130i to form a vortex so as to separate oil from the expelled gas via the centrifugal effect of the vortex. The separator portion 130a includes an internal chamber 413 having a truncated cone portion 415 and a cylindrical portion 417. The cylindrical portion 417 is contiguous with the truncated cone portion 415. The expelled gas enters the chamber 413 from the oil separator inlet 130i via the cylindrical portion 417. Gas exits the chamber 413 through the gas outlet 130o via the cylindrical portion 417.

[0408] The outlet portion 130b is arranged substantially below the separator portion 130a. In the illustrated embodiment, the outlet potion 130b is mounted to an apex 415a of the truncated cone portion 415 via a push-fit mounting arrangement. In alternative embodiments (not shown), the outlet portion 130b may be mounted to the separator portion 130a via any suitable means (e.g. via bonding, and / or one or more fasteners).

[0409] In operation, the separated oil runs down a wall 414 of the chamber 413 to the apex 415a, and then to the outlet portion 130b, as indicated by the dashed arrows in Figure 20a. In alternative embodiments (not shown), the separator potion 130a may have any suitable configuration for separating oil from the expelled gas (e.g. the oil separator may be an active centrifugal oil separator).

[0410] The crankcase 104 includes an inlet portion 416 including an oil inlet 420. The oil inlet 420 is in fluid communication with the oil reservoir 105. Oil entering the oil inlet 420 travels within the engine structure 102 to the oil reservoir 105 under gravity.

[0411] The outlet portion 130b is mounted to the inlet portion 416 such that oil exiting the oil outlet 412 enters the oil inlet 420, and such that the separator portion 130a is mounted to the engine structure 102. Advantageously, mounting the separator portion 130a to the engine structure 102 via mounting of the outlet portion 130b to the inlet portion 416 helps to improve the packaging of the ventilation system and simplify assembly of the engine, since no additional piping is required to transport the drained oil from the separator portion 130a to the engine structure 102 and no additional lower mounting bracket is required for the oil separator 130. In alternative embodiments (not shown), any suitable portion of the engine structure 102 may include the inlet portion 416 (e.g. the cylinder block 108 or the cylinder head 106).

[0412] As shown in Figures 4 and 15, in the illustrated embodiment, the separator portion 130a is also mounted to the cylinder block 108 of the engine structure 102 via a fastener 423 passing through a mounting bracket 425 of the oil separator 130, and received in an aperture in the cylinder block 108. The mounting bracket 425 extends from the separator portion 130b. This additional mounting connection between the oil separator 130 and the engine structure 102 provides a stronger and more rigid connection between the two components. In alternative embodiments (not shown), the separator portion 130a may be mounted to the engine structure 102 solely via mounting of the outlet portion 130b to the inlet portion 416.

[0413] In the illustrated embodiment, the outlet portion 130b includes a male portion 422, and the inlet portion 416 includes a female portion 424. The male portion 422 includes the oil outlet 412. The female portion 424 includes the oil inlet 420. The male portion 422 is received in the female portion 424. Advantageously, the male and female portions 422, 424 provide a locating feature for helping to simplify assembly of the engine 100. In alternative embodiments (not shown), the outlet portion 130b may include the female portion 424 and the inlet portion 416 may include the male portion 422. Alternatively, the outlet and inlet portions 130b, 416 may not include such male and female portions.

[0414] In the illustrated embodiment, the male portion 422 includes male screw threads on a surface 426 thereof extending around the outlet 412. The female portion 424 includes corresponding female screw threads. The outlet portion 130b is mounted to the inlet portion 416 via engagement of the male and female screw threads.

[0415] The male portion 422 is rotatable relative to the separator portion about a screw axis 428 of the male portion 422 so as to engage the male and female screw threads. In the illustrated embodiment, the outlet portion 130b includes a housing 430 and a barrel 432. The housing 430 is mounted to the separator portion 130a. The barrel 432 extends through a bore in the housing 430, and is rotatable about the screw axis 428 relative to the housing 430. The barrel 432 includes the male portion 422. In the illustrated embodiment, the barrel 432 includes a recess 434 engageable with a tool, such as a screwdriver or Allen key, for rotating the male portion 422 about the screw axis 428. The recess 434 is opposite to the oil outlet 412.

[0416] The barrel 432 includes an axial bore 435 substantially aligned with the screw axis 428, and a plurality of radial bores 437 extending radially from the axial bore 435. The axial and radial bores 435, 437 are arranged such that oil draining from the separator portion 130a travels along one of the radial bores 437, along the axial bore 435 and then exits through the oil outlet 412, regardless of the orientation of the barrel 432 relative to the housing 430.

[0417] In alternative embodiments (not shown), the recess 434 may have any suitable location on the outlet portion 130b. For example, in some embodiments, rotation of the recess 434 via a tool may rotate the barrel 432 via an intervening mechanism, such as a gear mechanism, of the outlet portion 130b.

[0418] In the illustrated embodiment, the oil separator 130 is mounted to the engine structure 102 such that the separator portion 130a is adjacent the inlet portion 416. This helps to reduce the space envelope of the oil separator 130, and thus help to improve the packaging of the ventilation system 110. In alternative embodiments, the oil separator 130 may have any suitable mounting configuration.

[0419] As shown in Figure 20a, the separator portion 130a is elongate and has a longitudinal axis 440. The longitudinal axis 440 is substantially perpendicular to an axis of the oil outlet 412, which in the illustrated embodiment is aligned with the screw axis 428. Advantageously, such a configuration helps to improve the packaging of the ventilation system 110.

[0420] In the illustrated embodiment, a maximum length of the outlet portion 130b is less than a maximum length of the separator portion 130a. Moreover, a volume of the outlet portion 130b is less than a volume of the separator portion 130a. Advantageously, this helps to improve the packaging of the ventilation system 110.

[0421] The oil separator 130 includes a first sealing arrangement between the outlet portion 130b and the inlet portion 416. The first sealing arrangement is configured to inhibit leakage of oil travelling from the oil outlet 412 towards the oil inlet 420. In the illustrated embodiment, the sealing arrangement includes a first sealing member 442a (represented by dashed circles in Figure 20a), in the form of an O-ring, although any suitable sealing member may be used. The first sealing member 442a is in sealing contact with the surface 426 extending around the outlet 412 and the oil inlet 420. In alternative embodiments (not shown), the engine 100 may include any suitable first sealing arrangement. For example, the inlet portion 416 may additionally or alternatively include one or more sealing members.

[0422] The oil separator 130 includes a second sealing arrangement between the separator portion 130a and the outlet portion 130b configured to inhibit leakage of oil therebetween. In the illustrated embodiment, the second sealing arrangement includes a second seal member 442b and a third sealing member 442c in sealing contact with opposing axial ends of the barrel 432 and the housing 430. The second sealing arrangement further includes a fourth sealing member 442d in sealing contact with the truncated cone portion 415 of the separator portion 130a, and the housing 430.

[0423] Figure 20b shows an oil separator 130' according to an alternative embodiment. Features in common with the oil separator 130 shown in Figures 19 and 20a share common reference numerals, and their description will not be repeated for brevity.

[0424] In contrast to the previous embodiment, the housing 430' of the outlet potion 130b' of the oil separator 130’ shown in Figure 20b and the apex 415a of the truncated cone portion 415 are formed as a single monolithic piece of material (e.g. via a casting or moulding process). As such, no fourth sealing member 442d is required. Such a configuration of the oil separator 130' simplifies assembly of the engine 100. In alternative embodiments (not shown), said housing and any suitable portion of the separator portion may be formed as a single monolithic piece of material.

[0425] In the illustrated embodiment, the engine 100 is powered by hydrogen. As such, the blowby gas includes gases formed from the combustion of hydrogen, which includes water vapour. The water vapour in the expelled gas is prone to freezing if subjected to sufficient cold outside temperatures. Such ice formation may cause blockages in the ventilation path and damage components of the ventilation system 110. Sections of the outflow portion 126 within the engine structure 102 are heated by the heat energy released from combustion of the gaseous fuel in the cylinders 112, which inhibits the water vapour travelling along this section from freezing even when ambient temperatures are below freezing. However, one or more sections of the outflow portion 126, such as the external conduit 126a, are external to the engine structure 102, and therefore water vapour in these sections is more prone to freezing.

[0426] With reference to Figures 21 and 22, to inhibit ice formation in such exposed sections of the outflow portion 126, an embodiment of the engine 100 includes a heat transfer arrangement 500 configured to transfer combustion generated heat from the engine structure 102 to the external conduit 126a for heating the expelled gas transported therein. Advantageously, transferring the combustion generated heat to the external conduit 126a helps to inhibit water vapour in the expelled gas from freezing. Moreover, using combustion generated heated to heat the external conduit 126a rather than electrically generated heat for example, negates the need for electrical heating of the external conduit 126a and thus helps to reduce the parasitic energy losses of the engine 100.

[0427] As shown in Figures 21 and 22, the heat transfer arrangement 500 includes a heat transfer path 502 (represented by a dot-dash line in Figure 22) and a fluid pressure source 504, which in the illustrated embodiment is a pump. The fluid pressure source 504 is configured to transport a heat transfer fluid along the heat transfer path 502 from the engine structure 102 to a portion 501 of the external conduit 126a (represented by a solid double line in Figure 22) for transferring the combustion generated heat thereto. The heat transfer path 502 may take a tortuous route through at least the cylinder block 108 so as to increase heat transfer from the cylinder block 108 to the heat transfer path 502.

[0428] In alternative embodiments (not shown), the heat transfer arrangement 500 may transfer combustion generated heat from the engine structure 102 to all of the external conduit 126a.

[0429] In the illustrated embodiment, the heat transfer arrangement 500 includes a heat exchanger 506 (e.g. a radiator) in the heat transfer path 502. The heat transfer arrangement 500 is further configured to transfer combustion generated heat from the engine structure 102 via engine fluid passages including cylinder cooling jackets to the heat exchanger 506 so as to cool the engine structure 102 as is conventional for internal combustion engines. Advantageously, such a configuration of the heat transfer arrangement 500 negates the need for separate plumbing for an engine cooling system and for a heating system for the outflow portion 126. In alternative embodiments (not shown), the heat transfer arrangement 500 may be separate from the engine cooling system, and thus may not include the heat exchanger 506.

[0430] In the illustrated embodiment, the heat transfer fluid includes water, and may also include anti-freeze additives. In alternative embodiments (not shown), the heat transfer fluid may include any suitable liquid or gas. For example, the heat transfer fluid may be exhaust gas, i.e. combustion gas exhausted from the cylinders 112. In such embodiments, the fluid pressure source 504 may be compression of the exhaust gas by the pistons 113 in the cylinders 112.

[0431] As shown in Figure 22, the heat transfer path 502 is a closed path. As such, the fluid pressure source 504 circulates the heat transfer fluid around the heat transfer path 502.

[0432] The heat transfer path 502 exits the engine structure 102 via a first aperture 508 in the engine structure 102, passes along the portion 501 of the external conduit 126a, and then enters the engine structure 102 via a second aperture 510 in the engine structure 102.

[0433] As shown in Figure 21, in the illustrated embodiment, the portion 501 of the external conduit 126a is adjacent the cylinder head 106 and the rocker cover 107. The first aperture 508 and the second aperture 510 are in the cylinder head 106. This helps to reduce the length of piping 512 between the first aperture 508 and the external conduit 126a, and piping 514 between the second aperture 510 and the external conduit 126a. In alternative embodiments (not shown), the portion 501 of the external conduit 126a may be adjacent one or both of the cylinder head 106 and the cylinder block 108. In such embodiments, each of the first aperture 508 and the second aperture 510 may be in the cylinder head 106 or the cylinder block 106.

[0434] With further reference to Figure 23, which shows a view along section Xll-Xll in Figure 21, the heat transfer path 502 includes an annular duct 518 substantially surrounding the portion 501 of the external conduit 126a, for transferring the combustion generated heat from the heat transfer fluid in the duct 518 to the portion 501. Advantageously, this helps to maximise the area of the outer surface of the portion 501 in contact with the heat transfer fluid, so as to transfer combustion generated heat from engine structure 102 to the external conduit 126a more efficiently. In alternative embodiments (not shown), the duct 518 may not be annular, and may instead only partially surround the portion 501 of the external conduit 126a.

[0435] Figure 24 shows a schematic representation of a heat transfer arrangement 500' according to a further embodiment. Features in common with the heat transfer arrangement 500 shown in Figures 21 to 23 share common reference numerals, and their description will not be repeated for brevity.

[0436] With reference to Figure 24, the heat transfer arrangement 500' includes a passive heat transfer device 528 configured to transfer the combustion generated heat from the engine structure 102 to the portion 501 of the external conduit 126a. A 'passive heat transfer device' is defined as a heat transfer device that requires no external power source to transfer heat from the engine structure 102 to the external conduit 126a.

[0437] In alternative embodiments (not shown), the passive heat transfer device 528 may transfer the combustion generated heat to all of the external conduit 126a.

[0438] In the illustrated embodiment, the passive heat transfer device 528 includes a heat transfer member 530 connected to a portion 102a of the engine structure 102 and to the portion 501 of the external conduit 126a. The heat transfer member 530 is configured to transfer the combustion generated heat from the portion 120a of the engine structure 102 to the portion 501 of the external conduit 126a.

[0439] In the illustrated embodiment, the heat transfer member 530 includes an annular portion 532 substantially surrounding the portion 501 of the external conduit 126a, similar to the duct 518 shown in Figure 23. This helps to increase the contact surface area between the heat transfer member 530 and the portion 501 so as to transfer combustion generated heat from the engine structure 102 to the external conduit 126a more efficiently. In alternative embodiments (not shown), the heat transfer member may only partially surround the portion 501 of the external conduit 126a.

[0440] The heat transfer member 530 further includes a connector portion 534 connecting the annular portion 532 to an outer surface 102b of the portion 102a of the engine structure 102. The connector portion 534 may have any suitable geometry. For example, in some embodiments, the connector portion 534 may be planar. In some embodiments, the connector portion 534 may be formed from two or more separate sections, each connected to the engine structure 102 and the portion 501.

[0441] The connector portion 534 and the annular portion 532 may be formed as a single monolithic piece of material (e.g. via a casting process), or may be formed as two parts secured to each other (e.g. via a welding or bonding process and / or via one or more fasteners). The connector portion 534 may be secured to the outer surface 102b of the engine structure 102 via any suitable means (e.g. via welding, bonding, and / or one or more fasteners). A layer of a thermal paste may be included between the outer surface 102b of the engine structure 102 and the connector portion 534, and / or between the connector portion 534 and the annular portion 532.

[0442] The portion 102a of the engine structure 102 may be formed from a first material, and the heat transfer member 530 may be formed from a second material having a thermal conductivity greater than or equal to the first material. This helps to transfer the combustion generated heat to the portion 501 more efficiently. For example, the portion 102a of the engine structure 102 may be formed from iron (which has a thermal conductivity of approximately 80 W / m K) and / or steel (which has a thermal conductivity of approximately 50 W / m K), and the heat transfer member 530 may be formed from copper (which has a thermal conductivity of approximately 385 W / m K), aluminium (which has a thermal conductivity of approximately 205 W / m K), and / or brass (which has a thermal conductivity of approximately 109 W / m K). The heat transfer member 530 may be formed via any suitable manufacturing process (e.g. casting, extruding, and / or milling).

[0443] As shown in Figure 24, in the illustrated embodiment, the engine 100 includes a thermally insulative material 540 covering the external conduit 126a, for increasing the thermal insulation thereof. The thermally insulative material 540 is more thermally insulative relative to the material from which the external conduit 126a is formed. For example, the thermally insulative material 540 may be formed from a foam material (e.g. polyurethane foam), polystyrene, fibreglass, and / or mineral wool. Likewise, the thermally insulative material 540 may also be employed in the heat transfer arrangement 500 shown in Figures 21 to 23. In alternative embodiments (not shown), the thermally insulative material 540 may only cover part of the external conduit 126a (e.g. the portion 501).

[0444] In some embodiments, the passive heat transfer device 528 may additionally or alternatively include one or more heat pipes, for example connected to the outer surface 102b of the engine structure 102 and to the annular portion 532 (and / or directly connected to the portion 501). Such a configuration of the passive heat transfer device 528 helps to transfer combustion generated heat from the engine structure 102 to the external conduit 126a more efficiently.

[0445] 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

CLAIMS1. A gaseous fuel internal combustion engine comprising: an engine structure comprising: a crankcase; and a gearcase; and a ventilation system comprising a gas pressure source and a ventilation path, the gas pressure source configured to transport ventilation gas along the ventilation path from a gas inlet to a first portion of the gearcase and then to the crankcase, and to transport a combination of the ventilation gas and a blow-by gas including the gaseous fuel from the crankcase via a separate outlet as an expelled gas.

2. The engine of claim 1, wherein the outlet comprises an outflow portion of the ventilation path and a section of the outflow portion is arranged in the engine structure.

3. The engine of claim 2, wherein the engine structure further comprises a cylinder block, a cylinder head and a rocker cover, and wherein the outflow portion passes through one or more of the cylinder block, the cylinder head, the rocker cover and a second portion of the gearcase, said second portion separate from the first portion of the gearcase.

4. The engine of claim 3, wherein the outflow portion passes in series through at least the cylinder block, the cylinder head and the rocker cover.

5. The engine of any one of claims 2 to 4, wherein the outflow portion passes through a second portion of the gearcase, said second portion separate from the first portion of the gearcase.

6. The engine of any preceding claim, wherein the gas pressure source is configured to transport the ventilation gas along an inflow portion of the ventilation path from the gas inlet to the crankcase, wherein the outlet comprises an outflow portion of the ventilation path, wherein the ventilation system comprises a routing unit mounted adjacent to the engine structure, wherein the routing unit comprises: a housing; an inflow conduit in the inflow portion of the ventilation path; and an outflow conduit in the outflow portion of the ventilation path, wherein the inflow conduit and the outflow conduit are at least partially housed within the housing.

7. The engine of claim 6, wherein the outflow conduit comprises an oil pre-separator configured to reduce a concentration of oil in the expelled gas; optionally, wherein the oil pre-separator is a passive oil pre-separator.

8. The engine of claims 6 or 7, wherein the gas pressure source is downstream of the crankcase, and wherein the outflow conduit is upstream of the gas pressure source.

9. The engine of any one of claims 6 to 8, wherein the routing unit is mounted adjacent to the gearcase.

10. The engine of claim 9, wherein the inflow portion of the ventilation path enters the first portion of the gearcase via an aperture in the gearcase, wherein said gearcase aperture is downstream of the inflow conduit, and wherein the routing unit is mounted to the gearcase adjacent to the gearcase aperture; optionally, wherein the routing unit overlies the gearcase aperture, for example, wherein the inflow conduit and the first portion of the gearcase are contiguous.

11. The engine of claim 10, wherein the gearcase aperture is in a forward facing wall of the gearcase.

12. The engine of claims 10 or 11, wherein the gearcase aperture is above a cam gear mounted to an engine camshaft.

13. The engine of any one of claims 6 to 12, wherein the outflow portion of the ventilation path enters the engine structure (e.g. a second portion of the gearcase separate to the first portion) via an outflow aperture in the engine structure, where said outflow aperture is downstream of the outflow conduit.

14. The engine of claim 13, wherein the routing unit is mounted to the engine structure adjacent to the outflow aperture; optionally, wherein the gearcase comprises the outflow aperture.

15. The engine of any preceding claim, wherein the separate outlet comprises an outflow portion of the ventilation path passing within the engine structure from the crankcase to an engine structure outlet, wherein the outflow portion is configured to promote flow of the ventilation gas across an axial extent of the engine structure with respect to a crankshaft axis of the engine, so as to inhibit stagnation of the blow-by gas in the engine structure.

16. The engine of any preceding claim, wherein the gas pressure source is downstream of the crankcase, wherein the ventilation system comprises an oil pre-separator upstream of the gas pressure source, the oil pre-separator configured to reduce a concentration of oil in the expelled gas transported from the crankcase to the gas pressure source; optionally, wherein the oil pre-separator is a passive oil pre-separator.

17. The engine of any preceding claim, wherein the gas pressure source is a pump.

18. The engine of any preceding claim, wherein the gas pressure source is configured to induce a below-atmospheric pressure in the crankcase; optionally, in the range of -100 to -10 mbar relative to atmospheric pressure; for example, -80 to -20 mbar relative to atmospheric pressure.

19. The engine of claim 18, wherein the gas pressure source is downstream of the crankcase.

20. The engine of any preceding claim, wherein the ventilation system comprises an oil separator configured to reduce a concentration of oil in the expelled gas transported from the crankcase; optionally, further comprising an oil passage arranged to transport oil removed from the expelled gas by the oil separator to the crankcase.

21. The engine of claim 20, wherein the oil separator is a passive oil separator; optionally, a cyclonic oil separator.

22. The engine of claims 20 or 21, wherein the oil separator is arranged downstream of the gas pressure source; optionally, wherein the oil separator is mounted to the gas pressure source.

23. The engine of any preceding claim, wherein the engine structure comprises one or more cylinders, wherein the engine further comprises an intake system configured to supply air to the one or more cylinders, and wherein the ventilation system is configured to transport the expelled gas to the intake system for supply to the one or more cylinders via the outlet, e.g. via an outflow portion of the ventilation path.

24. The engine of claim 23, wherein the gas inlet is in fluid communication with a supply of air, wherein the intake system comprises an intake passage arranged to transport air from the gas inlet to the one or more cylinders, and wherein the ventilation system isconfigured to draw air as the ventilation gas into the ventilation path from the intake passage at a first location.

25. The engine of claim 24, further comprising a compressor along the intake passage, wherein the first location is upstream of the compressor; optionally, wherein the compressor is a turbocharger or a supercharger.

26. The engine of claim 25, wherein the gas pressure source is configured to induce a lower pressure in the crankcase relative to a pressure at an inlet to the compressor; optionally, wherein the compressor is configured to induce a pressure at the inlet to the compressor of -60 to 0 mbar relative to atmospheric pressure.

27. The engine of any one of claims 24 to 26, wherein the ventilation system is configured to exhaust the expelled gas from the separate outlet, e.g. via an outflow portion of the ventilation path, to a second location of the intake passage, the second location being downstream of the first location with respect to the intake passage, and, optionally, upstream of the compressor.

28. The engine of any preceding claim, wherein the gas inlet comprises a filter.

29. A gaseous fuel internal combustion engine comprising: an engine structure comprising a crankcase; and a ventilation system comprising a gas pressure source and a ventilation path, the gas pressure source configured to transport ventilation gas along an inflow portion of the ventilation path from a gas inlet to the crankcase, and to transport a combination of the ventilation gas and a blow-by gas including the gaseous fuel from the crankcase along an outflow portion of the ventilation path as an expelled gas, wherein the ventilation system comprises a routing unit mounted adjacent to the engine structure, the routing unit comprising: a housing; an inflow conduit in the inflow portion of the ventilation path; and an outflow conduit in the outflow portion of the ventilation path, wherein the inflow conduit and the outflow conduit are at least partially housed within the housing.

30. The engine of claim 29, wherein the outflow conduit comprises an oil separator configured to reduce a concentration of oil in the expelled gas in the ventilation path.

31. The engine of claim 30, wherein the oil separator is a passive oil separator.

32. The engine of claims 30 or 31, wherein the oil separator is configured to change a flow direction of the expelled gas travelling along the ventilation path at least once (e.g. at least twice).

33. The engine of claim 32, wherein the oil separator comprises a wall arranged so as to divert expelled gas travelling along the ventilation path; optionally, wherein the wall is arranged substantially normal to a flow direction of the expelled gas immediately upstream of the wall.

34. The engine of any one of claims 30 to 33, wherein the oil separator comprises a textured surface arranged for contact with the expelled gas.

35. The engine of claim 34, wherein the oil separator comprises a wall arranged so as to divert expelled gas travelling along the ventilation path, and wherein the wall comprises the textured surface; optionally, wherein the wall is arranged substantially normal to a flow direction of the expelled gas immediately upstream of the wall.

36. The engine of any one of claims 30 to 35, wherein the oil separator is configured to reduce a speed of the expelled gas travelling along the ventilation path; optionally, wherein the outflow conduit comprises a first portion upstream of a second portion, wherein a cross-sectional area of the second portion normal to the flow direction is greater than the first portion so as to reduce a speed of the expelled gas in the second portion relative to the first portion.

37. The engine of any one of claims 30 to 36, wherein the outflow conduit comprises an oil drainage outlet for draining oil separated from the expelled gas by the oil separator.

38. The engine of any one of claims 29 to 37, wherein the outflow conduit is upstream of the gas pressure source.

39. The engine of any one of claims 29 to 38, wherein the inflow portion of the ventilation path enters the engine structure via an inflow aperture in the engine structure, wherein said inflow aperture is downstream of the inflow conduit, and wherein the routing unit is mounted to the engine structure adjacent to said inflow aperture.

40. The engine of claim 39, wherein the engine structure comprises a gearcase comprising the inflow aperture.

41. The engine of any one of claim 40, wherein the inflow aperture is in a forward facing wall of the gearcase.

42. The engine of claims 40 or 41, wherein the inflow aperture is above a cam gear mounted to engine camshaft.

43. The engine of any one of claims 39 to 42, wherein the routing unit overlies the inflow aperture.

44. The engine of any one of claims 29 to 43, wherein the outflow portion of the ventilation path enters the engine structure via an outflow aperture in the engine structure, where said outflow aperture is downstream of the outflow conduit, and wherein the routing unit is mounted to the engine structure adjacent to said outflow aperture.

45. The engine of claim 44, wherein the engine structure comprises a gearcase comprising the outflow aperture.

46. The engine of any one of claims 29 to 45, wherein the inflow and outflow conduits are integrally formed.

47. A gaseous fuel internal combustion engine comprising: an engine structure comprising a crankcase; and a ventilation system comprising a gas pressure source and a ventilation path, the gas pressure source configured to transport ventilation gas along the ventilation path from a gas inlet to the crankcase via a crankcase inlet, and to transport a combination of the ventilation gas and a blow-by gas including the gaseous fuel along an outflow portion of the ventilation path as an expelled gas, the outflow portion passing within the engine structure from the crankcase to an engine structure outlet, wherein the outflow portion is configured to promote flow of the ventilation gas across an axial extent of the engine structure with respect to a crankshaft axis of the engine, so as to inhibit stagnation of the blow-by gas in the engine structure.

48. The engine of claim 47, wherein the crankcase inlet and the engine structure outlet are at or towards a first axial end of the engine structure, and wherein the outflow portionis configured to promote flow of the ventilation gas towards an opposite second axial end of the engine structure.

49. The engine of claim 47, wherein the crankcase inlet is at or towards a first axial end of the engine structure, and wherein the engine structure outlet is at or towards an opposite second axial end of the engine structure, and wherein the outflow portion is configured to promote flow of the ventilation gas towards the second axial end of the engine structure.

50. The engine of any one of claims 47 to 49, wherein the engine structure comprises a chamber protruding from a body of the engine structure, wherein the outflow portion passes from the body to the chamber, and wherein the chamber comprises the engine structure outlet.

51. The engine of claim 50, wherein the chamber has a greater flow cross-sectional area relative to the engine structure outlet; optionally, wherein a flow cross-sectional area of the chamber upstream and / or adjacent the engine structure outlet is greater than the flow cross-sectional area of the engine structure outlet.

52. The engine of claims 50 or 51, wherein, in a normal operating orientation of the engine, the chamber is configured such that the expelled gas travels generally upwards before passing through the engine structure outlet; optionally, wherein the chamber protrudes substantially upwardly from the body of the engine structure.

53. The engine of any one of claims 50 to 52, wherein the engine structure outlet comprises an outlet conduit passing through a peripheral wall defining the chamber, wherein the outlet conduit has first and second open ends in fluid communication with each other, wherein the first open end is within the chamber and spaced from the peripheral wall; optionally, wherein the second open end is external to the chamber and spaced from the peripheral wall.

54. The engine of claim 54, wherein a length of the outlet conduit between the first open end and the peripheral wall is more than 20%, e.g. more than 30 %, e.g. more than 40%, e.g. more than 50%, of a corresponding width of the chamber.

55. The engine of any one of claims 50 to 54, wherein the engine structure comprises an oil fill conduit for receiving oil for replenishing the engine therewith, and wherein the oil fill conduit comprises the chamber.

56. The engine of any one of claims 47 to 55, wherein the engine structure further comprises a rocker cover, wherein the outflow portion passes from the crankcase to the rocker cover, and wherein the rocker cover is configured to promote flow of the ventilation gas across the axial extent of the engine structure.

57. The engine of claim 56 when dependent on claim 55, wherein the oil fill conduit protrudes from a body of the rocker cover; optionally, wherein the oil fill conduit is on a top side of the rocker cover, e.g. wherein the oil fill conduit protrudes, e.g. upwardly, from a top surface of the rocker cover.

58. The engine of claims 56 or 57, wherein the rocker cover comprises a cavity for receiving one or more rocker arms, and a channel, wherein the outflow portion passes sequentially from the crankcase through at least the cavity, the channel, and then the engine structure outlet, wherein the channel is configured to promote flow of the ventilation gas across the axial extent of the engine structure; optionally wherein the rocker cover comprises the engine structure outlet.

59. The engine of claim 58, wherein the channel comprises a downstream portion at or towards a first axial end of the engine structure, and an upstream portion closer to an opposite second axial end of the engine structure relative to the downstream portion, wherein the upstream portion is more open to the cavity relative to the downstream portion.

60. The engine of claim 59, wherein the upstream portion comprises a plurality of openings, each providing a passage for the expelled gas from the cavity to the channel.

61. The engine of claims 59 or 60, wherein the downstream portion comprises one or more openings, each providing a passage for the expelled gas from the cavity to the channel.

62. The engine of any one of claims 59 to 61, wherein the upstream portion extends 5 to 50% of a width of the cavity between the first and second axial ends; optionally, 10 to 50% of the width; optionally, 20 to 50% of the width.

63. The engine of any one of claims 58 to 62, wherein the channel extends generally parallel to the axis of the crankshaft.

64. The engine of any one of claims 58 to 63, wherein the channel is adjacent an internal top side of the rocker cover.

65. The engine of any one of claims 58 to 64, wherein the rocker cover comprises a main body and a member, such as a plate, mounted to an internal top side of the main body, wherein the channel is formed between said internal top side of the main body and the member; optionally, wherein the main body is formed as a single monolithic piece of material (e.g. via a casting or pressing process).

66. The engine of any one of claims 47 to 65, wherein the engine structure further comprises a cylinder block and / or a cylinder head, wherein the outflow portion passes within the cylinder block and / or cylinder head, and is configured to promote flow of the ventilation gas across the axial extent of the cylinder block and / or cylinder head, so as to inhibit stagnation of the blow-by gas therein.

67. The engine of any one of claims 47 to 66, wherein the outflow portion is wholly within the engine structure.

68. The engine of any preceding claim, wherein the gaseous fuel is hydrogen.

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