Method of Operating a Hydrogen Engine, Computer Program Computer-Readable Medium, Control Arrangement, Hydrogen Engine, and Vehicle

Abstract

A method (100) of operating a hydrogen engine (1 , 1', 1”) is disclosed. The method (100) comprises the steps of obtaining (110) a desired torque quantity, obtaining (120) a maximum thermal load capacity of the hydrogen engine (1 , 1', 1 ”), obtaining (130) a desired heat capacity ratio of a gas mixture charge in a combustion chamber (5) based on the desired torque quantity and the maximum thermal load capacity, determining (140) the proportion of hydrogen (H2), oxygen gas (02), and the monatomic gas (Ar) that results in the desired heat capacity ratio, and supplying (150) the hydrogen (H2), the oxygen gas (02), and the monatomic gas (Ar) to the combustion chamber (5) in the determined proportion. The present disclosure further relates to a computer program, a computer-readable medium (200), a control arrangement (21), a hydrogen engine (1 , 1', 1”), and a vehicle (2).

Description

The present disclosure relates to a method of operating a hydrogen engine. The present disclosure further relates to a computer program, a computer-readable medium, a control arrangement, a hydrogen engine, and a vehicle.BACKGROUNDInternal combustion engines are used to provide motive power to vehicles, commonly via a drivetrain and driven wheels of the vehicle. In many vehicles, the drivetrain comprises a transmission controllable between at least two different gears to provide at least two different transmission ratios between the engine and the driven wheels of the vehicle.Internal combustion engines, such as four-stroke internal combustion engines, comprise one or more cylinders and a piston arranged in each cylinder. The pistons are connected to a crankshaft of the engine via a respective connecting rod and normally each comprise one or more piston rings to seal the area between the piston and the cylinder. The pistons are arranged to reciprocate within the cylinders upon rotation of the crankshaft.The engine usually further comprises one or more inlet valves and one or more exhaust valves as well as one or more fuel supply arrangements. The one or more inlet valves and exhaust valves are controlled by a respective valve control arrangement usually comprising one or more camshafts rotatably connected to a crankshaft of the engine, via a belt, chain, gears, push rods, or similar. A four-stroke internal combustion engine completes four separate strokes while turning a crankshaft two revolutions. A stroke refers to the full travel of the piston along the cylinder, in either direction. The uppermost position of the piston in the cylinder is usually referred to as the top dead centre TDC, and the lowermost position of the piston in the cylinder is usually referred to as the bottom dead centre BDC.The strokes are completed in the following order, inlet stroke, compression stroke, expansion stroke and exhaust stroke. During operation of a conventional four-stroke internal combustion engine, the inlet valve control arrangement controls inlet valves of a cylinder to an open state during the inlet stroke of a piston within the cylinder, to allow air, or a mixture of air and fuel, to enter the cylinder. During the compression stroke, all valves should be closed to allow compression of the air, or the mixture of the air and fuel, in the cylinder. If the engine is in a power producing state, fuel in the cylinder is ignited, usually towards the end of the compression stroke, by an ignition device or compression heat. The combustion of fuel within the cylinder significantly increases pressure and temperature in the cylinder. The combustion of the fuel usually continues into a significant portion of the subsequent expansion stroke. The increased pressure and temperature in the cylinder obtained by the combustion is partially converted into mechanical work supplied to the crankshaft in the expansion stroke.Obviously, all valves should remain closed during the expansion stroke to allow the increased pressure and temperature to be converted into mechanical work. The expansion stroke is also usually referred to as the combustion stroke, because usually, the majority of the combustion takes place during the expansion stroke. In the subsequent exhaust stroke, the exhaust valve control arrangement controls exhaust valves of the cylinder to an open state to allow exhaust gases to be expelled out of the cylinder into an exhaust system. The exhaust stroke is then followed by an inlet stroke.General problems when designing an internal combustion engine is the emission levels from the engine as well as the fuel consumption of the engine. Emissions generated by an internal combustion engine normally comprise a range of gaseous and particulate substances. A primary constituent of exhaust gases is carbon dioxide (CO2), which results from the combustion of hydrocarbons present in the fuel. While carbon dioxide is not directly harmful in low concentrations, its release in significant quantities contributes to the greenhouse effect and global climate change by trapping heat in the Earth's atmosphere.In addition to carbon dioxide, exhaust gases contain carbon monoxide (CO), which is produced by incomplete combustion when there is insufficient oxygen present to fully oxidize the carbon in the fuel. Carbon monoxide is a toxic gas that can be harmful to both humans and animals.Nitrogen oxides (NOx), another significant component of exhaust emissions, are formed due to the high temperatures and pressures within the engine cylinder, where nitrogen from the air reacts with oxygen. Nitrogen oxides contribute to the formation of smog and acid rain and are also linked to respiratory problems in humans and animals.Unburned hydrocarbons (HC) are released when fuel does not completely combust within the cylinder. These hydrocarbons can contribute to the formation of ground-level ozone, which is a major component of smog. Ground-level ozone can irritate the respiratory system and reduce lung function. Additionally, some hydrocarbons are classified as carcinogens, presenting long-term health risks.Particulate matter (PM), consisting of microscopic solid or liquid particles, is primarily generated by incomplete combustion of fuel, particularly in engines running on diesel. These particulates can penetrate deep into the lungs and can be harmful to both humans and animals. Furthermore, particulate matter contributes to environmental issues such as air quality degradation and reduced visibility.Each of these emissions, individually and collectively, contributes to environmental degradation and poses health risks to humans and animals. Due to environmental concerns, almost all vehicles for sale today comprise some sort of exhaust aftertreatment system. Examples are catalytic converters, particulate filters, and Selective catalytic reduction (SCR) arrangements. These exhaust aftertreatment systems are efficient in reducing the amount of carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (HC), and particulate matter (PM) exhausted from vehicles.However, such exhaust aftertreatment systems cannot reduce the amount of carbon dioxide (CO2) in the exhaust gas because carbon dioxide is a direct product of the combustion process itself, resulting from the oxidation of carbon in the fuel. Unlike other harmful emissions that can be chemically transformed or filtered out, the formation of carbon dioxide is an inherent aspect of burning hydrocarbons, and its reduction requires alternative strategies. These strategies typically include improving the overall efficiency of the engine to reduce fuel consumption, thereby lowering carbon dioxide (CO2) output, or transitioning to alternative, low-carbon energy sources, such as electric propulsion or hybrid systems that rely less on internal combustion engines.Despite the advancements in aftertreatment technology, the rising global focus on climate change and stringent emissions regulations are pushing the automotive industry toward the development of more efficient engines and alternative powertrains. Electrification, in particular, is seen as a key solution to minimize or eliminate tailpipe emissions, as electric vehicles (EVs) do not produce exhaust gases during operation. Nonetheless, internal combustion engines continue to play a critical role in the automotive market, especially in hybrid systems or in regions where charging infrastructure for electric vehicles is still underdeveloped.One promising alternative is the hydrogen engine, which is an internal combustion engine operating on hydrogen instead of conventional hydrocarbon-based fuels. In a hydrogen engine, the combustion of hydrogen with oxygen produces water vapor as the primary byproduct. The chemical reaction between hydrogen and oxygen produce no carbon dioxide (CO2). However, in these hydrogen engines, nitrogen oxides (NOx) can still be produced due to the high combustion temperatures and the presence of nitrogen from the air entering the combustion chambers.Producing hydrogen gas requires a significant input of energy, often sourced from electricity through processes like water electrolysis. For hydrogen to serve as a viable and environmentally friendly fuel, it is essential that the hydrogen production process relies on renewable energy sources, such as solar, wind, or hydropower, to prevent the release of carbon dioxide (CO2) associated with fossil fuel-based energy production. Given the energyintensive nature of hydrogen production, it is advantageous if a hydrogen engine can be operated at high efficiency. High operational efficiency minimizes the amount of hydrogen fuel consumed to achieve a desired power output, thereby reducing overall energy demand and conserving the resources needed for hydrogen production. This approach supports both economic and environmental goals by making the best use of the energy invested in producing hydrogen fuel.In addition to efficiency, a hydrogen engine benefits significantly from high torque and power density. High torque and power density allow the engine to deliver substantial power output for its size, making it well-suited for applications requiring strong acceleration and highperformance capabilities. For vehicles, high torque enables rapid acceleration and improves drivability, while high power density allows the engine to maintain strong performance without increasing its physical size or weight. This is particularly beneficial in applications where space and weight constraints are important, such as in passenger vehicles, busses, and trucks. Achieving these characteristics in a hydrogen engine can make it a more competitive alternative to conventional internal combustion engines.However, operating the hydrogen engine at high efficiency and with high torque and power density can cause excessive thermal and mechanical stress on the engine components. Excessive thermal and mechanical stress can lead to thermal stress on engine parts, potentially causing premature wear, deformation, or even failure. Excessive mechanical stress, especially at high torque outputs, places additional loads on components such as pistons, connecting rods, and crankshafts, increasing the risk of fatigue and reducing the longevity of the engine.It is an object of the present invention to overcome, or at least alleviate, at least some of the above-mentioned problems and drawbacks. The object is achieved by the subject-matter of the appended independent claim(s).According to a first aspect of the present disclosure, the object is achieved by a method of operating a hydrogen engine, the hydrogen engine comprising one or more cylinders, a piston arranged in each cylinder to delimit a combustion chamber inside the cylinder, an exhaust outlet and a gas inlet each connected to the combustion chamber, and a gas supply arrangement configured to supply hydrogen, oxygen gas, and a monatomic gas to the combustion chamber. The method comprises the steps of:- obtaining a desired torque quantity of the hydrogen engine,- obtaining a maximum thermal load capacity of the hydrogen engine,- obtaining a desired heat capacity ratio of a gas mixture charge in the combustion chamber based on the desired torque quantity and the maximum thermal load capacity, - determining the proportion of hydrogen, oxygen gas, and the monatomic gas that results in the desired heat capacity ratio, and- supplying the hydrogen, the oxygen gas, and the monatomic gas to the combustion chamber in the determined proportion.Thereby, the hydrogen engine can be operated at high efficiency, with high torque and power density, without imposing excessive thermal and mechanical stress on the engine. This is because by supplying the hydrogen, the oxygen gas, and the monatomic gas to the combustion chamber in the determined proportion, the hydrogen engine can operate at or just below its maximum thermal load capacity, thereby obtaining high operational efficiency along with high torque and power density. Additionally, the control enables the hydrogen engine to maintain operation at or just below its maximum thermal load capacity across the entire operating range, ensuring optimal efficiency under varying conditions.Furthermore, since the method comprises the step of supplying the hydrogen, the oxygen gas, and the monatomic gas to the combustion chamber, the need for utilizing carbon-based fuel is circumvented. In this manner, the release of carbon dioxide (CO2), carbon monoxide (CO), unburned hydrocarbons (HC), and particulate matter (PM) typically associated with traditional combustion engines can be eliminated. Accordingly, conditions are provided for obtaining a zero-emission hydrogen engine. In this context, the wording a zero-emission hydrogen engine refers to an engine that produces no emissions other than pure water as a result of combustion.As a further result, the need for one or more exhaust aftertreatment systems on the engine is circumvented. In this manner, the complexity and cost associated with maintaining and integrating systems such as catalytic converters, particulate filters, and selective catalytic reduction (SCR) units are eliminated. This simplifies the overall design of the hydrogen engine and contributes to enhanced efficiency and reliability. Additionally, by removing the dependence on exhaust aftertreatment systems, the engine can achieve a lower overall weight, further improving fuel efficiency and performance.Accordingly, a method is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.Optionally, the step of supplying the hydrogen, the oxygen gas, and the monatomic gas to the combustion chamber in the determined proportion comprises:- controlling the proportion of the supplied hydrogen, oxygen gas, and the monatomic gas by controlling a supply pressure in the gas inlet.Thereby, the proportion of the supplied hydrogen, oxygen gas, and the monatomic gas can be controlled in a simple and efficient manner so as to operate the hydrogen engine at or just below its maximum thermal load capacity, thereby obtaining high operational efficiency along with high torque and power density, while also preserving the structural integrity and longterm performance of the engine.Optionally, the engine comprises at least one inlet valve arranged in each cylinder, wherein the at least one inlet valve is configured to control the transfer of gas from the gas inlet into the combustion chamber, and wherein the step of supplying the hydrogen, the oxygen gas, and the monatomic gas to the combustion chamber in the determined proportion comprises: - controlling the proportion of the supplied hydrogen, oxygen gas, and the monatomic gas by controlling at least one of an opening time and a closing time of the at least one inlet valve.Thereby, the proportion of the supplied hydrogen, oxygen gas, and the monatomic gas can be controlled in an efficient and more precise manner so as to operate the hydrogen engine at or just below its maximum thermal load capacity, thereby obtaining high operational efficiency along with high torque and power density, while also preserving the structural integrity and long-term performance of the engine.Optionally, the step of supplying the hydrogen, the oxygen gas, and the monatomic gas to the combustion chamber in the determined proportion comprises:- supplying at least one of the hydrogen and the oxygen gas directly into the combustion chamber.Thereby, a more precise control of the proportion of the supplied hydrogen, oxygen gas, and the monatomic gas can be ensured under a wide range of operating conditions, including part-load scenarios of the hydrogen engine.Optionally, the step of supplying the hydrogen, the oxygen gas, and the monatomic gas to the combustion chamber in the determined proportion comprises:- supplying the at least one of the hydrogen and the oxygen gas at the end, or near the end, of a compression stroke of the piston.Thereby, the hydrogen engine can be operated with compression ignition, further ensuring high operational efficiency along with high torque and power density under a wide range of operating conditions, including part-load scenarios of the hydrogen engine.Optionally, the step of supplying the hydrogen, the oxygen gas, and the monatomic gas to the combustion chamber in the determined proportion comprises:- supplying one of the hydrogen and the oxygen gas at the end, or near the end, of a compression stroke of the piston, and- supplying the other of the hydrogen and the oxygen gas during an intake stroke of the piston.Thereby, the hydrogen engine can be operated with compression ignition, further ensuring high operational efficiency along with high torque and power density under a wide range of operating conditions, while having conditions for being manufactured and assembled in a cost-efficient manner.Optionally, the step of supplying the hydrogen, the oxygen gas, and the monatomic gas to the combustion chamber in the determined proportion comprises:- supplying hydrogen to the combustion chamber during an intake stroke of the piston, and- supplying the oxygen gas to the combustion chamber at the end, or near the end, of a compression stroke of the piston.Thereby, the need for using a compressor is circumvented for compressing the hydrogen prior to supplying the hydrogen to the hydrogen engine. This is because the pressure inside the combustion chamber is considerably lower during an intake stroke of the piston as compared to at the end, or near the end, of a compression stroke of the piston.Furthermore, the liquefaction of oxygen is much easier than the liquefaction of hydrogen since it has higher critical temperature compared to hydrogen, -147°C for oxygen vs -240°C for hydrogen. This means that the need for arranging a compressor for compressing the oxygen gas also can be circumvented by storing oxygen in liquified state for use by the hydrogen engine. As indicated, the liquefaction of oxygen is much easier than liquefaction of hydrogen. Also, the boil off rate of liquified oxygen is less of a problem compared to the boil off rate of liquified hydrogen. The term boil off rate refers to the amount of liquid that is evaporating from a storage tank due to heat leakage.A compressor configured to compress gas prior to supplying the gas to the combustion chamber at the end, or near the end, of a compression stroke of the piston requires the input of energy that has parasite effect on the hydrogen engine which reduces the overall efficiency of the hydrogen engine. Accordingly, by circumventing the need for such a compressor, the overall energy efficiency of the hydrogen engine can be significantly improved.The wording “at the end, or near the end, of a compression stroke of the piston, as used herein, may encompass that the gaseous mixture referred to is supplied within a maximum of 70 crank angle degrees, or a maximum of 40 crank angle degrees, from the top dead centre of the piston. According to some embodiments, this may include supplying the gaseous mixture within a maximum of 70 crank angle degrees, or a maximum of 40 crank angle degrees, before the top dead centre, and within a maximum of 40 crank angle degrees, or a maximum of 20 crank angle degrees, after the top dead centre of the piston.According to a second aspect of the present disclosure, the object is achieved by a computer program comprising instructions which, when the program is executed by a control arrangement of a hydrogen engine, cause the control arrangement to carry out the method according to some embodiments of the first aspect of the present disclosure. Since the computer program comprises instructions to cause the control arrangement to carry out the method according to some embodiments described herein, a computer program is provided which provides conditions for overcoming, or at least alleviating, at least some of the abovementioned drawbacks. As a result, the above-mentioned object is achieved.According to a third aspect of the present disclosure, the object is achieved by a computerreadable medium comprising instructions which, when executed by a control arrangement of a hydrogen engine, cause the control arrangement to carry out the method according to some embodiments of the first aspect of the present disclosure. Since the computer-readable medium comprises instructions to cause the control arrangement to carry out the method according to some embodiments described herein, a computer-readable medium is provided which provides conditions for overcoming, or at least alleviating, at least some of the abovementioned drawbacks. As a result, the above-mentioned object is achieved.According to a fourth aspect of the present disclosure, the object is achieved by a control arrangement configured to control operation of a hydrogen engine, the hydrogen engine comprising one or more cylinders, a piston arranged in each cylinder to delimit a combustion chamber inside the cylinder, an exhaust outlet and a gas inlet each connected to the combustion chamber, and a gas supply arrangement configured to supply hydrogen, oxygen gas, and a monatomic gas to the combustion chamber. The control arrangement is configured to:- obtain a desired torque quantity of the hydrogen engine,- obtain a maximum thermal load capacity of the hydrogen engine,- obtain a desired heat capacity ratio of a gas mixture charge in the combustion chamber based on the desired torque quantity and the maximum thermal load capacity,- determine the proportion of hydrogen, oxygen gas, and the monatomic gas that results in the desired heat capacity ratio, and- control the gas supply arrangement to supply the hydrogen, the oxygen gas, and the monatomic gas to the combustion chamber in the determined proportion.Thereby, the hydrogen engine can be operated at high efficiency, with high torque and power density, without imposing excessive thermal and mechanical stress on the engine. This is because by supplying the hydrogen, the oxygen gas, and the monatomic gas to the combustion chamber in the determined proportion, the hydrogen engine can operate at or just below its maximum thermal load capacity, thereby obtaining high operational efficiency along with high torque and power density. Additionally, the control arrangement enables the hydrogen engine to maintain operation at or just below its maximum thermal load capacity across the entire operating range, ensuring optimal efficiency under varying conditions.Furthermore, since the gas supply arrangement is configured to supply hydrogen, oxygen gas, and a monatomic gas to the combustion chamber, the need for utilizing carbon-based fuel is circumvented. In this manner, the release of carbon dioxide (CO2), carbon monoxide (CO), unburned hydrocarbons (HC), and particulate matter (PM) typically associated with traditional combustion engines can be eliminated. Accordingly, conditions are provided for obtaining a zero-emission hydrogen engine. In this context, the wording a zero-emission hydrogen engine refers to an engine that produces no emissions other than pure water as a result of combustion.As a further result, the need for one or more exhaust aftertreatment systems on the engine is circumvented. In this manner, the complexity and cost associated with maintaining and integrating systems such as catalytic converters, particulate filters, and selective catalytic reduction (SCR) units are eliminated. This simplifies the overall design of the hydrogen engine and contributes to enhanced efficiency and reliability. Additionally, by removing the dependence on exhaust aftertreatment systems, the engine can achieve a lower overall weight, further improving fuel efficiency and performance.Accordingly, a control arrangement is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.It will be appreciated that the various embodiments described for the method are all combinable with the control arrangement as described herein. That is, the control arrangement according to the fourth aspect of the invention may be configured to perform any one of the method steps of the method according to the first aspect of the invention.According to a fifth aspect of the present disclosure, the object is achieved by a hydrogen engine comprising one or more cylinders, a piston arranged in each cylinder to delimit a combustion chamber inside the cylinder, an exhaust outlet and a gas inlet each connected to the combustion chamber, a gas supply arrangement configured to supply hydrogen, oxygen gas, and a monatomic gas to the combustion chamber, and a control arrangement. The control arrangement is configured to:- obtain a desired torque quantity of the hydrogen engine,- obtain a maximum thermal load capacity of the hydrogen engine,- obtain a desired heat capacity ratio of a gas mixture charge in the combustion chamber based on the desired torque quantity and the maximum thermal load capacity, - determine the proportion of hydrogen, oxygen gas, and the monatomic gas that results in the desired heat capacity ratio, and- control the gas supply arrangement to supply the hydrogen, the oxygen gas, and the monatomic gas to the combustion chamber in the determined proportion.Thereby, the hydrogen engine can be operated at high efficiency, with high torque and power density, without imposing excessive thermal and mechanical stress on the engine. This is because by supplying the hydrogen, the oxygen gas, and the monatomic gas to the combustion chamber in the determined proportion, the hydrogen engine can operate at or just below its maximum thermal load capacity, thereby obtaining high operational efficiency along with high torque and power density. Additionally, the control arrangement enables the hydrogen engine to maintain operation at or just below its maximum thermal load capacity across the entire operating range, ensuring optimal efficiency under varying conditions.Furthermore, since the gas supply arrangement is configured to supply hydrogen, oxygen gas, and a monatomic gas to the combustion chamber, the need for utilizing carbon-based fuel is circumvented. In this manner, the release of carbon dioxide (CO2), carbon monoxide (CO), unburned hydrocarbons (HC), and particulate matter (PM) typically associated with traditional combustion engines can be eliminated. Accordingly, conditions are provided for obtaining a zero-emission hydrogen engine. In this context, the wording a zero-emission hydrogen engine refers to an engine that produces no emissions other than pure water as a result of combustion.As a further result, the need for one or more exhaust aftertreatment systems on the engine is circumvented. In this manner, the complexity and cost associated with maintaining and integrating systems such as catalytic converters, particulate filters, and selective catalytic reduction (SCR) units are eliminated. This simplifies the overall design of the hydrogen engine and contributes to enhanced efficiency and reliability. Additionally, by removing the dependence on exhaust aftertreatment systems, the engine can achieve a lower overall weight, further improving fuel efficiency and performance.Accordingly, a hydrogen engine is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.Optionally, the engine is a compression ignition engine. Thereby, a hydrogen engine is provided that is capable of operating with compression ignition further ensuring high operational efficiency along with high torque and power density under a wide range of operating conditions.Optionally, the engine comprises a loop assembly connecting the exhaust outlet to the gas inlet, thereby forming a closed loop that includes the exhaust outlet, the gas inlet, and the combustion chamber. Thereby, the hydrogen inside the combustion chamber can be combusted without the presence of atmospheric air, and thereby also the presence of nitrogen, which prevents the formation of nitrogen oxides (NOx). As a further result, the need for arranging one or more exhaust aftertreatment systems on the engine is further circumvented. In addition, the consumption of the monatomic gas can be eliminated, or at least significantly reduced.Optionally, the loop assembly comprises a separator unit configured to separate water from the monatomic gas. Thereby, reliable and efficient operation of the hydrogen engine can be ensured while obtaining water as the only emission from the hydrogen engine.Optionally, the monatomic gas is argon. Thereby, the use of argon, due to its chemical inertness and non-reactive properties, ensures that it does not interfere with the combustion process within the hydrogen engine. Argon is also more cost-effective compared to other monatomic gases, such as helium or neon, making it an economical choice while maintaining safety and performance in high-temperature operating conditions.According to a sixth aspect of the present disclosure, the object is achieved by a vehicle comprising a hydrogen engine according to the fifth aspect of the present disclosure. Since the vehicle comprises a hydrogen engine according to the fifth aspect of the present disclosure, a vehicle is provided comprising a hydrogen engine having zero-emission potential with the ability to operate at high efficiency, with high torque and power density, without imposing excessive thermal and mechanical stress on the engine.Furthermore, the need for one or more exhaust aftertreatment systems on the vehicle is circumvented. In this manner, the complexity and cost associated with maintaining and integrating systems such as catalytic converters, particulate filters, and selective catalytic reduction (SCR) units are eliminated. This simplifies the overall design of the vehicle and contributes to enhanced efficiency and reliability.Accordingly, a vehicle is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.Optionally, the vehicle is a heavy wheeled vehicle, such as a truck or a bus. Thereby, a heavy wheeled vehicle is provided having at least some of the above mentioned advantages.Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following detailed description.BRIEF DESCRIPTION OF THE DRAWINGSVarious aspects of the present disclosure, including its particular features and advantages, will be readily understood from the example embodiments discussed in the following detailed description and the accompanying drawings, in which:Fig. 1 schematically illustrates a vehicle according to some embodiments,Fig. 2 illustrates a cross sectional view of a hydrogen engine of the vehicle illustrated in Fig. 1 ,Fig. 3 illustrates a cross sectional view of a hydrogen engine according to some further embodiments,Fig. 4 illustrates a cross sectional view of a hydrogen engine according to some further embodiments,Fig. 5 schematically illustrates a method of operating a hydrogen engine, andFig. 6 illustrates a computer-readable medium.DETAILED DESCRIPTIONAspects of the present disclosure will now be described more fully. Like reference signs refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and / or clarity.Fig. 1 schematically illustrates a vehicle 2 according to some embodiments. According to the illustrated embodiments, the vehicle 2 is a truck, i.e., a type of heavy wheeled vehicle as well as a heavy commercial vehicle. According to further embodiments, the vehicle 2, as referred to herein, may be another type of heavy or lighter manned or unmanned vehicle for land or water propulsion, such as a lorry, bus, construction vehicle, tractor, car, boat, ship, or similar.The vehicle 2 comprises a hydrogen engine 1. As is further explained herein, the hydrogen engine 1 is a type of internal combustion engine configured to operate on hydrogen H2. Therefore, throughout this disclosure, the wording “hydrogen engine 1” may be replaced by the wording “internal combustion engine”. According to the illustrated embodiments, the hydrogen engine 1 is operably connected to driven wheels 27 of the vehicle 2. In other words, the hydrogen engine 1 is configured to provide motive power to the vehicle 2 via the driven wheels 27 of the vehicle 2.According to the illustrated embodiments, the vehicle 2 comprises two driven wheels 27 which constitute rear-wheels of the vehicle 2. The vehicle 2 further comprises two non-driven wheels 27’, which according to the illustrated embodiments constitute front-wheels of the vehicle 2. However, according to further embodiments, the vehicle 2 may comprise another configuration of driven and non-driven wheels.Fig. 2 illustrates a cross sectional view of the hydrogen engine 1 of the vehicle 2 illustrated in Fig. 1. For the reason of brevity and clarity, the hydrogen engine 1 is in some places herein referred to as “the combustion engine”, or simply “the engine 1”. Below, simultaneous reference is made to Fig. 1 and Fig. 2, if not indicated otherwise.Even though the engine 1 is described as being configured to provide motive power to a vehicle 2 according to embodiments herein, the engine 1, as referred to herein, may be configured to power a unit, system, or arrangement other than a vehicle, such as, for example, an electric generator.The engine 1 comprises one or more cylinders 3 and a piston 12 arranged in each cylinder 3 to delimit a combustion chamber 5 inside the cylinder 3. In Fig. 2, only one cylinder 3 of the engine 1 is seen and consequently also only one combustion chamber 5 and one piston 12. However, the engine 1 may comprise more than one cylinder 3 each delimiting a combustion chamber 5 together with a piston 12 arranged in the cylinder 3. The engine 1 may for example comprise four, six, or eight cylinders 3.The engine 1 further comprises a crankshaft 16. Each piston 12 of the engine 1 is connected to the crankshaft 16 via a respective connecting rod 13. The pistons 12 move forwards and backwards in the respective cylinder 3 between a top dead centre and a bottom dead centre upon rotation of the crankshaft 16.The engine 1 further comprises an exhaust outlet 7 and a gas inlet 9 each connected to the combustion chambers 5 of the engine 1. The exhaust outlet 7 may also be referred to as an exhaust outlet manifold, an exhaust manifold, or the like. Likewise, the gas inlet 9 may also be referred to as a gas inlet manifold, an inlet manifold, or the like.According to the illustrated embodiments, the engine 1 is a four-stroke hydrogen engine 1 which comprises at least one inlet valve 19 arranged in each cylinder 3. The at least one inlet valve 19 is configured to control the transfer of gas from the gas inlet 9 into the combustion chamber 5 as is further explained herein. The engine 1 further comprises an inlet valve control arrangement 29 configured to control each inlet valve 19 on the basis of a rotational position of the crankshaft 16.The engine 1 further comprises at least one exhaust valve 17 arranged in each cylinder 3. The at least one exhaust valve 17 is configured to control the transfer of gas from the combustion chamber 5 into the exhaust outlet 7. The engine 1 further comprises an exhaust valve control arrangement 27 configured to control each exhaust valve 17 on the basis of the rotational position of the crankshaft 16.In Fig. 2, the at least one inlet valve 19 is illustrated in an open position and the at least one exhaust valve 17 is illustrated in a closed position. In a closed position, each valve 17, 19 abuts against a respective valve seat to close fluid connection between the combustion chamber 5 and the respective gas inlet 9 and the exhaust outlet 7 respectively.The inlet valve control arrangement 29 is arranged to control the at least one inlet valve 19 between the closed position and an open position by displacing the at least one inlet valve 19 in a direction into the cylinder 3. A fluid connection is thereby opened between the gas inlet 9 and the combustion chamber 5. Likewise, the exhaust valve control arrangement 27 is arranged to control the at least one exhaust valve 17 between the closed position and an open position by displacing the at least one exhaust valve 17 in a direction into the cylinder 3. Thereby, a fluid connection is opened between the combustion chamber 5 and the exhaust outlet 7. Upon displacement of a valve 17, 19 from the closed position to the open position, the valve 17, 19 is lifted from its valve seat.The exhaust valve control arrangement 27 and the inlet valve control arrangement 29 may each comprise one or more camshafts rotatably connected to the crankshaft 16, wherein the camshafts comprise cam lobes arranged to displace valves 17, 19 to an open position by pressing on valve stems of the valves 17, 19 upon rotation of the camshaft. The exhaust valve control arrangement 27, and / or the inlet valve control arrangement 29, may according to further embodiments comprise electric, pneumatic, or hydraulic actuators arranged to control valves on the basis of the rotational position of the crankshaft 16. The rotational position of the crankshaft 16 may be obtained using data from a crank angle sensor.Moreover, the hydrogen engine 1 may comprise an inlet valve phase-shifting device and an exhaust valve phase-shifting device. The inlet valve phase-shifting device and the exhaust valve phase-shifting device may each comprise a hydraulic arrangement, for example using engine oil as hydraulic fluid, to phase-shift control of the valves 17, 19 in relation to the crankshaft 16. Such hydraulic arrangement may form part of a belt pulley (not illustrated) arranged to transfer rotation from the crankshaft 16 to a camshaft of the exhaust valve control arrangement 27 and / or the inlet valve control arrangement 29, wherein the hydraulic arrangement is arranged to regulate an angular relationship between a first portion of the belt pulley, being connected to the crankshaft 16, and a second portion of the belt pulley, being connected to the camshaft, in order to phase-shift control of the at least one inlet valve 19 and / or the at least one exhaust valve 17.In embodiments wherein the exhaust valve control arrangement 27 and / or the inlet valve control arrangement 29 comprises electric, pneumatic, or hydraulic actuators, the exhaust valve phase-shifting device and / or the inlet valve phase-shifting device may phase-shift control of the at least one valve 17, 19 in another manner, for example by an electronic phase-shift of control.According to the illustrated embodiments, the engine 1 is a compression ignition engine, i.e., a type of engine 1 that ignites the fuel, i.e., the hydrogen according to embodiments herein, through the heat generated by compressing the air in the cylinder, rather than relying on a spark. However, according to further embodiments, the engine 1 as referred to herein may be an Otto engine with a spark-ignition device configured to ignite the hydrogen in the combustion chamber 5.According to the illustrated embodiments, the hydrogen engine 1 comprises a loop assembly 11 connecting the exhaust outlet 7 to the gas inlet 9, thereby forming a closed loop 1 T that includes the exhaust outlet 7, the gas inlet 9, and the combustion chamber 5. Moreover, the hydrogen engine 1 comprises a monatomic gas Ar contained within the closed loop 1 T. In other words, the loop assembly 11 connects the exhaust outlet 7 to the gas inlet 9 such that the monatomic gas Ar is circulated within the closed loop 1 T upon operation of the hydrogen engine 1 , as is further explained herein.According to the illustrated embodiments, the monatomic gas Ar is Argon. However, according to further embodiments, the hydrogen engine 1 may comprise another type of monatomic gas contained within the closed loop 11’, such as helium (He), neon (Ne), krypton (Kr), or xenon (Xe). The term monatomic gas refers to a gas that exists as individual atoms rather than molecules made of two or more bonded atoms. These gases are often noble gases, characterized by their chemical inertness due to complete outer electron shells, which make them non-reactive under typical engine operating conditions. The non-reactive nature of monatomic gases ensures they do not participate in or interfere with the combustion process. Instead, they remain stable within the closed loop 11’, where they contribute to thermal management and stability, helping to maintain efficient and safe operation of the hydrogen engine 1.The hydrogen engine 1 further comprises a gas supply arrangement 6. As is further explained herein, the gas supply arrangement 6 is configured to supply hydrogen H2 and the monatomic gas Ar to the combustion chamber 5 of the hydrogen engine 1. Moreover, as is further explained herein, the gas supply arrangement 6 is configured to supply an oxygen gas O2 to the combustion chamber 5.In more detail, according to the embodiments illustrated in Fig. 2, the gas supply arrangement 6 comprises a monatomic gas tank At configured to accommodate the monatomic gas Ar. The monatomic gas tank At is also indicated in Fig. 1. The monatomic gas tank At may be a cryogenic tank configured to accommodate the monatomic gas tank At in liquid form or a pressure tank configured to accommodate pressurized monatomic gas tank At.The hydrogen engine 1 further comprises a monatomic gas injector Ai. According to the embodiments illustrated in Fig. 2, the monatomic gas injector Ai is configured to inject the monatomic gas Ar from the monatomic gas tank At into the gas inlet 9 of the hydrogen engine 1.Moreover, the gas supply arrangement 6 comprises a hydrogen tank H2t configured to accommodate hydrogen H2. The hydrogen tank H2t is also indicated in Fig. 1. The hydrogen tank H2t may be a cryogenic tank configured to accommodate hydrogen H2 in liquid form or a pressure tank configured to accommodate pressurized hydrogen H2.The hydrogen engine 1 comprises a first injector i1. According to the embodiments illustrated in Fig. 2, the first injector i1 is configured to inject hydrogen H2 from the hydrogen tank H2t into the gas inlet 9 of the hydrogen engine 1.As mentioned, the piston 12 is configured to reciprocate in the cylinder 3 between a top dead centre and a bottom dead centre. During an intake stroke of the piston 12, the piston 12 moves from the top dead centre towards the bottom dead centre. Moreover, the at least one inlet valve 19 is controlled to the open position during the intake stroke of the piston 12. In this manner, the monatomic gas Ar and the hydrogen H2 gas is sucked from the gas inlet 9 into the combustion chamber 5 during the intake stroke of the piston 12. Therefore, according to the embodiments illustrated in Fig. 2, the gas supply arrangement 6 can be said to be configured to supply hydrogen H2 and the monatomic gas Ar to the combustion chamber 5 during an intake stroke of the piston 12.The at least one inlet valve 19 is closed when the piston 12 is at the bottom dead centre. The compression stroke of the piston 12 refers to the subsequent stroke of the piston 12, in which the piston 12 moves from the bottom dead centre towards the top dead centre. Each of the at least one inlet valve 19 and the at least one exhaust valve 17 is controlled to the closed position during the compression stroke of the piston 12. In this manner, the monatomic gas Ar and the hydrogen H2 is compressed in the combustion chamber 5 during the compression stroke of the piston 12.According to the embodiments illustrated in Fig. 2, the gas supply arrangement 6 of the hydrogen engine 1 comprises an oxygen gas source O2t. The oxygen gas source O2t is also indicated in Fig. 1. The oxygen gas source O2t may comprise a cryogenic tank configured to accommodate oxygen O2 in liquid form or a pressure tank configured to accommodate pressurized oxygen O2.Furthermore, according to the embodiments illustrated in Fig. 2, the hydrogen engine 1 comprises a second injector i2. The second injector i2 is configured to supply the oxygen gas O2 from the oxygen gas source O2t directly into the combustion chamber 5 at the end, or near the end, of a compression stroke of the piston 12.The hydrogen engine 1 further comprises a control arrangement 21 configured to control operation of the hydrogen engine 1. The control arrangement 21 is configured toobtain a desired torque quantity of the hydrogen engine 1.The term desired torque quantity refers to the specific amount of torque that the hydrogen engine 1 is intended to produce, for example based on vehicle requirements or driver inputs. The desired torque quantity may vary according to factors such as acceleration demands, load conditions, or specific driving scenarios, such as hill climbing or overtaking. Achieving the desired torque quantity allows the engine to provide the necessary power output to meet these demands effectively.The control arrangement 21 can obtain the desired torque quantity from various sources within the vehicle’s systems. These sources may include direct inputs from the driver, such as throttle position or accelerator pedal signals, reflecting the driver’s acceleration or deceleration intentions. Additionally, in vehicles equipped with at least partially autonomous driving systems, such as a cruise control system, the control arrangement 21 may obtain the desired torque quantity from such at least partially autonomous driving system. The at least partially autonomous driving system may for example determine the desired torque quantity based on preset speed or distance settings. Higher-level control systems, such as the vehicle's drivetrain control unit or central vehicle control unit, may also contribute to defining the desired torque quantity based on parameters like speed, traction, and road conditions.The control arrangement 21 is further configured to obtain a maximum thermal load capacity of the hydrogen engine 1. The maximum thermal load capacity refers to the highest amount of heat energy the engine components can withstand during operation without risking thermal stress or damage. The control arrangement 21 can obtain this maximum thermal load capacity through pre-set engine specifications and / or real-time data, for example from temperature sensors within the hydrogen engine 1.Furthermore, the control arrangement 21 is configured to obtain a desired heat capacity ratio of a gas mixture charge in the combustion chamber 5 based on the desired torque quantity and the maximum thermal load capacity. The control arrangement 21 may be configured to obtain the desired heat capacity ratio of the gas mixture charge in the combustion chamber 5 by setting the desired heat capacity ratio based on the desired torque quantity and the maximum thermal load capacity. The setting of the desired heat capacity ratio may be performed such that maximum thermal load capacity is reached, or is nearly reached, upon operation of the hydrogen engine 1. In this context, the term “nearly reached” may be interpreted as meaning that the hydrogen engine 1 reaches a thermal load being more than 90% of the maximum thermal load capacity upon operation of the hydrogen engine 1.The control arrangement 21 is further configured to determine the proportion of hydrogen H2, oxygen gas O2, and the monatomic gas Ar that results in the desired heat capacity ratio. The control arrangement 21 may be configured to determine the proportion on the basis of data of thermodynamical properties of the hydrogen H2, the oxygen gas 02, and the monatomic gas Ar and / or of mixtures thereof. The control arrangement 21 may be configured to utilize mathematical equations, functions, tabular data, and / or other computational methods to calculate the proportion of hydrogen H2, oxygen gas O2, and the monatomic gas Ar that results in the desired heat capacity ratio.Moreover, according to embodiments herein, the control arrangement 21 is configured to control the gas supply arrangement 6, 6’, 6” to supply the hydrogen H2, the oxygen gas O2, and the monatomic gas Ar to the combustion chamber 5 in the determined proportion.Thereby, the hydrogen engine 1 can be operated at high efficiency, with high torque and power density, without imposing excessive thermal and mechanical stress on the engine 1. This is because by supplying the hydrogen H2, the oxygen gas 02, and the monatomic gas Ar to the combustion chamber 5 in the determined proportion, the hydrogen engine 1 can operate at or just below its maximum thermal load capacity, thereby obtaining high operational efficiency along with high torque and power density. Additionally, the control arrangement 21 enables the hydrogen engine 1 to maintain operation at or just below its maximum thermal load capacity across the entire operating range, ensuring optimal efficiency under varying conditions.Furthermore, since the gas supply arrangement is configured to supply hydrogen H2, the oxygen gas O2, and the monatomic gas Ar to the combustion chamber 5, the need for utilizing carbon-based fuel is circumvented. In this manner, the release of carbon dioxide (CO2), carbon monoxide (CO), unburned hydrocarbons (HC), and particulate matter (PM) typically associated with traditional combustion engines can be eliminated. Accordingly, conditions are provided for obtaining a zero-emission hydrogen engine 1. In this context, the wording a zero-emission hydrogen engine 1 refers to an engine that produces no emissions other than pure water as a result of combustion.As understood from the above described, the compression heat and the oxygen gas O2 initiate combustion of the hydrogen H2 inside the combustion chamber 5. The expansion stroke refers to the stroke following the compression stroke, during which the piston 12 moves from the top dead centre to the bottom dead centre. During the expansion stroke, each of the at least one inlet valve 19 and at least one exhaust valve 17 is controlled to remain in the closed position. In this manner, at least part of the increased pressure and temperature resulting from the combustion of hydrogen can be transferred to the crankshaft 16 of the hydrogen engine 1 to perform useful work.The exhaust stroke refers to the stroke following the expansion stroke, during which the piston 12 moves from the bottom dead centre to the top dead centre. During this stroke, the at least one exhaust valve 17 is controlled to open, allowing the combustion gases to be expelled from the combustion chamber 5 into the exhaust outlet 7. The at least one inlet valve 19 remains in the closed position during the exhaust stroke. This process enables the removal of exhaust gases from the combustion chamber 5, preparing the combustion chamber 5 for the next intake of hydrogen H2 in the subsequent intake stroke.The combustion of hydrogen H2, i.e., the chemical reaction between hydrogen H2 and oxygen O2 results in water H2O. Accordingly, the exhaust gas expelled from the combustion chamber 5 into the exhaust outlet 7 during the exhaust stroke of the piston 12 is composed of water H2O vapor and the monatomic gas Ar.As can be seen in Fig. 2, according to the illustrated embodiments, the hydrogen engine 1 comprises a separator unit 15. The separator unit 15 is configured to separate water H2O from the monatomic gas Ar in the closed-loop 11'. In other words, the separator 15 is configured to remove water H2O from the closed-loop 11' as the monatomic gas Ar circulates within the closed-loop 11'. As can be seen in Fig. 2, according to the illustrated embodiments, the separator 15 is arranged within the loop assembly 11 such that the exhaust gas circulating in the closed-loop 11' flows through the separator 15.The separator 15 may comprise a heat exchanger for cooling the exhaust gas flowing through the separator to thereby condense water H2O in the exhaust gas thereby separating the water H2O from the monatomic gas Ar. The heat exchanger of the separator 15 may comprise an evaporator or may be cooled using an evaporator. The evaporator may be part of a heat pump circuit that comprises the evaporator, a condenser, a compressor, an expansion valve arranged upstream of the evaporator, and the like components. As an alternative, or in addition, the separator 15 may employ centrifugal forces or cyclonic action and / or coalescing filters to isolate and collect the water H2O, preventing it from remaining in the inert gas flow. The separated water H2O is either stored in a designated reservoir or expelled from the hydrogen engine 1 as required.As a further result of the hydrogen engine 1 according to embodiments herein, the need for one or more exhaust aftertreatment systems on the engine 1 is circumvented. In this manner, the complexity and cost associated with maintaining and integrating systems such as catalytic converters, particulate filters, and selective catalytic reduction (SCR) units are eliminated. This simplifies the overall design of the hydrogen engine 1 and contributes to enhanced efficiency and reliability. Additionally, by removing the dependence on exhaust aftertreatment systems, the engine 1 can achieve a lower overall weight, further improving fuel efficiency and performance.That is, since the hydrogen engine 1 comprises the monatomic gas Ar contained within the closed loop, the hydrogen H2 inside the combustion chamber 5 can be combusted without the presence of atmospheric air, and thereby also the presence of nitrogen, which eliminates the formation of nitrogen oxides (NOx). Additionally, by eliminating the need for any carbonbased fuels, the hydrogen engine 1 eliminates the release of carbon dioxide (CO2), carbon monoxide (CO), unburned hydrocarbons (HC), and particulate matter (PM) typically associated with traditional combustion engines.Moreover, since the gas supply arrangement 6 is configured to supply the oxygen gas O2 into the combustion chamber 5 at the end, or near the end, of a compression stroke of the piston 12, and the hydrogen H2 during the intake stroke of the piston 12, a hydrogen engine 1 is provided circumventing the need for a compressor configured to compress the hydrogen H2 prior to supplying the hydrogen to the hydrogen engine 1. This is because the pressure inside the combustion chamber 5 is considerably lower during an intake stroke of the piston 12 as compared to at the end, or near the end, of a compression stroke of the piston 12.Furthermore, the liquefaction of oxygen O2 is much easier than the liquefaction of hydrogen H2 since it has higher critical temperature compared to hydrogen, -147°C for oxygen vs -240°C for hydrogen. This means that the need for arranging a compressor for compressing the oxygen gas O2 also can be circumvented by storing oxygen O2 in liquified state for use by the hydrogen engine 1. As indicated, the liquefaction of oxygen O2 is much easier than liquefaction of hydrogen H2. Also, the boil off rate of liquified oxygen O2 is less of a problem compared to the boil off rate of liquified hydrogen. The term boil off rate refers to the amount of liquid that is evaporating from a storage tank due to heat leakage.A compressor configured to compress gas prior to supplying the gas to the combustion chamber 5 at the end, or near the end, of a compression stroke of the piston 12 requires the input of energy that has parasite effect on the hydrogen engine 1 which reduces the overall efficiency of the hydrogen engine 1. Accordingly, by circumventing the need for such a compressor, the overall energy efficiency of the hydrogen engine 1 can be significantly improved.Another potential problem with supplying hydrogen H2 to the combustion chamber 5 during the intake stroke of the piston 12 and supplying oxygen O2 to the combustion chamber 5 at the end, or near the end, of the compression stroke could be that that the oxygen O2 won’t have enough time to completely react with hydrogen H2 inside the combustion chamber 5. If so, some oxygen will end-up in the exhaust outlet 7 which will be sent back to the gas inlet 9 in the closed loop 11’ engine solution. This can result in pre-ignition or knocking in the engine 1. Moreover, a mixture between oxygen O2 and hydrogen H2 in the closed loop 1 T could potentially be dangerous because its flammability.However, these potential problems are overcome by the hydrogen engine 1 according to the embodiments illustrated in Fig. 2, since the gas supply arrangement 6 is configured to supply the oxygen gas O2 to the combustion chamber 5 which can ensure that the oxygen O2 completely reacts with the supplied hydrogen H2. Thus, as a result, a hydrogen engine 1 is provided having conditions for increased efficiency and a reduced tendency of pre-ignition and knocking.Moreover, according to some embodiments, the control arrangement 21 is configured to operate the gas supply arrangement 6 in a fuel rich manner, meaning that more hydrogen H2 is supplied to the combustion chamber 5 than the amount needed to achieve the stoichiometric ratio between hydrogen H2 and oxygen O2. This fuel-rich operation provides an excess of hydrogen H2 relative to oxygen O2, which can influence combustion characteristics such as flame speed and temperature. In addition, in this manner, it can be further ensured that no oxygen O2 is exhausted from the combustion chamber 5 via the at least one exhaust valve 17.Alternatively, according to some embodiments, the control arrangement 21 is configured to operate the gas supply arrangement 6 in an oxygen-rich manner, supplying more oxygen O2 to the combustion chamber 5 than the amount needed to achieve the stoichiometric ratio between hydrogen H2 and oxygen O2. This oxygen-rich operation provides an excess of oxygen O2 relative to hydrogen H2, which can ensure that no hydrogen H2 is exhausted from the combustion chamber 5 via the at least one exhaust valve 17.According to some embodiments, the control arrangement 21 is configured to control the proportion of the supplied hydrogen H2, oxygen gas O2, and the monatomic gas Ar by controlling a supply pressure in the gas inlet 9. The term “supply pressure” in this context means the pressure in the gas inlet 9 of the hydrogen engine 1 upon opening of the at least one inlet valve 9. The supply pressure in the gas inlet 9 may be controlled by controlling the amount of gas supplied to the gas inlet 9 by the first injector i1 and / or the monatomic gas injector Ai. Moreover, according to some embodiments, the hydrogen engine 1 may comprise a compressor configured to compress gas to the gas inlet 9 of the hydrogen engine 1. Such a compressor may for example be a compressor of a turbocharger or a mechanically driven compressor. In such embodiments, the control arrangement 21 may be configured to control the supply pressure in the gas inlet 9 by controlling the operation rate of the compressor.Furthermore, according to some embodiments, the control arrangement 21 is configured to control the proportion of the supplied hydrogen H2, oxygen gas O2, and the monatomic gas Ar by controlling at least one of an opening time and a closing time of the at least one inlet valve 19. In such embodiments, the control arrangement 21 may be configured to control at least one of an opening time and a closing time of the at least one inlet valve 19 by controlling the operation of the inlet valve control arrangement 29.Fig. 3 illustrates a cross sectional view of a hydrogen engine 1' according to some further embodiments. As indicated in Fig. 1, the vehicle 2 may comprise a hydrogen engine 1' according to the embodiments illustrated in Fig. 3. The hydrogen engine 1' according to the embodiments illustrated in Fig. 3 comprises the same features, functions, and advantages as the hydrogen engine 1 according to the embodiments illustrated in Fig. 2, with some differences explained below. For reasons of brevity and clarity, only the differences are explained in detail below.According to the embodiments illustrated in Fig. 3, the gas supply arrangement 6’ of the hydrogen engine 1' is configured to supply the oxygen gas O2 during an intake stroke of the piston 12 and the hydrogen H2 at the end, or near the end, of a compression stroke of the piston 12.That is, in more detail, according to the embodiments illustrated in Fig. 3, the first injector i1 is connected to the oxygen gas source O2t. The oxygen gas O2 therefrom is thus injected by the first injector i1 into the gas inlet 9. When the at least one inlet valve 19 is opened during the intake stroke of the piston 12, the oxygen gas O2 is transferred from the gas inlet 9 into the combustion chamber 5.Each of the at least one inlet valve 19 and the at least one exhaust valve 17 is controlled to the closed position in the subsequent compression stroke of the piston 12. In this manner, the inert gas Ar and the oxygen gas O2 is compressed in the combustion chamber 5 during the compression stroke of the piston 12 according to the embodiments illustrated in Fig. 3.As can be seen in Fig. 3, the hydrogen tank H2t is connected to the second injector i2, wherein the second injector i2 is configured to supply the hydrogen H2 directly into the cylinder at the end, or near the end, of a compression stroke of the piston 12. In this manner, combustion of the hydrogen H2 is initiated by the compression heat in the combustion chamber 5 during the intake stroke of the piston 12.Thus, also in this manner, a hydrogen engine 1' is provided with the ability to operate at high efficiency, with high torque and power density, without imposing excessive thermal and mechanical stress on the engine 1.A drawback with the engine 1' according to the embodiments illustrated in Fig. 3, as compared to the engine 1 according to the embodiments illustrated in Fig. 2, is that the hydrogen H2 is injected into the combustion chamber 5 when the pressure in the combustion chamber 5 is relatively high. Therefore, the hydrogen engine 1' according to the embodiments illustrated in Fig. 3 may need a compressor for compressing the hydrogen H2 before it is injected into the combustion chamber 5, and / or a cryogenic storage solution for the hydrogen H2 in the hydrogen tank H2t.According to the embodiments illustrated in Fig. 3, the control arrangement 21 may be configured to operate the fuel supply arrangement 6’ in an oxygen-rich manner, supplying more oxygen O2 to the gas inlet 9 than the amount needed to achieve the stoichiometric ratio between hydrogen H2 and oxygen O2. Moreover, in these embodiments, the control arrangement 21 may be configured to operate the fuel supply arrangement 6’ to supply hydrogen H2 in an amount set to meet the desired torque quantity of the hydrogen engine 1’.According to the embodiments illustrated in Fig. 3, the control arrangement 21 may be configured to operate the fuel supply arrangement 6 in a hydrogen-rich manner, supplying more hydrogen H2 to the gas inlet 9 than the amount needed to achieve the stoichiometric ratio between hydrogen H2 and oxygen O2. Moreover, in these embodiments, the control arrangement 21 may be configured to operate the fuel supply arrangement 6’ to supply oxygen O2 in an amount set to meet the desired torque quantity of the hydrogen engine 1.Fig. 4 illustrates a cross sectional view of a hydrogen engine 1” according to some further embodiments. As indicated in Fig. 1, the vehicle 2 may comprise a hydrogen engine 1” according to the embodiments illustrated in Fig. 4. The hydrogen engine 1” according to the embodiments illustrated in Fig. 4 comprises the same features, functions, and advantages as the hydrogen engine 1 according to the embodiments illustrated in Fig. 2, with some differences explained below. For reasons of brevity and clarity, only the differences are explained in detail below.According to the embodiments illustrated in Fig. 4, each of the first and second injectors i1 , i2 of the gas supply arrangement 6” is configured to supply gas directly into the combustion chamber 5 of the hydrogen engine 1”.In these embodiments, the gas supply arrangement 6” may be configured to supply one of the hydrogen H2 and the oxygen gas O2 during an intake stroke of the piston 12, and the other of the hydrogen H2 and the oxygen gas O2 at the end, or near the end, of a compression stroke of the piston 12.According to the embodiments illustrated in Fig. 4, only the inert gas Ar is conducted into the combustion chamber 5 from the gas inlet 9 during the intake stroke of the piston 12, wherein one of the hydrogen H2 and the oxygen gas O2 is supplied directly into the combustion chamber 5 during the intake stroke of the piston 12.Preferably, the hydrogen H2 is supplied directly into the combustion chamber 5 during the intake stroke of the piston 12 using the second injector i2, wherein the oxygen gas O2 is supplied directly into the combustion chamber 5 by the first injector i1 at the end, or near the end, of a compression stroke of the piston 12.In this manner, the need for a compressor compressing the hydrogen H2 prior to supplying it to the combustion chamber 5 is eliminated, as well as the need for storing the hydrogen H2 using a cryogenic storage solution.However, according to some further embodiments, the engine 1” according to the embodiments illustrated in Fig. 4 may be configured to supply the oxygen gas O2 directly into the combustion chamber 5 during the intake stroke of the piston 12 using the first injector i1, wherein hydrogen H2 is supplied directly into the combustion chamber 5 by the second injector i2 at the end, or near the end, of a compression stroke of the piston 12.Since the hydrogen engine 1” according to the embodiments illustrated in Fig. 4 is configured to supply the oxygen gas O2 to the combustion chamber 5, a hydrogen engine 1” is provided with the ability to operate at high efficiency, with high torque and power density, without imposing excessive thermal and mechanical stress on the engine 1.As indicated above, even though the engine 1 , 1’, 1” is described as being configured to provide motive power to a vehicle 2 according to the illustrated embodiments, the engine 1, 1’, 1”, as referred to herein, may be configured to power a unit, system, or arrangement other than a vehicle, such as, for example, an electric generator.The wording “at the end, or near the end, of a compression stroke of the piston 12”, as used herein, may encompass that the gaseous mixture referred to is supplied within a maximum of 70 crank angle degrees, or a maximum of 40 crank angle degrees, from the top dead centre of the piston 12. According to some embodiments, this may include supplying the gaseous mixture within a maximum of 70 crank angle degrees, or a maximum of 40 crank angle degrees, before the top dead centre, and within a maximum of 40 crank angle degrees, or a maximum of 20 crank angle degrees, after the top dead centre of the piston 12.Since each of the first injector i1 and the second injector i2 is configured to supply a gaseous substance, each of the first injector i1 and the second injector i2 may also be referred to as a gas injector, a gas injector nozzle, a gas nozzle, or similar. Accordingly, according to embodiments herein, gas supply arrangement 6, 6’, 6” is configured to supply hydrogen gas H2 to the combustion chamber 5. Therefore, the wording “hydrogen H2” as used herein, may be replaced by the wording "hydrogen gas H2”.Fig. 5 schematically illustrates a method 100 of operating a hydrogen engine. The hydrogen engine may be a hydrogen engine 1, 1', 1” according to the embodiments illustrated in Fig. 2 - Fig. 4, which may be comprised in a vehicle 2 according to the embodiments illustrated in Fig. 1. Therefore, below, simultaneous reference is made to Fig. 1 - Fig. 5, if not indicated otherwise.The method 100 is a method of operating a hydrogen engine 1 , 1', 1”, the hydrogen engine 1, 1', 1” comprising one or more cylinders 3, a piston 12 arranged in each cylinder 3 to delimit a combustion chamber 5 inside the cylinder 3, an exhaust outlet 7 and a gas inlet 9 each connected to the combustion chamber 5, and a gas supply arrangement 6, 6’, 6” configured to supply hydrogen H2, oxygen gas O2, and a monatomic gas Ar to the combustion chamber 5.The method 100 comprises the steps of:- obtaining 110 a desired torque quantity of the hydrogen engine 1 , 1', 1”,- obtaining 120 a maximum thermal load capacity of the hydrogen engine 1, T, 1”, - obtaining 130 a desired heat capacity ratio of a gas mixture charge in the combustion chamber 5 based on the desired torque quantity and the maximum thermal load capacity,- determining 140 the proportion of hydrogen H2, oxygen gas O2, and the monatomic gas Ar that results in the desired heat capacity ratio, and- supplying 150 the hydrogen H2, the oxygen gas O2, and the monatomic gas Ar to the combustion chamber 5 in the determined proportion.According to some embodiments, the step of supplying 150 the hydrogen H2, the oxygen gas O2, and the monatomic gas Ar to the combustion chamber 5 in the determined proportion comprises:- controlling 152 the proportion of the supplied hydrogen H2, oxygen gas 02, and the monatomic gas Ar by controlling a supply pressure in the gas inlet 9.According to some embodiments, the engine 1, 1', 1” comprises at least one inlet valve 19 arranged in each cylinder 3, wherein the at least one inlet valve 19 is configured to control the transfer of gas from the gas inlet 9 into the combustion chamber 5, and wherein the step of supplying 150 the hydrogen H2, the oxygen gas O2, and the monatomic gas Ar to the combustion chamber 5 in the determined proportion comprises:- controlling 154 the proportion of the supplied hydrogen H2, oxygen gas 02, and the monatomic gas Ar by controlling at least one of an opening time and a closing time of the at least one inlet valve 19.The step of supplying 150 the hydrogen H2, the oxygen gas O2, and the monatomic gas Ar to the combustion chamber 5 in the determined proportion may comprise:- supplying 155 at least one of the hydrogen H2 and the oxygen gas 02 directly into the combustion chamber 5.According to some embodiments, the step of supplying 150 the hydrogen H2, the oxygen gas O2, and the monatomic gas Ar to the combustion chamber 5 in the determined proportion comprises:supplying 156 the at least one of the hydrogen H2 and the oxygen gas 02 at the end, or near the end, of a compression stroke of the piston 12.According to some embodiments, the step of supplying 150 the hydrogen H2, the oxygen gas O2, and the monatomic gas Ar to the combustion chamber 5 in the determined proportion comprises:supplying 157 one of the hydrogen H2 and the oxygen gas 02 at the end, or near the end, of a compression stroke of the piston 12, andsupplying 159 the other of the hydrogen H2 and the oxygen gas 02 during an intake stroke of the piston 12.According to some embodiments, the step of supplying 150 the hydrogen H2, the oxygen gas O2, and the monatomic gas Ar to the combustion chamber 5 in the determined proportion comprises:- supplying 157’ hydrogen H2 to the combustion chamber 5 during an intake stroke of the piston 12, andsupplying 159’ the oxygen gas 02 to the combustion chamber 5 at the end, or near the end, of a compression stroke of the piston 12.It will be appreciated that the various embodiments described for the method 100 are all combinable with the control arrangement 21 as described herein. That is, the control arrangement 21 may be configured to perform any one of the method steps 110, 120, 130, 140, 150, 152, 154, 155, 156, 157, 157’, 159, and 159’.Fig. 6 illustrates a computer-readable medium 200 comprising instructions which, when executed by a computer, cause the computer to carry out the method 100 according to some embodiments of the present disclosure. According to some embodiments, the computerreadable medium 200 comprises a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method 100 according to some embodiments. The computer may be comprised in the control arrangement 21.One skilled in the art will appreciate that the method 100 of operating a hydrogen engine 1 , 1', 1” may be implemented by programmed instructions. These programmed instructions are typically constituted by a computer program, which, when it is executed in the control arrangement 21, ensures that the control arrangement 21 carries out the desired control, such as the method steps 110, 120, 130, 140, 150, 152, 154, 155, 156, 157, 157’, 159, and 159’ described herein. The computer program is usually part of a computer program product which comprises a suitable digital storage medium on which the computer program is stored, such as the computer-readable medium 200 illustrated in Fig. 6. In other words, the computer program product may be a computer readable medium 200 and the computer program may be stored in the computer readable medium 200.The control arrangement 21 may comprise a computer which may take the form of substantially any suitable type of hardware or hardware / firmware device implemented using processing circuity such as, but not limited to, a processor, Central Processing Unit (CPU), a controller, an arithmetic logic unit (ALU), a digital signal processor, an Application Specific Integrated Circuit (ASIC), a circuit for digital signal processing (digital signal processor, DSP), a microcomputer, a field programmable gate array (FPGA), a System-on-Chip (SoC), a programmable logic unit, a microprocessor, an application-specific integrated circuit, or any other device capable of electronically performing operations in a defined manner, or other processing logic that may interpret and execute instructions. The herein utilised expression “computer” may represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above.The control arrangement 21 may further comprise a memory unit, wherein the computer may be connected to the memory unit, which may provide the computer with, for example, stored program code and / or stored data which the computer may need to enable it to do calculations. The computer may also be adapted to store partial or final results of calculations in the memory unit. The memory unit may comprise a physical device utilised to store data or programs, i.e., sequences of instructions, on a temporary or permanent basis. According to some embodiments, the memory unit may comprise integrated circuits comprising silicon-based transistors. The memory unit may comprise e.g. a memory card, a flash memory, a USB memory, a hard disc, or another similar volatile or non-volatile storage unit for storing data such as e.g. ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), etc. in different embodiments.The control arrangement 21 is connected to components of the hydrogen engine 1, 1', 1” and / or the vehicle 2 for receiving and / or sending input and output signals. These input and output signals may comprise waveforms, pulses, or other attributes which the input signal receiving devices can detect as information and which can be converted to signals processable by the control arrangement 21. These signals may then be supplied to the computer. One or more output signal sending devices may be arranged to convert calculation results from the computer to output signals for conveying to other parts of the vehicle's control system and / or the component or components for which the signals are intended. Each of the connections to the respective components of the vehicle 2 for receiving and sending input and output signals may take the form of one or more from among a cable, a data bus, e.g. a CAN (controller area network) bus, a MOST (media orientated systems transport) bus or some other bus configuration, or a wireless connection.In the embodiments illustrated, the hydrogen engine 1 , 1’, 1” comprises a control arrangement 21 but might alternatively be implemented wholly or partly in two or more control arrangements, two or more control arrangements, or two or more control units.Control systems in modern vehicles generally comprise a communication bus system consisting of one or more communication buses for connecting a number of electronic control units (ECUs), or controllers, to various components on board the vehicle. Such a control system may comprise a large number of control units and taking care of a specific function may be shared between two or more of them. Vehicles and engines of the type here concerned are therefore often provided with significantly more control arrangements than depicted in Fig. 2 - Fig. 4, as one skilled in the art will surely appreciate.The computer-readable medium 200 may be provided for instance in the form of a data carrier carrying computer program code for performing at least some of the method steps 110, 120, 130, 140, 150, 152, 154, 155, 156, 157, 157’, 159, and 159’ according to some embodiments of the method 100 when being loaded into one or more computers of the control arrangement 21. The data carrier may be, e.g. a CD ROM disc, as is illustrated in Fig. 6, or a ROM (read-only memory), a PROM (programable read-only memory), an EPROM (erasable PROM), a flash memory, an EEPROM (electrically erasable PROM), a hard disc, a memory stick, an optical storage device, a magnetic storage device or any other appropriate medium such as a disk or tape that may hold machine readable data in a non-transitory manner. Accordingly, in some embodiments, the computer-readable medium 200 may be a non-transitory computer-readable medium, such as a tangible electronic, magnetic, optical, infrared, electromagnetic, and / or semiconductor system, apparatus, and / or device. The computer-readable medium 200 may furthermore be provided as computer program code on a server and may be downloaded to the control arrangement 21 remotely, e.g., over an Internet or an intranet connection, or via other wired or wireless communication systems.It is to be understood that the foregoing is illustrative of various example embodiments and that the invention is defined only by the appended independent claims. A person skilled in the art will realize that the example embodiments may be modified, and that different features of the example embodiments may be combined to create embodiments other than those described herein, without departing from the scope of the present invention, as defined by the appended independent claims.As used herein, the term "comprising" or "comprises" is open-ended, and includes one or more stated features, elements, steps, components, or functions but does not preclude the presence or addition of one or more other features, elements, steps, components, functions, or groups thereof.

Claims

1. A method (100) of operating a hydrogen engine (1, 1', 1 ”), the hydrogen engine (1 , 1 1”) comprising:one or more cylinders (3),- a piston (12) arranged in each cylinder (3) to delimit a combustion chamber (5) inside the cylinder (3),an exhaust outlet (7) and a gas inlet (9) each connected to the combustion chamber (5), and- a gas supply arrangement (6, 6’, 6”) configured to supply hydrogen (H2), oxygen gas (O2), and a monatomic gas (Ar) to the combustion chamber (5),wherein the method (100) comprises the steps of:obtaining (110) a desired torque quantity of the hydrogen engine (1, 1', 1 ”), obtaining (120) a maximum thermal load capacity of the hydrogen engine (1, 1', 1 ”), obtaining (130) a desired heat capacity ratio of a gas mixture charge in the combustion chamber (5) based on the desired torque quantity and the maximum thermal load capacity,determining (140) the proportion of hydrogen (H2), oxygen gas (O2), and the monatomic gas (Ar) that results in the desired heat capacity ratio, andsupplying (150) the hydrogen (H2), the oxygen gas (O2), and the monatomic gas (Ar) to the combustion chamber (5) in the determined proportion.

2. The method (100) according to claim 1 , wherein the step of supplying (150) the hydrogen (H2), the oxygen gas (O2), and the monatomic gas (Ar) to the combustion chamber (5) in the determined proportion comprises:- controlling (152) the proportion of the supplied hydrogen (H2), oxygen gas (O2), and the monatomic gas (Ar) by controlling a supply pressure in the gas inlet (9).

3. The method (100) according to claim 1 or 2, wherein the engine (1, 1', 1”) comprises at least one inlet valve (19) arranged in each cylinder (3), wherein the at least one inlet valve (19) is configured to control the transfer of gas from the gas inlet (9) into the combustion chamber (5), and wherein the step of supplying (150) the hydrogen (H2), the oxygen gas (O2), and the monatomic gas (Ar) to the combustion chamber (5) in the determined proportion comprises:controlling (154) the proportion of the supplied hydrogen (H2), oxygen gas (O2), and the monatomic gas (Ar) by controlling at least one of an opening time and a closing time of the at least one inlet valve (19).

4. The method (100) according to any one of the preceding claims, wherein the step of supplying (150) the hydrogen (H2), the oxygen gas (O2), and the monatomic gas (Ar) to the combustion chamber (5) in the determined proportion comprises:supplying (155) at least one of the hydrogen (H2) and the oxygen gas (O2) directly into the combustion chamber (5).

5. The method (100) according to any one of the preceding claims, wherein the step of supplying (150) the hydrogen (H2), the oxygen gas (O2), and the monatomic gas (Ar) to the combustion chamber (5) in the determined proportion comprises:- supplying (156) the at least one of the hydrogen (H2) and the oxygen gas (O2) at the end, or near the end, of a compression stroke of the piston (12).

6. The method (100) according to any one of the preceding claims, wherein the step of supplying (150) the hydrogen (H2), the oxygen gas (O2), and the monatomic gas (Ar) to the combustion chamber (5) in the determined proportion comprises:supplying (157) one of the hydrogen (H2) and the oxygen gas (O2) at the end, or near the end, of a compression stroke of the piston (12), andsupplying (159) the other of the hydrogen (H2) and the oxygen gas (O2) during an intake stroke of the piston (12).

7. The method (100) according to any one of the preceding claims, wherein the step of supplying (150) the hydrogen (H2), the oxygen gas (O2), and the monatomic gas (Ar) to the combustion chamber (5) in the determined proportion comprises:supplying (157’) hydrogen (H2) to the combustion chamber (5) during an intake stroke of the piston (12), andsupplying (159’) the oxygen gas (O2) to the combustion chamber (5) at the end, or near the end, of a compression stroke of the piston (12).

8. A computer program comprising instructions which, when the program is executed by a control arrangement (21) of a hydrogen engine (1, 1 ’, 1 ”), cause the control arrangement (21) to carry out the method (100) according to any one of the claims 1 - 7.

9. A computer-readable medium (200) comprising instructions which, when executed by a control arrangement (21) of a hydrogen engine (1, 1’, 1”), cause the control arrangement (21) to carry out the method (100) according to any one of the claims 1 - 7.

10. A control arrangement (21) configured to control operation of a hydrogen engine (1, 1’, 1”), the hydrogen engine (1, 1’, 1”) comprising:one or more cylinders (3),a piston (12) arranged in each cylinder (3) to delimit a combustion chamber (5) inside the cylinder (3),an exhaust outlet (7) and a gas inlet (9) each connected to the combustion chamber (5), and- a gas supply arrangement (6, 6’, 6”) configured to supply hydrogen (H2), oxygen gas (O2), and a monatomic gas (Ar) to the combustion chamber (5),wherein the control arrangement (21) is configured to:obtain a desired torque quantity of the hydrogen engine (1, 1', 1 "),obtain a maximum thermal load capacity of the hydrogen engine (1, 1’, 1”), obtain a desired heat capacity ratio of a gas mixture charge in the combustion chamber (5) based on the desired torque quantity and the maximum thermal load capacity,determine the proportion of hydrogen (H2), oxygen gas (O2), and the monatomic gas (Ar) that results in the desired heat capacity ratio, andcontrol the gas supply arrangement (6, 6’, 6”) to supply the hydrogen (H2), the oxygen gas (O2), and the monatomic gas (Ar) to the combustion chamber (5) in the determined proportion.

11. A hydrogen engine (1, 1’, 1 ”) comprising:- one or more cylinders (3),a piston (12) arranged in each cylinder (3) to delimit a combustion chamber (5) inside the cylinder (3),an exhaust outlet (7) and a gas inlet (9) each connected to the combustion chamber(5),a gas supply arrangement (6, 6’, 6”) configured to supply hydrogen (H2), oxygen gas (O2), and a monatomic gas (Ar) to the combustion chamber (5), and- a control arrangement (21) according to claim 10.

12. The engine (1, 1', 1”) according to claim 11 , wherein the engine (1, 1', 1”) is a compression ignition engine.

13. The engine (1, 1', 1”) according to claim 11 or 12, wherein the engine (1, 1', 1”) comprises a loop assembly (11) connecting the exhaust outlet (7) to the gas inlet (9), thereby forming a closed loop (1 T) that includes the exhaust outlet (7), the gas inlet (9), and the combustion chamber (5).

14. The engine (1, 1', 1”) according to claim 13, wherein the loop assembly (11) comprises a separator unit (15) configured to separate water (H2O) from the monatomic gas (Ar).

15. The engine (1, 1', 1”) according to any one of the claims 11 - 14, wherein the monatomic gas (Ar) is argon.

16. A vehicle (2) comprising a hydrogen engine (1 , 1', 1 ”) according to any one of the claims 11 - 15.

17. The vehicle (2) according to claim 16, wherein the vehicle (2) is a heavy wheeled vehicle, such as a truck or a bus.