Fuel-management system for a hydrogen vehicle

Abstract

The invention relates to a fuel-management system (20) for a hydrogen-powered machine, which machine comprises a fuel-supply system (3) for supplying hydrogen fuel from at least one fuel tank (1) to a power source (6) of the machine when the machine is in an operating state. In order to propose an improved fuel management for a non-operating period of a hydrogen-powered machine, the invention provides that the fuel-management system (20) is adapted to transfer hydrogen fuel from at least a portion of the fuel-supply system (3) to a buffer (22) in response to the machine entering a non-operating state and to temporarily store the hydrogen fuel in the buffer (22), wherein the buffer (22) comprises a compound tank (50) with an external wall (51), a primary volume (53) and a secondary volume (54), an internal wall (52) interposed between the volumes (53, 54), an interconnection port (55) in the internal wall (52) being adapted for receiving an insert module (60-62) to be interposed between the volumes (53, 54), and at least one external access port (56-58) in communication with one volume (53, 54), wherein at least one access port (56-58) is at least indirectly connected to the fuel-supply system (3).

Description

FUEL-MANAGEMENT SYSTEM FOR A HYDROGEN VEHICLETechnical Field

[0001] The invention relates to a fuel-management system for a hydrogen vehicle and to a method for fuel recovery in a hydrogen vehicle.Background Art

[0002] With the increasing demand to reduce CO2 emissions from road vehicles, alternatives to traditional internal combustion engines like Diesel or gasoline engines have been developed. Apart from electric vehicles that are powered by batteries, mostly Li-ion batteries, hydrogen-powered vehicles are a promising option. These vehicles fall into two major categories. The first category are hydrogen fuel cell electric (HFCE) vehicles, which also have an electric traction motor, but are powered by fuel cells in which the chemical energy of hydrogen and oxygen is converted into electric energy. The other category are hydrogen internal combustion engine (H2ICE) vehicles. In a H2ICE, hydrogen (H2) is used as a gaseous fuel and burned with oxygen, the reaction product being water.

[0003] The hydrogen fuel is stored in one or several hydrogen fuel tanks, which are connected to the engine or the fuel cell(s) by a fuel-supply system, which normally comprises a plurality of pipes, manifolds and valves. These components must be filled with hydrogen when the vehicle is operating. When the vehicle is parked, the fuel-supply system is disconnected from the fuel tanks, but unconsumed hydrogen can reside inside the fuel-supply system itself. After some time, hydrogen can leak out, in particular since the hydrogen inside the fuel-supply system typically has a pressure considerably above atmospheric pressure. If the leakage is uncontrolled, the hydrogen - or rather a hydrogen-air mixture - can accumulate in volumes and cavities inside the engine and other parts of the vehicle, which poses an explosion risk, particular at the restart of the vehicle.

[0004] It is also sometimes necessary to reduce the pressures in various parts of the engine system to a safe “near atmospheric” state when the vehicle is not used for long periods of time or before servicing. This can be done by purging, i.e., releasing hydrogen from the respective system. After purging, the pressure should be sufficiently low that any further leakage would not lead to a combustible mixture.Such a target pressure is typically below 2 bar(a), wherein “(a)” indicates absolute pressure. In contrast to this, the typical operating pressures of the fuel-supply system are the range of 5 to 50 bar(a). To achieve this reduction, it has been proposed to either purge hydrogen directly into the atmosphere or to purge it into a buffer tank where it is temporarily stored before it is finally released into the atmosphere. On the one hand, releasing hydrogen into the atmosphere may still lead to the formation of a combustible mixture, depending on the circumstances. On the other hand, hydrogen is considered as a greenhouse gas. Finally, a considerable amount of hydrogen may be simply wasted, especially when the vehicle is parked frequently, which makes this approach uneconomical.Technical Problem

[0005] It is thus an object of the present invention to propose an improved fuel management for a non-operating period of a hydrogen-powered machine.

[0006] This problem is solved by a fuel-management system according to claim 1 , by a method according to claim 14 and by a compound tank according to claim 15.General Description of the Invention

[0007] The invention provides a fuel-management system for a hydrogen- powered machine. The term “hydrogen-powered machine” refers to any machine that uses hydrogen as a source of energy. In particular, the hydrogen-powered machine can be a hydrogen vehicle, which is considered synonymous with “hydrogen-powered vehicle”. As a rule, this refers to a road vehicle like a passenger car, a truck, or a motorcycle. However, it is conceivable to employ the inventive fuelmanagement system in other vehicles, e.g., in a boat, or in a stationary machine or a machine that is mobile but does not use hydrogen fuel to power its traction system. The system is adapted for fuel recovery, wherein here and in the following, the terms “fuel”, “hydrogen fuel” and “hydrogen” are synonymous. While the system comprises physical or “hardware” components, some of its functions may be software- implemented. Although it is conceivable that some components (in particular control components) of the system could be located outside the hydrogen vehicle, it is normally fully integrated into the machine. The fuel-management system maycomprise a control unit that controls various functions and may receive sensor signals.

[0008] The machine comprises a fuel-supply system for supplying hydrogen fuel from at least one fuel tank to a power source of the machine when the machine is in an operating state. In the fuel tank(s), hydrogen fuel is stored either in gaseous form under high pressure or in liquid form. The power source is a device where hydrogen fuel is converted - normally with oxygen - to release energy, which in turn can be used to power various functions of the machine, in particular to drive the machine, e.g., the vehicle. As a rule, the reaction product of the power source is water. The fuel-supply system, which may also be referred to as “fuel supply”, physically connects the at least one fuel tank to the power source. During operation of the machine, the fuel-supply system also establishes a fluid connection between the at least one fuel tank and the power source, thereby enabling operation of the power source. The “operating state” is a state in which the power source is operated, hydrogen is consumed and energy is produced so that the machine can perform its functions. In case of a vehicle, this is the state in which the vehicle moves or at least is ready to move. In a machine with an internal combustion engine, like a H2ICE vehicle, this is usually equivalent to an “ignition on” state. The fuel-supply system may comprise at least one pipe to conduct the hydrogen fuel, as well as at least one valve, in particular a shut-off valve for controlling the connection to the at least one fuel tank.

[0009] The fuel-management system is adapted to transfer hydrogen fuel from at least a portion of the fuel-supply system to a buffer in response to the machine entering a non-operating state and to temporarily store the hydrogen fuel in the buffer. I.e., in a first step, the fuel-management system transfers hydrogen fuel from at least a portion of the fuel-supply system to a buffer. The hydrogen fuel may be transferred through a buffer path, which may be considered as part of the fuel-management system. Such a buffer path may be branched or unbranched. It may comprise at least one pipe that connects the fuel-supply system to the buffer and / or at least one valve to control fuel flow through a pipe. However, the buffer could be disposed adjacent to the fuel-supply system, e.g., only being separated therefrom by a valve, in which case the valve (or its interior) constitutes the buffer path. The hydrogen fuel is transferred from at least a portion of the fuel-supplysystem, i.e. , either a portion, several portions, or the fuel-supply system as a whole. It will be understood that transferring hydrogen fuel from the fuel-supply system to the buffer decreases the amount of hydrogen in the fuel-supply system and also decreases the pressure inside (or in the respective portion thereof). Preferably, the pressure at least inside a portion of the fuel-supply system is decreased to 5 bar(a) or less, preferably 2 bar(a) or less, more preferably 1 ,5 bar(a) or less. Also, preferably at least 50 %, at least 70 %, at least 90% or at least 95% of the hydrogen fuel initially contained in at least a portion of the fuel-supply system is transferred to the buffer. After the transfer, the pressure in the fuel-supply system is reduced so that the leakage rate of any potential leakage from the fuel-supply system is so low that it is unlikely to lead to a combustible mixture. The transfer is started in response to the machine entering a non-operating state, i.e., entering the non-operating state causes the transfer. The non-operating state normally corresponds to the engine of the machine being stopped and the fuel supply to the power source being stopped. Specifically, each fuel tank can be separated from the fuel-supply system by a shutoff valve in the non-operating state. Additionally, a portion of the fuel-supply system from which the hydrogen fuel is to be transferred may be separated from an adjacent portion of the fuel-supply system by a shut-off valve. It is possible that the transfer is started immediately when the non-operating state is entered. However, the fuelmanagement system may perform the transfer only with a predefined time delay after the machine has entered the non-operating state. This is reasonable since short non-operating periods are unlikely to lead to any significant leakage from the fuel-supply system. Moreover, a time delay may be required to monitor a pressure in the fuel-supply system to verify its tightness and integrity. Such pressure monitoring can be part of machine diagnostics, as well as part of a strategy to transfer hydrogen fuel into the buffer only if required (e.g., due to the leakage rate or the leakage quantity exceeding a predefined limit), thereby reducing number of hydrogen transfer operations.

[0010] In a second step, which may partially overlap with the first step, the hydrogen fuel is stored in the buffer. In other words, the hydrogen fuel is contained in the buffer. In some embodiments, the fuel-management system may isolate the buffer by blocking any fluid connection with other elements, in particular with the fuel-supply system. The fuel is stored temporarily, wherein the storage time mayvary e.g., between several minutes and several days. During the storage time, the fuel-management system may optionally monitor at least one parameter of the buffer and / or the hydrogen fuel contained therein, e.g., a pressure, a temperature, or the like.

[0011] Optionally, the fuel-management system may be adapted to release hydrogen fuel from the buffer and at least indirectly transfer it to the power source in response to the machine re-entering the operating state. In this embodiment, at least a major part of the hydrogen fuel is recovered, wherefore the fuel-management system can then also be referred to as a fuel-recovery system. Preferably, at least 50%, at least 70% or at least 90% of the hydrogen fuel is released from the buffer, i.e. , the buffer is preferably emptied to a large extent. Furthermore, the released fuel is transferred, either directly or indirectly, to the power source. Indirect transfer means that the fuel-management system transfers the hydrogen fuel from the buffer to a device or system from where it will be further transferred to the power source without the influence of the fuel-management system. Direct transfer means that the buffer has a direct connection to the power source through which the hydrogen fuel is transferred. Irrespective of whether direct or indirect transfer is employed, at least some of the stored hydrogen fuel, preferably a major part thereof, can be used in the power source. The fuel is not wasted by venting it into the atmosphere. Since no hydrogen fuel (or only a small amount thereof) is released into the atmosphere, there is basically no risk of a combustible mixture. Also, the release of a potentially harmful gas into the atmosphere is minimized, if not prevented.

[0012] According to the invention, the buffer comprises a compound tank with an external wall, a primary volume and a secondary volume, an internal wall interposed between the volumes, an interconnection port in the internal wall being adapted for receiving an insert module to be interposed between the volumes, and at least one external access port in communication with one volume, wherein at least one access port is at least indirectly connected to the fuel-supply system.

[0013] While the compound tank may be somewhat similar to a fuel tank, it may be less pressure-resistant than a fuel tank, since the pressure of the hydrogen fuel released from the fuel-supply system is normally lower than the pressure in the fuel tank. Also, while the fuel tank is designed for permanent storage of hydrogen fuel, the compound tank is only needed for temporary storage. In any case, thecompound tank is designed to receive and at least temporarily contain hydrogen fuel. It comprises an external wall, which delimits the compound tank to the outside. The external wall provides mechanical stability and at least a certain degree of pressure resistance. It may be made of a single piece or of a plurality of connected pieces. The compound tank also comprises a primary volume and a secondary volume, wherein an internal wall is interposed between the volumes. These volumes could also be referred to as a primary chamber and secondary chamber. At least one of the volumes is at least partially defined by the external wall. Moreover, the volumes are at least partially separated from each other by the internal wall, which is interposed between them. While a distinction is made between the internal wall and the external wall based on the position of the internal wall, it is conceivable that the internal wall and the external wall are at least partially made of a single piece. Also, the internal wall may be connected to the external wall. In general, the terms “primary” and “secondary” do not imply any configuration or other properties of the volumes, but simply serve to distinguish the two volumes.

[0014] The interconnection port in the internal wall is adapted for receiving an insert module to be interposed between the volumes. The interconnection port defines a through-opening in the internal wall. If no insert module is inserted in the interconnection port, fluid exchange between the primary volume and the secondary volume is possible through this through-opening. However, if an insert module is received in the interconnection port, such fluid exchange is controlled or even prevented. The interconnection port and the insert module may comprise complementary structures, like internal and external threadings, which facilitate a connection. However, it is also conceivable that an insert module is glued into the interconnection port. Depending on the intended configuration of the compound tank, and the fuel-management system as a whole, different insert modules may be selected. In general, any appropriate shapes or attachment method to fix the insert module in place in the interconnection port.

[0015] The compound tank also comprises at least one external access port in communication with one of the volumes, wherein at least one access port is at least indirectly connected to the fuel-supply system. The external access port may be provided on the external wall, and may at least partially be formed by the external wall. It is accessible externally, i.e. , from the outside of the compound tank. It is incommunication with one volume, i.e. , a fluid can be transferred into the volume or out of the volume through the access port. As will be explained below, there may be a plurality of access ports, which may be connected to the same volume or to different volumes. At least one access port is at least indirectly connected to the fuel-supply system. Specifically, it may be connected to the abovementioned transfer path. Optionally, at least one access port is adapted to receive an insert module. In order to minimize the number of different components, the access port and the interconnection port may be adapted to receive the same type of insert module, e.g., they may have the same connection structures.

[0016] The modular design of the compound tank with the possibility to combine one tank with various insert modules, depending on the individual requirements, provides a high versatility and also helps to reduce production costs. Another advantage is the “compound” concept that combines two volumes in one tank. The internal wall, which is interposed between the volumes, is only subjected to the pressure difference between the primary volume and the secondary volume. In many embodiments, it may therefore be designed less pressure-resistant than the wall of a tank with a single volume. This also helps to reduce cost and weight. Also, the compound tank normally requires less installation space than two separate tanks for the primary and secondary volume. Another advantage is that any possible leakage through the internal wall or the interconnection port is of minor importance, since the leaking fluid does not escape to the outside but will still be contained in one of the volumes.

[0017] The machine could be a HFCE machine, and the power source could be a fuel cell. In this fuel cell, hydrogen and oxygen react to produce water, and the chemical energy is directly converted into electrical energy. This may be used to power an electric drive motor and other electrically operated systems of the machine. Another preferred embodiment provides that the power source of the machine is a hydrogen internal combustion engine, and the fuel-supply system comprises at least one of a fuel rail assembly and a hydrogen regulation module. The hydrogen internal combustion engine (H2ICE) is used to burn hydrogen with oxygen, the reaction product being water. It will be understood that since not pure oxygen but air is used, the combustion may produce minor amounts of other products. As a rule, the HICE has at least one cylinder with an intake valve throughwhich it communicates with an intake duct. A movable piston is disposed in the cylinder, which piston in turn can be connected to a crankshaft. Each cylinder may have a direct injector for injecting hydrogen fuel directly into the cylinder. Here and in the following, “intake duct” refers to any duct through which the engine and / or at least one cylinder of the engine receives air. Therefore, the term explicitly includes an intake manifold. Normally, the cylinder also has an exhaust valve through which it communicates with an exhaust duct (which term explicitly includes an exhaust manifold). Hydrogen fuel may be directly injected into the respective cylinder. It may also be injected into the intake duct, corresponding to an indirect injection. Both possibilities may be combined. Each injector may be connected to a fuel rail or fuel rail assembly, from which it receives the hydrogen fuel and which is part of the fuelsupply system. Normally, the fuel rail is not directly connected to the fuel tank(s) but via a hydrogen regulation module (HRM), which may perform several functions. It may comprise an electronic pressure regulator, which reduces the pressure of the hydrogen fuel, e.g., from about 50 bar(a) at the outlet of the fuel tank to between 5 and 40 bar(a), which is an adequate pressure for operation of some fuel injection systems. However, there are also fuel injection systems with higher operating pressure (up to a maximum of 350 bar(a)) or lower operating pressure (up to a maximum of 5 bar(a)). If the fuel-supply system comprises both a fuel rail assembly and a hydrogen regulation module, the fuel recovery system may enable a transfer from one or both of them. In other words, one of them or both may be a portion of the fuel-supply system from which hydrogen fuel is transferred to the buffer.

[0018] Although it is generally desirable to prevent hydrogen from being released to the atmosphere, this may be done in some situations for safety reasons. According to one embodiment, the fuel-management system is adapted to release hydrogen fuel from the buffer to the atmosphere if a buffer pressure in the buffer exceeds a pressure limit (or threshold). The pressure limit may correspond to a limit under which the buffer can be operated safely. As the pressure limit is exceeded, hydrogen fuel is released into the atmosphere. It is understood that the pressure limit is above atmospheric pressure. The release may be controlled by a relief valve that opens if a pressure difference between the buffer pressure and the atmospheric pressure exceeds a certain value. Alternatively, the buffer pressure could bemeasured by a sensor and a relief valve could be actively opened according to the measurement.

[0019] In case of the abovementioned HICE, it is conceivable that hydrogen fuel is transferred from the buffer to the fuel-supply system, from where it could e.g., be directly injected into the engine. According to another possibility, the fuelmanagement system can be adapted to transfer hydrogen fuel from the buffer to an intake duct of the engine. The intake duct, as mentioned above, is any duct that supplies the engine with air. In this embodiment, hydrogen fuel is injected into the air stream before it enters the engine, corresponding to an indirect injection. It should be noted that it is possible that the fuel-supply system is also connected to a direct injector so that indirect injection is performed independently of the fuelmanagement system. In this case, fuel-management system could use the fuelsupply system to transfer the fuel into the intake duct.

[0020] According to one embodiment, the fuel-management system is adapted to transfer hydrogen from the buffer through a recovery path, which bypasses the fuel-supply system, at least indirectly to the power source. Like the buffer path, the recovery path may be considered as part of the fuel-management system. It may be branched or unbranched. It may comprise at least one pipe that connects the buffer either directly or indirectly to the power source and / or at least one valve to controls fuel flow through a pipe. The recovery path bypasses the fuelsupply system. In particular, it could lead directly to the engine or an intake duct of the engine. Another embodiment provides that the fuel-management system is adapted to transfer hydrogen from the buffer through the buffer path to the fuelsupply system. This is normally an alternative to the use of the abovementioned recovery path, but it is conceivable to combine both embodiments. In this embodiment, hydrogen fuel is re-transferred to the fuel-supply system through the same path through which it was transferred to the buffer. This approach is difficult to pursue if (only) a pressure difference is applied, since it would require the pressure in the buffer to be (significantly) above the pressure in the fuel-supply system. If, however, a chemical adsorbent is used, the transfer direction through the buffer path can be largely controlled by controlling the buffer temperature. With this embodiment, a buffer valve may be used to control the transfer. However, the buffer valve may be omitted completely, and the transfer is only controlled by thetemperature. This, however, requires the buffer temperature to be in a suitable range for effective adsorption during the entire non-operating time.

[0021] Preferably, the primary volume is at least partially surrounded by the secondary volume. Herein “partially” on the one hand can mean that only a part of the primary volume is surrounded by the secondary volume, as well as the primary volume (or a part of it) being not fully surrounded, e.g., partially being defined by the external wall. In any case, at least a part of the primary volume is interposed between parts of the secondary volume. As far as the primary volume is surrounded by the secondary volume, it is defined by the internal wall, which is subjected to the pressure difference between the volumes, and not to the pressure difference between the primary volume and the outside of the compound tank. Preferably, at least 80% or at least 90% of the primary volume is surrounded by the secondary volume. In such an embodiment, the primary volume can also be referred to as an “inner volume” and the secondary volume can be referred to as an “outer volume”. It will be understood that leakage from the primary volume (through the internal wall) is of minor concern, since the fluid (e.g., the hydrogen fuel) leaks from the primary volume into the secondary volume.

[0022] The fuel-management system is preferably adapted to store hydrogen fuel in the primary volume at a higher pressure and to store hydrogen fuel in the secondary volume at a lower pressure. This is particularly advantageous if the primary volume is partially or fully disposed inside the secondary volume. Then, the external wall delimiting the secondary volume is only subjected to the pressure difference between the lower pressure and the ambient pressure, while the internal wall is only subjected to the pressure difference between the higher pressure and the lower pressure. The fuel-management system may be adapted to actively control the fuel transfer to the volumes so that the primary volume receives a higher pressure than the secondary volume. However, as will be explained below, there are also embodiments in which the secondary volume receives a lower pressure without the need for an active control.

[0023] According to one embodiment, a valve is received in the interconnection port. I.e., the insert module is a valve. Accordingly, fluid exchange between the volumes is possible, but is controlled by the valve. The valve can be an active valve that is controlled by an actuator. It can also be a passive valve, i.e.,a valve that responds passively to the pressure difference between the volumes. For instance, it can be a relief valve that is designed to open if the pressure difference exceeds a certain safety threshold. It can also be a check valve that opens if there is a positive pressure difference in one direction but closes otherwise, thereby allowing for a basically unhindered fluid exchange in one direction (e.g., from the primary volume to the secondary volume). The functions of both valve types may also be combined in a single valve.

[0024] According to another option, a plug is received in the interconnection port, whereby fluid exchange between the volumes is prevented. In this case, the insert module is a plug which seals the interconnection port. No fluid exchange is possible through the interconnection port and the primary and secondary volume are effectively isolated from each other. In this embodiment, there is preferably at least one access port for each volume. Otherwise, one volume would be completely inaccessible. However, such a configuration is not completely ruled out. For example, the respective volume could serve for thermal insulation of the other volume or it could serve as a crush zone that mechanically protects the other volume in case of an accident.

[0025] One embodiment provides that the compound tank comprises at least one primary access port in communication with the primary volume and at least one secondary access port in communication with the secondary volume. This configuration enables independent access to both volumes. I.e., a dedicated connection to each of the volumes can be established. If such dedicated connections are established, fluid can be transferred into and / or from one volume independently of the other. However, this does not rule out that fluid exchange through the interconnection port is possible. On the contrary, a suitable insert module like a valve can be received in the interconnection port which enables hydrogen fuel to flow from one volume to another.

[0026] According to another embodiment, the compound tank comprises two access ports in communication with the same volume. In other words, it may comprise two primary access ports in communication with the primary volume and / or two secondary access ports in communication with the secondary volume. While it is possible that one of the access ports is closed by a plug and thus is “inactive”, both access ports may be connected to a respective line for guidinghydrogen fuel or some other fluid. In this configuration, the fluid may be transferred into the volume through one access port and out of the volume through the other access port. Specifically, the compound tank may comprise a single primary access port and two secondary access ports. However, other configurations are possible and may be advantageous.

[0027] One embodiment provides that the fuel-management system is adapted to transfer the hydrogen fuel to the buffer by consecutively connecting the volumes to the fuel-supply system, so that one volume is connected to the fuelsupply system while the other volume is disconnected from the fuel-supply system. This embodiment is much more effective than using a single volume, at least if the transfer only relies on pressure equalization. The hydrogen transfer is performed in two stages. During each stage, the fuel-supply system is connected with one volume, and (at least partial) pressure equalization is performed. After fuel transfer to the primary volume, the primary volume is disconnected from the fuel-supply system and the secondary volume is connected. With each transfer, the pressure in the fuel-supply system is reduced, until finally a target pressure is reached. Accordingly, after all transfers have been completed, there is a different pressure in each volume. As can be shown by calculation, a considerably smaller total volume is needed to achieve a certain targe pressure in comparison to a concept that uses only a single volume. Optionally, a subsequent pressure equalization could be performed between the volumes. This could be beneficial in that the primary volume would not be exposed to a high pressure for an extended time period, wherefore its walls could possibly be constructed simpler and / or cheaper. Specifically, the internal wall would not be subjected to any pressure difference once the pressure equalization has been completed.

[0028] The effectiveness of the buffer can be greatly increased if at least one volume comprises a sorbent configured to sorb hydrogen. This sorbent can be provided as a filler or a lining inside the respective volume. The sorption effect relies on an interaction between the sorbent and the hydrogen. This may refer to an adsorption as well as to an absorption, which may also be combined with each other. Also, the sorption may be based on a physical and / or chemical process. After sorption, at least a major part of the hydrogen is no longer present in gaseous form but is chemically or physically bound by the sorbent. The sorbent may comprise orconsist of a metal hydride, a metal alloy, a metal-organic framework, a molecular sieve, a zeolite, an activated carbon, a carbon nanotube material, or another suitable material, or a mixture thereof. Irrespective of whether the sorption process is based on chemical absorption, chemical adsorption, physical absorption and / or physical adsorption, hydrogen is bound to the sorbent so that it is no longer present as a gas. This coincides with a significant increase of the amount of substance that can be contained in a given volume. In other words, a volume at least partially filled with a suitable sorbent is capable of containing a much higher amount of hydrogen than without the adsorbent. Although the binding and releasing of the hydrogen depends on the characteristics of the specific sorbent, it is normally possible to promote the sorption by reducing the temperature and / or by increasing the pressure in the volume, while it is normally possible to promote hydrogen release be increasing the temperature and / or by decreasing the pressure.

[0029] At least in some configurations, it is possible to further improve the performance if the primary volume comprises a first sorbent and the secondary volume comprises a second sorbent. The second sorbent is preferably chemically and / or physically different from the first sorbent. This results in different sorption and release characteristics of the two sorbents. For example, the first sorbent could sorb hydrogen at a different pressure than the second sorbent. If combined with the abovementioned embodiment where the primary volume receives hydrogen fuel at a higher pressure, the first sorbent could effectively sorb hydrogen at a higher pressure than the second sorbent. Correspondingly, it would start to release hydrogen at a higher pressure than the second sorbent. Alternatively or additionally, the two sorbents could have different temperature-dependent sorption characteristics.

[0030] As already mentioned above, even though an access port is present, it does not need to be employed for fluid exchange. One embodiment provides that the at least one secondary access port is closed by a plug and a valve is received in the interconnection port. Accordingly, no secondary access port is open for fluid exchange, wherefore fluid exchange with the secondary volume is only possible via the interconnection port. This is made possible by the valve installed in the interconnection port. The respective valve could be a combination valve that opens towards the secondary volume if a pressure in the primary volume is greater than apressure in the secondary volume by a certain threshold and that opens towards the primary volume whenever the pressure in the secondary volume is greater than the pressure in the primary volume. As hydrogen fuel is transferred into the primary volume, the pressure therein would increase until the valve opens. Then, hydrogen fuel would be transferred to both volumes while a certain pressure difference is maintained (otherwise, the valve would close). Then, when fuel is released from the primary volume, the pressure would drop until it falls below the pressure in the secondary volume so that the valve opens again. The pressure in both volumes would then drop further while hydrogen is transferred from the secondary volume through the valve, the primary volume and the primary access port out of the compound tank.

[0031] In the abovementioned embodiment, but also in other cases, it is advantageous if a valve is received in the interconnection port, which valve is adapted to open towards the primary volume in response to a relative overpressure in the secondary volume. The valve can be a simple check valve that only allows for fuel transfer into the primary volume. It could also be a combination valve as described above that opens towards the secondary volume if a relative overpressure in the primary volume exceeds a certain threshold.

[0032] The fuel transfer to and / or from the compound tank may be driven by a pressure difference, e.g., at least one volume could be connected to a low- pressure source to lower its pressure. As an alternative to connecting to a low- pressure source, or in combination therewith, a temperature of the volume may be used to promote the hydrogen fuel transfer. One such embodiment provides that the secondary access ports are connected to a fluid path of the vehicle, and the fuelmanagement system is adapted to influence a temperature of the primary volume by heat transfer through the internal wall. In this case, the secondary volume is not used for hydrogen storage, but for containing a fluid that receives heat from the primary volume and / or transfers heat to the primary volume. The fluid enters the secondary volume through one of the secondary access ports and exits through the other secondary access port. The fluid path may in particular be adapted to conduct oil, cooling fluid, or exhaust gas. In this context, the compound tank not only works as a buffer, but also as a heat exchanger. In some embodiments, the fuel-management system is adapted to control the flow through the fluid path or through the secondary volume, respectively.

[0033] The fuel-management system may be adapted to reduce a temperature in the primary volume to facilitate transferring the hydrogen fuel to the primary volume and to increase the temperature to facilitate releasing the hydrogen fuel from the primary volume. In this context, the term “facilitate” is not to be construed in that the fuel-management system necessarily uses additional means to effect the transfer of the hydrogen fuel, although this is possible and usually beneficial. The fuel-management system may also comprise at least one temperature sensor for detecting the temperature. When the temperature is reduced, this at least helps to transfer hydrogen fuel to the primary volume, while increasing the temperature helps to release hydrogen from the primary volume. This can be due to several effects. One effect is that the amount of substance n (in mol) of an ideal gas that can be contained in a certain volume at a certain pressure is inverse proportional to the temperature T, i.e. , n~T1. However, this effect is normally small unless very significant temperature changes take place. However, when combined with other mechanisms (like employing an underpressure), it can enhance the effectiveness. However, temperature variation is effective on its own if the primary volume comprises a sorbent as described above.

[0034] The invention further relates to a method for providing a fuelmanagement system for a hydrogen-powered machine, which machine comprises a fuel-supply system for supplying hydrogen fuel from at least one fuel tank to a power source of the machine when the machine is in an operating state, wherein the fuel-management system is adapted to transfer hydrogen fuel from at least a portion of the fuel-supply system to a buffer in response to the machine entering a non-operating state and to temporarily store the hydrogen fuel in the buffer. The method comprises providing a compound tank with an external wall, a primary volume and a secondary volume, an internal wall interposed between the volumes, an interconnection port in the internal wall being adapted for receiving an insert module to be interposed between the volumes, and at least one external access port in communication with one volume. Optionally, the method comprises inserting an insert module into the interconnection port. If this insertion is performed, it will normally be before or during the previously mentioned step of providing thecompound tank, since the interconnection port may no longer be accessible once the compound tank is otherwise completed. The method further comprises at least indirectly connecting at least one access port to the fuel-supply system.

[0035] All these terms have been explained above with respect to the inventive fuel-management system and therefore will not be explained again. Preferred embodiments of the inventive method correspond to those of the inventive fuel-management system.

[0036] The invention further relates to a compound tank for temporarily storing hydrogen fuel from a fuel-supply system of a hydrogen-powered machine, wherein the compound tank comprises an external wall, a primary volume and a secondary volume, an internal wall interposed between the volumes, an interconnection port in the internal wall being adapted for receiving an insert module to be interposed between the volumes, and at least one external access port in communication with one volume, wherein at least one access port is adapted to be at least indirectly connected to the fuel-supply system.

[0037] All these terms have been explained above with respect to the inventive fuel-management system and therefore will not be explained again. Preferred embodiments of the inventive compound tank correspond to those of the inventive fuel-management system.Brief Description of the Drawings

[0038] Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:Fig.1 is a schematic sectional view of a first embodiment of an inventive compound tank;Fig. 2 is a schematic view of components of a hydrogen vehicle with a fuelmanagement system according to a first embodiment of the present invention;Fig.3 is a schematic view of components of a hydrogen vehicle with a fuelmanagement system according to a second embodiment of the present invention;Fig.4 is a schematic view of components of a hydrogen vehicle with a fuelmanagement system according to a third embodiment of the present invention;Fig.5 is a schematic view of components of a hydrogen vehicle with a fuelmanagement system according to a fourth embodiment of the present invention; andFig.6-8 are schematic sectional views of further embodiments of an inventive compound tank.Description of Preferred Embodiments

[0039] Fig.1 is a schematic sectional view of an inventive compound tank 50.It comprises an external wall 51 and an internal wall 52, which is mostly disposed inside the external wall 51 . The internal wall 52 defines a primary volume 53, while both walls 51 , 52 together define a secondary volume 54 that surrounds the primary volume 53. A primary access port 56 communicates with the primary volume 53, while two secondary access ports 57 communicate with the secondary volume 54. Furthermore, an interconnection port 55 is disposed in the internal wall 51 and defines a through-opening between the primary volume 53 and the secondary volume 54. The interconnection port 55 is adapted to receive an insert module 60- 62, as will be explained below.

[0040] Fig.2 shows a schematic view of some elements of a hydrogen vehicle, more specifically an H2ICE vehicle, with a first embodiment of an inventive fuel-management system 20. The vehicle comprises a hydrogen internal combustion engine 6, which is shown in a highly simplified form with only a single cylinder 7 visible. The engine 6 is connected to an intake duct 8 (normally of an intake manifold) and an exhaust duct 9 (normally of an exhaust manifold). For each cylinder 7, a direct injector 10 is arranged to inject hydrogen fuel directly into a cylinder head, whereas an injector nozzle 11 is arranged to inject hydrogen fuel into the intake duct 8. The engine 6 represents a power source of the vehicle, in which gaseous hydrogen is burned with oxygen to convert chemical energy intomechanical energy. The mechanical energy is used to drive the vehicle and may also be converted through a generator (not shown) into electrical energy.

[0041] The hydrogen fuel needed to supply the engine 6 is stored in at least one fuel tank 1 , which is highly pressure-resistant. In the fuel tank 1 , the gas pressure may be of up to 350 to 700 bar(a). Typically, the fuel tank 1 includes a pressure regulator, such that hydrogen is discharged at a pressure of several dozen bar, e.g. about 50 bar(a). The fuel tank 1 is connected to the engine 6 via a fuelsupply system 3, which is only shown schematically. It comprises a fuel rail 5, which is connected to the direct injector 10, and a hydrogen regulation module (HRM) 4, which may comprise various elements, like a pressure regulator, which reduces / controls the pressure of the hydrogen fuel from the tank 1 to desired operating pressures, e.g. between 5 and 40 bar(a), a filter to remove foreign particles or droplets from the hydrogen fuel, and optionally one or more of a lubricating device, a heating or cooling device for adjusting the temperature of the hydrogen fuel etc. The fuel-supply system 3 is connected to the fuel tank 1 via a shut-off valve 2 (which may be integrated into the HRM). While the vehicle is in an operating state, hydrogen fuel is supplied to the direct injector 10 and the shut-off valve 2 is open. When the vehicle enters a non-operating state in which the engine 6 is turned off, the shut-off valve 2 is closed so that the fuel-supply system 3 is isolated from the fuel tank 1 . However, a considerable amount of hydrogen fuel still resides in the fuel-supply system 3 and is still under considerable pressure, e.g., between 5 and 40 bar(a).

[0042] The function of the fuel-management system 20 is to mitigate any explosion risk originating from hydrogen fuel leaking out of the fuel-supply system 3 while avoiding any unnecessary waste of hydrogen. In the embodiment shown in fig. 2 the fuel-management system 20 comprises a buffer 22 with a single compound tank 50, the primary access port 56 of which is connected to the fuel-supply system 3 via a buffer path 25. Both secondary access ports 57, 58 are closed by plugs 60. A combination valve 61 is received in the interconnection port 55. Although the buffer path 25 is shown connected to the HRM 4, this is just by way of example and it could additionally or exclusively be connected to the fuel rail 5. The buffer path 25 comprises a buffer valve 26, which is a shut-off valve controlled by a control unit 21 of the fuel-management system 20. The control unit 21 normally comprises at leastone processor and is configured (by way of computer code instructions) to implement the control steps of the fuel-management system 20 as described herein. The control unit 21 may be independent or integrated with the Engine control unit. A temperature sensor 40 and a pressure sensor 41 are arranged to measure a temperature and a pressure in the buffer path 25. The sensors 40, 41 transmit measurement signals / values to the control unit 21 . The buffer 22 is also connected to the injector nozzle 11 via a recovery path 28, which in this embodiment branches from the buffer path 25 but could also be completely independent. The recovery path 28 comprises a recovery valve 29, which is also a shut-off valve controlled by the control unit 21 , and an orifice 30. The fuel-management system 20 further comprises a relief path 31 that branches from the buffer path 25 and is directly connected to the atmosphere around the vehicle. A relief valve 32 is disposed in the relief path 31 .

[0043] While the vehicle is in its operating state, the control unit 21 keeps the buffer valve 26 closed but opens the recovery valve 29 so that the primary volume 53 is connected to the intake duct 8. While the engine 6 is operating, the intake duct 8 is a low-pressure source, wherefore an underpressure (e.g., 0.5 bar(a)) in the primary volume 53 is created, with respect to the outer atmosphere and especially with respect to the fuel-supply system 3. The same applies to the secondary volume 54, since the combination valve 61 opens towards the primary volume 53 when the pressure in the secondary volume 54 is higher than in the primary volume 53. When the control unit 21 senses through the pressure sensor 41 that the pressure in the compound tank 50 is below a certain value, it may close the recovery valve 29. If, due to some leakage, the pressure on the compound tank 50 rises again above the specified value, the recovery valve 29 may be reopened. When the vehicle enters a non-operating state, the engine 6 is stopped and the shut-off valve 2 is closed. The control unit 21 may either control the shut-off valve 2 itself or may at least receive a signal that indicates that the vehicle as enter the non-operating state.

[0044] In response to the vehicle entering the non-operating state, the fuelmanagement system 20 transfers hydrogen fuel from the fuel-supply system 3 to the buffer 22. Preferably, this is performed after a delay time in order to disregard short non-operating periods. In order to transfer the fuel, the control unit 21 opens the buffer valve 26 while keeping the recovery valve 29 closed. Due to theunderpressure in the compound tank 50, hydrogen fuel flows from the fuel-supply system 3 into the primary volume 53 until pressure equalization has been achieved. Also, the combination valve 61 opens towards the secondary volume 54 if a pressure difference between the primary volume 53 and the secondary volume 54 exceeds a certain threshold. Accordingly, hydrogen fuel is also stored in the secondary volume 54, but at a lower pressure than in the primary volume 53. This means that the external wall 51 is only subjected to the pressure difference between the relatively low pressure in the secondary volume 54 and the ambient pressure, while the internal wall 52 is only subjected to the pressure difference between the pressure in the primary volume 53 and the pressure in the secondary volume 54. Accordingly, neither of the walls 51 , 52 has to withstand the pressure difference between the pressure in the primary volume 53 and the ambient pressure. When the control unit 21 detects via the pressure sensor 41 that the pressure has reached an equilibrium or is below the target pressure, it closes the buffer valve 26. A major part of the hydrogen previously present in the fuel supply system 3 is now stored in the buffer 22, where it remains while the vehicle is in the non-operating state.

[0045] When the vehicle re-enters the operating state, the shut-off valve 2 is reopened and the pressure in the fuel-supply system 3 again reaches a high value of e.g., up to 40 bar(a). As the control unit 21 detects the re-activation of the vehicle, it releases hydrogen fuel from the buffer 22 by opening the recovery valve 29. At first, hydrogen fuel is released from the primary volume 53, but when the pressure drops below the pressure in the secondary volume 54, hydrogen fuel is released from both volumes 53, 54. A considerable portion of the hydrogen fuel is sucked out of the compound tank 50 into the intake duct 8, wherein the injector nozzle 11 functions as an indirect injector. When the pressure sensor 41 indicates that the pressure in the compound tank 50 has reached its previous value (e.g., 0.5 bar (a)), the control unit 21 may again close the recovery valve 29.

[0046] Under normal conditions, no hydrogen fuel is intentionally vented into the atmosphere. However, if at any point in time the pressure on the buffer path 25 exceeds a certain threshold, the pressure-relief valve 32 opens, whereby some hydrogen is vented through the relief path 31 into the atmosphere.

[0047] Fig. 3 shows elements of a vehicle with a second embodiment of an inventive fuel-management system 20, which is largely identical to the one shownin fig. 2 and insofar will not be explained again. Also, for sake of simplicity, apart from the fuel-management system 20, only the fuel-supply system 3 and the injector nozzle 11 are shown. In this embodiment, the primary access port 56 and a first secondary access port 57 are connected to the fuel-supply system 3 by a branching buffer path 25, while a second secondary access port 58 is closed by a plug. A check valve 62 is received in the interconnection port 55. Also, a first sorbent 64 is disposed in the primary volume 53, while a second sorbent 65 is disposed in the secondary volume 54. Both sorbents 64, 65 are adapted to sorb hydrogen fuel, while the first sorbent 64 is adapted to sorb and release hydrogen at a higher pressure than the second sorbent 65. A first buffer valve 26 is adapted for separating the primary volume 53 from the fuel-supply system 3 and a second buffer valve 27 is adapted to separate the secondary volume 54. A likewise branching recovery path 28 connects the compound tank via a single recovery valve 29 to the injector nozzle 11 , recovery bath 28 being connected to the primary access port 56. The check valve 62 interposed between the volumes 53, 54 is adapted to open if the pressure in the second volume 54 is higher than the pressure in the first volume 53.

[0048] In this embodiment, when the vehicle enters the non-operating state, the control unit 21 opens the first buffer valve 26 while keeping the second buffer valve 27 closed. As hydrogen fuel enters the primary volume 53, it is absorbed and / or adsorbed by the first sorbent 64. After a short period of time, pressure equalization between the fuel-supply system 3 and the primary volume 53 has been achieved. However, due to a relatively small volume of the primary volume 53, the target pressure has not been reached yet. The control unit 21 closes the first buffer valve 26 and opens the second buffer valve 27, so that hydrogen fuel flows into the secondary volume 54 until pressure equalization between the fuel-supply system 3 and the secondary volume 54 has been reached. Hydrogen fuel is now absorbed and / or adsorbed by the second sorbent 65. Since the pressure in the fuel-supply system 3 has already been lowered by the first pressure equalization, it is possible to reach the target pressure even though the volume of the second buffer tank 24 is relatively small. Also, the total size of the compound tank 50 can be significantly reduced due to the presence of the first and second sorbent 64, 65.

[0049] When the vehicle re-enters the operating state, fuel from both volumes 53, 54 can be released through the single recovery valve 29, since they are coupledby the check valve 62, which opens when the pressure in the secondary volume 54 exceeds the pressure in the primary volume 53.

[0050] Fig.4 shows a third embodiment of an inventive fuel-management system 20, which differs from the previous embodiments in that the buffer 22 is not connected to the injector nozzle 11 by a recovery path. Also, a bypass path 38 is connected to the buffer path 25 on opposite sides of the buffer valve 26. Accordingly, hydrogen fuel can be transferred to the fuel-supply system 3 in a passive manner through a bypass valve 39 whenever the pressure in the buffer 22 exceeds the pressure in the fuel-supply system 3. Therefore, the buffer valve 26 only needs to be opened temporarily to allow for hydrogen transfer from the fuel-supply system 3 to the buffer 22.

[0051] Again, the primary volume 53 is partially filled with the first sorbent 64. The interconnection port 55 is closed by a plug 60. The sorption of hydrogen in the primary volume 53 is temperature-dependent, so that reducing the temperature leads to an increased adsorption, whereas increasing the temperature releases hydrogen from the primary volume 53. Furthermore, it can control a flow valve 36 in a fluid path 34 that is connected to both secondary access ports 57, 58. If the flow valve 36 is opened, a fluid flows through the fluid path 34 and the secondary volume 54, which, due to heat transfer through the internal wall 52, can influence the temperature in the primary volume 53. The fluid path 34 may be part of a coolant system or an engine oil circulation system.

[0052] While the vehicle is in the operating state, the control unit 21 keeps the buffer valve 26 closed. When the vehicle enters the non-operating state, the control unit 21 opens the buffer valve 26. Since the temperature of the buffer 22 is comparatively low (e.g., between 10°C and 30°C), adsorption of hydrogen fuel in the primary volume 53 is facilitated. After the sorption process has been completed, the control unit 21 closes the buffer valve 26.

[0053] When the vehicle re-enters the operating state, the control unit 21 opens the flow valve 36. To accelerate the warming of the primary volume 53 during the initial phase of the vehicle operation, the control unit 21 could also activate an electrical heater 37 (shown in fig.5), which may be switched off after some time when enough heat is transferred through the internal wall 52. As the buffertemperature increases, hydrogen is released from the first sorbent 64 and re-enters the gas phase. Accordingly, the pressure in the primary volume 53 rises and the bypass valve 39 opens automatically, so that hydrogen fuel is returned to the fuelsupply system 3 via the bypass path 38.

[0054] Fig.5 shows a fourth embodiment that is similar to the third embodiment. However, the first secondary port 57 is closed by a plug 60 and the second secondary access port 58 is connected to the bypass path 38. It would be possible that the bypass valve 39 is received in the second secondary access port 58. No insert module is received in the interconnection port 55, which is therefore open for gas exchange at all times. Both the primary volume 53 and the secondary volume are partially filled by the first sorbent 64. In order to control or at least influence the temperature in the compound tank 50, the control unit 21 can control an electric heater 37 that is in thermal contact with the external wall 51 .

[0055] Like in the third embodiment, transfer of hydrogen fuel to and from the buffer 22 is at least partially controlled by the temperature. Accordingly, while the vehicle is in operating state, the control unit 21 keeps the electrical heater 37 deactivated to keep the temperature low, while keeping the buffer valve 26 closed. Then, when the vehicle enters the non-operating state, the control unit 21 opens the buffer valve 26, so that hydrogen fuel flows into both volumes 53, 54, where it is absorbed and / or adsorbed by the first sorbent 64. When the vehicle re-enters the operating state, the control unit 21 uses the electrical heater 37 to increase the temperature so that the hydrogen fuel is largely expelled from the compound tank 50.

[0056] There are a multitude of possible configurations of the fuelmanagement system 20 and the compound tank 50, which cannot be shown here in their entirety. However, figs. 6-8 by way of example show some more embodiments of the inventive compound tank 50. Fig.6 shows an embodiment in which both secondary access ports 57, 58 are closed by plugs 60, while a combination valve 61 is received in the interconnection port 55. The primary volume 53 comprises the first sorbent 64 and the secondary volume 54 comprises the second sorbent 65. Fig.7 shows an embodiment in which the first secondary access port 57 and the interconnection port 55 are closed by plugs 60, while the second secondary access port 58 is open and may e.g., be connected in a similar manneras shown in fig.3. Fig.8 shows a configuration that is almost identical to the one shown in fig. 5, the difference being that the interconnection port 55 is closed by a plug 60.

[0057] It will be understood that all examples of the compound tank 50 shown here are based on a common design that is modified and adapted depending on the requirements of the fuel-management system 20. Specifically, during construction of the compound tank 50, an insert module 60-62 can be selected, if needed, and be inserted into the interconnection port 55. Also, a sorbent 64, 65 can be optionally introduced into the primary volume 53 and / or the secondary volume 54.

[0058] The compound tank 50 can be made of any appropriate material(s). Depending on embodiments, the internal wall 51 and external wall 52 may be made of same or different materials, which may be selected from polymers, e.g. polyamide, polyphthalamide, polypropylene, etc., or metals e.g. stainless steel. If desirable, composite structures can be used, e.g. a fluid-tight envelope (metal or polymer) reinforcement by a surrounding layer of reinforced polymer, such as e.g. resin coated carbon fibers.Legend of Reference Numbers:1 fuel tank 33 check valve2 shut-off valve 34 fluid path3 fuel-supply system 36 flow valve4 hydrogen regulation module 37 electrical heater5 fuel rail 38 bypass path6 engine 39 bypass valve7 cylinder 40 temperature sensor8 intake duct 41 pressure sensor9 exhaust duct 50 compound tank10 direct injector 51 external wall11 injector nozzle 52 internal wall20 fuel-management system 53 primary volume21 control unit 54 secondary volume22 buffer 55 interconnection port25 buffer path 56 primary access port26,27 buffer valve 57,58 secondary access port28 recovery path 60 plug29 recovery valve 61 combination valve30 orifice 62 check valve31 relief path 64,65 sorbent32 relief valve

Claims

Claims1 . A fuel-management system (20) for a hydrogen-powered machine, which machine comprises a fuel-supply system (3) for supplying hydrogen fuel from at least one fuel tank (1) to a power source (6) of the machine when the machine is in an operating state, wherein the fuel-management system (20) is adapted to transfer hydrogen fuel from at least a portion of the fuel-supply system (3) to a buffer (22) in response to the machine entering a non-operating state and to temporarily store the hydrogen fuel in the buffer (22), wherein the buffer (22) comprises a compound tank (50) with an external wall (51 ), a primary volume (53) and a secondary volume (54), an internal wall (52) interposed between the volumes (53, 54), an interconnection port (55) in the internal wall (52) being adapted for receiving an insert module (60-62) to be interposed between the volumes (53, 54), and at least one external access port (56-58) in communication with one volume (53, 54), wherein at least one access port (56-58) is at least indirectly connected to the fuelsupply system (3).

2. The fuel-management system according to claim 1 , wherein the primary volume (53) is at least partially surrounded by the secondary volume (54).

3. The fuel-management system according to any one of the preceding claims, being adapted to store hydrogen fuel in the primary volume (53) at a higher pressure and to store hydrogen fuel in the secondary volume (54) at a lower pressure.

4. The fuel-management system according to any one of the preceding claims, wherein a valve (61 , 62) is received in the interconnection port (55).

5. The fuel-management system according to any one of the preceding claims, wherein a plug (60) is received in the interconnection port (55), whereby fluid exchange between the volumes (53, 54) is prevented.

6. The fuel-management system according to any one of the preceding claims, wherein the compound tank (50) comprises at least one primary access port (56)in communication with the primary volume (53) and at least one secondary access port (57, 58) in communication with the secondary volume (54).

7. The fuel-management system according to any one of the preceding claims, wherein the compound tank (50) comprises two access ports (56-58) in communication with the same volume (53, 54).

8. The fuel-management system according to any one of the preceding claims, being adapted to transfer the hydrogen fuel to the buffer (22) by consecutively connecting the volumes (53, 54) to the fuel-supply system (3), so that one volume (53, 54) is connected to the fuel-supply system (3) while the other volume (53, 54) is disconnected from the fuel-supply system (3).

9. The fuel-management system according to any one of the preceding claims, wherein at least one volume (53, 54) comprises a sorbent (64, 65) configured to sorb hydrogen.

10. The fuel-management system according to any one of the preceding claims, wherein the primary volume (53) comprises a first sorbent (64) and the secondary volume (54) comprises a second sorbent (65).11 . The fuel-management system according to any one of the preceding claims, wherein the at least one secondary access port (56-58) is closed by a plug (60) and a valve (61 , 62) is received in the interconnection port (55).

12. The fuel-management system according to any one of the preceding claims, wherein a valve (61 , 62) is received in the interconnection port (55), which valve (61 , 62) is adapted to open towards the primary volume (53) in response to a relative overpressure in the secondary volume (54).

13. The fuel-management system according to any of the preceding claims, wherein the secondary access ports (57, 58) are connected to a fluid path (34) of the vehicle, and the fuel-management system (20) is adapted to influence atemperature of the primary volume (53) by heat transfer through the internal wall(52).

14. A method for providing a fuel-management system (20) for a hydrogen-powered machine, which machine comprises a fuel-supply system (3) for supplying hydrogen fuel from at least one fuel tank (1 ) to a power source (6) of the machine when the machine is in an operating state, wherein the fuel-management system (20) is adapted to transfer hydrogen fuel from at least a portion of the fuel-supply system (3) to a buffer (22) in response to the machine entering a non-operating state and to temporarily store the hydrogen fuel in the buffer (22), wherein the method comprises- providing a compound tank (50) with an external wall (51 ), a primary volume(53) and a secondary volume (54), an internal wall (52) interposed between the volumes (53, 54), an interconnection port (55) in the internal wall (52) being adapted for receiving an insert module (60-62) to be interposed between the volumes (53, 54), and at least one external access port (56-58) in communication with one volume (53, 54),- optionally inserting an insert module (60-62) into the interconnection port (55), and- at least indirectly connecting at least one access port (56-58) to the fuel-supply system (3).

15. A compound tank (50) for temporarily storing hydrogen fuel from a fuel-supply system (3) of a hydrogen-powered machine, wherein the compound tank (50) comprises an external wall (51 ), a primary volume (53) and a secondary volume(54), an internal wall (52) interposed between the volumes (53, 54), an interconnection port (55) in the internal wall (52) being adapted for receiving an insert module (60-62) to be interposed between the volumes (53, 54), and at least one external access port (56-58) in communication with one volume (53, 54), wherein at least one access port (56-58) is adapted to be at least indirectly connected to the fuel-supply system (3).

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