Fuel-recovery system for a hydrogen-powered machine

Abstract

The invention relates to a fuel-recovery system (20) for a hydrogen 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 machine, the invention provides that the fuel-recovery system (20) is adapted to transfer hydrogen fuel from at least a portion of the fuel-supply system (3) through a buffer path (25) to a buffer (22) with at least one buffer tank (23, 24) in response to the machine entering a non-operating state, to temporarily store the hydrogen fuel in the buffer (22), and to release hydrogen fuel from the buffer (22) and at least indirectly transfer it to the power source (6) in response to the machine reentering the operating state.

Description

FUEL-RECOVERY SYSTEM FOR A HYDROGEN-POWERED MACHINETechnical Field

[0001] The invention relates to a fuel-recovery system for a hydrogen- powered machine and to a method for fuel recovery in a hydrogen-powered machine.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 energy of a chemical reaction of hydrogen and oxygen is converted into electric energy. The other category are hydrogen internal combustion engine (HICE) vehicles. In a HICE, hydrogen (H2) is used as a 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 (e.g., between 20 and 40 bar). 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 shouldbe 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) or more specifically, 20 to 40 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. Similar problems can arise with other hydrogen-powered machines, e.g., stationary machines that use hydrogen fuel.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-recovery system according to claim 1 and by a method according to claim 15.General Description of the Invention

[0007] The invention provides a fuel-recovery 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 fuelrecovery 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 isnormally fully integrated into the machine. The fuel-recovery system may comprise 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 HICE 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-recovery system is adapted to transfer hydrogen fuel from at least a portion of the fuel-supply system through a buffer path to a buffer with at least one buffer tank in response to the machine entering a non-operating state, to temporarily store the hydrogen fuel in the buffer, and 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. Accordingly, one could say that the fuelrecovery system is adapted to perform three steps.

[0010] In a first step, the fuel-recovery system transfers hydrogen fuel from at least a portion of the fuel-supply system through a buffer path to a buffer, which buffer comprises at least one buffer tank. The buffer tank may be similar to a fuel tank. However, 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 thepressure in the fuel tank. Also, while the fuel tank is designed for permanent storage of hydrogen fuel, the buffer tank is only needed for temporary storage, as will be explained below. In any case, the buffer tank is designed to receive and at least temporarily contain hydrogen fuel. The hydrogen fuel is transferred through a buffer path, which may be considered as part of the fuel-recovery system. The 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-supply system, i.e., either a portion, several portions or the fuelsupply 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 fuelsupply 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 fuelsupply 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 shut-off valve in the non-operating state. Additionally, a portion of the fuel-supply system from which the hydrogen fuel is to be transferred can 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 fuel-recovery system may perform the transfer only with a predefined time delay after the machine has entered the nonoperating 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 tightnessand 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.

[0011] 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 at least one buffer tank. In some embodiments, the fuel-recovery system may isolate the buffer tank by blocking any fluid connection with other elements, in particular with the fuel-supply system. The fuel is stored temporarily, wherein the storage time may vary e.g., between several minutes and several days. During the storage time, the fuel-recovery 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.

[0012] In a third step, which may partially overlap with the second step, hydrogen fuel is released from the buffer and is at least indirectly transferred to the power source in response to the machine re-entering the operating state. 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-recovery 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-recovery system. Direct transfer means that 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.

[0013] 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 themachine. 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 (HICE) 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 through which 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 20 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.

[0014] 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 be reintroduced into the engine through the normal injectors (either into the intake duct or directly into the combustion chamber, depending on the design of the injectionsystem). In this case, the fuel-recovery system transfers hydrogen fuel from the buffer indirectly (via the fuel-supply system) to the engine. According to another possibility, the fuel-recovery 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. For example, it could be an intake manifold or a system connected to the intake manifold. It may be an inlet to a crankcase ventilation pump or circuit. Another possibility is a venturi pump supplied with boost air from turbocharger and pulling hydrogen from buffer. There are other possibilities, too. In this embodiment, hydrogen fuel is injected into the air stream before it enters the engine, corresponding to a manifold injection..

[0015] The fuel-recovery system is preferably adapted to transfer the hydrogen fuel to the buffer by creating an underpressure in the at least one buffer tank with respect to the fuel-supply system while keeping the buffer path closed, and subsequently opening the buffer path so that the hydrogen fuel is transferred by the underpressure. In other words, the fuel-recovery system first creates an underpressure in the at least one buffer tank, i.e. , a pressure that is lower than the pressure in the fuel-supply system. Optionally, but not necessarily, this pressure may be below atmospheric pressure. While this underpressure is created, the buffer path is closed so that the buffer and the fuel-supply system are disconnected, i.e., there is no (significant) gas exchange possible. As a rule, the underpressure is created while the machine is in the operating state. However, it is not ruled out that it is at least partially created when the machine is already in the non-operating state. In order to effect the transfer of the hydrogen fuel, the fuel-recovery system connects the fuel-supply system with the buffer, i.e., it opens the buffer path. Due to the pressure difference, hydrogen fuel flows into the buffer. This, of course, happens when the machine is in the non-operating state.

[0016] The fuel-recovery system preferably comprises a buffer valve between the fuel-supply system and the buffer and is adapted to transfer hydrogen fuel to the buffer by opening the buffer valve. This buffer valve is a shut-off valve, which is adapted to block gas exchange between the fuel-supply system and the buffer. By closing the buffer valve, the fuel-supply system and the buffer are disconnected, and by opening the buffer valve, the fuel-supply system and the buffer are connected. The buffer valve is actively controllable, e.g., by a control unit of the fuel-recoverysystem. The buffer valve is opened when the machine enters or has entered the non-operational state. If the buffer comprises a plurality of buffer tanks, it may comprise one buffer valve for each buffer tank. Each buffer valve may be individually controllable so that hydrogen fuel can be selectively transferred to each buffer tank.

[0017] According to one embodiment, the fuel-recovery system is adapted to create the underpressure by connecting the at least one buffer tank to a low- pressure source and to disconnect the at least one buffer tank from the low-pressure source when the underpressure has been created. The low-pressure source may in particular be adapted to create a pressure below atmospheric pressure. Specifically, the low-pressure source may be an intake duct of the engine. The low-pressure source may also comprise a venturi pump or a crankcase ventilation pump. In order to create the underpressure, the at least one buffer tank is connected to the low- pressure source. Then, when the underpressure has been created, but not necessarily immediately, the at least one buffer tank is disconnected from the low- pressure source. It may be isolated, i.e. , any gas exchange with other elements may be prevented to preserve the underpressure. Alternatively, it may be connected to the fuel-supply system without any (significant) delay.

[0018] Preferably, the fuel-recovery system is adapted to release hydrogen fuel from the buffer and transfer it to the power source by connecting the at least one buffer tank to the low-pressure source. In this embodiment, the hydrogen fuel is sucked out of the buffer by the low-pressure source. If this embodiment is employed, the release of the hydrogen fuel from the buffer and the creation of the underpressure - as a preparation for the next storing phase - are combined in a single process, which enhances the efficiency of the fuel-recovery system. The low- pressure source is preferably connected to the power source. In particular, the low- pressure source may be the intake duct as describe above.

[0019] One embodiment provides that the buffer comprises a plurality of buffer tanks and the fuel-recovery system is adapted to transfer the hydrogen fuel to the buffer by consecutively connecting the buffer tanks to the fuel-supply system, so that one buffer tank is connected to the fuel-supply system while the remaining at least one buffer tank is disconnected from the fuel-supply system. This embodiment is much more effective than using a single buffer tank, at least if the transfer only relies on pressure equalization. The hydrogen transfer is performed inseveral stages. During each stage, the fuel-supply system is connected with one buffer tank, and (at least partial) pressure equalization is performed. After fuel transfer to the first buffer tank, the first buffer tank is disconnected from the fuelsupply system and the second buffer tank is connected. If present, a third buffer tank can be connected to the fuel-supply system after fuel transfer to the second buffer tank is complete. 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 buffer tank. 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 buffer tank. Optionally, a subsequent pressure equalization could be performed between the buffer tanks. This could be beneficial in that the first buffer tank would not be exposed to a high pressure for an extended time period, wherefore it could possibly be constructed simpler and / or cheaper. The volume-reducing benefits of this concept increase with the number of buffer tanks. On the other hand, individual ducts and valves are needed for each buffer tank, which increases cost and complexity. Accordingly, if a plurality of buffer tanks is used, a total number of two or three buffer tanks is usually optimal.

[0020] The effectiveness of the buffer can be greatly increased if it comprises a sorbent configured to sorb hydrogen. This sorbent can be provided as a filler or a lining inside a buffer tank. The sorbtion 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 a metal hydride, a metal alloy, a metal-organic framework, a molecular sieve, a carbon nanotube material, or another suitable material. 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 its quantity in gas phase is reduced. This coincides with a significant increase of the amount of substance that can be contained in a given volume. In other words, a buffer tank at least partially filled with a suitable sorbent is capable of containing a much higher amount of hydrogen thanwithout 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 buffer temperature and / or by increasing the pressure in the buffer, while it is normally possible to promote hydrogen release be increasing the buffer temperature and / or by decreasing the pressure.

[0021] According to one embodiment, the fuel-recovery system is adapted to transfer hydrogen from the buffer through a recovery path, which bypasses the fuelsupply system, at least indirectly to the power source. Like the buffer path, the recovery path may be considered as part of the fuel-recovery 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 control fuel flow through a pipe. The recovery path bypasses the fuel-supply system. In particular, it could lead directly to the engine or an intake duct of the engine. It is at least partially separate from the buffer path so that the hydrogen fuel flows along two distinct paths to the buffer and to the power source, respectively. This is especially preferred if the transfer and release of the hydrogen fuel is largely or entirely driven by a pressure difference. As a rule, the fuel-recovery system is adapted to close the recovery path while the buffer path is open and while the hydrogen fuel is stored in the buffer. Also, the buffer path is normally closed while the recovery path is open. It should be noted that the recovery path may possibly be designed simpler and / or less pressure resistant, since it only needs to withstand the maximum pressure of the buffer after storage, which can be significantly lower than the pressure in the fuel-supply system.

[0022] Another embodiment provides that the fuel-recovery 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 sorbent is used, the transfer direction through the buffer path can be largely controlled by controlling the buffer temperature. With thisembodiment, a buffer valve may be used to control the transfer. However, the buffer valve may be omitted completely, and the transfer may only be controlled by the temperature. This, however, requires the buffer temperature to be in a suitable range for effective sorption during the entire non-operating time. Correspondingly, when the machine re-enters the operating state, the buffer temperature should be in a range that promotes effective release of hydrogen from the sorbent, so that storage capacity can be effectively retrieved during engine operation or prior to engine restart.

[0023] As an alternative to connecting the at least one buffer tank to a low- pressure source, or in combination therewith, the temperature of the buffer may be used to promote the hydrogen fuel transfer. One such embodiment provides that the fuel-recovery system is adapted to reduce a buffer temperature to facilitate transferring the hydrogen fuel to the buffer and to increase the buffer temperature to facilitate releasing the hydrogen fuel from the buffer. In this context, the term “facilitate” is not to be construed in that the fuel-recovery system necessarily uses additional means to effect the transfer of the hydrogen fuel, although this is possible. The fuel-recovery system may also comprise at least one temperature sensor for detecting the buffer temperature. The “buffer temperature” can be a specific temperature of a certain part or element of the buffer (like one buffer tank) or it could be an average temperature (like the average of the temperatures of several buffer tanks). When the buffer temperature is reduced, this at least helps to transfer hydrogen fuel to the buffer, while increasing the buffer temperature helps to release hydrogen from the buffer. 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 buffer comprises an adsorbent as described above.

[0024] The fuel-recovery system may comprise at least one heat exchanger for transferring heat between the buffer and a fluid path of the machine, and be adapted to influence the buffer temperature by heat transfer through at least one heat exchanger. The fluid path may in particular be adapted to conduct oil, coolingfluid, or exhaust gas. In this context, the term “heat exchanger” is not to be construed in a limiting manner, but rather refers to any device that enables heat transfer without substance transfer. In some embodiments, the fuel-recovery system is adapted to control the flow through the fluid path or through the heat exchanger, respectively.

[0025] As an alternative to the abovementioned heat exchanger or in addition thereto, the fuel-recovery system may comprise an electrical heater adapted to increase the buffer temperature. The electrical heater can be useful in various situations. For instance, when the machine has been non-operative for a longer time period, the temperature of a cooling fluid is low and even the exhaust system - if present - may initially have a low temperature. In situations like these, it may take several minutes before enough heat is available to effectively increase the buffer temperature, e.g., via the abovementioned heat exchanger. An electric heater can increase the buffer temperature without significant delay. The heater can be activated even before the engine is started. The electrical heater may be controlled regarding its operating times as well as regarding its power output.

[0026] 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-recovery system is adapted to release hydrogen fuel from the buffer to the atmosphere if a buffer pressure in the buffer exceeds a pressure limit. 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 be measured by a sensor and a relief valve could be actively opened according to the measurement.

[0027] The invention further provides a method for fuel recovery for a hydrogen 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. According to the invention, the method comprises:- transferring hydrogen fuel from at least a portion of the fuel-supply system through a buffer path to a buffer with at least one buffer tank in response to the machine entering a non-operating state,- temporarily storing the hydrogen fuel in the buffer, and- releasing hydrogen fuel from the buffer and at least indirectly transferring it to the power source in response to the machine re-entering the operating state.

[0028] All these terms have been explained above with respect to the inventive fuel-recovery system and therefore will not be explained again. Preferred embodiments of the inventive method correspond to those of the inventive fuelrecovery system.Brief Description of the Drawings

[0029] 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 view of components of a hydrogen vehicle with a fuelrecovery system according to a first embodiment of the present invention;Fig.2 is a schematic view of components of a hydrogen vehicle with a fuelrecovery system according to a second embodiment of the present invention;Fig.3 is a schematic view of components of a hydrogen vehicle with a fuelrecovery system according to a third embodiment of the present invention;Fig.4 is a schematic view of components of a hydrogen vehicle with a fuelrecovery system according to a fourth embodiment of the present invention; andFig.5 is a schematic view of components of a hydrogen vehicle with a fuelrecovery system according to a fifth embodiment of the present invention.Description of Preferred Embodiments

[0030] Figs.1 shows a schematic view of some elements of a hydrogen- powered machine, in this case a hydrogen vehicle, more specifically an HICEvehicle, with a first embodiment of an inventive fuel-recovery system 20. This 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 an intake manifold) and an exhaust duct 9 (normally 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. Instead of the injector nozzle 11 , an open end of a pipe could be arranged to inject the hydrogen. Also, instead of the direct injector 10, or additionally, an indirect injector could be employed, which e.g., injects hydrogen fuel into the intake duct 8. The engine 6 represents a power source of the vehicle, in which hydrogen is burned with oxygen to convert chemical energy into mechanical energy. The mechanical energy is used to drive the vehicle and may also be converted through a generator (not shown) into electrical energy.

[0031] 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 pressure may be several hundred bar(a), e.g., up to 700 bar(a). The fuel tank 1 typically includes a regulator stage configured to deliver hydrogen fuel at a pressure of about 50 bar(a). The fuel tank 1 is connected to the engine 6 via a fuel-supply system 3, which is only shown schematically. A shut-off valve, which is not shown here, may be integrated into the fuel tank 1 or may be interposed between the fuel tank 1 and the fuel-supply system 3. The fuel-supply system 3 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 the pressure of the hydrogen fuel, e.g., from about 50 bar(a) downstream of the regulator stage to between 20 and 40 bar(a), a heating or cooling device for adjusting the temperature of the hydrogen fuel etc. The fuel-supply system 3 comprises a shut-off valve 2, by which the fuel rail 5 can be isolated from HRM 4 and the fuel tank 1 (i.e. , flow of fuel downstream of the shut-off valve 2 is prevented when the valve is closed). Shut-off valve 2 may be independent or integrated in the hydrogen regulation module 4. 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 rail 5 is isolated from the HRM 4 and the fuel tank1 . However, a considerable amount of hydrogen fuel still resides in the fuel rail 5 and is still under considerable pressure, e.g., between 20 and 40 bar(a).

[0032] The function of the fuel-recovery system 20 is to mitigate any explosion risk originating from hydrogen fuel leaking out of the fuel-supply system 3, specifically out of the fuel rail 5, while avoiding any unnecessary waste of hydrogen. In the embodiment shown in fig. 1 the fuel-recovery system 20 comprises a buffer22 with a single buffer tank 23, which is connected to the fuel-supply system 3 via a buffer path 25. Although the buffer path 25 is shown connected to the fuel-supply system 3 between the HRM 4 and the fuel rail 5, this is just by way of example and it could be connected directly to the fuel rail 5. In other embodiments, the buffer path 25 could additionally or exclusively be connected to the HRM 4. The buffer path 25 comprises a buffer valve 26, which is a shut-off valve controlled by a control device 21 of the fuel-recovery system 20. 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 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. Conventionally, an orifice 30 defines a flow cross-section narrower than the piping / conduit in which it is installed. The orifice 30 may optionally be integrated into the recovery valve 29. The fuel-recovery 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 .

[0033] 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 buffer tank 23 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 buffer tank 23 is created, with respect to the outer atmosphere and especially with respect to the fuel-supply system 3. When the control unit 21 senses through the pressure sensor 41 that the pressure in the buffer tank 23 is below a certain value, it may close the recovery valve 29. If, due to some leakage, the pressure on the buffer tank23 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 shutoff 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 has entered the nonoperating state.

[0034] In response to the vehicle entering the non-operating state, the fuelrecovery system 20 transfers hydrogen fuel from the fuel-supply system 3 (specifically, from the fuel rail 5) 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 the underpressure in the buffer tank 23, hydrogen fuel flows from the fuel-supply system 3 into the buffer 22 until pressure equalization has been achieved. In order to reach a target pressure in the fuel-supply system 3 that is considered safe, the volume of the buffer tank 23 has to be considerably larger than that of the fuel-supply system 3. By way of example, if the pressure in the fuel-supply system 3 is 40 bar(a), the pressure in the buffer tank 23 is 0,5 bar(a) and the target pressure is 1 ,5 bar(a), the volume of the buffer tank 23 has to be larger by a factor of 38,5. 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.

[0035] When the vehicle re-enters the operating state, the shut-off valve 2 is reopened and the pressure in the fuel-supply system again reaches a high value of e.g., 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. A considerable portion of the hydrogen fuel is sucked out of the buffer tank 23 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 buffer tank 23 has reached its previous value (e.g., 0,5 bar (A)), the control unit 21 may again close the recovery valve 29.

[0036] 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 25exceeds a certain threshold, the pressure-relief valve 32 opens, whereby some hydrogen is vented through the relief path 31 into the atmosphere.

[0037] Fig. 2 shows elements of a vehicle with a second embodiment of an inventive fuel-recovery system 20, which is largely identical to the one shown in fig.I and insofar will not be explained again. Also, for the sake of simplicity, apart from the fuel-recovery system 20, only the fuel-supply system 3 and the injector nozzleI I are shown. In this embodiment, the buffer 22 comprises a first buffer tank 23 and a second buffer tank 24, which are connected to the fuel-supply system 3 by a branching buffer path 25. Both buffer tanks 23, 24, individually and even combined, have a volume which may be considerably smaller than the volume of the single buffer tank 23 in the first embodiment. A first buffer valve 26 is adapted for separating the first buffer tank 23 from the fuel-supply system 3 and a second buffer valve 27 is adapted to separate the second buffer tank 24. A likewise branching recovery path 28 connects both buffer tanks 23, 24 via a single recovery valve 29 to the injector nozzle 11 . A check valve 33 is interposed between the buffer tanks 23, 24 and is adapted to open if the pressure in the second buffer tank 24 is higher than the pressure in the first buffer tank 23.

[0038] 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 transferable 27 closed. After a short period of time, pressure equalization between the fuel-supply system 3 and the first buffer tank 23 has been achieved. However, due to the smaller volume of the first buffer tank 23, 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 second buffer tank 24 until pressure equalization between the fuel-supply system 3 and the second buffer tank 24 has been reached. 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. By way of example, if the initial pressure in the fuel-supply system 3 is 40 bar(a), the initial pressure in both buffer tanks 23, 24 is 0,5 bar(a) and the target pressure is 1 ,5 bar(a), the volume of the first buffer tank 23 can be 5,8 times larger than that of the fuel-supply system and the volume of the second buffer tank 24 canbe 4,8 times larger, corresponding to a total factor of 10,6 (as compared to 38,5 in the first embodiment).

[0039] When the vehicle re-enters the operating state, fuel from both buffer tanks 23, 24 can be released through the single recovery valve 29, since they are coupled by the check valve 33, which opens when the pressure in the second buffer tank 24 exceeds the pressure in the first buffer tank 23.

[0040] Fig.3 shows a third embodiment of an inventive fuel-recovery system20, which differs from the previous embodiments in that the buffer 22 is not connected to the injector nozzle 11 by a recovery path. Also, the single buffer tank 23 is partially filled with a sorbent which can adsorb and / or absorb hydrogen. The sorption of hydrogen in the buffer tank 23 may be based on a physical and / or a chemical process. It is temperature-dependent, so that reducing the buffer temperature leads to an increased sorption, whereas increasing the buffer temperature releases hydrogen from the buffer tank 23. In order to control or at least influence the buffer temperature, the control unit 21 can control an electric heater 37 that is in thermal contact with the buffer tank 23. Furthermore, it can control a flow valve 36 in a fluid path 34 that comprises a heat exchanger 35. If the flow valve 36 is opened, a fluid flows through the fluid path 34 and the heat exchanger 35. In this embodiment, the fluid path connects the exhaust duct 9 with the intake duct 8 and may be an EGR line. Accordingly, the fluid is an exhaust gas. Alternatively, the fluid path 34 could be part of a coolant system or an oil circulation system.

[0041] 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 is comparatively low (e.g., between 10°C and 30°C), sorption of hydrogen fuel in the buffer tank 23 is facilitated. By way of example, the sorbent may be LaNi5 having a density of 8,4 kg / l. In order to reach a target pressure of 1 ,5 bar(a), starting from an initial pressure in the fuel-supply system 3 of 40 bar(a), it may be sufficient if the volume of the buffer tank 23 corresponds to 75% of the volume of the fuel-supply system. This is considerably less than in the first or second embodiment. After the sorption process has been completed, the control unit 21 closes the buffer valve 26.

[0042] When the vehicle re-enters the operating state, the control unit 21 opens the flow valve 36. To accelerate the warming of the buffer tank 23 during the initial phase of the vehicle operation, the control unit 21 also activates the electrical heater 37, which may be switched off after some time when enough heat is transferred through the heat exchanger 35. As the buffer temperature increases, hydrogen is released from the adsorbent and re-enters the gas phase. Before or after the heating of the buffer tank 23 has started, the control unit 21 opens the buffer valve 26, so that hydrogen fuel flows through the buffer path 25 into the fuelsupply system 3. When at least the majority of the hydrogen has been released from the adsorbent, the buffer valve 26 can be closed again. If the pressure in the buffer path 25 exceeds a threshold value, hydrogen can be released into the atmosphere through the relief path 31 with the relief valve 32.

[0043] Fig.4 shows a fourth embodiment that is largely identical to the third embodiment. In this case, however, the relief path 31 has been replaced with a bypass path 38 that 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 tank 23 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.

[0044] Fig.5 shows a fifth embodiment that is also largely identical to the third embodiment. However, the relief path 31 is completely omitted as well as the buffer valve 26. Accordingly, the buffer path 25 is open for gas exchange at all times. The transfer of hydrogen fuel to and from the buffer 22 is completely controlled by the buffer temperature. Accordingly, while the vehicle is in operating state, the control unit 21 uses the heat exchanger 35 and / or the electrical heater 37 to keep the buffer temperature sufficiently high to largely prevent any sorption of hydrogen in the buffer 22. Then, when the vehicle enters the non-operating state, the control unit 21 closes the flow valve 36 and de-activates the electrical heater 37. Thus, the buffer temperature drops towards the temperature of its surroundings and starts to adsorb hydrogen from the fuel-supply system 3. While the vehicle is in its non-operating state, the buffer 22 stores the hydrogen as long as its temperature does not increase significantly. When the vehicle re-enters the operating state, the control unit 21 usesthe heat exchanger 35 and / or the electrical heater 37 to increase the buffer temperature so that the hydrogen is largely expelled from the buffer tank 23.Legend of Reference Numbers:1 fuel tank 30 orifice2 shut-off valve 31 relief path3 fuel-supply system 32 relief valve4 hydrogen regulation module 33 check valve5 fuel rail 34 fluid path6 engine 35 heat exchanger7 cylinder 36 flow valve8 intake duct 37 electrical heater9 exhaust duct 38 bypass path10 direct injector 39 bypass valve11 injector nozzle 40 temperature sensor20 fuel-recovery system 41 pressure sensor21 control unit22 buffer23,24 buffer tank25 buffer path26,27 buffer valve28 recovery path29 recovery valve

Claims

Claims1 . A fuel-recovery system (20) for a hydrogen 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-recovery system (20) is adapted to transfer hydrogen fuel from at least a portion of the fuel-supply system (3) through a buffer path (25) to a buffer (22) with at least one buffer tank (23, 24) in response to the machine entering a non-operating state, to temporarily store the hydrogen fuel in the buffer (22), and to release hydrogen fuel from the buffer (22) and at least indirectly transfer it to the power source (6) in response to the machine re-entering the operating state.

2. The fuel-recovery system according to claim 1 , wherein the power source (6) of the machine is a hydrogen internal combustion engine, and the fuel-supply system (3) comprises at least one of a fuel rail assembly (5) and a hydrogen regulation module (4).

3. The fuel-recovery system according to claim 2, being adapted to transfer hydrogen fuel from the buffer (22) to an intake duct (8) of the engine.

4. The fuel-recovery system according to any one of the preceding claims, being adapted to transfer the hydrogen fuel to the buffer (22) by creating an underpressure in the at least one buffer tank (23, 24) with respect to the fuel-supply system (3) while keeping the buffer path (25) closed, and subsequently opening the buffer path (25) so that the hydrogen fuel is transferred by the underpressure.

5. The fuel-recovery system according to any one of the preceding claims, being adapted to create the underpressure by connecting the at least one buffer tank (23, 24) to a low-pressure source (8) and to disconnect the at least one buffer tank (23, 24) from the low-pressure source (8) when the underpressure has been created.

6. The fuel-recovery system according to any one of the preceding claims, being adapted to release hydrogen fuel from the buffer (22) and transfer it to the powersource (6) by connecting the at least one buffer tank (23, 24) to the low-pressure source (8).

7. The fuel-recovery system according to any one of the preceding claims, wherein the buffer (22) comprises a plurality of buffer tanks (23, 24) and the fuel-recovery system (20) is adapted to transfer the hydrogen fuel to the buffer (22) by consecutively connecting the buffer tanks (23, 34) to the fuel-supply system (3), so that one buffer tank (23, 24) is connected to the fuel-supply system (3) while the remaining at least one buffer tank (23, 24) is disconnected from the fuel-supply system (3).

8. The fuel-recovery system according to any one of the preceding claims, wherein the buffer (22) comprises a sorbent configured to sorb hydrogen.

9. The fuel-recovery system according to any one of the preceding claims, being adapted to transfer hydrogen from the buffer (22) through a recovery path (28), which bypasses the fuel-supply system (3), at least indirectly to the power source (6).

10. The fuel-recovery system according to any one of the preceding claims, being adapted to transfer hydrogen from the buffer (22) through the buffer path (25) to the fuel-supply system (3).11 . The fuel-recovery system according to any one of the preceding claims, being adapted to reduce a buffer temperature to facilitate transferring the hydrogen fuel to the buffer (22) and to increase the buffer temperature to facilitate releasing the hydrogen fuel from the buffer (22).

12. The fuel-recovery system according to any of the preceding claims, comprising at least one heat exchanger (35) for transferring heat between the buffer and a fluid path (34) of the machine, and being adapted to influence the buffer temperature by heat transfer through at least one heat exchanger (35).

13. The fuel-recovery system according to any one of the preceding claims, comprising an electrical heater (37) adapted to increase the buffer temperature.

14. The fuel-recovery system according to any one of the preceding claims, being adapted to release hydrogen fuel from the buffer (22) to the atmosphere if a buffer pressure in the buffer (22) exceeds a pressure limit.

15. A method for fuel recovery for a hydrogen 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 method comprises:- transferring hydrogen fuel from at least a portion of the fuel-supply system (3) through a buffer path (25) to a buffer (22) with at least one buffer tank (23) in response to the machine entering a non-operating state,- temporarily storing the hydrogen fuel in the buffer (22), and- releasing hydrogen fuel from the buffer (22) and at least indirectly transferring it to the power source (6) in response to the machine re-entering the operating state.

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