Hydrogen tank pressure flow monitoring, and thermal pumping of liquid hydrogen

Abstract

A hydrogen (H2) tank monitoring system includes first and second sensors are configured to sense a condition of the quantity of H2 within the tank. A computerized analysis and detection module cross-checks sensor data from the first sensor with sensor data from the second sensor to detect an abnormal condition within the tank. Also described is a liquid hydrogen (LH2) fuel storage system for a fuel cell-powered vehicle and includes a main LH2 storage fuel tank configured for close to ambient pressure storage of LH2, and one or more gas accumulator tanks (GATs) smaller than the main LH2 storage fuel tank and configured for elevated pressure storage of LH2 and for feeding pressurized LH2 to the fuel cell.

Description

CI-ZERO 23.10 / 13 PCT HYDROGEN TANK PRESSURE FLOW MONITORING, AND THERMAL PUMPING OF LIQUID HYDROGEN

[0001] The present disclosure relates to hydrogen (H2) tank pressure flow monitoring and to thermal pumping of liquid hydrogen (LH2). The disclosure has particular utility in connection with H2tank pressure flow monitoring and to thermal pumping of LH2for fueling H2 fuel cells for use in powering electric engines for transport vehicles including aircraft and will be described in connection with such utility, although other utilities are contemplated.

[0002] This section provides background information related to the present disclosure which is not necessarily prior art. This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all its features.

[0003] Exhaust emissions from transport vehicles are a significant contributor to climate change. Conventional fossil fuel–powered aircraft engines release CO2 emissions. Also, fossil fuel–powered aircraft emissions include non-CO2effects due to nitrogen oxide (NOx), vapor trails, and cloud formation triggered by the altitude at which aircraft operate. These non-CO2effects are believed to contribute twice as much to global warming as aircraft CO2 and are estimated to be responsible for two-thirds of aviation’s climate impact. Additionally, the high-speed exhaust gases of conventional fossil fuel– powered aircraft engines contribute significantly to the extremely large noise footprint of commercial and military aircraft, particularly in densely populated areas.

[0004] Rechargeable battery-powered, terrestrial vehicles, i.e., “EVs”, are slowly replacing conventional fossil fuel–powered terrestrial vehicles. However, the weight of batteries and limited energy storage of batteries makes rechargeable battery-powered aircraft generally impractical.

[0005] H2 fuel cells offer an attractive alternative to fossil fuel–burning engines. H2 fuel cell tanks may be quickly filled and store significant energy, and other than the relatively small amount of unreacted H2 gas, the reaction output exhausted from H2 fuel cells comprises essentially only water. However, storage of LH2under conditions suitable for use in feeding a H2 fuel cell presents a challenge, particularly in the case of aircraft.

[0006] A fuel cell is an electrochemical cell that converts chemical energy into electrical energy by electrochemical reduction-oxidation (redox) reactions. Fuel cells include an anode and a cathode separated by a membrane and an ionically-conductive electrolyte. During operation, a fuel (e.g., H2) is supplied to the anode and an oxidant (e.g., oxygen or air) is supplied to the cathode. The fuel is oxidized at the anode, producing positivelyCI-ZERO 23.10 / 13 PCT charged ions (e.g., H2ions) and electrons. The positively charged ions travel through the electrolyte from the anode to the cathode, while the electrons simultaneously travel from the anode to the cathode outside the cell via an external circuit, which produces an electric current. The oxidant supplied to the cathode is reduced by the electrons arriving from the external circuit and combines with the positively charged ions to form water. The reaction between oxygen and H2 is exothermic, generating heat that needs to be removed from the fuel cell.

[0007] Fuel cells may be used as power sources for electric motors of electric vehicles and hybrid electric vehicles, including aircraft. In such applications, it is often desirable to use H2 as a fuel within the fuel cell, due in part to the cost, efficiency, energy output, and environmental benefits that H2 can offer over similar fuel sources, such as fossil fuels. However, a common problem with H2 is that it presents serious risks of flammability if leaks in the fuel cell systems are present and not detected. Even in the absence of any ignition risk, uncontrolled loss of H2can prevent a vehicle from safely completing its intended mission. For aircraft in particular, the uncontrolled loss of H2 can lead to emergency situations which can present significant hazards to aircraft passengers, aircraft personnel, and others. For example, an inadvertent loss of H2 can force the aircraft into emergency landings or operate with scaled back performance.

[0008] In conventional H2 fuel cell systems, mass flow sensor (MFS) modules are used to sense the mass flow rates of air ingested into a fuel cell cathode and the mass flow rate of H2 from a fuel tank ingested into an anode, which can provide an indication of the quantity of gas consumed from a tank. FIG.1 depicts a conventional H2fuel cell system 12 which is carried on an aircraft 10. The H2 fuel cell system 12 includes a fuel tank 20 containing H2, and a H2fuel cell 14 with an MFS module 16 positioned proximate thereto, such as in fluid communication with the H2 fuel cell 14 or in communication with an engine 18 of the aircraft 10. While the MFS module 16 offers benefits to determining the level of H2, they are somewhat unreliable. If the MFS module 16 fails on an H2fuel cell-powered aircraft, the consequence may include damage to the fuel cell itself and resulting loss of engine power.

[0009] Additionally, many MFS modules use Coriolis force and strain gauges in their operation and are therefore sensitive to settings with significant movement and mechanical forces. Given the movement and vibration that is common to aircraft operation, MFS modules often are inaccurate and unreliable.CI-ZERO 23.10 / 13 PCT

[0010] Various solutions to the unreliability of MFS modules have been proposed, but these proposals have shortcomings. One such proposal uses a differential pressure transmitter to measure mass flow rate of H2, but this type of system requires significant calibration to provide accurate results. Another proposal detects the rate of pressure rise in H2fueling systems and compares that to measured pressure and flow rate, e.g., Hydrogen Vehicle Fueling Standards such as those disclosed by SAE International. If the pressure increases less than expected for a given amount of flowage, then a leak may be suspected, and valves may be closed automatically to limit the amount of fuel lost. If the pressure rises more than expected for a given flow rate, then a flow restriction may be suspected. Flow can be interrupted to prevent further damage or misbehavior. An operator can be alerted to check for proper configuration of the equipment.

[0011] In both of these proposals, detection of an anomaly, such as a leak or blockage, results in the system closing valves, shutting off the H2 tank, and stopping all flow of gas. This approach is akin to how a circuit breaker operates, where a fault situation causes the entire system to shut off. When this occurs, however, the H2-powered aircraft would be forced to abandon its mission and land, possibly at great risk before the anomaly can be investigated further. As such, even falsely detected anomalies can result in significant inefficiencies in the operation of the aircraft and present disruptions to the aircraft’s ability to complete its mission, and moreover great risk to the life of passengers and crew.

[0012] As such, there is a need to address the aforementioned deficiencies and inadequacies of conventional systems. In accordance with the present disclosure, we provide a solution to this problem by providing systems and methods to cross-check data from H2fuel cell system sensors to increase reliability of the operation of a H2-powered vehicle.

[0013] In accordance with the present disclosure, we provide an H2fuel cell system for powering an aircraft comprising at least one fuel tank configured to hold a quantity of H2 therein and at least one fuel cell; at least first and second sensors configured to sense a condition of at least one of: the fuel tank or the quantity of H2 within the fuel cell system; and a computerized analysis and detection module in communication with the first and second sensors, wherein the analysis and detection module is configured to cross-check sensor data from the first sensor with sensor data from the second sensor to detect an abnormal condition within the fuel cell system or an abnormal H2 flow condition in the fuel cell system, wherein the detected abnormal condition further comprises aCI-ZERO 23.10 / 13 PCT determined leak in the fuel tank based on monitoring pressure in the fuel tank over a period of time, wherein the leak is determined based on a difference between a calculated pressure within the fuel tank relative to a measured pressure from sensor data, and wherein a leak rate is determined; and when the abnormal condition is detected, the fuel cell system is configured to continue to maintain operation of the fuel cell system unchanged until the aircraft lands, and if continuing operation of the fuel cell system is not possible, the fuel cell system is configured to reduce operation of the H2 fuel cell system to a safe operating mode; and if unable to continue the safe operating mode of the H2fuel cell system, the fuel cell system is configured to enter a safe shutdown mode of the H2 fuel cell system.

[0014] According to aspect A of the present disclosure there is provided a H2 tank monitoring system comprising: a fuel cell system comprising at least one fuel tank configured to hold a quantity of H2 therein and at least one fuel cell; at least first and second sensors configured to sense a condition of at least one of: the fuel tank or the quantity of H2 within the fuel tank, and wherein the first and second sensors comprise one of: a mass flow sensor; a pressure sensor; a flow sensor; an acoustic senso; an optical sensor; an electrochemical sensor; a thermal sensor or a flame ionization sensor; and a computerized analysis and detection module in communication with the first and second sensors, wherein the analysis and detection module is configured to cross-check sensor data from the first sensor with sensor data from the second sensor to detect an abnormal H2 flow condition within the fuel cell system wherein the detected abnormal H2 flow condition comprises a H2leak in the fuel cell system based on monitoring pressure in the fuel tank over a period of time, wherein the H2 leak is determined based on a difference between a calculated pressure within the fuel tank relative to a measured pressure from sensor data, and wherein a H2 leak rate is determined; and when the abnormal H2 flow condition is detected, the fuel cell system is configured to continue to maintain operation of the fuel cell system unchanged using substitute sensor data until the aircraft lands, and if continuing operation of the fuel cell system is not possible if the abnormal H2flow condition is determined to be minor based on the abnormal H2 flow condition, the fuel cell system is configured to reduce operation of the H2fuel cell system to a safeoperating mode; and if unable to continue the safe operating mode of the H2fuel cellsystem based on the abnormal H2flow condition, the fuel cell system is configured to enter a safe shutdown mode of the H2 fuel cell system, to transmit an alarm message or error message to aircraft personnel of the aircraft on which the H2 fuel cell system isCI-ZERO 23.10 / 13 PCT located, and to accept an override command from the aircraft personnel so that he aircraft may be safely landed.

[0015] According to one embodiment, the analysis and detection module is configured to cross-check sensor data from the first sensor with sensor data from the second sensor to detect sensor failure.

[0016] In a still further embodiment, sensor data from the first and second sensors is received by the analysis and detection module independently of one another.

[0017] In yet another embodiment, the system further comprises a communication module configured to trigger an alarm when the abnormal condition is detected.

[0018] In another embodiment, sensor data from the first sensor further comprises at least one of: a pressure calculated from historically determined pressure; a time interval; or a temperature difference, and the sensor data from the second sensor further comprises at least one of: integrated fuel cell current; integrated flow rate; or pressure.

[0019] According to aspect B of the present disclosure there is provided a method of monitoring a H2 fuel cell system comprising at least one fuel tank configured to hold a quantity of H2therein and at last one fuel cell for powering an aircraft, using the H2tank monitoring system of aspect A of the present disclosure.

[0020] According to aspect C of the present disclosure there is provided a method of monitoring a H2 fuel cell system, comprising at least one fuel tank configured to hold a quantity of H2therein and at least one fuel cell for powering an aircraft, the method comprising steps of: analyzing sensor data inputs from at least two sensors configured to sense a condition of the at least one fuel tank having a quantity of H2therein; detecting an abnormal condition within the fuel tank or the quantity of H2the fuel tank or an abnormal H2flow condition in the fuel cell system, by cross-checking sensor data from one sensor with at least another sensor; distinguishing between a sensor failure and an operational defect of the fuel tank; and substituting a parameter value for a signal from a failed sensor when a sensor failure is determined, wherein after the sensor failure is detected: continuing operation of the H2fuel cell system is unchanged using substitute sensor data; or if continuing operation of the H2 fuel cell system unchanged is not possible, reducing operation of the H2fuel cell system to a safe operating mode; and ifunable to continue the safe operating mode of the H2fuel cell system, entering a safeshutdown mode of the H2fuel cell system, transmitting an alarm message or an error message to aircraft personnel of the aircraft on which the H2 fuel cell system is located,CI-ZERO 23.10 / 13 PCT and accepting an override command from the aircraft personnel so that the aircraft can be safely landed.

[0021] In one embodiment, substituting the parameter value for the signal from the failed sensor further comprises at least one of: using parameter values measured by equivalent parallel sensors; substituting parameter values derived from remaining dissimilar functional sensors; synthesizing probable parameter values based on operating conditions; or inserting an error code to indicate that a signal value of the failed sensor is invalid.

[0022] In another embodiment, the abnormal condition is identified based on an anomalous or inconsistent value within the sensor data.

[0023] In another embodiment, the method further comprises substituting a parameter value for a signal from a failed sensor when a sensor failure is determined.

[0024] In yet another embodiment, substituting the parameter value for the signal from the failed sensor further comprises at least one of: using parameter values measured by equivalent parallel sensors; substituting parameter values derived from remaining dissimilar functional sensors; synthesizing probable parameter values based on operating conditions; or inserting an error code to indicate that a signal value of the failed sensor is invalid.

[0025] In a further embodiment, the abnormal condition is identified based on an anomalous or inconsistent value within the sensor data.

[0026] According to aspect D of the present disclosure there is a method of mapping error conditions of a H2fuel cell system using the H2tank monitoring system of aspect A of the present disclosure.

[0027] According to aspect E of the present disclosure there is a method of mapping error conditions of a H2 fuel cell system using the method of monitoring a H2 fuel cell system of aspect B of the present disclosure.

[0028] According to aspect F of the present disclosure there is a method of mapping error conditions of a H2fuel cell system using the method of monitoring a H2fuel cell system of aspect C of the present disclosure.

[0029] According to aspect G of the present disclosure there is a method of mappingerror conditions of a H2fuel cell system, the method comprising: identifying a systemdesign of a H2fuel cell system; determining an ideal system behavior of the H2fuel cell system; correlating proper behavior of the H2 fuel cell system with at least two measuredCI-ZERO 23.10 / 13 PCT sensor signals; setting allowable variation limits to the at least two measured sensor signals; and correlating measured sensor signals with desired behavior.

[0030] In another embodiment, the method further comprises reporting at least one of: an alarm message; an error message; or a status report of the H2 fuel cell system.

[0031] In yet another embodiment, the method further comprises operating at least one actuator to adjust a physical property of the H2 fuel cell system.

[0032] In a further embodiment, the method further comprises measuring a level of liquid or mass of H2 fuel in a fuel tank of the H2 fuel cell system.

[0033] LH2storage allows high potential mass fractions of H2as a percentage of the total system weight (tank + fuel), up to 40% in the lightweight composite cryogenic storage dewar structures appropriate for an aircraft. However, the lightweight cryogenic storage dewar structures desirable for aviation are rated only for close to ambient pressure of LH2 / H2 gas mix inside the tank — which generally is incompatible with driving a fuel cell directly from such a LH2 / H2gas mix due to a typical fuel cell requiring 5–10 bar gas pressure input. LH2 storage tanks rated to 5–10 bar is 2–3 times heavier than the ones designed for close to ambient pressure storage, thereby negating a significant part of the mass advantage of LH2 storage for aircraft.

[0034] In accordance with aspect H of the present disclosure we provide an LH2storage system comprising a primary tank configured for close to ambient pressure storage, and one or more small, high-pressure, gas accumulator tanks (GATs) rated for, e.g., 5–10 bar or more gas pressure for feeding a fuel cell. The primary tank may be formed as a relatively light-weight composite structure designed to store LH2 / H2gas mixture at close to ambient pressure and sized to store sufficient LH2 to provide a desired operating range of the aircraft. Also, being designed to operate at close to ambient pressure, the primary tank may be shaped to fit within the wings or fuselage of the aircraft.

[0035] In accordance with the present disclosure, we provide one or more small GATs with a thermal pumping system to provide the necessary conditioning to raise the pressure of the LH2gas for use as a fuel cell feed. Preferably two or more GATs are provided, operating out-of-phase with one another to provide an uninterrupted supply of LH2pressurized for use as a fuel cell feed.

[0036] The overall system employs a thermal pumping scheme and operates as follows: one of the GATs is cooled by circulating LH2from the main tank through a cooling interface on the GAT. Cooling the GAT lowers the temperature within the GAT and creates a vacuum in the GAT. LH2 is then delivered from the main tank into the cooledCI-ZERO 23.10 / 13 PCT GAT via an inlet conduit valve. The LH2may be delivered via gravity, pumping or pulled into the GAT by vacuum, or via a combination of two or more of gravity, pumping and vacuum. The inlet valve is then closed, and the contents of the GAT are heated by heating the tank via a heating interface which is heated by heat from the aircraft propulsion system. By way of example but not limitation, the heat may be provided by heat exchanger with coolant from the vehicle propulsion system downstream of the propulsion system turbine. As another example, the heat may be supplied by heat exchanger with the fuel cell cathode exhaust. Heating the GAT increases the pressure in the tank due both to evaporation of the LH2into H2gas and thermodynamic gas pressure. The LH2 is then delivered at elevated pressure to a downstream gasifier for feed to the fuel cell. In a preferred embodiment, a second GAT is provided comprising a second GAT, equipped with cooling and heating interfaces, valves, etc., and configured to operate in parallel but out-of-phase with the first GAT which permits us to provide an uninterrupted supply of LH2at a desired pressure to the fuel cell gasifier.

[0037] More particularly, in accordance with a preferred embodiment of the present disclosure, there is provided a LH2storage system for an aircraft comprising a main LH2tank configured to operate at or near ambient pressure and two or more GATs configured to raise the pressure of the LH2within the GATs for use as a fuel cell feed rise. An increased pressure, typically 5–10 bar, is achieved and maintained by a thermal pumping scheme utilizing heat flow within the GAT. An interface between the main LH2tank and GATs comprises a simple LH2 valve allowing gravity or pump-and / or vacuum-assisted flow of ambient pressure LH2from the main LH2tank into the GATs. The GATs each are equipped with two thermal interfaces — a cooling interface configured to allow LH2 from the main tank to selectively cool the GATs in sequence, and a heating interface allowing warm working liquid / gas (e.g., excess heat from the aircraft propulsion system) to selectively heat the contents of the GATs in sequence) to raise the pressure of the LH2 in the GATs to a working pressure, e.g., to 5 to 10 bar, for feed to the fuel cells.

[0038] In a preferred embodiment, the system works in the following cycle: 1. A first GAT, GAT-1, is cooled by contact with a cooling interface which is cooled by LH2from the main tank. As the tank is cooled, the interior pressure within the GAT drops. 2. Once the pressure in GAT-1 drops below the LH2tank pressure, an inlet valve is opened to permit LH2 to flow into GAT-1. The LH2 flows into GAT- 1 by the force of gravity or is pumped into GAT-1 or pulled into GAT-1 viaCI-ZERO 23.10 / 13 PCT vacuum or a combination of two or more of gravity, pumping and vacuum. An amount of LH2 is introduced to partially fill GAT-1, and the GAT-1 inlet valve is closed. 3. GAT-1 heating interface is then activated by circulating hot fluid from the aircraft propulsion system, causing GAT-1 to heat up, increasing the pressure in GAT-1 due to both evaporation of LH2 into H2 gas and thermodynamic gas pressure rise due to temperature increase. A desired elevated pressure of 5 to 10 bar is achieved and maintained via control of the heat flow into GAT-1. 4. The GAT-1 outlet valve is opened to allow flow of LH2under elevated pressure to a gasifier supplying the fuel cell. 5. While GAT-1 is supplying the fuel cell with pressurized LH2, a second GAT, GAT-2, undergoes a similar pressure charging cycle as described above. 6. Once the GAT-1 H2 contents are depleted or close to depletion, the GAT-1 outlet valve is closed, and GAT-1 is again chilled, refilled and pressurized with LH2 and repressurized as before. 7. While GAT-1 is being chilled, refilled and pressurized, GAT-2 becomes the primary source of H2 for the fuel cell, and the cycle repeats.

[0039] According to aspect I of the present disclosure, there is provided a LH2fuel storage system for a fuel cell-powered vehicle, comprising a main LH2 storage fuel tank configured for close to ambient pressure storage of LH2, and one or more gas accumulator tanks (GATs) smaller than the main fuel tank and configured for elevated pressure storage of LH2and for feeding pressurized LH2to the fuel cell, wherein the one or more GATs each have a cooling interface configured to cool the GAT employing LH2 from the main fuel tank, and a heating interface configured to heat contents of the GAT with warm working fluid from the fuel cell-powered vehicle whereby to raise pressure of the LH2in the GAT to a working pressure for feeding the LH2to the fuel cell.

[0040] According to one embodiment, the main LH2 storage fuel tank comprises a composite structure.

[0041] In another embodiment the vehicle is an airplane.

[0042] In yet another embodiment, the LH2fuel storage system comprises two or more GATs configured to run out-of-phase with one another.

[0043] In a further embodiment the working pressure is 5-10 bar.

[0044] In a still further embodiment, the warm working fluid comprises coolant from a vehicle propulsion system.CI-ZERO 23.10 / 13 PCT

[0045] In yet another embodiment, the warm working fluid comprises cathode exhaust from the fuel cell.

[0046] According to aspect J of the present disclosure, there is provided a method for providing LH2 fuel to a fuel cell-powered vehicle, comprising the steps of: (a) providing LH2fuel storage system as above described, the system including a main LH2 storage fuel tank configured for close to ambient pressure storage of LH2, and one or more gas accumulator tanks (GATs) smaller than the main fuel tank and configured for storage of LH2 and feeding of pressurized LH2 to the fuel cell; (b) cooling the one or more GATs by heat transfer with LH2from the main LH2 storage fuel tank; (c) transferring a quantity of LH2 from the main LH2 storage fuel tank to a cooled GAT, and raising pressure of the LH2 in the cooled GAT to a working pressure suitable for feeding the fuel cell by heat transfer with warm working fluid from the fuel cell-powered vehicle; and (d) feeding the LH2 at working pressure to the fuel cell.

[0047] In one embodiment of the method two or more GATs are provided, wherein steps (a), (b), (c) and (d) are sequentially applied to the two or more GATs out-of-phase with one another.

[0048] In another embodiment of the method each GAT is first cooled by thermal transfer with LH2from the main LH2storage tank, a quantity of LH2is then transferred from the main LH2 storage fuel tank to the cooled GAT, and the contents of the cooled GAT heated by heat exchange with warm working fuel from the vehicle propulsion system, whereby to raise a pressure of the LH2 in the GAT to a working pressure, and the LH2is delivered to the fuel cell at working pressure.

[0049] In a further embodiment of the method the vehicle comprises an aircraft.

[0050] In still yet another embodiment of the method the working pressure is 5 to 10 bar.

[0051] In another embodiment of the method the warm working fluid comprises coolant from the vehicle propulsion system.

[0052] In a further embodiment the warm working fluid comprises cathode exhaust from the fuel cell.

[0053] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.CI-ZERO 23.10 / 13 PCT

[0054] Further features and advantages of the disclosure will be seen in the following detailed description, taken in conjunction with the accompanying drawings. The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure. In the drawings: FIG.1 is a diagrammatical illustration of a conventional mass flow sensor (MFS) module used with a H2 fuel cell in accordance with the prior art; FIG.2 is a diagrammatical illustration of a first exemplary arrangement of a fuel cell system monitoring system, in accordance with the present disclosure; FIG.3 is a diagrammatical illustration of a second exemplary arrangement of a fuel cell system monitoring system, in accordance with the present disclosure; FIG.4 is a diagrammatical illustration of a third exemplary arrangement of a fuel cell system monitoring system, in accordance with the present disclosure; FIG.5 is a flowchart illustrating a method of monitoring a fuel cell system, in accordance with the present disclosure; FIG.6 is a flowchart illustrating a method of mapping error conditions of a fuel cell system, in accordance with the present disclosure; FIG.7 is a system block diagram showing an embodiment of two GATs per LH2storage tank in accordance with the present disclosure; FIG.8 is a flow chart illustrating a complete cycle of a single GAT in accordance with the present disclosure; and FIG.9 illustrates an LH2storage tank installed in an airplane in accordance with the present disclosure.

[0055] Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments are provided so that this disclosure will be thorough and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth, such as examples of specific components, devices, and methods to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms, and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.CI-ZERO 23.10 / 13 PCT

[0056] The terminology used herein and is not intended to be limiting, is for the purpose of describing particular example embodiments only. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, components and / or groups, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0057] When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected, or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0058] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and / or sections, these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the example embodiments.

[0059] Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated inCI-ZERO 23.10 / 13 PCT the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0060] The term “bar” is a metric unit of pressure measurement which is equal to 100,000 Pa (100 kPa), or slightly less than the current average atmospheric pressure on Earth at sea level (approximately 1.013 bar, which is about 14.7 pounds per square inch).

[0061] While all conventional approaches to H2 fuel cell anomaly detection result in the system shutting down when an anomaly is detected, the present disclosure approaches to anomaly (leak) detection are comparable to a circuit breaker, e.g., by closing valves, shutting off H2tanks, or otherwise stopping flow of gas, the present disclosure is directed to H2 tank monitoring which can detect anomalies and still allow the aircraft or other vehicle which is powered by the H2fuel cells to continue its mission safely. Specifically, the present disclosure employs orthogonal sensing to cross-check MFS module with pressure sensors and other sensors. In accordance with this disclosure, orthogonal sensing may be characterized as being able to sense independent failure modes of sensors, such that the sensor data from each sensor is independent from other sensors, and that sensor data can be cross-checked to compare the data to detect abnormal conditions either within the H2fuel cell system or within the sensors themselves. The system may independently monitor all available sensors, and the resulting sensor data from those sensors, such that orthogonal sensing can be used for detecting abnormal conditions.

[0062] This is important because it provides increased safety and reliability for aircraft and other vehicles which are powered by H2 fuel cell systems. For instance, with an H2- powered aircraft, in the event of sensor failure, orthogonal sensing using independent sensor failure modes enables the aircraft control system to determine which sensor failed, allowing fuel cell operation to continue and the aircraft to proceed to a safe landing, and potentially to continue to the original destination.

[0063] Referring to FIG. 2, a monitoring system for a fuel cell system 100 in accordance with the present disclosure includes at least one fuel cell 110 having a quantity of H2 therein. The fuel cell 110 may include any type of fuel cell or system which usesCI-ZERO 23.10 / 13 PCT contained H2as an energy source, such as for the propulsion of a vehicle. The fuel cell 110 may be carried on a vehicle, such as an aircraft, and provide propulsion to the aircraft. While one fuel cell 110 is depicted, system 100 may include any number of fuel cells 110 positioned in any arrangement.

[0064] The fuel cell 110 may have a plurality of sensors 120 positioned proximate thereto for sensing conditions of the fuel cell 110, the H2 within the fuel cell 110, or other parameters of the fuel cell 110. These sensors may include at least a first sensor 122 and a second sensor 124 but may include any number of additional sensors. For instance, as shown in FIG.2, the fuel cell 110 is depicted with first sensor 122 which is a pressure sensor for sensing a pressure within the fuel cell 110, a second sensor 124 which is a temperature sensor for sensing a temperature of the fuel cell 110 or the H2 therein, and third and fourth sensors 126, 128 which may include any type of sensor. A mass flow sensor (MFS) module 130 is also depicted. Depending on the type of sensor and the intended use, the sensor may be located within the fuel cell 110, such as is the case with first, second, and third sensors 122, 124, 126, or the sensor may be positioned external to the fuel cell 110, as is the case with the fourth sensor 128 and the MFS module 130. It may be common for fuel tanks for LH2 or gaseous hydrogen (GH2) to have at least a pressure sensor 113 and a temperature sensor 115 directly connected to the fuel tank 111.

[0065] The sensors 120 may include any one or a combination of a mass flow sensor, a pressure sensor, a temperature sensor, a flow sensor, an acoustic sensor, an optical sensor, an electrochemical sensor, a thermal sensor, or a flame ionization sensor, or another type of sensor not specifically identified in this disclosure. The sensors 120 may be capable of sensing various conditions, including, for example, absolute pressures, differential pressures, temperatures, flow rates, sound emissions, optical changes (e.g., shimmer, fog), electrochemical H2concentration detectors, as well as flame infrared and flame ionization detection.

[0066] The sensors 120 are in communication with a computerized analysis and detection module 140 such as through a wired or wireless communication connection, including any type of computerized or electronic network connection. The sensor data from any of the sensors 120 may be received by the analysis and detection module 140 independently of one another which may utilize common or independent communication connections. The computerized analysis and detection module 140 may be implemented in any type of computing environment, such as within a computerized device whichCI-ZERO 23.10 / 13 PCT includes a non-transitory memory, a database, and a processor. The analysis and detection module 140 may be in communication with an aircraft control unit 150, such as through a network connection or through a direct connection where the analysis and detection module 140 is one or many modules within the aircraft control unit 150.

[0067] In operation, the analysis and detection module 140 cross-checks sensor data from at least two of the sensors 120, such as the first sensor 122 with sensor data and the second sensor 124 to detect an abnormal condition within the fuel cell 110 or the quantity of H2 in the fuel cell 110. The abnormal condition may be any condition or state of the fuel cell 110 or H2within the fuel tank 111 which is outside of normal or expected operating instance, the abnormal condition may be a pressure readingwhich is or a temperature reading which is higher than expected, or another physical parameter which indicates a deviation from normal operation.

[0068] While sensor data from a single sensor 120 may provide a reading to make an initial and uncorrelated determination of an abnormal condition, the analysis and detection module 140 may use secondary sensor data to cross-check or correlate sensor data from two or more sensors 120. This can be used to determine more accurately if an abnormal condition with the fuel cell 110 or fuel tank 111 is present, or if a sensor 120 is providing faulty data which is inaccurately suggesting an abnormal condition in a fuel cell 110 or fuel tank 111. For example, the analysis and detection module 140 may use, for instance, pressure differentials in the system to detect abnormal flow conditions, such as a leak, gasifier failure, or flow beyond maximum design flow rate in the fueling system. The analysis and detection module 140 can also detect abnormal conditions such as a proton-exchange membrane (PEM) fault, which may indicate that fuel is going through membrane from anode to cathode. The system 100 can be used to detect various types of anomalies, such as leaks of any dangerous gas, including gases that are combustible or toxic.

[0069] In one example, sensor data from one sensor 120 may be compared to a pressure calculated from historically determined pressure, a time interval, and / or a temperature difference, and the sensor data from another sensor 120 may include a fuel cell current, integrated flow rate, and / or actual pressure. In another example, a detected abnormal condition may include a leak in the fuel tank determined based on monitoring of one or more, or any combination, of pressure, temperature, fluid level, density, or mass in the fuel tank over a period of time. Here, it may be possible for the leak to be determined based on a difference between a calculated pressure, temperature, fluid level, density, orCI-ZERO 23.10 / 13 PCT mass within the fuel tank 111 relative to a measured respective pressure, temperature, fluid level, density, or mass from sensor data, such that a leak rate can be determined.

[0070] Cross-checking data between two or more sensors 120 also allows the analysis and detection module 140 to cross-check sensor data from sensors 120 to detect sensor failure. This can be used to make a determination if an anomaly is a legitimate anomaly with the fuel cell system 100 or if a false anomaly is being caused by a sensor fault. This ability can provide significant benefits in the field since it can be used to make an accurate determination about a condition on an aircraft without the need to first land that aircraft and inspect the fuel cell system 100 or the sensors 120. For example, if the first sensor 122 provides sensor data which indicates an anomaly with the fuel cell system 100, the analysis and detection system 140 can cross-check the sensor data from the first sensor 122 with sensor data from a second sensor 124. If the sensor data from the second sensor 124 provides a different indication than the first sensor data, such as an indication that there is not an anomaly with the fuel cell system 100, then the analysis and detection system 140 can determine that the first sensor 122 may be faulty. It is further possible to cross-check this sensor data with the sensor data from additional sensors to further verify a sensor fault or the presence of a legitimate anomaly.

[0071] For a fuel cell system 100 positioned on an aircraft, when an abnormal condition is detected based on sensor data, it may be possible for the aircraft to maintain continued fuel cell system 100 operation. This may be the case for an abnormal condition which is deemed to be minor. Similarly, when an abnormal condition is detected based on sensor data, but additionally cross-checked sensor data is used to determine that the original sensor providing the data is faulty, the aircraft may maintain continued fuel cell system operation since it has been determined that the fuel cell system 100 is not faulty.

[0072] Referring to FIG.3, a second exemplary arrangement of the fuel cell system monitoring system 101 is depicted, where the system 101 is used to determine a pressure differential between two locations within a system of fuel cells 110 which may be interconnected with pipes 112 or similar conduits. As shown, a plurality of sensors 120 are positioned within the system of fuel cells 110 to provide sensed data readings from various locations. In one example, a flow sensor can be implemented by measuring pressure at two locations with a restriction between them.

[0073] For instance, if there is a restriction in a pipe 112, a sensor 120 before and after that restriction can measure the pressure at each location, which can be used to calculate a flow rate, since the difference in pressure is proportional to the flow rate through theCI-ZERO 23.10 / 13 PCT restriction. This can be used, for example, to determine if a valve(s) 114 or a similar feature within a fuel cell system 100 is faulty and restricting flow.

[0074] In another example, a single differential sensor, such as sensor 120A, may have pressure ports located in a venturi 116 and in a nearby duct 118 that can measure mass flow. The difference between the two pressure ports can be used to determine the flow rate through the venturi 116 or any other conditions associated with the venturi 116 or the unrestricted duct 118. Similarly, a pitot port or impact tube may be used to give a differential pressure relative to a static port that is proportional to the square of mass flow rate, as is given by the equation for dynamic pressure: where q is the dynamic pressure in3the fluid mass density (kg / m ), and u is the flow speed in m / s.

[0075] Referring to FIG. 4, fuel cell system monitoring system 300 is depicted as a block diagram illustrating various components and modules which may be used. The sensor data 319 from the plurality of sensors 320 is provided to the analysis and detection module 340, which can process the data derived from the sensors. Similar to that previously discussed with respect to FIGS. 2 and 3, the analysis and detection module 340 may include a non-transitory memory 342, a processor 344 such as a CPU, and a database 346. Additionally, the analysis and detection module 340 may also include any number of other computing features, such as a power supply, input / output devices, display devices, applications, programs, or other types of hardware, firmware, or software.

[0076] Additionally, the analysis and detection module 340 may include modules for providing additional data. For instance, the analysis and detection module 340 may include a calculation and prediction module 360 which may provide calculated or predicted values or differences from expected values and measured values which are obtained from the sensor data. Derived data may be based on prior knowledge and measurements of the correct behavior of the system, which may be stored or processed within a historical data analysis module 362. An anomaly detection module 364 may be used to cross-check or correlate sensor data, or other data, to detect anomalies. Anomalies may be detected if measured or derived data departs from the expected values associated with correct system behavior. In other words, if not all sensor values areCI-ZERO 23.10 / 13 PCT internally consistent, then an error is detected in either a sensor 320 or the system of fuel cells 110 as discussed above relative to FIGS. 2-3.

[0077] The analysis and detection module 340 also includes a communication module 366 which allows for communication of alarms, alert messages, error messages, status messages, or other messages to be transmitted from the analysis and detection module 340 and received by the analysis and detection module 340. For instance, the communication module 366 may allow for communication of data to aircraft control unit 350 and to aircraft personnel 352, such as a pilot, a flight engineer, flight crew, a ground control individual, or another individual associated with the maintenance, operation, or functioning of the aircraft. The communication module 366 may trigger an alarm when the abnormal condition is detected, where the alarm may be in the form of an electronic message or visible, auditory, or tactile indication of an abnormal condition. The analysis and detection module 340 also includes a condition mapping module 368 which may be used to perform mapping of error conditions of a H2fuel cell, as discussed relative to FIG.6.

[0078] One way that sensor failure can be detected is by comparing the results from two or more similar sensors 320 operating in parallel. If two sensors 320 measuring the same parameter diverge, then at least one of the sensors 320 can be determined to be faulty or in error. If there are three or more sensors 320, then it may be possible for the anomaly detection module 364 to implement one or more voting algorithms which may be used to choose the most probable value of the measured parameter. Because similar sensors may have similar failure modes, use of diverse sensing methods offers redundancy benefits. For example, the mass of fuel in a tank may be determined by measurement of weight or liquid level, and also by pressure and temperature. The diverse sensor types cannot fail in the same way. Analysis of the specific reported sensor values can be used to identify the type of error or defect. This information can be communicated to the pilot, or to operating equipment, and an appropriate response for the conditions can be undertaken.

[0079] FIG.5 is a flowchart 200 illustrating a method of monitoring a fuel cell system in accordance with the present disclosure. It should be noted that any process descriptions or blocks in flow charts should be understood as representing modules, segments, portions of code, or steps that include one or more instructions for implementing specific logical functions in the process, and alternate implementations are included within the scope of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrent or in reverse order,CI-ZERO 23.10 / 13 PCT depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present disclosure.

[0080] As is shown by block 202, sensor data inputs from at least two sensors configured to sense a condition of at least one fuel cell having a quantity of H2 therein are analyzed. This may include analysis of any available sensor inputs. At block 204, an abnormal condition within the fuel cell or the quantity of H2 in the fuel cell is detected by cross- checking sensor data from one sensor with at least another sensor. This may detect any anomalous or inconsistent reported values, such as an anomalous or inconsistent value within the sensor data. Then, based on the cross-checking of the sensor data, the method distinguishes between a sensor failure and an operational defect of the fuel cell at block 206.

[0081] The method may further include any number of additional and optional steps, functions, processes, or variants thereof, including any disclosed relative to any other figure of this disclosure. For example, a parameter value may be substituted for a signal from a failed sensor when a sensor failure is determined. When this occurs and a parameter value is substituted, the substitute value may be a parameter value measured by equivalent parallel sensors or derived from remaining dissimilar functional sensors. It may also include synthesizing probable parameter values based on operating conditions, as shown in block 208. The method may also include inserting an error code into the software, such as “NaN,” to indicate that a signal value of the failed sensor is invalid, as shown in block 210.

[0082] When a sensor failure is detected, it may be possible to continue operation of the H2 fuel cell using substitute sensor data, which may be most desirable, and thus a highest priority. If it is not possible to continue operation of the fuel cell, the next priority action is reducing the fuel cell to a safe operating mode, and if the system is unable to continue safe operating mode of the fuel cell, the next priority action is entering a safe shutdown mode of the fuel cell. This is depicted in block 212. With any action that occurs, it is possible to transmit an alarm message, or an error message, or a status message, as shown in block 214. For example, the alarm, error, or status message may be transmitted to aircraft personnel of an aircraft on which the H2fuel cell is located, as shown in block 216. The aircraft personnel may include a pilot, a flight engineer, a flight crew, a ground control individual, or another individual associated with the maintenance, operation, or functioning of the aircraft. The aircraft personnel can transmit an override command, which may be accepted, as indicated in block 218. Optionally, the method may includeCI-ZERO 23.10 / 13 PCT actuating an actuator to adjust a physical property of the fuel cell system, as shown in block 220.

[0083] For any particular fuel cell system design and the set of sensors associated with it, it may be possible to generate a map of proper operating conditions and resulting sensor signals. Similarly, it may be possible to conduct mapping of the error conditions for each specific design.

[0084] FIG.6 is a flowchart 221 illustrating a method of mapping error conditions of a fuel cell system in accordance with the present disclosure. It should be noted that any process descriptions or blocks in flow charts should be understood as representing modules, segments, portions of code, or steps that include one or more instructions for implementing specific logical functions in the process, and alternate implementations are included within the scope of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrent or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present disclosure.

[0085] As is shown by block 222, a system design of a fuel cell system is identified. An ideal system behavior of the fuel cell system is determined at block 224, and proper behavior of the fuel cell system is correlated with at least two measured sensor signals, as shown at block 226. Allowable variation limits may be set to the at least two measured sensor signals at block 228. Measured sensor signals are correlated with desired behavior at block 230, which may include implementing or configuring a device to make the correlation.

[0086] The method may further include any number of additional and optional steps, functions, processes, or variants thereof, including any disclosed relative to any other figure of this disclosure. For example, it may be desirable to report at least one of: an alarm message; an error message; or a status report of the fuel cell system, as shown in block 232, which may include the use of an automated device which reports state or alarm conditions as needed. Similarly, it may be desirable to operate at least one actuator to adjust a physical property of the fuel cell system, as shown in block 234. For instance, an automated device or combination of devices may operate actuators to shut off valves or perform other physical actions within the fuel cell system. For LH2, it may bedesirable to measure a level of liquid or mass of fuel in a fuel tank of the fuel cell system.CI-ZERO 23.10 / 13 PCT

[0087] Referring to FIG. 7, an LH2storage tank in accordance with the present disclosure comprises a primary LH2 storage tank 512 configured to hold a quantity of LH2sufficient to power a fuel cell-powered aircraft for a desired range. Primary LH2storage tank 512 comprises a dewar tank formed of a relatively light-weight composite material or other form of relatively light-weight insulated cryogenic tank configured to store LH2 at or close to ambient pressure.

[0088] The LH2 fuel storage system 510 also includes two small high pressure (e.g., 10 bar) gas accumulator tanks (GATs), a first GAT-1 tank 514 and a second GAT-2 tank 516. GAT-1 tank 514 and GAT-2 tank 516 are connected to the main LH2storage tank 512 via conduits 518 and 520. Flow of LH2 from main LH2 storage tank 512 to GAT-1 tank 514 and GAT-2 tank 516 is controlled by inlet valves 522 and 524, respectively. LH2 from main LH2 storage tank 512 may flow via gravity or may be pulled into GAT-1 tank 514 and GAT-2 tank 516 via vacuum, or pumped into GAT- 1 tank 514 and GAT-2 tank 516 via optional pumps 515 and 517.

[0089] GAT-1 tank 514 also includes an outlet conduit 530 connected through outlet valve 532 with the inlet side of fuel cell 534, while GAT-2 tank 516 includes an outlet conduit 536 connected through outlet valve 538 to the inlet side of fuel cell 534. GAT-1 tank 514 and GAT-2 tank 516 are each equipped with cooling interfaces 540 and 542, respectively, and heating interfaces 544 and 546, respectively. Cooling interfaces 540, 542 are configured to allow LH2circulated from the main tank 512 via conduits 550 and 552, pumps 554 and 556 and valves 558 and 560, respectively, to selectively cool the respective GAT-1 tank 514 and GAT-2 tank 516, as the case may be. Heating interfaces 544, 546 in turn are configured to allow warm fluid from the aircraft propulsion system 561, e.g., coolant from the vehicle propulsion system, or cathode exhaust air from the fuel cells, delivered via conduits 562 and 564 and valves 566 and 568, to selectively heat the contents of the GAT-1 tank 514, GAT-2 tank 516, respectively, as the case may be. Not shown for the ease of simplicity are pressure and temperature gauges and connectors to a controller 580.

[0090] In operation, LH2 is circulated through cooling interface 540 of GAT-1 tank 514, chilling GAT-1 tank 514. Inlet valve 522 is opened, and GAT-1 tank 514 is partiallyfilled with LH2. Inlet valve 522 is then closed. The internal pressure of the LH2in GAT-1 tank 514 is then raised by heat exchange with heating interface 544 which receives heat from the vehicle propulsion system and / or heat from the warm exhaust air from the fuel cell 534. Heating raises the pressure of the H2 in LH2 GAT-1 tank 514 to 10 bar. TheCI-ZERO 23.10 / 13 PCT LH2at elevated pressure is then delivered to a downstream gasifier (not shown) and from the gasifier as feed to fuel cell 534. As LH2 is being delivered from the GAT-1 tank 514, GAT-2 tank 516 is chilled by LH2from main tank 512. Once chilled, inlet valve 524 is opened, and a quantity of LH2 is allowed to flow from main tank 512 to refill GAT -2 tank 516. The LH2in GAT-2 tank 516 is then heated by heat exchange with warm exhaust air from the fuel cell 534 to raise the pressure H2 in LH2 in GAT-2 tank 516 to 10 bar. GAT-2 tank 516 operates in parallel but out-of-phase with GAT-1 tank 514 so that there is an uninterrupted supply of LH2 at a desired pressure, typically 10 bar, to the gasifier.

[0091] FIG.8 depicts an operation of one complete cycle for a single GAT in accordance with the present disclosure. As will be appreciated, while the first GAT, e.g., GAT-1, is delivering conditioned LH2 to the gasifier at an elevated pressure, the second GAT, i.e., GAT-2, can be recharged and pressurized for subsequent use in delivering pressurized LH2to the gasifier.

[0092] FIG.8 is a flow chart 600 illustrating one complete cycle for a single GAT in accordance with the present disclosure. The cycle begins (block 602) with an empty GAT. The empty GAT is chilled by heat transfer with LH2 from the main LH2 storage fuel tank (block 604). Upon sensing the internal pressure level of the GAT as being less than the internal pressure level of the LH2 storage tank (block 606), the GAT inlet valve is opened and a quantity of LH2is transferred from the main LH2storage tank to the GAT to at least partially fill the GAT with LH2 from the main LH2 storage fuel tank (block 608), and achieve a desired LH2 / gas mixture ratio (block 610). When sufficient LH2 is transferred to the GAT, the inlet valve to the GAT is closed and the GAT is heated to raise the pressure of the H2in the GAT to a working pressure suitable for feeding to the fuel cell by heat transfer with warm working fluid from the fuel cell- powered vehicle (block 612). Once the pressure of the LH2in the GAT reaches a desired level (block 614), the heating of the GAT is maintained (block 616) and the GAT outlet is opened to permit flow of the pressurized gasified H2to the fuel cell (block 618). Once the GAT is largely emptied, the GAT outlet valve is closed (block 620) and the cycle is repeated.

[0093] FIG. 9 illustrates an LH2storage tank installed in an airplane in accordance withthe present disclosure. Airplane 670 includes electric motors 672A, 672B which are supplied with electric power by parallel fuel cell systems 674A, 674B for driving electric motors 672A, 672B and for powering other instruments and subsystems of the airplane.CI-ZERO 23.10 / 13 PCT The airplane also has fuel tank systems 676A, 676B, comprising main fuel tanks and GATs in accordance with the present disclosure as illustrated above in FIGS. 7 and 8.

[0094] It is thus seen that the disclosed system provides the ability to achieve superior mass fractions and source redundancy without the need for a complex LH2 pump system. It also allows to fully utilize the cooling capacity of the LH2to reduce the thermal rejection requirements of the aircraft systems such as the aircraft propulsion system.

[0095] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. By way of example, but not limitation, one or more thermally-pumped GATs as above described can be employed. In one embodiment with only one GAT employed, the supply of LH2 at elevated pressure to the fuel cell will be discontinuous, which would be acceptable for intermittent applications, e.g., to boost glide vehicles, or for battery charging. In another embodiment, three or more GATs may be provided to sequentially alternate outputs to provide a continuous supply of pressure-conditioned H2. The number of GATs needed can be determined by the ratio of fill-and-pressurize time to supply time. Also, the heating interfaces can use heat from other parts of the fuel cell aircraft, e.g., coolant from the vehicle propulsion system, for heating the GAT(s). And control of the flow valves and pumps, etc., can be automated or manual. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. Various changes and advantages may be made in the above disclosure without departing from the spirit and scope thereof.CI-ZERO 23.10 / 13 PCT List of References: 346 database 10 aircraft 350 aircraft control unit 12 H2fuel cell system 352 aircraft personnel 14 H2 fuel cell 360 calculation and prediction 16 MFS module module 18 engine 362 historical data analysis module 20 fuel tank 364 anomaly detection module 100 H2 tank monitoring system 366 communication module 101 Fuel cell monitoring system 368 condition mapping module 110 fuel cell 510 LH2 fuel storage system 111 fuel tank 512 LH2 storage tank 112 pipes 514 first GAT-1 tank 113 pressure sensor 515 pumps 114 valves 516 second GAT-2 tank 115 temperature sensor 517 pumps 116 venturi 518 conduits 118 duct 520 conduits 120 sensors 522 valves 120A differential sensor 524 valves 122 first sensor 530 outlet conduit 124 second sensor 532 outlet valve 126 third sensor 534 fuel cell 128 fourth sensor 536 outlet conduit 130 MFS module 538 outlet valve 140 detection module 540 cooling interface 150 aircraft control unit 542 cooling interface 200-220 flowchart and blocks 544 heating interface 221-234 flowchart and blocks 546 heating interface 300 H2 tank monitoring system 550 conduits 319 sensor data 552 conduits 320 sensors 554 pumps 340 analysis and detection module 556 pumps 342 non-transitory memory 558 valves 344 processor 560 valvesCI-ZERO 23.10 / 13 PCT aircraft propulsion systems conduit conduit valve valve controller -620 flow chart and blocks aircraft A electric motor B electric motor A fuel cell system B fuel cell system A fuel tank system B fuel tank system

Claims

CI-ZERO 23.10 / 13 PCT CLAIMS What is claimed is:

1. A hydrogen (H2) fuel cell system for powering an aircraft comprising at least one fuel tank configured to hold a quantity of H2therein and at least one fuel cell; at least first and second sensors configured to sense a condition of at least one of: the fuel tank or the quantity of H2 within the fuel, wherein the first and second sensors comprise one of: a mass flow sensor; a pressure sensor; a flow sensor; an acoustic sensor; an optical sensor; an electrochemical sensor; a thermal sensor or a flame ionization sensor; and a computerized analysis and detection module in communication with the first and second sensors, wherein the analysis and detection module is configured to cross-check sensor data from the first sensor with sensor data from the second sensor to detect an abnormal H2flow condition in the fuel cell system, wherein the detected abnormal H2flow condition comprises a H2 leak in the fuel tank based on monitoring pressure in the fuel tank over a period of time, wherein the H2leak is determined based on a difference between a calculated pressure within the fuel tank relative to a measured pressure from sensor data, and wherein a H2leak rate is determined; and when the abnormal H2 flow condition is detected, the fuel cell system is configured to continue to maintain operation of the fuel cell system unchanged using substitute sensor data until the aircraft lands, and if continuing operation of the fuel cell system is not possible if the abnormal H2 flow condition is determined to be minor based on the abnormal H2 flow condition, the fuel cell system is configured to reduce operation of the H2 fuel cell system to a safe operating mode; and if unable to continue the safe operating mode of the H2fuel cell system based on the abnormal H2flow condition, the fuel cell system is configured to enter a safe shutdown mode of the H2 fuel cell system, to transmit an alarm message or error message to aircraft personnel of the aircraft on which the hydrogen fuel cell system is located, and to accept an override command from the aircraft personnel so that he aircraft may be safely landed.

2. The system of claim 1, wherein the analysis and detection module is configured to cross- check sensor data from the first sensor with sensor data from the second sensor to detect sensor failure, wherein sensor data from the first and second sensors is received by the analysis and detection module independently of one another.

3. The system of claim 1 or claim 2, further comprising a communication module configured to trigger an alarm when the abnormal condition is detected.CI-ZERO 23.10 / 13 PCT 4. The system of any preceding claim, wherein sensor data from the first sensor further comprises at least one of: a pressure calculated from historically determined pressure; a time interval; or a temperature difference, and the sensor data from the second sensor further comprises at least one of: integrated fuel cell current; integrated flow rate; or pressure.

5. A method of monitoring an H2fuel cell system, comprising at least one fuel tank configured to hold a quantity of H2 therein and at least one fuel cell for powering an aircraft, the method comprising steps of: analyzing sensor data inputs from at least two sensors configured to sense a condition of the at least one fuel tank having a quantity of H2 therein; detecting an abnormal condition within the fuel tank or the quantity of H2 within the fuel tank or an abnormal H2flow condition in the fuel cell system, by cross-checking sensor data from one sensor with at least another sensor; distinguishing between a sensor failure and an operational defect of the fuel tank; and substituting a parameter value for a signal from a failed sensor when a sensor failure is determined, wherein after the sensor failure is detected: continuing operation of the H2 fuel cell system is unchanged using substitute sensor data; or if continuing operation of the H2 fuel cell system unchanged is not possible, reducing operation of the H2fuel cell system to a safe operating mode; and if unable to continue the safe operating mode of the H2 fuel cell system, entering a safe shutdown mode of the H2 fuel cell system, transmitting an alarm message or an error message to aircraft personnel of the aircraft on which the hydrogen fuel cell system is located, and accepting an override command from the aircraft personnel so that the aircraft can be safely landed.

6. The method of claim 5, wherein substituting the parameter value for the signal from the failed sensor further comprises at least one of: using parameter values measured by equivalent parallel sensors; substituting parameter values derived from remaining dissimilar functional sensors; synthesizing probable parameter values based on operating conditions; or inserting an error code to indicate that a signal value of the failed sensor is invalid, and / or wherein the abnormal condition is identified based on an anomalous or inconsistent value within the sensor data.

7. A liquid hydrogen (LH2) fuel storage system for a fuel cell-powered vehicle, comprisingCI-ZERO 23.10 / 13 PCT a main LH2storage fuel tank configured for close to ambient pressure storage of LH2, and one or more gas accumulator tanks (GATs) smaller than the main fuel tank and configured for elevated pressure storage of LH2 and for feeding pressurized LH2 to the fuel cell, wherein the one or more GATs each have a cooling interface configured to cool the GAT employing LH2from the main fuel tank, and a heating interface configured to heat contents of the GAT with warm working fluid from the fuel cell-powered vehicle whereby to raise pressure of the LH2 in the GAT to a working pressure for feeding the LH2to the fuel cell.

8. The LH2fuel storage system of claim 7, characterized by comprising one or more of the following features: (a) wherein the main LH2 storage fuel tank comprises a composite structure; (b) wherein the vehicle is an aircraft; (c) comprising two or more GATs configured to run out-of-phase with one another; (d) wherein the working pressure is 5–10 bar; (e) wherein the warm working fluid comprises coolant from a vehicle propulsion system; and (f) wherein the warm working fluid comprises cathode exhaust from the fuel cell.

9. A method for providing LH2 fuel to a fuel cell-powered vehicle, comprising the steps of: (a) providing LH2fuel storage system as claimed in claim 8, the system including a main LH2 storage fuel tank configured for close to ambient pressure storage of LH2 and one or more gas accumulator tanks (GATs) smaller than the main fuel tank and configured for storage of LH2and feeding of pressurized LH2to the fuel cell; (b) cooling the one or more GATs by heat transfer with LH2from the main LH2storage fuel tank; (c) transferring a quantity of LH2 from the main LH2 storage fuel tank to a cooled GAT and raising pressure of the LH2in the cooled GAT to a working pressure suitable for feeding the fuel cell by heat transfer with warm working fluid from the fuel cell- powered vehicle; and (d) feeding the LH2at working pressure to the fuel cell.

10. The method of claim 9, characterized by one or more of the following: (e) wherein two or more GATs are provided, wherein steps (a), (b), (c) and (d) are sequentially applied to the two or more GATs out-of-phase with one another;CI-ZERO 23.10 / 13 PCT (f) wherein each GAT is first cooled by thermal transfer with LH2from the main LH2storage fuel tank, a quantity of LH2 is then transferred from the main fuel tank to the cooled GAT, and the contents of the cooled GAT are heated by heat exchange with fuel from the vehicle propulsion system, whereby to raise a pressure of the LH2in the GAT to a working pressure, and the LH2 is delivered to the fuel cell at working pressure; (g) wherein the working pressure is 5 to 10 bar; (h) the warm working fluid comprises coolant from the vehicle propulsion system; and (i) wherein the warm working fluid comprises cathode exhaust from the fuel cell.

11. The method of claim 9 or claim 10, wherein the vehicle comprises an aircraft.

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