Patent ID: 12212025

While the features described herein may be susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to be limiting to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the subject matter as defined by the appended claims.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the various described embodiments. However, it will be apparent to one of ordinary skill in the art that the various described embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure aspects of the embodiments.

It will be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another.

The terminology used in the description of the various described embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various described embodiments and the appended claims, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

As used herein, the term “if” is, optionally, construed to mean “when” or “upon” or “in response to determining” or “in response to detecting” or “in accordance with a determination that,” depending on the context.

An embodiment of the present disclosure may include an aircraft electrical power supply system that may include a fuel cell auxiliary power unit (APU) that may supply auxiliary electrical power to an aircraft, a fuel cell power plant that may supply primary electrical power to the aircraft, and/or an on board fuel storage unit that may supply fuel to the fuel cell APU and the fuel cell power plant. The aircraft electrical power supply system may also include an off board refueling unit that may refuel the aircraft with fuel for the fuel cell APU and fuel cell power plant.

The fuel cell APU and fuel cell power plant may utilize fuel cells to generate electrical power for the aircraft. The fuel cells may include, for example, a proton exchange membrane (PEM) fuel cells (also referred to as polymer electrolyte membrane fuel cells), direct-methanol fuel cells, alkaline fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells or solid oxide fuel cells. The fuel that may be used in the fuel cells may include, for example, hydrogen fuel, a hydrocarbon fuel such as diesel, natural gas, methanol or ethanol, or a chemical hydride fuel.

By utilizing fuel cells, the fuel cell APU may produce auxiliary electrical power more efficiently that a conventional APU (e.g., gas turbine engine APU). The fuel cell power plant may also produce primary electrical power more efficiently that a conventional primary electrical power source (e.g., a motor-generator connected to an engine of the aircraft).

FIG.1Aillustrates an overview of an aircraft electrical power supply system100, according to one or more embodiments of the present disclosure. As illustrated inFIG.1A, the aircraft electrical power supply system100may generate electrical power and supply the generated electrical power to the electrical power distribution system of the aircraft1.

The aircraft electrical power supply system100may include a hydrogen storage unit120located inside the aircraft1. The hydrogen storage unit120may comprise a gas storage tank which is configured to store and maintain hydrogen that is used to fuel the fuel cells in the aircraft electrical power supply system100. The aircraft electrical power supply system100may also include a fuel cell auxiliary power unit (APU)140inside the aircraft1that may supply auxiliary electrical power to the aircraft1, and/or a fuel cell power plant160inside the aircraft that may supply primary electrical power to the aircraft1. The hydrogen storage unit120may supply hydrogen to the fuel cell APU140and/or the fuel cell power plant160via a hydrogen fuel transmission line2on the aircraft1. It should be noted that the aircraft electrical power supply system100is not limited to use in airplanes, but may also be used in other aircraft, such as helicopters and airships, and also reusable spacecraft. Furthermore, while a jet aircraft1is schematically illustrated inFIG.1A, a smaller propeller powered aircraft1may be used.

The aircraft electrical power supply system100may also include an off board hydrogen refueling unit180that may refuel the aircraft1with hydrogen. The aircraft electrical power supply system100may use one or more transfer hoses3for transferring hydrogen and/or other gases and liquids on and off of the aircraft1. During a refueling operation, for example, one or more storage vessels (e.g., tanks) storing liquids and/or gases (e.g., hydrogen, oxygen, nitrogen, etc.) in the off board hydrogen refueling unit180may be coupled to storage vessel(s) (e.g., tank(s)) on board the aircraft1(e.g., in the hydrogen storage unit120) by the transfer hoses3.

The off board hydrogen refueling unit180may be located, for example, at an airport. In that case, for example, a refueling operation may be performed by the off board hydrogen refueling unit180between flights of the aircraft1. Alternatively, the off board hydrogen refueling unit180may be a mobile unit that may be located, for example, on a refueling truck or a refueling aircraft. For example, when located on a refueling aircraft, the off board hydrogen refueling unit180may perform the refueling operation while the aircraft1is in flight.

The fuel cell APU140may utilize one or more fuel cells in a first fuel cell stack to generate auxiliary electrical power in the aircraft1. The fuel cell power plant160may utilize one or more fuel cells in a second fuel cell stack to generate primary electrical power in the aircraft1.

FIG.1Billustrates a fuel cell10that may be utilized in the aircraft electrical power supply system100, according to one or more embodiments. The fuel cell10may include, for example, a PEM fuel cell. The fuel cell10may include an anode12and cathode14on opposing sides of a polymer electrolyte membrane16. An anode-side backing layer (e.g., gas diffusion layer)18may be disposed on the anode12, and a cathode side backing layer (e.g., gas diffusion layer)20may be disposed on the cathode14. A fuel flow field22may be disposed on the anode-side backing layer18, and an oxidant flow field24may be disposed on the cathode side flow field20.

In operation, wherein hydrogen is used as the fuel and air (e.g., oxygen) is used as the oxidant, hydrogen may be caused to flow through flow plates of the hydrogen flow field22to the anode12, and air may be caused to flow through flow plates of the oxidant flow field24to the cathode14. The anode12may include a catalyst (e.g., platinum catalyst) that causes the hydrogen to split into positive hydrogen ions (protons) and negatively charged electrons. The polymer electrolyte membrane18may allow only the positively charged ions to pass through it to the cathode14. The negatively charged electrons may travel along a circuit25that is external to the cathode14creating an electrical current that may power a load25a. At the cathode14, the electrons and hydrogen ions may combine with oxygen in the air to form water that flows out of the fuel cell10.

A plurality (e.g., tens or hundreds) of the fuel cells10may be connected together (e.g., in series) to form a fuel cell stack. In the aircraft1, the fuel cell APU140and the fuel cell power plant160may each include one or more fuel cell stacks that may generate electrical power sufficient to power all of the electrical devices on the aircraft1.

FIG.2illustrates the hydrogen storage unit120, according to one or more embodiments. The hydrogen storage unit120may store and maintain hydrogen that may be used to fuel the fuel stacks in the fuel cell APU140and/or the fuel cell power plant160.

The hydrogen storage unit120may include a hydrogen storage area121. The hydrogen storage area121may include one or more hydrogen storage tanks122for storing hydrogen, a hydrogen purifier123for purifying the hydrogen stored in the hydrogen storage tank122, and a nitrogen tank124that may store nitrogen that has been extracted from the hydrogen by the hydrogen purifier123. The nitrogen tank124may also be coupled to the hydrogen storage tank122, and under certain circumstances, nitrogen from the nitrogen tank124may be used to dilute the hydrogen in the hydrogen storage tank122. One or more hydrogen-filled cannisters125may also be stored in the hydrogen storage area121. The hydrogen-filled cannisters125may be used to supply hydrogen on the aircraft1in place of or in supplement to the hydrogen stored in the hydrogen storage tank122.

The hydrogen purifier123may include an electrochemical pump or cascade of electrochemical pumping stages that continuously purify the hydrogen stored in the hydrogen storage tank122. This may be particularly useful in the case that off-gassing (e.g., in the hydrogen storage tank122) creates impurities in the hydrogen stored therein.

One or more sensors122amay be disposed in or on the hydrogen storage tank122. The sensors122amay include gas composition sensors which detect conditions inside the hydrogen storage tank122such as a concentration of various gases such as hydrogen and nitrogen, and may also detect impurities in the hydrogen. The sensors122amay also include temperature and/or pressure sensors which detect temperature and/or pressure in the hydrogen storage tank122.

The hydrogen storage area121may also include a hydrogen storage area control unit126that may be electrically coupled to the sensors122a, the hydrogen purifier123and the nitrogen tank124. The hydrogen storage area control unit126may control an operation of the hydrogen storage tank122, hydrogen purifier123and nitrogen tank124based on data supplied by the sensors122a. In particular, the hydrogen storage area control unit126may control opening and closing of valves for transmitting gases to and from the hydrogen storage tank122, hydrogen purifier123and nitrogen tank124.

The sensors122amay indicate when a combustible mixture is included in the hydrogen storage tank122, and thus may indicate a “hazard” condition. When the hydrogen storage tank122does not contain hydrogen or other fuels in a “hazard” condition (e.g., when the hydrogen storage tank122is backfilled with an inert gas such as nitrogen, argon or helium), then the hydrogen storage tank122may be indicated to be in a “safe” condition. In particular, the sensors122amay detect a dangerous hydrogen condition, and may be arranged in a coincidence logic arrangement such that, for example, a certain percentage of the sensors122a(e.g., ¾ of the sensors122a) must indicate “safe” to prove safe, a certain percentage of the sensors122a(e.g., 2/4 of the sensors122a) must indicate “danger” to prove danger, etc.

The sensors122a(e.g., low level sensors) may also notify the hydrogen storage area control unit126when a condition in the hydrogen storage tank122(e.g., hydrogen purity) is at a boundary of safe operation. The hydrogen storage area control unit126may then pass this information on to the hydrogen supply control unit135which may then notify the fuel cell APU140and fuel cell power plant160of the condition.

The hydrogen storage area control unit126may include a processing device (e.g., processor, central processing unit (CPU)) for executing instructions to cause an operation (e.g., opening valves, closing valves, etc.) to be performed in the hydrogen storage area121. The hydrogen storage area control unit126may also include a memory device (random access memory (RAM), read only memory (ROM), etc.) for storing instructions to be executed by the processor. The memory device may also store other data such as history data (e.g., hydrogen concentration, temperature, pressure, etc.) collected by the sensors122a. The processor may access the data in the memory device and perform operations on the data, utilize the data in executing instructions, etc.

One or more additional sensors127may be located in the hydrogen storage area121. The sensors127may detect conditions inside the hydrogen storage area121such as temperature, pressure and humidity. The sensors127may also detect a level of hydrogen, oxygen and other gases in the ambient air inside the hydrogen storage area121. The hydrogen storage area121may also include an air monitoring and treatment unit128that may receive data from the sensor127, and may use the data to treat the air inside the hydrogen storage area121. The air monitoring and treatment unit128may include, for example, a heating and cooling unit, humidifier, dehumidifier, etc. The hydrogen storage area control unit126may control the air monitoring and treatment unit128.

In particular, the sensors127may include hydrogen sensors that may detect an amount of hydrogen in the ambient air in the hydrogen storage area121. The sensors127may, therefore, detect a hydrogen leak in the hydrogen storage area121that may cause the air monitoring and treatment unit128to set off an alarm (e.g., visual alarm, audible alarm, etc.) if the level of hydrogen in the ambient air is above a lower limit (e.g., a potential flammability level).

The hydrogen storage area control unit126may also control the air monitoring and treatment unit128to ventilate the hydrogen storage area121at a negative pressure, and/or to remove oxygen from the ambient air in the hydrogen storage area121. The hydrogen storage area control unit126may also control an opening/closing of an outlet valve on the nitrogen tank124in order to release nitrogen from the nitrogen tank124into the hydrogen storage area121.

The hydrogen storage area121may also include an electrolysis unit139that is connected to the connected to aircraft's power supply and supplied with water from the aircraft's water supply. The electrolysis unit139may produce hydrogen under the control of the hydrogen storage area control unit126. In particular, the electrolysis unit139may be directed to produce hydrogen in the event that the sensor122adetect a low level of hydrogen in the hydrogen storage tank122.

The hydrogen storage unit120may also include a plurality of inlet/outlet ports129(e.g., inlet ports and/or outlet ports) that may be coupled to the hydrogen storage tank122. In a refueling operation, the transfer hoses3(seeFIG.1) may be connected to the inlet/outlet ports129in order to transfer gases between hydrogen storage tank122and the off board hydrogen refueling unit180. For example, the inlet/outlet ports129may be used to transfer hydrogen from the off board hydrogen refueling unit180into the hydrogen storage tank122. This inlet/outlet ports129may also be used to transfer hydrogen from the hydrogen storage tank122to one or more storage tanks in the off board hydrogen refueling unit180. This may be done, for example, to empty the hydrogen storage tank122or to have the hydrogen reprocessed by the off board hydrogen refueling unit180. The inlet/outlet ports129may also be used to be used transfer nitrogen (e.g., backfill nitrogen) into the hydrogen storage tank122during a refueling operation as a safety precaution.

The inlet/outlet ports129may also be connected, for example, to an emergency buoyancy system in order to rapidly fill a safety balloon with hydrogen. The inlet/outlet ports129may also be connected to a hydrogen dumping port in the aircraft1in order to rapidly empty the hydrogen storage tank122.

The hydrogen storage unit120may also include a sensor131that may be formed in a part of the hydrogen fuel transmission line2that supplies hydrogen from the hydrogen storage tank122to the fuel cell APU140. The sensor131may be a gas composition sensor configured to detect a purity of the hydrogen in that part of the hydrogen fuel transmission line2. The hydrogen storage unit120may also include a hydrogen purifier132that is formed in that part of the hydrogen fuel transmission line2and may purify the hydrogen there based on data (e.g., purity data) from the sensor131.

The hydrogen storage unit120may also include a sensor133that may be formed in a part of the hydrogen fuel transmission line2that supplies hydrogen from the hydrogen storage tank122to the fuel cell power plant160. The sensor133may be a gas composition sensor configured to detect a purity of the hydrogen in that part of the hydrogen fuel transmission line2. The hydrogen storage unit120may also include a hydrogen purifier134that is formed in that part of the hydrogen fuel transmission line2and may purify the hydrogen there based on data (e.g., purity data) from the sensor133.

The hydrogen storage unit120may also include a hydrogen supply control unit135for controlling an operation in the hydrogen storage unit120. The hydrogen supply control unit135may include a processing device (e.g., processor, central processing unit (CPU)) for executing instructions to cause an operation (e.g., opening valves, closing valves, etc.) to be performed in the hydrogen storage unit120. The hydrogen supply control unit135may also include a memory device (random access memory (RAM), read only memory (ROM), etc.) for storing instructions to be executed by the processor. The memory device may also store other data such as history data (e.g., hydrogen concentration, temperature, pressure, etc.) collected by the various sensors in the hydrogen storage unit120. The processor may access the data in the memory device and perform operations on the data, utilize the data in executing instructions, etc.

The hydrogen supply control unit135may be communicatively coupled (e.g., by wire or wireless) to the hydrogen purifier132and the hydrogen purifier134. The hydrogen supply control unit135may thereby control a purifying operation in the hydrogen purifier132and the hydrogen purifier134. The hydrogen supply control unit135may also be communicatively coupled (e.g., by wire or wireless) to the inlet/outlet ports129and may thereby control a transfer of hydrogen, nitrogen or other gases to and from the hydrogen storage tank122. The hydrogen supply control unit135may also be communicatively coupled (e.g., by wire or wireless) to the hydrogen storage area control unit126to facilitate an exchange of information (e.g., history data, software updates, etc.) between the hydrogen supply control unit and the hydrogen storage area control unit126.

The hydrogen supply control unit135may also be communicatively coupled (e.g., by wire or wireless) to the fuel cell APU140and the fuel cell power plant160in order or coordinate a supplying of hydrogen (e.g., increasing/decreasing flow rates, supply timing, hydrogen purity requirements, etc.) to the fuel cell APU140and the fuel cell power plant160. The hydrogen supply control unit135may also be communicatively coupled (e.g., by wire or wireless) to various flowmeters, actuators and valves (e.g., ball valves, butterfly valves, etc.) that may be formed in the hydrogen fuel transmission line2. The hydrogen supply control unit135may thereby further control a supplying of hydrogen to the fuel cell APU140and to the fuel cell power plant160.

The hydrogen storage unit120may also include a wireless transceiver136that is connected to the hydrogen supply control unit135. The wireless transceiver136may communicate wirelessly with the off board hydrogen refueling unit180and facilitate wireless communication between the hydrogen supply control unit135and the off board hydrogen refueling unit180. The hydrogen supply control unit135may thereby coordinate an operation (e.g., hydrogen refueling operation, hydrogen reprocessing operation, etc.) and exchange information about the operation (e.g., time, date, quantity, hydrogen purity level, etc.) with the off board hydrogen refueling unit180.

Further, hydrogen may be stored in the hydrogen storage tank122as a gas mixture of hydrogen and inert gas (e.g., nitrogen, argon) such that the concentration in the hydrogen storage tank122is below the upper explosive limit for hydrogen. For example a forming gas mixture of nitrogen and a low percentage of hydrogen (e.g., less than 20 volume percent, such as 1-4 volume percent) may be stored. Later, when this gas mixture is supplied from the hydrogen storage tank122to a fuel cell stack in the fuel cell APU140and/or the fuel cell power plant160, a purifying recirculation such as via electrochemical pumping may be used in the anode loop of the fuel cell stack to remove the inert gas in the gas mixture. The inert gas that is removed from the gas mixture may be saved on board via a compressor. In addition, multiple stages of purifying recirculation may be used.

The sensor122amay perform a sensing operation in the hydrogen storage tank122based on a reference gas that may be generated in situ. For example, the reference gas may be generated by the hydrogen purifier123that may include, for example, a hydrogen pumping element. A sensing operation performed, for example, by the sensor122aor sensor127, can be potentiometric or amperometric. The actual type of sensing operation to be used may depend on the electrochemical activity of an impurity that is to be detected. If the impurity is inert or adsorbing, then the sensing operation may be potentiometric. If the impurity is electrochemically active, then the sensing operation may refer to that potential and record the current draw. Regardless of the type of sensing operation used, if the impurity concentration is very low, then a multistage hydrogen pumping operation (e.g., by the hydrogen purifier123) may be performed in order to increase the sensitivity of the sensor. The hydrogen storage unit may also include a transient condition response unit138. In the condition of landing while the aircraft1still contains a large amount of hydrogen on board (e.g., in the hydrogen storage tank122) the hydrogen supply control unit135may direct the transient condition response unit138to take a precautionary action with respect to the stored hydrogen. The precautionary action may include diluting the hydrogen (e.g., with nitrogen from the nitrogen tank124) and/or dumping the hydrogen from a wing of the aircraft1or from another trailing surface such as the tail of the aircraft1. For example, in the condition of landing the aircraft1when there is not time to dump the hydrogen, the transient condition response unit138may cause nitrogen (or another inert gas such as argon or helium) to be rapidly mixed with the stored hydrogen. This may help to ensure that the aircraft1can perform a hydrogen fuel dumping operation without creating a combustible hydrogen/oxygen mixture (e.g., a mixture where hydrogen is less than 4% or greater than 80%).

The transient response control unit138may be connected to the hydrogen storage tank122, and may be composed of various valves, pumps and piping necessary to perform the response (e.g., diluting and/or dumping hydrogen). The precautionary action may also include, in the condition of catastrophic failure of the main propulsion system, transferring the stored hydrogen to an emergency buoyancy system. The emergency buoyancy system may include, for example, a balloon made of Kevlar or other high strength material that, when filled with hydrogen, may to provide capability for controlled descent of the aircraft1.

FIG.3illustrates the electrical power distribution system5in the aircraft1, according to one or more embodiments. The electrical power distribution system5may include electrical transmission wires and cables and electrical devices (e.g., inverters) that are used to distribute electrical power to the various electrical/electronic devices on the aircraft1. The electrical power distribution system5may be connected, for example, to the aircraft's gas turbine engines1a(or to one or more propellers in a propeller powered aircraft), the forward electrical/electronics (E/E) equipment bay6and the aft E/E equipment bay7. The fuel cell APU140and the fuel cell power plant160may be connected to the electrical power distribution system5in order to power the aircraft's electrical/electronic devices (e.g., onboard lighting, galley electronics and cockpit avionics). A backup power supply150that may include, for example, a secondary battery (e.g., lithium ion battery) may also be connected to the electrical power distribution system5.

FIG.4illustrates the fuel cell APU140, according to one or more embodiments. The fuel cell APU140may generate auxiliary electrical power for use in the aircraft1, which may be distributed by the aircraft's electrical power distribution system5. The auxiliary electrical power generated by the fuel cell APU140may be used, for example, to start one or more of the engines (e.g., gas turbine engines1aor propeller engines) on the aircraft1. The auxiliary electrical power may also be used to power onboard lighting, galley electronics and cockpit avionics, such as while the aircraft1is on the ground. The fuel cell APU140may also be communicatively coupled to the aircraft's backup power supply150.

As illustrated inFIG.4, the fuel cell APU140may include one or more APU fuel cell stacks141that each may include a plurality of fuel cells (e.g., PEM fuel cells). The APU fuel cell stacks141may be located in an APU fuel cell cabinet142that may include tightly monitored ambient conditions (e.g., temperature, humidity). The APU fuel cell cabinet142may include one or more sensors143(e.g., infrared cameras) for monitoring the conditions in the APU fuel cell cabinet142. An air monitoring and treatment unit145may be connected to the APU fuel cell cabinet142and may treat the air inside the APU fuel cell cabinet142based on data from the sensors143.

The fuel cell APU140may be supplied with hydrogen from the hydrogen storage unit120via the hydrogen fuel transmission line2. One or more sensors144may be connected to the APU fuel cell stack141. The sensors144may comprise pressure and/or temperature sensors configured to detect a condition (e.g., temperature, pressure, etc.) in the APU fuel cell stack141. The sensors144may also include, for example, a voltage probe and/or a current sensor, which measures voltage or current output by the APU fuel cell stack141.

The fuel cell APU140may also include an APU remediation unit146that may remedy an undesirable condition in the APU fuel cell cabinet142. The APU remediation unit146may provide emergency humidification to the APU fuel cell cabinet142, purge the air in the APU fuel cell cabinet142, and supply emergency hydrogen and/or oxygen to the APU fuel cell cabinet142. Thus, the APU remediation unit146may include a water or water vapor source, a blower and/or fan, and one or more gas (e.g., hydrogen and/or oxygen) tanks and/or pipes.

The fuel cell APU140may also include an APU transient condition response unit147. The APU transient condition response unit147may respond to a condition (e.g., an undesirable condition) in the APU fuel cell stack141. In particular, the APU transient condition response unit147may inject compressed air into the cathode side of the APU fuel cell stack141, or may heat or cool the APU fuel cell stack141as needed to improve a performance of the APU fuel cell stack141. APU transient condition response unit147may include an air blower or fan that provides cool or warm air to the APU fuel cell stack141.

The fuel cell APU140may also include an APU control unit148that may control an operation of the fuel cell APU140. The APU control unit148may be communicatively coupled (e.g., by wire or wireless) to and thereby control an operation of the sensors143, sensors144, air monitoring and treatment unit145, APU remediation unit146, APU transient condition response unit147and the backup power supply150.

The APU control unit148may include a processing device (e.g., processor, central processing unit (CPU)) for executing instructions to cause an operation (e.g., remediation operation, transient condition response, etc.) to be performed in the fuel cell APU. The APU control unit148may also include a memory device (random access memory (RAM), read only memory (ROM), etc.) for storing instructions to be executed by the processor. The memory device may also store other data such as history data and performance data (e.g., hydrogen concentration, temperature, pressure, etc.) collected by the sensors143and144. The processor may access the data in the memory device and perform operations on the data, utilize the data in executing instructions, etc.

The fuel cell APU140may provide auxiliary electrical power to one or more of the gas turbine engines1aof the aircraft1. The gas turbine engines1amay have a configuration so as to accommodate the use of the fuel cell APU140. For example, the gas turbine engines1amay include sensors and detectors (e.g., “fire eye” wave-length fire detectors) that may detect a hydrogen-air fire inside the aircraft1, the fuel cell APU140, the fuel cell power plant140, and/or in the gas turbine engine1aitself.

The fuel cell APU140may be higher in efficiency than conventional APUs, such as turbine based APUs. The fuel cell APU140may be sized sufficiently to provide power to a motor-generator that is mounted on a shaft of the gas turbine engine1a. The motor-generator may normally be used to provide electrical power to the aircraft power, but in an emergency condition, the fuel cell APU may motor the motor-generator to provide some additional thrust to the aircraft1.

In addition, the auxiliary electrical power generated by the fuel cell APU140and supplied to the motor-generator of the gas turbine engines1amay be used for thrust reversal during a landing of the aircraft1. The motor-generator generated power from one of the gas turbines1amay be used to power as a motor another one of the gas turbine engines1ain the event of a casualty condition.

The fuel cell APU140may be designed for extremely rapid start/stop operation as needed for casualty power. The fuel cell APU140may also have a modular design such that failure of a single fuel cell stack in a plurality of APU fuel cell stacks141may not necessarily create a failure of the entire fuel cell APU140. For example, the power electronics of the fuel cell APU140may create individually DC wired circuits from stack elements of the APU fuel cell stack141to power electronic devices on the aircraft1.

FIG.5illustrates the fuel cell power plant160, according to one or more embodiments. The fuel cell power plant160may generate primary electrical power for use in the aircraft1which may be distributed by the aircraft's electrical power distribution system5. The fuel cell power plant160may be used to power devices, for example, in the forward electrical/electronics (E/E) equipment bay6and the aft E/E equipment bay7. In particular, the fuel cell power plant160may power onboard lighting, galley electronics and cockpit avionics, such as while the aircraft1is in flight. The fuel cell power plant160may also be communicatively coupled to the aircraft's backup power supply150.

As illustrated inFIG.5, the fuel cell power plant160may include one or more fuel cell stacks161that each may include a plurality of fuel cells (e.g., PEM fuel cells). The fuel cell stacks161may be located in a fuel cell cabinet162that may include tightly monitored ambient conditions (e.g., temperature, humidity). The fuel cell cabinet162may include one or more sensors163(e.g., temperature sensor, humidity sensor, one or more infrared cameras, etc.) for monitoring the conditions in the fuel cell cabinet162. An air monitoring and treatment unit165may be connected to the fuel cell cabinet162and may treat the air inside the fuel cell cabinet162based on data from the sensors163. The air monitoring and treatment unit165may comprise at least one pump, blower or fan which may evacuate the fuel cell cabinet and/or provide air into the fuel cell cabinet162. Water generated in the fuel cell stack161(as well as the APU fuel cell stack141) may be used as water for utilities on the aircraft1, or as water for the electrolysis unit139(seeFIG.2) on board the aircraft1.

In one embodiment, the fuel cell cabinet162may include, for example, an air-tight chamber. The air monitoring and treatment unit165may include a vacuum device (e.g., vacuum pump or blower) for maintaining the fuel cell cabinet162at a negative pressure relative to the outside. The sensors163may include hydrogen sensors for detecting leaks above a lower flammability level. The sensors163may also include one or more infrared (IR) cameras (e.g., IR-based thermal cameras) for detecting local hot spots in the fuel cell cabinet162(e.g., in the fuel cell stack161).

The fuel cell power plant160may be supplied with hydrogen from the hydrogen storage unit120via the hydrogen fuel transmission line2. One or more sensors164may be connected to the fuel cell stack161. The sensors164may comprise temperature and/or pressure sensors configured to detect a condition (e.g., temperature, pressure, etc.) in the fuel cell stack161. The sensors164may also include voltage probes that are placed at various points in the fuel cell stack161. Data from the voltage probes may be used by the fuel cell power plant control unit168to determine the distribution of reactants in the fuel cell stack and output voltage of the fuel cell stack161using DC voltage measurements and/or AC impedance spectroscopy (i.e., electrochemical impedance spectroscopy (EIS)) performed by an EIS analyzer.

The fuel cell power plant160may also have a fuel cell performance monitor169that receives data from the sensors164to monitor a performance of the fuel cell stack161. The fuel cell performance monitor169may perform electrochemical impedance spectroscopy to determine the various losses (e.g., ohmic vs. activation vs. mass transport) in the fuel cell stack161. The fuel cell performance monitor169may determine a recommended action based on the results of the spectroscopy, and the fuel cell power plant control unit168may control the various elements of the fuel cell power plant160in order to take the recommended action.

The fuel cell performance monitor169may be designed to enable AC impedance measurements by injecting an AC impedance ripple into the fuel cell stack161. The ripple may be applied continuously or applied periodically (e.g., as required) to ensure proper operation of the fuel cell stack161. In particular, the AC impedance spectroscopy may include a low frequency ripple to monitor for issues (e.g., alarming conditions) such as water management issues in the fuel cell power plant160. The AC impedance spectroscopy may also include a 1 kHz frequency ripple to monitor for dry out conditions of a humidified fuel cell power plant160. Further, in conducting AC impedance spectroscopy, the fuel cell performance monitor169may perform tests, such as a) ripple injection and analysis by fast Fourier transform of cell voltage to calculate impedance as may be performed without interrupting load to or from electrochemical cells; or b) current interrupt and cell monitoring decay, or c) a combination of these two tests.

The fuel cell performance monitor169may also be able to conduct AC impedance spectroscopy on electrochemical batteries (e.g., lithium ion batteries) on the aircraft1. Such batteries may be included, for example, in the backup power supply150. The fuel cell performance monitor169may thereby detect a hazardous condition (e.g., fire hazard) in a battery and notify the fuel cell power plant control unit168to remove current from the battery.

The fuel cell power plant160may also include a remediation unit166that may remedy an undesirable condition in the fuel cell cabinet162. The remediation unit166may remedy conditions (e.g., improper conditions) that are detected by the fuel cell performance monitor169, for example, by AC impedance spectroscopy, voltage analysis, or a combination of both.

The remediation unit166may include a humidifier/dehumidifier166athat may provide emergency humidification and/or dehumidification to the fuel cell cabinet162. The humidifier/dehumidifier166amay provide emergency humidification to restore an operation of the fuel cell stack161in the case of a loss of humidification or dry out to restore proper voltage-current operation of the fuel cell stack161. The remediation unit166may also include a purging device166bthat may rapidly purge the air in the fuel cell cabinet162. The purging device166bmay include, for example, a vacuum pump or blower and/or an evacuated vacuum chamber that may be used to clear a “flooding” of the fuel cell stack161if water management issues are detected to restore proper voltage-current operation of the fuel cell stack161.

The remediation unit166may also include a hydrogen and oxygen supply unit166cthat may provide a hydrogen supply and/or oxygen supply (e.g., emergency hydrogen and/or oxygen) to the fuel cell cabinet162. The hydrogen and oxygen supply unit166cmay provide emergency hydrogen and oxygen that may be contained for use in the case of starvation of anode or cathode reactants as triggered by AC impedance and voltage monitoring by the fuel cell performance monitor169. For example, in the case of cathode starvation, the hydrogen and oxygen supply unit166cmay boost the oxygen supply, and in the case of anode starvation, the hydrogen and oxygen supply unit166cmay boost the hydrogen supply.

The remediation unit166may include a metal hydride supply166dthat can provide emergency hydrogen via metal hydride. The metal hydride supply166dmay comprise a metal gas storage material located in a gas tank. The metal gas storage material may comprise any metal (e.g., magnesium, palladium, lithium or alloys of aluminum or transition metal (e.g., Ni, Co, Mn, Fe, etc.), with a rare-earth, alkaline earth metals or another transition metal) which forms a metal hydride (such as palladium hydride, MgH2, NaAlH4, LiAlH4, LiH, LaNi5H6, TiFeH2, etc.) upon reaction with hydrogen. The metal hydride may be recharged, for example, by using hydrogen generated on board the aircraft1. Since the recharging reaction of metal and hydrogen (e.g., M+H2→MH2) is exothermic, the remediation unit166may include a cooling device that removes heat generated by the reaction to maintain an optimal absorption rate. Oxygen may be supplied to the hydrogen and oxygen supply unit166cby using unutilized thermal energy (e.g., heat generated by the production of metal hydride) for oxygen concentration or by using an oxygen electrochemical pump utilizing either PEM or solid oxide fuel cell technology.

The fuel cell power plant160may also include a transient condition response unit167that may respond to a condition (e.g., an undesirable condition) in the fuel cell stack161. The transient condition response unit167may include an air supply port167athat may receive air (e.g., ram air, compressed air) from an external source, and supply the air to the fuel cell stack161. In particular, the air supply port167amay direct the air supply into the cathode side of the fuel cell stack161as needed to improve a performance of the fuel cell stack161. The transient condition response unit167may also include an air compressor, blower, fan or pump167bthat generate compressed air to be supplied to the fuel cell stack161.

In the case of normal flight, the air supply port167amay be connected to a shaft-connected turbo-charging unit to provide compressed air for anode recirculation, and/or connected to a ram air source to reduce the requirement for cathode air compression. In the case of a stall condition that may cause a loss of ram air, the air compressor167b(e.g., or other mechanical compression device) may supply compressed air to the fuel cell stack161to ensure sufficient cathode flow when ram air pressure is dropping.

The transient condition response unit167may also monitor an elevation of the aircraft1and provide emergency anode and cathode flows (e.g., via the air supply port167aor the air compressor167b) when the aircraft's elevation rate of change exceeds a nominal value.

The transient condition response unit167may also include a heating/cooling unit167cthat may heat or cool the fuel cell stack161as needed to improve a performance of the fuel cell stack161. For example, in the condition of loss of temperature control for the fuel cell cabinet162, the heating/cooling unit167cmay provide emergency heating or emergency cooling in order to hold the fuel cell cabinet162in a nominal temperature range.

The fuel cell power plant160may also include a fuel cell power plant control unit168that may control an operation of the fuel cell power plant160. The fuel cell power plant control unit168may be communicatively coupled (e.g., by wire or wireless) to and thereby control an operation of the sensors163, sensors164, fuel cell performance monitor169, air monitoring and treatment unit165, remediation unit166, transient condition response unit167and the backup power supply150.

The backup power supply150may provide backup power through energy storage such as by batteries or supercapacitors (e.g., ultracapacitors). The backup power supply150may provide electrical power to the aircraft1, for example, if the fuel cell power plant168needs to be shut down. The fuel cell power plant control unit168may coordinate an operation of the fuel cell stack161and the backup power supply150to effectively form a “hybrid” power system that simultaneously draws power from both the fuel cell stack161and the power generation devices of the backup power supply150(e.g., batteries, supercapacitor, etc.) provide or support a pulse power draw.

The fuel cell power plant control unit168may also be communicatively coupled to the APU control unit148, the hydrogen supply control unit135and the backup power supply150. This coupling may allow these four units to work together to maintain an optimal condition in the electrical power supply system100of the aircraft1. For example, if the sensor122ain the hydrogen storage tank122detects a low level of hydrogen, the hydrogen supply control unit135may transmit a signal to the fuel cell power plant control unit168which may activate the backup power supply150.

The fuel cell power plant control unit168may include a processing device (e.g., processor, central processing unit (CPU)) for executing instructions to cause an operation (e.g., remediation operation, transient condition response, etc.) to be performed in the fuel cell power plant160. The fuel cell power plant control unit168may also include a memory device (random access memory (RAM), read only memory (ROM), etc.) for storing instructions to be executed by the processor. The memory device may also store other data such as history data and performance data (e.g., hydrogen concentration, temperature, pressure, etc.) collected by the sensors163and164. The processor may access the data in the memory device and perform operations on the data, utilize the data in executing instructions, etc.

FIG.6illustrates the off board hydrogen refueling unit180, according to one or more embodiments. The off board hydrogen refueling unit180may store hydrogen that can be used to refuel the aircraft1. The off board hydrogen refueling unit180may also produce hydrogen at the time of refueling, and refuel the aircraft1with the produced hydrogen.

The off board hydrogen refueling unit180may include one or more off board hydrogen storage tanks182for storing the hydrogen. One or more inlet/outlet ports189may be connected to the off board hydrogen storage tank182. Hydrogen and other gases (e.g., nitrogen) may be transferred into and out of the off board hydrogen storage tank182via the inlet/outlet ports189.

The off board hydrogen refueling unit180may also include an electrolysis unit199that may be connected to a water supply (e.g., municipal water supply). The electrolysis unit199may comprise a PEM type electrolyzer configured to perform an electrolysis operation on the water from the water supply to produce hydrogen that may be stored in the off board hydrogen storage tank182. The oxygen that is produced by the electrolysis operation may be stored in the oxygen tank198.

The off board hydrogen refueling unit180may also include a hydrogen purity monitoring device (e.g., a gas sensor)186that may monitor a purity of the hydrogen in the off board hydrogen storage tank182. The off board hydrogen refueling unit180may also include a hydrogen purifier (e.g., any suitable gas purifier device)183for purifying the hydrogen stored in the off board hydrogen storage tank182, and a nitrogen tank184that may store nitrogen that has been extracted from the hydrogen by the hydrogen purifier183. The nitrogen tank184may also be coupled to the off board hydrogen storage tank182, and under certain circumstances, nitrogen from the nitrogen tank184may be used to dilute the hydrogen in the off board hydrogen storage tank182.

The off board hydrogen refueling unit180may also include a hydrogen cannister fill device (e.g., a gas pump, blower or conduit)191that may transfer hydrogen from the off board hydrogen storage tank182(or directly from the electrolysis unit199) to one or more hydrogen-filled cannisters185. The hydrogen-filled cannisters185may be stored at a location of the off board hydrogen refueling unit180and may be used to refuel the aircraft1with hydrogen in place of or in supplement to the hydrogen stored in the hydrogen storage tank182. This may allow for the aircraft1to be rapidly refilled and reduce a risk of hydrogen fuel leakage during a refueling operation.

In one embodiment, the hydrogen purifier183may include an electrochemical pump or cascade of electrochemical pumping stages that continuously purify the hydrogen stored in the hydrogen storage tank182. This may be particularly useful in the case that off-gassing (e.g., in the hydrogen storage tank182) creates impurities in the hydrogen stored therein. The electrochemical pump may comprise a PEM based hydrogen pump that selectively pumps hydrogen across the polymer membrane from one electrode to an opposite electrode.

One or more sensors (e.g., temperature, pressure and/or gas composition sensors)182amay be disposed in or on the off board hydrogen storage tank182. The sensors182amay detect conditions inside the off board hydrogen storage tank182such as a concentration of various gases including hydrogen and nitrogen, and may also detect impurities in the hydrogen. The sensors182a(e.g., low level sensors) may also notify the hydrogen purity monitoring device186when a condition in the hydrogen storage tank182(e.g., hydrogen purity) is at a boundary of safe operation. The sensors182amay also detect temperature and pressure in the hydrogen storage tank182.

The hydrogen purity monitoring device186may be electrically coupled to the sensors182a, the hydrogen purifier183and the nitrogen tank184. The hydrogen purity monitoring device186may control an operation of the off board hydrogen storage tank182, hydrogen purifier183and nitrogen tank184based on data supplied by the sensors182a. In particular, the hydrogen purity monitoring device186may control an opening and closing of valves for transmitting gases to and from the off board hydrogen storage tank182, hydrogen purifier183and nitrogen tank184.

The sensors182amay indicate when a combustible mixture is included in the off board hydrogen storage tank182, and thus may indicate a “hazard” condition. When the off board hydrogen storage tank182does not contain hydrogen or other fuels in a “hazard” condition (e.g., when the off board hydrogen storage tank182is backfilled with an inert gas such as nitrogen, argon or helium), then the off board hydrogen storage tank182may be indicated to be in a “safe” condition. In particular, the sensors182amay detect a dangerous hydrogen condition, and may be arranged in a coincidence logic arrangement. For example, a certain percentage of the sensors182a(e.g., ¾ of the sensors182a) must indicate “safe” to prove safe, a certain percentage of the sensors182a(e.g., 2/4 of the sensors182a) must indicate “danger” to prove danger, etc.

If the hydrogen purity monitoring device186determines that the hydrogen in the off board hydrogen storage tank182is too low in gas quality (i.e., having too many impurities), then it may direct the hydrogen purifier183to process the hydrogen in the off board hydrogen storage tank182to increase gas quality, and then continuously or periodically use data from the sensors182ato re-analyze the stored hydrogen and recertify the hydrogen to confirm that the quality meets aviation hydrogen requirements. The hydrogen purifier183may purify (e.g., reprocess) the hydrogen in the off board hydrogen storage tank182, for example, by liquifying the hydrogen. In particular, the hydrogen purifier may liquefy the hydrogen, re-gasify the hydrogen and then recompress the hydrogen. The hydrogen purifier183may also purify the stored hydrogen by performing a drying process by using, for example, a pressure swing adsorption (PSA), thermal swing adsorption (also referred to as temperature swing adsorption) (TSA) or hybrid pressure/thermal swing adsorption (HP/TSA) process in one or more PSA and/or TSA adsorber material beds. The drying process (e.g., by PSA, TSA or HP/TSA) may remove impurities in the stored hydrogen. The hydrogen purifier183may also purify (e.g., reprocess) the stored hydrogen by removal of impurities by preferential oxidation of impurities and/or catalytic combustion in a fuel-rich reactor to convert reactive non-hydrogen compounds to CO2and/or water. The hydrogen purifier183may then perform removal of the CO2and/or water by PSA, TSA or HP/TSA.

The off board hydrogen refueling unit180may also include a refueling control unit188that controls the overall operation of the off board hydrogen refueling unit180. The refueling control unit188may be electrically coupled to the hydrogen purity monitoring device186and may thereby control an operation of the hydrogen purity monitoring device186. The hydrogen purity monitoring device186may also transmit data that it obtains from the sensors182a, the hydrogen purifier183and the nitrogen tank184to the refueling control unit188.

The refueling control unit188may, for example, create and/or assemble data such as a record (e.g., automated record) of the hydrogen purity obtained by the hydrogen purity monitoring device186, and wirelessly transmit that data to the aircraft1. In particular, the refueling control unit188may create a “finger print” by measuring and recording the amount (e.g., percentage) of one or more isotopes of hydrogen including1H,2H (deuterium), and3H of the hydrogen that is stored and/or produced by the off board hydrogen refueling unit180. For example, the hydrogen purity monitoring device may utilize the sensors182ato perform gas chromatography or other gas concentration analysis to record H2, O2, CO, CO2, Ar, He, CH4, NH3and other gas concentrations while transferring hydrogen from the off board hydrogen storage tank182into the aircraft1.

The refueling control unit188may control other operations of the off board hydrogen refueling unit180based on data that it obtains from the hydrogen purity monitoring device186. In particular, the refueling control unit188may activate the hydrogen cannister fill device191and may control an opening and closing of valves for or transmitting gases to and from the off board hydrogen storage tank182, hydrogen purifier183and nitrogen tank184.

The refueling control unit188may also control an operation of the inlet/outlet ports189. The refueling control unit188may thereby control the transfer of gas onto and off of the aircraft1in a refueling operation. The refueling control unit188may also control an operation of the electrolysis unit199and the oxygen tank198(e.g., dispensing oxygen from the oxygen tank198). That is, the electrolysis unit199may produce hydrogen under the control of the refuel control unit188. For example, the refueling control unit188may direct the electrolysis unit199to produce hydrogen in the event that the sensor182adetects a low level of hydrogen in the hydrogen storage tank182.

The refueling control unit188may direct the electrolysis unit199to perform water electrolysis at the time of fueling the aircraft1. Thus, only a water supply (and not stored hydrogen) may be required to be maintained at the off board hydrogen refueling unit180.

The oxygen generated by the electrolysis unit199may be transferred to the aircraft1for use in the fuel cell power plant160. For example, the oxygen may be stored by the hydrogen and oxygen supply unit166cor by the transient condition response unit167for transient (e.g., emergency) conditions when air quality in the fuel cell cabinet162is too low. The oxygen may alternatively be transferred to the aircraft1for other uses on board such as emergency oxygen for passengers or pilots.

The refueling control unit188may include a processing device (e.g., processor, central processing unit (CPU)) for executing instructions to cause an operation (e.g., remediation operation, transient condition response, etc.) to be performed in the off board hydrogen refueling unit180. The refueling control unit188may also include a memory device (random access memory (RAM), read only memory (ROM), etc.) for storing instructions to be executed by the processor. The memory device may also store other data such as history data and performance data (e.g., hydrogen concentration, temperature, pressure, etc.) collected by the sensors182a. The processor may access the data in the memory device and perform operations on the data, utilize the data in executing instructions, etc.

The refueling control unit188may be connected to a wireless transceiver188a. The wireless transceiver188amay communicate wirelessly with the hydrogen supply control unit135onboard the aircraft1, to enable communication between the refueling control unit188and the hydrogen supply control unit135. The refueling control unit188may thereby coordinate an operation (e.g., hydrogen refueling operation, hydrogen reprocessing operation, etc.) and exchange information about the operation (e.g., time, date, quantity, hydrogen purity level, etc.) with the hydrogen storage unit120onboard the aircraft1.

The refueling control unit188may initiate a refueling operation by removing any hydrogen that is being stored on the aircraft1while the aircraft1is on the ground for enhanced safety. For example, the fuel control unit188may direct the hydrogen supply control unit135onboard the aircraft1to vent the hydrogen storage tank122(e.g., using the transient condition response unit138) to remove the hydrogen remaining therein. In particular, the hydrogen storage tank122may be vented into the off board hydrogen storage tank182with compressors or electrochemical H2pumps for transfer compression from the hydrogen storage tank122to the off board hydrogen storage tank182.

The refueling control unit188may also direct the hydrogen supply control unit135onboard the aircraft1to backfill the hydrogen storage tank122with some amount of nitrogen to ensure that the hydrogen storage tank122cannot contain a combustible mixture.

Then, at the time of refueling, the refueling control unit188may direct the off board hydrogen storage tank182to “purge” the hydrogen/nitrogen mixture (e.g., “safe” hydrogen) in the hydrogen storage tank122onboard the aircraft1, with pure hydrogen. The refueling control unit188may remove the purged hydrogen/nitrogen mixture, store it (e.g., in the off board hydrogen storage tank182), and purify it by removing the nitrogen using the hydrogen purifier183. This purification operation may be performed repeatedly (e.g., continuously) to remove the nitrogen from the stored mixture (e.g., in the off board hydrogen storage tank182).

The off board hydrogen storage tank182when empty may be backfilled with an inert gas or mixture of gases such as nitrogen or argon to create a diluted mixture of “forming gas.” The forming gas may include, for example, 90% nitrogen and 10% hydrogen which cannot become a combustible mixture. At the time of refueling, the stored “forming gas” may be purified by the hydrogen purifier183(e.g., by performing a purifying compression such as electrochemical separation via a PEM stack), and then “pumped” into the hydrogen storage tank122onboard the aircraft1. This may provide the advantage of holding hydrogen in the off board hydrogen storage tank182only in a non-combustible form. The nitrogen that is used in the backfilling operation may include nitrogen from the nitrogen tank184, or nitrogen produced by the off board hydrogen refueling unit180via air separation (e.g., in advance of refueling). The nitrogen may alternatively come from the nitrogen tank124in the hydrogen storage unit120onboard the aircraft, or via air separation (e.g., in advance of refueling; during flight) by the hydrogen storage unit120.

FIG.7illustrates a method of supplying electrical power to an aircraft, according to one or more embodiments. The method may include a Step710of generating auxiliary electrical power by a fuel cell auxiliary power unit (APU) and supplying the auxiliary electrical power to the aircraft. The method may also include a Step720of generating primary electrical power by a fuel cell power plant and supplying the primary electrical power to the aircraft. The method may also include a Step730of storing hydrogen in a hydrogen storage unit and supplying the hydrogen to the fuel cell APU and the fuel cell power plant.

The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the scope of the claims to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen in order to best explain the principles underlying the claims and their practical applications, to thereby enable others skilled in the art to best use the embodiments with various modifications as are suited to the particular uses contemplated.

It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.