Patent Description:
Aircraft typically include propulsion systems, such as gas turbine engines or other engines or propulsion systems. Further, for aircraft that include passenger compartments, air conditioning is required to maintain a cabin at desired pressures and temperatures for passengers and/or crew. Conventionally, an aircraft will include an environmental control system (ECS) for generating and supplying conditioned air to a cabin or for other onboard purposes. Fuel burn consumption associated with aircraft ECS depends on different factors, such as the amount of bleed and ram air usage, electric power consumption, and the weight of the system. Improved systems for propulsion, power generation, and environmental control may be desirable for aircraft. Aircraft systems are disclosed in <CIT> and <CIT>. <CIT> describes a fuel and air system comprising a turbine and a compressor connected by a shaft, a pressurized fuel tank, a heat exchanger and a fuel cell. The turbine receives pressurized fuel from the fuel tank. The compressor has an inlet for oxidation gas. The compressor outlet is connected to the fuel cell. Heat exchangers receiving a secondary working fluid are positioned between the fuel tank and the turbine, between the turbine and the fuel cell, and between the compressor and the fuel cell.

According to one aspect, aircraft systems are provided as defined by claim <NUM>.

In embodiments of the aircraft systems may include that the pressurized fuel is pressurized hydrogen.

In further embodiments of the aircraft systems may include that the pressurized fuel is pressurized ammonia.

In further embodiments of the aircraft systems may include a motor operably coupled to the shaft and configured to generate at least one of electrical power and mechanical power.

In further embodiments of the aircraft systems may include an electric generator operably coupled to the turbo expander by a shaft, the electric generator configured to generate electric power.

In further embodiments of the aircraft systems may include that the fuel consumption system is a fuel cell.

In further embodiments of the aircraft systems may include that the fuel cell is one of a solid oxide fuel cell and a proton exchange membrane (PEM).

In further embodiments of the aircraft systems may include that the fuel cell receives pressurized air containing oxygen.

In further embodiments of the aircraft systems may include that the pressurized air is pressurized in the compressor operably coupled to the turbo expander.

In further embodiments of the aircraft systems may include that the fuel consumption system is a hydrogen burning engine.

In further embodiments of the aircraft systems may include an additional heat exchanger arranged between the fuel-to-air heat exchanger and the fuel consumption system, wherein the additional heat exchanger receives the fuel from the fuel-to-air heat exchanger as a first working fluid and an aircraft system working fluid as a second working fluid.

In further embodiments of the aircraft systems may include that the aircraft system working fluid is a fluid used to cool aircraft powered electronics.

In further embodiments of the aircraft systems may include a fan configured to direct air into the fuel-to-air heat exchanger.

According to another aspect, aircraft are provided as defined by claim <NUM>.

In embodiments of the aircraft may include that the fuel consumption system is a fuel cell system configured to generate power for flight of the aircraft.

In further embodiments of the aircraft may include a fan configured to direct air into the fuel-to-air heat exchanger when the aircraft is on the ground.

In further embodiments of the aircraft may include that the air in the fuel-to-air heat exchanger is recirculated cabin air from a cabin of the aircraft.

The foregoing features and elements may be executed or utilized in various combinations without exclusivity, unless expressly indicated otherwise.

Referring to <FIG>, a schematic illustration of an aircraft <NUM> that may incorporate embodiments of the present disclosure is shown. The aircraft <NUM> includes a fuselage <NUM>, wings <NUM>, and a tail <NUM>. In this illustrated embodiment, the aircraft <NUM> includes wing-mounted aircraft power systems <NUM>. The wing-mounted aircraft power systems <NUM> may be convention gas turbine engines, fuel-cell based propulsion systems, or other propulsion systems as known in the art. In other configurations, aircraft employing embodiments of the present disclosure may include fuselagemounted and/or tail-mounted configurations. Further, any number of fuel-cell based propulsion systems may be employed, from one to four or more, depending on the aircraft configuration and power and thrust needs thereof. The aircraft power systems <NUM> may be used to generate thrust for flight and may also be used to generate onboard electrical power, particularly in a fuel cell configuration. The aircraft <NUM> may also include auxiliary power units <NUM> that may be fuel cell based, or otherwise configured to generate power. The aircraft power systems <NUM>, in other configurations, may be fuel burning engines similar to conventional gas turbine engines.

Such fuel cell based power systems (for power generation and/or for propulsion) and/or combustion engine power systems may employ various types of fuel, including hydrogen. For example, turning now to <FIG>, a schematic diagram of an aircraft power system <NUM> in accordance with an embodiment of the present disclosure is shown. The aircraft power system <NUM> is a non-combustion system, and includes a fan <NUM>, a drive shaft <NUM>, a motor <NUM>, and an aircraft power generation system <NUM>. The fan <NUM> is operably coupled to and configured to be rotated by the drive shaft <NUM> to generate thrust, similar to a fan and fan section of a conventional gas turbine engine. But, in the fuel cell configuration of <FIG>, there is no core flow path and no turbine section(s) driven by combusted and expanded gas. Rather, the drive shaft <NUM> that drives rotation of the fan <NUM> is operably coupled to and driven by the motor <NUM>. The motor <NUM> may be an electric motor that converts electrical power to mechanical (rotational) energy. The motor <NUM> receives power from the aircraft power generation system <NUM> along an electrical connection <NUM>. The aircraft power system <NUM> may be configured to operate within similar limits and envelops as a conventional gas turbine engine.

The fan <NUM>, the drive shaft <NUM>, and the motor <NUM> may be arranged along a propulsion system central longitudinal axis A. The fan <NUM>, the drive shaft <NUM>, the motor <NUM>, and the aircraft power generation system <NUM> can be mounted, installed, or otherwise housed within a propulsion system housing <NUM> (e.g., a nacelle for wing-mounted applications) which includes an exit nozzle <NUM> for directing an airflow therethrough for the purpose of driving flight of an aircraft (e.g., generating thrust). The propulsion system housing <NUM> may be configured to be mounted to a wing or fuselage of an aircraft.

The aircraft power generation system <NUM> may be a fuel cell or similar power source (e.g., a solid oxide fuel cell, proton exchange member (PEM), or the like). The aircraft power generation system <NUM> can be configured to not only power the motor <NUM> but also may be used as a power source for other propulsion system components and/or other aircraft electrical systems and components. In one non-limiting example, the aircraft power generation system <NUM> may be configured to output about <NUM> MW to about <NUM> MW electrical power. In accordance with embodiments of the present disclosure, the aircraft power generation systems may be configured to generate at least <NUM> MW of electrical power (e.g., less power may be used if the system is not used for propulsion). It will be appreciated that when used as a propulsion configuration, the aircraft power generation systems described herein are configured to generate, at least, sufficient power to drive the fan <NUM> and provide sufficient thrust and propulsion for flight at cruise altitudes. The amount of electrical power may be selected for a given aircraft configuration (e.g., size, operating envelope requirements, etc.).

Whether used for propulsion or only onboard electrical power, the aircraft power generation system <NUM> may be configured to combine hydrogen (e.g., liquid, compressed, supercritical, etc.) or other organic fluids as a fuel source using a fuel cell for generation of electricity. The hydrogen can also be used as the cold sink to cool aircraft environmental control system working fluids and/or provide other onboard thermal management, prior to being supplied to the fuel cell. In some embodiments, the fuel cell of the aircraft power generation system <NUM> can be configured to provide base electric power (e.g., suited for cruise operation). In some non-limiting configurations, some fuel (hydrogen) may be directed to bypass the fuel cell and be used in a small gas turbine to generate additional power for take-off and climb peak power needs.

Turning now to <FIG>, a schematic diagram of an aircraft power generation system <NUM> in accordance with an embodiment of the present disclosure is shown. The aircraft power generation system <NUM> includes a fuel cell <NUM> and a fuel source <NUM> (such as a hydrogen fuel source). The fuel cell <NUM> is configured to generate electricity, as will be appreciated by those of skill in the art (e.g., a solid oxide fuel cell, PEM, or the like). In this illustrative configuration, the fuel cell <NUM> includes an anode <NUM>, a cathode <NUM>, and an electrolyte membrane <NUM> arranged therebetween. The fuel cell <NUM> is supplied hydrogen (H<NUM>) from the fuel source <NUM>. The fuel source <NUM> may be a container or tank that houses liquid, compressed gas, supercritical fluid (e.g., the hydrogen in this example), or other fluid state of a fuel (e.g., gas phase hydrogen). The fuel cell <NUM> is supplied with oxygen (O<NUM>) from an oxygen source at an inlet <NUM>. In some embodiments, the O<NUM> may be supplied from ambient air, such as using an intake or scoop on a housing assembly, as will be appreciated by those of skill in the art. The O<NUM> and the H<NUM> are combined within the fuel cell <NUM> across the electrolyte membrane <NUM>, which frees electrons for electrical power output <NUM>. The combined O<NUM> and H<NUM> results in the formation of water (H<NUM>O), which may be passed through an outlet <NUM> and dumped overboard, supplied into an onboard water tank, or otherwise used onboard an aircraft, as will be appreciated by those of skill in the art.

The electrical power output <NUM> may be electrically connected to a motor that is configured to drive a shaft and a fan of a propulsion system to generate thrust (e.g., as shown in <FIG>). The electrical power output <NUM> may also or alternatively be electrically connected to other electrical systems of a propulsion system and/or aircraft system(s), as will be appreciated by those of skill in the art to provide electrical power thereto.

In some fuel cell systems, highly pressurized hydrogen may be stored within a pressure tank or container and extracted to be used within a fuel cell for power generation. Before using highly pressurized Hz in a fuel cell, it is required to reduce the pressure of the H<NUM> to more manageable and/or safe pressure levels. Accordingly, embodiments of the present disclosure are directed to, in part, systems for expanding and reducing the pressure of pressurized H<NUM> that is supplied to a fuel cell for generation of electrical power onboard an aircraft (for propulsion or otherwise).

Fuel burn consumption associated with aircraft Environmental Control Systems (ECS) depends on different factors, such as the amount of bleed and ram air usage, electric power consumption, and the weight of the system. The use of cryogenic or high pressure low carbon fuels, such as hydrogen (H<NUM>), ammonia (NH<NUM>) and the like, in aircrafts has the potential to significantly reduce the ECS fuel burn consumption.

In order to reach a manageable H<NUM> volume, the hydrogen must either be highly compressed (between <NUM>-<NUM> bar) or cryogenically cooled to liquid state (~-<NUM> = ~<NUM>). Because the use of liquid hydrogen in aircrafts presents several challenges, the development of pressurized fuel systems for aircraft that employ compressed fuels may be advantageous. However, a drawback of compressed fuels is the heavy tanks required to maintain the pressures of the fuel (e.g., pressurized gaseous H<NUM>) can make such applications difficult to implement.

Embodiments of the present disclosure are directed to pressurized fuel onboard an aircraft that has reduced weights and improved system performance as compared to prior systems. Advantageously, in some embodiments, the ECS systems of the aircraft may be overhauled such that the ECS pack is eliminated partially or entirely, and replaced or supplemented by a fuel-based system that cools air for use onboard the aircraft (e.g., for cabin air conditioning).

Referring now to <FIG>, an aircraft pressurized hydrogen power system <NUM> is schematically shown. The pressurized hydrogen power system <NUM> includes a pressurized H<NUM> tank <NUM>, a turbo-compressor <NUM>, an optional electric motor <NUM> operably connected to a shaft <NUM> of the turbo-compressor <NUM>, a fuel-to-air heat exchanger <NUM>, and a fuel cell system <NUM>. The fuel cell system <NUM> may be configured similar to that shown and described above, such as in <FIG>, for example. In some embodiments, the fuel cell system <NUM> may be configured to generate electrical power sufficient for flight propulsion or may be configured to generate electrical power for use onboard the aircraft (e.g., to power electrical systems of the aircraft).

The turbo-compressor <NUM> includes a turbo expander <NUM> and a compressor <NUM> operably coupled to the shaft <NUM>. In operation, highly pressurized H<NUM> expands within the turbo expander <NUM>. The expansion of the H<NUM> within the turbo expander <NUM> drives rotation of the shaft <NUM>. The shaft <NUM>, in this configuration, is operably connected to the compressor <NUM> and the optional electric motor <NUM>. As such, the rotation of the turbo expander <NUM> causes the compressor <NUM> to rotate. In some configuration the optional electric motor <NUM> may be used to impart additional power or rotation to the shaft <NUM> to assist in driving rotation of the compressor <NUM>. The compressor <NUM> is configured to receive ram air <NUM> from a ram air source, such as a scoop or other inlet onboard the aircraft. In this configuration, the compressor <NUM> is used to increase the pressure of the ram air <NUM> to generate compressed ram air <NUM>. The compressed ram air <NUM> is passed through the fuel-to-air heat exchanger <NUM> which cools the compressed ram air <NUM> to sufficient temperatures to be delivered to a space onboard an aircraft, such as a cabin of the aircraft and used for cabin air conditioning <NUM>. The compressed ram air may also be used in the fuel cell to achieve improved performance (e.g., efficiency and/or power density) during cruise (e.g., flight) when ambient pressure is too low to achieve desired or necessary fuel cell power density.

The treating of the ram air <NUM> is driven by the pressurized H<NUM> sourced from the pressurized H<NUM> tank <NUM>. An optional pump or other device, not shown, may be used to extract the pressurized H<NUM> from the pressurized H<NUM> tank <NUM> and direct the H<NUM> to the turbo expander <NUM> of the turbo-compressor <NUM>. As the H<NUM> passes through the turbo expander <NUM>, the pressure of the H<NUM> will be reduced. The expanded H<NUM> <NUM> is then passed through the fuel-to-air heat exchanger <NUM> where the compressed ram air <NUM> is cooled by the expanded H<NUM> <NUM> while the expanded H<NUM> <NUM> is increased in temperature.

While expanding in the turbo expander <NUM>, the temperature of the H<NUM> is reduced. However, before the expanded H<NUM> <NUM> is fed into the fuel cell system <NUM>, the temperature of the expanded H<NUM> <NUM> must be increased to proper levels for use within the fuel cell system <NUM>. Therefore, the relatively cold expanded H<NUM> is used within the fuel-to-air heat exchanger <NUM> to cool down the compressed ram air <NUM> before it enters an optional mixing chamber <NUM>. The optional mixing chamber <NUM> may be arranged downstream of the fuel-to-air heat exchanger <NUM> to receive the conditioned air from the fuel-to-air heat exchanger <NUM> and recycled or recirculated air from the space it is supplied to (e.g., an aircraft cabin). As such, a mixture of conditioned and recycled air may be supplied to the space (e.g., cabin) of the aircraft.

In one non-limiting embodiment, the H<NUM> stored within the pressurized H<NUM> tank <NUM> may be at temperatures of approximately -<NUM> (about <NUM>) and stored at pressures of approximately <NUM>,<NUM> kPa. The expanded H<NUM> <NUM> may be cooled to temperatures of about -<NUM> (about <NUM>) but has a pressure of about <NUM> kPa. This relatively cold but relatively low pressure H<NUM> is supplied into the fuel-to-air heat exchanger <NUM>. In this same non-limiting embodiment, the ram air <NUM> may have ambient air temperatures and be at a pressure of about <NUM> kPa. As the ram air <NUM> is compressed within the compressor <NUM>, the temperature of the compressed ram air <NUM> may be about <NUM> (about <NUM>) and the pressure may be increased to about <NUM> kPa and supplied into the fuel-to-air heat exchanger <NUM>. As these two flows are passed into the fuel-to-air heat exchanger <NUM>, the air portion (the compressed ram air <NUM>) will decrease in temperature and the H<NUM> will be increased in temperature. For example, the air may be reduced in temperature down to about <NUM> (about <NUM>) and the H<NUM> may be increased in temperature up to about -<NUM> (about <NUM>). The output results in cool cabin air conditioning <NUM> and Hz at appropriate temperatures for catalyzing within the fuel cell system <NUM> for the purpose of generating power <NUM>. It will be appreciated that the values discussed in this non-limiting embodiment are merely for explanatory and illustrative purposes, and other values may be employed without departing from the scope of the present disclosure. Further, the various pressures and temperatures may be governed, at least in part, on the size and configuration of the pressurized H<NUM> tank <NUM>, the size and configuration of the turbo compressor <NUM>, and the size, configuration, and number of the heat exchangers that are employed. It will be appreciated that the relatively high pressure of the compressed fuel may be at least three times or greater in pressure than the pressure of the low pressure fuel after passing through the fuel-to-air heat exchanger. In some embodiments, the change in pressure from the high pressure compressed fuel to the low pressure fuel may be three times reduction in pressure or density, ten times reduction in pressure or density, one hundred times reduction in pressure or density, or other change in pressure or density as the fuel is warmed and expanded through the fuel-to-air heat exchanger.

The fuel cell system <NUM> requires a source of O<NUM>, as discussed above. In some embodiments, bleed air or ram air may be used to provide the O<NUM> to the fuel cell system <NUM>. Such air is typically compressed, and thus a compressed air <NUM> is provided to the fuel cell system <NUM>. In some embodiments, a source of the O<NUM> of the fuel cell system <NUM> may be the compressed ram air <NUM> that is compressed in the compressor <NUM> of the turbo compressor <NUM> (e.g., air <NUM> and air <NUM> are the same). In such a configuration, the energy stored as compressed H<NUM> is converted to support both the cabin air <NUM> and the fuel cell system airflow <NUM>.

The fuel cell system <NUM> will combine the H<NUM> and the O<NUM> from the compressed air <NUM> to generate power and output a fuel cell exhaust <NUM>, in the form of water, as discussed above. The water of the fuel cell exhaust <NUM> may be dumped overboard, captured for use onboard the aircraft, or otherwise used onboard the aircraft, as appreciated by those of skill in the art.

In some configurations, additional warming of the H<NUM> may be required after passing through the fuel-to-air heat exchanger <NUM> before the H<NUM> is fed into the fuel cell system <NUM>. Accordingly, the warmed H<NUM> may be passed through an optional additional H<NUM> heat exchanger <NUM>. As an example, the relatively still cold H<NUM> may be used within the additional H<NUM> heat exchanger to cool down other components such as power electronics or electric motors of the aircraft. In some such embodiments, the additional H<NUM> heat exchanger <NUM> may have a liquid or gas as the other working fluid, depending upon the type of additional cooling provided. This working fluid will be cooled by the H<NUM> and thus the H<NUM> will be increased in temperatures before being supplied into the fuel cell system <NUM>.

The cooling of the compressed ram air <NUM> within the fuel-to-air heat exchanger <NUM> may be sufficient for use directly to a cabin, or with minimal additional processing. As such, in accordance with some embodiments of the present disclosure, the pressurized hydrogen power system <NUM> described herein may eliminate the need for an environmental control system (ECS) pack onboard the aircraft. If such ECS pack is eliminated from the aircraft system, an additional fan <NUM> may be required to be used when the aircraft is on the ground to bring external air into the system. When the aircraft is on the ground, a fresh air flow from the fan <NUM> does not require to be compressed, and such air may bypass the compressor <NUM> and flow directly into the fuel-to-air heat exchanger <NUM>.

Referring now to <FIG>, an aircraft pressurized hydrogen power system <NUM> is schematically shown. The pressurized hydrogen power system <NUM> includes a pressurized H<NUM> tank <NUM>, a turbo expander <NUM>, a fuel-to-air heat exchanger <NUM>, and a fuel cell system <NUM>. The fuel cell system <NUM> may be configured similar to that shown and described above, such as in <FIG>, for example. For example, fuel cell system <NUM> may be configured to generate electrical power sufficient for flight propulsion or may be configured to generate electrical power for use onboard the aircraft (e.g., to power electrical systems of the aircraft).

In this system, the turbo expander is operably coupled to an electric generator <NUM> by a shaft <NUM>. In this configuration, the highly pressurized H<NUM> sourced from the pressurized H<NUM> tank <NUM> expands within the turbo expander <NUM> to drive rotation of the shaft <NUM>. The electric generator <NUM> is configured to convert rotational energy from the shaft <NUM> into electrical power. The electrical power produced by the electric generator <NUM> can be stored, for example in batteries or distributed and/or used onboard the aircraft. For example, the electrical power output of the electric generator <NUM> may be used to drive a compressor or pump to produce compressed air for the fuel cell system <NUM> and/or to be passed into the fuel-to-air heat exchanger <NUM> for treating and conveyance to a cabin ventilation system or otherwise fed to other components in an ECS or other aircraft system. In some cases, the electric generator <NUM> may be configured to generate and output up to <NUM> kW, although a specific sized generator may be selected to be used on a particular aircraft (e.g., based on energy demands of such aircraft). As the generator will add weight to the system, the sizing and output may be optimized to a particular aircraft configuration (e.g., based on passengers or other requirements).

In this system, the fuel-to-air heat exchanger <NUM> may be configured to receive recirculated cabin air and/or compressed ram air. In either case, the ram air may be compressed using an electrically driving compressor. It will be appreciated that recirculated cabin air may not require any additional compression, and it is the ram air that is compressed. The power for such compressor may be supplied from the electric generator <NUM>. Similar to the embodiment of <FIG>, while expanding in the turbo expander, the temperature of the H<NUM> will be reduced. As such, before the H<NUM> is fed into the fuel cell system <NUM>, it is required that the temperature of the H<NUM> be increased. Similar to the embodiment of <FIG>, the relatively cold hydrogen can be used within one or more heat exchangers to cool down air and/or other working fluids onboard the aircraft. For example, the fuel-to-air heat exchanger <NUM> may receive air flowing in a cabin air recirculation loop. Alternatively, or additionally, compressed air sourced from ambient may be used for cabin supply and/or other onboard purposes, with such air being cooled within the fuel-to-air heat exchanger <NUM>. Further, similar to the embodiment of <FIG>, and additional heat exchanger <NUM> may be arranged downstream of the fuel-to-air heat exchanger <NUM> and upstream of the fuel cell system <NUM>.

The fuel-to-air heat exchanger <NUM> may be sufficient to cool cabin air (regardless of source), thus eliminating the need of an ECS pack, as described above. Because such a configuration can allow for the complete elimination of an ECS pack, an additional fan <NUM> may be used on the ground to bring external (ambient) air into the system.

Turning now to <FIG>, an aircraft pressurized hydrogen engine system <NUM> is schematically shown. The pressurized hydrogen engine system <NUM> includes a pressurized H<NUM> tank <NUM>, a turbo-compressor <NUM>, a fuel-to-air heat exchanger <NUM>, and a hydrogen engine system <NUM>. The hydrogen engine system <NUM> may be a combustion engine configured to combust hydrogen, in contrast to the fuel cell systems described above. The turbo-compressor <NUM>, similar to that described above, includes a turbo expander <NUM> and a compressor <NUM> operably coupled by a shaft <NUM>. An additional heat exchanger <NUM> may be arranged between the fuel-to-air heat exchanger <NUM> and the hydrogen engine system <NUM>. It will be appreciated that the system of <FIG> is schematic and could be arranged, alternatively, similar to the configuration of <FIG> and may include additional components such as additional heat exchangers, generators, motors, and the like.

It will be appreciated that although described herein as a hydrogen-based system, various other types of low carbon or no carbon fuels may be employed and replace the hydrogen described herein. For example, in a non-limiting embodiment, the fuel may be ammonia (NH<NUM>). In such a configuration, the output may be nitrogen (N<NUM>) and water (H<NUM>O).

As such, in accordance with embodiment of the present disclosure, a pressurized fuel may be directed from a pressurized fuel tank to a fuel consumption system. The pressurized fuel may be hydrogen, ammonia, or other pressurized fuel. The fuel consumption system may be a fuel cell, a hydrogen burning engine, or system that consumed the fuel for generation of power (e.g., electrical power, thrust, or the like).

Advantageously, embodiments of the present disclosure provide for use of hydrogen or other low temperature fuels to be used to supplement and/or replace other convention aircraft systems, such as ECS components. Because such systems and configurations may not require the installation of an ECS pack, this results in lower system weight and less energy consumption to condition the cabin air. Further, because there is no ram air usage within a primary and/or main heat exchanger to cool down the cabin air, there may be a reduction in ECS associated fuel burn consumption. Advantageously, the cooling fluid used for conditioning the ram air is the H<NUM>, so that there is no need of ram air to be used to cool the external air from outside as in traditional ECS configurations. This eliminates the fuel burn penalty due to the ram drag. Additionally, by using the hydrogen or other cold fuel to cool the cabin air, the fuel has heat pick up and thus may be warmed to appropriate temperatures for use within a fuel cell and/or fuel burning engine. Additionally, in embodiments that couple a compressor to a fuel turbo expander, no additional power may be required to increase the pressure of the ram air for use in a cabin air system. Furthermore, advantageously, embodiments described herein can include motor and/or generators to generate additional electrical power onboard aircraft, such as beyond a fuel cell power generator.

As used herein, the term "about" is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, "about" may include a range of ± <NUM>%, or <NUM>%, or <NUM>% of a given value or other percentage change as will be appreciated by those of skill in the art for the particular measurement and/or dimensions referred to herein.

It should be appreciated that relative positional terms such as "forward," "aft," "upper," "lower," "above," "below," "radial," "axial," "circumferential," and the like are with reference to normal operational attitude and should not be considered otherwise limiting.

While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions, combinations, sub-combinations, or arrangements not heretofore described, as long as they are within the scope of the present invention as defined by the claims. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments.

Claim 1:
A fuel and air system for an aircraft comprising:
a pressurized fuel tank (<NUM>) containing a pressurized fuel;
a turbo expander (<NUM>) configured to receive the pressurized fuel from the pressurized fuel tank, the turbo expander configured to decrease a pressure of the pressurized fuel to generate low pressure fuel, wherein the low pressure fuel has a pressure that is less than the pressurized fuel;
a fuel-to-air heat exchanger (<NUM>) configured to receive the low pressure fuel from the turbo expander as a first working fluid and air as a second working fluid, the heat exchanger configured to cool the air and warm the low pressure fuel to generate treated fuel;
a space configured to receive the cooled air; and
a fuel consumption system (<NUM>) configured to consume the treated fuel to generate power; wherein
the turbo expander is part of a turbo-compressor (<NUM>) comprising a compressor (<NUM>) operably coupled to the turbo expander by a shaft, and the compressor is configured to receive ram air and compress said ram air and increase pressure thereof, the increased pressure ram air being directed to the fuel-to-air heat exchanger.