Patent Description:
Hydrogen is usable as a fuel source in both a liquid and a gaseous state. Hydrogen provides a cleaner burning fuel than traditional fossil fuels, resulting in fewer greenhouse gas emissions. However, the design of a hydrogen fuel system presents a number of challenges. For example, the hydrogen must be stored safely, and the volume and nature of hydrogen poses challenges to effective storage, especially on transportation vessels such as aircrafts, trains, or ships that have limited space and weight capacity.

It is not currently feasible to store sufficient quantities of gaseous hydrogen-for example, onboard an aircraft-because gaseous hydrogen must be kept highly pressurized (e.g., around <NUM> bar) to be routed to an engine as fuel. Maintaining this high pressure to store gaseous hydrogen requires large and heavy pressure vessels. Liquid hydrogen may be stored more easily at a lower pressure of around <NUM> bar, but this pressure alone is not sufficient to route the liquid hydrogen into an engine to serve as fuel.

Traditional fuel systems may utilize mechanical pumps to generate pressure and pump liquid, but using mechanical pumps has proven to be unreliable with cryogenic fuel sources like liquid hydrogen. The temperature of liquid hydrogen is about <NUM> Kelvin. Mechanical pumps exposed to such low temperatures tend to suffer adverse effects, including breakage.

The present disclosure describes systems and methods for pumping a cryogenic liquid (e.g., liquid hydrogen) without mechanical pumps. In certain examples, the cryogenic liquid is a fuel for an engine. These systems and methods avoid or minimize using fuel sources that generate carbon dioxide emissions. In certain examples, the systems use liquid hydrogen as a fuel source that is pressurized to a gaseous state, but any suitable cryogenic liquid may be used. In various examples, the delivery systems and methods disclosed herein can be used in a variety of engines such as in aircrafts, ships or other water vessels, vehicles, manufacturing or machinery, or any other suitable engine.

In certain examples of the present disclosure, a liquid (e.g., fuel) delivery system systems comprise a source tank housing liquid hydrogen, at least one transition tank, and at least one pumping tank, and a series of valves connecting the tanks. In certain examples, the liquid delivery system also can include at least one dump tank. In certain examples, a cryogenic liquid disposed in the storage tank is held under low pressure (e.g., about <NUM> bar). The cryogenic liquid is subjected to higher pressures (e.g., about <NUM> bar) at the pumping tank. Accordingly, the larger storage tank can be structured to hold low pressure fluids while only the smaller pumping tank is structured to hold high pressure fluids.

In certain implementations, low pressure (e.g., about <NUM> bar) cryogenic liquid from the source tank may be directed to the pumping tank and the transition tank. The transition tank may heat the cryogenic liquid to convert it to a pressurized gaseous state (e.g., about <NUM> bar). The pressurized gas from the transition tank is routed to the pumping tank to exert pressure on the cryogenic liquid therein. The pressurized gas pushes the cryogenic liquid in the pumping tank through an outlet and towards the engine at the higher pressure. In various implementations, the transition tank heats the liquid hydrogen using ambient air flow, combustion, or a heating element.

In certain examples, the delivery systems also include one or more heat exchangers. The heat exchangers may take the gaseous hydrogen from the dump dank and convert it to liquid hydrogen that is routed back to the source tank. The heat exchanger can convert the gaseous hydrogen to liquid hydrogen using the liquid hydrogen expelled from the outlet of the pumping tank and routed past the heat exchanger towards the engine.

The invention relates to a liquid delivery system as defined in claim <NUM>. The liquid delivery system (e.g., a fuel delivery system for an engine) includes a source tank having a first internal pressure, the source tank being configured to hold a liquid (e.g., a cryogenic liquid) at the first internal pressure; a transition tank including a heat supply region, a liquid receiving region, and a gas holding region, the transition tank being configured to use the heat supply region to heat liquid disposed at the liquid receiving region to a gas, which collects in the gas holding region, thereby pressurizing the gas above the first internal pressure; and a pumping tank including a liquid region and a gaseous region, the pumping tank having an outlet. A first low pressure line is configured to selectively supply a first portion of the liquid from the source tank to the liquid region of the pumping tank. A second low pressure line is configured to selectively supply a second portion of the liquid from the source tank to the liquid receiving region of the transition tank. A high pressure line is configured to selectively supply the pressurized gas collected within the gas holding region of the transition tank to the gaseous region of the pumping tank, whereby the pressurized gas expels the first portion of the liquid out of the pumping tank through the outlet.

The invention also relates to a method of delivering fuel to an engine as defined in claim <NUM>.

A variety of additional inventive aspects will be set forth in the description that follows. The inventive aspects can relate to individual features and to combinations of features. It is to be understood that both the forgoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad inventive concepts upon which the embodiments disclosed herein are based.

The accompanying drawings, which are incorporated in and constitute a part of the description, illustrate several aspects of the present disclosure. A brief description of the drawings is as follows:.

Reference will now be made in detail to exemplary aspects of the present disclosure that are illustrated in the accompanying drawings.

<FIG> illustrates an example liquid delivery system <NUM> including a source tank <NUM>, a pumping tank <NUM>, and a transition tank <NUM>. In certain implementations, the liquid delivery system <NUM> also includes a dump tank <NUM>. In certain implementations, the liquid delivery system <NUM> can be utilized to supply fuel to an engine <NUM> (e.g., shown in <FIG>). The source tank <NUM> is configured to store a cryogenic liquid <NUM> (e.g., that can be used to fuel an engine <NUM>). In certain examples, the liquid <NUM> is liquid hydrogen, though other suitable cryogenic liquids may be used such as nitrogen, oxygen, or helium. In certain implementations, the source tank <NUM> is configured to hold liquid hydrogen <NUM> at a pressure (e.g., of <NUM> bar to <NUM> bar, of <NUM>-<NUM> bar, of about <NUM> bar, of about <NUM> bar, of about <NUM> bar) and temperature (e.g., of less than <NUM>, of less than <NUM>, of about <NUM>) in order to keep the hydrogen in a liquid state. When the fuel delivery system <NUM> is used in an aircraft, storing the liquid hydrogen <NUM> at a low pressure inhibits the liquid hydrogen from boiling, e.g., when the atmospheric pressure reduces at high altitudes.

In operation, liquid hydrogen <NUM> is pumped through the fuel delivery system <NUM> to an engine <NUM> using an intake stroke and a discharge stroke. During the intake stroke, a portion of the liquid hydrogen is supplied from the source tank <NUM> to the pumping tank <NUM> by means of a pressure differential between the source tank <NUM> and the pumping tank <NUM>. During the discharge stroke, that portion of the liquid hydrogen is expelled from the source tank <NUM> using a pressurized gas provided to the pumping tank <NUM> from the transition tank <NUM>. In certain implementations, the pressurized gas is produced from transitioning another portion of the liquid hydrogen supplied from the source tank <NUM>.

The source tank <NUM> has a first internal pressure that is initially greater than the internal pressure of the pumping tank <NUM>, the transition tank <NUM>, and the dump tank <NUM>. In certain implementations, the first internal pressure is about <NUM> bar. In other implementations, the first internal pressure of the source tank <NUM> is greater than ambient air pressure. The dump tank <NUM> is at a lower internal pressure than both the pumping tank <NUM> and the transition tank <NUM>. In certain examples, the dump tank <NUM> has an internal pressure of less than <NUM> bar. In certain examples, the dump tank <NUM> has an internal pressure of less than <NUM> bar. In certain examples, the dump tank <NUM> has an internal pressure of less than <NUM> bar. In an example, the dump tank <NUM> has an internal pressure of <NUM> bar. In certain implementations, the dump tank <NUM> can be vented to atmosphere to reduce the pressure within the dump tank <NUM>.

The source tank <NUM> is connected to the pumping tank <NUM> with a first low pressure line <NUM>. A first valve arrangement <NUM> controls flow through the first low pressure line <NUM>. Valve arrangement <NUM> can be any type of valve or other suitable arrangement for controlling the flow of liquid. The pumping tank <NUM> is configured to hold both liquid and gaseous hydrogen. Inside the pumping tank <NUM> is a liquid region <NUM>, where the liquid hydrogen <NUM> is deposited when it flows from the source tank <NUM> through valve arrangement <NUM> to the pumping tank <NUM>. The pumping tank <NUM> also includes gaseous region <NUM> continuous with the liquid region 120f. The pumping tank <NUM> includes an outlet <NUM> through which the output liquid hydrogen <NUM> from the pumping tank <NUM> flows (e.g., towards the engine <NUM>). The pumping tank <NUM> is configured to withstand higher pressure than the source tank <NUM>. In an example, the pumping tank <NUM> is configured to withstand high pressures (e.g., <NUM> bar - <NUM> bar, <NUM> bar - <NUM> bar, <NUM> bar - <NUM> bar, <NUM> bar, <NUM> bar, <NUM> bar, etc.).

In certain examples, the transition tank <NUM> defines two chambers that are physically separated but thermally linked-a main chamber <NUM> and a heat supply chamber <NUM>. The main chamber <NUM> defines a liquid receiving region <NUM> and a gas holding region <NUM> that are continuous with each other. When liquid hydrogen <NUM> is heated, the resulting gaseous hydrogen sits at or above the liquid hydrogen <NUM> in the gas holding region <NUM>, forming a liquid/gas interface. The heat supply region <NUM> transmits sufficient heat to the main chamber <NUM> to transition some or all of the liquid hydrogen <NUM> within the main chamber <NUM> to a gas.

In certain implementations, the transition tank <NUM> is connected to the source tank <NUM> by a second low pressure line <NUM>. In certain examples, liquid hydrogen <NUM> can be directed from the source tank <NUM> to the main chamber <NUM> of the transition tank <NUM>, where the liquid hydrogen <NUM> flows to the liquid receiving region <NUM>. In some implementations, the transition tank <NUM> only receives liquid hydrogen <NUM> from the source tank <NUM> during initial system priming. In other implementations, the transition tank <NUM> can be replenished from the source tank <NUM>. A valve arrangement <NUM> controls flow through the second low pressure line <NUM>. In other implementations, the transition tank <NUM> receive liquid hydrogen indirectly from the source tank <NUM> via the pumping tank <NUM>, which will be described in more detail herein. In certain examples, the transition tank <NUM> receives liquid hydrogen directly from the source tank <NUM> at the beginning of an operation (e.g., a flight) and receives replenishment of the liquid hydrogen via the pumping tank throughout the operation.

In some implementations, ambient air can be used as a heat source to drive the system. For example, ambient air can be directed to the heat supply region <NUM> from an interior of the aircraft or other structure holding the liquid delivery system <NUM>. In another example, ambient air can be directed to the heat supply region <NUM> from an exterior of the aircraft or other structure holding the liquid delivery system <NUM>. In other implementations, one or more heating elements <NUM> may be disposed within the heat supply region <NUM>. In some examples, the one or more heating elements <NUM> include burners. In certain examples, the one or more burners may combust gaseous hydrogen as will be described in more detail herein. In other examples, the one or more heating elements <NUM> include an electric heating element.

In operation, liquid hydrogen <NUM> is pumped through the liquid delivery system <NUM> to an output using an intake stroke and a discharge stroke. During the intake stroke, the outlet <NUM> of the pumping tank <NUM> leading to the engine <NUM> is closed. For example, a check valve <NUM> may close the outlet <NUM> when not supplied with a sufficient amount of pressure (e.g., about <NUM> bar). The third valve arrangement <NUM> connecting the pumping tank <NUM> to the dump tank <NUM> is open to enable gaseous hydrogen contained within the pumping tank <NUM> to move to the dump tank <NUM>, thereby ensuring the pressure within the pumping tank <NUM> is lower than the pressure within the source tank <NUM> during the intake stroke. Also, a second valve arrangement <NUM> closes a high pressure line <NUM> from the transition tank <NUM> to the pumping tank <NUM>.

The valve arrangement <NUM> opens the first low pressure line <NUM> from the source tank <NUM> to the pumping tank <NUM>. Because the first internal pressure <NUM> of the source tank <NUM> is higher than the internal pressure in the pumping tank <NUM>, a first portion <NUM> of the liquid hydrogen <NUM> flows from the source tank <NUM> through the first low pressure line <NUM> to the pumping tank <NUM> when the first valve arrangement <NUM> is opened. After the first portion <NUM> of liquid hydrogen <NUM> reaches the liquid region <NUM> of the pumping tank <NUM>, valve arrangement <NUM> closes the first low pressure line <NUM>. In certain examples, the first valve arrangement <NUM> may open and close the first low pressure line <NUM> based on a sensor reading from a sensor arrangement at the pumping tank <NUM>.

In certain examples, during the intake stroke, a second portion <NUM> of liquid hydrogen <NUM> flows from source tank <NUM> to transition tank <NUM> through a second low pressure line <NUM> when a fifth valve arrangement <NUM> is open. For example, a pressure differential between the source tank <NUM> and the transition tank <NUM> may direct the flow to the transition tank <NUM>. The second portion <NUM> of the liquid hydrogen <NUM> flows into the liquid receiving region <NUM> of the main chamber <NUM>. In certain implementations, a fourth valve arrangement <NUM> opens a second dump line <NUM> between the transition tank <NUM> and the dump tank <NUM>, thereby enable flow from the transition tank <NUM> to the dump tank <NUM>. In certain examples, the second dump line <NUM> leads from the gas holding region <NUM> of the main chamber <NUM> to the dump tank <NUM> so that hydrogen gas can be moved from the main chamber <NUM> to the dump tank <NUM> as the liquid hydrogen enters the liquid receiving region <NUM>. After the second portion <NUM> of the liquid hydrogen <NUM> flows into the transition tank <NUM>, the fifth valve arrangement <NUM> closes the second low pressure line <NUM>.

In certain examples, liquid hydrogen <NUM> flows from the source tank <NUM> to the transition tank <NUM> in a single instance during the use of the engine <NUM> (e.g., at engine start up). In such a case, the second portion <NUM> has the capacity to produce sufficient hydrogen gas for use in each discharge stroke for the duration of a flight or other operation of the engine <NUM>. In other examples, a second portion <NUM> of the liquid hydrogen <NUM> flows from the source tank <NUM> to the transition tank <NUM> in multiple instances during the use of engine <NUM>. For example, the liquid hydrogen of the transition tank <NUM> may be replenished from the source tank <NUM> on each intake stroke. In other examples, the liquid hydrogen of the transition tank <NUM> may be replenished from the source tank <NUM> on periodic intake strokes or when a sensor arrangement indicates that liquid levels are low within the main chamber <NUM>.

The heat supply region <NUM> of the transition tank <NUM> heats the liquid hydrogen <NUM> in the liquid receiving region <NUM>, thereby transitioning a portion of the liquid hydrogen <NUM> to gaseous hydrogen. The gaseous hydrogen, which fills the gas holding region <NUM> of the transition tank <NUM>, has a higher pressure than the liquid hydrogen. Accordingly, transitioning the liquid hydrogen to a gas increases the internal pressure within the transition tank <NUM>. In certain implementations, a sensor arrangement (e.g., a temperature sensor, a pressure sensor, a combination of the two, a gas sensor, etc.) may be disposed at the gas holding region <NUM> or elsewhere within the transition tank <NUM> to detect the internal pressure. When enough gas has been produced to generate pressure at a predetermined threshold (e.g., <NUM> bar), the heat supply region <NUM> reduces the amount of heat or ceases heating the main chamber <NUM>. For example, a heating element can be turned down or off. In another example, a passage connected to ambient air may be closed.

The discharge stroke is performed to expel the first portion <NUM> of liquid hydrogen <NUM> from the pumping tank <NUM> towards the engine <NUM>. During the discharge stroke, the second valve arrangement <NUM> opens the high pressure line <NUM> between the gas holding region <NUM> of the transition tank <NUM> and a gaseous region <NUM> of the pumping tank <NUM>. The gaseous hydrogen flows through a high pressure line <NUM> to the gaseous region <NUM> of the pumping tank <NUM> because the gaseous hydrogen exists at a higher pressure than the pumping tank <NUM>. The gaseous hydrogen applies pressure to the surface of the first portion <NUM> of liquid hydrogen <NUM> held within the liquid region <NUM> of the pumping tank <NUM>. When the exerted pressure (e.g., <NUM> bar) exceeds the pressure downstream of the check valve <NUM>, the first portion <NUM> of the liquid hydrogen <NUM> is expelled through check valve <NUM>.

In certain examples, once the volume of liquid hydrogen <NUM> in the pumping tank <NUM> is depleted, the discharge stroke ends and the intake stroke begins again. The discharge stroke is completed by closing the high pressure line <NUM> using the second valve arrangement <NUM>. In certain implementations, during the intake stroke, the pumping tank <NUM> is depressurized by opening the first dump line <NUM> to the dump tank <NUM> using the third valve arrangement <NUM>. Opening the first dump line <NUM> enables a sufficient amount of the remaining gaseous hydrogen in the pumping tank <NUM> to flow into the dump tank <NUM> to lower the internal pressure of the pumping tank below the internal pressure of the source tank <NUM>.

In some implementations, when the liquid receiving region <NUM> of the transition tank <NUM> needs to be replenished, the main chamber <NUM> can be depressurized by opening the second dump line <NUM> using the fourth valve arrangement <NUM>. With the second dump line <NUM> open, a sufficient amount of gaseous hydrogen in the gas holding region <NUM> of the transition tank <NUM> can flow into the dump tank <NUM> to lower the internal pressure within the transition tank <NUM> to less than the source tank <NUM>. In other implementations, however, the liquid hydrogen in the transition tank <NUM> need not be replenished. In such cases, the fourth valve arrangement <NUM> maintains the second dump line <NUM> closed so that any pressure within the main chamber <NUM> of the transition tank <NUM> is preserved. Maintaining the pressure within the main chamber <NUM> increases the speed at which the hydrogen transitions from a liquid to a gas. In certain examples, if replenishment is not needed during operation or is needed rarely, then the heat supply region <NUM> can be continuously heating the second portion <NUM> of the hydrogen to a sufficient level to maintain the desired pressure within the main chamber <NUM>, e.g., throughout both the intake stroke and the discharge stroke.

The intake stroke and the discharge stroke of liquid delivery system <NUM> repeat cyclically to deliver pressurized liquid hydrogen <NUM> into the engine <NUM>. This cycle eliminates the need for mechanical and rotating pumps, which are prone to breakage when using cryogenic liquids at low temperatures.

In certain implementations, check valves may be disposed at the outlet of each tank <NUM>, <NUM>, <NUM>, <NUM> to inhibit backflow. For example, a check valve may be disposed at each low pressure lines <NUM>, <NUM> to inhibit backflow into the source tank <NUM> during the intake stroke. Similarly, in certain examples, a check valve may inhibit backflow into the transition tank main chamber <NUM> from the dump tank <NUM>. In certain examples, a check valve may inhibit backflow into the pumping tank <NUM> from the dump tank <NUM>.

Referring now to <FIG>, the liquid delivery system <NUM> can include a controller <NUM> that manages operation of the valve arrangements <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In some examples, the controller <NUM> is an electronic controller that communicates with an operating system C (e.g., one or more processors and memory storing operation instructions). In an example, the operating system C includes the flight management system of an aircraft. In other examples, the controller <NUM> can operate the valve arrangements <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> hydraulically, pneumatically, electro-mechanically, etc..

In certain implementations, the controller <NUM> (or a different controller) can operate the heating element <NUM> within the transition tank <NUM>. For example, the controller <NUM> may turn the heating element <NUM> on and off. Alternatively, the controller <NUM> may control the amount of heat produced by the heating element (e.g., control the amount of flow through the heat supply region <NUM>, control the amount of fuel being combusted within the heat supply region <NUM>, etc..

In certain implementations, the controller <NUM> (or a different controller) can operate one or more sensor arrangements S1, S2, S3 disposed throughout the liquid delivery system <NUM>. In certain examples, the controller <NUM> may operate the valve arrangements <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> and/or the heating element <NUM> based on readings obtained from the sensor arrangements S1, S2, S3. In certain implementations, a first sensor arrangement S1 may be disposed at the pumping tank <NUM> to monitor a liquid fill level of the pumping tank <NUM>. For example, a level sensor may be disposed in the pumping tank <NUM>. In other examples, the liquid fill level may be monitored indirectly by sensing an internal pressure within the pumping tank <NUM>. In an example, the controller <NUM> may open the first valve arrangement <NUM> during an intake stroke based on the first sensor S1 determining the liquid fill level within the pumping tank is lower than an amount desired to be expelled during the next discharge stroke. In such an example, the controller <NUM> also may open the third valve arrangement <NUM> to relieve the internal pressure within the pumping tank <NUM> to facilitate refilling.

In certain implementations, a second sensor arrangement S2 may be disposed within the main chamber <NUM> of the transition tank <NUM>. The second sensor arrangement S2 may monitor a liquid fill level within the liquid receiving region <NUM> of the main chamber <NUM>. In certain examples, the controller <NUM> may open the fifth valve arrangement <NUM> during an intake stroke if the second sensor arrangement S2 reports the liquid fill level within the liquid receiving region <NUM> to be insufficient to create the desired amount of pressurized gas when heated. In such an example, the controller <NUM> also may open the fourth valve arrangement <NUM> to relieve the internal pressure within the transition tank <NUM> to facilitate refilling.

In certain implementations, a third sensor arrangement S3 may be disposed within the dump tank <NUM> to monitor an internal pressure of the dump tank <NUM>. When the third sensor arrangement S3 determines the pressure within the dump tank <NUM> exceeds a predetermined threshold (e.g., <NUM> bar, <NUM> bar, <NUM> bar, etc.), the controller <NUM> may vent the dump tank <NUM> to atmosphere or otherwise act to release some of the pressure within the dump tank <NUM>.

In some implementations, the predetermined thresholds for the sensor arrangements S1, S2, S3 are stored within the controller <NUM>. In other implementations, the predetermined thresholds for the sensor arrangements S1, S2, S3 are stored within the operating system C.

With reference to <FIG>, multiple pumping tanks <NUM> and multiple transition tanks <NUM> are utilized within the liquid delivery system <NUM>. In the example shown, the delivery system <NUM> includes a first pumping tank 118a and a second pumping tank 118b. The first pumping tank 118a is connected to a first transition tank 110a using a first high pressure line 134a. The second pumping tank 118b is connected to a second transition tank 110b using a second high pressure line 134b. In certain examples, the second pumping tank 118b is the same as the first pumping tank 118a. In certain examples, the second transition tank 110b is the same as the first transition tank 110a. In certain examples, the pumping tanks 118a, 118b are the same as the pumping tank <NUM> shown in <FIG> and <FIG>. Accordingly, reference to pumping tank <NUM> and features described above with reference to pumping tank <NUM> apply to both the first pumping tank 118a and the second pumping tank 118b. In certain examples, the transition tanks 110a, 110b are the same as the transition tank <NUM> shown in <FIG> and <FIG>. Accordingly, reference to transition tank <NUM> and features described above with reference to transition tank <NUM> apply to both the first transition tank 110a and the second transition tank 110b.

The first transition tank 110a supplies gaseous hydrogen through the first high pressure line 134a to expel fluid from the first pumping tank 118a. The second transition tank 110b supplies gaseous hydrogen through the second high pressure line 134b to expel fluid from the second pumping tank 118b. In certain implementations, the output lines 124a, <NUM> of each pumping tank 118a, 118b are routed to a common output line <NUM>. In certain implementations, the first and second pumping tanks 118a, 118b are operated in alternate so the first pumping tank 118a is performing a discharge stroke while the second pumping tank 118b is performing an intake stroke and vice versa so that a continuous or near continuous flow is supplied to the common output line <NUM>. In certain examples, the output of a greater number (e.g., three, four, etc.) pumping tanks <NUM> and corresponding transition tanks <NUM> can be connected together and the stroke cycle of the pumping tanks <NUM> staggered to enhance consistency of the flow.

In the depicted implementations, the first and second pumping tanks 118a, 118b are refilled using the same source tank <NUM>. In other implementations, the first and second pumping tanks 118a, 118b may be supplied from different source tanks. In the depicted example, the first and second transition tanks 110a, 110b are supplied from the same source tank <NUM>. In other implementations, the first and second transition tanks 110a, 110b may be supplied from different source tanks. In certain examples, the first and second pumping tanks 118a, 118b and the first and second transition tanks 110a, 110b are supplied by a common source tank <NUM>.

In the depicted implementations, the first and second pumping tanks 118a, 118b are vented to the same dump tank <NUM>. In other implementations, the first and second pumping tanks 118a, 118b may be vented to different dump tanks. In the depicted example, the first and second transition tanks 110a, 110b are vented to the same dump tank <NUM>. In other implementations, the first and second transition tanks 110a, 110b may be vented to different dump tanks. In certain examples, the first and second pumping tanks 118a, 118b and the first and second transition tanks 110a, 110b are vented to a common dump tank <NUM>.

The fuel delivery system <NUM> of <FIG> uses a continuous cycle of intake strokes and discharges strokes, as described above with reference to <FIG>. In operation, the first pumping tank 118a and first transition tank 110a perform the intake stroke and then the discharge stroke. While the first pumping tank 118a and the first transition tank 110a perform the discharge stroke, the second pumping tank 118b and the second transition tank 110b perform the intake stroke. Conversely, while the first pumping tank 118a and the first transition tank 110a perform the intake stroke, the second pumping tank 118b and the second transition tank 110b perform the discharge stroke. In this example of the fuel delivery system <NUM>, one set of the pumping tank <NUM> and the transition tank <NUM> delivers liquid hydrogen <NUM> to the engine <NUM> in the discharge stroke while the other set of the pumping tank <NUM> and the transition tank <NUM> refills on the intake stroke. This arrangement provides a continuous or near-continuous flow of liquid hydrogen <NUM> to the engine <NUM>. In other examples, the first pumping tank 118a and the second pumping tank 118b use a single transition tank <NUM> to perform the intake stroke and the discharge stroke.

Now referring to <FIG>, example additional features are shown with the liquid delivery system <NUM> of <FIG>. A liquid delivery system <NUM> configured in accordance with the principles of the present disclosure may include any combination of none, one, two, or all of these additional features.

In accordance with certain aspects of the disclosure, the liquid hydrogen within the source tank <NUM> can be replenished using the excess gaseous hydrogen collected in the dump tank <NUM>. In certain implementations, a heat exchanger <NUM> is disposed along a return line <NUM> extending between the dump tank <NUM> and the source tank <NUM>. A portion of the gaseous hydrogen from the dump tank <NUM> may be routed through the heat exchanger <NUM> to remove sufficient heat to transition the gaseous hydrogen back to a liquid state. In some examples, the liquid hydrogen output from the pumping tank <NUM> during a discharge stroke is routed past the heat exchanger <NUM> to absorb the heat from the gaseous hydrogen. In other examples, the heat exchanger <NUM> may have a separate cooling system. In certain implementations, the gaseous hydrogen is directed from the dump tank <NUM> to the heat exchanger when the internal pressure of the dump tank <NUM> exceeds a predetermined threshold (e.g., <NUM> bar, <NUM> bar, <NUM> bar, etc.). For example, it may be desirable to use the heat exchanger <NUM> to convert gaseous hydrogen from the dump tank <NUM> to liquid hydrogen <NUM> as opposed to venting excess gaseous hydrogen to the atmosphere to avoid wasting hydrogen. In certain implementations, the gaseous hydrogen is directed from the dump tank <NUM> to the heat exchanger when the liquid fill level of the source tank <NUM> drops below a predetermined threshold (e.g., based on the amount of liquid hydrogen needed to operate the engine <NUM> throughout the flight or other operation of the engine <NUM>).

In accordance with certain aspects of the disclosure, the liquid hydrogen <NUM> within the liquid receiving region <NUM> of the transition tank <NUM> can be replenished from the pumping tank <NUM>. In some implementations, a fill line <NUM> extends between the liquid region <NUM> of the pumping tank <NUM> and the liquid receiving region <NUM> of the transition tank <NUM>. Fill line <NUM> allows some of the liquid hydrogen <NUM> from the pumping tank <NUM> to be supplied to the transition tank <NUM>. For example, a seventh valve arrangement <NUM> is configured to open and close the fill line <NUM>. Providing liquid hydrogen <NUM> from the pumping tank <NUM> to the transition tank <NUM> can be used to "top up" the transition tank <NUM> with liquid hydrogen <NUM>, instead of supplying liquid hydrogen <NUM> from the source tank <NUM>. In some implementations, the fill line <NUM> extends from the pumping tank <NUM> separate from the output line <NUM>. In other implementations, the output line <NUM> splits between the transition tank <NUM> and a path towards the engine <NUM>. Yet another example implementation for replenishing the cryogenic liquid within the transition tank <NUM> from the pumping tank <NUM> is shown in <FIG>.

In other implementations, the fill line <NUM> may extend to the liquid receiving region <NUM> of the transition tank <NUM> from the dump tank <NUM> (e.g., via the heat exchanger <NUM>). For example, the heat exchanger <NUM> may condense some of the gaseous hydrogen from the dump tank <NUM> and direct the resulting liquid hydrogen to the transition tank <NUM> instead of to the source tank <NUM> (e.g., see <FIG>).

In certain implementations, a top up chamber can be disposed within or above the transition tank <NUM>.

In accordance with certain aspects of the disclosure, a supply line <NUM> extends from the dump tank <NUM> to the heat supply region <NUM> of the transition tank <NUM>. Supply line <NUM> provides gaseous hydrogen from the dump tank <NUM> to the heat supply region <NUM> when the supply line <NUM> is opened by a sixth valve arrangement <NUM>. In some examples, the gaseous hydrogen can be used by a heating element <NUM> in the heat supply region <NUM> to generate heat to transition the liquid hydrogen <NUM> in the liquid receiving region <NUM> to a gas. For example, the heating element <NUM> may burn the supplied gaseous hydrogen to produce the heat.

<FIG> is a schematic view of liquid delivery system <NUM> configured to supply fuel to one or more engines <NUM> on an aircraft <NUM>. In certain implementations, the aircraft <NUM> includes wings <NUM> extending outwardly from a fuselage <NUM>. The source tank <NUM> may be disposed within the fuselage <NUM>. One or more engines <NUM> may be mounted to the wings <NUM>. In the example shown, a first engine 102a is mounted to a first wing 184a and a second engine 102b is mounted to a second wing 184b. In other example, multiple engines <NUM> can be mounted to each wing <NUM>.

In certain implementations, the fuel delivery system <NUM> has two pumping tanks 118a, 188b and two transition tanks 110a, 110b as described above with reference to <FIG>. In certain implementations, each of the pumping tanks 118a, 118b is connected to a respective one of the transition tanks 110a, 100b, the dump tank <NUM>, the source tank <NUM>, and a respective one of the engines <NUM>. In the depicted example of <FIG>, the engine 102a is connected to the first pumping tank 118a and the engine 102b is connected to the second pumping tank 118b. In certain implementations, the fuel delivery system <NUM> has two pumping tanks 118a, 188b and two transition tanks 110a, 110b for each engine <NUM>. The fuel delivery system <NUM> may perform the intake stroke and the discharge stroke using both sets of pumping tanks 118a, 118b and combustion tanks 110a, 110b as described above. In certain examples, the engines <NUM> are turbine engines configured to propel the aircraft <NUM>.

Referring to <FIG>, a separate top-up chamber <NUM> can be disposed within the transition tank <NUM> or above the transition tank <NUM>. For example, the top-up chamber <NUM> can be located within the gas holding region <NUM> of the transition tank <NUM>. In certain examples, the top-up chamber <NUM> is smaller than the liquid receiving region <NUM> of the transition tank <NUM>. In an example, the top-up tank <NUM> may hold about <NUM> liter of the cryogenic liquid. The top-up chamber <NUM> is designed to be independently fluidly connected (e.g., via valve arrangements <NUM>, <NUM>, <NUM>) to the dump tank <NUM>, the gas holding region <NUM> of the transition tank <NUM>, and the liquid region <NUM> of the pumping tank <NUM>, but with only one connection being open at any one time. The top-up chamber <NUM> is used as a way of passing a small quantity of liquid hydrogen from the pumping tank <NUM> to the transition tank <NUM>.

Claim 1:
A liquid delivery system (<NUM>) comprising:
a source tank (<NUM>) having a first internal pressure, the source tank (<NUM>) being configured to hold a cryogenic liquid (<NUM>) at the first internal pressure;
a transition tank (<NUM>) including a heat supply region (<NUM>), a liquid receiving region (<NUM>), and a gas holding region (<NUM>), the transition tank (<NUM>) being configured to use the heat supply region (<NUM>) to heat the cryogenic liquid (<NUM>) disposed at the liquid receiving region (<NUM>) to a gas, which collects in the gas holding region (<NUM>), thereby pressurizing the gas above the first internal pressure;
a pumping tank (<NUM>) including a liquid region (<NUM>) and a gaseous region (<NUM>), the pumping tank (<NUM>) having an outlet (<NUM>);
a first low pressure line (<NUM>) configured to selectively supply a first portion (<NUM>) of the cryogenic liquid (<NUM>) from the source tank (<NUM>) to the liquid region (<NUM>) of the pumping tank (<NUM>);
a second low pressure line (<NUM>) configured to selectively supply a second portion (<NUM>) of the cryogenic liquid (<NUM>) from the source tank (<NUM>) to the liquid receiving region (<NUM>) of the transition tank (<NUM>); and
a high pressure line (<NUM>) configured to selectively supply the pressurized gas collected within the gas holding region (<NUM>) of the transition tank (<NUM>) to the gaseous region (<NUM>) of the pumping tank (<NUM>), whereby the pressurized gas expels the first portion (<NUM>) of the cryogenic liquid (<NUM>) out of the pumping tank (<NUM>) through the outlet (<NUM>).