Patent Description:
In order to limit emissions of carbon dioxide, use of hydrogen as an alternative to hydrocarbon fuel in gas turbine engines has historically only been practical in land-based installations. Such engines are typically supplied with hydrogen derived from natural gas via concurrent steam methane reformation, which hydrogen is injected into large-volume series staged dry low NOx burners. This type of burner is not suitable for use in an aero engine primarily due to its size and the difficulties in maintaining stable operation during transient manoeuvres.

Experimental programmes have been conducted to develop aero engines operable to be fuelled with hydrogen, however these have typically been high-Mach afterburning turbojets or expander cycles and thus not practical for use on civil airliners operating in the Mach <NUM> to <NUM> regime.

There is therefore a need for technologies to facilitate combustion of hydrogen in aero gas turbine installations, in particular around the fuel system.

US patent <CIT> discloses a reciprocal type of pump structure wherein a piston has a linear function actuated by a pair of coils energized alternately and includes a plurality of tapered flutes. A check valve in an outlet of the structure which stretches to open said outlet under the impact of expelled fluids and of its own volition retracts to the closed position immediately upon the cessation of fluids being expelled.

In a first aspect there is provided a fluid pump as set out in claims <NUM> to <NUM>. In a second aspect there is provided a fuel delivery system as set out in claims <NUM> and <NUM>.

In a third aspect there is provided a method of pumping a cryogenic fluid as set out in claims <NUM> to <NUM>.

A hydrogen-fuelled airliner is illustrated in <FIG>. In this example, the airliner <NUM> is of substantially conventional tube-and-wing twinjet configuration with a central fuselage <NUM> and substantially identical underwing-mounted turbofan engines <NUM>. The turbofan engines <NUM> may for example be geared turbofan engines.

A hydrogen storage tank <NUM> located in the fuselage <NUM> for a hydrogen fuel supply is connected with core gas turbines <NUM> in the turbofan engines <NUM> via a fuel delivery system. In the illustrated example, the hydrogen storage tank <NUM> is a cryogenic hydrogen storage tank that stores the hydrogen fuel in a liquid state, in a specific example at <NUM>. The hydrogen fuel may be pressurised to between around from <NUM> to <NUM> bar, for example around <NUM> bar.

A block diagram identifying the flow of hydrogen fuel is shown in <FIG>. Hydrogen fuel is obtained from a hydrogen storage tank <NUM> by a fuel delivery system <NUM> and is supplied to a core of a gas turbine <NUM>. Only one of the gas turbines is shown for clarity. In this illustrated embodiment, the gas turbine <NUM> is a simple cycle gas turbine engine. In other embodiments, complex cycles may be implemented via fuel-cooling of the gas path.

Referring again to <FIG>, the gas turbine <NUM> comprises, in axial flow series, a low-pressure compressor <NUM>, an interstage duct <NUM>, a high-pressure compressor <NUM>, a diffuser <NUM>, a fuel injection system <NUM>, a combustor <NUM>, a high-pressure turbine <NUM>, a low-pressure turbine <NUM>, and a core nozzle <NUM>. The fuel injection system <NUM> may be a lean direct fuel injection system. The high-pressure compressor <NUM> is driven by the high-pressure turbine <NUM> via a first shaft <NUM> and the low-pressure compressor <NUM> is driven by the low-pressure turbine <NUM> via a second shaft <NUM>. In alternative examples, the gas turbine <NUM> may comprise more than two shafts.

In a geared turbofan engine the low-pressure turbine <NUM> also drives a fan <NUM> via a reduction gearbox <NUM>. The reduction gearbox <NUM> receives an input drive from the second shaft <NUM> and provides an output drive to the fan <NUM> via a fan shaft <NUM>. The reduction gearbox <NUM> may be an epicyclic gearbox, which may be of planetary, star or compound configuration. In further alternatives, the reduction gearbox <NUM> may be a layshaft-type reduction gearbox or another type of reduction gearbox. It will also be appreciated that the principles disclosed herein may be applied to a direct-drive type turbofan engine, i.e. in which there is no reduction gearbox between the low-pressure turbine <NUM> and the fan <NUM>.

In operation, the fuel delivery system <NUM> is configured to obtain hydrogen fuel from the hydrogen storage tank <NUM> and provide the fuel to the fuel injection system <NUM>. <FIG> is a block diagram illustrating the fuel delivery system <NUM> in greater detail. The fuel delivery system <NUM> comprises a pump <NUM>, a vaporiser <NUM>, a metering device <NUM> and a heater <NUM> for heating the hydrogen fuel to an injection temperature for the fuel injection system <NUM>. A vent system (not shown) may be included in the fuel delivery system <NUM> close to the fuel injection system <NUM> to vent hydrogen fuel should a rapid shut-off be required, for example in response to a shaft-break event. It is envisaged that the vent system may vent the excess hydrogen fuel into the bypass duct of the turbofan engine <NUM>, or alternatively vent it outside of the nacelle of the engine <NUM>. An igniter may be provided to flare off the excess hydrogen in a controlled manner.

In alternative arrangements, the fuel delivery system may deliver fuel to an aircraft powerplant other than a gas turbine engine, for example a fuel cell. In a general aspect therefore, the fuel delivery system may deliver fuel to an aircraft powerplant, which may comprise a fuel cell and/or a gas turbine engine. The gas turbine engine may for example drive a turbofan engine or a turboprop engine or may be used as a generator for generating electricity for propulsion or otherwise.

<FIG> illustrate schematically an embodiment of the pump <NUM> for the fuel delivery system <NUM>, which is not in accordance with the present invention. The pump <NUM> comprises a chamber <NUM> defining a cylinder <NUM> in which a piston <NUM> is slidably disposed. The chamber <NUM> comprises an inlet <NUM> at one end of the chamber <NUM> and an outlet <NUM> at an opposing end of the chamber <NUM>. The outlet <NUM> comprises a non-return valve <NUM>. In the illustrated example, the piston <NUM> comprises a plurality of Tesla valves <NUM>. Each Tesla valve <NUM> is in fluid communication with the inlet <NUM>. The pump <NUM> is configured to pump fluid, for example a cryogenic fluid such as hydrogen or helium or a supercritical fluid, from the inlet <NUM> to the outlet <NUM> by reciprocation of the piston <NUM> within the cylinder <NUM>. In this example, the piston <NUM> comprises a plurality of Tesla valves <NUM>, although in general terms one or more Tesla valves may be used. In the orientation shown the inlet <NUM> is at the top of the pump <NUM> and the outlet <NUM> is at the bottom, although the pump <NUM> may operate in other orientations. In the configuration shown in <FIG> the piston <NUM> is located at the top of the cylinder <NUM>, the lower part of the cavity <NUM> contains fluid and the non-return valve <NUM> is closed, while in the configuration shown in <FIG> the piston <NUM> is located at the bottom of the cylinder <NUM>, the fluid is ejected through the outlet <NUM> and fluid enters the cylinder <NUM> through the inlet <NUM>.

The outlet <NUM> comprises a biasing mechanism <NUM> to maintain the valve <NUM> closed below a preset pressure. The biasing mechanism <NUM> may be adjustable to allow the present pressure to be set. This may for example be achieved by selecting a spring with a spring constant defining a desired force to maintain the valve <NUM> closed. In other arrangements the biasing mechanism may be pneumatically, hydraulically or electrically controllable. An adjustable biasing mechanism may for example comprise a solenoid, which in some examples may be superconducting when pumping cryogenic fluids.

In operation, the piston <NUM> is driven downwards towards the bottom of the cylinder as depicted in <FIG>. As the piston <NUM> is driven downwards, the fluid in the lower part of the cavity <NUM> increases in pressure. When the fluid reaches the desired pressure level corresponding the adjustable biasing mechanism setting, the non-return valve <NUM> begins to allow fluid to flow through the outlet <NUM> as the piston <NUM> continues to move downwards, and the high pressure fluid exits the pump <NUM> through the outlet <NUM>. The Tesla valves <NUM> (described in further detail below in relation to <FIG>) limit fluid from flowing back through the piston <NUM> as the piston <NUM> is driven downwards by flow through the Tesla valves having a preferred flow direction indicated by the arrows T. The flow rate of fluid through the pump <NUM> is determined by the driving speed of the piston <NUM>, i.e. the faster the piston reciprocates in the cylinder the greater the overall flow rate will be. A sufficient amount of fluid is required to enter the Tesla valves <NUM> in the upwards direction to create adequate downwards pressure by redirecting the fluid to mitigate backflow. Only a small portion of the fluid may therefore return to the top of the cavity <NUM> as the piston <NUM> is driven downwards. Once the piston <NUM> reaches the bottom of the cylinder it is driven in the reverse direction and begins to move to the top of the cylinder as in <FIG>. The Tesla valves <NUM> then allow fluid to move more freely into the lower part of the cavity in the preferred flow direction T.

The piston <NUM> may be driven in various ways. Options may for example include linear actuators (electrical linear motors) or mechanical driving arrangements driving the piston either electrically via rotating parts or via linear actuators located outside or inside the pump housing. A nutating disk engine may for example be driven electrically or mechanically, or may be driven by expanding hot or cold gases or by combustion of hydrogen. Direct mechanical coupling with a prime mover may be used, with optional mechanical gearing to control the rotating speeds.

The piston may be formed of materials such as steel, e.g. stainless steel, a nickel-base alloy, e.g. an Inconel (RTM), or composite materials. The Tesla valves <NUM> may be formed of similar materials to the surrounding piston. The piston <NUM> may comprise an outer surface coating or layer of a low friction material such as polytetrafluoroethene (PTFE) or another dry lubricant layer such as graphite. The inner side of the chamber <NUM> may also be coated with a similar low coefficient material. In an example where the piston <NUM> is driven electrically from outside of the chamber <NUM>, the piston <NUM> may comprise a PTFE outer layer, an inner stainless steel shell and Tesla valves formed of an Inconel alloy.

<FIG> illustrates an end view and a sectional view of the example piston <NUM> comprising a plurality of Tesla valves <NUM>, which is not in accordance with the present invention. In this example, six Tesla valves 408a-f are provided in the piston <NUM> in a parallel rotationally symmetric arrangement with the Tesla valves 408a-f in an annular arrangement. Using a plurality of Tesla valves in a parallel arrangement allows for a greater fluid flow rate through the pump <NUM>. The Tesla valves may be arranged in different configurations and greater or fewer than six may be used.

<FIG> illustrates a sectional diagram of an example Tesla valve <NUM>, showing the internal arrangement of the valve that allows for a preferred fluid flow direction T. In this orientation the fluid moves with little resistance in the flow direction T but will have much higher resistance in the reverse direction due to flow in the reverse direction causing turbulent flow within the valve <NUM>. The orientation of the valve <NUM>, i.e. with the preferred flow direction T downwards, corresponds to that shown in <FIG>.

<FIG> illustrates schematically an embodiment of the pump <NUM>' comprising Tesla valves, in which the fluid pump <NUM>' has an 'H' configuration rather than the linear configuration of the example in <FIG>. As with the fluid pump of <FIG>, the pump <NUM>' comprises a chamber <NUM> having a cavity <NUM> comprising a cylinder <NUM>, a piston <NUM> being slidably disposed within the cylinder, and a Tesla valve <NUM>, <NUM>. The pump <NUM>' comprises a first inlet <NUM>, a first outlet <NUM>, a second inlet <NUM> and a second outlet <NUM>. The first outlet <NUM> comprises a first non-return valve <NUM> and the second outlet <NUM> comprises a second non-return valve <NUM>. A first fluid passage <NUM> extends between the first inlet <NUM> and the first outlet <NUM>. A second fluid passage <NUM> extends between the second inlet <NUM> and the second outlet <NUM>.

A first Tesla valve <NUM> is in fluid communication with the first inlet <NUM> and a second Tesla valve <NUM> is in fluid communication with the second inlet <NUM>. The cylinder <NUM> within which the piston <NUM> is provided extends between the first fluid passage <NUM> and the second fluid passage <NUM>. Because in this example the piston reciprocates between the first and second passages, fluid flow is alternately pumped through the first and second outlets <NUM>, <NUM>, allowing for a more continuous flow of fluid through the pump <NUM>' compared to the pump <NUM> of <FIG>. As the piston is driven from left to right as shown by arrow P, fluid enters the first fluid passage <NUM> through the first Tesla valve <NUM> via the first inlet <NUM> and is compressed in the second fluid passage <NUM>. The Tesla valve <NUM> in fluid communication with the second inlet <NUM> prevents backflow, provided a minimum fluid flow rate passing through the pump <NUM>' is achieved. When the pressure exceeds a pre-set pressure, the second non-return valve <NUM> opens and high-pressure fluid exits the passage <NUM> through the second outlet <NUM>. When the piston <NUM> then travels from right to left, the process repeats for the first passage <NUM>, causing fluid to exit via the first outlet <NUM> and be drawn into the second passage <NUM> via the second inlet <NUM>.

In the embodiment illustrated in <FIG>, Tesla valves <NUM>, <NUM> are located in the respective first and second passages <NUM>, <NUM> at or proximate the respective first and second inlets <NUM>, <NUM>. These Tesla valves, allowing fluid to flow more easily in one direction than an opposing direction, effectively acting as non-return valves. In some alternatives, for example involving slow fluid flow rates, further non-return valves may be provided at the first and second inlets <NUM>, <NUM>, which may be in the form of the non-return valve in the example shown in <FIG>. In other alternatives, for example involving faster fluid flow rates, Tesla valves may be used as non-return valves for the inlets <NUM>, <NUM> and the outlets <NUM>, <NUM>, i.e. the non-return valve at each outlet may also comprise or be in the form of a Tesla valve. To allow for a controlled or adjustable pressure at which the outlets allow fluid to pass through, the outlets may also comprise a non-return valve of the type described above in relation to <FIG>.

As with the example illustrated in <FIG>, the piston <NUM> may be similarly coated with a low coefficient material such as PTFE. The inner surface of the cylinder <NUM> may also similarly coated for pumping cryogenic fluids.

As with the example in <FIG>, each passage <NUM>, <NUM> may comprise one or more Tesla valves, for example in an arrangement as shown in <FIG>. The Tesla valves may be provided at the first and second inlets <NUM>, <NUM> as in the illustration of <FIG> or may be provided at other points within the first and second passages <NUM>, <NUM>, in each case with a preferred flow direction towards the first and second outlets <NUM>, <NUM>.

In both of the illustrated examples, a sufficient flow rate of fluid through the pump <NUM>, <NUM>' mitigates fluid leakage around the piston sides and through the Tesla valves.

A fluid pump of the type disclosed herein may be used as a fuel pump for a hydrogen-powered turbofan engine in an aircraft. The fluid pump may, however, also be used in other applications for pumping fluids, particularly cryogenic fluids.

Claim 1:
A fluid pump (<NUM>, <NUM>') comprising:
a first inlet (<NUM>) and a second inlet (<NUM>);
a first outlet (<NUM>) comprising a first non-return valve (<NUM>), and a second outlet (<NUM>) comprising a second non-return valve (<NUM>);
a chamber (<NUM>) comprising a first passage (<NUM>) extending between the first inlet (<NUM>) and the first outlet (<NUM>), a second passage (<NUM>) extending between the second inlet (<NUM>) and the second outlet (<NUM>), and a cavity having a cylinder (<NUM>) extending between the first and second passages (<NUM>, <NUM>);
a piston (<NUM>) slidably disposed within the cylinder (<NUM>); and
a first Tesla valve (<NUM>) in fluid communication with the first inlet (<NUM>), and a second Tesla valve (<NUM>) in fluid communication with the second inlet (<NUM>);
wherein the fluid pump is configured to pump fluid from the first and the second inlets (<NUM>, <NUM>) to the first and second outlets (<NUM>, <NUM>) by reciprocation of the piston (<NUM>) within the cylinder (<NUM>).