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. However, hydrogen fuelled airliners have recently been proposed.

Hydrogen combustion in aircraft gas turbines presents a number of challenges. In particular, the low storage temperature of hydrogen and the relatively high temperatures within the combustor can result in large temperature differentials, which may result in "thermal fight", where different components are contracting and expanding due to their different temperatures. Such temperature differences can cause stress in various components, affecting component life. Additionally, hydrogen is difficult to contain, as it can readily leak through joints. In view of the high flammability of hydrogen, fuel leakage in hot parts of the engine where oxygen is present can represent a significant safety hazard.

United States patent application <CIT> discloses an additively manufactured attritable engine which includes an engine case, a fuel ring integral and conformal with the engine case, and a fuel manifold attached to the fuel ring and configured to deliver fuel to the fuel ring. The engine also includes a fuel injector attached to the fuel ring and configured to receive fuel from the fuel ring.

The invention is directed towards a hydrogen combusting gas turbine engine.

According to the invention, there is provided a gas turbine engine configured to combust gaseous hydrogen fuel, the gas turbine engine comprising:.

Advantageously, the invention provides a gas turbine engine having a fuel system with minimal joints, since a single fuel manifold which is integral to the combustion chamber outer casing is used to supply multiple fuel injectors.

Each fuel injector is coupled to the fuel manifold via a coupling provided within the combustion chamber outer casing. The coupling is provided within the inner combustor case. Advantageously, the coupling, which may be susceptible to leakage, is provided within a zone which is tolerant of the high temperatures which may be caused by leaking hydrogen combusting.

Each fuel injector is coupled to the fuel manifold via a respective fuel feed arm. Each fuel feed arm is integral with the fuel manifold.

Advantageously, the number of joints is minimised. Alternatively, each fuel feed arm may be joined to the manifold by a coupling provided within the combustion chamber outer casing. Advantageously, any leaks occur within the combustion chamber outer casing.

Each fuel feed arm may be double walled, having an inner wall separated from an outer wall via an air gap. Advantageously, the relatively cold hydrogen fuel is insulated from the relatively hot compressor delivery air, thereby reducing thermal shock and stress. Each fuel feed arm may be mounted to an annular compressor gas washed wall of the combustion chamber outer casing by the outer wall, and may be mounted to each fuel injector by the outer wall. The fuel feed arm inner wall may have a lower stiffness than the outer wall. Advantageously, a relatively stiff mounting is provided, which also protects the inner gas tight wall from damage from Foreign Object Damage (FOD), while thermal expansion can be accommodated by the relatively less stiff inner wall.

The fuel manifold is provided on a radially outer side of the combustion chamber outer casing annular wall. The fuel manifold is joined to the combustion chamber outer casing by the fuel feed arm, and is spaced from the combustion chamber outer casing annular wall by the fuel feed arm. Advantageously, the relatively cold fuel manifold is prevented from making direct contact with the annular wall of the combustion chamber outer casing.

The fuel manifold may be generally toroidal. Advantageously, the high-pressure hydrogen gas is efficiently contained, and corners, which would act as stress concentrators, are avoided. Alternatively, the fuel manifold may comprise a box section. Advantageously, space within the gas turbine engine is more efficiently utilised.

A block diagram of a hydrogen fuelled gas turbine engine <NUM> is shown in <FIG>.

The gas turbine engine <NUM> comprises a core gas turbine <NUM>.

The core gas turbine <NUM> comprises, in fluid flow series, a low-pressure compressor <NUM>, a high-pressure compressor <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 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>. The gas turbine also comprises a fan <NUM> driven by the second shaft <NUM>. It will be appreciated that in alternative embodiments, the core gas turbine could be of three-shaft configuration.

In operation, hydrogen fuel is pumped through a fuel line <NUM> from a hydrogen storage tank <NUM>, in either a liquid, supercritical or gaseous state to the fuel injection system <NUM>. The fuel is typically a gas or a supercritical fluid once it arrives at the fuel injection system, but may still be relatively cold.

Elements of a first embodiment of the combustor <NUM> is shown in further detail in <FIG>.

The combustor <NUM> comprises a plurality of fuel injectors <NUM>, which are arranged in an annular configuration. The combustor <NUM> comprises a combustion chamber defined by radially inner <NUM> and outer <NUM> casings which extend annularly around the circumference of the combustor <NUM>, and axially toward an outlet adjacent the high-pressure turbine <NUM>. In use, fuel flows into the combustion chamber through the fuel injectors <NUM>, while air flows into the combustion chamber both through apertures <NUM> provided in the fuel injectors <NUM>, and through dilution holes (not shown) in the combustion chamber inner wall <NUM>. Substantially all combustion takes place within the inner casing <NUM>, with the outer casing <NUM> providing structural support and cooling air.

The combustion chamber outer casing <NUM> is a structural component, which forms part of the engine core outer casing, and bears flights loads in use. As such, the outer casing <NUM> is stiff, but may flex somewhat in use due to flight loads. The combustion chamber outer casing <NUM> comprises several components which are integrally formed. As will be understood, each of the integrally formed components are either produced as a single item, or are joined to form an integral whole. For example, the outer casing <NUM> may be formed by machining a unitary billet of material. Suitable processing methods include Computerised Numerical Control (CNC) machining, and other similar processes. Other suitable processes include near-net-shape processes, such as sintering, or additive manufacturing processes such as selective laser sintering (SLS). A combination of such processes may be used. In other cases, the combustion chamber outer casing <NUM> may be formed from separate sub-assemblies, and subsequently permanently joined together to form a unitary whole without removable fasteners. For example, the combustion chamber outer casing <NUM> may be joined by welding. Accordingly, no seals or joints need be present in the unitary combustion chamber outer casing <NUM>.

The combustion chamber outer casing <NUM> comprises a generally cylindrical pressure chamber, configured to provide an air-tight containment for combustor entry air in use, and is joined to upstream and downstream engine components by joints <NUM>. An annular wall <NUM> of the casing <NUM> is in direct contact with (i.e. is gas-washed with) compressor exit / combustor entry air in use.

At a radially outer side of the annular wall <NUM> is a generally toroidal hydrogen fuel manifold <NUM>. The manifold <NUM> is supplied with hydrogen from the tank <NUM> via an inlet port (not shown) by a coupling. Consequently, a single (or relatively few) couplings are required to link the hydrogen tank <NUM> to the fuel supply. Typically, the manifold <NUM> is configured to be supplied with hydrogen in a gaseous or a supercritical state, at a pressure adequate to supply the fuel injectors <NUM>.

The manifold <NUM> is integral with the combustion chamber outer casing, and is joined to the outer casing wall <NUM> by a plurality of feed arms <NUM>. Each feed arm <NUM> extends between the manifold and a respective fuel injector <NUM> through the annular wall <NUM>. Since the annular wall <NUM>, manifold <NUM> and feed arms <NUM> are formed of a single integral part, no joints, seals or fasteners penetrate the outer wall <NUM>, which aids in maintaining a gas tight seal in operation.

The manifold <NUM> is spaced from the outer casing wall <NUM> by a section of the feed arm <NUM> which extends from the radially outer side of the outer casing wall <NUM>. Accordingly, the relatively cold manifold <NUM>, which is cooled by the cold hydrogen therein, is spaced from the outer wall <NUM>, which is subject to high temperatures by contact with the combustor entry air. Accordingly, thermal stress is reduced.

The feed arm <NUM> portion which extends from the radially outer side of the outer casing wall <NUM> is typically single-walled, in view of the relatively low temperature environment. Additionally, the single wall can be relatively flexible, which allows for differential thermal expansion. Optionally, features such as undulations (not shown) in the feed arm <NUM> may be provided, to further reduce stiffness of the feed arm <NUM>, and so permit movement of the manifold <NUM> relative to the outer casing wall <NUM>.

The feed arm <NUM> portion which extends from the radially inner side of the outer casing wall, which extends to the injector <NUM>, is double-walled, having inner <NUM> and outer <NUM> tubular walls. The walls <NUM>, <NUM> are spaced by an air gap through at least part of their length, such that thermal insulation is provided between the walls. Consequently, thermal expansion and contraction caused by the close proximity between the relatively cold hydrogen and the relatively hot combustor entry air is reduced.

Preferably, the inner wall <NUM> has a reduced stiffness, i.e. a greater flexibility than the outer wall <NUM>. This reduced stiffness may be provided by the reduced diameter of the inner wall <NUM> relative to the outer wall, and / or reduced wall thickness and geometric features such as undulations. Consequently, the inner wall <NUM> can flex due to temperature fluctuations and differentials, while the outer wall <NUM> provides structural strength and resistance to damage from FOD.

Each fuel injector <NUM> is coupled to the feed arm <NUM> by a coupling comprising a plurality of removable fasteners <NUM>, which are provided at an axially forward end of the injectors <NUM>, within the envelope defined by the combustor outer casing <NUM> and the inner casing <NUM>. Consequently, individual fuel injectors <NUM> can be removed for maintenance, without removing the whole combustor <NUM>. On the other hand, the joint between the injectors <NUM> and the feed arm <NUM> represents a potential leak risk. However, since the joint is provided within the outer casing <NUM>, any leaks will flow into the combustor, where the hydrogen can be safely burned.

<FIG> illustrates an alternative combustor <NUM>. The combustor <NUM> is similar to the combustor <NUM>, differing only in the shape of the manifold <NUM>. In the embodiment of <FIG>, the manifold <NUM> forms an annulus having a box section, having rounded corners, as shown in <FIG>. Consequently, the manifold <NUM> is more space efficient than the arrangement shown in <FIG>. This is particularly advantageous, given that the area within the engine where the manifold is located is typically heavily populated with engine hardware.

<FIG> shows a further alternative combustor <NUM>, which is not in accordance with the present invention. This embodiment differs from the first embodiment in two major ways.

Firstly, the fuel manifold <NUM> is configured differently. Rather than being toroidal, and spaced from the combustor outer wall, the combustor outer wall <NUM> of the casing <NUM> forms the radially inner wall of the fuel manifold <NUM>, such that fuel within the manifold <NUM> is in contact with the combustor outer wall <NUM> in use. This design may save weight relative to the first embodiment. Additionally, hydrogen fuel within the fuel manifold <NUM> may cool the outer wall of the combustor, thereby reducing thermal stresses within the combustion system. Such an arrangement also further reduces the volume occupied by the fuel manifold <NUM>.

A radially outer wall <NUM> of the fuel manifold <NUM> is radially spaced from the inner wall <NUM>, and is generally cylindrical. Side walls <NUM> extend radially from axially upstream and downstream ends, such that the manifold <NUM> is generally annular, having a box section. Such an arrangement forms a relatively stiff construction, thereby contributing to the stiffness of the casing. As such, the manifold <NUM> forms an integral structural component, thereby providing further weight savings.

A second difference between the embodiments of <FIG> and <FIG>, is the provision of a coupling <NUM> between the manifold <NUM> and feed arms <NUM>. The coupling <NUM> is provided at the radially inner side of the combustor wall <NUM>, within the combustor casing <NUM> envelope. Typically, the coupling comprises through holes provided in the feed arm <NUM>, which coincide with threaded blind holes provided in the combustor casing outer wall <NUM>, into which bolts are threaded. Consequently, the feed arms <NUM> can be removed separately to the combustor outer casing <NUM>, which may be convenient for maintenance. Nevertheless, the coupling <NUM> is provided within combustor casing <NUM>, ensuring that any fuel leaks leak into the combustor, rather than other spaces of the engine where the fuel may represent a fire risk.

<FIG> shows a further embodiment, which combines features of the embodiments of <FIG> and <FIG>, and which is not in accordance with the present invention. The fuel manifold <NUM> is similar to that of <FIG>, in which the combustor casing outer wall <NUM> forms an inner wall of the manifold <NUM>. However, in this embodiment, the feed tube <NUM> is integral with the manifold <NUM> and casing <NUM>, with no coupling being provided between the two. <FIG> also illustrates the inlet port <NUM>, which provides fuel to the manifold <NUM>. This configuration presents a sealed fuel system with only one mechanical connection to the main fuel delivery pipe, minimising the chance of fuel leakage.

<FIG> and <FIG> illustrate a still further embodiment of a combustor <NUM>, and which are not in accordance with the present invention. In this embodiment, the manifold <NUM>, combustor outer casing <NUM>, feed arm <NUM> and at least part of the injectors <NUM> are integrally formed. In this embodiment, the combustor casing <NUM> forms the radially outer wall <NUM> of the manifold <NUM>, such that the manifold <NUM> is contained within the combustor outer casing <NUM>, within the structural outer wall <NUM> of the combustor casing <NUM>. The inlet port <NUM> is provided at a radially outer wall of the manifold, and is coupled to the fuel line <NUM> by a coupling <NUM>.

In this embodiment, the manifold <NUM> is internal to the combustion chamber and therefore does not occupy the space within the volume surrounding the combustor outer casing <NUM>, which may be at a premium. Consequently, this design is more volumetrically efficient, unless space within the combustor casing <NUM> is at a higher premium. An internal fuel manifold is also potentially safer than an external manifold, since any fuel will immediately automatically ignite. In the zone outside of the combustion chamber the temperature is typically not sufficient to automatically ignite the fuel, so any leaked fuel may collect and form an explosive pocket in the engine zone. Additionally, the feed arms <NUM> can be shorter, thereby resulting in a weight saving. Finally, the hydrogen fuel dwells within the manifold <NUM>, which is surrounded by relatively hot high-pressure compressor exit air, and separated by the relatively thin, non-structural walls of the manifold <NUM>. As such, the hydrogen is heated, which may reduce the heating requirement of hydrogen fuel upstream (which may be energy intensive and inefficient).

Each injector <NUM> also differs from the previous designs. Each injector <NUM> includes a second annular fuel manifold <NUM>, which supplies a plurality of fuel ports in each injector. The injectors <NUM> may be wholly integrally formed with the feed arm <NUM>, manifold <NUM> and combustor casing <NUM>, which may reduce production and assembly costs, or only part of each injector may be integrally formed. In a similar manner to the embodiment shown in <FIG>, this configuration presents a sealed fuel system with only one mechanical connection to the main fuel delivery pipe, minimising the chance of fuel leakage.

Finally, <FIG> shows a still further embodiment of the fuel injector <NUM>, which is not in accordance with the present invention. This embodiment is similar to the fuel injector <NUM>, but the manifold <NUM> and feed arms <NUM> are modified to include a double-walled structure comprising inner <NUM> and outer <NUM> walls, which extend around the inner wall of the manifold <NUM> and the feed arms, within a combustor casing <NUM> to form an air gap <NUM>. Ports <NUM> are provided at a radially outer end and in communication with the air gap <NUM>, which permit "zone <NUM>" air from outside of the casing <NUM> to circulate within the air gap <NUM>. The double wall provides additional safety from foreign body impact damage. It also provides better thermal transition and reduces thermal stresses in the walls as a result of the temperature difference between the inner zone and out zone. Additionally, the temperature of the hydrogen within the feed arm <NUM> and manifold <NUM> can be controlled by controlling air flow through the air gap.

Any of the features disclosed herein may be employed separately or in combination with any other features and thus the disclosed subject-matter extends to and includes all such combinations and sub-combinations of the or more features described herein. Alternative embodiments of the disclosed design are also envisaged.

Claim 1:
A gas turbine engine (<NUM>) configured to combust gaseous hydrogen fuel, the gas turbine engine (<NUM>) comprising:
a combustor (<NUM>) comprising an annular combustion chamber outer casing (<NUM>) having an annular wall (<NUM>), surrounding an inner combustor case (<NUM>) and a fuel manifold (<NUM>) configured to provide gaseous fuel to a plurality of fuel injectors (<NUM>); wherein
the fuel manifold (<NUM>) is formed integrally with the combustion chamber outer casing (<NUM>); and
each fuel injector (<NUM>) is coupled to the fuel manifold (<NUM>) via a coupling (<NUM>) provided within the combustion chamber outer casing (<NUM>), wherein the fuel manifold (<NUM>) is provided on a radially outer side of the combustion chamber outer casing wall (<NUM>);
characterised in that:
each fuel injector (<NUM>) is coupled to the fuel manifold (<NUM>) via a respective fuel feed arm (<NUM>);
the fuel manifold (<NUM>) is joined to the combustion chamber outer casing wall (<NUM>) by the fuel feed arms (<NUM>), and is spaced from the combustion chamber outer casing annular wall (<NUM>) by the fuel feed arms (<NUM>), wherein each fuel feed arm (<NUM>) is integral with the fuel manifold (<NUM>).