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. Hydrogen burns very fast and at high temperatures, and consequently may produce relatively large quantities of oxides of nitrogen (NOx) when burned.

"Micro-mix" injectors have been proposed, in which a plurality of small fuel apertures is provided adjacent to a plurality of small air apertures. Flame miniaturisation has been shown to result in faster and improved mixing with air, short diffusion flames and reduced residence times. A large array of small flames produces a similar flame intensity as one large flame but with reduced NOx production. The design and construction of such injectors can be challenging owing to the complex internal arrangements required within the injector to provide the flows. Additionally, maintaining consistent air / fuel ratios within the various air / fuel streams is difficult.

<CIT> discloses an injector and an associated method for injecting and mixing gases, comprising a carbonaceous fuel and oxygen, in a combustion chamber of a combustion device. The injector has jets, which can be used to separately inject different combustion fuels. The injector is compatible with combustion devices that inject only gases, for example, a reheater that provides initial combustion in a power generation cycle or a reheater that recombusts a discharged gas from a gas generator and turbine. Further, the injector defines an annular space through which a recycle gas can be injected into the combustion chamber to lower the combustion temperature.

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

In a first aspect there is provided a fuel injector for a hydrogen combusting aircraft gas turbine engine having at least one air through-passage extending axially from a front face to a rear face;
a fuel manifold in communication with a hydrogen fuel feed line; wherein a plurality of fuel outlets is provided surrounding the or each air passage and an annular fuel gallery is provided around each air through passage configured to supply the fuel outlets, each annular fuel gallery communicating with the fuel manifold; characterised in that:
the injector comprises an injector front plate which forms the front face of the injector, and an injector rear plate which forms the rear face of the injector, the injector front plate and injector rear plate being coupled together, and wherein the injector comprises a feed plate located between the injector front plate and the injector rear plate comprising a plurality of air through-holes.

Advantageously, the design provides effective air/fuel mixing positions distributed across the face of the injector to achieve a micro-mix reduced NOx hydrogen fuel injector.

Each fuel outlet may be arranged to direct fuel towards air exiting a respective air through passage.

The injector comprises an injector front plate which forms the front face of the injector, and an injector rear plate which forms the rear face of the injector, the injector front plate and injector rear plate being coupled together. The injector front plate and rear plate may be coupled by diffusion bonding or brazing.

The injector comprises a feed plate located between the injector front plate and the injector rear plate. Advantageously, the additional feed plate enables adjustment of the feed hole sizes by the designer to adjust flow characteristics without affecting the design of the rear plate and front plate. As such, a common design can be utilised across different engines, with only the feed plate being altered between engines. This feature also enables the axial depth of the injector head to be adjusted without affecting the design of the rear plate and front plate. The injector feed plate may comprise a plurality of axially extending fuel through-holes and a plurality of axially extending air through-holes. The injector front plate, rear plate and feed plate may be coupled by diffusion bonding or brazing.

The injector front plate comprises the fuel manifold and comprises a plurality of axially extending air through-holes. The injector rear plate comprises a plurality of axially extending air through-holes. When assembled, the axially extending air-through holes of the injector rear plate, injector feed plate and injector front plate align to form a plurality of air through-passages.

The injector rear plate may comprise one or more fuel distribution channels which communicate between two or more annular fuel galleries. The annular fuel galleries may communicate with axially extending fuel through holes of the injector feed plate via the fuel distribution channels.

Each of the axially extending fuel through-holes of the injector feed plate may communicate with the fuel manifold of the injector front plate.

According to a second aspect of the invention there is provided a combustor for a gas turbine engine comprising a combustion chamber and a plurality of fuel injectors according to the first aspect of the invention.

According to a third aspect of the invention there is provided a gas turbine engine comprising a combustor according to the first aspect.

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 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 the combustor <NUM> are 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> walls 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 from the fuel injectors <NUM>, while air flows into the combustion chamber both through the fuel injectors <NUM>, and through dilution holes (not shown) in the combustion chamber walls <NUM>, <NUM>.

Each fuel injector <NUM> is supplied with fuel from a feed arm <NUM>, which extends into the combustor from an annularly outer combustor casing (not shown), toward a front, axially forward-facing face <NUM> of each injector <NUM>.

The feed arm <NUM> comprises a fuel manifold <NUM> at a distal end thereof, adjacent the front face <NUM> of the injector <NUM>. The manifold <NUM> is configured to supply fuel to the injector <NUM>, and comprises an annular chamber surrounding a central air passage <NUM>, which extends in a generally axial direction through the feed arm, and into the front face <NUM>.

<FIG> and <FIG> show an exploded view of parts of the injector <NUM>. As can be seen, each injector <NUM> comprises three principal components - a first unitary component comprising the feed arm <NUM> and front injector plate <NUM>, a second unitary component comprising a rear injector plate <NUM>, and a third unitary component comprising a feed plate <NUM>, which is provided axially between the rear and front plates <NUM>, <NUM>. Each plate <NUM>, <NUM>, <NUM> comprises through-holes, which enable fuel and air to flow through the injector to enable efficient mixing and distribution of air and fuel to enable combustion.

Referring again to <FIG>, each injector comprises a plurality of air through-passages <NUM> arranged around a generally axially rearwardly facing injector rear face <NUM>, which extend axially from the front face <NUM> of the injector front plate <NUM>, through the feed plate <NUM>, to provide an air flow path from a compressor outlet, through the injector <NUM> and into the combustion chamber <NUM>. In the present embodiment, seven air through-passages <NUM> are provided, as shown more clearly in <FIG>. Each air through-passage <NUM> is generally cylindrical, and comprises a chamfered edge <NUM> at an inlet end <NUM> at the front face <NUM> to ensure smooth flow into the passage, and a sharp edge at an outlet <NUM> at the rear face <NUM>, to promote turbulent flow at the outlet <NUM>.

Six of the air passages <NUM> are arranged in a ring adjacent an outer circumference of the rear plate <NUM>, with a seventh <NUM> extending through a centre of the rear plate <NUM>. The six air passages <NUM> arranged in a ring are supplied from inlets in the front face <NUM> around the central air passage <NUM>. It will be understood that other arrangements of air through-passages <NUM> could be provided, with more or fewer passages arranged in a different pattern.

Arrayed around each air passage <NUM> is a plurality of fuel through-passages <NUM> which terminate at a fuel outlet <NUM> at the injector rear face <NUM>. The fuel passages <NUM> also extend in a generally axial direction, though may be aligned somewhat inward toward the respective air passage outlet <NUM> to promote mixing. In the described embodiment, the fuel passages <NUM> are arranged as a ring, surrounding and spaced from a respective air outlet <NUM>. In the described embodiment, each air outlet <NUM> is surrounded by nine fuel outlets <NUM>, though it will be understood that fewer or more outlets <NUM> could be provided. Each fuel passage <NUM> is in communication with fuel from the fuel manifold <NUM>. Again, the fuel outlets <NUM> are typically circular, and have a sharp outlet to promote turbulence.

It will be appreciated that delivering air to seven separate air outlets and sixty-three separate fuel outlets <NUM> could necessitate a complex arrangement for the fuel injector <NUM>, which may be difficult to construct. Additionally, it is desirable to ensure consistent fuel and air flow between the different outlets to prevent hotspots from occurring, and ensuring good control of stoichiometry in the combustor <NUM>. It is also desirable to have multiple flow paths between the fuel manifold <NUM> and each fuel outlet <NUM>, such that blockages are prevented. For example, ice crystals may form in or around fuel passages during start-up where the fuel is cold. This may lead to difficulty starting, or uneven fuel / air ratios, which may in turn lead to unacceptable emissions of NOx. NOx emissions during start-up are particularly important, since the aircraft is in the vicinity of people on the ground, where air quality is most important. In the present arrangement, an arrangement which provides one or more of the above design considerations is provided with only three separate components.

Referring now to <FIG>, it can be described how fuel and air are delivered to the respective outlets <NUM>, <NUM>.

As shown most clearly in <FIG>, the front injector plate <NUM> comprises a plurality of fuel inlet apertures <NUM>, which extend into the fuel manifold <NUM> to receive fuel therefrom. In the present embodiment, six inlet apertures <NUM> are provided, though again different numbers of apertures could be provided in other embodiments.

As shown most clearly in <FIG>, each fuel inlet aperture <NUM> communicates with a fuel channel <NUM> which is set into a rear face <NUM> of the front injector plate <NUM>. Each fuel channel <NUM> extends generally normal to the axial direction, across the rear face <NUM> of the front injector plate <NUM>, and communicates with at least two fuel through-holes 72A, 72B in the injector feed plate <NUM>. Typically, the fuel channels <NUM> are formed in the injector plate <NUM> by a near net shape casting or injection moulding process, and / or may be machined into the face of the injector plate <NUM> by a milling or other material removal process.

The injector feed plate <NUM> is shown in more detail in <FIG>. The injector feed plate <NUM> is generally disc shaped, and comprises a plurality of through holes, comprising first and second sets of fuel through-holes 72A, 72B and a set of air through-holes <NUM>.

The seven air through-holes <NUM> are distributed in the same pattern as the air outlets <NUM> and are aligned with a respective outlet, such that the injector feed plate <NUM> provides a straight-through passage for air from the front face <NUM> to the rear face <NUM> of the injector <NUM>.

The first set of fuel through-holes 72A is arranged to form a ring, in communication with and aligned with the inlet apertures <NUM> of the front injector plate <NUM> to provide a straight flow of fuel therethrough from the manifold <NUM>.

The second set of fuel through-holes 72B is also arranged to a form a ring radially outward of the first set of fuel through holes 72A. Each fuel through hole of the second set 72B is aligned with a distal end of a respective fuel channel <NUM>, such that fuel is supplied via the fuel channel <NUM>, as can be seen from <FIG>.

Referring now to <FIG>, the injector rear plate <NUM> comprises a fuel distribution arrangement comprising an annular fuel gallery <NUM> extending around each air hole <NUM>, and aligned with and in communication with the fuel passages <NUM> arranged around each air hole <NUM>, which lead to respective fuel outlets <NUM>. The annular fuel gallery <NUM> is set in to the injector rear plate <NUM>, and may similarly be formed from a casting, injection moulding or milling process.

The fuel distribution arrangement further comprises a plurality of distribution channels <NUM>, which communicate between annular fuel galleries. The fuel through holes 72A, 72B are aligned with and in communication with the distribution channels <NUM>.

The distribution channels <NUM> are arranged such that each annular fuel gallery <NUM> communicates with at least one further annular fuel gallery <NUM>, and in the present embodiment, each annular fuel gallery <NUM> communicates with three other annular fuel galleries <NUM>. Distribution channels <NUM> are provided between the annular fuel gallery <NUM> surrounding the central air passage <NUM> and the ring of air passages <NUM>. Additional fuel distribution channels <NUM> are provided between each air passage <NUM> in the ring. Each of the first set of fuel through-holes 72A of the feed plate <NUM> are aligned with a central part of the fuel distribution channels <NUM> which extend between the annular fuel galleries <NUM> surrounding the central air passage <NUM>, and the outer ring of air passages <NUM>. The second set of fuel through-holes 72B are aligned with the distribution channels <NUM> which extend between the annular channels <NUM> arranged in a ring around the circumference of the rear injector plate <NUM>.

Consequently, each fuel outlet <NUM> is provided with fuel via the annular fuel gallery <NUM> in either a clockwise or anticlockwise direction, and also from any one of three distribution channels <NUM>. Consequently, a blockage in any one of a part of an annular channel <NUM>, distribution channel <NUM> or fuel through hole 72A 72B does not prevent fuel from flowing to any fuel outlet. Additionally, pressure throughout the injector is equalised by the various flow paths, thereby preventing hot spots, flame outs and uneven distribution of fuel, which might result in uneven air / fuel mixtures, and so poor control of NOx emissions.

It can now be explained how fuel and air flow through each injector <NUM> with the air of the arrows shown in <FIG>, in which solid arrows represent fuel flow, and dashed arrows represent air flow.

Fuel is initially supplied through the feed arm <NUM> to each injector <NUM>. Fuel from the feed arm <NUM> then collects in the fuel manifold <NUM>, and is supplied under relatively even flow conditions to each fuel inlet aperture <NUM> of the injector front plate <NUM>.

Fuel from the manifold <NUM> flows through the fuel inlet apertures directly through the first set of fuel through-holes 72A in the injector feed plate <NUM>, and through the second set of fuel through-holes 72B via the fuel channels <NUM>.

Fuel then enters the distribution channels <NUM> from the fuel through holes 72A, 72B, and is distributed to the annular fuel galleries <NUM>. Fuel then flows around the annular fuel galleries <NUM>, and out through the fuel outlets <NUM> in the injector rear face via the fuel passages <NUM>.

On the other hand, the air flow through the injector <NUM> follows a relatively straight path through the injector. Each of the respective air through holes <NUM>, <NUM>, <NUM> in the injector front plate, rear plate and feed plate <NUM>, <NUM>, <NUM> are axially aligned, such that air flows uninterrupted in an axial direction. Consequently, a relatively high air velocity can be maintained, while pressure losses are reduced. Additional air flow may then be added from the dilution holes (not shown).

Consequently, the disclosed arrangement provides an effective means of providing fuel and air to a large number of small outlets, while being robust to blockages, and ensuring that even distribution of air and fuel is provided throughout the injector. Additionally, the arrangement is simple to construct, requiring only three separate components, which can be brazed or otherwise joined together to form a single part for installation in the gas turbine engine.

<FIG> illustrate an alternative combustor <NUM> for the engine <NUM>, which differs in the arrangement of the air and fuel holes, and does not form part of the claimed invention.

As in the previous arrangement, the combustor <NUM> comprises a plurality of injectors <NUM>. Each injector <NUM> comprises a feed-arm <NUM>, which provides fuel to each injector <NUM>, and at least partly mounts the injector to a combustor casing. The feed-arm <NUM> defines an annular fuel manifold <NUM>.

The feed-arm <NUM> is coupled to a single-piece injector head <NUM>. Typically, the feed-arm <NUM> and injector head <NUM> are brazed or diffusion bonded together. In other embodiments, the single-piece injector head could comprise multiple components joined together.

A single air through-passage <NUM> is provided for each injector <NUM>. The air through-passage <NUM> is annular, and comprises a generally cylindrical aperture having an axis extending generally parallel to the air flow direction within the combustor <NUM>.

The air through-passage <NUM> is bounded at a radially outer side by an outer wall <NUM>, which is defined by the injector head <NUM>. An inner wall of the air through-passage is defined by a central body <NUM>, which is configured to condition air-flow through the air through-passage <NUM>.

The body <NUM> has a generally conical profile at a forward end, to aid air-flow around the body <NUM>. At an axially central region, a plurality of generally radially extending support struts <NUM> are provided, which again are profiled at their forward end to minimise air flow disruption.

The body <NUM> comprises a blunt aft end <NUM>. As will be understood, the blunt end <NUM> at the aft end of the body <NUM> will tend to cause flow separation, and thus cause eddies or vortices in the air flow downstream of the body <NUM>. Such vortices improve mixing in the region downstream of the body <NUM>.

Radially outward of the air through-passage are a plurality of fuel passages <NUM>, which are provided in a ring within the injector head <NUM>. Each fuel passage <NUM> extends between an annular fuel gallery <NUM> formed from a recess in the injector head where it meets the fuel feed arm <NUM>, which is in turn supplied with fuel from the fuel manifold <NUM> in the feed arm <NUM> via a plurality of fuel through-holes <NUM>. Each fuel passage <NUM> is angled radially inward, such that fuel emanating from each fuel passage <NUM> is directed towards the air-flow emanating from the air through-passage <NUM>. As such, fuel / air mixing is improved, resulting in rapid combustion, relatively small flames and low NOx emissions.

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 fuel injector (<NUM>) for a hydrogen combusting aircraft gas turbine engine having at least one air through-passage (<NUM>, <NUM>) extending axially from a front face (<NUM>) to a rear face (<NUM>);
a fuel manifold (<NUM>) in communication with a hydrogen fuel feed line (<NUM>); wherein a plurality of fuel outlets (<NUM>) is provided surrounding the or each air passage (<NUM>, <NUM>) and an annular fuel gallery (<NUM>) is provided around each air through passage (<NUM>, <NUM>) configured to supply the fuel outlets (<NUM>), the annular fuel gallery (<NUM>) communicating with the fuel manifold (<NUM>); characterised in that:
the injector (<NUM>) comprises an injector front plate (<NUM>) which forms the front face (<NUM>) of the injector (<NUM>), and an injector rear plate (<NUM>) which forms the rear face (<NUM>) of the injector (<NUM>), the injector front plate (<NUM>) and injector rear plate (<NUM>) being coupled together, wherein the injector (<NUM>) comprises a feed plate (<NUM>) located between the injector front plate (<NUM>) and the injector rear plate (<NUM>) comprising a plurality of air through-holes (<NUM>),
wherein the injector front plate (<NUM>) comprises the fuel manifold (<NUM>) and comprises a plurality of axially extending air through-holes (<NUM>),
wherein the injector rear plate (<NUM>) comprises a plurality of axially extending air through-holes (<NUM>), and
wherein, when assembled, the axially extending air-through holes of the injector rear plate (<NUM>), injector feed plate (<NUM>) and injector front plate (<NUM>) align to form a plurality of air through-passages (<NUM>).