Patent Description:
Fuel staging systems in gas turbine engines are used to distribute fuel to mains burners and pilot burners of a plurality of fuel injectors within a gas turbine engine. The fuel injectors are for injecting fuel and air into a combustion chamber of a gas turbine engine for burning. A fuel staging system may be used to control the amount of fuel and air injected by the fuel injectors in order to reduce emissions.

<CIT> discloses a fuel staging system for a gas turbine engine which comprises a fuel metering unit having a fuel metering valve which is controlled to meter the flow in use, and a fuel staging unit which receives fuel from the fuel metering valve. The staging unit supplies fuel to the pilot and main burners.

<CIT> discloses a fuel supply system that includes a metering unit having a piston. The metering unit is further connected to a fuel distribution valve for the main and pilot burner.

According to a first aspect, there is provided a fuel staging system for a gas turbine engine the fuel staging system having the features of claim <NUM>.

The check valve may close when the pressure of fuel in the main delivery line is below the threshold pressure to prevent any flow. The check valve may close to prevent flow of fuel from the mains manifold to the mains delivery line. There may be no check valve provided at each of the fuel injectors.

The fuel staging system may comprise a splitter valve for splitting a fuel supply between the mains delivery line and a pilot delivery line. The plurality of fuel injectors may each comprise a pilot burner which is configured to receive fuel through the pilot delivery line. The splitter valve may be configured to variably split the fuel supply between the mains delivery line and the pilot delivery line.

The fuel staging system may comprise a pilot manifold connected to the pilot delivery line and configured to distribute fuel from the pilot delivery line to the pilot burner of each of the plurality of injectors.

The mains manifold is in heat exchange relationship with a secondary fuel line. The mains manifold may comprise a common mains distribution line, and a plurality of feed lines which are configured to direct fuel to the mains burner of each of the fuel injectors. The common mains distribution line may be in heat exchange relationship with the secondary fuel line.

The fuel staging system may comprise a pipe-in-pipe arrangement in which a portion of the mains manifold is in heat exchange relationship with a portion of a secondary fuel line. The expression pipe-in-pipe arrangement is intended to mean that a portion of the mains manifold is disposed within the portion of the secondary fuel line or vice versa.

Each fuel injector may be provided with a weight distribution valve at the main burner, the weight distribution valve having a variable size opening, through which fuel is permitted to flow. The size of the opening may be a function of the orientation of the fuel injector within the gas turbine engine. The plurality of weight distribution valves may be configured to counteract effects on flow rate of a fuel head pressure through the respective fuel injectors which varies around a gas turbine engine.

Each fuel injector may be provided with a weight distributor valve at the pilot burner.

The fuel staging system may comprise a further check valve disposed in the main delivery line upstream of the mains manifold.

The fuel staging system comprises a bypass line forming part of a main cooling circuit. The bypass line is configured to receive fuel from the main delivery line when the check valve is closed and recirculate the fuel back into the main delivery line.

The secondary fuel line may be a portion of the pilot delivery line. The secondary fuel line may be a portion of the bypass line.

According to a second aspect, there is provided a gas turbine engine for an aircraft, the gas turbine engine comprising a fuel staging system according to the first aspect.

The resultant hot combustion products then expand through, and thereby drive, the high pressure and low pressure turbines <NUM>, <NUM> before being exhausted through the core exhaust nozzle <NUM> to provide some propulsive thrust.

Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in <FIG> has a split flow nozzle <NUM>, <NUM> meaning that the flow through the bypass duct <NUM> has its own nozzle <NUM> that is separate to and radially outside the core exhaust nozzle <NUM>. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct <NUM> and the flow through the core <NUM> are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine <NUM> may not comprise a gearbox <NUM>.

<FIG> shows a schematic view of an example fuel staging system <NUM> which may form part of the combustion equipment <NUM> of the gas turbine engine <NUM>.

The fuel staging system <NUM> comprises a plurality of fuel injectors <NUM> which are configured to mix fuel with air, and to inject the fuel-air mixture into a combustion chamber for combustion. Each fuel injector <NUM> comprises a mains burner 102a and a pilot burner 102b.

The staging unit <NUM> comprises a fuel flow splitting valve <NUM> which receives fuel from a fuel source <NUM> via a fuel supply line <NUM>. The fuel flow splitting valve <NUM> is configured to split the flow into a mains delivery line <NUM> and a pilot delivery line <NUM>. The mains delivery line <NUM> and the pilot delivery line <NUM> are configured to deliver fuel to the mains burner 102a and pilot burner 102b respectively of each fuel injector <NUM>.

The fuel flow splitting valve <NUM> comprises a spool <NUM> which is disposed within a bore <NUM> of a housing <NUM>. The spool <NUM> is movable in a longitudinal direction within the bore <NUM>, so as to selectively expose or cover a mains outlet <NUM> and pilot outlet <NUM> to thereby permit or block fuel flow respectively through the mains outlet <NUM> and pilot outlet <NUM>. The mains outlet <NUM> is connected to the mains delivery line <NUM> and the pilot outlet <NUM> is connected to the pilot delivery line <NUM>.

The fuel flow splitting valve <NUM> is configured to variably split the fuel supply between the mains delivery line <NUM> and the pilot delivery line <NUM>. In other words, the fuel flow splitting valve <NUM> is configured to enable the fuel flow from the fuel supply line <NUM> to be split between the mains delivery line <NUM> and the pilot delivery line <NUM> in variable proportions. In this example, the proportions of fuel flow split into the mains delivery line <NUM> and the pilot delivery line <NUM> depend on the position of the spool <NUM> within the bore <NUM> of the housing <NUM>.

In this example, the staging unit <NUM> also comprises a fuel splitting servo valve <NUM> which is configured to control the movement of the spool <NUM>, and thus the position of the spool <NUM> within the bore <NUM>, to thereby control the flow of fuel into the mains delivery line <NUM> and the pilot delivery line <NUM>.

The mains delivery line <NUM> is connected to a mains manifold <NUM> which is configured to distribute the flow from the mains delivery line <NUM> to the mains burner 102a of each of the fuel injectors <NUM>. The mains manifold <NUM> comprises a mains distribution line <NUM> extending circumferentially around the gas turbine engine, and a plurality of feed lines <NUM> distributed around the mains distribution line <NUM>. Each feed line <NUM> is configured to feed fuel from the mains distribution line <NUM> to the mains burner 102a of a fuel injector <NUM>.

In this example, the pilot delivery line <NUM> is split into two lines 112a, 112b which are each connected to a respective pilot manifold 116a, 116b. The pilot manifolds 116a, 116b are configured to distribute the fuel flow from the split pilot lines 112a, 112a to the pilot burners 102b in each of the fuel injectors <NUM>. In some examples, there may be only one pilot delivery line which is connected to a pilot manifold.

Splitting the pilot delivery line <NUM> into two lines 112a, 112b enables the system to control delivery of fuel to the pilot burner 102b of specific groups of fuel injectors <NUM>, in order to allow preferential fuelling of certain pilot burners 102b connected to one of the two lines 112a.

The staging unit <NUM> comprises a pilot fuel flow reducing valve <NUM> and a lean blow out fuel control valve <NUM> to act as a restrictor and control fuel flow into one of the split pilot lines 116b. This allows the fuel staging unit <NUM> to preferentially provide fuel to pilot burners 102b of specific injectors <NUM>.

The fuel staging system <NUM> comprises a check valve <NUM> disposed in the mains delivery line <NUM>, upstream of the mains manifold <NUM>. The check valve <NUM> is configured to permit the fuel to flow from the mains delivery line <NUM> into the mains manifold <NUM> if the pressure of fuel in the mains delivery line <NUM> exceeds a threshold delivery pressure. The check valve <NUM> is also configured to prevent any flow therethrough if the pressure in the mains delivery line <NUM> is below a threshold pressure, and to prevent any flow from the mains manifold <NUM> to the mains delivery line <NUM>.

Having a check valve <NUM> in the mains delivery line <NUM> enables the staging system <NUM> to omit check valves at each of the fuel injectors <NUM>. This ensures that there will be no fuel maldistribution to the fuel injectors <NUM> which would otherwise occur in the event of a check valve at a fuel injector failing open. In the design of previously-considered fuel staging systems, it was believed that a feed line to each fuel injector should remain primed with fuel at all times by providing a check valve at each fuel injector. However, the inventors have found that fuel can be replenished downstream of a check valve in the mains delivery line sufficiently rapidly such that check valves at the individual injectors can be omitted without detrimentally affecting the performance of the engine.

As explained above, the fuel flow into the mains delivery line <NUM> is controlled by the position of the spool <NUM> in the bore <NUM> of the splitting valve <NUM>. Therefore, the pressure of fuel in the mains delivery line <NUM> is also determined by the splitting valve <NUM>.

Each of the fuel injectors <NUM> is provided with a mains weight distributor valve 140a at the mains burner 102a and a pilot weight distributor valve 140b at the pilot burner 102b. The mains weight distributor valves 140a of each fuel injector <NUM> are together configured to evenly distribute the fuel flow to the mains burners 102a to avoid maldistribution of fuel (i.e. to ensure an equal flow of fuel into each main burner 102a). The pilot weight distribution valves 140b of each fuel injector <NUM> are together configured to evenly distribute the fuel flow in the pilot burners 102b, to avoid maldistribution of fuel (i.e. to ensure equal flow of fuel into each pilot burner 102b).

The weight distributor valves <NUM> comprise a weight and a spring, wherein the weight acts either with the force from the spring or against it, depending on the orientation of the weight distributor valve <NUM> (i.e. depending on the orientation of the fuel injector <NUM> within the gas turbine engine <NUM>). The orientation of the fuel injectors <NUM> around the gas turbine engine <NUM> varies depending on the circumferential position of the fuel injector <NUM> around the gas turbine engine <NUM>.

The weight distributor valves <NUM> comprise an opening through which fuel is permitted to flow. The size of the opening is variable and is determined by the combined force of the weight and the spring force of the weight distributor valve <NUM>. Therefore, the size of the opening is dependent on the orientation of the respective weight distributor valve <NUM>, and therefore the orientation of the respective fuel injector <NUM>. Varying the size of the opening depending on the orientation of the fuel injector <NUM> can counteract effects on fuel flow rate of varying fuel head pressure around the mains distribution line <NUM>.

The staging system <NUM> comprises a balancing pressure check valve <NUM>, which is disposed between the fuel flow splitting valve <NUM> and the pilot fuel flow reducing valve <NUM>. The balancing pressure check valve <NUM> is configured to return the flow upstream to the pilot delivery line <NUM> if the pressure downstream of the balancing pressure check valve <NUM> is too high. The balancing pressure check valve <NUM> together with the pilot weight distributor valves <NUM> therefore controls the pressure and fuel distribution in the pilot manifolds 116a, 116b.

The staging system <NUM> comprises a main cooling circuit comprising a bypass line <NUM> which is configured to receive fuel from the main delivery line <NUM> when the check valve <NUM> is closed. The fuel in the main delivery line <NUM> is recirculated through the bypass line <NUM> when the check valve <NUM> is closed, so as to maintain the main delivery line <NUM> primed.

The bypass line <NUM> comprises a recirculation valve <NUM> which is configured to open when the check valve <NUM> is closed, and to close when the check valve <NUM> is open. In this example, the recirculation valve <NUM> is controlled to open when the spool <NUM> is moved in the fuel flow splitting valve <NUM> to prevent the supply of fuel to flow into the main delivery line <NUM>, and is controlled to close when the spool <NUM> is moved in the fuel flow splitting valve <NUM> to permit the supply of fuel into the main delivery line <NUM>.

When the recirculation valve <NUM> is opened, flow is permitted through the recirculation valve <NUM> and a check valve <NUM>. The fuel in the bypass line <NUM> is kept cool by the fact that it is circulated away from the fuel injectors <NUM>, and therefore away from the main burners 102a and pilot burners 102b. It is then directed back into the mains delivery line <NUM>. The fuel in the main delivery line <NUM> and bypass line <NUM> may also be cooled by air flows passing over the bypass line <NUM> or any other pipes in the main cooling circuit. Keeping the fuel in the main delivery line <NUM> and bypass line <NUM> cool prevents thermal degradation of the fuel.

In this example, a portion of the mains manifold <NUM> is in heat exchange relationship with a secondary line, as shown for example in <FIG> shows the mains distribution line <NUM> of the mains manifold <NUM> intertwined with the bypass line <NUM>, such that it is in heat exchange relationship with the bypass line <NUM>. The mains distribution line <NUM> and the bypass line <NUM> may be helically intertwined. The feed lines <NUM> extend from the mains distribution line <NUM> to the mains burner 102a of the fuel injectors <NUM>. In other examples, the mains manifold may additionally or alternatively be in a heat exchange relationship with one or both of the pilot manifolds 116a 116b.

Having the mains manifold <NUM> in heat exchange relationship with the bypass line <NUM> ensures that any stagnant fuel or fuel residue in the mains manifold <NUM> when the check valve <NUM> is closed, is cooled by exchange of heat with the fuel in the bypass line <NUM>. The fuel to the bypass line <NUM> is circulating in the main cooling circuit and so continues to be cooled so as to receive heat from the mains manifold <NUM>.

<FIG> shows a cross sectional view of an alternative arrangement in which the mains manifold <NUM> is in heat exchange relationship with a secondary line. In this example, a portion of one of the pilot manifolds 116a, 116b is enclosed within the mains distribution line <NUM> of the mains manifold <NUM> in a pipe-in-pipe arrangement, such that the mains manifold <NUM> is in heat exchange relationship with the pilot manifold 116a, 116b. In some examples, a portion of the mains manifold may be enclosed within a portion of one or both of the pilot manifolds, or within a portion of the bypass line in a pipe-in-pipe arrangement. In other examples, a portion of the bypass line may be enclosed within a portion of the mains manifold in a pipe-in-pipe arrangement.

Although it has been described that a single check valve <NUM> is disposed in the main delivery line <NUM>, in some examples, there may be two or more check valves <NUM> disposed in the main delivery line <NUM> to provide redundancy, in the event that one of the check valves <NUM> fails open.

Claim 1:
A fuel staging system (<NUM>) for a gas turbine engine, the fuel staging system comprising:
a plurality of fuel injectors (<NUM>) each comprising a mains burner (102a);
a mains manifold (<NUM>) connected to a mains delivery line (<NUM>) and configured to distribute fuel from the mains delivery line (<NUM>) to the mains burner (102a) of each of the plurality of fuel injectors (<NUM>); and
a check valve (<NUM>) disposed in the mains delivery line (<NUM>) upstream of the mains manifold (<NUM>), the check valve (<NUM>) being configured to permit flow of fuel from the mains delivery line (<NUM>) to the mains manifold (<NUM>) when the pressure of fuel in the mains delivery line (<NUM>) exceeds a threshold pressure;
the fuel staging system (<NUM>) being characterised in that the mains manifold (<NUM>) is in heat exchange relationship with a secondary fuel line; and the fuel staging system further comprising a bypass line (<NUM>) forming part of a main cooling circuit, wherein the bypass line is configured to receive fuel from the main delivery line (<NUM>) when the check valve (<NUM>) is closed and recirculate the fuel back into the main delivery line.