Patent Description:
Fuel management systems are conventionally used for providing fuel to a gas turbine engine and for management of thermal loads. Fuel can be used as a heat sink into which heat from the thermal loads may be rejected prior to the fuel being provided to a combustor or a reheat of a gas turbine engine. Heat exchange apparatus is typically provided for the purpose of facilitating heat rejection from the thermal loads into the fuel within a fuel management system.

Known fuel management systems can be complex in nature, with a large mass or installation volume. It is therefore desirable to provide an improved fuel management system.

<CIT> discloses a thermal management system for an aircraft and a method of using the same. The system includes a fuel reservoir, a fuel recirculation loop, a fuel mixing valve, and a control module. The fuel recirculation loop includes a fuel recirculation tank, heat exchanger that transfers waste thermal energy to the fuel, and another heat exchanger that transfers waste thermal energy out of the heated fuel. The fuel recirculation loop supplies heated fuel to a combustion engine and is configured to return a portion of the heated fuel to the recirculation tank via a return line. The fuel mixing valve fluidly couples the fuel reservoir and the fuel recirculation tank to provide a mixture of the two fuel sources based on the temperature of the heated fuel. The thermal management system increases an aircraft thermal endurance over that which can be attained by a single tank fuel flow topology.

<CIT> discloses a fuel control system for an aircraft gas turbine engine that includes a thrust augmentation system. An augmentor fuel pump is arranged to provide pressurized fuel to an exhaust nozzle throat area actuation system to eliminate the need for a separate hydraulic pump to provide pressurized fluid for exhaust nozzle actuation. An augmentor fuel bypass arrangement is provided to enable the augmentor fuel pump to provide pressurized fuel to the main fuel pressurizing valve and to components operated by the main fuel system in the event of failure of the main fuel pump. The augmentor fuel pump pressure and output flow are controlled as a function of thrust augmentation demand and main fuel system operation. The system provides redundancy by enabling either the main fuel system or the augmentor fuel system to maintain engine operation if one of the fuel systems fails or provides inadequate fuel flow.

<CIT> discloses a fuel system for a gas turbine engine having a combustor that is fed fuel from a fuel tank. The fuel system includes a main fuel line providing fuel flow from the fuel tank to the combustor, and at least one pump pumping fuel from the fuel tank to the combustor via a fuel metering unit. The at least one pump includes an ejector pump. The fuel metering unit directs a portion of the fuel into a motive flow line. The motive flow line provides return of the portion of the fuel to the ejector pump. A first heat exchanger and a second heat exchanger are disposed in serial flow communication within the main fuel line between the at least one pump and the fuel metering unit. The second heat exchanger is downstream from the first heat exchanger. The first heat exchanger is a fuel-to-fuel heat exchanger providing heat transfer communication between the main fuel line and the motive flow line. A method of heating fuel in a fuel system of a gas turbine engine is also presented.

According to a first aspect of the present disclosure, there is provided a gas turbine engine according to claim <NUM> comprising a combustor and a fuel management system, the fuel management system comprising: a fuel supply line configured to supply fuel to the combustor; a recirculation line configured to recirculate excess fuel from the fuel supply line to an engine-located fuel tank via a fuel cooling device configured to reject heat from the excess fuel; and a heat exchanger configured to reject heat from a thermal load of the gas turbine engine to fuel in the fuel management system, wherein the heat exchanger is disposed on the fuel supply line or on the recirculation line; wherein the fuel supply line is configured to receive fuel from an external source and from the engine-located fuel tank, and a fuel pump on the fuel supply line, wherein the fuel pump is downstream from a mixing point where the excess fuel from the recirculation line flows into the fuel supply line and upstream from a recirculation point where the recirculation line receives the excess fuel from the fuel supply line.

It may be that the gas turbine engine further comprises a combustor valve on the fuel supply line configured to control flow of a burn portion of fuel passing through the combustor valve to the combustor, wherein the combustor valve is disposed on the supply line so that a remaining portion of fuel flowing in the supply line is directed into the recirculation line.

The gas turbine engine may further comprise a burn controller configured to: receive a burn signal relating to a fuel demand of the combustor; and control the combustor valve to meet the fuel demand based on the burn signal. The gas turbine engine may further comprise a burn flow sensor configured to monitor a burn flow rate of the burn portion of fuel. The burn controller is configured to control the combustor valve to meet the fuel demand based on the monitored burn flow rate.

It may be that the gas turbine engine further comprises a fuel flow controller configured to: receive a cooling signal relating to a cooling demand of the thermal load; control fuel flow in the fuel management system based on the cooling signal to meet the cooling demand. The thermal load may comprise a process flow circuit configured to reject heat from a process fluid to fuel within the heat exchanger; and the cooling signal may relate to a temperature of the process fluid at a temperature monitoring location of the process flow circuit.

The fuel flow controller may be further configured to receive a burn signal relating to a fuel demand of the combustor; and wherein the fuel flow controller is configured so that the control of the fuel flow in the fuel management system is based on at least the cooling signal and the burn signal to meet the cooling demand and the fuel demand, and wherein control of fuel flow in the fuel management system includes controlling the combustor valve. The gas turbine engine may further comprise a combustor flow sensor configured to monitor a burn flow rate of the burn portion of fuel; wherein the fuel flow controller is configured so that the control of the fuel flow in the fuel management system to meet the fuel demand is based on the monitored burn flow rate.

It may be that the gas turbine engine further comprises a fuel pump on the fuel supply line, wherein the fuel flow controller is configured so that the control of the fuel flow in the fuel management system includes controlling the fuel pump. In addition, the gas turbine engine may further comprise an input control valve configured to control mixing of fuel received into the fuel supply line from the external source and from the engine-located fuel tank. The fuel flow controller may be configured so that the control of the fuel flow in the fuel management system to meet the cooling demand includes controlling the input control valve to vary mixing of fuel received into the fuel supply line from the external source and from the engine-located fuel tank.

For example, it may be that the fuel flow controller is configured to vary flow rates of fuel received into the fuel supply line from the external source and from the engine-located fuel tank based on a monitored temperature of fuel in the fuel management system upstream of the heat exchanger to meet the cooling demand. The fuel flow controller may receive a signal relating to a temperature of fuel in the fuel supply line and may control the ratio based on the temperature of fuel in the fuel supply line to meet the cooling demand. Additionally, or alternatively, the fuel flow controller may receive signals relating to temperatures of fuel from the external source and fuel from the engine-located fuel tank and may control the ratio based on the respective temperatures to meet the cooling demand.

It may be that the gas turbine engine further comprises a sensor configured to monitor a fill parameter relating to a quantity of fuel stored in the engine-located fuel tank, wherein the fuel flow controller is configured so that the control of the fuel flow in the fuel management system includes controlling the fuel pump and the combustor valve based on the monitored fill parameter to target a target fill parameter while continuing to meet the cooling demand.

It may also be that the gas turbine engine further comprises: a tank bypass line configured to receive fuel from the fuel cooling device and bypass the engine-located fuel tank; and a bypass controller configured to control a tank bypass valve provided to the tank bypass line so as to vary a tank bypass flow rate of fuel received from the fuel cooling device and bypassing the engine-located fuel tank based on the monitored fill parameter; wherein the fuel supply line is configured to receive fuel from: the external source and the recirculation line, and to selectively receive fuel from the engine-located fuel tank via the recirculation line.

The fuel flow controller may comprise the bypass controller, and the fuel flow controller may control the tank bypass valve to vary the tank flow rate depending on the cooling demand of the thermal load. For example, it may be that fuel received from the ram air heat exchanger is at a different temperature to fuel contained in the engine-located fuel tank (e.g. at a cooler temperature), such that by controlling the flow rate of the tank bypass flow, a temperature of fuel received into the fuel supply line can be varied to meet the cooling demand.

The gas turbine engine may further comprise: a reheat fuel supply line extending from the recirculation line to a reheat of the gas turbine engine to extract a reheat portion of fuel; and a reheat controller configured to control a reheat supply valve on the reheat fuel supply line to control a flow rate of the reheat portion of fuel supplied to the reheat based on a reheat signal relating to a fuel demand of the reheat.

Additionally, the gas turbine engine may further comprise a reheat flow sensor configured to monitor a flow rate of the reheat portion of fuel. The reheat controller may be configured to control the reheat supply valve to meet the reheat fuel demand based on the monitored reheat flow rate.

It may be that the fuel flow controller comprises the reheat controller and is configured so that the control of the fuel flow in the fuel management system is to meet the cooling demand of the thermal load, the fuel demand of the combustor, and the fuel demand of the reheat.

According to a second aspect of the present disclosure, there is provided an aircraft comprising a gas turbine engine in accordance with the first aspect and an airframe, wherein the airframe comprises an airframe-located fuel tank which provides the external source for the fuel supply line. It may be that a fuel capacity of the airframe-located fuel tank is equal to or greater than a fuel capacity of the engine-located fuel tank.

The gearbox may be a reduction gearbox (in that the output to the fan is a lower rotational rate than the input from the core shaft). Any type of gearbox may be used. For example, the gearbox may be a "planetary" or "star" gearbox, as described in more detail elsewhere herein.

According to an aspect, there is provided an aircraft comprising a gas turbine engine as described and/or claimed herein.

The engine core <NUM> comprises, in axial flow series, a low pressure compressor <NUM>, a high-pressure compressor <NUM>, combustor <NUM>, a high-pressure turbine <NUM>, a low pressure turbine <NUM> and a core exhaust nozzle <NUM>.

The compressed air exhausted from the high pressure compressor <NUM> is directed into the combustor <NUM> where it is mixed with fuel and the mixture is combusted.

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 engine 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 gas turbine engine <NUM> comprising a fuel management system <NUM> according to the present disclosure. In the example of <FIG>, the gas turbine engine further comprises a combustor <NUM> and a reheat <NUM>. However, it will be appreciated that in variants of the example there may be no reheat <NUM>.

The fuel management system <NUM> comprises a fuel supply line <NUM> configured to receive fuel from an external source <NUM> via a fuel management system inlet <NUM> and to supply fuel to the combustor <NUM> of the gas turbine engine. The external source may comprise, for example a fuel tank of an airframe <NUM>. The fuel management system <NUM> further comprises a recirculation line <NUM> configured to recirculate excess fuel (i.e. an excess portion of fuel) from the fuel supply line <NUM> to an engine-located fuel tank <NUM> via a fuel cooling device <NUM>. The fuel cooling device <NUM> is generally configured to reject heat from the excess fuel in the recirculation line <NUM> to a heat sink.

The recirculation line <NUM> extends from a recirculation point <NUM> on the fuel supply line <NUM> to the engine-located fuel tank <NUM>, as will be described further below. From the engine-located fuel tank <NUM>, the recirculation line <NUM> extends back to the fuel supply line <NUM> to provide fuel into the supply line <NUM> at a mixing point <NUM>. The fuel cooling device <NUM> is configured to reject heat from the excess fuel in the recirculation line <NUM>. As an example, the fuel cooling device <NUM> may be provided by a ram-air heat exchanger <NUM> configured to reject heat from the excess fuel to ram air provided thereto such that the ram-air serves as the heat sink. The ram-air heat exchanger <NUM> may be disposed within a ram-air duct of the gas turbine engine <NUM>. As another example, the fuel cooling device <NUM> may be provided by an evaporator <NUM> of a refrigeration circuit. The refrigeration circuit may in turn reject heat via a condenser to ambient air (e.g. ram-air) or via the condenser to fuel at another location within the fuel management system <NUM> such that the fuel at the other location serves as the heat sink. Other apparatus which may provide the fuel cooling device <NUM> will be apparent to those skilled in the art.

The fuel management system <NUM> further comprises a heat exchanger <NUM> configured to reject heat from a thermal load <NUM> of the gas turbine engine <NUM> to fuel in the fuel management system <NUM>. In the example of <FIG>, the heat exchanger <NUM> is disposed on the recirculation line <NUM> upstream of the engine-located fuel tank <NUM>. The heat exchanger <NUM> is therefore configured to reject heat from the thermal load <NUM> of the gas turbine engine <NUM> to fuel in the recirculation line <NUM>.

However, in other examples, it may be that the heat exchanger <NUM> is disposed elsewhere, such as on the fuel supply line <NUM> at a location between the mixing point <NUM> and the recirculation point <NUM>.

The fuel management system <NUM> is configured to supply fuel from the system inlet <NUM> and/or from the mixing point <NUM> to the engine-located fuel tank <NUM> via the heat exchanger <NUM> and the fuel cooling device <NUM> such that fuel provided to the engine-located collector tank <NUM> has cooled the thermal load <NUM> (i.e. received rejected heat from the thermal load) within the heat exchanger <NUM>, and subsequently been cooled itself by rejecting heat at the fuel cooling device <NUM>.

Fuel flow within the fuel management system <NUM> may be maintained and controlled using various example devices shown in <FIG> and described below.

The fuel management system <NUM> may comprise a combustor valve <NUM> configured to control flow of a burn portion of fuel from the fuel supply line <NUM> to the combustor <NUM>. References herein to a portion of fuel should be understood as referring to a flow rate of fuel, which in turn constitute a portion of a total flow rate of fuel in the fuel supply line <NUM> of the fuel management system <NUM> (e.g. between the mixing point <NUM> and the recirculation line).

The burn portion of fuel is a portion of the total flow of fuel within the fuel supply line <NUM> between the input mixing point <NUM> and the recirculation point <NUM> which is passed to the combustor <NUM> for combustion therein. The excess portion of fuel is a remaining portion of the total flow of fuel which is not passed to the combustor <NUM> for combustion therein. Instead, the excess portion of fuel is recirculated by the recirculation line <NUM>. Accordingly, in this example the combustor valve <NUM> is configured to direct the excess portion of fuel from the fuel supply line <NUM> into the recirculation line <NUM>. In the example of <FIG>, the recirculation point <NUM> is located at the combustor valve <NUM>, but in other examples the recirculation point <NUM> may be between the mixing point <NUM> and the combustor valve <NUM>, or preferably between a pump on the fuel supply line (such as the fuel pump <NUM> described below) and the combustor valve <NUM>.

It may be that the combustor valve <NUM> comprises a two-port valve which is configured to restrict the flow of fuel passing to the combustor <NUM>, such that the remaining excess portion of fuel is directed into the recirculation line <NUM> at some upstream recirculation point. Otherwise, it may be that the combustor valve <NUM> comprises a three-way valve which is configured to receive fuel from the supply line <NUM> and to selectively direct fuel into the recirculation line <NUM> and to pass fuel to the combustor <NUM>, as shown in the example of <FIG>.

As noted above, the fuel supply line <NUM> is configured to receive fuel from the engine-located fuel tank <NUM>, at the mixing point <NUM> and via the recirculation line <NUM>. The fuel management system <NUM> is configured to mix fuel received from the external source <NUM> and the engine-located fuel tank <NUM> at a mixing point <NUM> on the fuel supply line <NUM> such that the fuel supply line <NUM> is configured to receive fuel from the external source <NUM> and the engine-located fuel tank <NUM> (or selectively from only one of these, depending on an operating mode of the fuel management system). In the example of <FIG>, the fuel management system <NUM> further comprises an input control valve <NUM> at the fuel mixing point <NUM>, the input control valve <NUM> being configured to control mixing of fuel received into the fuel supply line <NUM> from the external source <NUM> and from the engine-located fuel tank <NUM>. The input control valve <NUM> may be a three-way valve, for example.

In the example of <FIG>, the fuel management system <NUM> comprises a fuel pump <NUM> located on the fuel supply line <NUM> between the mixing point <NUM> and the recirculation point <NUM> such that the total flow rate of fuel in the fuel supply line is controllable by control of the fuel pump <NUM>. The fuel pump <NUM> may be further configured to increase a pressure of fuel within the fuel supply line <NUM> and thereby pressurise fuel to a delivery pressure for the combustor <NUM>.

The total flow rate fuel in the fuel supply line may be dependent on a cooling demand of the thermal load <NUM> and/or a fuel demand of the combustor <NUM>. For example, the cooling demand of the thermal load <NUM> may require that the flow rate of fuel is increased to increase heat transfer at the heat exchanger <NUM>, independently of any variation in the fuel demand of the combustor <NUM>. Separately, the fuel demand of the combustor <NUM> may require the total flow of fuel in the fuel supply line to be increased such that the combustor <NUM> can be supplied with a flow rate of fuel which is sufficient to operate the combustor <NUM> at an operational setpoint thereof (the burn flow rate). Such an increase may be required, for example, when there is a relatively large fuel demand of the combustor <NUM> together with a relatively small cooling demand of the thermal load <NUM>.

The cooling demand of the thermal load <NUM> corresponds to a flow rate of fuel which is required to be passed through the heat exchanger <NUM> in order to provide a sufficient rate of heat rejection from the thermal load <NUM> to the fuel at the heat exchanger <NUM>. The cooling demand of the thermal load <NUM> is dependent on a thermal dissipation rate of the thermal load <NUM>. The thermal dissipation rate of the thermal load <NUM> may vary continuously and/or discretely while the fuel management system <NUM> is in use, and so the cooling demand of the thermal load <NUM> may vary continuously and/or discretely while the fuel management system <NUM> is in use. It may be that the thermal dissipation rate of the thermal load <NUM> rapidly varies in use such that the fuel management system <NUM> is required to handle transient spikes in the cooling demand of the thermal load <NUM>.

The fuel demand of the combustor <NUM> corresponds to a flow rate of fuel which is required to be burned (i.e. combusted) by the combustor <NUM> in order to operate the combustor <NUM> at an operational setpoint (i.e. the burn flow rate as referred to herein). An operational setpoint of the combustor <NUM> may be related to a quantity of thrust demanded from the gas turbine engine by, for example, an electronic fly-by-wire control system. The quantity of thrust demanded (i.e. the thrust demand) may vary continuously and/or discretely while the fuel management system <NUM> is in use, and so the fuel demand of the combustor <NUM> (and therefore the flow rate of the burn portion of fuel) may vary continuously and/or discretely while the fuel management system <NUM> is in use.

In view of the discussion above, it follows that the total flow rate of fuel in the supply line is dependent on both the fuel demand of the combustor <NUM> and on the cooling demand of the thermal load <NUM>. As discussed above, the heat exchanger <NUM> may be disposed on the recirculation line <NUM> upstream of the engine-located fuel tank <NUM> as shown in <FIG>. If so, a flow rate of the burn portion of fuel corresponds to the fuel demand of the combustor <NUM>, whereas a flow rate of the excess portion of fuel corresponds to the cooling demand of the thermal load <NUM>. The total flow rate of fuel in the fuel supply line <NUM> is a sum of the burn flow rate and the flow rate of the excess portion of fuel.

Otherwise, as mentioned above, the heat exchanger <NUM> may be disposed on the fuel supply line <NUM> between the mixing point <NUM> and the recirculation point <NUM>. If so, the total flow rate of fuel in the fuel supply line <NUM> may be determined by whichever of the fuel demand and the cooling demand requires the larger flow rate of fuel. It may be that the burn flow rate is greater than a flow rate required to meet the cooling demand, such the excess portion of fuel is zero or minimal. Otherwise, it may be that the flow rate to meet the cooling demand is greater than the burn flow rate required to meet the fuel demand of the combustor <NUM>, such that there is a non-zero excess portion of fuel.

A ratio of fuel received by the fuel supply line <NUM> from the external source <NUM> to fuel received from the engine located fuel tank <NUM> can be controlled by the input control valve <NUM>.

The total flow rate of fuel within the fuel supply line <NUM> may be a function of the operation of one or more pumps of the fuel management system, and so control of fuel flow in the fuel management system may be performed by acting on the one or more pumps accordingly. It may be that the total flow rate of fuel in the fuel supply line <NUM> (i.e. between the mixing point <NUM> and the recirculation point <NUM>) is dependent only on operation of a pump on the fuel supply line <NUM>, for example the combustor pump <NUM>. For example, certain types of pumps (e.g. positive displacement pumps) may only permit a limited flow rate therethrough when operating at a respective speed. Otherwise, it may be that the total flow rate of fuel in the fuel supply line is dependent on operation of two or more pumps. For example, the flow rate may additionally depend on operation of an external source pump <NUM> which may be provided upstream of the mixing point for conveying fuel from the external source <NUM> to the fuel management system <NUM>; and/or on a pump <NUM> on the recirculating line <NUM> for returning fuel to the fuel supply line. For example, as shown in <FIG> there may be an engine-located fuel tank pump <NUM> associated with the engine-located fuel tank <NUM> and configured to convey fuel from the engine-located fuel tank <NUM> to the mixing point.

Accordingly, a controller of the fuel management system <NUM> may control the or each pump respectively to target or maintain a total flow rate of fuel in the fuel supply line, as will be further described below.

Similarly, while the example of <FIG> includes an input control valve <NUM> which can be controlled to control how much fuel is drawn from the external source <NUM> and from the engine-located fuel tank <NUM> respectively, in variants of this example this mixing could additionally or alternatively be controlled by control of the respective pumps. For example, it may be that there is an engine-located fuel tank pump <NUM> within or associated with the engine-located fuel tank <NUM> (e.g. between the engine-located fuel tank <NUM> and the mixing point <NUM>), and an external source pump <NUM> provided upstream of the mixing point <NUM> along the fuel supply line <NUM>, such as between the system inlet <NUM> and the mixing point <NUM> (as shown in the example of <FIG>). In such examples, the engine-located fuel tank pump <NUM> and/or the external input pump <NUM> may be controlled (e.g. by a controller of the fuel management system) to target or maintain both a total flow rate of fuel within the fuel supply line <NUM> between the mixing point <NUM>, and also a target mixing of fuel from the external source <NUM> and from the recirculation line <NUM>.

As described above, the cooling demand corresponds to a flow rate of fuel which is required to be passed through the heat exchanger <NUM> in order to provide a sufficient rate of heat rejection from the thermal load <NUM> to fuel at the heat exchanger <NUM>. This may be dependent on a temperature of fuel entering the heat exchanger <NUM>.

In use, a temperature of fuel received by the fuel supply line <NUM> from the external source <NUM> may be different to a temperature of fuel received by the fuel supply line <NUM> from the recirculation line <NUM> (e.g. from the engine-located fuel tank <NUM>). In particular, the temperature of fuel received by the fuel supply line <NUM> from the external source <NUM> may be generally higher than the temperature of fuel received by the fuel supply line <NUM> from the engine-located fuel tank <NUM>.

The temperature of fuel received by the fuel supply line <NUM> from the external source <NUM> may be dependent on a variety of factors which are unable to be controlled by the fuel management system <NUM>. For example, it may be that the external source <NUM> is provided by an airframe-located fuel tank of an aircraft in which the gas turbine engine <NUM> is incorporated. If so, the temperature of fuel received by the fuel supply line <NUM> from the external source <NUM> may be dependent on an ambient temperature when the airframe-located fuel tank was provided with fuel. Further, the airframe itself may utilise fuel stored within the airframe-located fuel tank as a coolant/heat sink for cooling of various thermal loads of the airframe. Accordingly, the temperature of fuel stored within the airframe-located fuel tank may increase during flight as a result of heat rejection from the airframe into fuel within the airframe-located fuel tank.

In some practical examples to illustrate how fuel may be received at different temperatures from different sources, it is worth noting that a temperature of fuel received by the fuel supply line <NUM> from the external source <NUM> may be <NUM> or more above an ambient temperature (i.e. the temperature of an external air flow around the gas turbine engine), for example <NUM> or more.

On the other hand, the temperature of fuel received by the fuel supply line <NUM> from the recirculation line <NUM> is either the temperature of fuel stored within the engine-located fuel tank <NUM>, or if the tank <NUM> is bypassed (as will be discussed below), it is the temperature of fuel being recirculated. In turn, the temperature of fuel recirculating in the recirculation line and being provided to the engine-located fuel tank <NUM> is dependent on a temperature to which the cooling device (e.g. ram-air heat exchanger) <NUM> is able to cool the excess fuel in the recirculation line <NUM>. A temperature of ram air provided to the ram-air heat exchanger is approximately equal to the ambient temperature of the gas turbine engine <NUM>. Therefore, the fuel cooling device <NUM> may be configured to cool the excess fuel within the recirculation line <NUM> to a lower temperature than the fuel in the external source <NUM>, for example within a cooled range of up to about <NUM> above the ambient temperature.

In use, it may be that a temperature of fuel received from the fuel cooling device <NUM> is different to a temperature of fuel within the engine-located fuel tank <NUM>. In particular, it may be that the temperature of fuel within the engine-located fuel tank <NUM> is lower than the temperature of fuel leaving the fuel cooling device <NUM>. This may occur when the thermal dissipation rate of the thermal load <NUM> is relatively large and/or has been subject to a sharp increase (i.e. during a transient spike in the cooling demand of the thermal load <NUM>). Under such conditions, relatively warm fuel from the fuel cooling device <NUM> is mixed with relatively cool fuel in the engine-located fuel tank <NUM> which is subsequently flushed through the engine-located fuel tank <NUM> and received into the fuel supply line <NUM>.

Because of a fuel storage capacity of the engine-located fuel tank <NUM>, mixing relatively warm fuel from the fuel cooling device <NUM> with relatively cool fuel within the engine-located fuel tank <NUM> results in only a gradual increase in the temperature of fuel within the engine-located fuel tank <NUM>. It follows that a temperature of the fuel flushed through the engine-located fuel tank <NUM> does not sharply increase in response to a sharp increase in the temperature of fuel received from the fuel cooling device <NUM>. Consequently, an impact of the transient spike in the cooling demand of the thermal load <NUM> on the temperature of fuel within the fuel supply line <NUM> is effectively dampened by the mixing of fuel within the engine-located fuel tank <NUM> and the subsequent mixing of fuel from the engine-located fuel tank <NUM> and the external source <NUM> at the mixing point <NUM>. Accordingly, fuel supplied to the fuel supply line <NUM> may originate from multiple sources each having different associated temperatures, including from the external source <NUM>, from the engine-located fuel tank <NUM>, and from a tank bypass flow of recirculating excess fuel that bypasses the engine-located fuel tank <NUM> (as will be described further below). A controller of the fuel management system may therefore control the temperature of fuel entering the heat exchanger <NUM> by selectively controlling the source(s) of the fuel and/or the mixing between different sources respectively.

As the fuel supply line <NUM> is configured to selectively receive fuel the external source <NUM> and/or from the engine-located fuel tank <NUM>, the temperature of fuel received by the fuel supply line <NUM> may selectively be lower than if the fuel supply line <NUM> were only configured to receive fuel from the external source <NUM>. Accordingly, compared with previously-considered systems, the fuel management system <NUM> may therefore be better able to accommodate transient spikes in the cooling demand of the thermal load <NUM> by selectively using relatively-lower temperature fuel, instead of attempting to meet such a cooling demand by significantly increasing fuel flow rates.

As may be appreciated, an alternative solution of significantly increasing fuel flow rates may require larger pumps or increase an operating pressure of the fuel management system, which may be associated with additional system complexity and cost. Further, in contrast to previously-considered systems, transient spikes in the cooling demand may be adequately handled without requiring fuel to be returned to the external source <NUM> via a fuel management system outlet. Therefore, a need for interfacing apparatus between the gas turbine engine <NUM> and the airframe <NUM> may be reduced, which may increase an ease of installation of the gas turbine engine <NUM>.

The fuel management system <NUM> of <FIG> further comprises a fuel flow controller <NUM> configured to receive a cooling signal relating to a cooling demand of the thermal load <NUM>. The fuel flow controller <NUM> is configured to control fuel flow in the fuel management system <NUM> based on at least the cooling signal in order to meet the cooling demand of the thermal load <NUM>. As shown in <FIG>, in this example the heat exchanger <NUM> is disposed on the recirculation line <NUM> upstream of the engine-located fuel tank <NUM>, and the fuel flow controller <NUM> is configured to control the combustor pump <NUM> and the combustor valve <NUM> so as to vary the flow rate of the excess portion of fuel and thereby meet the cooling demand of the thermal load <NUM>. In particular, the fuel flow controller <NUM> is configured to control the combustor pump <NUM> and the combustor valve <NUM> so as to increase the flow rate of the excess portion of fuel and thereby meet the cooling demand of the thermal load <NUM>.

In this example, the fuel flow controller <NUM> is further configured to receive a burn signal relating to a fuel demand of the combustor <NUM>. The fuel flow controller <NUM> is configured to control fuel flow in the fuel management system <NUM> based on the cooling signal and the burn signal in order to meet both the cooling demand of the thermal load <NUM> and the fuel demand of the combustor <NUM>. For example, the fuel flow controller <NUM> may be configured to control the combustor pump <NUM> so as to vary the total flow rate of fuel in the supply line in order to meet the cooling demand of the thermal load <NUM>, and to simultaneously control the combustor valve <NUM> to vary the flow rate of the burn portion of fuel in order to meet the fuel demand of the combustor <NUM>. As noted above, the controller may control the total flow rate in the supply line, the burn flow rate and/or the flow rate of excess fuel in various ways to meet the cooling demand and fuel demand, which may depend on the particular location of the heat exchanger (e.g. whether the heat exchange is located on the recirculation line <NUM> as shown in <FIG>, or on the fuel supply line).

In the example of <FIG>, the thermal load <NUM> comprises a process fluid circuit <NUM> which is configured to circulate a process fluid through the heat exchanger <NUM>. The process fluid circuit <NUM> is configured to reject heat from the process fluid therein to fuel within the heat exchanger <NUM>. As an example, the thermal load <NUM> may include a gearbox <NUM> of the gas turbine engine. The process fluid may be, for example, a lubricant provided to the gearbox <NUM> of the gas turbine engine.

The cooling signal may relate to an operating state of the thermal load <NUM>. For example, if the thermal load <NUM> comprises a gearbox <NUM> of the gas turbine engine, the operating state of the thermal load <NUM> may be determined based on an operating speed of the gearbox <NUM>, an operating mode of the gearbox <NUM>, a temperature of a lubricant flow for the gearbox <NUM> (e.g. as recovered from the gearbox) and/or an operating throughput power of the gearbox <NUM>.

The cooling signal may relate to a temperature of the process fluid at a process fluid temperature monitoring location of the process flow circuit <NUM>. The process fluid circuit <NUM> may comprise a process fluid temperature sensor <NUM> configured to monitor the temperature of the process fluid at the process fluid temperature monitoring location of the process fluid circuit <NUM> and configured to provide the cooling signal to the fuel flow controller <NUM>, wherein the cooling signal relates to the temperature of the process fluid at the process fluid temperature monitoring location.

The fuel flow controller <NUM> may control the combustor pump <NUM> to vary flow through the heat exchanger <NUM> to maintain the temperature of the process fluid at the process fluid temperature monitoring location within a target temperature range of a process fluid temperature setpoint, or to reduce a temperature error between the process fluid temperature setpoint and the temperature of the process fluid at the process fluid temperature monitoring location (e.g. using a PID controller or any other suitable control process).

The fuel management system <NUM> may further comprise a combustor flow sensor <NUM> configured to monitor a burn flow rate of the burn portion of fuel. The fuel flow controller <NUM> may control the combustor pump <NUM> and the combustor valve <NUM> so as to vary the flow rate of the burn portion of fuel in order to meet the fuel demand of the combustor <NUM> based at least on the monitored burn flow rate. The fuel flow controller <NUM> may control the combustor pump <NUM> and the combustor valve <NUM> to vary the flow rate of the burn portion of fuel to maintain the monitored burn flow rate within a target flow rate range of a flow rate of fuel required to match the fuel demand of the combustor <NUM>.

It may be that the fuel demand of the combustor <NUM> tends to require a lower flow rate of the burn portion of fuel than the flow rate of the total mixed portion of fuel which is required to meet the cooling demand of the thermal load <NUM>. Decentralised control of the fuel flow for the combustor <NUM> and for cooling the thermal load <NUM> may be appropriate in such conditions. For example, the fuel management system <NUM> may comprise a separate burn controller <NUM> to the fuel flow controller <NUM>, the burn controller <NUM> being configured to receive the burn signal and to control the combustor valve <NUM> based on the burn signal in order to match the fuel demand of the combustor <NUM>, without reference to the cooling signal or the cooling demand. In such examples, the fuel flow controller <NUM> may be configured to act independently of the burn controller <NUM> and vice versa. Further, the burn controller <NUM> may be configured to control the combustor valve <NUM> so as to vary the flow rate of the burn portion of fuel in order to meet the fuel demand of the combustor <NUM> based on the burn flow rate as monitored by the combustor flow sensor <NUM>.

As noted above, the fuel flow controller <NUM> may be configured to vary flow rates and/or mixing of fuel from the external source <NUM> and from recirculation line (including optionally controlling between receipt of fuel from the engine-located fuel tank <NUM> and from a tank bypass line <NUM>), based on a monitored temperature of fuel in the fuel management system <NUM>, for example based on a temperature of fuel upstream of the heat exchanger <NUM>. To this end, the fuel management system <NUM> may further comprise a primary fuel temperature sensor <NUM>' configured to monitor a temperature of fuel at a primary fuel temperature monitoring location of the fuel management system <NUM>. In the example of <FIG>, the primary fuel temperature monitoring location is on the fuel supply line <NUM> such that the primary fuel temperature sensor <NUM>' is configured to monitor a temperature of fuel within the fuel supply line <NUM> downstream of the mixing point <NUM> and upstream of the heat exchanger <NUM>. However, it will be appreciated that in other examples, the primary fuel temperature monitoring location may be elsewhere, for example on the recirculation line <NUM> upstream of the heat exchanger <NUM>. The fuel flow controller <NUM> may receive a signal from the primary fuel temperature sensor <NUM>' relating to the temperature of fuel at the primary fuel temperature monitoring location and may then control the respective flow rates and/or mixing of fuel received into the fuel supply line <NUM> from the external source <NUM> and from the recirculation line <NUM> accordingly (including optionally controlling between receipt of fuel from the engine-located fuel tank <NUM> or from a tank bypass line <NUM> around the tank <NUM>), based on the temperature of fuel at the primary fuel temperature monitoring location to meet the cooling demand of the thermal load <NUM>.

For example, the fuel flow controller <NUM> may be configured to control the input control valve <NUM> so as to vary the mixing of fuel at the mixing point <NUM> such that the proportion of fuel received into the fuel supply line <NUM> from the engine-located fuel tank <NUM> is increased relative to the proportion of fuel received into the fuel supply line <NUM> from the external source <NUM> in response to a determination that the monitored temperature of fuel upstream of the heat exchanger <NUM> exceeds a threshold fuel temperature value. Because the temperature of fuel received from the external source <NUM> may be higher than the temperature of fuel received from the engine-located fuel tank <NUM>, increasing the proportion of fuel received form the engine-located collector tank <NUM> relative to the proportion of fuel received from the external source <NUM> may reduce the temperature of fuel entering the heat exchanger <NUM>, which in turn increases the rate of heat rejection from the thermal load <NUM> to the fuel at the heat exchanger <NUM>.

The threshold fuel temperature valve may be predetermined. Otherwise, the threshold fuel temperature value may be dependent on, for example, the cooling demand of the thermal load <NUM> and/or the flow rate of the total mixed portion of fuel between the mixing point <NUM> and the recirculation point <NUM>. Accordingly, the threshold fuel temperature value may vary continuously and/or discretely while the fuel management system <NUM> is in use.

The fuel management system <NUM> may comprise additional or alternative fuel temperature sensors configured to monitor a temperature of fuel from the external source <NUM> at a location upstream of the mixing point <NUM> and/or a temperature of fuel from the engine-located fuel tank <NUM> at a location upstream of the mixing point <NUM>. The fuel flow controller <NUM> may receive signals from the additional or alternative fuel temperature sensors relating to the temperature of fuel from the external source <NUM> upstream of the mixing point <NUM> and the temperature of fuel from the engine-located fuel tank <NUM> upstream of the mixing point <NUM> and may then control the ratio of fuel received into the fuel supply line <NUM> from the external source <NUM> and from the engine-located fuel tank <NUM> based on the respective temperatures of fuel to meet the cooling demand of the thermal load <NUM>.

The engine-located fuel tank <NUM> is configured to store fuel received from the recirculation line <NUM> via the fuel cooling device <NUM> (e.g. the ram-air heat exchanger <NUM>). A flow rate into the fuel tank <NUM> may be different from a flow rate out of the fuel tank.

In a high-performance mode of the gas turbine engine <NUM>, the cooling demand of the thermal load <NUM> may be high and the fuel flow controller <NUM> may be configured to control fuel flow within the fuel management system <NUM> so that a proportion of fuel which is provided to the fuel supply line <NUM> from the recirculation line (e.g. from the engine-located fuel tank <NUM>) is relatively higher than in another mode of the engine (e.g. a normal operating mode), for example being provided exclusively from the recirculation line (e.g. from the engine-located fuel tank <NUM>). It may be that the rate of fuel supply from the engine-located fuel tank is typically greater than the rate at which fuel is replenished via the recirculation line <NUM>, such that the engine-located fuel tank <NUM> progressively drains when operated in this mode. The tank <NUM> may be sized to correspond to an anticipated duration of a mission event corresponding to the high-performance mode.

It may be that the fuel management system <NUM> further comprises an engine-located fuel tank sensor <NUM> configured to monitor a fill parameter relating to a quantity of fuel stored in the engine-located fuel tank <NUM>, as shown in the example of <FIG>. The engine-located fuel tank <NUM> may also be provided with an air-exchange valve <NUM> configured to allow air to pass in and out of the fuel tank during filling and emptying of the tank <NUM> with fuel. The fill parameter may relate to a volume or a mass of fuel stored within the engine-located fuel tank <NUM> and/or it may relate to a fraction of a fuel capacity of the engine-located fuel tank <NUM> which is filled with fuel. The fuel capacity of the engine-located fuel tank <NUM> defines a maximum quantity of fuel which may be stored within the engine-located fuel tank <NUM>.

When the gas turbine engine <NUM> is not in the high-performance mode, the fuel flow controller <NUM> may control fuel flow in the fuel management system <NUM> such that the quantity of fuel stored within the engine-located fuel tank <NUM> increases. The fuel flow controller <NUM> may control fuel flow in the fuel management system <NUM> based on the monitored fill parameter to target a target fill parameter of the engine-located fuel tank <NUM> while continuing to meet the cooling demand of the thermal load <NUM> and/or the fuel demand of the combustor <NUM> as applicable. For example, the fuel flow controller may control the fuel pump <NUM> and the combustor valve <NUM> so as to increase the flow rate of the excess portion of fuel recirculated by the recirculation line <NUM> so as to increase the quantity of fuel stored in the engine-located fuel tank <NUM> to target the target fill parameter while continuing to meet the cooling demand of the thermal load <NUM> and the fuel demand of the combustor <NUM> in accordance with the control regimes described above.

The target fill parameter corresponds to a target quantity of fuel which is to be stored in the engine-located fuel tank <NUM> so that, for example, the gas turbine engine <NUM> may be operated in the high-performance mode for a predetermined time period. In some examples, the target fill parameter may correspond to the fuel capacity of the engine-located fuel tank <NUM> such that when the target fill parameter is met, the engine-located fuel tank <NUM> is completely filled with fuel. Further, the fuel capacity of the engine-located fuel tank <NUM> may be chosen such that the engine-located fuel tank <NUM> is able to supply fuel to the fuel supply line <NUM> for a time period which is sufficiently long so as to enable the gas turbine engine <NUM> to operate in a high-performance mode for the predetermined period of time.

As discussed above, it may be that the fuel management system <NUM> comprises a tank bypass line <NUM> configured to receive fuel from the fuel cooling device <NUM> and to bypass the engine-located fuel tank <NUM>, such that fuel passing through the tank bypass line <NUM> may be provided to the mixing point <NUM> on the fuel supply line <NUM> without having passed through the engine-located fuel tank <NUM>. The tank bypass line <NUM> extends from a tank bypass point <NUM> on the recirculation line <NUM> between the fuel cooling device <NUM> and the engine-located fuel tank <NUM>. Accordingly, the fuel supply line <NUM> is configured to receive fuel from the external source <NUM> and from the recirculation line <NUM>. The fuel supply line <NUM> may receive fuel directly from the engine-located fuel tank <NUM> or from the tank bypass line <NUM> when receiving fuel from the recirculation line <NUM>.

The tank bypass line <NUM> is provided with a tank bypass valve <NUM> which is capable of varying a flow rate of fuel received from the fuel cooling device <NUM> into the tank bypass line <NUM>. Fuel received from the fuel cooling device <NUM> into the tank bypass line <NUM> may be referred to as a tank bypass portion of fuel. The tank bypass portion of fuel is derived from the excess portion of fuel, such that the flow rate of the tank bypass portion of fuel can never exceed the flow rate of the excess portion of fuel.

The fuel management system <NUM> may further comprise a bypass controller <NUM> configured to control the tank bypass valve <NUM> so as to vary the tank bypass flow rate of fuel based on the monitored fill parameter. For example, it may be that the bypass controller <NUM> is configured to control the tank bypass valve <NUM> so as to increase the tank bypass flow rate of fuel to be equal to the flow rate of the excess portion of fuel in response to a determination that the engine-located fuel tank <NUM> is full based on the monitored fill parameter. Alternatively, in such circumstances the bypass controller may not bypass the fuel tank, and fuel may pass into and out of the fuel tank at the same rate.

It may be that the fuel flow controller <NUM> comprises the bypass controller <NUM> such that the fuel flow controller <NUM> performs the above functions of the bypass controller <NUM>. If so, the fuel flow controller <NUM> may be additionally configured to control the tank bypass valve <NUM> to control the flow rate of the tank bypass portion of fuel based on the cooling demand of the thermal load <NUM>.

The engine-located fuel tank sensor <NUM> may be further or otherwise configured to monitor the temperature of fuel within the engine-located fuel tank <NUM>. In addition, the fuel management system <NUM> may comprise a secondary fuel temperature sensor <NUM>" configured to monitor a temperature of fuel at a secondary fuel temperature monitoring location of the fuel management system <NUM>. The secondary fuel temperature monitoring location is on the recirculation line <NUM> downstream of the fuel cooling device <NUM> and upstream of the engine-located fuel tank <NUM> (and upstream of the tank bypass point <NUM>) such that the secondary fuel temperature sensor <NUM>" is configured to monitor the temperature of fuel leaving the fuel cooling device <NUM>.

As described above, in use it may be that the temperature of fuel received from the fuel cooling device <NUM> is different to the temperature of fuel within the engine-located fuel tank <NUM>. The fuel flow controller <NUM> may control the flow rate of the tank bypass portion of fuel to vary the temperature of fuel received into the fuel supply line <NUM> depending on the cooling demand of the thermal load.

As an example, in response to a determination that the temperature of fuel within the engine-located fuel tank <NUM> is greater than the temperature of fuel leaving the fuel cooling device <NUM> and that the cooling demand of the thermal load <NUM> is not currently being met, the fuel flow controller <NUM> may control the tank bypass valve <NUM> to increase the flow rate of the tank bypass portion of fuel and thereby reduce the temperature of fuel received into the fuel supply line <NUM> in order to meet the cooling demand of the thermal load <NUM>.

As another example, in response to a determination that the temperature of fuel within the engine-located fuel tank <NUM> is greater than the temperature of fuel leaving the fuel cooling device <NUM> and that the cooling demand of the thermal load <NUM> is currently being met, the fuel flow controller <NUM> may control the tank bypass valve <NUM> to reduce the flow rate of the tank bypass portion of fuel (and therefore increase the flow rate of fuel through the engine-located fuel tank <NUM>) so as to flush the engine-located fuel tank <NUM> with relatively cool fuel and thereby reduce the temperature of fuel within the engine-located fuel tank <NUM>, provided that the cooling demand of the thermal load <NUM> remains met. This effectively increases a store of cooling capacity within the fuel management system <NUM> in the form of relatively cool fuel within the engine-located fuel tank <NUM> until it is determined to be needed.

As an additional example, in response to a determination that the temperature of fuel within the engine-located fuel tank <NUM> is lower than the temperature of fuel leaving the fuel cooling device <NUM> and that the cooling demand of the thermal load <NUM> is currently being met, the fuel flow controller <NUM> may control the tank bypass valve <NUM> to increase the flow rate of the tank bypass portion of fuel and thereby increase the temperature of fuel received into the fuel supply line <NUM>, provided that the cooling demand of the thermal load <NUM> remains met while the relatively-low temperature fuel in the engine-located fuel tank <NUM> remains stored therein. This may effectively preserve the store of cooling capacity within the fuel management system <NUM> in the form of relatively cool fuel within the engine-located fuel tank <NUM> until it is determined to be needed as well as preventing fuel stagnation and/or fuel lacquering within the recirculation line <NUM>. As a further example, in response to a determination that the temperature of fuel within the engine-located fuel tank <NUM> is lower than the temperature of fuel leaving the fuel cooling device <NUM> and that the cooling demand of the thermal load <NUM> is not currently being met, the fuel flow controller <NUM> may control the fuel pump <NUM>, the combustor valve <NUM> and/or tank bypass valve <NUM> so as to control the flow rate of fuel being flushed through the engine-located fuel tank <NUM>. The fuel flow controller <NUM> may control a flow rate of fuel being flushed through the engine-located fuel tank <NUM> so as to control the temperature of fuel within the fuel supply line <NUM> and thereby continue to meet the cooling demand of the thermal load <NUM>. Because mixing relatively warm fuel from the fuel cooling device <NUM> with relatively cool fuel within the engine-located fuel tank <NUM> results in only a gradual increase in the temperature of fuel within the engine-located fuel tank <NUM>, causing fuel to be flushed through the engine-located fuel tank <NUM> may extend the period of time for which the store of cooling capacity in the form of relatively cool fuel within the engine-located fuel tank <NUM> may be used to dampen the impact of transient spikes in the cooling demand of the thermal load <NUM>.

The fuel management system <NUM> may comprise a cooling device bypass line <NUM>' configured to bypass the fuel cooling device <NUM>, such that fuel passing through the cooling device bypass line <NUM>' may be provided to the engine-located fuel tank <NUM> without having passed through the fuel cooling device <NUM>. The cooling device bypass line <NUM>' extends from a cooling device bypass point <NUM>' on the recirculation line <NUM> upstream of the fuel cooling device <NUM>.

The cooling device bypass line <NUM>' is provided with a cooling device bypass valve <NUM>' which is capable of varying a flow rate of fuel received from the recirculation line <NUM> into the cooling device bypass line <NUM>'. Fuel received into the cooling device bypass line <NUM>' may be referred to as a cooling device bypass portion of fuel. The cooling device bypass portion of fuel is derived from the excess portion of fuel, such that the flow rate of the cooling device bypass portion of fuel can never exceed the flow rate of the excess portion of fuel.

In use, it may be that the fuel cooling device <NUM> is unable to reject heat from the excess portion of fuel within the recirculation line <NUM> into a heat sink. For example, when the fuel cooling device <NUM> is provided by a ram-air heat exchanger <NUM>, it may be that the ambient temperature of the flow of ram-air is sufficiently high that the excess flow of fuel passing through the ram-air heat exchanger <NUM> would be heated by the flow of ram-air. Under such conditions, the cooling device bypass line <NUM>' enables at least a fraction of the excess portion of fuel to be provided to the engine-located collector tank <NUM> without having been heated by the fuel cooling device. This may aid preservation of the store of cooling capacity within the fuel management system <NUM> in the form of relatively cool fuel within the engine-located fuel tank <NUM>.

Otherwise, it may be that the fuel cooling device <NUM> is likely to overcool the excess portion of fuel within the recirculation line <NUM> in use. For example, when the fuel cooling device <NUM> is provided by a ram-air heat exchanger <NUM>, it may be that the temperature of ram air provided to the ram-air heat exchanger is sufficiently low such that solid frozen crystals form within the excess portion of fuel passing through the ram-air heat exchanger <NUM>. For example, the fuel may comprise water which may form ice crystals if the fuel cooling device overcools the excess portion of fuel within the recirculation line <NUM> in use. Under such conditions, the cooling device bypass line <NUM>' enables at least a fraction of the excess portion of fuel to be provided to the engine-located collector tank <NUM> without having been cooled by the fuel cooling device <NUM>. This may deter the formation of blockages within the recirculation line <NUM> as a result of overcooling of the excess portion of fuel.

The fuel management system <NUM> may further comprise a reheat fuel supply line <NUM> which is configured to supply fuel from the fuel supply line <NUM> to the reheat <NUM> of the gas turbine engine <NUM> via the recirculation line <NUM>. In the example of <FIG>, the reheat fuel supply line <NUM> extends from a reheat branching point <NUM> on the recirculation line <NUM> to the reheat <NUM> via a reheat pump <NUM> and a reheat control valve <NUM>. The reheat fuel supply line <NUM> is generally configured to extract a reheat portion of fuel from the recirculation line <NUM> and to provide the reheat portion of fuel to the reheat <NUM> of the gas turbine engine. In the example of <FIG>, a flow rate of the reheat portion of fuel is maintained by the reheat pump <NUM> and the reheat control valve <NUM>. However, it will be appreciated that in other examples, the flow rate of the reheat portion of fuel is maintained by the reheat control valve <NUM> alone. The fuel management system <NUM> may also further comprise a reheat controller <NUM> configured to receive a reheat signal relating to a fuel demand of the reheat <NUM>. The reheat controller <NUM> may be additionally configured to control the reheat pump <NUM> and/or the reheat control valve <NUM> to control the flow rate of the reheat portion of fuel supplied to the reheat <NUM> in order to meet the fuel demand of the reheat <NUM> based on at least the reheat signal.

The fuel management system <NUM> may further comprise a reheat flow sensor <NUM> configured to monitor a flow rate of the reheat portion of fuel. That is to say that the reheat flow sensor <NUM> is configured to monitor the flow rate of fuel passed to the reheat <NUM> by the reheat control valve <NUM>. The reheat controller <NUM> may then control the reheat pump <NUM> and/or the reheat control valve <NUM> in order to meet the fuel demand of the reheat <NUM> based at least on the monitored flow rate of the reheat portion of fuel. The reheat controller <NUM> may control the reheat pump <NUM> and/or the reheat control valve <NUM> to vary the flow rate of fuel provided to the reheat <NUM> and thereby maintain the monitored flow rate of the reheat portion of fuel within a target flow rate range of a flow rate of fuel required to meet the fuel demand of the reheat <NUM>.

It may be that the fuel flow controller <NUM> comprises the reheat controller <NUM> such that the fuel flow controller <NUM> performs the above functions of the reheat controller <NUM>. If so, the fuel flow controller <NUM> is configured so that control of fuel flow within the fuel management system <NUM> is to simultaneously meet the cooling demand of the thermal load <NUM>, the fuel demand of the combustor <NUM> and the fuel demand of the reheat <NUM>.

By providing the reheat fuel supply line <NUM> branching from the recirculation line <NUM>, the flow rate and/or pressure of the reheat portion fuel provided to the reheat <NUM> may be controlled independently of the flow rate and/or pressure of the burn portion of fuel which is provided to the combustor <NUM>.

<FIG> shows an aircraft <NUM> comprising a gas turbine engine <NUM> and an airframe <NUM>. The gas turbine engine <NUM> comprises a fuel management system <NUM> in accordance with the examples described above with respect to <FIG>. The airframe <NUM> comprises an airframe-located fuel tank <NUM> which provides the external source for the fuel supply line <NUM> via the fuel management system inlet <NUM>.

It may be that a fuel capacity of the airframe-located fuel tank <NUM> is equal to or greater than the fuel capacity of the engine-located fuel tank <NUM>. As discussed above with respect to <FIG>, it may be that the fuel capacity of the engine-located fuel tank <NUM> may be chosen such that the engine-located fuel tank <NUM> is able to supply fuel to the fuel supply line <NUM> for a time period which is sufficiently long so as to enable the gas turbine engine <NUM> to operate in a high-performance mode for the predetermined period of time. The gas turbine engine <NUM> may be required to operate in the high-performance mode when the aircraft <NUM> is performing airborne manoeuvres, for example.

Consequently, the fuel capacity of the engine-located fuel tank <NUM> may be chosen such that the engine-located fuel tank <NUM> is able to supply fuel to the fuel supply line <NUM> for a time period which is sufficiently long so as to enable the aircraft <NUM> to perform various airborne manoeuvres. However, the fuel capacity of the airframe-located fuel tank <NUM> is greater than or equal to the fuel capacity of the engine-located fuel tank <NUM> so that the gas turbine engine <NUM> does not have an excessive mass or installation volume.

Claim 1:
A gas turbine engine (<NUM>) comprising a combustor (<NUM>) and a fuel management system (<NUM>), the fuel management system comprising:
a fuel supply line (<NUM>) configured to supply fuel to the combustor;
a recirculation line (<NUM>) configured to recirculate excess fuel from the fuel supply line to an engine-located fuel tank (<NUM>) via a fuel cooling device (<NUM>) configured to reject heat from the excess fuel; and
a heat exchanger (<NUM>) configured to reject heat from a thermal load (<NUM>) of the gas turbine engine to fuel in the fuel management system, wherein the heat exchanger is disposed on the fuel supply line or on the recirculation line;
wherein the fuel supply line is configured to receive fuel from an external source (<NUM>) and from the engine-located fuel tank,
characterised in that the fuel management system further comprises
a fuel pump (<NUM>) on the fuel supply line (<NUM>), wherein the fuel pump is downstream from a mixing point (<NUM>) where the excess fuel from the recirculation line (<NUM>) flows into the fuel supply line and upstream from a recirculation point (<NUM>) where the recirculation line receives the excess fuel from the fuel supply line.