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-based thermal management system comprising a heat exchanger configured to thermally couple a fluid and a fuel. A controller is configured to modulate a flow of the fluid to the heat exchanger. A tangible, non-transitory memory is configured to communicate with the controller, which determines a temperature of the fluid, estimates a dissolved oxygen concentration in the fuel using a first fuel temperature, a flight cycle time, and at least one of an altitude measurement or a ambient pressure measurement, and modulates the flow of the fluid to the heat exchanger based on the dissolved oxygen concentration.

<CIT> discloses an aircraft system that includes a fuel reservoir, a turbine engine and a fuel-to-fuel heat exchanger. The heat exchanger is fluidly coupled between the fuel reservoir and the turbine engine.

According to a first aspect there is provided a fuel management system for a gas turbine engine according to claim <NUM>, the fuel management system comprising: a fuel supply line to configured to supply fuel from an inlet to a combustor of the gas turbine engine via a combustor valve, the fuel supply line comprising a first pump and a second pump, the first pump being configured to receive fuel and discharge it at a first low pressure, the second pump being provided by a combustor pump, the second pump being configured to receive fuel discharged from the first pump and discharge it at a second higher pressure for supply to the combustor; the combustor pump being disposed along the fuel supply line upstream of the combustor valve, configured to pressurise fuel to a delivery pressure for the combustor; a downstream heat exchanger configured to reject heat from a downstream thermal load of the gas turbine engine to fuel in the fuel supply line between the inlet and the combustor valve; wherein the combustor valve is configured to pass a burn portion of fuel from the fuel supply line to the combustor; and wherein the fuel management system further comprises a downstream recirculation line configured to recirculate a downstream excess portion of fuel from the fuel supply line, the downstream recirculation line extending from a downstream recirculation point on the fuel supply line between the heat exchanger and the combustor valve; wherein the downstream recirculation line is configured to recirculate the downstream excess portion of fuel for resupply to the fuel supply line, characterised in that the fuel management system further comprises an upstream heat exchanger configured to reject heat from an upstream thermal load of the gas turbine engine to fuel in the fuel supply line upstream of the second pump; and an upstream recirculation line configured to recirculate an upstream excess portion of fuel from the fuel supply line, the upstream recirculation line extending from an upstream recirculation point on the fuel supply line between the upstream heat exchanger and the second pump; wherein the upstream recirculation line is configured to recirculate the upstream excess portion of fuel for resupply to the fuel supply line; and wherein the downstream heat exchanger is downstream of the upstream heat exchanger.

It may be that the heat exchanger is located downstream of the combustor pump. It may be that the downstream recirculation line is configured to recirculate the downstream excess portion of fuel to a fuel tank for subsequent resupply to the fuel supply line.

The fuel management system may further comprise a fuel flow controller configured to: receive a cooling signal relating to a cooling demand of the thermal load; and control the combustor pump to vary a flow rate of fuel through the heat exchanger based on at least the cooling signal to meet the cooling demand of the thermal load.

It may be that the thermal load comprises a process fluid circuit configured to circulate a process fluid, wherein the heat exchanger is configured to reject heat from the process fluid to fuel in the fuel supply line between the combustor pump and the combustor valve; and wherein the cooling signal relates to a temperature of the process fluid at a temperature monitoring location of the process fluid circuit.

It may also be that the fuel management system further comprises 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 at least the burn signal.

Otherwise, it may be that the fuel flow controller is configured to: receive a burn signal relating to a fuel demand of the combustor; and control the combustor pump and the combustor valve based on at least the cooling signal and the burn signal to meet the cooling demand of the thermal load and to meet the fuel demand of the combustor. The fuel management system may further comprise a flow sensor configured to monitor a burn flow rate of the burn portion of fuel and the control of the combustor pump and the combustor valve to meet the fuel demand of the combustor may be based on at least the monitored burn flow rate.

It may be that the upstream heat exchanger is located between the first pump and the second pump. It may be that the upstream heat exchanger is configured to reject the heat from the upstream thermal load to fuel in the fuel supply line between the first pump and the second pump.

The fuel management system may be configured to control flow through each of the upstream recirculation line and the downstream recirculation line using respective upstream and downstream recirculation valves, the downstream recirculation valve being provided by the combustor valve; wherein the fuel management system is operable in at least: an upstream recirculation mode in which the upstream recirculation valve is open and the downstream recirculation valve is closed; and a downstream recirculation mode in which the upstream recirculation valve is closed and the upstream recirculation valve is open.

It may be that the downstream recirculation valve comprises a three-way valve configured to receive fuel from the fuel supply line and selectively discharge fuel to the combustor or the downstream recirculation line.

It may be that, in the upstream recirculation mode, the fuel flow controller is configured to control the first pump to vary a flow rate of fuel through the upstream heat exchanger to meet the upstream cooling demand. It may also be that, in the downstream recirculation mode, the fuel flow controller is configured to control at least the second pump to vary a flow rate of fuel through the downstream heat exchanger to meet the downstream cooling demand. In each of the modes, it may be that the fuel flow controller controls the first pump, the second pump and the downstream recirculation valve to meet the fuel demand of the combustor.

The fuel management system may be further operable in a dual recirculation mode in which the upstream recirculation valve is open and the downstream recirculation valve is open; wherein in the dual recirculation mode, the fuel flow controller is configured to: control the first pump to vary a flow rate of fuel through the upstream heat exchanger to meet the upstream cooling demand; control at least the second pump to vary a flow rate of fuel through the downstream heat exchanger to meet the downstream cooling demand; control the upstream recirculation valve to cause or permit the upstream excess portion of fuel to be recirculated by the upstream recirculation line for resupply to the fuel supply line, the excess portion of fuel corresponding to a difference between the flow rates of fuel through the upstream and downstream heat exchangers.

Further, it may be that the fuel flow controller is configured to receive a cooling signal relating to a cooling demand of the upstream thermal load and that the fuel flow controller is configured to control the first and second pumps and the combustor valve to meet the cooling demands of the upstream and downstream thermal loads, and to meet the fuel demand of the combustor.

The fuel management system may further comprise a reheat fuel supply line configured to supply fuel from the system inlet to a reheat of the gas turbine engine, the reheat fuel supply line extending from a reheat branching point on the upstream recirculation line to the reheat via a reheat pump and a reheat control valve. The fuel flow controller may be additionally configured to control the reheat pump and/or the reheat control valve to meet a fuel demand of the reheat.

According to a second aspect, there is provided a gas turbine engine comprising a fuel management system according to the first aspect, wherein the gas turbine engine directs fuel to the system inlet, and the gas turbine engine provides the combustor, the downstream thermal load, and where present the upstream thermal load and/or the reheat.

As noted elsewhere herein, the present disclosure relates to a gas turbine engine.

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.

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 a previously considered fuel management system <NUM>. The fuel management system <NUM> comprises a fuel supply line <NUM> configured to supply fuel from a fuel management system inlet <NUM> to a combustor <NUM> of the gas turbine engine via a combustor valve <NUM>. The inlet <NUM> is configured to receive fuel from a bulk fuel storage system, such as a fuel tank <NUM> of the gas turbine engine and/or a fuel tank <NUM> of an aircraft. The fuel management system <NUM> further comprises a first pump <NUM> and a second pump <NUM> on the fuel supply line <NUM>. The first pump <NUM> is configured to receive fuel from the system inlet <NUM> and to discharge fuel at a first low pressure. The second pump <NUM> is configured to receive fuel discharged by the first pump <NUM> at the first low pressure and to discharge fuel at a second higher pressure for supply to the combustor <NUM> of the gas turbine engine (that is, the delivery pressure for the combustor <NUM>).

The present disclosure refers to a downstream heat exchanger, and the expression downstream may relate to the heat exchanger being downstream of another heat exchanger on the fuel supply line, being downstream of a pump which pressurises the fuel to a pressure for discharge through the combustor. The disclosure envisages variants of the specific examples in which the respective heat exchanger is downstream of neither of these things (i.e. not downstream of any other heat exchanger, and not downstream of the pump). For example, the heat exchanger may be upstream of the pump, and the pump may otherwise function as described below to draw a flow of fuel through the heat exchanger. As such, while several of the examples refer to a downstream heat exchanger, the disclosure envisages implementations in which the heat exchanger is not "downstream". The same applies to discussion of a "downstream thermal load" which is referred to in the examples because of its association with the downstream heat exchanger.

The fuel management system <NUM> comprises a downstream heat exchanger <NUM> located downstream of the second pump <NUM>. The downstream heat exchanger <NUM> is configured to exchange heat from a downstream thermal load <NUM> of the gas turbine engine to fuel in the fuel supply line <NUM> at a location between the second pump <NUM> and the combustor <NUM>. The combustor valve <NUM> is configured to pass a burn portion of fuel from the fuel supply line <NUM> to the combustor <NUM> via the second pump <NUM> and the downstream heat exchanger <NUM>. Accordingly, the fuel supply line <NUM> is configured to supply fuel from the system inlet <NUM> to the combustor <NUM> via the combustor valve <NUM> such that fuel being passed to the combustor <NUM> (i.e. the burn portion of fuel) has been subject to pressurisation to the delivery pressure by the second pump <NUM> and has also passed through the downstream heat exchanger <NUM>.

The fuel management system <NUM> further comprises a recirculation line <NUM> configured to recirculate an excess portion of fuel from the fuel supply line <NUM> for resupply to the fuel supply line <NUM>. The recirculation line <NUM> extends from the combustor valve <NUM> to a fuel management system outlet <NUM>. Further, the recirculation line <NUM> is configured to recirculate the excess portion of fuel to the fuel tank <NUM> via the fuel management system outlet <NUM> for subsequent resupply to the fuel supply line <NUM>.

The fuel management system further comprises a recirculation heat exchanger <NUM> located on the recirculation line <NUM> between the combustor valve <NUM> and the system outlet <NUM>. The recirculation heat exchanger <NUM> is configured to reject heat from the downstream thermal load <NUM> of the gas turbine engine to fuel in the recirculation line <NUM> (i.e. to the excess portion of fuel).

The excess portion is the portion of fuel flowing in the fuel supply line <NUM> that does not pass to the combustor <NUM>, and so a flow rate of the excess portion is equal to the total flow rate in the fuel supply line (upstream of the recirculation line) less the flow rate of the burn portion. A flow rate of the excess portion of fuel is dependent on both a fuel demand of the combustor <NUM> and a cooling demand of the downstream thermal load <NUM>.

The fuel demand corresponds to a flow rate of fuel which is required to be passed to and burned by the combustor <NUM> in order to operate the combustor <NUM> at an operational setpoint. The cooling demand corresponds to an amount of heat rejection required from the downstream thermal load <NUM> according to operation of the downstream thermal load (which may be separately controlled). The cooling demand is met by heat exchange between fuel in the fuel management system <NUM> and the downstream thermal load <NUM> , which in this example occurs in both the downstream heat exchanger <NUM> and the recirculation heat exchanger <NUM> in order to provide adequate cooling to the downstream thermal load <NUM>.

The provision of the recirculation heat exchanger <NUM> along the recirculation line <NUM> provides cooling capacity to the fuel management system <NUM> in addition to that provided by the downstream heat exchanger <NUM> on the line to the combustor <NUM>, such that the fuel management system <NUM> is able to meet the cooling demand of the downstream thermal load <NUM> independently of controlling the fuel demand of the combustor <NUM>, in particular by varying the recirculating flow of excess fuel.

<FIG> shows a schematic view of a first example fuel management system 500A for a gas turbine engine not forming part of the claimed invention. The fuel management system 500A comprises a fuel supply line <NUM> configured to supply fuel from a fuel management system inlet <NUM> to a combustor <NUM> of the gas turbine engine via a combustor valve <NUM>. The inlet <NUM> is configured to receive fuel from a bulk fuel storage system, such as a fuel tank <NUM> of the gas turbine engine and/or a fuel tank <NUM> of an aircraft. The fuel management system 500A further comprises a combustor pump <NUM> located upstream of the combustor valve <NUM> along the fuel supply line <NUM>. The combustor pump <NUM> is 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 fuel management system 500A comprises a downstream heat exchanger <NUM> located on the fuel supply line <NUM> located between the system inlet <NUM> and the combustor valve <NUM> (for example downstream of the combustor pump <NUM>). The downstream heat exchanger <NUM> is configured to exchange heat from a downstream thermal load <NUM> of the gas turbine engine to fuel in the fuel supply line <NUM> at a location between the system inlet <NUM> and the combustor valve <NUM> (for example between the combustor pump <NUM> and the combustor valve <NUM>). Accordingly, the fuel supply line <NUM> is configured to supply fuel from the system inlet <NUM> to the combustor <NUM> via the combustor valve <NUM> such that fuel passing through the combustor valve <NUM> has been subject to pressurisation to the delivery pressure by the combustor pump <NUM> and has also passed through the downstream heat exchanger <NUM>.

The combustor valve <NUM> is configured to pass 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 the fuel, constituting a portion of a total or maximum flow rate in the fuel management system, which.

The fuel management system 500A further comprises a downstream recirculation line <NUM> configured to recirculate a downstream excess portion of fuel from the fuel supply line <NUM> for resupply to the fuel supply line <NUM>. The downstream recirculation line extends from a downstream recirculation point <NUM> on the fuel supply line <NUM>, which is located between the downstream heat exchanger <NUM> and the combustor valve <NUM>, inclusive. In the example of <FIG>, the downstream recirculation point <NUM> is located at the combustor valve <NUM>. In variants of this example, the downstream recirculation point <NUM> may be located at an outlet <NUM> of the downstream heat exchanger <NUM>, or at an intermediate position between the outlet <NUM> of the downstream heat exchanger <NUM> and the combustor valve <NUM>.

In the example of <FIG>, the downstream recirculation line <NUM> is configured to recirculate the downstream excess portion of fuel to the fuel tank <NUM> via a fuel management system outlet <NUM> for subsequent resupply to the fuel supply line <NUM>. However, it will be appreciated that in variants of this example, the downstream recirculation line <NUM> may be configured to recirculate the downstream excess portion of fuel to the fuel supply line <NUM> at a location on the fuel supply line <NUM> which is upstream of the downstream heat exchanger <NUM>, either directly or via one or more other components (such as a local engine-located fuel tank) without returning to the fuel tank <NUM>. Also in the example of <FIG>, the downstream recirculation line <NUM> is provided with a pressure reducing element <NUM> (such as a pressure reducing valve or an orifice plate). The downstream excess portion of fuel is received from the fuel supply line <NUM> at the delivery pressure for the combustor <NUM>. The pressure reducing element <NUM> is configured to reduce the pressure of the downstream excess portion of fuel prior to subsequent resupply to the fuel supply line <NUM>.

The total flow rate of fuel within the fuel supply line <NUM> between the combustor pump <NUM> and the combustor valve <NUM> is controllable by control of the combustor pump <NUM> and may be referred to as a total downstream portion of fuel. This downstream portion of fuel passes through the downstream heat exchanger <NUM>, such that heat transfer at the downstream heat exchanger is controllable by control of the combustor pump <NUM>.

The burn portion is a portion of the total downstream portion of fuel within the fuel supply line <NUM> between the combustor pump <NUM> and the combustor valve <NUM> which is passed to the combustor <NUM> for combustion therein. The downstream excess portion of fuel is a portion of the total downstream portion of fuel which is not passed to the combustor <NUM> for combustion therein. Instead, the downstream excess portion of fuel is passed through the downstream heat exchanger <NUM> and is then recirculated by the downstream recirculation line <NUM>.

As described above, the combustor valve <NUM> is configured to pass the burn portion of fuel from the fuel supply line <NUM> to the combustor <NUM>. Any fuel within the fuel supply line <NUM> between the downstream heat exchanger <NUM> and the combustor valve <NUM> which is not passed to the combustor <NUM> by the combustor valve <NUM> (i.e. the downstream excess fuel portion) is recirculated by the downstream recirculation line <NUM>. A split between the burn portion and the downstream excess portion is therefore controlled by 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 downstream excess portion is directed into the downstream recirculation line <NUM>.

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

The cooling demand of the downstream thermal load <NUM> corresponds to a flow rate of fuel which is required to be passed through the downstream heat exchanger <NUM> in order to provide a sufficient rate of heat transfer at the downstream heat exchanger <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. An operational setpoint of the combustor <NUM> may be related to a quantity of thrust demanded from 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 500A 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 500A is in use.

In view of the discussion above, it follows that the flow rate of the downstream excess portion of fuel is dependent on both the fuel demand of the combustor <NUM> and the cooling demand of the downstream thermal load <NUM>.

When the fuel demand of the combustor <NUM> corresponds to a flow rate of the burn portion of fuel which is greater flow rate of the total downstream flow than is required to meet the cooling demand, it may be that the flow rate of the downstream excess portion of fuel is zero or minimal.

Conversely, when the cooling demand corresponds to a greater flow rate of the total downstream portion of fuel than the flow rate of the burn portion required to meet the fuel demand of the combustor <NUM>, the flow rate of the downstream excess portion is equal to the difference between the flow rate of the total downstream portion and the flow rate of the burn portion.

The fuel management system 500A may further comprise a fuel flow controller <NUM> configured to receive a downstream cooling signal relating to a cooling demand of the downstream thermal load <NUM>. The fuel flow controller <NUM> may be configured to control the combustor pump <NUM> so as to vary a flow rate of the total downstream portion of fuel based on at least the downstream cooling signal in order to meet the cooling demand of the downstream thermal load <NUM>.

The fuel flow controller <NUM> may be further configured to receive a burn signal relating to a fuel demand of the combustor <NUM>. The fuel flow controller <NUM> may be configured to simultaneously control the combustor pump <NUM> so as to vary flow rate of the total downstream portion of fuel in order to meet the cooling demand of the downstream thermal load <NUM>, and to control the combustor valve <NUM> and also the combustor pump <NUM> where necessary so as to vary a flow rate of the burn portion of fuel in order to match the fuel demand of the combustor <NUM>.

The combustor <NUM> generally receives a flow rate of fuel as required to operate the combustor <NUM> at a selected operational setpoint. It may be that the downstream thermal load <NUM> is relatively tolerant of receiving excess cooling (e.g. unlikely to suffer damage or underperformance if there is excess cooling), but less tolerant to insufficient cooling. Therefore, controller <NUM> may be configured to ensure that the fuel demand of the combustor <NUM> is matched and to ensure that the cooling demand of the downstream thermal load <NUM> is met. In some operating conditions, it may only be possible to ensure that the fuel demand of the combustor <NUM> is met by providing excess cooling to the downstream thermal load <NUM> (which is still considered to be meeting the cooling demand), and the controller may be configured to permit such excess cooling.

In the example of <FIG>, the downstream thermal load <NUM> comprises a downstream process fluid circuit <NUM> which is configured to circulate a process fluid through the downstream heat exchanger <NUM>. In such examples, the downstream heat exchanger <NUM> is configured for heat exchange from the process fluid to fuel in the fuel supply line <NUM> between the combustor pump <NUM> and the combustor valve <NUM>. As an example, the downstream 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 downstream cooling signal may relate to an operating state of the downstream thermal load <NUM>. For example, if the downstream thermal load <NUM> comprises a gearbox <NUM> of the gas turbine engine, the operating state of the downstream 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 downstream cooling signal may relate to a temperature of the process fluid at a downstream temperature monitoring location of the downstream process flow circuit <NUM>. The downstream process fluid circuit <NUM> may comprise a downstream temperature sensor <NUM> configured to monitor the temperature of the process fluid at the downstream temperature monitoring location of the downstream process fluid circuit <NUM> and configured to provide the downstream cooling signal to the fuel flow controller <NUM>, wherein the downstream cooling signal relates to the temperature of the process fluid at the downstream temperature monitoring location.

The fuel flow controller <NUM> may control the combustor pump <NUM> to vary the flow rate of the total downstream portion of fuel and thereby maintain the temperature of the process fluid at the downstream 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 temperature monitoring location (e.g. using a PID controller or any other suitable control process).

The fuel management system 500A may further comprise a combustor flow sensor <NUM> configured to monitor a burn flow rate of the burn portion of fuel (i.e. the flow rate of fuel passed to the combustor <NUM> by the combustor valve <NUM>). The fuel flow controller <NUM> may control the combustor pump <NUM> and the combustor valve <NUM> so as to vary the burn flow rate in order to meet the fuel demand of the combustor, 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 burn flow rate 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 tends to require a lower burn flow rate than the flow rate of the total downstream fuel portion to meet the downstream cooling demand. Decentralised control of the fuel flow for the combustor and for cooling may be appropriate. For example, the fuel management system 500A may comprise a separate burn controller <NUM> to the fuel flow controller <NUM>, 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 demand signal. The fuel flow controller <NUM> may be configured to act independently to receive the cooling signal and to control the combustor pump <NUM> based on the cooling signal only.

Considering the above disclosure, the fuel management system 500A is configured to selectively vary cooling capacity so as to meet the cooling demand of the downstream thermal load <NUM> while matching the fuel demand of the combustor <NUM>, by recirculating the downstream excess portion of fuel which is required to meet the cooling demand of the downstream thermal loads but which is not required to match the fuel demand of the combustor <NUM>. In contrast to the previously-considered example of <FIG>, the cooling demand is adequately met without requiring an additional heat exchange apparatus on the downstream recirculation line <NUM> itself. Such apparatus is associated with an increased mass and an increased size of the fuel management system 500A.

The fuel management system 500A may further comprise a reheat fuel supply line <NUM> which is configured to supply fuel from the system inlet <NUM> to a reheat <NUM> of the gas turbine engine via the fuel supply line <NUM> (e.g. via an upstream portion of the fuel supply line <NUM>), a reheat pump <NUM> and a reheat control valve <NUM>. In the example of <FIG>, the reheat fuel supply line <NUM> extends from a reheat branching point <NUM> on the fuel supply line <NUM> to the reheat <NUM> via the reheat pump <NUM> and the reheat control valve <NUM>, wherein the reheat branching point <NUM> is located upstream of the combustor pump <NUM>.

<FIG> shows a schematic view of a second example fuel management system 500B for a gas turbine engine according to the present invention. The second example fuel management system 500B is generally similar to the fist example fuel management system 500A, with like reference numerals indicating common or similar features. In contrast to the first example fuel management system 500A, the second fuel management system 500B comprises a first pump <NUM> and a second pump <NUM> on the fuel supply line <NUM>. The first pump <NUM> is configured to receive fuel from the system inlet <NUM> and to discharge fuel at a first low pressure. The second pump <NUM> corresponds to the combustor pump <NUM> discussed above with respect to <FIG>, and the two expressions "second pump" and "combustor pump" may be referred to interchangeably throughout this disclosure. The second pump <NUM> is configured to receive fuel discharged by the first pump <NUM> at the first low pressure and to discharge fuel at a second higher pressure for supply to the combustor <NUM> of the gas turbine engine (that is, the delivery pressure for the combustor <NUM>).

The fuel management system 500B further comprises an upstream heat exchanger <NUM> and an upstream recirculation line <NUM>. The upstream heat exchanger <NUM> is located upstream of the second pump <NUM> (for example between the first pump <NUM> and the second pump <NUM>) and is configured to transfer heat from an upstream thermal load <NUM> of the gas turbine engine to fuel in the fuel supply line <NUM> at a location upstream of the second pump <NUM>. The upstream recirculation line <NUM> is configured to recirculate an upstream excess portion of fuel from the fuel supply line <NUM> for resupply to the fuel supply line <NUM>. The upstream recirculation line <NUM> extends from an upstream recirculation point <NUM> on the fuel supply line <NUM>, the upstream recirculation point <NUM> being located between the upstream heat exchanger <NUM> and the second pump <NUM>, inclusive.

Accordingly, the fuel supply line <NUM> is configured to supply fuel from the system inlet <NUM> to the combustor <NUM> via the combustor valve <NUM> such that fuel passing through the combustor valve <NUM> has been subject to pressurisation to the delivery pressure by the second pump <NUM>, having also passed through the first pump <NUM>, the upstream heat exchanger <NUM> and the downstream heat exchanger <NUM>. When referring to the example of <FIG>, the combustor valve <NUM> may be referred to as a downstream circulation valve <NUM> and functions as such.

In the example of <FIG>, the upstream recirculation line <NUM> is configured to recirculate the upstream excess portion of fuel to the fuel tank <NUM> via a path which joins with the downstream recirculation line <NUM> for subsequent resupply to the fuel supply line <NUM>, such that portions of fuel within the upstream and downstream recirculation lines are in parallel with each other and join to define a combined recirculation line.

If present, the pressure reducing element <NUM> is configured to reduce the pressure of the downstream excess portion of fuel prior to joining the combined recirculation line to prevent the prevent the downstream excess portion of fuel (which is at the second higher pressure) from causing the upstream excess portion of fuel (which is at the first low pressure) to be driven back through the upstream recirculation line <NUM> toward the upstream recirculation point <NUM> and/or to reduce the pressure of the downstream excess portion of fuel prior to subsequently resupply to the fuel supply line <NUM>. Additionally or alternatively, the upstream recirculation line <NUM> may be provided with a non-return valve <NUM> configured to prevent the downstream portion of fuel from causing the upstream portion of fuel to be driven back through the upstream recirculation line <NUM> toward the upstream recirculation point <NUM>, as shown in the example of <FIG>.

It will be appreciated that in other examples, the upstream recirculation line <NUM> (or the combined recirculation line) may be configured to recirculate the upstream excess portion of fuel to the fuel supply line <NUM> at a location on the fuel supply line <NUM> which is upstream of the upstream heat exchanger <NUM>, either directly or via one or more other components (such as a local engine-located fuel tank) without returning to the fuel tank <NUM>.

In the example of <FIG>, the upstream recirculation point <NUM> is located at an upstream recirculation valve <NUM>. In variants of this example, the upstream recirculation point <NUM> may be located at an outlet of the upstream heat exchanger <NUM>, or at an intermediate position between the outlet of the upstream heat exchanger <NUM> and the second recirculation valve <NUM>. The upstream valve <NUM> is configured to direct the upstream excess portion of fuel from the fuel supply line <NUM> into the upstream excess recirculation line <NUM> and to pass fuel to the second pump <NUM>. As a result, a split between the total downstream portion of fuel and the upstream excess portion of fuel is controllable by actuation of the upstream recirculation valve <NUM>.

The total flow rate of fuel within the fuel supply line <NUM> between the first fuel pump <NUM> and the second fuel pump <NUM> (the total upstream flow rate) may be controllable by control of the first fuel pump <NUM>. Consequently, heat exchange at the upstream heat exchanger <NUM> is also controllable by control of the first fuel pump <NUM>.

In the examples of <FIG> and <FIG>, the total downstream portion of fuel is provided at the delivery pressure for the combustor <NUM> by the second fuel pump <NUM>. In the example of <FIG>, the flow rate of the total downstream portion of fuel cannot exceed a total upstream flow rate because the second fuel pump <NUM> is only configured to receive fuel discharged by the first pump <NUM>.

Like the combustor valve <NUM>, it may be that the upstream recirculation valve <NUM> comprises a two-port valve which is configured to restrict the flow of fuel within the fuel supply line <NUM> passing through to the combustor pump <NUM> (i.e. the total downstream portion of fuel) such that a remaining portion of the fuel is directed into the upstream recirculation line <NUM> as the upstream excess portion of fuel. The fuel management system 500B may be configured to control the flow of fuel through the upstream recirculation line <NUM> and through the downstream recirculation line <NUM> by actuating the upstream recirculation valve <NUM> and the combustor valve <NUM>, which may be referred to as a downstream recirculation valve <NUM>.

In a variant of this example, the fuel management system 500B may not comprise the upstream recirculation valve <NUM>, and the flow rate of the upstream recirculation excess portion of fuel recirculated by the upstream recirculation line <NUM> may be controlled according to a differential flow rate between the first fuel pump <NUM> and the second fuel pump <NUM>. For example, this may occur when the second pump <NUM> is configured to accept only a limited flow rate corresponding to an operating speed of the second pump itself (e.g. a positive displacement pump).

The flow rate of the total upstream portion of fuel is dependent on a cooling demand of the upstream thermal load <NUM>, the cooling demand of the downstream thermal load <NUM> and/or the fuel demand of the combustor <NUM>. For example, the cooling demand of the upstream thermal load <NUM> may require that the flow rate of the total upstream portion of fuel be increased so as to promote heat rejection from the upstream thermal load <NUM>. Additionally or alternatively, the flow rate of the total downstream portion of fuel required to meet the cooling demand of the downstream thermal load <NUM> and/or to match the fuel demand of the combustor <NUM> may require that the flow rate of the total upstream portion of fuel be increased.

In a similar way to the cooling demand of the downstream thermal load <NUM>, the cooling demand of the upstream thermal load <NUM> corresponds to a flow rate of fuel which is required to be passed through the upstream heat exchanger <NUM> in order to provide a sufficient rate of heat transfer from the upstream thermal load <NUM> to the fuel in the fuel supply line <NUM>.

A flow rate of the upstream excess portion of fuel is equal to a difference between the flow rate of the total upstream portion of fuel and the flow rate of the total downstream portion of fuel and may be zero in some conditions.

The fuel flow controller <NUM> may be configured to receive an upstream cooling signal relating to the cooling demand of the upstream thermal load <NUM> in a similar manner to that described above with respect to the downstream cooling signal. In the example of <FIG>, the upstream thermal load <NUM> comprises an upstream process fluid circuit <NUM> which is configured to circulate a process fluid through the upstream heat exchanger <NUM>. In such examples, the upstream heat exchanger <NUM> is configured to transfer heat from the process fluid to fuel in the fuel supply line <NUM>. In various examples, the upstream thermal load <NUM> may include a heat source <NUM>' of the gas turbine engine. The upstream thermal load <NUM> may otherwise have similar features to the downstream thermal load <NUM>, and the upstream cooling signal may relate to similar states or parameters with respect to the upstream thermal load <NUM> compared to which the downstream cooling signal relates with respect to the downstream thermal load <NUM>.

For instance, the upstream cooling signal may relate to a temperature of the process fluid at an upstream temperature monitoring location of the upstream process flow circuit <NUM>. The upstream process fluid circuit <NUM> may comprise an upstream temperature sensor <NUM> configured to monitor the temperature of the process fluid at the upstream temperature monitoring location of the upstream process fluid circuit <NUM> and configured to provide the upstream cooling signal to the fuel flow controller <NUM>, wherein the upstream cooling signal relates to the temperature of the process fluid at the upstream temperature monitoring location. The fuel flow controller <NUM> may control the first pump <NUM> to vary the flow rate of the total upstream portion of fuel and thereby maintain the temperature of the process fluid at the upstream temperature monitoring location within a target temperature range of a process fluid temperature setpoint.

Generally, the fuel flow controller <NUM> may configured to receive the downstream cooling signal, the upstream cooling signal and the burn signal. The fuel flow controller <NUM> may be further configured to control the first pump <NUM>, the second pump <NUM>, the downstream recirculation valve <NUM> and where present the upstream recirculation valve <NUM> based on the upstream cooling signal, the downstream cooling signal and the burn signal to meet all of: the cooling demand of the upstream thermal load <NUM>, the cooling demand of the downstream thermal load <NUM>, and the fuel demand of the combustor <NUM>.

In examples in which it is present, the upstream recirculation valve <NUM> has an open state and a closed state. In the open state, the upstream recirculation valve <NUM> is configured to direct fuel into the upstream recirculation line <NUM> for recirculation thereby. In the closed state, the upstream recirculation valve <NUM> is configured to prevent fuel from being directed into the upstream recirculation line <NUM> for recirculation thereby. Similarly, the downstream recirculation valve <NUM> (which in the example of <FIG> is the combustor valve <NUM>) has an open state and a closed state. In the open state, the downstream recirculation valve <NUM> is configured to direct fuel into the downstream recirculation line <NUM> for recirculation thereby. In the closed state, the downstream recirculation valve <NUM> is configured to prevent fuel from being directed into the downstream recirculation line <NUM> for recirculation thereby.

The fuel management system 500B is configured to selectively operate in an upstream recirculation mode in which the upstream recirculation valve <NUM> is open such that the upstream excess portion of fuel is recirculated by the upstream recirculation line <NUM>, and in which the downstream recirculation valve <NUM> is closed such that no fuel is recirculated by the downstream recirculation line <NUM>. The fuel management system 500B is also configured to selectively operate in a downstream recirculation mode in which the downstream recirculation valve <NUM> is open such that the downstream excess portion of fuel is recirculated by the downstream recirculation line <NUM>, and in which the upstream recirculation valve <NUM> is closed such that no fuel is recirculated by the upstream recirculation line <NUM>.

To this end, it may be that the upstream recirculation valve <NUM> comprises a three-way valve which is configured to receive fuel from the supply line <NUM> and to selectively discharge fuel into the upstream recirculation line <NUM> and pass fuel to the second pump <NUM>. Likewise, it may be that the downstream recirculation valve <NUM> comprises a three-way valve which is configured to receive fuel from the supply line <NUM> and to selectively discharge fuel into the downstream recirculation line <NUM> and pass fuel to the combustor <NUM>, as shown in the example of <FIG>. Use of three way valves for the respective recirculation valves enables the fuel management system 500B to selectively close the respective recirculation lines.

When in the upstream recirculation mode, the fuel flow controller <NUM> may be configured to control the first pump <NUM> to vary the flow rate of fuel through the upstream heat exchanger <NUM> (i.e. to vary the flow rate of the total upstream portion of fuel) to meet the upstream cooling demand. When in the downstream recirculation mode, the fuel flow controller <NUM> may be configured to control the second pump <NUM> and optionally also the first pump <NUM> to vary the flow rate of fuel through the downstream heat exchanger <NUM> (i.e. to vary the flow rate of the total downstream portion of fuel) to meet the downstream cooling demand. Additionally, in both modes, the fuel flow controller <NUM> controls the first pump <NUM>, the second pump <NUM> and the downstream recirculation valve <NUM> to match the fuel demand of the combustor <NUM>. This configuration provides a simple control logic which is able to meet the respective cooling demands while simultaneously matching the fuel demand of the combustor <NUM>.

In addition, the fuel management system 500B may be configured to selectively operate in a dual recirculation mode in which the upstream recirculation valve <NUM> is open such that the upstream excess portion of fuel is recirculated by the upstream recirculation line <NUM> and in which the downstream recirculation valve <NUM> is open such that the downstream excess portion of fuel is recirculated by the downstream recirculation line <NUM>. This may permit a higher flow rate in the upstream heat exchanger to meet the upstream cooling demand than the flow rate required in the downstream heat exchanger, which may also be larger than the burn flow rate required by the combustor. By permitting the upstream excess flow to be recirculated upstream of the second pump, additional work on that quantity of fuel by second pump is avoided, and excessive cooling at the downstream heat exchanger can be avoided, thereby conserving cooling capacity in the recirculated fuel for subsequent use.

As in the example of <FIG>, the fuel management system 500B further comprises a reheat fuel supply line <NUM> which is configured to supply fuel from the system inlet <NUM> to a reheat <NUM> of the gas turbine engine via the fuel supply line <NUM>, the upstream recirculation line <NUM>, a reheat pump <NUM> and a reheat control valve <NUM>. In the example of <FIG>, the reheat fuel supply line <NUM> extends from a reheat branching point <NUM> on the upstream recirculation line <NUM> to the reheat <NUM> via the reheat pump <NUM> and the reheat control valve <NUM>. A flow rate of fuel provided to the reheat <NUM> is maintained by the reheat pump <NUM> and the reheat control valve <NUM>. The fuel flow controller <NUM> may be further configured to receive a reheat signal relating to a fuel demand of the reheat <NUM>. The fuel flow controller <NUM> may be additionally configured to control the reheat pump <NUM> and/or the reheat control valve to a match a fuel demand of the reheat <NUM> based on at least the reheat signal.

The fuel management system 500B may further comprise a reheat flow sensor <NUM> configured to monitor a reheat flow rate of the fuel provided to the reheat <NUM>. 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 fuel flow controller <NUM> may then control the reheat pump <NUM> and the reheat control valve <NUM> in order to match the fuel demand of the reheat <NUM> based at least on the monitored reheat flow rate. The fuel flow controller <NUM> may control the reheat pump <NUM> and the reheat control valve <NUM> to vary the flow rate of fuel provided to the reheat <NUM> and thereby maintain the monitored reheat flow rate within a target flow rate range of a flow rate of fuel required to match the fuel demand of the reheat <NUM>.

By providing the reheat fuel supply line <NUM> branching from the upstream recirculation line <NUM>, the reheat line receives fuel at the first low pressure and so the flow and pressure of the fuel provided to the reheat <NUM> may be controlled independently of the fuel which is provided to the combustor <NUM>.

<FIG> shows a schematic view of a gas turbine engine <NUM> comprising a fuel management system <NUM>. The fuel management system <NUM> may be in accordance with the examples discussed above with respect to <FIG> and <FIG>. The gas turbine engine <NUM> provides fuel to the fuel management system inlet <NUM> and further comprises combustor <NUM>, the downstream thermal load <NUM> and optionally the upstream thermal load <NUM> and/or the reheat <NUM>. In the example of <FIG>, the gas turbine engine <NUM> provides fuel to the fuel management system inlet <NUM> from a fuel tank <NUM>. As shown in the example of <FIG>, the gas turbine engine <NUM> may return fuel to the fuel tank <NUM> via the fuel management system outlet <NUM> for subsequent resupply to the fuel management system <NUM>. The fuel tank <NUM> may be disposed within an airframe in which the gas turbine engine <NUM> is incorporated.

Claim 1:
A fuel management system (500B) for a gas turbine engine (<NUM>), the fuel management system comprising:
a fuel supply line (<NUM>) to configured to supply fuel from an inlet (<NUM>) to a combustor (<NUM>) of the gas turbine engine via a combustor valve (<NUM>), the fuel supply line comprising a first pump (<NUM>) and a second pump (<NUM>), the first pump being configured to receive fuel and discharge it at a first low pressure, the second pump being provided by a combustor pump (<NUM>), the second pump being configured to receive fuel discharged from the first pump and discharge it at a second higher pressure for supply to the combustor (<NUM>);
the combustor pump (<NUM>) being disposed along the fuel supply line upstream of the combustor valve, configured to pressurise fuel to a delivery pressure for the combustor;
a downstream heat exchanger (<NUM>) configured to reject heat from a downstream thermal load (<NUM>) of the gas turbine engine to fuel in the fuel supply line between the inlet and the combustor valve;
wherein the combustor valve is configured to pass a burn portion of fuel from the fuel supply line to the combustor;
wherein the fuel management system further comprises a downstream recirculation line (<NUM>) configured to recirculate a downstream excess portion of fuel from the fuel supply line, the downstream recirculation line extending from a downstream recirculation point (<NUM>) on the fuel supply line between the heat exchanger and the combustor valve; and
wherein the downstream recirculation line is configured to recirculate the downstream excess portion of fuel for resupply to the fuel supply line;
characterised in that the fuel management system further comprises:
an upstream heat exchanger (<NUM>) configured to reject heat from an upstream thermal load (<NUM>) of the gas turbine engine (<NUM>) to fuel in the fuel supply line upstream of the second pump; and
an upstream recirculation line (<NUM>) configured to recirculate an upstream excess portion of fuel from the fuel supply line, the upstream recirculation line extending from an upstream recirculation point (<NUM>) on the fuel supply line between the upstream heat exchanger and the second pump;
wherein the upstream recirculation line is configured to recirculate the upstream excess portion of fuel for resupply to the fuel supply line; and
wherein the downstream heat exchanger is downstream of the upstream heat exchanger.