A method of operating a gas turbine engine including: a combustor arranged to combust a fuel; and a fuel management system arranged to provide the fuel to the combustor, wherein the fuel management system includes two fuel-oil heat exchangers through which oil and fuel flow, which are arranged to transfer heat between the oil and fuel and include primary and secondary fuel-oil heat exchangers; a fuel pump arranged to deliver the fuel to the combustor, wherein the fuel pump is located between the heat exchangers; and a recirculation valve located downstream of the primary heat exchanger, the recirculation valve arranged to allow a controlled amount of fuel which has passed through the primary heat exchanger to be returned to the inlet. The method includes selecting one or more fuels such that the calorific value of the fuel provided to the gas turbine engine is at least 43.5 MJ/kg.

A method of operating a gas turbine engine including: a combustor arranged to combust a fuel; and a fuel management system arranged to provide the fuel to the combustor, wherein the fuel management system includes two fuel-oil heat exchangers through which oil and fuel flow, which are arranged to transfer heat between the oil and fuel and include primary and secondary fuel-oil heat exchangers; a fuel pump arranged to deliver the fuel to the combustor, wherein the fuel pump is located between the heat exchangers; and a recirculation valve located downstream of the primary heat exchanger, the recirculation valve arranged to allow a controlled amount of fuel which has passed through the primary heat exchanger to be returned to the inlet. The method includes selecting one or more fuels such that the calorific value of the fuel provided to the gas turbine engine is at least 43.5 MJ/kg.

A method for reducing an engine core speed is disclosed, which includes determining a condition of an engine during operation of the engine, and controlling an engine turbine clearance based on the condition of the engine so as to influence the engine core speed. An engine system comprising an engine core speed reducing system is also disclosed.

A method for reducing an engine core speed is disclosed, which includes determining a condition of an engine during operation of the engine, and controlling an engine turbine clearance based on the condition of the engine so as to influence the engine core speed. An engine system comprising an engine core speed reducing system is also disclosed.

A fuel system for an aircraft is provided having an improved fluid circuit and method of operation. Un-burnt fuel is directed via a return loop towards a fuel tank reservoir. A turbine is located in the return loop and upstream from the fuel tank. The pressurized un-burnt fuel energizes the turbine and the fuel passes to the fuel tank. The turbine is harnessed to a generator for providing a power.

A fuel system for an aircraft is provided having an improved fluid circuit and method of operation. Un-burnt fuel is directed via a return loop towards a fuel tank reservoir. A turbine is located in the return loop and upstream from the fuel tank. The pressurized un-burnt fuel energizes the turbine and the fuel passes to the fuel tank. The turbine is harnessed to a generator for providing a power.

A fluid supply system (1) for turbine engine, includes a high pressure volumetric pump (4), a fluid metering device (6) and a control valve (8) configured to vary the flow rate of fluid in a bypass circuit (14) so as to regulate the pressure difference between an input and an output of the metering device (6). The control valve (8) includes an obturator, the variable position of which is measured by a sensor (20). An electronic regulation system (3) compares the measured position of the obturator with a position set-point of the obturator determined as a function of a flight condition of the aircraft and/or a measured fluid temperature and corresponding to a fluid flow rate set-point in the bypass circuit (14). The flow rate of the high pressure pump (4) is commanded so that the measured position of the obturator adapts to the position set-point.

In accordance with at least one aspect of this disclosure, a variable displacement pump system can include, a variable displacement pump disposed in a main line and configured to supply pressure to receive a low pressure fluid and to output a high pressure fluid. The main line can connect a hydraulic fluid source to a plurality of system actuators, where the variable displacement pump is disposed in the main line between the hydraulic fluid source and the plurality of system actuators to pressurize the hydraulic fluid.

In accordance with at least one aspect of this disclosure, a variable displacement pump system can include, a variable displacement pump disposed in a main line and configured to supply pressure to receive a low pressure fluid and to output a high pressure fluid. The main line can connect a hydraulic fluid source to a plurality of system actuators, where the variable displacement pump is disposed in the main line between the hydraulic fluid source and the plurality of system actuators to pressurize the hydraulic fluid.

A fuel system is provided that includes a boost stage, a positive displacement pump and a first bypass valve configured to bypass fuel to one of the boost stage and the positive displacement pump. A second bypass valve is configured to bypass fuel to the other of boost stage and the positive displacement pump.