A gas turbine engine includes: a combustor that combust the fuel and having an exit, a combustor exit temperature (T40) is the average temperature of flow and a combustor exit pressure (P40) is the total pressure there; a turbine including a rotor having a leading edge and a trailing edge, and wherein a turbine rotor entry temperature (T41) is an average temperature of flow at the leading edge and a turbine rotor entry pressure (P41) is the total pressure there; and a compressor having an exit, wherein a compressor exit temperature (T30) is the average temperature of flow at the exit from the compressor and a compressor exit pressure (P30) is the total pressure there (all at cruise conditions). A method of determining at least one fuel characteristic includes changing a fuel supplied to the engine; and determining a change in a relationship between T30 or P30, T40 and T41, or of P40 and P41, respectively.

A method of operating an aircraft that includes a propulsion system. The propulsion system includes a gas turbine engine and a fuel tank arranged to provide fuel to the gas turbine engine. The method includes: determining at least one fuel characteristic of the fuel arranged to be provided to the gas turbine engine; and controlling the propulsion system based on the at least one fuel characteristic.

A method of operating an aircraft that includes a propulsion system. The propulsion system includes a gas turbine engine and a fuel tank arranged to provide fuel to the gas turbine engine. The method includes: determining at least one fuel characteristic of the fuel arranged to be provided to the gas turbine engine; and controlling the propulsion system based on the at least one fuel characteristic.

A method of generating a maintenance schedule for an aircraft including one or more gas turbine engines powered by an aviation fuel. The method includes: determining one or more fuel characteristics of the fuel; and generating a maintenance schedule according to the one or more fuel characteristics. Also disclosed is a method of maintaining an aircraft, a maintenance schedule generation system and an aircraft.

A method of operating an aircraft including a gas turbine engine and a plurality of fuel tanks arranged to provide fuel to the gas turbine engine, where at least two of the fuel tanks contain fuels with different fuel characteristics. The method includes obtaining a flight profile for a flight of the aircraft; and determining a fuelling schedule for the flight based on the flight profile and the fuel characteristics. The fuelling schedule governs the variation with time of how much fuel is drawn from each tank. Fuel input to the gas turbine engine may then be controlled in operation in accordance with the fuelling schedule.

A method of controlling a propulsion system of an aircraft, the propulsion system comprising a gas turbine engine arranged to be powered by a fuel and at least one variable inlet guide vane—VIGV, comprises obtaining at least one fuel characteristic of the fuel being provided to the gas turbine engine; and making a change to scheduling of the at least one VIGV based on the at least one obtained fuel characteristic.

A propulsion system for an aircraft comprises a gas turbine engine; a plurality of fuel tanks arranged to contain different fuels to be used to power the gas turbine engine, wherein the fuels have different calorific values; and a fuel manager. The fuel manager is arranged to store information on the fuel contained in each fuel tank and to control fuel input to the gas turbine engine in operation by selection of a specific fuel or fuel combination from one or more of the plurality of fuel tanks based on thrust demand of the gas turbine engine such that a fuel with a lower calorific value is supplied to the gas turbine engine at lower thrust demand.

A gas turbine fuel heating system is disclosed having at least one coalescing filter configured to accept a main fuel supply and a plurality of fuel circuit heaters. Each fuel circuit heater can be configured to accept an independent fuel circuit portion of the main fuel supply leaving the at least one coalescing filter and also configured to accept a heating medium circuit portion of a heating medium. The system can have a plurality of scrubbers, a plurality of fuel circuit manifolds, and a plurality of fuel premix tubes. A controller circuit determines the MWI for each independent fuel circuit portion and adjusts the heating medium circuit portion passed to the corresponding fuel circuit heater to maintain at least one parameter selected from the group consisting of a baseline independent fuel circuit portion MWI setpoint and a predetermined independent fuel circuit portion nozzle gas injector pressure ratio.

A gas turbine arrangement for dual fuel operation has a first manifold that delivers a first fuel or compressor bleed fluid and is connected to a bleed port and a first passage for ejecting fuel or fluid into a combustor space. A second manifold delivers a second fuel and is connected to a second passage for ejecting the second fuel into the combustor space. A control system, when operated with the second fuel, provides the second fuel to the second manifold and continuously opens the bleed valve to provide bleed fluid into the first manifold to replace the first fuel. The control system controls the bleed valve over time by throttling a mass flow of the bleed fluid provided to the first passage or by increasing a mass flow of the bleed fluid provided to the first passage to adapt to fuel properties of the second fuel.

A gas turbine arrangement for dual fuel operation has a first manifold that delivers a first fuel or compressor bleed fluid and is connected to a bleed port and a first passage for ejecting fuel or fluid into a combustor space. A second manifold delivers a second fuel and is connected to a second passage for ejecting the second fuel into the combustor space. A control system, when operated with the second fuel, provides the second fuel to the second manifold and continuously opens the bleed valve to provide bleed fluid into the first manifold to replace the first fuel. The control system controls the bleed valve over time by throttling a mass flow of the bleed fluid provided to the first passage or by increasing a mass flow of the bleed fluid provided to the first passage to adapt to fuel properties of the second fuel.