Abstract: There is provided a method of operating a gas turbine engine including a combustor. The combustor includes a combustion chamber and a plurality of fuel spray nozzles configured to inject fuel into the chamber. The nozzles include a first and second subset of fuel spray nozzles. The combustor is operable in a condition wherein the first subset is supplied with more fuel than the second. A ratio of the number of nozzles in the first subset to the second is 1:2 to 1:5. The method includes operating the engine so a reduction of 20-80% in an average of particles/kg of nvPM in the exhaust when the engine is operating at 85% available thrust for given operating conditions and when the engine is operating at 30% is obtained when fuel provided to the nozzles is a sustainable aviation fuel instead of a fossil-based hydrocarbon fuel. Also provided is a gas turbine engine for an aircraft.

Abstract: A gas turbine engine includes an engine core with a combustor; a turbine including turbine blades; a compressor as a source of cooling air for the turbine blades; and an inducer to accelerate and direct the cooling air onto the turbine blades, and a modulating valve to allow or block cooling air flow into a subset of airflow passageways of the inducer; and a fuel management system to provide fuel to the combustor. The fuel management system includes a primary fuel-oil heat exchanger and a secondary fuel-oil heat exchanger through which oil and the fuel flow, to transfer heat between the oil and the fuel. A method of operating the engine includes using the modulating valve to adjust the cooling air flow based on turbine inlet temperature; and transferring 200-600 kJ/m3 of heat to the fuel from the oil in the primary fuel-oil heat exchanger at cruise conditions.

Abstract: A gas turbine engine has a first subset of fuel spray nozzles and a second subset of fuel spray nozzles. A combustor is operable with the first subset of fuel spray nozzles supplied with fuel at a greater flow rate than each of the second subset of fuel spray nozzles. A ratio of the first subset of fuel spray nozzles to the second subset of fuel spray nozzles is 1:2 to 1:5. A first idle-MTO nvPM emissions index ratio is: EI idle EI max ? TO , where: EIidle is the nvPM emissions index in mg/kg operating at around 7% available thrust; EImaxTO is the nvPM emissions index in mg/kg of the gas turbine engine operating at around 100% available thrust; and the first idle-MTO nvPM emissions index ratio of the gas turbine engine is less than 60. A sustainable aviation fuel (SAF) can be provided to the fuel spray nozzles.

Abstract: A gas turbine engine for an aircraft, comprising: a combustor; a fuel-oil heat exchanger arranged to receive fuel from a fuel tank on board the aircraft and transfer heat from the oil to the fuel; a fuel return line arranged to return at least some fuel that has passed through the heat exchanger to the fuel tank; and a modulator valve arranged to modulate the flow of fuel along the fuel return line such that a ratio of a temperature, in Kelvin, of fuel in the fuel tank to a temperature, in Kelvin, of fuel being delivered to the combustor is less than 0.56. Methods of operating a gas turbine engine are also disclosed.

Abstract: A gas turbine engine for an aircraft, comprising: a combustor; a fuel-oil heat exchanger arranged to receive fuel from a fuel tank onboard the aircraft and transfer heat from the oil to the fuel; a fuel return line arranged to return at least some fuel that has passed through the heat exchanger to the fuel tank; and a modulator valve arranged to modulate the flow of fuel along the fuel return line, wherein the modulator valve is arranged to initiate return of fuel to the fuel tank when fuel having passed through the heat exchanger is at a temperature of at least 120° C. A method of operating a gas turbine engine is also disclosed.

Abstract: A gas turbine engine for an aircraft, comprising: a combustor; a fuel-oil heat exchanger arranged to receive fuel and transfer heat from the oil to the fuel so as to raise the fuel temperature to at least 120° C. on entry to the combustor; a fuel recirculation line arranged to recirculate at least some fuel on a fuel flow path from a first point on the fuel flow path to a second point on the fuel flow path, the second point upstream of the first point; and a modulator valve arranged to modulate the flow of fuel along the fuel recirculation line. A method of operating a gas turbine engine is also disclosed.

Abstract: A gas turbine engine for an aircraft, comprising: a combustor; a fuel-oil heat exchanger arranged to receive fuel and transfer heat from the oil to the fuel so as to raise the fuel temperature to at least 120° C. on entry to the combustor; a fuel recirculation line arranged to recirculate at least some fuel on a fuel flow path from a first point on the fuel flow path to a second point on the fuel flow path, the second point upstream of the first point; and a modulator valve arranged to modulate the flow of fuel along the fuel recirculation line. A method of operating a gas turbine engine is also disclosed.

Abstract: A gas turbine engine for an aircraft, comprising: a combustor; a fuel-oil heat exchanger arranged to receive fuel from a fuel tank on board the aircraft and transfer heat from the oil to the fuel; a fuel return line arranged to return at least some fuel that has passed through the heat exchanger to the fuel tank; and a modulator valve arranged to modulate the flow of fuel along the fuel return line such that a ratio of a temperature, in Kelvin, of fuel in the fuel tank to a temperature, in Kelvin, of fuel being delivered to the combustor is less than 0.56. Methods of operating a gas turbine engine are also disclosed.

Abstract: A method of operating an aircraft including 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 proposing or initiating a change to a flight profile of the aircraft based on the at least one fuel characteristic. For example, intended route and/or altitude of the aircraft may be changed based on the one or more fuel characteristics.

Abstract: A method of operating a gas turbine engine including an engine core including a turbine, compressor, combustor to combust a fuel, and core shaft connecting the turbine and compressor; a fan upstream of the engine core; a fan shaft; a gearbox that receives an input from the core shaft and outputs drive to the fan via the fan shaft; a primary oil loop system to supply oil to the gearbox; and a heat exchange system. The method includes controlling the heat exchange system to adjust fuel viscosity to be lower than or equal to 0.58 mm2/s on entry to the combustor at cruise conditions.

Abstract: A gas turbine engine includes an engine core with a combustor; a turbine including turbine blades; a compressor as a source of cooling air for the turbine blades; and an inducer to accelerate and direct the cooling air onto the turbine blades, and a modulating valve to allow or block cooling air flow into a subset of airflow passageways of the inducer; and a fuel management system to provide fuel to the combustor. The fuel management system includes a primary fuel-oil heat exchanger and a secondary fuel-oil heat exchanger through which oil and the fuel flow, to transfer heat between the oil and the fuel. A method of operating the engine includes using the modulating valve to adjust the cooling air flow based on turbine inlet temperature; and transferring 200-600 kJ/m3 of heat to the fuel from the oil in the primary fuel-oil heat exchanger at cruise conditions.

Abstract: 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. At least two of the fuel tanks contain fuels with different fuel characteristics. The method includes obtaining a flight profile for a portion of a flight of the aircraft; and determining a fueling schedule for the portion of the flight based on the flight profile and the fuel characteristics, the fueling schedule governing 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 fueling schedule.

Abstract: A power system for an aircraft includes one or more gas turbine engines arranged to burn a fuel so as to provide power to the aircraft; a plurality of fuel tanks each arranged to contain a fuel to be used to provide power to the aircraft; and a fuel manager. At least two of the fuel tanks contain different fuels, which have different proportions of a sustainable aviation fuel. The fuel manager is arranged to store information on the fuel contained in each fuel tank; and to control fuel supply so as to select a specific fuel accordingly to power at least the majority of operations on the ground. The fuel manager may additionally identify which tank contains the fuel with the highest proportion of a sustainable aviation fuel; and that fuel may be used to power at least the majority of operations on the ground.

Abstract: A gas turbine engine comprising a variable geometry combustor having fuel injectors, a rich-burn zone, a quick-quench zone, and a lean-burn zone, and further comprising quench ports for admitting quench air to the quick-quench zone; a variable geometry airflow arrangement for the variable geometry combustor, which is configured to vary an airflow through the fuel injectors and/or the quench ports; and a control system configured to control the variable geometry airflow arrangement in dependence upon an airflow delivered to the combustor, a fuel flow to the fuel injectors, and a target index of soot emissions to control the quantity of soot produced by combustion.

Abstract: A gas turbine engine for an aircraft includes a staged combustion system having pilot fuel injectors and main fuel injectors. The gas turbine engine further includes a fuel delivery regulator arranged to control delivery of fuel to the pilot and main fuel injectors, and a fuel characteristic determination module configured to determine one or more fuel characteristics of the fuel being supplied to the staged combustion system. A controller is configured to determine a staging point defining the point at which the staged combustion system is switched between pilot-only operation and pilot-and-main operation, the staging point being determined based on the determined one or more fuel characteristics, the controller being configured to control the staged combustion system according to the determined staging point.

Abstract: A gas turbine engine for an aircraft includes a staged combustion system having pilot fuel injectors and main fuel injectors. The gas turbine engine further includes a fuel delivery regulator arranged to control delivery of fuel to the pilot and main fuel injectors, and a fuel characteristic determination module configured to determine one or more fuel characteristics of the fuel being supplied to the staged combustion system. A controller is configured to determine a staging point defining the point at which the staged combustion system is switched between pilot-only operation and pilot-and-main operation, the staging point being determined based on the determined one or more fuel characteristics, the controller being configured to control the staged combustion system according to the determined staging point.

Abstract: A gas turbine engine includes a staged combustion system having pilot fuel injectors and main fuel injectors. A fuel delivery regulator controls delivery of fuel to the pilot and main fuel injectors, receives fuel from a first fuel source containing a first fuel having a first fuel characteristic and a second fuel source containing a second fuel having a second fuel characteristic. In a transition range of operation between the pilot-only and the pilot-and-main ranges of operation, fuel is delivered to both the pilot and main fuel injectors at a transition staging ratio different from the pilot-and-main staging ratio. The fuel delivery regulator delivers fuel to one or both the pilot and main fuel injectors during the transition range of operation having a different fuel characteristic from fuel delivered to one or both the pilot and main fuel injectors during at least part of the pilot-and-main range of operation.

Abstract: A method of operating a gas turbine engine; the gas turbine engine includes a combustor. The combustor includes a combustion chamber and a plurality of fuel spray nozzles configured to inject fuel into the combustion chamber. The plurality of fuel spray nozzles includes a first subset of fuel spray nozzles and a second subset of fuel spray nozzles. The combustor is operable in a condition in which the first subset of fuel spray nozzles are supplied with more fuel than the second subset of fuel spray nozzles. A ratio of the number of fuel spray nozzles in the first subset of fuel spray nozzles to the number of fuel spray nozzles in the second subset of fuel spray nozzles is in the range of 1:2 to 1:5. The method includes: providing fuel to the one or more fuel-oil heat exchangers. Also provided is a gas turbine engine for an aircraft.

Abstract: A gas turbine engine has a combustor with a combustion chamber and a plurality of fuel spray nozzles including a first subset of nozzles and a second subset of nozzles. The first subset of nozzles are supplied with more fuel than the second subset of nozzles. A ratio of the number of nozzles in the first subset to the number of nozzles in the second subset is in the range of 1:2 to 1:5. A method includes providing fuel to the one or more fuel-oil heat exchangers, transferring heat from oil to the fuel, and providing the fuel from the one or more fuel-oil heat exchangers to the fuel spray nozzles. Heat is transferred from the oil to the fuel to lower a viscosity of the fuel to 0.58 mm2/s or lower on injection of the fuel into the combustion chamber at cruise conditions.

Abstract: A gas turbine engine for an aircraft, including: staged combustion system having pilot fuel injectors and main fuel injectors, staged combustion system being operable in pilot-only range of operation and pilot-and-main range of operation; and fuel delivery regulator arranged to control delivery of fuel to pilot and main fuel injectors. Fuel delivery regulator arranged to receive fuel from a first fuel source containing a first fuel having a first fuel characteristic and a second fuel source containing a second fuel having a different second fuel characteristic. The fuel delivery regulator is arranged to deliver fuel to the pilot fuel injectors during at least part of the pilot-only range of operation having a different fuel characteristic from fuel delivered to one or both of the pilot and main fuel injectors during at least part of the pilot-and-main range of operation. A method of operating a gas turbine engine is also disclosed.