Aircraft engine and method of operating aircraft engine for reducing nonvolatile particulate matter emissions

A method of operating a gas turbine engine, the gas turbine engine comprising:

• a fuel distribution system comprising a controller and a fuel metering unit;
• and
• a combustor comprising a combustion chamber and a plurality of fuel spray nozzles, wherein the plurality of fuel spray nozzles are configured to inject fuel into the combustion chamber with a total mass flow rate controlled by the fuel metering unit,
• the plurality of fuel spray nozzles comprises a first subset of fuel spray nozzles and a second subset of fuel spray nozzles,
• the combustor is operable so that each fuel spray nozzle of the first subset of fuel spray nozzles is supplied with a first portion of the fuel at a first mass flow rate,
• each fuel spray nozzle of the second subset of fuel spray nozzles is supplied with a second portion of the fuel at a second mass flow rate, and the first mass flow rate is greater than the second mass flow rate,
• a ratio of a number of the fuel spray nozzles of the first subset of fuel spray nozzles to a number of the fuel spray nozzles of the second subset of fuel spray nozzles is in a range of 1:2 to 1:5;
• maximum take-off (MTO) non-volatile particulate matter (nvPM) emissions index ratio-modified fuel flow rate in kg/s is defined as:
• EI
• maxTO
• ,
• SAF
• EI
• maxTO
• ,
• FF
• ×
• W
• f
• ,
• maxTO
• EImaxTO,SAF is nvPM emissions index in mg/kg of the gas turbine engine when operating at around 100% available thrust for given operating conditions, when the fuel provided to the plurality of fuel spray nozzles comprises a sustainable aviation fuel;
• EImaxTO,FF is nvPM emissions index in mg/kg of the gas turbine engine when operating at around 100% available thrust for the given operating conditions, when the fuel provided to the plurality of fuel spray nozzles is a fossil-based hydrocarbon fuel;
• and
• Wf,maxTO is a total mass flow rate in kg/s of the fuel provided to the plurality of fuel spray nozzles when the gas turbine engine is operating at around 100% available thrust for the given operating conditions;
• the method further comprising using the fuel metering unit to control the fuel comprising the sustainable aviation fuel and provided to the plurality of fuel spray nozzles to achieve around 100% available thrust for the given operating conditions and the MTO nvPM emissions index ratio-modified fuel flow rate is less than 2 kg/s.