Gas turbine engine and method for reducing nonvolatile particulate matter emissions in the exhaust

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

• a combustor, comprising a combustion chamber and a plurality of fuel spray nozzles configured to inject fuel into the combustion chamber, wherein the plurality of fuel spray nozzles comprises a first subset of fuel spray nozzles and a second subset of fuel spray nozzles, wherein the combustor is operable in a condition in which each of the fuel spray nozzles of the first subset of fuel spray nozzles is supplied with fuel at a greater fuel flow rate than each of the fuel spray nozzles of the second subset of fuel spray nozzles, wherein 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;
• and
• wherein:
• a first idle-maximum take-off (MTO) non-volatile particulate matter (nvPM) emissions index ratio is defined as:
• EI
• idle
• EI
• max
• ⁢
• TO
• where:
• EIidle is the nvPM emissions index in mg/kg of the gas turbine engine operating at around 7% available thrust for given operating conditions;
• and
• EImaxTO is the nvPM emissions index in mg/kg of the gas turbine engine operating at around 100% available thrust for the given operating conditions;
• and
• the first idle-MTO nvPM emissions index ratio of the gas turbine engine is less than 60;
• and
• the method comprises providing fuel comprising a sustainable aviation fuel to the plurality of fuel spray nozzles.