Emissions of non-volatile particulate matter from gas turbine engines combusting sustainable aviation fuel and fossil-based hydrocarbon fuel

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

• a rich burn, quick quench, lean burn (RQL) combustor having a number of fuel spray nozzles in the range of 14-22 or a number of fuel spray nozzles per unit engine core size in the range 2 to 6 where engine core size is defined, at a top of climb operating condition, as:
• Core
• ⁢
• size
• =
• m
• .
• 2
• ⁢
• T
• 3
• P
• 3
• ,
• where {dot over (m)}2=mass flow rate, in lbs per second, of air on entry to a high-pressure compressor, T3=temperature, in Kelvin, of air on exit from the high-pressure compressor, and P3=pressure, in lb inches per second squared per inch squared, of air on exit from the high-pressure compressor such that a unit of core size is expressed as:
• s
• ·
• K
• 1
• 2
• ·
• in
• ;
• and
• wherein an MTO nvPM emissions index ratio is defined as:
• EI
• maxTO
• ,
• SAF
• EI
• maxTO
• ,
• FF
• where:
• EImaxTO,SAF is the system loss corrected nvPM emissions index in mg/kg of the gas turbine engine when operating at around 100% available thrust for given operating conditions if a fuel provided to the fuel spray nozzles comprises a sustainable aviation fuel (SAF);
• and
• EImaxTO,FF is the system loss corrected nvPM emissions index in mg/kg of the gas turbine engine when operating at around 100% available thrust for the given operating conditions if a fuel provided to the fuel spray nozzles is a fossil-based hydrocarbon fuel;
• the MTO nvPM emissions index ratio of the gas turbine engine is less than 1;
• the gas turbine engine is configured to provide fuel comprising a SAF to the fuel spray nozzles;
• the fuel spray nozzles comprises one or more duplex nozzles and one or more single flow nozzles;
• and
• the combustor comprises one or more ignitors each arranged adjacent to one or more of the duplex nozzles, and/or wherein the number of fuel spray nozzles per unit engine core size is in the range 2.5 to 4.5;
• wherein
• the method comprises providing fuel comprising a sustainable aviation fuel to the fuel spray nozzles.