FUEL TEMPERATURE

A method (11000) of operating a gas turbine engine (10) is disclosed, the gas turbine engine (10) comprising an engine core (11) comprising a turbine (19), a compressor (14), a combustor (16) arranged to combust a fuel, and a core shaft (26) connecting the turbine to the compressor; a fan (23) located upstream of the engine core; a fan shaft (42); a main gearbox (30) that receives an input from the core shaft (26) and outputs drive to the fan (23) via the fan shaft (42); a primary oil loop system (2000') arranged to supply oil to lubricate the main gearbox (30); and a heat exchange system (1004, 1006) arranged to transfer heat between the oil and the fuel, the oil having an average temperature of at least 180°C on entry to the heat exchange system (1004, 1006) at cruise conditions. The method (11000) comprises controlling the heat exchange system (1004, 1006) so as to raise the fuel temperature to at least 135°C on entry to the combustor (16) at cruise conditions.