Fuel viscosity
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 mm 2 /s on entry to the combustor at cruise conditions.
1. A method of operating a gas turbine engine, the gas turbine engine comprising:
an engine core comprising a turbine, a compressor, a combustor arranged to combust a fuel, and a core shaft connecting the turbine to the compressor;
a fan located 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 arranged to supply oil to the gearbox; and
a heat exchange system comprising:
an air-oil heat exchanger through which oil in the primary oil loop system flows;
a fuel-oil heat exchanger through which the oil in the primary oil loop system and the fuel flow such that heat is transferred between the oil and the fuel, and wherein the primary oil loop system branches such that a proportion of the oil can flow along each branch and the air-oil and fuel-oil heat exchangers are arranged in a parallel configuration on different branches of the primary oil loop system; and
a modulation valve arranged to allow the proportion of oil sent via each branch to be varied, wherein
the method comprises controlling the heat exchange system so as to adjust the fuel viscosity to a maximum of 0.58 mm 2 /s on entry to the combustor at cruise conditions,
the gas turbine engine further comprises:
an integrated drive generator; and
a secondary oil loop system arranged to provide oil to the integrated drive generator,
the heat exchange system further comprises a secondary fuel-oil heat exchanger arranged to receive the fuel and oil from the secondary oil loop system, and
the method comprises transferring heat between the oil from the secondary oil loop system and the fuel using the secondary fuel-oil heat exchanger.
2. The method of claim 1 , comprising controlling the heat exchange system so as to adjust the fuel viscosity to between 0.35 mm 2 /s and 0.53 mm 2 /s on entry to the combustor at cruise conditions.
3. The method of claim 1 , comprising controlling the heat exchange system so as to adjust the fuel viscosity to between 0.40 mm 2 /s and 0.48 mm 2 /s on entry to the combustor at cruise conditions.
4. The method of claim 1 , comprising controlling the heat exchange system so as to adjust the fuel viscosity to below 0.58 mm 2 /s on entry to the combustor at cruise conditions.
5. The method of claim 1 , wherein
the heat exchange system further comprises an oil-oil heat exchanger arranged to transfer heat between the oil of the primary oil loop system and the oil of the secondary oil loop system.
6. The method of claim 5 , wherein the oil-oil heat exchanger is downstream of the air-oil and fuel-oil heat exchangers of the primary oil system.
7. The method of claim 5 , wherein the primary oil loop system comprises two branches through which oil flows, to provide the parallel heat exchanger configuration, and wherein the oil-oil heat exchanger is on the same branch as the air-oil heat exchanger.
8. The method of claim 1 , wherein:
the fuel-oil heat exchanger through which oil of the primary oil system flows is a primary fuel-oil heat exchanger; and
the fuel flows through the secondary fuel-oil heat exchanger prior to flowing through the primary fuel-oil heat exchanger, such that heat is transferred from the oil in the secondary oil loop system to the fuel before heat is transferred from the oil in the primary oil system to the fuel.
9. The method of claim 1 , wherein the controlling the heat exchange system so as to adjust the fuel viscosity comprises adjusting an amount of fuel sent through at least one of the primary fuel-oil heat exchanger and the secondary fuel-oil heat exchanger.
10. The method of claim 1 , wherein the heat exchange system comprises at least one bypass pipe arranged to allow fuel to bypass at least one heat exchanger of the heat exchange system, and wherein the controlling the heat exchange system so as to adjust the fuel viscosity comprises adjusting the amount of fuel sent through the bypass pipe instead of through the heat exchanger.
11. The method of claim 1 , wherein the heat exchange system comprises at least one recirculation pipe arranged to take fuel which has already passed through a given heat exchanger of the heat exchange system back to an inlet of that heat exchanger, and wherein the controlling the heat exchange system so as to adjust the fuel viscosity comprises adjusting the amount of fuel sent through the recirculation pipe.
12. A gas turbine engine for an aircraft comprising:
an engine core comprising a turbine, a compressor, a combustor arranged to combust a fuel, and a core shaft connecting the turbine to the compressor;
a fan located upstream of the engine core, the fan comprising a plurality of fan blades;
a gearbox that is arranged to receive an input from the core shaft and output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft;
a primary oil loop system arranged to supply oil to the gearbox;
a heat exchange system comprising:
an air-oil heat exchanger through which oil in the primary oil loop system flows;
a fuel-oil heat exchanger through which the oil in the primary oil loop system and the fuel flow such that heat is transferred between the oil and the fuel, and wherein the primary oil loop system branches such that a proportion of the oil can flow along each branch and the air-oil and fuel-oil heat exchangers are arranged in a parallel configuration on different branches of the primary oil loop system; and
a modulation valve arranged to allow the proportion of oil sent via each branch to be varied;
an integrated drive generator; and
a secondary oil loop system arranged to provide oil to the integrated drive generator, wherein:
the heat exchange system is arranged to adjust the fuel viscosity to a maximum of 0.58 mm 2 /s on entry to the combustor at cruise conditions, and
the heat exchange system further comprises a secondary fuel-oil heat exchanger arranged to receive oil from the secondary oil loop system, wherein the secondary fuel-oil heat exchanger is arranged to transfer heat between the oil from the secondary oil loop system and the fuel with the secondary fuel-oil heat exchanger.
13. The gas turbine engine of claim 12 , wherein the heat exchange system is arranged to adjust the fuel viscosity to between 0.35 mm 2 /s and 0.53 mm 2 /s on entry to the combustor at cruise conditions.
14. The gas turbine engine of claim 12 , wherein the heat exchange system is arranged to adjust the fuel viscosity to between 0.40 mm 2 /s and 0.48 mm 2 /s on entry to the combustor at cruise conditions.
15. The gas turbine engine of claim 12 ,
wherein the heat exchange system further comprises an oil-oil heat exchanger arranged to transfer heat between the oil of the primary oil loop system and the oil of the secondary oil loop system.
16. The gas turbine engine of claim 15 , wherein the oil-oil heat exchanger is positioned downstream of the air-oil and fuel-oil heat exchangers of the primary oil loop system.
17. The gas turbine engine of claim 15 , wherein the oil-oil heat exchanger is positioned on the same branch as the air-oil heat exchanger.
18. The gas turbine engine of claim 12 , wherein:
the fuel-oil heat exchanger through which oil of the primary oil system flows is a primary fuel-oil heat exchanger; and
the heat exchange system is arranged such that fuel flows through the secondary fuel-oil heat exchanger prior to flowing through the primary fuel-oil heat exchanger, such that heat is transferred from the oil in the secondary oil loop system to the fuel before heat is transferred from the oil in the primary oil loop system to the fuel.