Oil coking mitigation in a gas turbine engine

1. A method comprising:

prior to shutdown of a gas turbine engine, predicting, by a processor, a projected oil-wetted metal temperature in a lubrication system of the gas turbine engine at shutdown based on one or more thermal models that predict one or more soak-back temperature projections of one or more engine components at or after shutdown of the gas turbine engine, wherein the one or more engine components comprise one or more bearing compartments;

determining, by the processor, a coking index based on the projected oil-wetted metal temperature and a coking limit threshold associated with the one or more engine components;

sensing a fuel temperature in a fuel system of the gas turbine engine, wherein the fuel system is in thermal communication with the lubrication system; and

triggering an oil coking mitigation action as a shutdown management event of the gas turbine engine based on the coking index and a margin in the sensed fuel temperature to take additional heat transfer from oil in the lubrication system without risk of fuel coking, the oil coking mitigation action adjusting heat transfer associated with the lubrication system prior to shutdown of the gas turbine engine.

2. The method of claim 1 , wherein the one or more thermal models determine one or more modeled temperatures of the one or more engine components based on at least one sensed engine temperature, a sensed rotor speed of the gas turbine engine, and at least one gas path temperature of the gas turbine engine.

3. The method of claim 1 , wherein the projected oil-wetted metal temperature is determined based on at least one sensed oil temperature.

4. The method of claim 1 , wherein the oil coking mitigation action comprises increasing fuel recirculation within the fuel system to increase oil-to-fuel heat transfer.

5. The method of claim 1 , wherein the oil coking mitigation action comprises actuating a fuel-return-to-tank valve to reduce generator heat loading on the lubrication system.

6. The method of claim 1 , wherein the oil coking mitigation action comprises increasing fuel flow beyond engine demands to increase cooling capacity of the fuel system with respect to the lubrication system.

7. The method of claim 1 , wherein the oil coking mitigation action comprises opening an air/oil cooler valve to increase air flow in an air/oil cooler of the lubrication system.

8. The method of claim 1 , wherein the oil coking mitigation action comprises reducing or shifting electrical generator loads of the gas turbine engine.

9. The method of claim 1 , wherein the oil coking mitigation action comprises increasing an idle dwell time prior to shutdown based on determining that the gas turbine engine is operating in a test mode.

10. A thermal management system of a gas turbine engine, the thermal management system comprising:

a lubrication system comprising an oil flow path between a plurality of engine components, wherein the engine components comprise one or more bearing compartments;

a fuel system operable to deliver fuel for combustion within the gas turbine engine, wherein the fuel system is in thermal communication with the lubrication system; and

a controller operable to:

predict, prior to shutdown of the gas turbine engine, a projected oil-wetted metal temperature in the lubrication system at shutdown of the gas turbine engine based on one or more thermal models that predict one or more soak-back temperature projections of one or more of the engine components at or after shutdown of the gas turbine engine;

determine a coking index based on the projected oil-wetted metal temperature and a coking limit threshold associated with one or more of the engine components;

sense a fuel temperature in the fuel system; and

trigger an oil coking mitigation action as a shutdown management event of the gas turbine engine based on the coking index and a margin in the sensed fuel temperature to take additional heat transfer from oil in the lubrication system without risk of fuel coking, the oil coking mitigation action adjusting heat transfer associated with the lubrication system prior to shutdown of the gas turbine engine.

11. The thermal management system of claim 10 , wherein the one or more thermal models determine one or more modeled temperatures of the one or more engine components based on at least one sensed engine temperature, a sensed rotor speed of the gas turbine engine, and at least one gas path temperature of the gas turbine engine.

12. The thermal management system of claim 10 , wherein the projected oil-wetted metal temperature is determined based on at least one sensed oil temperature.

13. The thermal management system of claim 10 , wherein the oil coking mitigation action comprises increasing fuel recirculation within the fuel system to increase oil-to-fuel heat transfer.

14. The thermal management system of claim 10 , wherein the oil coking mitigation action comprises actuating a fuel-return-to-tank valve to reduce generator heat loading on the lubrication system.

15. The thermal management system of claim 10 , wherein the oil coking mitigation action comprises increasing fuel flow beyond engine demands to increase cooling capacity of the fuel system with respect to the lubrication system.

16. The thermal management system of claim 10 , wherein the oil coking mitigation action comprises opening an air/oil cooler valve to increase air flow in an air/oil cooler of the lubrication system.

17. The thermal management system of claim 10 , wherein the oil coking mitigation action comprises reducing or shifting electrical generator loads of the gas turbine engine.

18. The thermal management system of claim 10 , wherein the oil coking mitigation action comprises increasing an idle dwell time prior to shutdown based on determining that the gas turbine engine is operating in a test mode.