A method of determining an onset of coking in fuel flowing through a gas turbine engine fuel system,
- the gas turbine engine fuel system comprising:
- a fuel delivery subsystem to deliver fuel to a gas turbine engine;
- an oil cooling subsystem configured to receive heated oil from the gas turbine engine;
- a fuel delivery conditioning system including a fuel/oil cooler that is downstream of and in fluid communication with the fuel delivery subsystem to receive the fuel and is in fluid communication with the oil cooling subsystem to receive the heated oil, the fuel/oil cooler configured to transfer heat from the heated oil to the fuel to increase a temperature of the fuel;
- a fuel manifold downstream of and fluidly connected to the fuel/oil cooler, the fuel manifold providing the fuel to fuel nozzles of the gas turbine engine;
- a fuel temperature sensor downstream of the fuel/oil cooler;
- a first optical coking sensor disposed upstream from the fuel/oil cooler and a second optical coking sensor disposed downstream from the fuel/oil cooler;
- wherein the first optical coking sensor outputs a first signal and the second optical coking sensor outputs a second signal;
- wherein the first signal corresponds to a first measurement of a first amount of ultraviolet light detected at various wavelengths having passed through the fuel indicating a first thermal stress of the fuel delivered by the fuel delivery subsystem, and the second signal corresponds to a second measurement of a second amount of ultraviolet light detected at the various wavelengths having passed through the fuel indicating a second thermal stress of the fuel downstream of the fuel/oil cooler and delivered into the fuel manifold;
- a controller in signal communication with the fuel temperature sensor, the first optical coking sensor and the second optical coking sensor;
- the controller configured to determine an onset of coking in the fuel, wherein the controller:
- compares the first measurement indicating the first thermal stress of the fuel to the second measurement indicating the second thermal stress of the fuel;
- determines a deviation of the second measurement compared to the first measurement in which the second amount detected is reduced compared to the first amount detected indicating a change in thermal stress of the fuel;
- upon detection of the deviation, the controller utilizes the deviation as a threshold indicative of the onset of coking in the fuel and determines a fuel temperature using a temperature measurement signal output from the fuel temperature sensor and sets the fuel temperature as a coking temperature indicative of the onset of coking in the fuel at the threshold;
- the method comprising:
- delivering the fuel from the fuel delivery subsystem to drive the gas turbine engine;
- delivering the fuel to the fuel delivery conditioning system including the fuel/oil cooler;
- selectively delivering the heated oil from the gas turbine engine to the oil cooling subsystem and to the fuel/oil cooler, the fuel/oil cooler configured to transfer heat from the heated oil to the fuel to increase the temperature of the fuel;
- outputting, via the first at least one optical coking sensor and the second optical coking sensor, respectively, the first signal and the second signal indicating, respectively, the first thermal stress and the second thermal stress a thermal stress of the fuel that occurs with a changing temperature of the fuel;
- and
- determining, via the controller, the onset of coking in the fuel based on the deviation of the second measurement of the second signal compared to the first measurement of the first signal, utilizing the deviation as the threshold indicative of the onset of coking and setting the fuel temperature measured by the fuel temperature sensor as the coking temperature.