Method of ice removal by inducing sudden variation of rotor speed in a gas turbine engine

1. A method of operating a gas turbine engine with discrete pulses in fuel flow causing variations in rotation speed, the gas turbine engine comprising:

a compressor section, the compressor section comprising a compressor rotor having compressor blades;

a combustor;

a turbine section;

a fuel system, the fuel system configured to feed a controlled flow rate of fuel to the combustor; and

a computer, the computer configured to control the controlled flow rate based on instructions stored in a non-transitory media;

the method comprising:

rotating the compressor rotor at a first speed for a period of time;

the computer receiving a signal indicative that icing is occurring or has occurred on the compressor rotor;

in response to the signal, the computer:

varying the controlled flow rate of fuel in the form of a discrete pulse from a first flow rate to a second flow rate to cause a variation of rotation speed of the compressor rotor from the first speed to a second speed to shock the compressor blades; and

varying the flow rate back to the first flow rate;

wherein the variation of rotation speed of the compressor rotor from the first speed to the second speed is performed within less than one second, and wherein the second rotor speed is different from the first rotor speed by at least 2% of the first rotor speed.

2. The method of claim 1 , wherein the signal is indicative that ice has accumulated on the compressor rotor.

3. The method of claim 1 , wherein the variation of rotation speed of the compressor rotor from the first speed to the second speed is performed within less than three quarters of a second.

4. The method of claim 1 wherein the second rotor speed is different from the first rotor speed by between 5 and 10% of the first rotor speed.

5. The method of claim 1 , wherein the period of time is at least 5 seconds.

6. The method of claim 5 , wherein the period of time is at least 10 seconds.

7. The method of claim 1 , wherein a ratio of a difference of the compressor rotor speed between the first speed and the second speed, in RPM, to a time elapsed between the varying of the compressor rotor speed from the first speed to the second speed and the return of the compressor rotor to the first speed, is between 100 and 400.

8. The method of claim 7 , wherein the ratio is between 150 and 300.

9. The method of claim 1 , further comprising discretely and intermittently repeating the method steps of:

rotating the compressor rotor at the first speed for a repetition time;

varying the controlled flow rate of fuel in the form of a discrete pulse from the first flow rate to the second flow rate to cause a variation of rotation speed of the compressor rotor from the first speed to the second speed to shock the compressor blades; and

varying the controlled flow rate back to the first flow rate.

10. The method of claim 9 , wherein the repetition time is between 10 and 20 seconds.

11. The method of claim 9 , wherein a ratio of the repetition time to an impulse time is of between 15 and 30, wherein the impulse time is the time elapsed between the variation of the compressor rotor speed from the first speed to the second speed and back to the first speed.

12. The method of claim 9 , wherein the discreetly and intermittently repeating is performed for a duration of between 1 minute and 10 minutes.

13. The method of claim 12 , wherein the discreetly and intermittently repeating is performed for a duration of between 1 minute and 4 minutes.

14. A computer program product for operating a gas turbine engine with discrete pulses in fuel flow causing variations in rotation speed,

wherein the computer program product is stored in a non-transitory memory, the computer program product comprising computer-readable instructions for controlling a flow rate of fuel supplied to a combustor of the gas turbine engine, wherein when the computer-readable instructions are executed by a processor of a computer in response to an input indicative that icing is occurring or has occurred on a compressor rotor of the gas turbine engine, the computer-readable instructions cause the processor to:

vary the flow rate of fuel in the form of a discrete pulse from a first flow rate to a second flow rate to cause a variation of rotation speed of the compressor rotor from a first speed to a second speed to shock the compressor blades; and

vary the flow rate back to the first flow rate;

wherein the variation of rotation speed of the compressor rotor from the first speed to the second speed is performed within less than one second, and wherein the second rotor speed is different from the first rotor speed by at least 2% of the first rotor speed.