Methods and systems for modulating fuel flow for gas turbine engines

1. A method of combustion stability control in a gas turbine engine, the method comprising:

a) receiving by a stability controller information regarding environmental and operating conditions;

b) comparing the environmental and operating conditions to pre-programmed information to determine if a likelihood of combustion instability exists;

c) determining optimal fuel modulation frequency and amplitude for the environmental conditions to reduce combustion instability, if a likelihood of combustion instability exists; and

d) actuating at least one fuel modulation valve to, at the optimal fuel modulation frequency and amplitude, reduce combustion instability, if a likelihood of combustion instability exists.

2. A method of combustion stability control in a gas turbine engine, the method comprising:

a) receiving by a stability controller information from at least one sensor regarding combustion pressure wave amplitude and frequency;

b) comparing the combustion pressure wave amplitude to a pre-programmed amplitude threshold to determine if excessive combustion instability exists;

c) determining optimal fuel modulation frequency and amplitude for the frequency of pressure waves to reduce the amplitude of the combustion pressure wave; and

d) actuating at least one fuel modulation valve to pulse fuel at a selected frequency and amplitude to reduce combustion pressure wave amplitude.

3. The method of claim 2 , further comprising:

selecting a fuel modulation frequency at which the fuel modulation valve pulses fuel that is substantially equal to the frequency of combustion pressure waves that exceed the pressure amplitude threshold, wherein the valve pulsation frequency is out-of-phase with the combustion pressure wave frequency.

4. The method of claim 3 , further comprising:

adjusting a relative phase of fuel pulsation, with respect to instability pressure waves, to minimize the magnitude of combustion instability pressure waves.