Online Combustor Stability Margin Assessment Using Dynamic Pressure Data

This paper describes a strategy for determining a combustor’s dynamic stability margin. Currently, when turbines are being commissioned or simply going through day to day operation, the operator does not know how the stability of the system is affected by changes to fuel splits or operating conditions unless, of course, pressure oscillations are actually present. We have developed a methodology for ascertaining the stability margin from dynamic pressure data that does not require external forcing and that works even when pressure oscillations have very low amplitudes. This method consists of signal processing and analysis that determines a real-time measure of combustor damping. When the calculated damping is positive, the combustor is stable. As the damping goes to zero, the combustor approaches its stability boundary. Changes in the stability margin of each of the combustor’s stable modes due to tuning, aging, or environmental changes can then be monitored through an on-line analysis of the pressure signal. This paper outlines the basic approach used to quantify acoustic damping and demonstrates the technique on combustor test data.