Predicting thermoacoustic combustion instability and lean blowout in turbulent combustors using recurrence quantification analysis

The gas turbine combustors are often suggested to operate at fuel-lean conditions to balance the trade-off between nitrogen oxides and soot formation. However, combustors operating in lean conditions are more susceptible to flame blowout and thermoacoustic instability. Due to the sudden loss of flame inside the combustor, blowout results in direct power loss, whereas thermoacoustic instability leads to large vibrations, loud noise, and structural failure—posing major challenges for the gas turbine combustors. In this research, first, we utilized nonlinear time series techniques like pressure traces, frequency spectra, phase portrait, and recurrence analysis to capture the transition in distinct dynamical regimes of the combustor, starting from combustion noise to flame blowout when air flow rates are varied. Next, we perform recurrence quantification analysis (RQA), which shows distinctive signatures preceding lean blowout (LBO) and thermoacoustic instability (TAI), thereby can be used as early warning measures for predicting both LBO and TAI. Using the recurrence plots (RPs), six different quantification measures are estimated by fixing the recurrence threshold value (ϵ0). Using these quantification measures, the change in dynamic characteristics of pressure signals is characterized as the system approaches LBO and TAI. The combustor shows increased in intermittent oscillations near the LBO and TAI. The results show that RPs and RQA stand out remarkably in performance to capture the dynamical complexity of the acoustic pressure signals. Furthermore, these tools contribute to a better distinction between a stable operation, an unstable operation, and a dynamic state near the blowout.