Dynamics of Limit Cycle Oscillations in a Multinozzle Lean Direct Injection Combustor

Thermoacoustic oscillations in a high-pressure multinozzle lean direct injection combustor with fuel staging have been examined. The combustor consists of three independently controlled fuel stages, i.e., the pilot, intermediate, and outer fuel stages. Limit-cycle oscillations have been identified for two cases with different fuel supplies to the three stages of the combustor, operating at different equivalence ratios. The oscillation dynamics of the two cases have been characterized and quantified by employing nonlinear time series analysis tools. Phase portraits, recurrence plots, and recurrence quantification methods were used by phase space reconstruction of the scalar pressure measurements. Further comparisons between the two cases were made by correlating the time-resolved OH* chemiluminescence images to the pressure oscillations. Phase averaging and spectral proper orthogonal decomposition were used to understand the flame dynamics between the three fuel stages.