Thermoacoustic oscillations in a staged multi-nozzle lean direct injection combustor are studied using dynamic pressure measurements and time-resolved OH~* chemiluminescence imaging. Two conditions, one with periodic oscillations and one with intermittent bursts of high-amplitude pressure waves are investigated. Proper orthogonal decomposition and dynamic mode decomposition are used to analyze the results from the flame imaging. Both decomposition techniques correctly extract the dominant fluctuations, related to the fundamental oscillation frequency, in the OH~* emission from the flames of the low-emission fuel stages. The flame response to higher order harmonics are also extracted by both decomposition techniques during limit cycle oscillations but in the case of quasi-periodic intermittent oscillations the modal decomposition methods are disrupted by the increasingly complex flame response. In addition to these decomposition techniques, recurrence analysis of phase space trajectory reconstructed from pressure time trace was performed in order to understand the temporal evolution of the oscillations. It has been identified that the two oscillatory states correspond to deterministic dynamical states. The bursting behavior observed during the intermittent combustion oscillations was identified to correspond to the previously reported dynamical state of intermittency, using recurrence analysis.
展开▼
