A STUDY OF THE ROLE OF EQUIVALENCE RATIO FLUCTUATIONS DURING UNSTABLE COMBUSTION IN A LEAN PREMIXED COMBUSTOR

The instability occurring in a single-injector lean premixed combustor equipped with an in-scale industrial injector (Solar Turbines' Centaur 50) was characterized from the measurements of pressure in the combustor, heat release from the flame and equivalence ratio in the premixing region. Results clearly show that equivalence ratio fluctuations play an important role in the process of sustaining combustion instabilities by providing the feedback between pressure and heat release fluctuations. Characteristic times associated with the feedback process were determined from the measurements and a detailed time-lag analysis was carried out. The role of equivalence ratio fluctuation in the observed instability seemed to be properly captured by the time-lag model, but the prediction of the occurrence of unstable combustion by the model produced contradictory results in tests employing a slightly modified injector. A passive control approach with the modification of acoustic characteristics in the fuel line resulted in a shift of the instability range towards higher equivalence ratios.