Thermoacoustic Coupling in a Multinozzle Staged Combustor

摘要

Periodic behavior in the reaction zone of a multiple-nozzle combustor undergoing self-sustaining combustion oscillations is examined. Understanding of the thermoacoustic interactions among heterogeneous arrays of swirl cups is important to enable the implementation of this low NO_x approach. This combustor has three stages: a high-swirl pilot stage, a low-swirl intermediate stage, and a low-swirl outer stage. Liquid jet A fuel is supplied to all three fuel stages, which is characteristic of the high-power operation mode. Four test conditions are examined in which thermoacoustic coupling is observed at a well-defined frequency. Phase-averaged images of the OH~* chemilumi-nescence emission show dramatic changes in the OH~* emission, which is dominated by recurrent weakening and reignition downstream of the low-stability intermediate and outer fuel stages. The pilot stage reaction zone also displays periodic variation in intensity that is 90 deg out of phase and precedes the intermediate and outer fuel stages. One operating condition results in pressure oscillation amplitude that is intermittently high and low. A new method using the proper orthogonal decomposition time coefficients is used to quantify the relative periodicity of the OH~* images. The nozzle design and the interactions between nozzle stages combine to allow significant thermoacoustic coupling in this burner under certain conditions.