Effect of Flame Shape on the Combustion Stability in a Low-Emission Combustor1

A computational and experimental investigation of the processes occurring in premix combustors with swirl stabilization similar to that used in modern gas-turbine engines is described. The combustor burner consists of main and pilot burners. The combustor operates on a mixture of natural gas and air with excess air coefficient from 10 to 2.6. The influence of the fuel fraction in the pilot burner (PFR) with fixed excess air coefficient á on the macrostructure of the flame — the relation between the shape and position of the flame front and the dominating structures of the flow — is examined. The flame front is investigated by means of three-dimensional numerical modeling. Four ma xxx crostructures are observed in the experimental PFR range from 0 to 100% with fixed excess air coefficient á. It is shown that each form of high-frequency combustion instability corresponds to a definite macrostructure of the flame. It is noted that the fuel fractions in the pilot burner at which changes are observed in the flame configuration are associated with the appearance of thermo-acoustic instability.