Injector-coupled transverse instabilities in a multi-element premixed combustor

Abstract

Combustion instabilities in a high-pressure, multi-element combustor are studied in order to understand the relationship between the chamber and injector dynamics. A linear array of seven injectors supplies premixed natural gas and air into a rectangular combustion chamber designed to promote high-frequency, transverse thermoacoustic instabilities. The effect of equivalence ratio on the combustion dynamics was investigated for two injector lengths, 62.5 and 125 mm. For all operating conditions, the 125 mm injectors promote high-amplitude instabilities of the fundamental transverse (1T) mode, which has a frequency of 1750–1850 Hz. Reducing the injector length significantly lowers the instability amplitudes for all operating conditions and, for lower equivalence ratio cases, excites an additional mode near 1550 Hz. The delineating feature controlling the growth of the instabilities in each injector configuration is the coupling with axial pressure fluctuations in the injectors that occur in response to the transverse modes in the chamber.

Thermoacoustic Instability Characteristics and Flame/Flow Dynamics in a Multinozzle Lean Premixed Gas Turbine Model Combustor Operated with High Carbon Number Hydrocarbon Fuels

“…The geometrical gap between single-nozzle academic burners and practical annual combustors has motivated the use of multinozzle combustors in the field of thermoacoustic instability research recently. Flame–flame interactions in multinozzle configurations can alter the characteristics of instability in gas turbine combustors significantly, especially the presence of transverse , and azimuthal , instability modes. Moreover, flame responses to acoustic excitation in single- and multinozzle combustors can be considerably different .…”