Thermo-acoustic instabilities are an important consideration in the design of modern power generation gas turbine combustors. While the design process must consider many competing requirements, such as temperature profiles, emissions, robustness to auto-ignition and flameholding, thermoacoustics is one of the most challenging to predict, and therefore design for. This is particularly true in the case of liquid-fueled systems, where the phenomenon results from a complex system of coupled multi-physics phenomena: fuel atomization and transport, mixing, reactive kinetics and acoustics. Nevertheless, emissions-compliant liquid fuel capability is becoming increasingly important to GT operators, thus it is critical to be able to predict the thermoacoustic instabilities of these combustors.
In this work we present an approach to model the thermoacoustic feedback loop for a realistic liquid fuel nozzle in a single burner configuration. The approach is based on an analytical liquid-fuel diffusion flame model to provide the fluctuating heat release response to inflow perturbations. This is coupled with a 3D FEM description of the acoustic response of the single burner rig through a time-domain Green’s function model to predict the growth and saturation of pressure oscillations. The necessary flame model parameters are calibrated based on a range of test data obtained from the single burner rig with a tunable combustor length. The results are shown to compare well with test data across a range of operating conditions, and for two different nozzle geometries.