Online prediction of the onset of combustion instability based on the computation of damping ratios

A weighed-least mean square algorithm is used to compute the damping ratios of the linearly stable combustion oscillations, which occur prior to the fully developed nonlinear oscillating stage of combustion instability. The computation of damping ratios is based on the model structure of linear second-order oscillators and the pressure spectrum. Pressure obtained from two experiments on a gas turbine combustion simulator is analyzed. In both cases, the damping ratio drops to the global minimum before combustion oscillations develop into the large-amplitude limit-cycle oscillating stage.