Identification of nonlinear characteristics of pressure fluctuations at spontaneous combustion instabilities

Combustion power systems are prone to combustion instabilities characterized by large pressure fluctuations and excessive heat transfer. In this study, pressure fluctuation data acquired from an experimental combustor prone to high-frequency combustion instabilities are systematically analyzed to investigate the characteristics of its combustion stability. Once combustion instability occurs, its onset can be identified by an abrupt increase in the root-mean-square value of the pressure fluctuations, and the characteristic frequencies of its sustaining pressure waves have been estimated using Fourier analysis. The application of the nonlinear time series analysis provides meaningful information from data measured before combustion instability occurs. The average mutual information for the determination of the time lag of a state vector shows distinctly different values depending on the eventual occurrence of combustion instability. The dimensions for unfolding any nonlinear structure in the phase space are estimated as five for both cases from the false nearest neighbor analysis. The results, shown as phase space plots constructed in a three-dimensional phase space, reveal contrasting structures closely related to the occurrence of high-frequency combustion instability, which implies that a prediction of combustion instability could be made based upon the analysis results using data taken before its occurrence.