Combustion instability characteristics of H2/CO/CH4 syngases and synthetic natural gases in a partially-premixed gas turbine combustor: Part II-Time lag analysis

In continuation of part I, which reported the characteristics of high-frequency multi-mode combustion instability for various compositions of syngases, this study analyzes the instability mechanism using the characteristic length and time scales relating the particular combustion instability of high multi-modes. Here, time lag analysis based on the Rayleigh criterion has been used and the times of convection, acoustic, ignition delay, chemical reaction, and newly developed skewness are considered. The skewness time, which reflects the wave distortion resulting from the addition of a higher harmonic component of combustion instability, is obtained from the analytic derivation of the interval between single-mode and multi-mode waves. The proportion of skewness time in the total lagging time was varied from zero for complete single mode to 11% for high harmonic multi-mode according to the fuel variation. The effectiveness of skewness time on the time lag analysis was verified from the experimental results of 98 cases and it showed remarkable improvement in the prediction accuracy of multi-mode instability from 88.8% to 99.0%. From the analysis results, it can be concluded that skewness time should be considered as an important parameter when calculating characteristic time scales for high multi-mode, and this method can be usefully applied for the development of an optimal design for and safe operation of a syngas-fired gas turbine combustor.