Analytical and Experimental Investigation of Frequency of Oscillation Modes in Combustion Chambers of Gas Turbines

Premixed combustion is widely used for simulation of combustion chambers of gas turbines, utilized for low NOx emission applications. However, this category of gas turbine is susceptible to combustion instability. The main aim of this investigation is to focus on thermo-acoustic instability modes in gas turbine combustion chambers. Both analytical and experimental methods are applied for this study. For this purpose, an experimental combustion chamber is designed and fabricated and various experiments are planned and performed in order to achieve the behavior of combustion chamber during stable and unstable conditions. In this research, gaseous propane is introduced as fuel and experiments are performed at nearly atmospheric pressure with equivalence ratios within the range of 0.7 to 1.2. To distinguish the frequency of combustion instability, through various operating conditions, probability density functions, spectral diagrams and the discretized fast Fourier transform of pressure wave oscillations are employed. Moreover, an analytical method is applied and a computer code is written and elaborated for this purpose. Instability frequencies are derived experimentally and analytically and the results are compared with each other. Accordingly, good agreements are observed between the results.