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Experimental Study of Combustion Instability in Premixed Gas Turbine Engines

Lean premixed combustion is widely used in recent years as a method to achieve the environmental standards with regard to NOx emission. In spite of the advantages, premixed combustion systems with equivalence ratios less than one are susceptible to combustion instability. To study the lean combustion instability experimentally, one premixed combustion setup, equipped with reactant supplying system, is designed and manufactured. 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 1.5 and fuel mass flow rates of 2 to 4 gr/s. It has been observed that the combustion chamber of the gas turbine becomes unstable when equivalence ratio is less than one. To distinguish the combustion instability, through various operating conditions, probability density functions, spectral diagrams, space distribution of pressure oscillations, along with Rayleigh criteria are employed. Accordingly, equivalence ratio effects in stabilizing the unstable combustion system is investigated experimentally. Moreover, convective delay time is calculated for all experiments and the results are compared with Rayleigh Criteria, showing relatively good agreements. Finally, stability limits are identified, based on inlet mass flow rate and equivalence ratio.