Study of thermo-acoustic instability in gas turbine combustion system fueled by methane enriched with hydrogen

In recent years, more and more efforts are being made toward the use of hydrogen as a fuel in burners designed to work with methane-air mixtures. The use of hydrogen in gas turbines is one of the most promising technical solutions to obtain sustainable combustion during the transition toward a carbon-free future. Interest by academic and industrial research in hydrogen derives from its being a carbon-free fuel and its properties such as higher Lower Heating Value (LHV) and wider flammability limits with respect to other conventional hydrocarbons. Despite these aspects, there are still several challenging technical issues that must be addressed such as the potential flashback and autoignition due to the significantly higher flame speeds and shorter autoignition times. Furthermore, combustion instabilities may occur toward ultra-lean operating points with hydrogen. It is important to be able to predict the behavior of a burner fueled with hydrogen in order to avoid these deleterious phenomena during the design phase. The objective of this thesis is to predict the thermo-acoustic behavior of gas turbine burner with hydrogen enriched fuels. The numerical simulations are performed by solving the problem in the frequency domain using the Helmholtz solver approach. At first, the numerical procedure relying on the combination of a Helmholtz solver and a linear flame law with the introduction of the mean flow has been developed. In this framework, a sensitivity study of the thermo-acoustic instability by varying the Mach number (M), which represents the velocity set at the burner inlet, has been carried out. The second section compares CFD simulations of various fuel combinations performed on laboratory-scale gas turbine burners and on the burner of the micro gas turbine (mGT) AE-T100. The swirled premixed burner developed at Louisiana State University and the bluff body stabilized premixed burner investigated at Vanderbilt University have been selected as laboratory-scale burners. These two laboratory burners, each with its own flame stabilization mechanism, have been demonstrated to be the most effective for adding hydrogen to the mixture. On the first burner, URANS simulations were used to compare the methane-air mixture and the methane enriched with hydrogen blend in terms of equivalence ratio distribution, velocities, and pollutants. RANS simulations of the Vanderbilt burner fueled by pure methane and pure hydrogen mixtures have been developed in order to compare the fluid-dynamic responses of two systems. This last activity has been performed in collaboration with Ansaldo Energia. The CFD simulation on the burner of the AE-T100 micro gas turbine has been performed with methane-air mixtures of 90%vCH4−10%vH2 and 70%vCH4−30%vH2. The simulations on the burner of AE-T100 micro gas turbine have been performed, during the visiting research period of my PhD course, in partnership with the Thermal Engineering and Combustion Unit of the University of MONS, and in particular with professor Ward De Paepe, and researchers Jérémy Bompas, and Alessio Pappa. Finally, the results of CFD simulations of Vanderbilt burner and AE-T100 burner, namely gaseous thermodynamic properties and time delay fields, have been used to perform a FEM analysis with the commercial code COMSOL Multiphysics® by applying a general flame response function (n-τ model). In this framework, an analysis of the physics that leads the thermoacoustic driving mechanism for each burner has been carried out with particular attention on the method of estimation of the time delay τ .