The Effect of Fuel Composition on Combustion Instability Mode Occurrence in a Model Gas Turbine Combustor

Recently, energy resource depletion and unstable energy prices have become global issues. Worldwide pressure to secure and make more gas and oil available to support global power needs has increased. To meet these needs, alternative fuels composed of various types of fuels have received attention, including biomass, dimethyl ether (DME), and low rank coal. For this reason, the fuel flexibility of the combustion system becomes more important. In this study, H2 and CH4 were selected as the main fuel composition variables and the OH-chemiluminescence measurement technique was also applied. This experimental study was conducted under equivalence ratio and fuel composition variations with a model gas turbine combustor to examine the relation between combustion instability and fuel composition. The combustion instability peak occurs in the H2/CH4 50:50 composed fuel and the combustion instability frequency shifted to higher harmonic of longitudinal mode based on the H2 concentration of the fuel. Based on instability mode and flame length calculation, the effect of the convection time during the instability frequency increasing phenomenon was found in a partially premixed gas turbine combustor. The time-lag analysis showed that the short convection time in a high H2 concentration fuel affects the feedback loop period reduction and, in these conditions, high harmonics of longitudinal mode instability occurs. This fundamental study on combustion instability frequency shifting characteristics was conducted for H2/CH4 composed fuel and the results contribute key information for the conceptual design of a fuel flexible gas turbine and its optimum operation conditions.