Premixing the fuel with more air than what is needed from a stoichiometric point of view leads to the desired flame with several hundred degrees lower temperature than the adiabatic flame temperature. Such lean flames are, however, Technology options and plant design issues for fuel-flexible gas turbines 273 prone to instabilities such as oscillating heat release which may in worst case interact with pressure fluctuations depending on the combustor design acoustic properties. The control of thermo-acoustic combustor oscillations is a key issue when developing lowemission gas turbines