The influence of humidity and fuel composition on thermoacoustic flame characteristics is investigated. This is an important aspect in the development of combustion chambers for humidified gas turbines. Thermoacoustic issues are in the focus of the current investigation. These pressure pulsations result from the interaction of combustor acoustics with an unsteady heat release of the flame and have a negative influence on the combustion process and can even damage components of the engine. A key point concerning combustion dynamics is the role of convective time lags which are determined by the temporal delay between the appearance of a perturbation and the response of the flame. Experiments are conducted with different fuel mixtures containing natural gas, hydrogen, and nitrogen, each with steam contents in the air mass flow of up to 40%. The multi-microphone method and OH* chemiluminescence measurements with a photomultiplier and an intensified CCD camera are used to determine the flame transfer function and flame dynamics. It is observed that the characteristics of the flame response are related to the flame shape and position rather than to the fuel composition or the steam content. Using a Strouhal-number normalization based on the bulk velocity of the annular jet and the distance between fuel injection and the flame, a good agreement between the phases of the flame transfer functions of all flames attached to the burner outlet is found.

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