Combustion instabilities in gas turbine engines often give rise to acoustic resonances. These resonances occur as manifestations of different acoustic modes, of which a single or multiple modes may be present. In this work, the acoustic behavior of a model gas turbine combustor, developed at DLR Stuttgart by Meier, was investigated using both syn(thetic) gas and standard hydrocarbon fuels. Syngas displayed significantly different behavior than hydrocarbon fuels, even when the laminar flame speeds of the fuels were matched. The following operating parameters were systematically varied: equivalence ratio, air mass flow rate, burner temperature, flame speed, and fuel type. The results did not correspond to any one known instability mechanism. It is concluded that, in the current burner configuration, integrated-acoustics occur that involve a combination of mechanisms. These include organ tone resonances, Helmholtz-type instability, and convective-acoustic effects. Another possible factor is the fluid mechanical switching observed between the two swirler air passages, due to blockage caused by flame position and shape. Flame characteristics such as anchoring and liftoff height appear to play a major role in the determination of instability strength. As hydrogen content in syngas is increased, a lifted flame eventually anchors, resulting in a drastic decrease in the acoustic amplitude associated with non-resonating flames. Thus, increasing the flame speed causes two competing effects to occur. Propane acoustic data are collapsed using scaling parameters that indicate that the burner temperature and the air mass flow effects behave independently.
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