Flame transfer function prediction for non-premixed syngas combustion

The thermo-acoustic behaviour of non-premixed turbulent syngas flames is investigated. For that purpose the flame transfer functions of two syngas fuel compositions are calculated with transient RaNS. Both compositions contain hydrogen (H₂), carbon monoxide (CO) and nitrogen (N2). One of them, also contains methane (CH4). Syngas is combusted in a non-premixed mode. The flame transfer function is an important parameter in investigating thermo-acoustic instabilities in gas turbine combustors. In this case, the flame transfer function is defined as the relation between a perturbation of the burner fuel exit velocity and the response of the rate of heat release. First of all, the steady state situation was calculated. After that, a transient calculation was started to find out whether any unsteady behaviour was present in the solution. As this was not the case, a perturbation on the mass flow of fuel was imposed. The method of impulse excitation was used for this. The flame transfer functions of the two fuel compositions will be presented. It shows that methane addition to syngas has a significant influence on the flame transfer function. The time delay in the transfer function is found to depend on fuel flow velocity and combustion characteristics. Because of different chemical kinetics the time delay is changed by the addition of methane to syngas.