Thermo acoustic flame transfer function prediction for turbulent non-premixed syngas flames

The thermo-acoustic behaviour of non-premixed turbulent syngas flames is investigated by means of transient RaNS Computational Fluid Dynamics simulations. Three cases with two different fuel compositions are considered. Both fuels are combusted in a turbulent non-premixed swirl stabilised mode, and are mixtures of hydrogen, carbon monoxide and nitrogen. One fuel contains methane in addition. The flame transfer function considered here, describes the relation between a perturbation of the fuel mass flow rate and the rate of heat release in the flame. The fuel mass flow is perturbed by an impulse excitation. The investigated geometry is a laboratory scale burner that is designed in the framework of the European Union sponsored HEGSA project. Experimental data are generated in tests at DLR (chemiluminescence and LIF). The CFD results show that methane addition to syngas has a significant influence on the flame transfer function. The addition of methane to syngas induces thermoacoustic damping for higher frequency (¿400 Hz) regions and increases amplification for low frequencies (!200 Hz). The time delay of the transfer function is affected by the addition of methane due to both calorific value and chemical time scale effects. A decrease in inlet temperature also affects the flame transfer function. This is due to the slower chemistry and lower velocity.