How to achieve high levels of excitation in the fuel line of a pressurized combustor

The Flame Transfer Function (FTF) is a well-studied key function describing the transient linear in amplitude coupling between aerodynamics and combustion and is used in predicting acoustic stability of a combustor system. However in case of an instability with positive growth rate, the amplitudes rapidly change and the FTF becomes dependent on amplitude; therefore the combustion- aerodynamics coupling becomes nonlinear. Hence for this situation non linearity must be taken into account. A nonlinear description of the flame dynamics can be investigated by increasing the perturbation levels of the aerodynamics upstream of the flame. The flame dynamic is best measured by determining the response of the flame to fluctuations in the fuel mass flow at the burner exit. With this method it is necessary to know the transfer between the fuel flow oscillating device and the mass flow at the burner exit. This fuel line transfer function describes the relationship between (fuel) mass flow fluctuations at the location of fuel injection and the oscillating device. Challenge is to design a fuel line which allows the maximum transfer of the perturbations through fuel injection nozzles. Therefore an investigation has been made to design the optimum fuel line and nozzle combination. Numerical calculations are performed with the commercial code ANSYS CFX 13.0. Variation of different parameters like length and diameter of the fuel line and number and diameter of nozzles are considered. Effect of these parameters on the mixing and propagation of acoustic is discussed.