An experimental study of the transfer function of a ducted, laminar premixed flame

This paper presents an experimental study of the transfer function of a ducted, laminar, premixed flame. This transfer function is defined as the ratio of the fluctuations in flame heat release to the flow velocity modulations at the base of the flame. A conical, laminar, propane/air premixed flame stabilised at the rim of the burner and confined in a glass tube is considered. The flame is excited by incident acoustic waves generated by a loud speaker over a range of forcing frequencies. The fluctuations of heat release due to corrugation of the flame by the acoustic wave is measured using a photo-multiplier tube (PMT) while the flow velocity fluctuation is determined by considering the loud speaker diaphragm motion and assuming conservation of classical acoustic energy within the burner. In keeping with other studies, the results clearly show qualitatively the low-pass filter nature of the flame. The decay of the amplitude of the flame transfer function by increase of forcing frequency is further supported by images of the excited flame