EXPERIMENTAL-DETERMINATION OF THE REFLECTION COEFFICIENT OF A PREMIXED FLAME IN A DUCT

In many situations, combustion instabilities involve a coupling between the non-steady combustion process and the acoustic modes of the combustor system. Useful information on this coupling may be obtained by measuring the reflection response of the flame to incident acoustic perturbations. This measurement may be performed with a modified impedance tube set-up described in this paper. The system comprises a group of driver units and a linear array of microphones placed on the upstream side of the combustor in a long test section. The signals detected by this array are first digitized and then converted in complex form with a discrete Hilbert transform. From these signals, the complex amplitudes of the incident and reflected waves propagating in the channel are deduced by using a least squares algorithm.