Experimentally study on distribution of flame transfer function in a lean premixed combustor

In order to intensively study the mechanisms of combustion instability in a lean premixed combustor, experiments were carried out to measure the axial distribution of the flame heat release under different conditions with various equivalent ratios and air flow rates. Thus the distribution of the flame transfer function especially the distribution of the phase were obtained and their relevance with all sorts of conditions. Experimental results indicate that the lag time corresponding to the phase of flame transfer function consists of three parts: the time for disturbances to propagate from the position of fuel injector to the dump plane, time lag for the formation of vortex ring near the dump plane, and the transport time of vortex ring from its seminary to the flame front. However, the phase increment resulting from the formation of vortex ring is the key factor as regard to the combustion instability. The phase increment changes from 0.5 to 1.0 while the equivalence ratio varies from 0.6 to 0.73. Two quite large modes exist in this combustor, which are the inlet mode 233Hz with self-locking trait and the transport mode 180 Hz. The frequency of the transport mode alters from 180Hz to 207 Hz with the change of phase increment.