Dynamic response of a ducted laminar premixed flame, part II: higher amplitude forcing

This paper presents an experimental study of the non-linear response of a conical, laminar, premixed flame to acoustic excitation. The linear dynamics of this flame were discussed in a companion paper. The amplitude of the velocity disturbances upstream of the flame is increased to about 90% of the mean upstream flow velocity. It is shown that the measured flame transfer functions at higher amplitude forcing differ significantly from those at low amplitudes. The disparity is mostly in phase and manifests itself as a systematic deviation from the linear phase response at low forcing amplitude, to a roughly constant phase at high amplitudes. The origin of this phase behaviour is then sought through analysis of the excited flame images. It is shown that the observed phase response is due to the difference in the flame disturbance evolution at low and high amplitude excitation