MIXING MECHANISM NEAR THE NOZZLE EXIT IN A TONE EXCITED NON-PREMIXED JET FRAME

An experimental investigation has been made with the objective of stud ying the mixing mechanism near the nozzle exit in a tone excited non-p remixed jet flame. The fuel jet was pulsed by means of a loudspeaker-d riven cavity. The excitation frequencies were chosen for the two cases of the non-resonant and resonant frequency identified as a pipe reson ance due to acoustic excitation. The effect of different sinusoidal ex citation conditions on mixing pattern near the nozzle exit and flame w as visualized using various techniques, including schlieren photograph and laser light scattering photograph from TiO2 seed particles.In ord er to clarify the details of the flame feature observed by visualizati on methods, hotwire measurements have been made. Excitation at the res onant frequency makes strong mixing near the nozzle. In this case, the fuel jet flow in the vicinity of nozzle exit breaks up into disturbed fluid parcels. This phenomenon affects greatly the combustion charact eristics of the tone excited jet and presumably occurs by Bow separati on from the wall inside the fuel nozzle. To qualitatively confirm the Bow feature inside the fuel tube, a simplified analytical model is als o presented.