Mixing Mechanism near the Nozzle Exit in a Tone Excited Non-Premixed Jet Flame

Abstract

An experimental investigation has been made with the objective of studying the mixing mechanism near the nozzle exit in a tone excited non-premixed jet flame. The fuel jet was pulsed by means of a loudspeaker-driven cavity. The excitation frequencies were chosen for the two cases of the non-resonant and resonant frequency identified as a pipe resonance due to acoustic excitation. The effect of different sinusoidal excitation conditions on mixing pattern near the nozzle exit and flame was visualized using various techniques, including schlieren photograph and laser light scattering photograph from TiO₂ seed particles.

In order to clarify the details of the flame feature observed by visualization methods, hotwire measurements have been made. Excitation at the resonant 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 characteristics of the tone excited jet and presumably occurs by flow separation from the wall inside the fuel nozzle. To qualitatively confirm the flow feature inside the fuel tube, a simplified analytical model is also presented.

Keywords:

• mixing mechanism
• non-premixed jet flame
• resonant frequency
• acoustic excitation
• phase-averaged
• unsteady separation