Effects of Acoustic Excitation and Annular Swirl Strength on a Non-Premixed and Swirl-Stabilized Flame

The stabilization of non-premixed flame is often done by coupling an annular swirling flow. Acoustic excitation, however, can improve combustion through fuel jet oscillation but can sometimes blow out the flame. The writers aimed to experimentally investigate the effects of annular swirl strength on acoustically excited non-premixed flame. Visual observations coupled with flame length measurements showed that the flame can be particularly shortened and transformed to blue at a low swirl strength. Flame and flow images obtained through the Mie scattering technique showed that the recirculation bubble enlarged proportionally in accordance with the swirl strength. Jet oscillations were diagnosed by using a laser Doppler anemometer at the central jet. Turbulence and mixing properties obtained from the central jet velocity were statistically compared to identify the best combination of swirl strength and acoustic excitation level. Combustion performance was finely validated through flame length and temperature measurements.