Plasma-Assisted Stabilization of Lifted Non-premixed Jet Flames
2018
Liao, Ying-Hao | Zhao, Xiang-Hong
The present study experimentally investigates the effects of plasma discharges on the stabilization of lifted non-premixed jet flames in a stream of co-flow air. The plasma discharge is produced on the sharp edge of the fuel nozzle exit, facilitating its impact on flame stabilization. It is observed that the application of plasma discharges has an impact on the enhancement of flame lift-off velocity, lift-off height, and hysteresis phenomenon and leads to plasma-attached flames, plasma-enhanced lifted flames, and plasma-ineffective lifted flames, depending on flame lift-off conditions. A maximum enhancement of approximately 84% is observed for the flame lift-off velocity when the co-flow velocity is sufficiently low. As the co-flow velocity or the jet Reynolds number is low, the flame is anchored at the nozzle by the discharge. As the co-flow velocity or the jet Reynolds number is increased, the flame detaches but with a decrease in lift-off height compared to the flame without the discharge. If the co-flow velocity of the jet Reynolds number is continuously increased such that the flame lift-off height is beyond a critical value, the effect of plasma discharges diminishes and the flame lift-off height becomes comparable to that without plasma discharges. In flame hysteresis studies, both of the flame lift-off and reattachment velocities are increased with 2-fold enhancement when the discharge is present. Spectroscopic study shows that the emission characteristics, particularly for those between 400 and 800 nm, in flames are intensified with the presence of plasma discharge, consistent with the flame luminosity visualization, probably due to the reduced lift-off height that leads to reduced air premixing, resulting in increased soot formation.
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