Effect of Sub-Breakdown Electric Field on the Stability of Laminar Premixed Bunsen Flame

This study innovatively investigated the blow-off characteristics of premixed flames under positive/negative DC electric field (EF) generated by ring electrodes. The blow-off velocity was precisely measured across a range of voltages (−7kV-6kV) and fuel-air equivalence ratios (0.75–1.0). The results showed that positive EF could increase flame blow-off velocity significantly (nearly 300% compared with the no-EF conditions) while negative EF could not. The conical Bunsen flame initially changed into a partially detached flame and eventually blew off with increasing jet velocity under DC EF. The blow-off velocity increased significantly with higher voltage; however, excessive voltage induced electric breakdown, reducing the flame-stabilizing effect of EF. The mechanism was discussed through comparing flame structure variation with positive/negative EF firstly. It could be deduced that the flame propagation speed enhancement is more important in flame stability compared with the reduced flow velocity with EF, and broadening of the burned zone induced by EF may play a more critical role in the increment of flame propagation through decreasing heat loss and flame local curvature. The effect of EF on blow-off velocity was mitigated with leaner conditions. The power consumption of EF was negligible (<0.5W) compared to the heat release of combustion, therefore, the application of EF is a useful low-energy technique to increase flame stability.