Effect of electric fields on the liftoff of nonpremixed turbulent jet flames

The effect of electric fields on the liftoff of nonpremixed turbulent jet flames has been investigated by applying high-voltage alternate current (ac) to the nozzle of propane fuel. Flame liftoff velocities and liftoff heights were measured as functions of applied voltage and frequency. The fuel jet velocity at flame liftoff increased and flame liftoff height decreased with increasing voltage, implying that the range of flame stability can be extended with the ac charging. Meanwhile, the effect was minimal when applying direct current (dc). This stabilization effect with ac charging was also influenced by the frequency. As the applied voltage increased, a streamer corona was generated between the flame edge and the nozzle. When the jet velocity and, thus, the liftoff height becomes large, then the ac charging effect disappeared in such a way that the flame liftoff height became comparable to that of a free jet without applying voltage. The liftoff velocity was correlated linearly with voltage in the corona-free electric field enhanced regime.