Extinction of flames in a nonuniform electric field

The extinction of hydrocarbon flames which are subjected to a nonuniform electric field has been studied. The experimental system consists of a candle type burner having a hemispherical tip and a horizontal conducting plate situated above the flame. A direct current high voltage was applied between the burner head and the conducting plate. The voltage was gradually increased until flame extinction is observed. It was found that the extinction voltage depends on the field polarity, the distance between the electrodes and the burner head curvature. For a flat head burner no extinction was observed up to the breakdown voltage. The extinction was observed to occur in two phases. In the first as the applied voltage increases, the luminous zone stretches upward up to a critical field strength for which a sudden flame contraction occurs. In the second phase the flame gradually contracts as the voltage is increased and is finally completely extinguished. It is concluded that the interaction between the electric field and the flame is associated with electric forces which are applied to the polarizable intermediate species in the flame zone. These forces are directed, irrespectively of the voltage polarity, away from the flame zone, mainly toward the burner tip where the intensity of the electric field higher.