Electrohydrodynamic instability of premixed flames under manipulations of dc electric fields

Transient analysis of the nonmonotonic response of counterflow laminar diffusion flames in alternating current and step electric fields using a one-dimensional ionic transport model

The electrohydrodynamic response of a counterflow laminar diffusion flame to applied alternating current (ac) electric fields is investigated experimentally and numerically. The flame positions are observed to show typical response to applied ac electric fields with high and moderate frequencies. The flame position does not respond above a threshold frequency corresponding to a certain collision response time, below which it oscillates in phase with the applied electric field. At a very low frequency (less than approximately 1 Hz), however, the flame position is observed to vary nonmonotonically as a function of time. To elucidate the nonmonotonic behaviors, a one-dimensional ionic transport model was employed by applying time-dependent electric fields. The responses of flame positions for ionized layers substituting for counterflow diffusion flames were systematically investigated with respect to one-way ionic wind (OIW) and two-way ionic wind (TIW) models. Consequently, it is demonstrated that the ionic models can produce not only harmonic flame oscillations for relatively low ac frequencies, but also free flame oscillations for stepwise voltages, which originated from the interaction between electrostatic force and ionic wind-induced force in the ionic system for both the OIW and TIW models.