Counterflow nonpremixed flame DC displacement under AC electric field

The impact of an AC electric field of sub-breakdown voltage and fast frequency on a counterflow nonpremixed flame, with the electric field applied orthogonal to the flame, is studied using a semi-empirical analytical model based on an oscillating porous disk. The range of applicability of the model expands the well-known effects at low frequency and DC fields to frequencies for which the flame modification is still due to an ion-driven wind but the ion oscillation is fully contained between the two electrodes. The model predicts that a symmetric oscillation of the flame ions leads to a reduction of the local strain rate that displaces the flame towards a new equilibrium position that is closer to the oxidizer side. If asymmetries in the oscillation of the charge are accounted for the stagnation plane between the two jets can also be displaced, the directionality of this displacement depends on the ion parameters at either side. Within the model's assumptions the displacement presents a maximum with the applied voltage amplitude and has a smaller dependency on the excitation frequency. The model is based on experimental observations using sub-breakdown voltage and frequencies between 500 Hz and 35 kHz, that are also presented. (C) 2015 Published by Elsevier Inc. on behalf of The Combustion Institute.