Effect of electric fields on the stabilization of premixed laminar bunsen flames at low AC frequency: Bi-ionic wind effect

The stabilization characteristics of laminar premixed bunsen flames have been investigated experimentally by applying AC electric fields at low frequency below 60 Hz together with DC in the single electrode configuration. The blowoff velocity has been measured for varying AC voltage and frequency. A transition frequency between low and high frequency regimes has been identified near 40-50 Hz, where AC electric fields have minimal effect on flame stabilization. In the low frequency regime, the blowoff velocity decreased linearly with AC voltage such that the flames became less stable. This was consistent with the DC result, implying the influence of the ionic wind effect. The variation of blowoff velocity with AC frequency showed a non-monotonic behavior in that the velocity decreased and then increased, exhibiting minimum blowoff velocity near 6-8 Hz. Based on the molecular kinetic theory, the developing degree of ionic wind was derived. By considering the ionic wind effects arising from both positive and negative ions in a flame zone, the bi-ionic wind effect successfully explained the non-monotonic behavior of blowoff velocity with AC frequency in the low frequency regime. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.