The influences of electric fields on soot formation and flame structure of diffusion flames

Abstract

The influences of DC and AC electric fields, at frequencies up to 1.48 MHz and the maximum strength of about 6 kV/cm, on soot formation and flame structure were investigated using a counterflow type acetylene diffusion flame. The distributions of flame luminosity, soot volume fraction, flame temperature and OH concentration in flame were measured by non-invasive detection methods. Under the influence of electric fields, the changes in distribution of the soot volume fraction were confirmed. Electric fields of high frequency and high intensity reduced the soot volume fraction, whereas other electric fields increased it. The maximum values of flame temperature and OH concentration decreased. In the relationship between the maximum value of the soot volume fraction and the maximum temperature, the maximum soot volume fraction showed both increase and decrease with maximum temperatures depending on the frequencies and intensities of the electric fields, and both of them occurred at temperatures lower than 1900 K. The production of the incipient particles seemed to be the dominant process controlling the soot volume fraction due to the electric fields. The luminosity of a sooting diffusion flame was found to depend on the volume fraction and temperature of the soot particles in the flame. As for the behavior of the flame in the electric fields, the ionic wind effect was not found to be dominant in the present work, and the result of the previous simulation based on the ionic wind theory was not consistent with the present experimental results.