Study of the influence of electric fields on flames using planar LIF and PIV techniques

Abstract

The interaction of electric fields with flames yields two main effects, stabilization of the flames and reduction of pollutant emissions. Most of former studies were carried out using conventional measurement systems, e.g., exhaust gas analysis or mechanical probing, which did inevitably disturb not only the flame itself, but also the electric field. Using non-invasive laser based measurement techniques enable nowadays a better understanding of the ongoing processes in detail. In the literature, two possible explanations exist for the electric field effects: The “ionic wind” as the prevailing mechanism and as an alternative mechanism, changes in flame chemistry due to the production of reactive radicals below the actual flame front. To answer these open questions, experiments with electric fields have been carried out in a laminar premixed Bunsen flame at different operating conditions. Two imaging measurement techniques have been applied, planar laser-induced fluorescence (PLIF) for measuring species concentrations and particle image velocimetry (PIV) to determine the flow fields. By this, for the first time two-dimensional information was achieved with high temporal and local resolution to study the influence of electric fields on premixed flames. One exemplary operating point is presented here and discussed. It is shown with the help of species profiles of formaldehyde and OH∗ radicals and flow velocity profiles that different processes happen in the flame dependent on the local position in the combustion field. Evidence was found that the so called “ionic wind” alone is responsible for the effect, an influence of the electric field on flame chemistry and radical production was not indicated.