Electrical and Spectroscopic Studies of the Effects of DC Electric Fields on Pre-Mixed Propane-Air Flames

Abstract

The effects of DC electric fields on temperature distributions within pre-mixed propane-air flames have been measured by the technique of thin filament pyrometry (TFP). We have focussed on the dramatic electric-field-induced modifications of the shape and size of the inner cone and the concomitant changes in the temperature profiles of fuel-rich mixtures with equivalence ratios of 1-1.35. Temperature profile measurements show large decreases in the reaction zone volume that is dependent upon the applied voltage polarity, indicating that electron impact excitation is not responsible for the observed effects. Additionally, the observed flame temperature profile modifications are not strongly dependent on the flow velocity. The TFP results have been verified by spectroscopic measurements of the rotational temperature of the CH(A2Δ X2Π) emission band at 431 nm. Due to the better coupling of the field to the flame in the present experiments, the magnitude of the externally applied voltage necessary to produce large changes in inner cone geometry are substantially smaller than those used in previous experiments. Electrical measurements that have been made include vertical and horizontal variations of the floating potential within the flames, and bulk current and voltage characteristics. High-speed imaging of the flame response to pulsed DC voltage has been performed to investigate the dynamics of the ionic wind effects. All measurements are consistent with the observed flame perturbations being a fluid mechanical response to the applied field.