The effect of nonsteady electric fields on sooting flames

Abstract

The effects of transient dc and 50-Hz ac fields acting on a sooting acetylene diffusion flame were compared with those of steady dc fields. The object was to separate the velocities of charged soot particles from those of the ionic wind by making use of the difference in their relative evolution times. This has not been considered previously, largely beacuse much of the research was carried out on flat counterflow flames, but is here shown to be important for conventional flame shapes. Laser Doppler and scattering methods were used to determine particle velocities and sizes. Soot particles of the order of 10 μm diameter were found to have mobilities of the order of 5 × 10 −6 m 2 s −1 V −1 and zero for particles exposed to a flux of positive and negative charge carriers, respectively. Major perturbations to flow due to ionic wind effects set in after a delay of the order of 10 ms. Similar results were obtained whether the transients followed the switching on of a dc field or occurred during the 50-Hz cycling of the ac field.