Experimental study of energy delivered to the filaments in high pressure nanosecond surface discharge

Nanosecond surface dielectric barrier discharge is an efficient tool of multipoint ignition of combustible mixtures at high pressure. At high voltage and pressure, the discharge transformation from streamer to filamentary form is observed. Experimental study of streamer-to-filament transition in molecular nitrogen and nitrogen:oxygen mixtures for the electrode systems with PVC or ceramics as dielectric is presented in the paper. Two polarities of the discharge are compared via microimaging and analysis of streamer-to-filament transition curves for voltage and pressure. For positive polarity, the velocity of filaments changes with the applied voltage but almost does not change with pressure. The specific delivered energy in the filamentary plasma measured from experiment can be as high as 6.4 eV/particle. The flow structure induced by a nanosecond sDBD was studied using particle image velocimetry. In the streamer mode the discharge creates a single vortex, formed in the vicinity of the exposed electrode. In the filamentary mode complex three-dimentional turbulence with a typical scale of 1-2 mm is present near the surface during 0.2-2 ms after the discharge pulse. A typical velocity magnitude for the flow induced by the filamentary nSDBD was within 0.5 m/s.