Interaction between a Non-thermal Plasma and a Flame

Interaction between non-thermal plasmas and flames has been experimentally investigated. Diffusion flames and dielectric barrier discharges (DBD) with a wire-cylinder type were considered. A burner consisted of round type fuel nozzle and concentric coflow confinement. Since the burner was used as a plasma reactor at the same time, it was made of quartz tube. Along the centerline of the burner, stainless steel wire of 1 mm diameter was protruded as a high voltage electrode. Firstly, the effects of flames on electric discharges were investigated in terms of discharge onset voltages and delivered powers to the reactor. As results, vigorous streamers were observed along with a flame owing to the elevated temperature. As a gas temperature increases gas density decreases simultaneously, which resulted in an increasing reduced electrical field (=E/n). The seeding of free electrons and ions generated by the flame also could affect to the enhanced plasma conditions. Secondly, the effects of streamers on flame behaviors were investigated. Flame lengths were significantly shortened as the applied voltage increased owing to the effect of intense mixing by the ionic wind and the electrically induced flow of soot. The yellow luminosity of a diffusion flame from the radiation of soot were also significantly reduced with increasing applied voltages, which can be resulted from the reduction of soot or decreasing flame temperature. To clarify the dominant mechanism, we measured the temperature of burnt gases, the concentration of major species, and the spatial distribution of OH radical, PAH (Poly-Aromatic Hydrocarbons), and soot. Flame temperatures and the concentration of major species measured by thermocouple and FTIR (Fourier Transform Infrared Spectrometer), respectively, were not changed with the plasma generation, which demonstrates that over-all chemistries of combustion are not affected by non-thermal plasmas. However, from the results of PAH and soot distributions measured by LIF (Laser Induced Fluorescence) and LII (Laser Induced Incandescence) technique, respectively, we could conclude that the formation of soot is strongly affected by the non-thermal plasma.