Application of Plasma Discharges to the Ignition of a Jet Diffusion Flame

The present study experimentally investigates the effect of plasma discharges on the ignition of a laminar methane jet diffusion flame in a stream of co-flow air. The Reynolds number of the jet flame, based on the nominal jet velocity and the nozzle diameter, is approximately Re = 2000. The plasma discharge, a corona type, is produced between two tungsten wires with a diameter of 0.5 mm and a gap of 15 mm. Results show that the application of plasma discharge in a near-nozzle region can ignite the flame. A non-reacting free jet similarity solution is applied to examine the ignition locations and it shows that many of the locations are outside the jet boundary, where the mixture is leaner than stoichiometry. The minimum input power required for flame ignition is seen to increase with radial distance away from the nozzle and decrease with downstream locations. A high input power required for ignition is found to be close to the nozzle exit, where a high strain can be expected. Spectroscopic study confirms the emission spectra in non-thermal air plasma and shows the intensity difference in spectra between discharges that ignite and do not ignite flames.