Experimental study of a methane diffusion flame under dielectric barrier discharge assistance

Plasma assistance is a promising method for improving combustion, especially for NO, reduction by burning hydrocarbons at lower fuel-air ratio or for flame stabilization under unfavorable conditions (supersonic combustion or small volume combustion where the chemical time is close to the fuel residence time). Thus, we conceived a combustion test bench where we could study the effect of a coaxial dielectric barrier discharge on a lifted nonpremixed methane flame. In this paper, we were especially interested in the effect of the discharge on the detachment height of the flame up to a blowout. There, we could achieve the anchoring of the flame (detachment height = 5-10 min as opposed to 50-60 mm without plasma) on a plasma channel leaving the burner exit. Electrical investigations demonstrated that only 1 W applied to the discharge at the nozzle of the burner was necessary for this anchoring. Coupling the electrical and optical measurements revealed the pulsed nature of the light emission of the plasma, while a spectroscopic study of OH, CH, and N-2* exhibits a 10-mm overlap between the plasma and the flame. Finally, the by-products of the discharge in methane were analyzed by gas chromatography.