On the low-temperature plasma discharge in methane/air diffusion flames

Abstract

Interest in methane has grown recently because of its encouraging characteristics. However, methane comes with serious concerns regarding stability and flammability limitations. Some methods have been proposed to improve the ignition characteristics of methane in diffusion flame burners such as electrical fields, dielectric barrier discharge, and low-temperature plasma. In this study, an innovative single-element coaxial shear injector coupled with a high-voltage nanosecond pulse generator has been used to study the effects of low-temperature plasma (LTP) discharge on methane/air inverse diffusion flame at different plasma and flow conditions. The stability analysis focuses on the detachment conditions of the flame and how RNP discharge can delay this phenomenon, explaining the presence of an optimal operating point with the least applied energy. Comparing the lean blow-off limits for the cases with and without plasma discharge, it is shown that low-temperature plasma discharge enhances the flammability of the diffusion flame. The effect of LTP discharge on laminar flames is also discussed using chemiluminescence photography. It shows that the shape of the diffusion flame becomes more similar to premixed flame with more air entrainment and stability. Resultantly, it is shown that RNP discharge can improve the flame stability and ignition characteristics.