Microwave Plasma Assisted Combustion of Premixed Ar/CH$_{4}$ and He/CH$_{4}$ Gases at Atmospheric Pressure

Low-temperature nonthermal plasma assisted combustion is of growing interest due to potential applications in the improvement of combustion efficiency, reduction of ignition delay time, fuel reforming, etc. A 2.45 GHz microwave plasma source was used to study the microwave plasma enhanced flame of premixed Ar/CH$_{4}$ and He/CH$_{4}$ gases at atmospheric pressure. We present the visual observations of the plasma-assisted flames sustained at different mixing ratios of Ar/CH$_{4}$ and He/CH$_{4}$ gases. Optical emission spectroscopy (OES) was employed to study the reactive species generated from plasma flame. Visual imaging clearly showed the effect of microwave power and difference in flame shapes created in the Ar/CH$_{4}$ and He/CH$_{4}$ combustion: for Ar/CH$_{4}$ continuous flames were observed; for He/CH$_{4}$ floating flames (flames sustained with an air-gap from the plasma orifice) were observed at low plasma powers and some particular gas mixing ratios of He/CH$_{4}$. Measured flame temperatures were much higher than plasma gas temperatures. Reactive species, such as OH, NO, N$_{2}$, and C$_{2}$, were observed using OES. Effect of various gas mixing ratios, flow rates, and plasma powers on flame shape and flame temperature were also studied.