Non-thermal Ignition of Premixed Hydrocarbon-air and co-air Flows by Nonequilibrium RF Plasma

Abstract

The paper presents results of nonequilibrium RF plasma assisted ignition and combustion experiments in premixed methane-air, ethylene-air, and CO-air flows. The results show that large volume ignition of these mixtures by the uniform and diffise RF plasma can be achieved at significantly higher flow velocities (up to u=25 rnls) and lower pressures (P=60-130 tom) compared to both a spark discharge and a DC arc discharge. The experiments also demonstrated flame stabilization by the RF plasma, without the use of any physical obstacle flameholders. Temperature measurements in the stable diffise RF discharge using Fourier transform infrared spectroscopy show that the flow temperature in the plasma prior to ignition (~=250-550' C at P=60-120 tom) is considerably lower than the autoignition temperatures for both ethylene-air and CO-air mixtures at these pressures (~=600-700' C). Spatially resolved temperature measurements show the transverse temperature nonuniformity in the RF discharge to be insignificant. Visible emission spectroscopy measurements in C~H4-air flows in the RF discharge detected presence of radical species such as CN, CH, C2, and OH, as well as 0 atoms. In CO-air flows, 0 and H atoms have been detected in the RF plasma region and COz emission (carbon monoxide flame bands) in the flame downstream of the RF plasma.