Abstract
An experimental study has been conducted to elucidate the effect of AC electric field on behaviors of laminar lifted flame in nitrogen-diluted methane coflow-jets. Our concerns are focued on the regime to show a decrease in liftoff height, H-L with increasing nozzle exit velocity, U-O (hereafter, decreasing-H-L). The H-L with U-O near flame extinction were measured by varying the applied AC voltage, V-AC and frequency, f(AC) in a single electrode configuration. The behavior of H-L with a functional dependency of V-AC and f(AC) was categorized into two regime : (I) H-L decreased for nozzle diameter, D = 1.0 mm, and (II) H-L increased in the increase of f(AC) for a fixed V-AC in a D = 4.0, 8.4 mm. The lifted flames in decreasing-H-L region was unstable in high voltage regimes while the HL showed a decreasing tendency with U-O except them. Such behaviors in H-L were also characterized by functional dependencies of related physical parameters such as V-AC, f(AC), U-O, fuel mole fraction (X-F.O) and D.