Arrangement of Flame Structure by Reaction Progress Variable and Its Gradient in Unsteady Counterflow Premixed Flame

Dominant parameters in unsteady flame structure of methane/air counterflow premixed flame are investigated by numerical simulation with detailed chemical kinetics model. Two boundary conditions are used for comparison of the difference in the countered gas. One is the twin counterflow premixed flames, which is spouted premixed gas from both nozzles, and the other is the single counterflow premixed flame countered premixed gas and air. In order to investigate unsteady flame behavior, a sinusoidal fluctuation is added to the spout velocity. The influences of average velocity and the fluctuation frequency of the spout velocity on flame structure are examined. It is shown that the flame structure in the single-flame is governed by a reaction progress variable defined with mass fraction of oxygen, Co, q, and its gradient, ∇Co, q evaluated at flame front. In the twin-flame, ∇Co, q and the gradient of a progress variable defined with temperature evaluated at flame front, ∇Cr, q, dominate the flame structure.