Abstract
Local burning velocities of flamelet in a burner-stabilized turbulent premixed propane-air flame in the reaction sheet regime are investigated by use of a four identical sensors electrostatic probe and a three-color six-beam laser-doppler velocimetry (LDV) that give components of the flame-front velocity and the gas velocity, respectively. With this technique, the three-dimensional local flame-front velocity vector can be measured by electrostatic probe, and simultaneously the three-dimensional local gas-velocity vector can be measured by the LDV systems. The local burning velocity vector can be obtained from the three-dimensional local flame-front velocity vector and the three-dimensional local gas-velocity vector.
Under the experimental conditions investigated, the average turbulent fluctuating velocity is the same order of magnitudes the laminar burning velocity of the planer, unstained, adiabatic laminar flame. The flamelet burning velocity found from nearly zero to several times the planer, unstrained, adiabatic laminar burning velocity. There are differences in results that depends on whether flamelets transverses the burnt-to-unburnt or unburnt-to-burnt direction are recorded for the first time. When the flame front passes in the unburnt-to-burnt direction, the velocity vectors of the flame-front movement are directed mainly toward the burner axis and upward, and the direction of burning velocity vector is same direction of flame front velocity vector. But when the flame front passes in the burnt-to-unburnt direction, the velocity vectors of the flame-front movement are directed mainly outward and downward, and the direction of burning velocity vector is opposite direction. When the flame front passes in the burnt-to-unburnt direction, unburnt mixture is below flame front, but when it passes in the unburnt-to-burnt direction, unburnt mixture is above flame front. Therefore the direction of burning velocity vector corresponds to the position of reactant from flame front.
