Optical Observation of Vortex-Flame Interaction Using Spark-Ignited Premixed Flames in a Quasi-Turbulent and Quiescent Wake

Abstract

Structure and behavior of spark-ignited propane-air premixed flames established in the quasi-turbulent and quiescent wake, which is generated by quickly moving a fine rod-array vertically downward in the quiescents stoichiometric propane-air mixtue, are observed and analyzed using tomography and PTV. It is found that the quasi-turbulent and quiescent wake proposed here is composed of Karman vortex streets with the characteristic length scale ranging 0.2∼0.5 mm and the tangential velocity of 4.0 m/s, and therefore that it satisfies rather small and intense turbulence conditions of l_d/δ_L〓1 and v_θ/S_L〓10. Since the interface between the unburnt and burnt gases exhibits complicated and rugged appearances and consists of a continuous series of wrinkled flame elements of the length scale ranging 0.2∼2 mm, the turbulent flame established in the quasi-turbulent and quiescent wake with the moderately intense turbulence conditions of l_d/δ_L〓1 and v_θ/S_L〓10 is classified into the finely wrinkled laminar flame.