Propagation of tribrachial flames with ozone in a laminar non-premixed jet

Abstract

Effects of ozone on the propagation characteristics of the tribrachial flame in a laminar co-flow jet are experimentally investigated. Ozone is generated by a coaxial plasma reactor which can produce a maximum O-3 concentration of 2850 ppm with a power consumption of 76.5 W. A high-speed camera is employed to record the stationary and propagating flames both with and without ozone, by which the flame displacement and propagation speeds can be determined. It is shown that the flame stability characteristics are altered with the addition of O-3, in which a flame with decreased lift-off height and enhanced lift-off, reattachment and blowout velocities is observed. The enhanced flame stability with O-3 addition is due to an increase in flame displacement and propagation speeds. A scaling argument shows that the enhanced flame propagation speed is strongly related to the O-3 kinetic enhancement on laminar flame speed. Due to the distinct flame structure, the accompanied hydrodynamic enhancement by O-3 addition facilitates the tribrachial flame propagation, implying an over-prediction of the O-3 kinetic enhancement. The hydrodynamic enhancement with O-3 presence originates from a stronger flow redirection, due to the higher sensitivity of off-stoichiometric flames to O-3 enhancement on laminar flame speed, and a more slanted flame front, due to the increased velocity gradient.