Abstract

Characteristics of lifted flames in laminar axisymmetric jets of propane with coflowing air have been investigated experimentally. Approximate solutions for velocity and concentration accounting virtual origins have been proposed for coflow jets to analyze the behavior of liftoff height. From the measurement of Rayleigh scattering to probe the concentration field of propane, the validity of the approximate solutions was substantiated. From the images of OH PLIF and CH chemiluminescence and the Rayleigh concentration measurement, it has been shown that the positions of maximum luminosity in direct photographs of lifted tribrachial flames can reasonably be located along the stoichiometric contour. The liftoff height in coflow jets was found to increase highly nonlinearly with jet velocity and was sensitive to coflow velocity. The blowout and reattachment velocities decreased linearly with the increase in coflow velocity. These behaviors of liftoff height and the conditions at reattachment and blowout can be successfully predicted from the approximate solutions.