Flame residence time and strain rate in turbulent hydrogen non-premixed jet flames with coaxial air

Abstract

Simultaneous measurements of velocity field and OH distribution were made using particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) of OH radicals in turbulent hydrogen non-premixed jet flames with coaxial air. The OH radical was used to indicate the chemical reaction zone approximately. The flame surface represented by the OH layer is correlated well with the location of the stoichiometric velocity, U S, which is reformulated to account for the coaxial air effect. Furthermore, the region of high strain rate almost coincides with the inner edge of the OH layer. The local residence time on the flame surface, estimated from the mean value of the radial velocity on the OH layer, is proportional to ( x/ d eff) 0.7 where d eff is the effective jet diameter in the far-field region. Also, the mean value of the principal strain rate on the OH layer scales well with ( x/ d eff) −0.7 for a wide range of coaxial air flames. Finally, it is found that the local flame residence time is inversely proportional to the local strain rate and this inverse relation is also globally observed for turbulent non-premixed jet flames with and without coaxial air, if the coaxial air effect is taken into consideration.