Planar imaging of CH, OH, and velocity in turbulent non-premixed jet flames

• Published in: Proceedings of the Combustion Institute 2002, Vol.29 (2), p.1921-1927
• Main Authors: Kothnur, P.S., Tsurikov, M.S., Clemens, N.T., Donbar, J.M., Carter, C.D.
• Format: Article
• Language: English
• ISSN: 1540-7489; 1873-2704
• DOI: 10.1016/S1540-7489(02)80233-4

Simultaneous planar laser-induced fluorescence of the CH and OH radicals and two-dimensional particleimage velocimetry were used to investigate the structure of turbulent non-premixed methane/nitrogen jet flames ( Re jet=18,600) in an oxygen coflow. The motivation for this study is to investigate the relationship among regions of high CH/OH concentration and kinematic quantities such as vorticity, strain rate, and dilatation. The results show that in the lower part of the flame, the direction of the two-dimensional principal compressive strain axis exhibits a preferred orientation of about 45° with respect to the flow direction, whereas near the flame tip, the strain exhibits a more random orientation. Furthermore, CH structures are more likely to align orthogonal to the principal compressive strain axis in the downstream half of the flame. Probability density functions (PDFs) show that the most probable value of vorticity on CH structures is about Δ U/δ (where Δ U is the difference between the jet centerline and coflow velocities and δ is the full width at half-maximum of velocity profile), but near zero on the OH structures. Furthermore, joint PDFs of strain and dilatation show that CH structures are more likely to be associated with positive dilatation than are OH structures. These results are consistent with previous studies that have shown that jet flame kinematics are substantially affected by heat release and further show that these effects are more closely correlated with zones of high CH concentration than with zones of high OH concentration.