Liftoff and blow off characteristics of laminar non-premixed planar jets
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The NOx emission from gas burners is essentially due to thermal NOx occuring at temperatures above 1500 K. Lean combustion reduces the flame temperature and hence thermal NOx production. However, operation at leaner mixtures creates problems in flame stability. It is well established that the closer the standoff distance of the flame to the burner, the more stable the flame. In the current paper, the liftoff and blow off characteristics of two dimensional planar jets (width/length ≪1) have been analyzed. The equations of mass, momentum, energy, and species have been transformed from compressible to incompressible form, then normalized, and converted into ordinary differential equations using an appropriate similarity variable, η. Explicit mixing solutions are obtained for a range of Schmidt numbers. The mixing solutions for single jets are used to determine flame standoff distance by matching the local axial velocity on the stoichiometric contour with the laminar burning velocity. The blow off velocity is then deduced. It has been verified, but not reported here, that the results are qualitatively similar for circular jets. It is envisioned that this model will be extrapolated to include multiple planar/cluster jets and thus allow the effect of flame interaction on liftoff height and blow off velocity to be studied.
author list (cited authors)
Tillman, S. T., Annamalai, K., & Caton, J. A.