Simultaneous measurement of velocity and CH layer distribution in turbulent non-premixed flames

Abstract

The velocity field and the location of the CH layer are measured simultaneously in diluted ethylene flames by applying particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) of CH radicals. CH layer measurements are used to locate the position of the flame front, and accompanying velocity fields provide the instantaneous velocity, strain, and residence time information simultaneously. The location of the CH layer is found to correspond well with the location of the stoichiometric velocity contour and also with high strain rate zones: however, significantly higher values of instantaneous velocity and strain rates, compared to the mean value, are frequently observed. The residence time on the flame surface is estimated by dividing the thickness of the CH layer by the mean value of radial velocity on the CH layer. The flame sheet residence time estimated by this method remains nearly constant with axial distance downstream. The mean value of the maximum principal strain rate on the CH layer is observed to decrease along the axial direction while the change in the value is relatively small except for the region near the nozzle exit. The mean value of the strain rate is found to show a good correlation to a S≈(x/d) −0.7 relation for a wide range of Reynolds number.