Simultaneous measurements of velocity and CH distributions. Part 1: jet flames in co-flow

Abstract

Velocity field and CH distribution are measured simultaneously using particle-image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) of CH in piloted, turbulent, jet flames in coflow. The CH distribution is found to correspond well with the location of the stoichiometric velocity, U S , both instantaneously and on average. In addition, the CH distribution is observed to align with high-strain rate regions; however, significantly higher values of the maximum strain rates, compared to the mean value, are frequently observed. The residence time in the flame surface as represented by CH, τ F , remains nearly constant with axial distance downstream and is found to scale as τ F ∼ d/ U b , where d and U b are nozzle exit diameter and bulk nozzle-exit velocity, respectively. The mean value of the compressive principal strain rate is observed to decrease along the axial direction and shows a good correlation to a S ∼ ( x/ d) −0.7 relation for a wide range of jet Reynolds numbers. Finally, the two-dimensional dilatation is not seen to be a good marker of the flame position, unlike the case for premixed flames.