Simultaneous measurements of flame geometry and flow field by OH-PLIF/Stereo PIV

Abstract

It is difficult to understand turbulent combustion, because the combustion process is very complex and unsteady. One of the useful parameters for discussion of the unsteady flame behaviors is the flame stretch rate, which is evaluated by local flame curvature and strain rate. In this study, we conducted simultaneous OH-PLIF/Stereo PIV measurements of turbulent premixed flames. Flame shape and flow field were obtained. Then, local flame curvature and strain rate were discussed. The turbulent flame was established by a cyclone-jet combustor for propane/air mixtures. The main jet velocity was U_m = 10, 30 m/s, and the equivalence ratio was Φ_m = 0.75, 0.90. The equivalence ratio of the cyclone jet was the same as that of the main jet, but the velocity of the cyclone jet was the constant of 10 m/s. It was found that the variation of flame curvature was large when the main jet velocity was high. Difference between curvature convex to unburned gas and curvature convex to burned gas was relatively small. Frequency of larger strain rate was high when the main jet velocity was large and equivalence ratio was small. It is suggested that the local flame extinction could be caused by the large strain rate because the local flame extinction occurs more frequently. At all conditions, compared with the positive strain rate, the frequency of negative strain rate was high.