Investigation of Local Behavior in a Turbulent Diffusion Flame by Rayleigh Scattering Image Velocimetry and OH Laser Induced Fluorescence

Abstract

Instantaneous and simultaneous measurements of two-dimensional temperature, velocity and OH concentration profiles by combining Rayleigh scattering image velocimetry (RIV) with OH laser induced fluorescence method (OH-LIF) were demonstrated in a turbulent nitrogen-diluted hydrogen (H₂ 30%+N₂ 70%) diffusion flame. This measuring technique mainly employed one double-pulsed Nd : YAG laser, one Nd : YAG pumped dye laser, and three image-intensified CCD cameras. OH concentration was measured quantitatively based on OH-LIF intensity and the calibration considering the OH-LIF quenching database. The strain rate along the flame surface (reaction zone of OH peak) was estimated by the velocity vectors and OH concentration profiles. The results obtained are as follows. (1) Local temperature and OH concentration depression in the flame tends to occur when the flame inclines toward the centerline and the strain rate becomes positive and high. On the other hand, the flame that has locally high temperature and OH concentration tends not to have positive and high strain rate. (2) When the flame surface is pushed outward by the lateral convection motion, the radial position of OH concentration peak tends to be located prominently outside of the temperature peak. Their profiles are much different from those of the laminar flame. The considerably high OH concentration as compared with the laminar flame was observed where the flame does not have positive and high strain rate.