Investigation of Flamelet in a Turbulent Diffusion Flame Using Simultaneous Measurements of Two-Dimensional Temperature and Velocity Profiles by Rayleigh Scattering.

Abstract

Instantaneous and simultaneous measurements of two-dimensional temperature and velocity profiles using Rayleigh scattering images were demonstrated in a turbulent nitrogen-diluted hydrogen (H2 30%+N2 70%) diffusion flame. A Nd: YAG laser produced two pulses separated by 20μs to yield a pair of instantaneous temperature profiles. The velocity profile was derived from the Rayleigh scattering images by the cross correlation technique (RIV: Rayleigh scattering Image Velocimetry). Strain rate and thermal dissipation rate were estimated from the temperature and velocity profiles. Local temperature depression in the flamelet near the shear layer tends to occur when the flamelet inclines toward the centerline and the strain rate becomes positive and high. The thin flamelet with high strain rate is sandwiched closely between two layers with high thermal dissipation rate, inducing temperature depression and local quenching. On the other hand, a flamelet which has a broad high temperature profile tends not to have positive and high strain rate and is surrounded by layers with relatively low thermal dissipation rate.