An Experimental Study of the Stabilization of the Lifted Jet Diffusion Flame Using Molecular Rayleigh Scattering Technique

haracteristics of flame stabilization. one another under many circumemixed” type lifted diffusion flame orne et al. and Eickhoff et al., and the influence to flame behaviors by the turbulent structures within the flow field postulated by Byggstoyl et al. and Broadwell et al. were recognized by Pitts, and he further combined them to explain the flame liftoff and blowout behaviors. Pitts [SI attempted to determind the stability behavior of turbulent jet diffusion flame by measuring the unignited cold flow characteristics such as concentration distribution and velocity profile. According to his prediction results, some accurate correlations of experimental data for liftoff heights and blowout velocities were determined. Recently, Chao and Jeng [7,8,9] investigated the stabilization of a jet diffusion flame from liffoff to blowout based on the traditional turbulent flame speed concept. And a new model of flame stabilization mechanism was derived baaed on theoretical considerations of turbulent heat transport and effect of turbulent intermittency. Moreover, Richard and Pitts 1101 measured the radial profile of the probability density function of the flammable premixture of an isothermal fuel jet at the flame base, and he recongnized , on an instantaneous basis that the mixture is seldom stoichiometric a t the flame base. However, the detailed discussion about the local turbulent mixing using the Pdf analysis has been still unaccomplished. Besides, advanced laser optical diagnostics offer important advantages in that they are non-intrusive and can prevent unacceptable perturbations to the system under study. Also, they can be used in the measurement in inaccessible environments [11]. Rayleigh scattering has been demostrated to be a powerful diagnostic tool for the measurement of local gas temperature 112,131 and concentration I14,15,10] in combustion studies. The objective of the present study is to develop the molecular Rayleigh scattering technique to investigate the probability distribution function ( pdf ) of concentration and the flame liftoff behavior. The measured pdf information together with other measurement data [Q] are applied to the newly derived lifted flame stabilization (81 to predict the flame location and flame zone structure. In addition, the dependence of the stabilization of lifted diffusion flame on the local mixing process and turbulent structures within flow field are also carefully delineated.