Experimental analysis of local flame extinction in a turbulent jet diffusion flame by high repetition 2-D laser techniques and multi-scalar measurements

In this paper, we present a detailed experimental study of turbulence chemistry interactions in the "DLR_B" turbulent jet diffusion flame. The flame operates on mixtures of CH4, H-2, and N-2 in the fuel stream at Re = 22,800 and is a target flame within the TNF workshop. Extinction and re-ignition events can be tracked in real time and related to the underlying flow field phenomena and temperature fields. Time resolved measurements of OH radical concentration fields are performed in combination with temperature and velocity field measurements. For this purpose, we combined high repetition rate (33 kHz) PLIF imaging with stereoscopic PIV and double pulse Rayleigh imaging techniques. Comparisons are made with results from multi-scalar Raman/Rayleigh/LIF point measurements that reveal the thermochemical state of the flame. The large deviations from equilibrium observed on resulting OH/temperature joint pdfs could be related to strain rate and Damkohler number variations caused by turbulent flow structures leading to frequent extinctions. The 2D measurement series uniquely reveal the underlying mechanism that can lead to such events. Finally, comparisons are made to strained laminar flame calculations, which are generally found to be in good agreement with the measured data. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.