Contribution to the analysis of temporal and spatial structures near the lift-off region of a turbulent hydrogen diffusion flame

Abstract

The upstream region of a turbulent H 2 /air jet diffusion flame near the lift-off position was investigated with respect to the local flame structure and its temporal development. Single- and double-pulse one-dimensional Raman/Rayleigh imaging was used to measure quantitative profiles of major species concentrations and temperature with high accuracy and good spatial resolution. With the experimental setup consisting of two narrowband tunable excimer lasers and the respective detection systems, new diagnostic approaches were demonstrated that permitted analysis of details of turbulent transport and flame stabilization in this region of the flame. From single-pulse experiments, the role of vortices in the flame stabilization process was examined; also, the momentary location of flame fronts in individual 1D images was determined. Two different types of double-pulse experiments were performed in addition. Using two consecutive pulses of varying delay, information on typical times for transport and chemical reaction was obtained. In specific cases, the local flame speed could also be determined. In the second type of double-pulse experiments, adjacent one-dimensional traces were monitored from which temperature gradients and scalar dissipation rates were determined simultaneously in two perpendicular directions. These diagnostic approaches provide quantitative multiscalar and structural information that is not available to point-wise or 2D measurements; they were combined in an attempt to reveal details of the combustion process under investigation.