Schlieren analysis of an oscillating gas-jet diffusion flame

Flow structure of a flickering gas-jet diffusion flame was investigated using quantitative rainbow schlieren deflectometry. The fuel was pure hydrogen exiting from a burner tube at 43 m/s. Angular deflection data were obtained across the whole field of color schlieren images taken at a spatial resolution of 0.14 mm and a temporal resolution of 60 Hz. These line-of-sight data were analyzed to determine power spectra and flame flicker frequency at different operating pressures to scale the effects of buoyancy. The measurements were tomographically inverted to obtain the refractive index and, hence, temperature distributions assuming chemical equilibrium in the flame. The oscillating flow is described quantitatively in terms of temporal evolution of the temperature field. The flame structure is also described statistically by mean, root-mean-square (RMS), and probability density function profiles of temperature. Results reveal global oscillations in the flow field of the flame. The oscillations were stronger in the outer flow as compared to those at the flame surface. The flame was clipped-off at a downstream location, where the outer vortical structures intensified and entrained cold fluid toward the center region. (C) 1999 by The Combustion Institute.