A two-dimensional visualization in conjunction with a reactive scheme to form Mie scattering particles was employed to study jet diffusion flames at conditions having a Reynolds number around 2500 (ethylene) and 1100 (propane). Single-point measurements of Mie scattering from the light sheet of a continuous laser were made to provide the spectrum of the diffusion flame. The result showed that there existed a predominant frequency of 12 and 13 Hz for ethylene and propane, respectively, which coincides with the flame flicker frequency. Outside the luminous flame, large toroidal vortices were seen in both flames.
For propane diffusion flames investigated, the flame flicker was found to be related to the vortex shedding occurring inside the luminous flame, and the flame structure and spectrum are more complex than the ethylene flame studied.