Measurements of the vaporization dynamics in the development zone of a burning spray by planar laser induced fluorescence and Raman scattering

A linear measurement technique based on simultaneous planar imaging of laser induced dye fluorescence and Raman scattering in the liquid phase is reported. Calibrations in a stream of monosized droplets doped with weak concentrations of rhodamin show that the intensities on the droplet images are proportional to the actual droplet volume for Raman scattering and to the initial volume of the droplet for fluorescence, as the mass of dissolved dye does not vaporize. Thus, the mass fraction of liquid fuel that has vaporized before the probing event can be derived from these simultaneous measurements. Experiments are performed in the early development of a burning spray to derive cumulative information on the vaporization dynamics in terms of mass fraction or evaporation constant. Size distribution from conjoined phase-Doppler measurements are also used to derive the rate of droplet consumption along the axis of the burning spray.