2D laser diagnostics of liquid methanol for investigation of atomization and vaporization dynamics in a burning spray jet

Abstract

Single-shot planar imaging of Raman scattering of liquid methanol, as well as laser-induced fluorescence of dissolved dye, has been used to investigate atomization and vaporization dynamics in the early stages of a burning sspray jet. Within the limited dynamic range of the camera, these linear techniques provide signal levels that are locally proportional to the mass of liquid intercepted by the laser sheet, whereas the techniques based on elastic interactions with the spray could not provide quantifiable data in this region of large size dispersion. High speed 2D maps of the condensed mass field of the initial jet display the dynamic behavior of thestructures induced by different regimes of air-blast atomization. The technique has enabled us to obtain planar instantaneous pictures of the liquid phase velocity field in the early development of the burning spray. When a droplet vaporizes, the signal level on its (blue) Raman image scales as its actual volume d3, whereas the signal level on its (red) dye fluorescence image scales as its initial volume d30, since the mass of dissolved dye does not vaporize. The comparison of the simultaneous images provides useful information on the vaporization dynamics in the burning spray. The data have been obtained in terms of evaporation constant from size reduction of single droplets or in terms of vaporized mass fraction of injected fuel from integrated measurements.