Characterization of Heavy Oil Sprays in Isothermal and Burning Conditions with Laser Light Scattering Measurements in the Sideward Region,
CONSIGLIO NAZIONALE DELLE RICERCHE NAPLES (ITALY) IST DI RICERCHE SULLA COMBUSTIONE
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A new drop-sizing technique for slightly absorbing liquid fuel is proposed. The technique relies on laser light scattering measurements at fixed scattering angle in the sideward region theta 60 deg and it exploits the effect of light absorption of the refracted rays that pass through the droplets. A theoretical calibration curve, computed on the ground of geometrical optics theory, relates a measurable plane polarization state of the gamma polarization ratio with droplet dimensions for different levels of liquid fuel transparencies. The reasonably good approximation of the geometrical optics to the exact solution of Maxwell equation for a plane electromagnetic field incident on a sphere is also discussed. The measure procedure and the sensitivity of the technique is illustrated through selected experimental examples. Heavy oil sprays were generated by an air assisted nozzle on a vertical unconfined burner in isothermal and burning conditions. Radial distribution of droplet sizes and polarization ratios allows a characterization of spray evolution in the early regions of flame.