  This study concerns the effects of pressure, spatial location, and
application of oil emulsions on the resulting droplet size, eccentricity, as
well as velocity distributions, all of which are crucial information in
determining the dispersion dynamics of the droplets during the spray
applications. Experiments were conducted with the abovementioned droplets
information measured using digital inline holography (DIH). Results show that
the volumetric droplet size distributions (VDSD) span widely from sub-200 um to
over 2 mm in size. The application of an oil-in-water emulsion results largely
in the suppression of smaller droplets, while the VDSD is relatively
insensitive to increasing the oil volume fraction beyond a critical level. DIH
additionally enables the determination of size-dependent droplet eccentricity
and velocity measurements. Interestingly, the application of oil-in-water
emulsion generally decreases the eccentricity, more significantly at the center
than at the edge of the spray fan. We attribute this decrease to the increase
in lamella sheet thickness and thus decrease in characteristic shrinkage rates,
consistent with the observation using high-speed shadowgraphs. In all
instances, oil-in-water emulsion droplets have higher velocities than
equivalent sized water droplets. We attribute this to the earlier action of the
spray breakup process in the oil-in-water emulsion, reduced surface energy
generation during a breakup (larger droplets), and reduce energy dissipation
during breakup with oil-in-water emulsions, leading to increased translational
energy after the breakup process. Therefore, it appears that oil-in-water
emulsion application simultaneously suppresses small droplet formation and
increases droplet velocity, and hence spray penetration in agricultural
application.
