Characterization of fully developed air-assisted spray unsteadiness using RP-3 jet fuel

The ideal spray theory of Edwards and Marx was utilized to investigate the dependence of fully developed intermittent air-assisted spray unsteadiness on operational conditions and fluid properties. Time series information of spray droplets was identified by Phase/Doppler Particle Analyzer and used for inter-particle arrival time statistics. Results demonstrated that spray unsteadiness along the spray axis and near the nozzle exit area is more significant than far-nozzle field and spray periphery. The unsteadiness on the spray axis shows a decreasing function with the fuel injection durations, while the increase of air injection duration significantly elongates the unstable region on the spray axis. The properties of test liquid fuels show a moderate effect on the stability of the air-assisted spray, which is most likely due to the effects of liquid properties on the atomization characteristics. Chi-square is generally the preferred method for quantifying the global spray unsteadiness when compared to the deviation of the first time gap of experimental and theoretical inter-particle time distribution. Unsteadiness results of high-velocity droplet spray stage are relatively distinct compared to droplet deceleration and suspension stages, which is due to the continuous energy input at the opening duration of the nozzle. This result further indicates that droplet velocity plays an important role in determining spray unsteadiness.