Parametrization of Pulsing Sprays

Both pulse-width modulation-controlled sprays and machine vision-based spot-spraying technologies have increased the precision of agricultural pesticide application. These methods both utilize short-duration spray bursts as their operating principle, as opposed to the continuous spraying used in conventional broadcast pesticide applications. This results in a much larger fraction of the application occurring during the startup and shutdown transience of the spray process, with a significant reduction in the fraction of time the spray is operating at steady state. Previous studies have shown that the volumetric median diameter (VMD) of a spray depends on where the measurement is made spatially within the spray fan, and there has likewise been shown to be a spatial dependence on the atomization mechanism within a spray when operating at steady state. As leading and trailing edges of a pulsing spray would not be expected to be governed by the same atomization physics as the center and sides of a steady-state spray, the present work characterizes shifts in the VMD of pulsing sprays across pulse durations in the range of 15 to 75 ms relative to their steady-state counterparts and identifies changes in the atomization mechanism associated with the transient regimes of each pulse. The role of nozzle and liquid components, such as formulated herbicides and adjuvants, in the spray was also evaluated, and we found that the addition of an emulsion-forming adjuvant tended to produce a more consistent spray across pulse durations as well as smaller shifts in VMD compared with a steady-state spray.