In-Flight Measurements of Spray System Droplet Size for Aerial Chemical Application

The spray application of pesticides, herbicides, fertilizers and growth regulators produces substantial benefits in crop yields. Aerial spray application of bulk materials offers advantages such as efficiency, speed, and access to constrained areas. However, a disadvantage with spray application is the unintended drift of spray droplets. Spray drift reduces efficiency, increases cost, and produces potential environmental hazards. The key issue is controlling the size of the spray droplets produced by application nozzles in flight. Nozzle performance is routinely characterized in wind tunnels by experimental measurements designed to mimic the in-flight process. However, imperfect models must be used to extend the wind tunnel test results to in-flight performance. This program will develop a droplet size measurement system that can be used in flight. Successful implementation will provide two key opportunities: (1) measurement of droplet size in flight for the development of improved nozzles and application processes, and (2) the potential for closed-loop control of droplet size to reduce spray drift in real time.Innovative Scientific Solutions, Inc. developed Particle Shadow Velocimetry (PSV) as a velocity, acceleration, and particle/droplet size measurement technique. PSV employs high magnification imaging of the shadows produced by flowing droplets or particles. Size measurements have been conducted on water droplets in a Mach 2 wind tunnel, and on propellant grains in an active solid rocket motor. The basic hardware of the proposed system consists of an LED for illumination and a digital camera for imaging. It totally eliminates the bulky and expensive laser components typically used in size measurement systems. As a result, PSV is very suitable for in-flight measurements of the size of agrochemical spray droplets in high speed air. The societal benefits of the overall SBIR Phase I and potential II program are to reduce the quantity of agrochemicals that need to be applied and the resultant environmental hazards from unintended spray drift.