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Research Project: Aerial Application Technology for Sustainable Crop Production

Location: Aerial Application Technology Research

Title: Droplet size and nozzle tip pressure from a pulse width modulation sprayer

item BUTTS, THOMAS - University Of Nebraska
item BUTTS, LIBERTY - University Of Nebraska
item LUCK, JOE - University Of Nebraska
item Fritz, Bradley - Brad
item Hoffmann, Wesley
item KRUGER, GREG - University Of Nebraska

Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2018
Publication Date: 11/23/2018
Citation: Butts, T., Butts, L., Luck, J., Fritz, B.K., Hoffmann, W.C., Kruger, G. 2018. Droplet size and nozzle tip pressure from a pulse width modulation sprayer. Biosystems Engineering. 178:52-69.

Interpretive Summary: Precise application of pesticides in the field is crucial to the success of site-specific management of pests while minimizing potential off-target movement and damage to sensitive species. Real-time modification of spray rate while maintaining proper droplet size using pulse modulation systems provides for on-the-fly adaptation to changing field and meteorological conditions. A pulse width modulation system, which allows for these types of changes, was evaluated for droplet size and spray pattern with a number of nozzles typically used in ground application conditions. Examining the characteristics of the sprays produced demonstrated that droplet size was in fact maintained across a broad ranged of pulse width duty cycles, allowing for consistent spray application rates and spray pressure, maintaining uniform and effective spray patterns. The pulse width modulation system provides for an effective tool in ensuring precise, site specific applications under changing weather, field and pest conditions optimizing efficacy and mitigating non-target species damage.

Technical Abstract: The complexity of pesticide applications has led to inaccurate and inefficient sprayer performance which is unacceptable in current production agricultural systems . Pulse-width modulation (PWM) sprayers can be utilized in site-specific management strategies to improve overall application efficiency through flow control by pulsing an electronically-actuated solenoid valve placed directly upstream of the nozzle. Flow is changed by controlling the relative proportion of time each solenoid valve is open (duty cycle). The objective of this experiment was to identify the droplet size distribution and pressure at the nozzle tip when influenced by PWM duty cycle, current nozzle technology (venturi versus non-venturi) and gauge application pressure to provide guidelines for PWM use. The experiment was conducted in the low-speed wind tunnel at the Pesticide Application Technology Laboratory in North Platte, NE using a SharpShooter® PWM system. Droplet size distributions and nozzle tip pressures were collected for comparisons across treatments. In general, for non-venturi nozzles, as duty cycle decreased, droplet size slightly increased between 40-100% duty cycles. Conversely, venturi nozzles did not always follow this pattern, and larger standard errors resulted . The lowest duty cycle evaluated (20%) negatively impacted droplet size and caused severe inconsistencies for all nozzles and pressures. Nozzle tip pressures were impacted by the flow rate of a nozzle. At a 100% duty cycle, as flow rate of the nozzle increased, the nozzle tip pressure decreased , indicating a restriction is present within the solenoid valves. Moreover, duty cycle had a minimal impact on reaching the gauge pressure at each pulse for most nozzles ; however, venturi nozzles were again inconsistent , specifically twin-fan with a single pre-orifice venturi nozzles. In conclusion, venturi nozzles are not recommended for PWM systems as the droplet size and nozzle tip pressure do not respond in a manner consistent to normal patterns and have the potential to lead to poor, non-uniform applications. Furthermore, spray pressures of 276 kPa or greater and PWM duty cycles of 40% or greater are recommended to ensure proper nozzle operation.