Droplet size spectrum, velocity, angle, and flow rate of pulse width modulated spray nozzles with adjuvants

Authors: RODRIGUES DA CUNHA, JOAO PAULO - Federal University Of Uberlandia; OZKAN, ERDAL - The Ohio State University; Jeon, Hongyoung; Zhu, Heping

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2026
Publication Date: 5/18/2026
Citation: Rodrigues Da Cunha, J.A., Ozkan, E., Jeon, H., Zhu, H. 2026. Droplet size spectrum, velocity, angle, and flow rate of pulse width modulated spray nozzles with adjuvants. Pest Management Science. https://doi.org/10.1002/ps.70932.
DOI: https://doi.org/10.1002/ps.70932

Interpretive Summary: This study demonstrates that pesticide spray performance is shaped by an interaction among PWM duty cycle, nozzle type, and adjuvant formulation. Flow rate was governed by duty cycle, whereas droplet size distribution and spray angle were more sensitive to nozzle design and adjuvant chemistry. Lower duty cycles produced larger droplets and narrower spray angles, with air-induction nozzles showing the greatest instability under short valve-open times. Adjuvants moderated these effects: the drift control agent substantially increased droplet size and reduced fines, while the nonionic surfactant produced moderate improvements compared to water. Both adjuvants enhanced droplet uniformity, counteracting PWM’s tendency to broaden size spectra at reduced duty cycles. These findings show that effective optimization of PWM spraying requires not only careful duty-cycle selection but also deliberate pairing of nozzle type and adjuvant chemistry to balance efficacy with potential adverse effects of pesticide applications. This work provides in-depth knowledge about new pesticide application technologies for the U.S. farmers to help them select emerging application technologies meeting their needs.

Technical Abstract: Droplet size distribution and velocity, spray angle, and flow rate are key factors that influence pesticide efficacy and environmental impact. However, their interaction with pulse-width modulation (PWM), nozzle types, and spray adjuvants is not well understood. This study investigated these factors for four flat-fan nozzle types (standard with 80º and 110º spray angles, pre-orifice, and air-induction). Water and two commercial adjuvant formulations (a nonionic surfactant (NIS), and a drift control agent (DCA)) were used across five PWM duty cycles (20, 40, 60, 80 and 100%). Flow rate was measured using a precision scale, droplet sizes were analyzed using a particle/droplet image analysis system, droplet velocity was assessed via particle image velocimetry, and spray angle was determined from photographs taken by a high-speed camera. PWM duty cycle primarily governed flow rate, which was mostly unaffected by spray solution. In contrast, droplet size distribution was strongly affected by adjuvant type, duty cycle, and nozzle type. Generally, droplet size increased as duty cycle decreased for all nozzle types, regardless of spray solution. Adjuvants further modified droplet size at each duty cycle: DCA markedly increased droplet size and reduced fine droplets, whereas NIS produced a moderate increase compared with water. Both adjuvants tended to produce more uniform droplet size spectra, mitigating the PWM tendency to increase the relative span index at lower duty cycles. Decreasing the duty cycle consistently narrowed the spray angle, with the air-induction nozzle showing the greatest sensitivity due to incomplete sheet development under short valve-open times. Overall, these findings indicate that optimizing PWM performance requires not only appropriate duty-cycle selection, but also careful selection of an adjuvant formulation tailored to each nozzle type.