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

Droplet size distribution, droplet velocity, spray angle and flow rate are key factors influencing pesticide efficacy and environmental impact. However, it remains poorly understood how these parameters are affected by the interaction among pulse-width modulation (PWM), nozzle types and, in particular, spray adjuvants. This study investigated these factors using four flat-fan nozzle types (standard with 80° and 110° 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%).

PWM duty cycle primarily governed flow rate, which was mostly unaffected by spray solution. By 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 owing to incomplete sheet development under short valve-open times.

These findings demonstrate that optimizing PWM-controlled spray performance requires not only appropriate duty cycle selection, but also the use of adjuvant formulations tailored to each nozzle type. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.