Droplet size distributions from PWM-controlled hollow-cone nozzles operated at high modulation frequencies and pressures

Authors: CAMPOS, JAVIER - The Ohio State University; Zhu, Heping; SALCEDO, RAMON - Technical University Of Catalonia; Jeon, Hongyoung; OZKAN, ERDAL - The Ohio State University; GIL, EMILIO - Technical University Of Catalonia

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2024
Publication Date: 1/10/2025
Citation: Campos, J., Zhu, H., Salcedo, R., Jeon, H., Ozkan, E., Gil, E. 2025. Droplet size distributions from PWM-controlled hollow-cone nozzles operated at high modulation frequencies and pressures. Journal of the ASABE. 68(1):51-60. https://doi.org/10.13031/ja.16094.
DOI: https://doi.org/10.13031/ja.16094

Interpretive Summary: Targeted variable-rate sprayers have been rapidly adopted in specialty crop production to significantly reduce pesticide waste, increase production profitability, and safeguard the environment. Flowrate modulation valves are a critical component of the sprayers to achieve precision applications. However, the valves still need improvements to further increase the sprayer precision capability. In this research, we investigated pulse width modulation valves with 12 different designs originally for industrial applications, and discovered two of them were able to accurately modulate flowrates of high-pressure nozzles commonly used in intelligent orchard sprayers. Tests also demonstrated that droplet size distributions were remained consistent for the nozzles manipulated by the valves operated at high speeds and pressures. Thus, these two valves would be recommended for future designs of new precision sprayers to further minimize pesticide inputs into the crop production.

Technical Abstract: Sprayers equipped with canopy detection sensors and pulse width modulated (PWM) solenoid valves allow real-time variable rate applications of pesticides to match canopy structures. However, the accuracy of variable-rate applications could be increased by accommodating the modulation speed of the PWM valves to the sensor detection speed. Based on previous investigations of 12 commercially available high-frequency PWM valves, two PWM valves with the highest modulation capability were selected for further evaluations. These investigations included the influence of modulation frequency and duty cycle on the droplet size distribution and uniformity of two disc-core hollow-cone nozzles (Teejet D4-DC13 and D5-DC25) manipulated with the two PWM valves operated at pressures of 1034, 1380, and 2068 kPa and modulation frequencies ranging from 10 to 40 Hz and duty cycles (DUCs) between 10% and 100%. Test results showed that droplet size distribution and uniformity remained consistent with varied modulation frequencies. However, DUCs slightly affected droplet size distribution and uniformity, especially when DUCs were below 30%. Therefore, there would be a potential to integrate these high-frequency PWM valves, properly operated at DUCs in the range between 30% and 100%, into orchard sprayers to further increase the variable-rate application accuracy while maintaining stable droplet size distributions.