Comprehension of PWM solenoid valves to control hollow-cone nozzles for precision variable-rate orchard sprayers

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

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/5/2022
Publication Date: 12/28/2022
Citation: Zhu, H., Salcedo, R., Jeon, H., Ozkan, E., Gil, E., Campos, J., Romain, C. 2022. Comprehension of PWM solenoid valves to control hollow-cone nozzles for precision variable-rate orchard sprayers. In: SIMA Agritech Day 5th Edition, November 5, 2022, Paris, France. p.291-304..

Interpretive Summary:

Technical Abstract: Pulse width modulation (PWM) technologies have been integrated into intelligent orchard sprayers to control hollow-cone nozzles to achieve precision variable-rate applications. However, little information is available on the spray characteristics of these PWM-controlled nozzles. In this research, comprehensive understanding of droplet sizes and flow rate modulation accuracy was established for the hollow-cone nozzles manipulated with PWM solenoid valves. Test variables included four disc-core hollow-cone nozzle capacities, five operating pressures, and 10 PWM duty cycles (DUCs) ranging from 10% to 100%. Droplet diameters were measured with a laser imaging particle system, and nozzle flow rates were measured by weighing mass of discharged liquid with a digital balance in real time. Test results illustrated that the measured flow rates increased linearly as DUCs increased from 10% to 90% for all PWM-controlled nozzles operated at pressures in the range of 276 to 827 kPa. Also, the measured flow rates were always greater than those calculated flow rates at all DUCs. Droplet sizes were affected by the operating pressure and nozzle disc orifice size, and slightly by DUC. In general, nozzles with larger disc orifice and higher operating pressures resulted in higher flowrates as expected, whilst higher operating pressures and larger nozzles generated droplets with more consistent size distributions across DUCs from 10% to 100%. Droplet size classifications, from very fine to coarse, varied with the nozzle capacity and operating pressure but were similar the same nozzles without the PWM control. For droplets smaller than 100 µm, the spray volume fraction remained relatively consistent or slightly decreased as DUC increased but increased as the pressure increased. In comparison, the spray volume fraction increased as both DUC and operating pressure increased for droplets between 100 and 300 µm and decreased for the portion of droplets greater than 300 µm. As a result, the discovered information would be applied for improvement of precision variable-rate spray systems equipped with PWM valves. This prospect would be facilitated by establishing and implementing a digital database of these characteristics in advanced automatic precision spray controllers.