Droplet size spectrum, activation pressure and flow rate discharged from PWM flat-fan nozzles

Authors: WEI, ZHIMING - Shandong Academy Of Agricultural Sciences; Zhu, Heping; ZHANG, ZHIHONG - Kunming University Of Science And Technology; SALCEDO, RAMON - The Ohio State University

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2020
Publication Date: 1/5/2021
Citation: Wei, Z., Zhu, H., Zhang, Z., Salcedo, R. 2021. Droplet size spectrum, activation pressure and flow rate discharged from PWM flat-fan nozzles. Transactions of the ASABE. 64(1):313-325. https://doi.org/10.13031/trans.14100.
DOI: https://doi.org/10.13031/trans.14100

Interpretive Summary: Current application practices with constant rates have caused excessive use of pesticides and fertilizers, leading frequent concerns on pollutions to the environment. To address this problem, the pulse width modulated (PWM) technology has been used in variable-rate spray systems to apply appropriate quantities of products to target areas based on crop needs. However, little information is available on how the valve activations in the pulse formation affect spray characteristics. In this research, we investigated droplet size distributions, activation pressures, and flow rates discharged from commonly used hydraulic nozzles controlled with PWM valves. It was revealed that these spray characteristics varied with the PWM duty cycles, nozzle orifice sizes, and valve manufacturers. To minimize the variations, regression equations were established for droplet sizes and activation pressures to correct errors, and additional time needed in each pulse form was determined for the solenoid valve modification. With these measures, the accuracy of the PWM technology could be greatly improved for pesticide and fertilizer applications.

Technical Abstract: Pulse width modulated (PWM) spray systems can produce variable spray rates to achieve precision application of pesticides and fertilizers, but they can also have potential concerns on producing inconsistent droplet sizes and inaccurate spray outputs. Droplet size distributions, activation pressures acting on nozzle orifices, and flow rates discharged from nozzles were investigated for test combinations of ten PWM duty cycles (10, 20, 30, 40, 50, 60, 70, 80, 90, 100%), six flat-fan nozzles with different orifice sizes (XR8001, XR8002, XR8003, XR8004, XR8005, XR8006) and two PWM solenoid valves from two different manufacturers. Test results showed that the droplet size distribution, activation pressure, and flow rate varied with the duty cycle, nozzle orifice size, and PWM solenoid valve source. For XR8001 and XR8002 nozzles, droplet sizes did not vary significantly with all duty cycles from 10% to 100%. To obtain relatively consistent droplet size distributions, XR8003 and XR8004 nozzles required PWM duty cycles to be at least 20% while XR8005 and XR8006 nozzles required duty cycles to be 30% or greater. The activation pressure increased as the duty cycle increased but decreased as the nozzle orifice size increased. Also, the same nozzles coupled with PWM solenoid valves from two different manufacturers discharged different flow rates for the same duty cycles in the range of 10% and 90%. Therefore, careful selection of PWM solenoid valves for different orifice nozzles operated in different duty cycle ranges was necessary to achieve consistent variable-rate spray performances.