Abstract
Highlights Electric air assist system was developed with electric fans, pulse width modulation (PWM) controllers, a custom-designed air channel, and a battery. Adjusting PWM duty cycles from 0% to 100% achieved average exit air velocities from 0 to 11.3 m s-1. Spray applications with the system at 50% and 70% power achieved canopy pass through spray coverages from 4.1% to 19.9% and 14.2% to 24.2%, respectively. A multivariable regression model was developed to adjust air assist outputs based on tree canopy density and off-target loss. Abstract. Air assist for apple orchard spray applications is a necessity to deliver pesticides to target crops. However, conventional orchard sprayers use axial fans to provide air assists which are generally designed for tall crops. Thus, these systems have very limited capabilities to control airflows to match canopy densities. An electric air assist system (EAAS) was developed with an electric fans, pulse width modulation (PWM) controllers, a custom-design air channel, and a 400-Ah LiFePO4 battery to address such limitations. The system could ramp up its airflow to nearly 80% of its maximum in 2.5 s, while it took approximately 4 s to reach 100% airflow from no air assist. The EAAS provided airflow of 11.3 and 5.3 m s-1 at the fan outlet and 1 m away, respectively, with 100% duty cycles (DC) of PWM. It was capable of modulating its average air velocities from 0 to 11.3 ms-1 by changing DCs. Spray coverage samples of constant rate applications with different air assist levels were collected from the behind apple tree canopies throughout the 2023 growing season to characterize the potential for off-target spray drift. A multivariable regression model for controlling DCs was developed with the spray coverage data and leaf area index (LAI) to minimize the off-target drift. The EAAS was a promising approach to developing more advanced air assist spraying systems to enable the adjustment of both air and liquid flows based on canopy characteristics to maximize spray depositions on intended targets while minimizing spray drift. Keywords: Air assisted sprayer, Automation, Crop protection, Fan, Penetration, Pesticide, Pulse width modulation, Variable air assistance.
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