Development of an electric variable air assist system for apple orchard sprayers

Authors: Jeon, Hongyoung; Zhu, Heping

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2024
Publication Date: 7/3/2024
Citation: Jeon, H., Zhu, H. 2024. Development of an electric variable air assist system for apple orchard sprayers. Journal of the ASABE. 67(4):853-864. https://doi.org/10.13031/ja.15853.
DOI: https://doi.org/10.13031/ja.15853

Interpretive Summary: Applying crop protection products (CPP) to protect specialty crops from diseases and pests are necessary to have high quality crops and yields. Although suitable air assist for specialty crop spray applications is a key to deliver CPPs for effective disease and pest control, conventional specialty crop sprayers typically have oversized air assist systems which provide excessive air spray drift. A prototype electric variable air assist system for new specialty crop sprayers was developed and tested for its performance in air flow and the speed of modulating air flow. In addition, spray coverages behind tree canopies were collected from spray application with different intensities of air assist over a growing season to measure the potential of spray drifts. The results showed the electric air assist system could change the intensities of air assist by simply modifying a control signal to the system. The system could reach air flow up to 80% of its capacity from a complete stop in approximately 2.5 seconds. In addition, a control model to determine air flow intensities of the system based on foliage density and tolerable spray drift was developed. The outcomes from this research can be used in developing new electric specialty crop sprayers for US growers to reduce fossil fuel use, optimize spray applications with delicate control of air assist intensities, and minimize spray drift to reduce the environmental impacts from CPP applications.

Technical Abstract: Air assist for specialty crop spray applications is a necessity to deliver pesticides to target crops. However, conventional specialty crop 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 fan, a pulse width modulation (PWM) controller, custom designed air channel and 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 complete stop. It also drew over 30 A current to start the system. The EAAS provided air flow 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 2023 growing season to characterize the potential of off target spray drift. A control model for determining DCs was developed with the spray coverage data and leaf area index (LAI) to minimize the off target drift. Test results showed the model errors were less than 10%. The EAAS was a promising approach to develop more advanced air assist spraying systems to adjust both air and liquid flows based on canopy characteristics to maximize spray depositions on intended targets while minimizing spray drift to unintended objects.