Design and experimental verification of the air outlet oscillation mechanism for a multi-duct sprayer

To enhance the droplet deposition effect on the inner canopy of fruit trees and the abaxial surfaces of leaves for air-assisted sprayers, an orchard spray mechanism with an oscillating air outlet was designed. Taking air outlet velocity, oscillation frequency, and oscillation angle as factors, single-factor experiments and three-factor, three-level droplet deposition experiments in fruit tree canopies were conducted. Meanwhile, a high-speed camera was used to capture the movement postures of leaves in oscillating and fixed wind fields, revealing that the oscillating wind field could induce significant forward-backward oscillation of leaves and enhance interference with droplet movement trajectories. The research results showed that, compared with the fixed air outlet, the oscillating air outlet not only increased the droplet deposition amount on the leaf abaxial surfaces, but also improved the droplet penetration rate in the fruit tree canopy. The order of influence of the three factors on the droplet deposition density of leaf abaxial surfaces (from largest to smallest) was: oscillation angle, oscillation frequency, and air outlet velocity; the order of influence on the droplet penetration rate (from largest to smallest) was: oscillation frequency, air outlet velocity, and oscillation angle. The optimal parameter combination obtained through response surface optimization was as follows: when the air outlet velocity was 23.15 m/s, the oscillation frequency was 1.875 Hz, and the oscillation angle was 11.92°, the droplet coverage density on the leaf abaxial surfaces was 46.90 particles/cm², the droplet penetration rate was 28.22%, and the coefficient of variation (CV) was 12.03%. In the verification test, the droplet deposition density on the leaf abaxial surfaces was 49.95 particles/cm², the droplet penetration rate was 25.71%, and CV was 13.25%. The relative error rates compared with the model predictions were 6.5%, 9.8%, and 9.2%, respectively, indicating that the results were basically consistent with the predictions. Field tests further confirmed that, when the air outlet was oscillating, the multi-duct sprayer achieved a 16.21% increase in average droplet deposition density on the leaf adaxial surfaces, a 40.33% increase in average deposition density on the leaf abaxial surfaces, a 33.58% increase in the droplet penetration rate, and a 39.8% decrease in CV compared with the fixed air outlet. © 2025 Society of Chemical Industry.