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This study aims to develop a low-drift air induction (AI) nozzle that meets the requirements of agricultural control unmanned aerial vehicles (UAVs). An AI nozzle was designed and manufactured to satisfy the design goals. The performance of the developed AI nozzle was quantitatively evaluated in terms of injection flow rate, air-to-liquid ratio (ALR), spray angle, and droplet size. The average value of the injection flow rate and the variation over time were measured using a gear-type positive displacement precision flow meter. The spray structure and spray angle were obtained at very high temporal resolution using the single image acquisition function of a two-dimensional particle image velocimetry (PIV) system. The droplet size of the spray was measured using a laser diffraction technique. The injection flow rate of the AI nozzle changes with the pressure recovery characteristics inside the nozzle mixing chamber and affects the dynamic stability of the AI nozzle. The spray angle of the AI nozzle with a flat-fan nozzle tip increases linearly with the injection pressure, and if there is additional consideration for the two-phase flow effect, the prediction equation for the single-phase flow can be applied to estimate the spray angle. The generation of air bubble-containing droplets in AI nozzles is formed by large-diameter ligament disintegration caused by a rolled-up liquid sheet and is larger than that of single-phase flow nozzles. The droplet size (Dv0.5) of the developed AI nozzle was 384 μm, which was smaller than that of a similar commercial AI nozzle. AI nozzle design, manufacturing and performance evaluation technology that satisfies the requirements of agricultural control UAVs, was established through this study.

Delivering pesticide droplets accurately to a target has always been a challenge for crop spraying. Pesticide spray that drifts or runs-off the crop are major sources of soil and groundwater pollution and encourage pesticide overuse. This study optimised an agricultural air-induction nozzle to overcome these difficulties. Various configurations were designed and manufactured to investigate the geometrical parameters. A range of experiments were designed and carried out to simulate field conditions and examine spray structure, stability, droplet size range, and the probability of microbubbles to determine correlations between droplet size and spray drift and droplet rebound potential with or without entrained microbubbles. The performance of the designed nozzle was compared to that of commercial nozzles. Optical diagnostic methods, including high-speed photography, laser diffraction-based droplet sizing, and microscopic flow visualisation, were employed to perform accurate investigations of droplet size range and microbubble presence potential. In addition, the spatial distribution of spray influenced by lateral wind was investigated in an open-type wind tunnel and measured using a 2-dimensional patternator and water-sensitive papers. The rebound potential of the droplets was investigated using high-speed photography for artificial leaves. The results demonstrate the significance of geometrical design factors on the performance of nozzles and the effectiveness of induced air on the reduction of drift and rebound potential. Droplets including microbubbles were found to distribute across the surface of the target leaves on impact and exhibit increased rebound resistance.

In this study, the atomization characteristics and drift potential of injection nozzles used in the pesticide injection system of agricultural drones currently used in Korea are evaluated. Furthermore, technical methods to reduce drift potential are determined. To this end, atomization characteristics were evaluated by selecting four representative nozzles commonly used in domestic agricultural drones. Additionally, an experimental device, consisting of a wind tunnel, was constructed to simulate the field situation. Moreover, drift potential was evaluated by using a water-sensitive paper under side wind conditions. The VMD and RSF of the nozzles used in the test were shown high in the order of TX–XR–TP, and the number density was low in in the order of TX–TP–XR. Thus, the evaluation of the droplet drift potential with respect to the side wind revealed that large amount of droplet drift occurs due to the side wind of 1 m/s, and the droplet drift of all nozzles used in the experiment, with the exception of the AI nozzle, was high. When the nozzle was installed obliquely, considering the flight speed and flight angle of the drone, it was confirmed that the tilt angle of the nozzle installation affects drift reduction. This applies even to nozzles that produce small droplets of less than 200 μm. Furthermore, as the speed of the side wind decreases, the drift reduction effect increases. Given that the drift potential of XR and TP nozzles, which are currently most commonly used in agricultural drones, are evaluated to be weak, auxiliary drift reduction methods, such as nozzle tilt angle, should be actively considered to reduce drift potential and minimize environmental damage.

This study aims to verify that the characteristics of the typical injection pumps and nozzles used in pesticide injection systems in current agricultural drones in Korea are consistent with those presented in the product specifications, and to provide experimental quantitative data for selecting the correct pump and nozzle. The performances of three types of pumps and 18 types of nozzles currently in use were evaluated in terms of the pressure-flow rate curve, injection flow rate, spray angle, and droplet size. For pesticide injection pumps, the maximum pressure and pressure-flow rate curve should include the nozzle’s injection pressure and flow rate range. Most of the 18 nozzles used in the test showed nearly the same results as the flow rates suggested from the manufacturer, but the spray angle showed a difference of up to 10%. The droplet size was slightly smaller than the value suggested by the manufacturer, and the relative span factor ranged from 0.2 to 1.2. The pressure-flow rate curves of the injection pumps and spray angles of the commercial nozzles used for agricultural control drones must be evaluated for official approval/assessment of such agricultural drones to ensure the performance of agricultural drone sprayers.