Charging and spraying performance test of bipolar contact electrostatic spraying system for unmanned aerial vehicle

Abstract: In recent years, pesticide application using unmanned aerial vehicle (UAV) has developed rapidly in China. It is very suitable for complex terrain, highly efficient, and capable of dealing with sudden disasters at low risk. Meanwhile, it can reduce the harm of pesticides to human and environmental pollution. However, aerial application is very sensitive to meteorological conditions, which leads to increase of spray drift and nonuniform deposition distribution. A bipolar contact charging electrostatic (BCCE) spraying system for UAV was designed. The electrostatic spray system consisted of power source of electrostatic generator, power source of spray unit, electrostatic generator unit (with power switch and voltage regulator), positive and negative output electrode, tanks, pumps, controller and centrifugal atomizers. The electrostatic generator unit was the key component of BCCE spraying system, which consisted of a negative output electrostatic generator and a positive output electrostatic generator in series connection. The electrostatic generator unit could not only enhance the charging effort but also ensure the electric balance on UAV. The electrostatic spraying system included 2 separate tanks, which were connected to the positive and negative output electrodes of the high voltage electrostatic generator, respectively. So spraying liquid in different tanks was charged positively or negatively, and the charged liquid was atomized into droplets by centrifugal nozzles and then adsorbed onto the leaves of the crop. The output voltage of BCCE spraying system could be adjusted from 15 to 35 kV, and its pump pressure varied from 0.02 to 0.1 MPa. The charge-mass ratio (CMR) and droplet spectrum of spraying liquid for electro-chargeable liquid (ED) and water were measured in the laboratory. The result showed that the volume medium diameter (VMD) of ED was significantly smaller than that of water sprayed by atomizers of BCCE spraying system connected with the positive and the negative output electrode. For water spraying, using BCCE spraying system in different electrostatic voltage (EV), there were no significant differences in VMD and relative span (RS) in both output electrodes; meanwhile, the atomizer of positive voltage could reduce the VMD of ED, while atomizer of negative voltage could enhance the VMD of ED. When the spray liquid was ED, the RSs of droplet spectrum increased as the increase of EV supplied by the positive and negative output electrodes. The test of charging performance showed that the CMR of spray liquids charged by positive and negative output electrodes both increased with the increase of EV. Using the same EV and output electrode, the CMR of water was much higher than ED. With the same EV and spray liquid the CMR charged by negative output electrode was obviously higher than positive output electrode. Experiments were conducted in wheat field, the BCCE spraying system was carried by a single rotor motor UAV 3WQF120-12 to spray ED, and the original spraying system of 3WQF120-12 equipped with 2 LU120-01 nozzles spraying ED and water-based pesticide was chosen for the comparison on pesticide deposition and control effect of wheat aphid and rust. The field experiment result showed that the deposition amounts of both ED treatments were 0.048 6 and 0.051 3 μg/cm2, respectively, which were significantly higher than that of the water-based pesticide solution with 0.035 6 μg/cm2. The ED treatment sprayed by BCCE spraying system had the best uniformity in deposition with a standard deviation of 0.015 μg/cm2 and a coefficient of variation of 30.43%. The control efficiency and pesticide persistence of 2 ED treatments on wheat aphid and rust were significantly higher than the conventional water-based treatment. There was no significant difference in control efficiency of rust, and in wheat aphid 14 days after treatment between 2 ED treatments. In addition, the control efficiency of wheat aphid 7 days after treatment for BCCE spraying system was 87.92%, which was significantly higher than that for the UAV's original spraying system that was 76.43%. Therefore, the BCCE spraying system with ED can improve the uniformity of deposition and increase biological control effect.