Design and experiment on electrostatic spraying system for unmanned aerial vehicle

Abstract: Unmanned aerial vehicle (UAV) has the advantages of flexible operation and good adaptability to the terrain. Low-speed operating conditions and downward airflow generated by rotor wing of UAV can be very suitable for the application in agricultural pest control. Electrostatic spray has the advantages of uniformity in droplet size and good property of deposition, maturely applied in aerial spray system driven by people. The droplet of electrostatic spray is most likely to be charged when its size ranges from 80 to 200 μm. Taking advantages of such the characteristics as low-speed and low-height flight, and downdraft airflow from rotor, the electrostatic spray technology based on UAV can achieve ultra-low spray volume and hence improve spray quality. The electrostatic spray system is designed for the XY8D UAV, especially electrostatic nozzle structure with conical electrode adapted to the spray angle. The ring-shaped support makes the air flow through the electrodes, which can not only improve the penetrating capability of the droplets, but also guarantee the electrodes to be dry and the voltage to be stable. The power supply of high-voltage electrostatic uses bipolar charge mode, making both sides of the electrodes charged with opposite polarity and keeping the current balance for the UAV. The electrostatic spray test system is established. Under the condition of simulated UAV static electrostatic spray, the atomization and charging property of electrostatic nozzle has been tested by the laser particle size analyzer and Faraday tube test method. The results show high charge-mass ratio of 2.08 mC/kg can be obtained with nozzle tip of 0.4 mm, spray pressure of 0.3 MPa and charging voltage of 8 kV. So 0.4 L/min flow, 0.3 MPa spray pressure and 8 kV charging voltage are successfully identified as the UAV field operating parameters. The XY8D UAV electrostatic spray system is tested at different altitudes with electrostatic or non-electrostatic spray. Results show that the flying altitude is greater, the spray swath becomes wider; and the maximum spray swath is 6.8 m. Compared with non-electrostatic spray, the spray swath under electrostatic condition reduces slightly. Droplet sedimentation and drift experiments are conducted using the UAV electro-spray system over a 50 m × 30 m rice field, with the methods of water-sensitive paper and polyester card collection, respectively. Test results show that for non-electrostatic spray, droplet deposition effect is better when flight altitude is 2 m compared with the flight heights of 1 and 3 m, and the number of droplet deposited on water-sensitive paper reaches 56 per square centimeter; electrostatic spray make droplet deposition increase, and droplet coverages averagely increased by 35.4, 26 and 9 per square centimeter in the target canopy, middle and lower layer respectively. When the flying attitudes are 1, 2 and 3 m, the drift results of electrostatic and non- electrostatic spray are similar, the average droplet drift distances are 12.1, 15.8 and 18.6 m respectively; the average drift amounts are 5.88, 10.31 and 14.98 μg/cm2 respectively. It indicates that the flying altitude has greater influence on droplet drift, and the electrostatic spray method has little effect on inhibiting spray drift. While comparing with non-electrostatic spray, the deposition concentration of the droplets on polyester cards with electrostatic spray under 3 flying attitudes increases by 2.36, 2.91 and 1.56 μg/cm2 respectively. Test results provide the reference for the research on electrostatic spraying technologies based on UAV.