Design Of Thermal Mist Spraying System For Maize Plant Protection UAV And Test Of Droplet Distribution Characteristics

Maize is an important food crop and industrial raw material in China,the planting area will reach 640 million mu in 2021 and it is great significance to ensuring China’s strategic food security.In the middle and late stages of maize growth,the field is closed and the plants are blocked,resulting in the difficulty of large high-ground gap plant protection machinery to get out of the field,while the existing plant protection drones are difficult to penetrate the maize canopy due to fog droplets,and the chemical solution cannot be directly sprayed to the site where the pests and diseases occur,resulting in its control effect also needing to be improved.In this paper,combined with the advantages of high efficiency prevention and control of plant protection unmanned aerial vehicles and the characteristics of uniform atomization liquid,small particle size and good dispersion performance of pulsed smoke machines,a smoke plant protection UAV was designed and developed,and the distribution characteristics of the rotor flow field were analyzed through numerical simulation,combined with site tests and field tests,and the distribution of droplets under different operating parameters was studied,and the main research contents were as follows:1)In view of the problem of plant protection in the middle and late stages of maize,the scheme of using a plant protection UAV equipped with a pulsed fog machine is proposed to achieve thermal fog spraying.The design of the whole machine structure and spray system was carried out,and the preliminary performance tests of the two kinds of smoke nozzles of straight pipe and curved pipe were carried out,and the results showed that the installation of curved pipes can effectively limit the drift of fog flow and improve the deposition of fog droplets,but it will increase the unevenness of fog droplets and limit the spray width of smoke plant protection UAVs.2)The flow field of smoke plant protection UAV is analyzed by using fluid dynamics software based on the lattice Boltzmann method,and the variation characteristics of the rotor flow field under different flight speeds and different flight moments are explored.The results show that when the UAV flight altitude is 4m and the flight speed is 2-5m/s,with the increase of speed,two distinct tail vortexes are gradually formed behind the fuselage,and the height of the tail vortex behind the fuselage also increases with the increase of speed.3)The site was set up for testing,and the droplet deposition and diffusion distribution data of the smoke plant protection UAV were measured without plant cover by the water-sensitive test strip method.The results showed that the median diameter of the droplet volume at each test point was about 50 μm,and the particle size range of the droplets met the requirements for the prevention and control of plant diseases and insect pests.The spatial distribution of droplets increased from top to bottom,and the trend of each layer in the horizontal direction was about the same,and at the same height and spray flow,the droplet particle size and sedimentation decreased with the increase of flight speed.4)In order to verify the spray effect of the smoke plant protection drone in the crop environment,the field experiment of the middle and late stage of maize was carried out,and the sedimentary characteristics of the leaves and ground fog droplets of maize plants were measured by water-sensitive dipstick method.The results show that the particle size of the mist droplets on the front and back of the leaves is not much different,the deposition is uniform,and the quantity change trend is obvious.Under the condition of adding smoke additives,the droplet coverage and sedimentation distribution change significantly,and the fog additives can improve the distribution uniformity of the droplets,but increase the droplet particle size.The canopy coverage at the location of the fog flow landing point reached35.38%,the middle layer reached 26.06%,and the bottom layer reached 15.97%.Compared with the undisturbed droplet additives,it is 1.96 times,1.93 times and 3.65 times.The results of this paper show that the smoke plant protection UAV designed and developed has stable working performance and convenient operation,and the droplet particle size and droplet deposition law under the smoke additive are systematically analyzed by the system,which is plant protection in the middle and late stage of maize The operation provides a new equipment and technical support.