Design and experiment of self-propelled air-assisted sprayer in orchard with dwarf culture

Abstract: Plant protection is very important for high yield and quality of fruits production. A new self-propelled sprayer with low height was developed accommodating small space and poor trafficability of conventional orchards which are densely planted with dwarf plants. The power transmission system of the machine was optimized and the air supply atomization device was designed. The power transmission system distributes power separately, so the fan, pump, walking and steering device can be controlled independently. Designing of the air supply device and main technical parameters of key parts were based on theories of fluid mechanics and pesticide delivery technique applications. The R+S channel, 9 impellers, 11 guide glades was adopted. The diameter of impellers was 0.6 m and the width of guide glades was 0.1 m. The fan property was tested and the performance curve graphic was drawn. Frequency transformer, torque meter, wind velocity indicator was used and the testing ring was put 1m ahead of the air enter which was connected with a set of rams to fan pipes. The ram's diameter are 0.6 m, as same as fan's. The results showed that air volume was 2.7 m3/s meet at 1400 r/min which demands design needs. The highest total pressure efficiency is 86% at 1600 r/min. As the speed increases, total pressure efficiency dropped rapidly but the power increased. The variation trends of the air volume and air pressure are not significant. The field experiment was conducted in an apple grove which was grown with "Jinshiji"apple trees. The experiment followed strictly the quality of air-assisted orchard sprayer (NY/T 992-2006) and evaluating regulations for the operation and spraying (GB/T17997-2008).The row space was 3 m×2 m, diameter of the tree crown was 2 m, the height of the tree was 2.5 m. Three trees were randomly selected as sample trees. The intersection points of three horizontal layers and three vertical layers of each tree were set as sample points, that is, 27 sample points totally for one tree. Water-sensitive paper card with the same size to apple leaves were put on sample points both front and rear sides receiving droplets to measure the cover ratio of droplets. The paper cards were numbered according to the sample points. Paper cards were collected after droplets got dry. Droplets cover ratio of each paper card was measured by micro camera and droplets image processing system. Results showed that the spraying coverage and droplets density increased significantly with the increase of the fan speed, spraying manipulation was conducted at the condition of 0.5 MPa spray pressure, 1400 r/min fan speed, and 1.26 m/s velocity, the spraying coverage in front and rear of the leaf was 58.76% and 19.06% inside the tree, and 69.35% and 32.66% outside the tree crown, droplets density in front and rear of the leaf was 115 and 79 droplets/cm2 inside the tree, and 105 and 96 droplets/cm2 outside the tree crown. The operation efficiency reached to 0.91 hm2/h when the proportion of auxiliary time and operation time is one to two.