Research On Precision Spraying System And Atomization Characteristics For Nozzles

Pest control is an important guarantee for fruit yield and quality.At present,air-assisted sprayer is commonly used in forest and fruit pest control because of its strong penetration and spray uniformity.However,for young fruit trees with small plants and sparse canopy,the air-assisted sprayer has the problems of ineffective spraying in fruit tree gap and intensified droplet drift,resulting in these problems such as low liquid utilization rate and serious environmental pollution,and excessive application also raises concerns about food safety.In order to reduce pesticide spraying and improve utilization rate,this study investigated the problems of pesticide application in the seeding stage and early transplantion stage of fruit trees as follows:(1)Aiming at the problem of inffective spraying between fruit trees and aggravating droplet drift in wind assisted sprayer,a swing arm precision target spraying vehicle for fruit trees pesticide application was developed based on a laser range sensor.The application vehicle identifies and locates the fruit canopy through the detection system(laser range sensor),and transmits the position information to the control system through the data acquisition card.The control system predicts the target position in real time by combining the movement speed and heading angle of the application platform,and transmits the spray signal to the application execution system at the appropriate time to achieve precise spraying,and records the spray volume data through the electronic flow meter.At the same time,this study developed multi-threaded control software based on MFC to realize the independent operation of the detection system,control system and application execution system of the precision spraying vehicle for tree pesticide barrier.(2)The pesticide solution is sprayed from the nozzle and atomized into droplet groups by the action of air.After a short time of flight,the droplet group acts on the target surface to complete the spraying process.In this process,droplet drift and rebound when hitting the target are key factors to reduce pesticide utilization.In this process,droplet drift and rebound when hitting the target surface are key factors in reducing pesticide utilization.In this study,the factors affecting droplet drift and rebound and round were analyzed and found that droplet size and velocity were the key to determine droplet drift and rebound.Therefore,in this study,the atomization characteristics of the flat fan nozzle for agriculture and forestry were analyzed by using the phase Doppler particle analyzer(PDPA),and the spray axis,longaxis surface and three-dimensional(3D)atomization models were analyzed and fitted according to the method from line to surface and finally extended to three-dimensional.The 3D atomization models based on the spray pressure,spray angle and equivalent orifice diameter were established and verified by actual tests.The validation results show that the average absolute error and relative error between the actual test data and the theoretical data of droplet size were 25.13?m and 8.79% respectively;and the average absolute error between the actual test data and the theoretical data of the droplet velocity was 0.53 m/s and the relative error is 12.80%.(3)In spraying operations,spray uniformity is an important indicator of nozzle quality and predicted spraying effect.At this stage,the span of droplet size distribution on the specified spray height section and the distribution of spray deposition along the long axis are the main methods to test the spray uniformity.However,these methods ignore the existence of a certain thickness of the three-dimensional spray field along the direction of travel of the spraying vehicle.Based on this,this study proposed a method to evaluate the spray uniformity by combining the coefficient of variation(C.V)of the span of droplet size distribution,the C.V of the liquid volume distribution and the C.V of the volume median diameter distribution,and futher discussed the effects of spray angle,equivalent orifice diameter,spray distance and spray pressure on the spray uniformity.The feasibility of using spray uniformity and nozzle three-dimensional atomization model to predict spray deposition effect was verified by droplet deposition test.