Air-assisted Sprayer Research Articles

Design and test of a novel crawler-type multi-channel air-assisted orchard sprayer

In order to solve the problem of poor traveling stability and excessive pesticide application during plant protection operations in hilly orchards, a novel crawler-type multi-channel air-assisted sprayer that is particularly appropriate for hilly orchards was designed in this study. Considering anti-rolling requirements and the orchard environment in hilly areas, this study selected limits for uphill and downhill rolling angles as well as the transverse rolling angle as the evaluation indexes for determining both the layout and parameter settings of the sprayer. According to freely submerged jets and the requirements in plant protection operation, a multi-channel air-assisted system was developed. The test results showed that the anti-rolling performance and the designed air-assisted system were adequate. At 2 m from the longitudinal center plane of the sprayer, the airflow exhibited wavy distribution patterns under different parameter combinations since the four streams of the airflow were not thoroughly intersected and mixed. At 3 m from the longitudinal center plane of the sprayer, the jet was ejected at great velocity but underwent rapid attenuation; the airflow velocity in most areas barely satisfied the requirements for plant protection operation. In addition, different air outlet layout schemes led to significant differences in the spatial distribution of the airflow field. Compared with a traditional air-assisted sprayer, using the developed multi-channel air-assisted sprayer enhanced the droplet coverage uniformity by 19.4%, and the mean droplet deposition in the front, middle, and rear of the canopy was enhanced by 32.9%, 50.3%, and 78.1%, respectively, while reducing ground deposition and air drift by 26.8%. Keywords: fan, dual-flow-channel, plant protection, air-assisted, test DOI: 10.25165/j.ijabe.20201306.5362 Citation: Qiu W, Li X L, Li C C, Ding W M, Lv X L, Liu Y D. Design and test of a novel crawler-type multi-channel air-assisted orchard sprayer. Int J Agric & Biol Eng, 2020; 13(6): 60–67.

Atomization behaviour of a hybrid air-blast-electrostatic atomizer for spray combustion

An analysis of the atomization region of a series of diesel sprays generated from a hybrid (air-blast & electrostatic) atomizer is presented. The atomizer has been specifically designed to operate on single or hybrid mode to enable the delivery of a charged and/or air-assisted spray for combustion applications. High speed microscopic backlit imaging is applied over a range of operating conditions. A noticeable influence of charge on the measured droplet and ligament size and their numbers is observed at all the tested aerodynamic Weber numbers (We = 2.4, 5.2, 8.2, 11.2). The experimental results reveal that an increase in spray specific charge can reduce both droplet and ligament sizes while a significant increase in droplet count is noted. The influence of charge is found to vary depending on the aerodynamic Weber number, with a more noticeable influence on the atomization behaviour for the lowest Weber number case (We = 2.4). When operating in a hybrid mode, a minimum spray specific charge (0.14C/m3) is required for the applied electric potential to influence the aerodynamically assisted spray.

Fundamental spray characteristics of air-assisted injection system using aviation kerosene

Spray characteristics of an air-assisted injector under various injection parameters and ambient conditions were investigated in a constant volume chamber experimentally. High-speed backlight imaging technique was used for spray visualization to obtain macroscopic characteristics such as spray shape while Phase Doppler Particle Analyzer (PDPA) was utilized to measure spray droplet diameter and velocity. Spray characteristics under flash boiling and non-flash boiling conditions were compared. The results show that flash-boiling substantially promotes spray atomization by increasing droplet spreading and reducing droplet size. Increasing of fuel injection duration increases the liquid fuel content in the jet, therefore consumes more gas kinetic energy to accelerate the fuel droplet and results in the decreasing of jet velocity and penetration, which in turn suppresses droplet aerodynamic breakup and induces the increasing of droplet size. By analyzing droplet diameter distribution and droplet-airflow interaction of air-assisted spray, we found that droplets less than 10 μm accounts for majority of the trapped droplets. Moreover, the Stokes numbers of considerable number of droplets are less than 0.1, which indicates a large number of droplets tend to flow with the air flow and droplet velocity can be treated as a practical approximation for gas-phase velocity.

Advancing Sustainability in Tree Crop Pest Management: Refining Spray Application Rate with a Laser-guided Variable-rate Sprayer in Apple Orchards

Advanced variable-rate spray technology, which applies pesticides based on real-time scanning laser rangefinder measurements of plant presence, size, and density, was developed and retrofitted to existing sprayers. Experiments were conducted to characterize the application of four programmed spray rates (0.03, 0.05, 0.07, or 0.09 L·m−3 of crop geometric volume) when applied to Malus domestica Borkh. ‘Golden Delicious’ apple trees using this crop sensing technology. Water-sensitive cards (WSCs) were used as samplers to quantify spray coverage, deposits, and deposit density in the target and nontarget areas, and an overspray index based on a threshold of greater than 30% coverage was calculated. The application rate ranged from 262 L·ha−1 at the programmed spray rate of 0.03 L·m−3 to 638 L·ha−1 at the rate of 0.09 L·m−3. For a given WSC position, spray coverage and deposits increased as the spray rate increased. WSC positions 1 and 2 were oversprayed at all rates. The effect of spray rate on deposit density varied with WSC positions, with high densities achieved by low spray rates for WSCs closest to the sprayer but by high spray rates for WSCs positioned either deeper within or under the canopy. When coalescing deposits were accounted for, deposit densities met or exceeded the recommended pesticide application thresholds (insecticides 20–30 droplets/cm2; fungicides 50–70 droplets/cm2) at all WSC positions for each spray rate tested. The lowest spray rate reduced off-target loss to the orchard floor by 81% compared with the highest rate, dramatically reducing potential exposure to nontarget organisms, such as foraging pollinators, to come into contact with pesticide residues. Applying the lowest rate of 0.03 L·m−3 met deposit density efficacy levels while reducing spray volume by 83% compared with the orchard standard application of 1540 L·ha−1 and by 87% compared with the 1950 L·ha−1 application rate recommended when using the tree row volume method. Thus, there is potential for growers to refine pesticide application rates to further achieve significant pesticide cost savings. Producers of other woody crops, such as nursery, citrus, and grapes, who use air-assisted sprayers, may be able to achieve similar savings by refining pesticide applications through the use of laser rangefinder-based spray application technology.

Evaluating the effectiveness of low volume spray application using air-assisted knapsack sprayers in wine vineyards

We evaluated spray coverage on grape leaves and bunches by a high-volume sprayer (HVS), an air-assisted, low volume knapsack sprayer (LVS), and a motorized knapsack dust applicator modified to spray liquid formulations (common sprayer – CS). At the full development of the vine canopy 1400, 250 and 150 L ha−1 were applied via HVS, CS and LVS, respectively. Sprayer type, leaf or bunch orientation, leaf position and leaf side significantly affected spray coverage (P < 0.001). Mean spray coverage on leaves or bunches was below 21% for CS, and above 40 and 55% for LVS and HVS, respectively. Downy mildew leaf infection was below 5% throughout the season, with a significant effect of sprayer, time and an interaction between sprayer and time (P < 0.001). Grape berry moth damage did not differ between sprayers and the untreated control. The current work suggests that LVS might be a viable alternative to HVS, but further work is needed to establish whether differences in spray coverage affect biological efficacy.

Deposition and distribution of myclobutanil and tebuconazole in a semidwarf apple orchard by hand-held gun and air-assisted sprayer application.

Sprayers have been shown in numerous reports to influence pesticide deposition and distribution significantly, and public concern for their potential risk has been increasing in recent years. In this study, a hand-held gun sprayer and two air-assisted sprayers (a conventional axial fan air-blast sprayer and a tower sprayer) were used to apply myclobutanil and tebuconazole, and their influence on pesticide distribution and deposition in a semidwarf apple orchard was systematically investigated. The coefficients of variation of different canopy zones associated with the tower sprayers were 38.9-41.9% for leaves and 35.5-36.4% for fruit, generally lower than the coefficients of variation related to the other two sprayers. Tests conducted using the air-assisted sprayers recorded an overall higher drift on the adjacent rows than experiments carried out with the hand-held gun sprayer. The results of drift in soil indicated that pesticide was mainly distributed within 5 m downwind of the treated area, and the distribution pattern was influenced by sprayer design. The total pesticide concentration deposited in soil within 5 m during application by the tower sprayer was 0.28 m mg kg-1 for myclobutanil and 0.90 m mg kg-1 for tebuconazole, much lower than that of the hand-held gun sprayer and the conventional axial fan air-blast sprayer. The results indicate that the tower sprayer gives a more uniform distribution and guarantees better effectiveness for the phytosanitary treatment. The tower sprayer also protected the soil better and reduced environmental pollution due to its scientific structural design. © 2020 Society of Chemical Industry.

Atomization characteristics of a fan air-assisted nozzle used for coal mine dust removal: an experimental study

ABSTRACT This article focuses on the atomization characteristics of fan air-assisted nozzles, which is important in the emerging process of dust removal via air-assisted nozzles in underground coal mines. An experimental study on atomization characteristics of a fan air-assisted nozzle was conducted using a custom-built air-assisted spray system. The results reveal that the volume flow rate of the medium, i.e., either water or air, showed a negative exponentially increasing trend as itself pressure increasing and showed a linearly decreasing trend as the other pressure increasing. The drop size distribution met the Rosin-Rammler function. When the air pressure was 0.5 MPa, the drop distribution moved right, and the uniformity coefficient of the distribution fell as the water pressure increased from 0.1 MPa to 0.9 MPa; the drop distribution moved left and the uniformity coefficient raised as the water pressure increased from 0.9 MPa to 1.0 MPa. When water pressure was 0.5 MPa, the drop distribution moved left, and the uniformity coefficient fell as the air pressure increased. The drop size grew downstream; the growth speed was proportional to droplet density and water volume fraction and inversely proportional to drop size. The drop size first tended to increase then showed a decreasing trend as the water pressure increased; the value of the cutoff point increased as the water pressure increased. The drop size decreased as the air pressure increased.

Orchard Spray Study: A Prediction Model of Droplet Deposition States on Leaf Surfaces

During air-assisted spraying operations in orchards, the interaction between the droplets and the target leaves has a decisive influence on the retention of the droplets on the leaves and the final deposition state. Based on the observation of the final deposition effect of the droplets in the spray test, the retention state of the droplets on the leaves is divided into three categories: uniform distribution (hereinafter referred to as uniform), accumulation, and loss. During the initial interaction between the droplets and the leaves, the adhesion or sliding state of the droplets has an important influence on the final deposition state of the droplets, which is determined by the target leaf adhesion work in this paper. Based on obtaining the characteristic parameters of the leaf surface, a theoretical model of adhesion work related to parameters such as the contact angle, rough factor, and initial tilt angle of the leaf is established. Afterward, through the connection of the droplet coverage on the macro level, the establishment of the deposition state model of the droplet group on the leaf is completed. By conducting the experiment test based on the Box-Behnken design of response surface methodology (RSM), the droplet deposition states under the influence of the spray distance, fan outlet wind speed and droplet size were studied and compared with the predicted values. The test results show that the prediction accuracies of the three states of uniform, accumulation, and loss were 87.5%, 80%, and 100%, respectively. The results of the study indicate that the established prediction model can effectively predict the deposition states of droplets on leaves and provide a reference for the selection of spray operation parameters.

Biphasic Computational Fluid Dynamics Modelling of the Mixture in an Agricultural Sprayer Tank.

Agitation inside agricultural sprayer tanks can be studied while using an international standard procedure, based on obtaining internal samples of liquid. However, in practice, this test is not easy to perform. Herein, we propose the explicit study of the mixing procedure with biphasic computer simulations using Computational Fluid Dynamics (CFD). An experimental test was performed on a 3000 L tank of a commercial air-assisted sprayer, with two different agitation system configurations, in order to compare the results of several theoretical physical models of biphasic flows for CFD, both Eulerian and Lagrangian. From the analysis of these theoretical models, we conclude that the Volume of Fluid model is not viable and the Discrete Phase Model produces erroneous results, while the Eulerian and Mixture models can both be useful. However, the results obtained suggest that complex streams generated by real-world agitation systems produce more errors in calculations. Both models can be conducted in the design phase, prior to the implementation of the machine. In addition, the computer simulations allow for researchers to analyse the mixing process in detail, making it possible to evaluate the efficiency of an agitation system according to the time that is required to reach mixture homogeneity.

Optimization of working parameters for 3MGY-200 axial air-assisted sprayer in kiwifruit orchards

Axial air-assisted sprayers can distribute pesticides efficiently in kiwifruit orchards. Because of improper parameter settings, most sprayers deliver either too much or too little pesticide. To identify appropriate sprayer parameters for kiwifruit trees, the vertical distribution profiles of the applied liquid spray were examined in this study. The effects of spray fan speed (SFS), spray pressure (SP) and spray distance (SD) on the distributions of the sprayed liquid in the vertical profiles were studied. Combined actions of the above parameters were systematically analysed using the quadratic general rotary design test method. Regression equations for the spray liquid distributions and working factors are presented. Field confirmation experiments were carried out to optimize the parameters. Data analysis showed that the optional sprayer working parameters are those of Group 3, with an SFS equal to 1900 r/min and SP equal to 3.25 MPa. The results of this study provide a reference for future applications of this type of axial air-assisted sprayer in kiwifruit orchards. Keywords: sprayer parameters, quadratic general rotary unitized design, regression equation, optimization, kiwifruit tree DOI: 10.25165/j.ijabe.20201302. Citation: Gu C C, Liu Z J, Pan G T, Pu Y J, Yang F Z. Optimization of working parameters for 3MGY-200 axial air-assisted sprayer in kiwifruit orchards. Int J Agric & Biol Eng, 2020; 13(2): 81–91.

A novel approach for conditional measurement of droplet size distribution within droplet clusters in sprays

A novel method for conditional measurement of droplet size distribution within droplet clusters in sprays is reported in this paper. The salient feature of this approach is the application of Voronoi analysis to droplets measured by the ILIDS technique, which is capable of providing planar measurement of size of individual droplets in a spray. The principle of the present technique is based on calculation of Voronoi tessellations around the droplets identified in the ILIDS image processing. Comparison of the distribution of areas of the Voronoi cells with that from a random distribution of droplets described by a Poisson function facilitates classification of the Voronoi cells as clusters or voids. Thus, individual clusters of droplets and void areas are recognized by identifying the interconnected cells. Since the sizes of individual droplets are known, conditional measurement of droplet size distribution within clusters and voids is possible. Since droplet images are always defocused in the ILIDS technique, correct identification of droplet centers is important, which is described in the paper. It is shown that in spite of the low validation ratio in the ILIDS image processing, the results on the cluster and void characterization agree well with those by Voronoi analysis of PIV images. The novel method is demonstrated for an air-assist spray where ILIDS measurements are obtained far downstream of the injector exit. Interestingly, the characteristic droplet size within droplet clusters is found to be smaller than that in voids, indicating size-based preferential segregation of droplets due to clustering in sprays.

On the role of vortex-ring formation in influencing air-assisted spray characteristics of n-heptane

Air-assisted spray characteristic in a constant-volume vessel has been investigated experimentally. Influences of injection control parameters such as fuel injection duration ΔTf, fuel-air injection interval ΔTf-a and air injection duration ΔTa on the spray characteristics were studied. Results show that two distinct spray shapes were observed under appropriate control parameters, namely, “spindle-shaped” spray and “anchor-shaped” spray. The “anchor-shaped” spray which promotes spray spread possesses relatively smaller spray tip penetration, but better spray spread which is beneficial to fuel/air mixing. The enhancement on spray spread for “anchor-shaped” spray is attributed to the formation of vortex-ring near spray tip under relatively low spray velocity. Non-monotonic spray dispersion area ratio Rd can be observed with increasing ΔTf, ΔTf-a and ΔTa. Droplet velocity decreases with ΔTf increasing, which suppresses droplet breakup therefore results in the increasing of droplet size. However, the formation of the vortex-ring weakens this increasing trend of droplet size. Increasing of ΔTf-a tends to generate stable vortex ring hence stable droplet velocity and SMD. In terms of air injection duration ΔTa, droplet velocity was observed to change non-monotonically with ΔTa increasing, due to the “spindle-shaped — anchor-shaped — spindle-shaped” spray shape transition.

Assessment of Spray Deposition and Losses in an Apple Orchard with an Unmanned Agricultural Aircraft System in China

Highlights Field tests were performed in an orchard to evaluate spray performance of an unmanned agricultural aircraft system. A conventional air-assisted orchard sprayer was applied as a reference for comparing the feasibility of UAAS. The canopy deposition, airborne drift, loss to ground, and sprayer external contamination were tested. Field test results can provide a reference for the application of UAAS for pest control in orchards. Abstract. Unmanned agricultural aircraft system (UAAS) technology has developed rapidly in China in recent years. Due to their high application efficiency, all-terrain operation, and low-volume spraying, UAASs have been widely used for pest management in field crops, achieving good pest control and reduced pressure on farmers. In this study, the applicability of UAAS for orchard protection was tested in an apple orchard by spraying with a four-rotor UAAS and a conventional air-assisted orchard sprayer. The spray characteristics of both sprayers, including canopy deposition, drift in the air, loss to the ground, and external contamination on the sprayer, were measured and compared. The field results showed that the effective spray swath width of the UAAS was 2.23 m, and the maximum droplet density was 132 droplets cm -2 in the center of the flight line. The actual deposition in the tree canopy was lower with the UAAS than with the air-assisted sprayer, but the normalized deposition of the UAAS was equivalent to that of the air-assisted sprayer, and the coefficient of variation for deposition in all parts of the canopy was obviously higher for the UAAS than for the air-assisted sprayer. Due to the airflow produced by the high-speed rotors, the spray drift in the air was much higher with the UAAS than with the air-assisted sprayer, whereas the ground loss of the UAAS was 1/5 that of the air-assisted sprayer. Moreover, the rotor airflow of the UAAS caused a large amount of droplets to attach to the sprayer fuselage, causing the external contamination on the UAAS to be five times that of the air-assisted sprayer. Results showed that the use of a multirotor UAAS for plant protection in an orchard had considerable influence on the spray drift and external contamination of the spray equipment. Based on the results, the following recommendations can be made: (1) plant protection with a UAAS should be attained by spraying at a reasonable height to reduce the drift in the air, and (2) UAAS manufacturers should develop adequate spraying systems as well as appropriate UAAS designs for plant protection. Keywords: Air-assisted orchard sprayer, Apple orchard, Spray deposition, Spray loss, UAAS.

Design and test of a novel crawler-type multi-channel air-assisted orchard sprayer

In order to solve the problem of poor traveling stability and excessive pesticide application during plant protection operations in hilly orchards, a novel crawler-type multi-channel air-assisted sprayer that is particularly appropriate for hilly orchards was designed in this study. Considering anti-rolling requirements and the orchard environment in hilly areas, this study selected limits for uphill and downhill rolling angles as well as the transverse rolling angle as the evaluation indexes for determining both the layout and parameter settings of the sprayer. According to freely submerged jets and the requirements in plant protection operation, a multi-channel air-assisted system was developed. The test results showed that the anti-rolling performance and the designed air-assisted system were adequate. At 2 m from the longitudinal center plane of the sprayer, the airflow exhibited wavy distribution patterns under different parameter combinations since the four streams of the airflow were not thoroughly intersected and mixed. At 3 m from the longitudinal center plane of the sprayer, the jet was ejected at great velocity but underwent rapid attenuation; the airflow velocity in most areas barely satisfied the requirements for plant protection operation. In addition, different air outlet layout schemes led to significant differences in the spatial distribution of the airflow field. Compared with a traditional air-assisted sprayer, using the developed multi-channel air-assisted sprayer enhanced the droplet coverage uniformity by 19.4%, and the mean droplet deposition in the front, middle, and rear of the canopy was enhanced by 32.9%, 50.3%, and 78.1%, respectively, while reducing ground deposition and air drift by 26.8%. Keywords: fan, dual-flow-channel, plant protection, air-assisted, test DOI: 10.25165/j.ijabe.20201306.5362 Citation: Qiu W, Li X L, Li C C, Ding W M, Lv X L, Liu Y D. Design and test of a novel crawler-type multi-channel air-assisted orchard sprayer. Int J Agric & Biol Eng, 2020; 13(6): 60–67.

Droplet Deposition Behavior on a Pear Leaf Surface under Wind-Induced Vibration

HighlightsDroplet deposition behavior on pear leaf surfaces under wind-induced vibration was investigated.The factors and limiting conditions affecting the vibration and spreading of droplets were analyzed.A mathematical model of the vibration and spreading of droplets on pear leaves was constructed.Abstract. Pear trees, a kind of fruit tree prone to diseases and insects, are sprayed 7-8 times a year in northern China and 8-10 times a year in the hot and humid areas of southern China. Air-assisted spraying is also the mainstream application technique for pear trees at present. To study the deposition behavior of droplets on pear leaves under the effect of air flow, the movement states of fluorescent droplets at different initial leaf angles and different leaf positions were measured with a high-speed camera. Based on the combined effect of the microstructure and the vibration of pear leaves, the factors and limiting conditions affecting the vibration and spreading of droplets were analyzed, and a mathematical model of the vibration and spreading of droplets on pear leaves was constructed. The experiment showed that the degree of influence of each factor on the velocity and acceleration of the droplets is in turn the inflow velocity, the drop position and the initial leaf angle. For pear hydrophilic plants, it is necessary to meet both conditions that the droplet velocity is less than the critical velocity of 1.1 m/s and the droplet acceleration is less than the critical acceleration of 20 m/s2 so that the droplet can deposit on the leaf surface. An inflow velocity of 7 m/s better facilitates droplet deposition and spreading. Keywords: Deposition behavior, Pear leaf, Wind-induced vibration.

Optimization of working parameters for 3MGY-200 axial air-assisted sprayer in kiwifruit orchards

Axial air-assisted sprayers can distribute pesticides efficiently in kiwifruit orchards. Because of improper parameter settings, most sprayers deliver either too much or too little pesticide. To identify appropriate sprayer parameters for kiwifruit trees, the vertical distribution profiles of the applied liquid spray were examined in this study. The effects of spray fan speed (SFS), spray pressure (SP) and spray distance (SD) on the distributions of the sprayed liquid in the vertical profiles were studied. Combined actions of the above parameters were systematically analysed using the quadratic general rotary design test method. Regression equations for the spray liquid distributions and working factors are presented. Field confirmation experiments were carried out to optimize the parameters. Data analysis showed that the optional sprayer working parameters are those of Group 3, with an SFS equal to 1900 r/min and SP equal to 3.25 MPa. The results of this study provide a reference for future applications of this type of axial air-assisted sprayer in kiwifruit orchards. Keywords: sprayer parameters, quadratic general rotary unitized design, regression equation, optimization, kiwifruit tree DOI: 10.25165/j.ijabe.20201302. Citation: Gu C C, Liu Z J, Pan G T, Pu Y J, Yang F Z. Optimization of working parameters for 3MGY-200 axial air-assisted sprayer in kiwifruit orchards. Int J Agric & Biol Eng, 2020; 13(2): 81–91.

Research Progress on Variable-Rate Spraying Technology in Orchards

HighlightsReview the research status of variable-rate spraying technology and point out the direction for the future researchDiscussed the advantages and disadvantages of different techniques to detect canopy volume and canopy biomassThe air speed and volume adjustment need to be controlled based on the canopy detection systemAbstract. Variable-rate pesticide application in orchards aims to solve the problems of low pesticide utilization rates and serious environmental pollution in traditional pesticide applications. In this article, we have reviewed the research status of the technology to point out the direction for future research. Orchard tree canopy volume detection, biomass detection, and variable-rate spraying control methods were systematically summarized and analyzed. The advantages and disadvantages of different sensing techniques for detecting canopy volume and canopy biomass have been discussed. Canopy volume is mainly detected by ultrasonic sensors and light detection and ranging (LiDAR) sensors. Canopy biomass detection can be realized by manual, ultrasonic sensors, LiDAR sensors, and other sensors. Variable-rate spraying control is in two parts: liquid flow rate regulation and air supply rate regulation. In order to determine the volume of the liquid variable-spray, the variable air supply of air-assisted sprayer has been proven to be important. Liquid flow regulation can be achieved by pipeline pressure control and nozzle flow rate control together with a series of algorithms. The direction of air supply is easy to determine, but the air speed and volume adjustment need to be controlled based on the canopy detection system. Finally, future research on variable-rate spraying technology should focus on: 1) the application of advanced sensing technology for accurate and real-time measurement of canopy volume and biomass, 2) accurate control algorithms for liquid flow rate regulation and methods for airflow regulation, and 3) design of variable-rate sprayers with both liquid and air regulations, and the establishment of different types of variable-rate models for different sprayer types. Keywords: Air supply rate regulation, Canopy biomass detection, Canopy volume detection, Liquid flow rate regulation, Orchard, Variable-rate spraying.

Design and performance evaluation of a variable-rate orchard sprayer based on a laser-scanning sensor

To improve the precision spraying strategy and reduce excessive pesticide application in orchards, an air-assisted sprayer integrated with a laser-scanning system was developed to realize the toward-target variable-rate spraying. In the spray control system, a method of calculating canopy gridding volumes was designed to ensure the canopy was divided into a uniform grid size, a variable-rate spray model was used in the flow rate decision software to control the spray output according to the canopy gridding volumes and travel speed, and a method of saving and accessing spray data was used to control the spray delay. The effects of different grid sizes and travel speeds on the spray performance were evaluated by quantifying spray coverage uniformity inside tree canopies. The results showed that spray coverage uniformity declined with increasing grid width from 0.14 to 0.28 m although the mean spray coverage on each target location showed no significant differences. Additionally, there were no significant variations in mean spray coverage at speeds of 1.0, 1.2 and 1.4 m/s for a tested tree of 1.6 m width and at any experimental speeds for a tested tree of 1.3 m width, which indicated that the variable-rate sprayer could provide good spray coverage uniformity under various travel speeds with a canopy size limitation. Compared with the same sprayer without the variable-rate spray function, the intelligent sprayer prototype realized effective toward-target spraying and avoided overspraying while providing sufficient spray coverage. Keywords: laser-scanning sensor, variable-rate spray, orchard, precision sprayer, pesticide application efficiency DOI: 10.25165/j.ijabe.20191206.4174 Citation: Cai J C, Wang X, Gao Y Y, Yang S, Zhao C J. Design and performance evaluation of a variable-rate orchard sprayer based on a laser-scanning sensor. Int J Agric & Biol Eng, 2019; 12(6): 51–57.

Fruit detection, yield prediction and canopy geometric characterization using LiDAR with forced air flow

Yield monitoring and geometric characterization of crops provide information about orchard variability and vigor, enabling the farmer to make faster and better decisions in tasks such as irrigation, fertilization, pruning, among others. When using LiDAR technology for fruit detection, fruit occlusions are likely to occur leading to an underestimation of the yield. This work is focused on reducing the fruit occlusions for LiDAR-based approaches, tackling the problem from two different approaches: applying forced air flow by means of an air-assisted sprayer, and using multi-view sensing. These approaches are evaluated in fruit detection, yield prediction and geometric crop characterization. Experimental tests were carried out in a commercial Fuji apple (Malus domestica Borkh. cv. Fuji) orchard. The system was able to detect and localize more than 80% of the visible fruits, predict the yield with a root mean square error lower than 6% and characterize canopy height, width, cross-section area and leaf area. The forced air flow and multi-view approaches helped to reduce the number of fruit occlusions, locating 6.7% and 6.5% more fruits, respectively. Therefore, the proposed system can potentially monitor the yield and characterize the geometry in apple trees. Additionally, combining trials with and without forced air flow and multi-view sensing presented significant advantages for fruit detection as they helped to reduce the number of fruit occlusions.

CFD Models as a Tool to Analyze the Performance of the Hydraulic Agitation System of an Air-Assisted Sprayer

A computational fluid dynamics (CFD) model of the fluid velocities generated by the agitation system of an air-assisted sprayer was developed and validated by practical experiments in a laboratory. The model was developed considering different settings of the agitation system: Three water levels in the tank (1000, 2000, and 3000 L); two different numbers of active nozzles (2 or 4); and three working pressures of the agitation circuit (8, 10, or 12 bar). Actual measurements of the fluid velocity into the tank were taken using an acoustic Doppler velocimeter (ADV). CFD simulations made it possible to estimate fluid velocities at 38% of the measuring points with relative errors of less than 30%. Additionally, the CFD models have allowed the correct prediction of the general behavior of the fluid in the tank considering mean velocities depending on the setting parameters of the agitation system (water level in the tank, hydraulic circuit pressure, and number of active nozzles).