Air-assisted Sprayer Research Articles

Pesticide dose based on canopy characteristics in apple trees: Reducing environmental risk by reducing the amount of pesticide while maintaining pest and disease control efficacy

Although many different designed air-assisted sprayers can be used for pesticide application in apple orchards, the lack of adequate adjustments according to specific crop characteristics leads to application inefficiencies and failures. To evaluate the spray coverage and biological efficacy of different application techniques combined with an alternative dosage adjustment based on tree row volume (TRV), field tests with five different techniques were carried out at three crop stages on a commercial apple orchard. The results showed that conventional mist-blower with a high application volume (800 L ha−1) exhibited an excessive coverage with a high risk of contamination at the early crop stage (BBCH19), whereas other treatments using different application techniques, with a reduced volume rate and pesticide dose of 75%, were equivalent with good uniformity, revealing the great importance of suitable adjustment for the sprayers. For the middle and late stages (BBCH64 and 75), the orchard sprayer equipped with vertical booms provided the maximum coverage, and the pneumatic sprayer achieved significantly higher impacts density, which revealed their advantages and high efficiency for dense apple trees. The newly developed multi-fan sprayer and pneumatic sprayer achieved consistent coverage during the entire crop stage, independent of the changes in canopy structure (TRV). This indicates that a suitable setting and adjustment of the sprayer can contribute to a consistent spray quality. In general, benefiting from these new spraying technologies, an average reduction of 60.7% in pesticide dose and volume rate were achieved within the entire season, maintaining the same threshold of pest and disease control as that of the higher reference dose normally applied. These results demonstrate the importance of an alternative dose adjustment method to meet the requirements of the Farm to Fork strategy.

Design and performance test of a novel UAV air-assisted electrostatic centrifugal spraying system

In order to improve the deposition and uniformity of the pesticide sprayed by the agricultural spraying drone, this study designed a novel spraying system, combining air-assisted spraying system with electrostatic technology. First, an air-assisted electrostatic centrifugal spray system was designed for agricultural spraying drones, including a shell, a diversion shell, and an electrostatic ring. Then, experiments were conducted to optimize the setting of the main parameters that affect the charge-to-mass ratio, and outdoor spraying experiments were carried out on the spraying effect of the air-assisted electrostatic centrifugal spray system. The results showed the optimum parameters were that the centrifugal rotation speed was 10 000 r/min, the spray pressure was 0.3 MPa, the fan rotation speed was 14 000 r/min, and the electrostatic generator voltage was 9 kV; The optimum charge-to-mass ratio of the spray system was 2.59 mC/kg. The average deposition density of droplets on the collecting platform was 366.1 particles/cm2 on the upper layer, 345.1 particles/cm2 on the middle layer, and 322.5 particles/cm2 on the lower layer. Compared to the results of uncharged droplets on the upper, middle, and lower layers, the average deposition density was increased by 34.9%, 30.4%, and 30.2%, respectively, and the uniformity of the distribution of the droplets at different collection points was better. Keywords: UAV spraying, droplet drift, centrifugal sprayer, air-assisted spraying, electrostatic spraying DOI: 10.25165/j.ijabe.20221505.6891 Citation: Hu H M, Kaizu Y, Huang J J, Furuhashi K, Zhang H D, Xiao X, et al. Design and performance test of a novel UAV air-assisted electrostatic centrifugal spraying system. Int J Agric & Biol Eng, 2022; 15(5): 34–40.

Status of Spray Penetration and Deposition in Dense Field Crop Canopies

HighlightsCrop production practices, spray drift control, and sprayer productivity affect spray penetration into dense crop canopies.Question is raised whether airflows near foliar surfaces or within the canopy can assist spray penetration under windy conditions.Current structural descriptions of canopies do not accommodate droplet trajectories to improve spray application.New nozzle tip designs, sensors, and air-assisted spraying need tuning to improve spray penetration and deposition.Abstract. The objective of this study was to review representative publications for improved knowledge of spraying dense field crop canopies to augment the current understanding of the interaction between target foliage characteristics, spray practices, and the environment. Emphasis was placed on measured deep-canopy spray deposits made by full-scale sprayers and studies of airflow within and around crop canopies. Airflow could act as a spray droplet carrier and/or indicator of the internal canopy structure that restricts droplet penetration. High variation in natural airflows was noted in several studies. Crop canopy descriptions for spray studies were generally limited to overall canopy/row dimensions, descriptions of individual plant structures, leaf shapes, and leaf area index. Few studies evaluated the internal canopy “openness” with characteristic shape and size of internal volumes that would accommodate spray droplet trajectories. There have been significant increases in available spray tip designs with multiple orifices, discharge configurations, and droplet sizes that offered the applicator many choices. Advanced sprayer technologies ranging from nozzle control to sensor navigation are available, provided that suitable algorithms can be developed in a timely manner that pertain to a wide variety of spray and crop conditions. The air-assist technique provides a dynamic alternative to traditional over-the-top sprays for increasing spray penetration and deposit, advocating that the specifics of air discharge, spray droplet sizes, and canopy structure can be integrated. The complexity of the spraying process needs an extensive collaborative effort of many stakeholders to develop solutions for sprays to penetrate foliage that is subject to diseases and pests. Keywords: Air-assisted sprayer, Airflow, Boom sprayer, Canopy openness, Droplet trajectory, Foliar canopy, Foliar density, Row crops, Spray blockage, Spray coverage, Spray deposit, Spray nozzles.

Enhancement of Physical Characteristics of Styrene-Acrylonitrile Nanofiber Membranes Using Various Post-Treatments for Membrane Distillation.

Insufficient mechanical strength and wide pore size distribution of nanofibrous membranes are the key hindrances for their concrete applications in membrane distillation. In this work, various post-treatment methods such as dilute solvent welding, vapor welding, and cold-/hot-pressing processes were used to enhance the physical properties of styrene–acrylonitrile (SAN) nanofiber membranes fabricated by the modified electrospinning process. The effects of injection rate of welding solution and a working distance during the welding process with air-assisted spraying on characteristics of SAN nanofiber membranes were investigated. The welding process was made less time-consuming by optimizing system parameters of the electroblowing process to simultaneously exploit residual solvents of fibers and hot solvent vapor to reduce exposure time. As a result, the welded SAN membranes showed considerable enhancement in mechanical robustness and membrane integrity with a negligible reduction in surface hydrophobicity. The hot-pressed SAN membranes obtained the highest mechanical strength and smallest mean pore size. The modified SAN membranes were used for the desalination of synthetic seawater in a direct contact membrane distillation (DCMD). As a result, it was found that the modified SAN membranes performed well (>99.9% removal of salts) for desalination of synthetic seawater (35 g/L NaCl) during 30 h operation without membrane wetting. The cold-/hot-pressing processes were able to improve mechanical strength and boost liquid entry pressure (LEP) of water. In contrast, the welding processes were preferred to increase membrane flexibility and permeation.

Numerical prediction of the spray from an air-assisted fuel injection system via Eulerian–Lagrangian approach

Air-assisted fuel injection (AAFI) systems may be installed in aviation piston engines for atomization of heavy fuels. However, there are few studies on the in-cylinder air-assisted spray characteristics, which affects the improvement of AAFI engine performance. In this study, an improved air-assisted spray simulation method based on ANSYS FLUENT was proposed to predict the changes in air-assisted spray characteristics alongside spray development, compared with previous simulations, the simulation in this paper was extended in both temporal and spatial domains and more accurate boundary conditions were given. The Eulerian–Lagrangian approach was used to represent the two-phase spray flow and a dynamic mesh model was used to simulate the movement of injector needle valve. The improved method was validated by comparison against experimental results in terms of spray shape, spray volume, spray penetration, spray droplet size spatial distribution, and overall Sauter mean diameter (SMD). By using the improved method, the average relative errors of the simulation results in spray volume and spray penetration were reduced by 13.5% and 10.2%, respectively. Additionally, some typical spray field parameters (gas phase pressure, gasified fuel mass fraction, etc.) were analyzed. The improved method can be used to study the in-cylinder air-assisted spray characteristics, which is beneficial for the fuel injection parameter optimization and the combustion chamber design of the AAFI engine.

Research advances of the drift reducing technologies in application of agricultural aviation spraying

With the gradual deterioration of the ecological environment and the increase in requirements for the quality of modern life, the use of pesticides is bound to develop towards higher pesticide utilization and less environmental pollution, and the low-volume spraying for agricultural aviation operation combined with the Drift Reducing Technologies (DRTs) may be a useful way to achieve this goal. Based on an analysis of the spray drift mechanism and the primary factors influencing aerial spraying, previous research on DRTs in aerial spraying were reviewed and summarized, and it was found that DRTs in aerial spraying can effectively reduce the environmental pollution caused by pesticide drift by reducing the spraying amount of pesticides and improving the control effect of pesticides, included aerial electrostatic spray technology, aerial spray adjuvant, aerial air-assisted spray technology, drift reducing nozzles and aerial variable-rate spray technology. And according to the analysis of the current research status, some suggestions and countermeasures to reduce droplet drift of agricultural aviation spraying were put forward from the aspects of strengthening the research on DRTs for plant protection Unmanned Aerial Vehicle (UAV) and adopting reasonable DRTs methods. It is hoped that provide reference and guidance for the enterprises’ product improvement and users’ practical operation, and play the advantages of precision agricultural aviation spraying fully. Keywords: agricultural aviation spraying, pesticide, drift, DRTs, precision agriculture DOI: 10.25165/j.ijabe.20211405.6225 Citation: Chen S D, Lan Y B, Zhou Z Y, Deng X L, Wang J. Research advances of the drift reducing technologies in application of agricultural aviation spraying. Int J Agric & Biol Eng, 2021; 14(5): 1–10.

Atomization and Droplet Dynamics Analysis of Air-assisted Spray under Different Gas-liquid Ratios

Atomization and Droplet Dynamics Analysis of Air-assisted Spray under Different Gas-liquid Ratios

CFD simulation and experiment on the flow field of air-assisted ultra-low-volume sprayers in facilities

In order to explore the performance of the B-ULV-616A knapsack sprayer, computational fluid dynamics (CFD) was used to simulate the B-ULV-616A knapsack air-assisted device, which features an ultra-low-volume electric sprayer. Field experiments were carried out to test the spraying effects, and the KANOMAX anemometer was used to verify the simulated results. First, the internal and external flow fields and droplet deposition distribution of the ultra-low-volume sprayer were established. The results showed that the air-assisted spray device can change the airflow speed and direction and produce a high-speed swirling airflow at the outlet of the air-assisted spray device. The high-speed airflow (maximum of 83.5 m/s) generates negative pressure (minimum of 0.099 MPa) and causes a rapid increase in the droplet velocity and a secondary droplets spray, allowing droplets to reach a longer distance. Then, the maximum relative error was 20.14%, and its average value was 9.59%, indicating that the CFD method is suitable for the flow field analysis of the air-assisted spray device. Finally, based on the greenhouse experiment, the knapsack air-assisted ultra-low-volume electric sprayer was found to effectively improve the deposition on the rear of the crop, increase the droplet density (maximum of 81/cm2; droplet density of conventional electric sprayer is 64/cm2), and reduce the deposition amount and coefficient of variation (below 20%) within and between regions. Further, it managed to reduce pesticide use (by 69.85%) and rural non-point source pollution. Keywords: CFD simulation, air-assisted sprayer, ultra-low spraying rate, deposition, air-velocity field, relative error DOI: 10.25165/j.ijabe.20211402.6013 Citation: Lu X Y, Gong Y, Liu D J, Wang G, Chen X, Zhang X, et al. CFD simulation and experiment on the flow field of air-assisted ultra-low-volume sprayers in facilities. Int J Agric & Biol Eng, 2021; 14(2): 26–34.

Experimental investigation of the spray characteristics for air-less nozzle, internal-mix nozzle and external-mix nozzle

ABSTRACT Spray technology has a widely application in all kinds of industrial field, it is important to investigate the spray characteristics of different nozzles which have a decisive effect on spray area. In this study, Phase Doppler Analyzer is used to measure and compare the spray characteristics of air-less nozzle, internal-mix nozzle and external-mix nozzle under different injection conditions. The results show that the increase of compressed air pressure reduces the SMD of air-assisted spray. The uniformity of the droplets size distribution of internal-mix nozzle is also improved by higher compressed air pressure, while that of external-mix nozzle deteriorates. As the axial distance increases, the Sauter Mean Diameter and uniformity index of all nozzles decrease first and then increase due to the collisions and coalescence of droplets. As the radial distance increases, the Sauter Mean Diameter of spray for the air-less nozzle and internal-mix nozzle decreases, and the uniformity index increases. While the change of the Sauter Mean Diameter and uniformity index for the external-mix nozzle are opposite because air and droplets interact intensely.

Spatially variable pesticide application in olive groves: Evaluation of potential pesticide-savings through stochastic spatial simulation algorithms.

Site-specific management using spatial crown volume characterization can greatly reduce the amount of pesticides applied in agricultural treatments performed with air-assisted sprayers, while helping farmers achieve the European legislation on safe use of pesticides. Nevertheless, variable rate treatments in olive groves have received little attention. Thus, field research was conducted in a 20.6-ha traditional olive grove. Two attributes of the trees - tree crown volume (V) and tree projected area - were determined, using 67 samples for V and all trees of the field (1433) for tree projected area. Spatial continuity of both attributes was modelled with exponential variograms. To gain a measure of local uncertainty, stochastic simulation algorithms were applied. One hundred simulated images were obtained for tree projected area using direct sequential simulation. Tree projected area simulations were used to improve spatial prediction of V, more difficult and more expensive to obtain, taking advantage of the high linear correlation between both variables (rxy=0.72,p<0.001). Thus, direct sequential cosimulation was employed to predict the spatial distribution of V, obtaining 100 geostatistical realizations of V. In order to estimate the potential reduction of pesticide use in the farm with variable rate treatments, two cut-off values of V were considered (50 and 100m3crown volume). Local uncertainty, understood as the probability of each tree belonging to a given crown volume interval was determined. Probability maps were further transformed to morphological maps and finally to variable prescription maps. Two scenarios with 2 and 3 management zones (MZs) were obtained. In comparison with a conventional phytosanitary application, the variable rate treatments could reduce the pesticide amounts by 21.3% with 2 MZs, and by 38% with 3 MZs. The joint use of V and tree projected area in stochastic sequential simulation algorithms has shown to be useful to determine MZs in olive groves.

Effects of leaf response velocity on spray deposition with an air-assisted orchard sprayer

The interaction between leaves and airflow has a direct effect on the droplet deposition characteristics of the leaf canopy. In order to make clear the mechanism of droplet deposition in terms of the interaction between the droplets and leaves from the point of the leaf aerodynamic response velocity, the leaf movement under different airflow velocities and the influence of the leaf aerodynamic response on droplet coverage ratio were investigated. The effect of the aerodynamic response velocity of a leaf on the droplet deposition of the leaf surface was investigated. The aerodynamic characteristics of the leaf were analyzed theoretically. Boundary layer theory from fluid mechanics was used to develop a model of the leaf aerodynamic response velocity to nonperiodic excitations based on a convolution integral method. Target leaf aerodynamic velocities were detected using a high-speed camera, and the results indicated that the modeled leaf aerodynamic response velocity matched the measured values. At given conditions of spray liquid and leaf surface texture, the spray test showed that the droplet coverage ratio was influenced by the leaf aerodynamic response velocity, the droplet coverage ratio increased and then decreased with the leaf response velocity. Through analyze four droplets deposition state, the highest droplet deposition ratio and best deposition state on the leaf surface occur when the leaf aerodynamic response velocity was less than 0.14 m/s. According to the analysis of droplet deposition states, the uniformity of the droplet size and quantity distribution of droplets on the leaf surface related to the leaf aerodynamic response velocity. The results can provide a basis for the design and optimization of orchard air sprayers. Keywords: air-assisted spray, leaf wind vibration, leaf aerodynamic response velocity, droplet deposition states, droplet retention, orchard DOI: 10.25165/j.ijabe.20211401.5435 Citation: Li J, Li Z Q, Ma Y K, Cui H J, Yang Z, Lu H Z. Effects of leaf response velocity on spray deposition with an air-assisted orchard sprayer. Int J Agric & Biol Eng, 2021; 14(1): 123–132.

Droplet breakup and coalescence of an internal-mixing twin-fluid spray

Droplet breakup and collision dynamics of an internal-mixing twin-fluid (air-assisted) spray were investigated experimentally. Time-resolved spray morphological evolutions were obtained by employing a high-speed spray visualization system, while droplet size and velocity were measured by using a phase-Doppler particle analyzer. The results show that the air-assisted spray is composed of a bulk of tiny droplets entrained by high-speed gas-phase flow. Droplets with a diameter of less than 5 µm account for the majority of samples on the basis of the distribution function. The calculated Stokes numbers of selected tracer droplets (0 µm–5 µm) show that these droplets tend to follow the air flow faithfully and thus can be used to estimate the local air flow velocity. By comparing with the critical Weber number, we found that droplet shear breakup is absent, but some droplets may undergo turbulent breakup. A theoretical analysis accounting for the effects of the turbulent dissipation rate on both droplet breakup and coalescence was performed, and the critical equilibrium length of breakup and coalescence is found to be less than 3.0 mm. In terms of droplet collision dynamics in the spray far-field, coalescence dominates droplet collision outcomes; therefore, the droplet size increases linearly as the spray downstream distance X increases. Particularly, the influence of the droplet size ratio [C. Tang, P. Zhang, and C. K. Law, “Bouncing, coalescence, and separation in head-on collision of unequal-size droplets,” Phys. Fluids 24, 022101 (2012)] was adopted to quantify the droplet coalescence probability. When compared to the n-octane spray, the n-dodecane spray accounts for more droplet bouncing (II) since n-dodecane possesses a relatively larger bouncing (II) region.

CFD simulation and experiment on the flow field of air-assisted ultra-low-volume sprayers in facilities

In order to explore the performance of the B-ULV-616A knapsack sprayer, computational fluid dynamics (CFD) was used to simulate the B-ULV-616A knapsack air-assisted device, which features an ultra-low-volume electric sprayer. Field experiments were carried out to test the spraying effects, and the KANOMAX anemometer was used to verify the simulated results. First, the internal and external flow fields and droplet deposition distribution of the ultra-low-volume sprayer were established. The results showed that the air-assisted spray device can change the airflow speed and direction and produce a high-speed swirling airflow at the outlet of the air-assisted spray device. The high-speed airflow (maximum of 83.5 m/s) generates negative pressure (minimum of 0.099 MPa) and causes a rapid increase in the droplet velocity and a secondary droplets spray, allowing droplets to reach a longer distance. Then, the maximum relative error was 20.14%, and its average value was 9.59%, indicating that the CFD method is suitable for the flow field analysis of the air-assisted spray device. Finally, based on the greenhouse experiment, the knapsack air-assisted ultra-low-volume electric sprayer was found to effectively improve the deposition on the rear of the crop, increase the droplet density (maximum of 81/cm2; droplet density of conventional electric sprayer is 64/cm2), and reduce the deposition amount and coefficient of variation (below 20%) within and between regions. Further, it managed to reduce pesticide use (by 69.85%) and rural non-point source pollution. Keywords: CFD simulation, air-assisted sprayer, ultra-low spraying rate, deposition, air-velocity field, relative error DOI: 10.25165/j.ijabe.20211402.6013 Citation: Lu X Y, Gong Y, Liu D J, Wang G, Chen X, Zhang X, et al. CFD simulation and experiment on the flow field of air-assisted ultra-low-volume sprayers in facilities. Int J Agric & Biol Eng, 2021; 14(2): 26–34.

CORRELATION BETWEEN CELL SURVIVAL AND ATOMIZATION CHARACTERISTICS IN AIR-ASSISTED BRONCHOSCOPIC SPRAYING

CORRELATION BETWEEN CELL SURVIVAL AND ATOMIZATION CHARACTERISTICS IN AIR-ASSISTED BRONCHOSCOPIC SPRAYING

Tunnel-convective air-assisted spraying technology for improving droplet deposition on hedgerow vines

Tunnel-convective air-assisted spraying technology for improving droplet deposition on hedgerow vines

The Motion of Strawberry Leaves in an Air-Assisted Spray Field and its Influence on Droplet Deposition

HighlightsA visualization method for the motion of strawberry leaves in an air-assisted spray field is proposed.Strawberry leaves showed two motion states in different critical velocity ranges of the sprayer airflow.The airflow instability and the turbulence effect are considered important factors for the leaf vibrations.A strawberry leaf azimuth angle in the range of 90° to 270° can provide good deposition with smaller droplets.Abstract. The reasonable motion of crop plants in an air-assisted spray field can improve droplet deposition. Therefore, this study focuses on the motion of strawberry leaves and the droplet deposition mechanism in an air-assisted spray field. First, this study proposes a descriptive method for strawberry leaf motion in an air-assisted spray field and clarifies the important influence of strawberry leaf motion on droplet deposition. Second, an experiment was performed on the motion and droplet capture of single strawberry leaves in multi-position postures in an air-assisted spray field. The results showed that the leaves had two motion states (i.e., low amplitude with low frequency and high amplitude with high frequency) at different airflow velocities and inclination angles, and the critical airflow velocity corresponding to the two motion states was determined to be 8.7 m s-1. When the azimuth angle of the strawberry leaves is in the range of 90° to 270°, a reasonable inclination angle of the airflow and the high frequency and high amplitude vibration state of the leaves driven by the airflow will provide good deposition and canopy penetration of droplets with smaller diameters. Keywords: Air-assisted spray field, Droplet deposition, Motion, Spray, Strawberry leaves.

Development and test of an autonomous air-assisted sprayer based on single hanging track for solar greenhouse

Manual spray operations of conventional pesticides in the greenhouse are highly dependent on labor and have been associated with potential health risks. To overcome the constraints the narrow crop space and the complexity of auxiliary facilities impose on ground autonomous sprayers, this study developed an autonomous air-assisted sprayer based on a single hanging track for solar greenhouses. The spray distribution from the boom and spray patterns were evaluated. Laboratory tests were conducted to investigate the airflow distribution and static spray distribution of the boom. The sprayer was tested on cucumber crops in a solar greenhouse to evaluate the performances of two spray patterns: spraying during boom rising-traveling (P1) and during traveling-falling (P2). The coefficient of variation of the static axial spray distribution was 33% based on liquid collection. The coefficient of variation of axial and radial spray distribution of P1 and P2 (based on coverage rate) were 37.2% and 58.3%, as well as 46.3% and 69.4%, respectively. This confirmed that the motion direction of the boom strongly influenced the spray distribution. The structure of the airflow also affected the radial spray distribution. Moreover, the axial spray distributions of both spray patterns had high correlation coefficients of 0.921 and 0.889 with a static distribution detected in the laboratory. Optimizing the configuration of the nozzles and airflow of the boom is expected to further improve the uniformity of the radial and axial spray distributions. This autonomous air-assisted sprayer based on single hanging track provides a predictable solution for plant protection in solar greenhouses.

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.