EXPERIMENTAL AIR-ASSISTED ELECTROHYDRODYNAMIC SPRAYING

A linear electrohydrodynamic (EHD) atomizer, operated at -25 kV, was u sed to quantify the effects of droplet size, charge to mass ratio, for ward speed and the addition of air assistance, on spray deposition in natural and artificial crop canopies. Spraying was done at 0.5, 1.0 an d 2.0 m s-1 forward speed, using three Risella EL oil:butanol EHD form ulations (80:20, 70:30 and 60:40) producing droplets with volume media n diameters of approximately 124, 71 and 48 mum and charge to mass rat ios of approximately 2.0, 7.5 and 9.5 mC kg-1, respectively. The two l evels of air assistance used (11.3 m s-1, 0.39 m3 s-1 and 21.2 m s-1, 0.72 m3 s-1) were produced by a commercial air-curtain device. Spray d eposition was compared with that obtained from medium-quality flat-fan hydraulic nozzles applying 238 l ha-1 without air assistance. Spray d rift was measured 2 m downwind over a winter wheat crop, in wind speed s of 1.5 and 2.5 m s-1. Using artificial targets, total spray depositi on and canopy penetration from the charged sprays increased as target density decreased. Larger droplets with a smaller charge to mass ratio penetrated the canopy better than smaller, more highly charged sprays but gave poorer abaxial surface deposits. Air assistance increased ca nopy penetration but reduced abaxial surface deposits. In a winter whe at crop at growth stage (GS) 22, decreasing charge to mass ratio resul ted in decreased plant deposits and increased ground contamination, al though in all cases this was significantly less than that with hydraul ic nozzle applications. Similar trends were measured at GS 37-39, wher e the addition of air assistance increased canopy penetration by highl y charged sprays and decreased the soil contamination found with the l arger-droplet, lower-charged applications. There was no consistent eff ect of forward speed. Spray drift from EHD sprays increased with incre asing charge to mass ratio and decreasing droplet size, and was signif icantly greater than that from the hydraulic nozzle spray at both wind speeds. The use of air assistance reduced spray drift from the smalle st droplets by approximately 93%.