Effect of nozzle type, size and pressure on spray droplet characteristics

The characteristics of agricultural sprays belong to the most critical factors affecting spray drift, deposition on plants, spray coverage and biological efficacy. Hence, within the framework of a research project about agricultural spray drift, the effect of nozzle type, size and pressure on spray droplet characteristics was investigated. The objective of this study was to develop a test rig and protocol for the characterisation of spray nozzles using a phase doppler particle analyser (PDPA). This test rig was able to measure droplet sizes and velocities based on light-scattering principles. It was composed of a climate room, a spray unit, a three-dimensional automated positioning system and an Aerometrics PDPA one-dimensional system. The droplet size and velocity characteristics of different nozzle-pressure combinations was measured and compared with the results obtained by other researchers using different measuring techniques and procedures. In total, 32 nozzle-pressure combinations were tested and classified based on droplet size spectra and the British Crop Protection Council (BCPC) classification scheme. The test results clearly show the effect of the nozzle type, size and pressure on the droplet size and velocity spectra. Comparison with the results from other researches confirms the need for reference nozzles to classify sprays because of the considerable variation of absolute results depending on settings and type of measuring equipment.