Pulse Width Modulation: Effect of duty cycle on nozzle flow rate, droplet characteristics and vertical spray distribution

Variable rate applications can be achieved through the use of pulse width modulation (PWM) systems. In this study, the effect of PWM duty cycle on nozzle flow rate, droplet characteristics, and vertical spray distribution of a vineyard sprayer was investigated using a DynaJet Flex system (TeeJet Spraying Systems Co., Wheaton, Illinois USA) operated at 20 Hz. The results showed a good linear relationship between duty cycle and nozzle flow rate, although flow rate deviations at 90% duty cycle were reported, and duty cycle induced spray pressure changes influenced this relationship. The presence of a solenoid valve reduced the droplet size and velocity, depending on the nozzle type. Duty cycle had no clear effect on droplet size, whereas droplet velocity generally decreased with decreasing duty cycle. The vertical spray profile was not substantially affected by changing the duty cycle from 100% to 30%, but the addition of the PWM system slightly lowered the spray distribution symmetry.