Assessment of chemical concentration accuracy and mixture uniformity of premixing in-line injection system

A premixing in-line injection system was developed and attached as a retrofit to a laser-guided variable-rate orchard sprayer. Chemical concentration accuracy and spray mixture uniformity produced from the premixing system was investigated with various viscosities of simulated pesticides and duty cycles of pulse-width -modulated (PWM) nozzles at different positions on the sprayer. The chemical concentration accuracy was accessed by calculating the relative error (RE) between measured and target concentrations, and mixture uniformity was evaluated by the coefficient of variation (CV) of the mixture concentration. Test results showed that the measured concentration was consistent across different nozzle positions, and RE and CV were observed within desirable ranges (< 5.0%) for all nozzle positions and target concentrations. The average measured concentration slightly decreased as the viscosity of simulated pesticides increased. This phenomenon was more obvious under higher target concentrations. In addition, effects of PWM duty cycle combinations on the chemical concentration accuracy and mixture uniformity varied with number of active nozzles. It was found that RE and CV were larger than the desirable level (greater than5.0%) but were lower than the acceptable level (< 10.0%) under conditions that nozzles were partly activated. For other treatments which all nozzles were activated, RE and CV were under the desirable level (< 5.0%) for all target concentrations and nozzle positions. Laboratory tests demonstrated that the premixing in-line injection system was able to adequately mix the simulated pesticides with water, and could provide accurate and consistent uniformity of spray mixtures for the variable-rate spray nozzles to discharge different viscosities of simulated pesticides at different duty cycle combinations.