Development of a variable-orifice spray nozzle with high pressure chemical injection for improved pesticide efficacy

The goal of this research was to develop and evaluate a pesticide application delivery system which combined high pressure, direct nozzle chemical injection with a direct-operated, variable orifice nozzle for carrier flow rate control. The prototype system was shown to maintain acceptable chemical application rates, ensure proper chemical concentrations prior to discharge, and preserve spray pattern uniformity and droplet size distribution of the applied spray material.;Discharge characteristics of the direct-operated, variable orifice nozzle indicated that turndown ratios of 2.4:1 were possible over a range of operating conditions. Spray patterns were considered acceptable (CV < 10%) at carrier pressures ranging from 138 to 414 kPa for nozzles spaced at 38.1 and 51.0 cm. Droplet spectra tests verified that the nozzle maintained the desired droplet size distribution. Evaluation of the nozzle actuation control system (closed-loop feedback) indicated settling times were maintained below 1.0 s for a full-step change at carrier pressures ranging from 138 to 414 kPa. Ramp-response tests showed that the nozzle could effectively compensate for flow rate changes from 2.97 to 6.39 ml s-2 for carrier pressures from 138 to 414 kPa.;A technique was developed for recalibrating the high pressure chemical injectors to compensate for fluid property variations (e.g., viscosity) which allowed the system to accurately meter the chemical concentrate in an open-loop configuration. Results demonstrated that injector flow rates could be predicted within 1.7% across the range of duty cycles tested.;The combined high pressure chemical injection and variable orifice nozzle was evaluated for chemical metering accuracy and preservation of the chemical concentrations in applied spray material. Results indicated that the proposed open-loop control of the injectors provided a means of accurately metering the chemical concentrate into the carrier stream with an average error less than 5.5%. Step-response tests (16% to 30% DCi) demonstrated the nozzle response time was less than 1.0 s while steady state errors in chemical concentration were below 7.5%. Ramp-response tests revealed that the variable-orifice nozzle operated similarly when coupled with the chemical injectors and chemical concentrations did not exceed minimum or maximum allowable rates according to pesticide label during testing.;KEYWORDS: Variable Rate Application, Precision Agriculture, Spraying Equipment, Agricultural Chemicals, Atomizers.