The Effect of Nozzle Body Volume on Pressure Dynamics in a PWM Sprayer System

Abstract

Highlights The variability in damping ratio between different sized nozzle tips was reduced with an increase in nozzle body volume, indicating that the previous works using pressure-sensing manifolds in PWM systems may have underestimated the nozzle pressure fluctuations. Pressure sensors installed at the nozzle body and the manifolds tested exhibited a different damping ratio, suggesting a slight change in sensor location might yield different measurements of transient pressure characteristics. A minimally invasive instrumented pressure sensor at the nozzle body is needed to accurately measure nozzle pressure dynamics. Abstract. Nozzle pressure measurements in agricultural sprayers are commonly conducted by adding a manifold between the nozzle body and nozzle tip. The additional component substantially increases the internal volume of the nozzle body, which affects nozzle pressure dynamics. This research focused on the effect of nozzle body volume on pressure dynamics when operating a spray nozzle under pulse-width-modulation control. A nozzle body and two manifolds of different volumes were instrumented with embedded pressure sensors. In a static test environment, pressure data were collected at 345 kPa nominal pressure at 50% duty cycle with a variety of nozzle orifice sizes. A second-order transfer function was used to model a portion of the dynamic pressure data. The damping ratio generally decreased as the volume of the nozzle body increased due to the addition of a manifold. The variability in damping ratio with respect to nozzle orifice size was reduced when adding a manifold. The lower damping ratios when a manifold was present generally resulted in more overshoot and slower settling time. Results also showed a slightly higher damping ratio at the nozzle body than at the manifold when either manifold was added. The differences in nozzle pressure dynamics with and without the addition of a pressure sensing manifold suggest that previous studies using instrumented nozzle bodies under PWM control may have underestimated the amplitude of pressure oscillations and the time to reach equilibrium. Keywords: Agricultural Sprayers, Measurement Accuracy, Nozzle Body Volume, Pressure Dynamics, Pulse Width Modulation (PWM).