Experimental Investigation of Flow Regulation and Spray Characteristics of a PWM-Based Variable-Rate Nozzle

PWM-based variable-rate spraying is an effective approach for improving pesticide application precision, but the coupling between nozzle actuation response, flow regulation, droplet size, and spray distribution under different operating parameters remains insufficiently clarified. This study aimed to evaluate the nozzle-level performance of a self-developed direct-acting PWM variable-rate nozzle and to identify suitable operating conditions for stable variable-rate spraying. An indoor integrated test bench was established to measure response time, PWM waveform retention, flow-rate characteristics, droplet-size distribution, and lateral spray distribution under pressures of 0.2–0.4 MPa, PWM frequencies of 5–30 Hz, and different duty cycles. The measured pull-in and release times were 8.00–9.50 ms and 12.00–13.00 ms, respectively, indicating rapid and stable actuation. The driving waveform was well retained, with an amplitude of 11.6–12.8 V and a measured frequency of 5.00–29.94 Hz. The flow rate increased monotonically with duty cycle, and the flow linearity ranged from 0.43% to 8.51%; better linearity was obtained at 5–25 Hz, whereas deterioration at 30 Hz was mainly associated with the shortened PWM period and increased switching-delay effect. The Dv50 ranged from 113.67 to 208.78 μm, and the relative span ranged from 1.173 to 1.323. The lateral distribution showed good symmetry, and the best uniformity was obtained at 20 Hz. Overall, the developed nozzle showed good potential for PWM variable-rate spraying and provides a reference for nozzle parameter matching and spray performance optimization.