Objective  To design an agricultural variable nozzle based on magnetorheological fluid, and realize variable spraying in agricultural protection area.

Method  Mechanical structure of the variable nozzle was designed based on the theory of magnetorheological effect. Structural parameters were optimized through software simulation. Nozzle flow rate was measured under different coil voltage and volume of magnetorheological fluid injected in the nozzle cavity. Effect of coil voltage and volume of magnetorheological fluid injected in the nozzle on flow rate were analyzed.

Result  When the pressure of the diaphragm pump kept at 0.3 MPa constantly, the nozzle flow rate decreased with the volume of magnetorheological fluid in the nozzle cavity increased from 0 to 2.5 mL. The reduction in flow rate was the least (14.29%) at the coil voltage of 24 V, while the reduction in flow rate was the largest (28.57%) at the coil voltage of 0 V. When the volume of magnetorheological fluid maintained at 1.5 mL and coil voltage increased from 0 to 28 V, the nozzle flow rate increased by 25.00%.

Conclusion  The variable nozzle based on magnetorheological fluid can realize variable flow rate control by controlling the external magnetic field, and therefore the designed variable nozzle can be used in precise variable agricultural spraying.