DIRECT NOZZLE INJECTION OF PESTICIDE CONCENTRATE INTO CONTINUOUS FLOW FOR INTERMITTENT SPRAY APPLICATIONS
A direct nozzle injection system was developed to intermittently inject concentrated solutions into continuous 
carrier liquid flow through a straight-stream spray nozzle used for targeted roadside spraying of post-emergent herbicide 
during pre-emergent herbicide application. The injection system was based on a 12 VDC direct-acting electrical solenoid 
valve with a 0.56 mm valve orifice and metering plate with a 0.2 mm diameter orifice. A conductivity-based sensor was used 
to measure the instantaneous concentration of NaCl tracer simulating a pesticide solution. Injection pulse durations ranged 
from 10 to 100 ms into carrier flows of 1.5 and 2.6 L/min from 1.55 and 2.18 mm nozzle orifice diameters, respectively. Lag 
times between initiation of the injection valve actuation and emission of the concentrate material from the spray nozzle were 
on the order of 25 ms. Concentrations of 1% (v/v) from injected solution into the flow emitted from the nozzle could be achieved 
within 100 ms after valve actuation. Increasing the injection pulse duration did not reduce lag time nor increase the temporal 
rate of concentration increase in the emitted spray; however, increasing the injection pressure increased the rate of 
concentration increase. Analysis of the injection event, using standard mixing criteria, determined that the injection mixing 
events were Gaussian in nature and did not represent ideal plug flow or short-circuiting events. For an intermittent, 
target-detecting system with a detector-to-nozzle distance of 4 m and a ground speed of 5 m/s, the direct nozzle injection 
system is a feasible configuration for spot spraying if the sum of detection time and time of flight for the emitted spray is less 
than 800 ms. For a prototype machine vision-based roadside sprayer, detection and spray flight times were less than 67 and 
400 ms, respectively; therefore, feasibility of spot spraying using at-nozzle injection was established.