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To realize site-specific and variable-rate application of agricultural pesticides, accurately metering and controlling the chemical injection rate is necessary. This study presents a prototype of a direct nozzle injection system (DNIS) by which chemical concentration transport lag was greatly reduced. In this system, a rapid-reacting solenoid valve (RRV) was utilized for injecting chemicals, driven by a pulse-width modulation (PWM) signal at 100 Hz, so with varying pulse width the chemical injection rate could be adjusted. Meanwhile, a closed-loop control strategy, proportional-integral-derivative (PID) method, was applied for metering and stabilizing the chemical injection rate. In order to measure chemical flow rates and input them into the controller as a feedback in real-time, a thermodynamic flowmeter that was independent of chemical viscosity was used. Laboratory tests were conducted to assess the performance of DNIS and PID control strategy. Due to the nonlinear input-output characteristics of the RRV, a two-phase PID control process obtained better effects as compared with single PID control strategy. Test results also indicated that the set-point chemical flow rate could be achieved within less than 4 s, and the output stability was improved compared to the case without control strategy.

A direct injection system (DIS) for pesticide injection at all nozzles was set up in order to ascertain its ability to be cleaned. Under laboratory conditions, the system was contaminated with a safe-to-use salty polyvinylpyrrolidone-water solution as a test pesticide and then cleaned in two steps: (1) reclaiming the test pesticide by pushing it back into the pesticide tank using pressurized air (pre-cleaning) and (2) rinsing the contaminated part of the hydraulic system with water. Tests on a 3 m wide test bench included gravimetric and conductivity measurements to determine the amount of residues in the test section and test pesticide concentrations in the rinsing water. Mechanical action inside the test section was varied by (1) increasing the air pressure for pre-cleaning, (2) increasing the rinsing water pressure, and (3) employing pulsed water-air flow. Initial test pesticide concentrations in the rinsing water could be as high as 25%, which is more than in common spray mixes and requires further dilution. While continuous rinsing at higher pressures saved up to 10% of the water, rinsing the test section with pulsed water led to water savings of more than 50%. Rinsing turned out to be a time-consuming procedure, as it took almost 10 min for test pesticide concentrations in the rinsing water to approach 0%.

A direct injection system that injects pesticides locally at all nozzles on a boom was assembled and investigated under laboratory conditions with regards to its ability to be cleaned. The system was contaminated with a safe-to-use polyvinylpyrrolidone-water solution as a test pesticide before cleaning. The cleaning process was divided into two steps: 1) reclaiming the simulated pesticide by pushing it back into the pesticide tank using pressurised air (pre-cleaning) and 2) rinsing the contaminated part of the hydraulic system with water. Cleaning performance was investigated systematically to ascertain the initial dynamics of the rinsing process as well as long term cleaning. Evaluations included variation of 1) pre-cleaning time and 2) water inlet position. Measurements showed that the concentration of the simulated pesticide in the rinsing water could initially be as high as 30%. As the pre-cleaning time was extended the initial concentration was reduced by one third. Changing the water inlet position reduced the initial concentration of the simulated pesticide in the rinsing water to 5%. These concentrations were much higher than in most common spray solutions. This means that if an active pesticide was used further dilution of the pesticide concentration in the rinsing water would be required for it to be sprayed on a crop. In some cases it took more than 10 min to dilute simulated pesticide residues in a 3 m test section down to 0% which clearly shows the need for more research on factors influencing the cleaning process and more development of cleaning processes.

Direct injection systems for Plant Protection Products (PPP) are developed to increase precision in application, to prevent the operator from contact with the chemical agents and to protect the environment against harm. They can be divided by the point where the PPP is injected in the pipes. These injection points cause different volumes of spray mixture in the piping system and therewith different response times until the desired spray mixture exits the nozzle. For sensor-based application, a short response time of the sprayer and variable rate application of different active ingredients are necessary.

A direct injection system that injects pesticides locally at all nozzles was assembled and investigated under laboratory conditions with regards to its ability to be cleaned. The test pesticide was a safe-to-use polyvenylpyrrolidone-water solution. Cleaning performance was investigated systematically to determine the total amount of test pesticide left in the pipe as well as the dynamics of the rinsing process and how both are affected by pre-cleaning time. Measurements showed that after 10-30 s of pre-cleaning test pesticide residues were still between 12-6% of what was initially in the injection pipeline. The concentration of the pure test pesticide in the rinsing water could initially be as high as 30%. As pre-cleaning time was extended initial concentrations in the rinsing water were reduced by a third.