Transient responses of three direct formulation injection systems for agricultural sprayers

Author

Ray Allen Maynard

Date of Award

5-1997

Degree Type

Thesis

Degree Name

Master of Science

Major

Biosystems Engineering

Major Professor

Alvin R. Womac

Committee Members

Fred D. Tompkins, William E. Hart

Abstract

Formulation injection into the spray diluent has many potential advantages, such as, less applicator exposure and improved application efficacy. However, there are some disadvantages associated with this technology that include formulation delivery delay time, inability to precisely deliver small amounts of formulation, and inadequate mixing of formulation into diluent

Three types of formulation injection systems were observed to determine the transient performance of each system. An orifice-regulated system was designed and installed on a conventional sprayer. The orifice was calibrated under laboratory conditions before field efficacy tests were conducted. The efficacy of "before pump" and "after pump" injection sites were compared with a conventional tank-mix application at the same formulation rates.

Commercially available, water-driven, piston-type injection unit(s) were tested in a three-branch system that provided variable system dilution rates using the fixed rate injection units. Two branches each contained an single water-driven injection unit while the third branch contained a throttling valve. Pressure transients from the pulsating units were of particular importance. Collected samples of nozzle discharge were measured for KBr concentration versus time. Flowrate through each branch was also measured.

An experimental, variable-speed, diaphragm unit was designed and operated for at-the-nozzle injection. The unit's flow was determined at different unit speeds and system pressures provided by an air back pressure arrangement. The unit also injected a KBr solution into an individual boom nozzle. The KBr solution was used as a tracer to determine the effects of diaphragm pulsation on nozzle discharge concentration uniformity versus time.

The orifice-regulated system delay time and nozzle-to-nozzle variation were measured using a manual method of KBr sample collection. The water-driven units' and the experimental unit's injection performance was measured using a rotary sampler of nozzle discharge that increased sample frequency compared to the manual method. The rotary method collected 103 samples per one minute test duration.

In the laboratory setup using a 5000 ppm KBr solution, the orifice-regulated system produced the desired formulation rate at the selected differential pressure [68.9 kPa (10 psi)] across the orifice for "after pump" injection. The differential pressure across the orifice for the "before pump" injection was affected by diluent pump suction, such that pressure supplied to the orifice had to be reduced by approximately 14-kPa (2-psi) to maintain the desired rate.

In the field study applying Gramoxone Extra (paraquat dichloride) and Latron AG-98 spreader activator, the orifice-regulated direct injection system provided broadleaf and grass control ratings that ranged from 26 to 90 percent, as compared to the tank-mix system ratings that ranged from 82 to 90 percent. The lowest rating (26 percent) was possibly caused by an orifice that plugged after calibration, or due to incorrect pressure differential across the orifice. The orifice-regulated system provided direct injection capability with efficacy comparable to conventional application, especially at higher formulation rates, i.e. larger orifice size. No significant difference (a=0.05) in control ratings were observed between "before pump" and "after pump" injection sites and conventional tank-mix applications for the 2.43 L/ha (0.25 gal/ac) formulation application rate.

The performance of the water-driven, piston pump unit varied based upon system branch selection, hose length configuration, and flowrate. The concept of using a bypass branch provided a potential method of varying KBr concentration by modulating flows through the bypass and the fixed-rate injection units. However, flow through the water-driven unit(s) was sensitive to adjustment of the bypass throttling valve due to the pressure loss [103 kPa (15 psi)] in the water-driven units. Dually-operated units did not generally lessen the intensity of the pressure pulse output, but rather tended to pulse simultaneously. The pressure measurements indicated this trend with individual water-driven unit operation variances that ranged from 71 kPa² (1.5 psi²) to 361 kPa² (7.6 psi²) compared to the range of dual unit variation from 532 kPa² (11.2 psi²) to 4150 kPa² (87.3 psi²). Pressure measurements showed no clear trend in variances between high and low system flowrates. Errors in KBr metering ranged from -57 to 26 percent and were attributed to KBr measurement accuracy, flowmeter accuracy, and the pumping efficiency of the water-driven unit at different flowrates. At higher flow rates, the water-driven units produced generally lower concentration variation (16 - 92 ppmi²) and generally improved KBr metering errors (-14 to 22.7%) compared to low flow KBr concentration variation (35 - 2037 ppmi²) and metering error (-57 - 26%).

The additional hose length downstream from the combining cross increased the upstream pressure variance range [436 - 2001 kPa² (9.2 - 42.1 psi²)] as compared to upstream pressure variance range [266 - 766 kPa² (5.6 -16.1 psi²)] without the additional hose length. In contrast, the downstream pressure variance range [5 -1635 kPa² (0.1 - 34.4 psi²)] with the additional hose length was less than the downstream pressure variance range [361 - 4474 kPa² (7.6 - 94.1 psi²)] without the additional hose length. Thus, the water-driven unit needs the additional hose length to smooth the pressure spikes that are inherent to its operation. The asymmetrical setup of the branches had no smoothing effect upon system operating characteristics.

The experimental-unit provided flowrates comparable to the rates required for injection at an individual nozzle. Specifically, the experimental unit produced flowrates for formulation application rates from 1.17 L/ha (0.125 gal/ac) to 4.68 L/ha (0.50 gal/ac) using a 6.4 km/h (4 mi/h) sprayer speed and 0.5 m (20 in) nozzle spacing. The experimental unit's flowrate range was provided by a twelve-fold increase in unit speed. Operating speeds greater than 10 rpm are required to increase the uniformity of nozzle discharge concentration versus time.

Recommended Citation

Maynard, Ray Allen, "Transient responses of three direct formulation injection systems for agricultural sprayers. " Master's Thesis, University of Tennessee, 1997.
https://trace.tennessee.edu/utk_gradthes/6783