PERFORMANCE OF A MULTIPOINT PULSE–WIDTH MODULATION METERING SYSTEM FOR AMMONIA

Abstract

Pulse-width modulation (PWM) was investigated as a means of metering and distributing anhydrous ammonia fertilizer. A multipoint system having one PWM valve for each knife was developed and tested for lateral distribution and flow characteristics. The PWM manifold was designed to promote cooling of the incoming ammonia, to ensure that liquid ammonia was fed to the PWM valves at all times. The flow from each PWM valve was determined by a dynamic water absorption method. Valve duty cycles ranging from 3% to 90% were tested. Lateral coefficients of variation were less than 10%, provided that the PWM valve duty cycle was 10% or higher. Ammonia flow was a function of duty cycle and pressure drop across the valves. The valve flow model indicates that a turn-down ratio of 50:1 is feasible, which will allow a single valve design to meet a wide range of fertilizer application rates.