Determining the drag coefficient of fertilizer grains using stereovision

Increased accuracy in fertilizer spreading performance is required to maximize the farmers’ profit and reduce several ecological effects. To allow for proper spreader calibration, a re-search system was developed to predict the spread pattern of centrifugal spreaders. By measuring the ejection parameters of the fertilizer grains and applying these in a ballistic flight model, the landing positions of these particles can be calculated, from which the spread pattern can be simulated. Simulations indicate the high sensitivity of the predicted spread pattern to the drag coefficient of the particles. In literature, this coefficient has mostly been determined at terminal velocity and/or for perfectly spherical particles. This paper describes a new method to determine the drag coefficient at velocities similar to those imposed by a cen-trifugal spreader. The ejection parameters of a single fertilizer particle were determined by means of image processing. Three dimensional information was obtained using a stereo ar-rangement of high speed cameras. The drag coefficient was calculated by parameter estima-tion using the registered position of the grain at a discrete distance after ejection. The accu-racy of the method was evaluated by simulation. Preliminary experiments with a common type of fertilizer (KAS 27%N) show promising results. However, some modifications are nec-essary to improve the quality of the data and to shorten the duration of testing.