Drifting property of falling oil rape seeds in longitudinal positive pressure airflow field without stalks

Abstract: Due to the oil rape's two biological characters of fragility and non-synchronization of maturity, a high loss rate (>8%) of rape seeds often appears when this plant is harvested by a combine harvester. The higher the maturity is (often accompanied by a lower moisture content), the greater the cutting platform loss is in the front part of the machine, and the smaller the loss of the threshing, separating and cleaning in the behind; and vice versa. Insufficient maturity causes low oil rate, while high moisture content will increase difficulty of the threshing, separating and cleaning. Therefore, consideration should be given to both the front and behind loss of the machine while methods and counter-measurements are tried to be found. It means that, while the threshing, separating and cleaning devices are optimized, new types of the cutting platform should be developed at the same time to fit a new harvest time which can be shifted to backwards appropriately or on a sunny afternoon for a higher maturity and lower moisture content. This paper proposed a novel method to collect the falling rape seeds in front of the harvester header by a line-by-line mode with the longitudinal airflow of positive pressure for rape which is mechanically transplanted or sown. Firstly, with a bench trial device, an orthogonal experiment based on the scheme of L9(34) was conducted to determine the significant level of relevant factors impacting on the collection effect of falling rape seeds in field of longitudinal positive pressure airflow without no straw. Then single factor tests for the important factors were implemented to obtain the corresponding regression equation for predicting the collection effect in further optimization of the structure and work parameters of the device. Experiments showed that factors affecting the collection amount of the falling seeds are the height and length of the collection monomer, the operating current frequency of the turbine (which determines the airflow velocity at the front place of the nozzle) and the elevation angle of the nozzle respectively, in which the effect of the first three factors on the collection performance are significant, while the effect of the elevation angle of the nozzle is not significant. The influence trends of these four factors on the collection performance are in line with the quadratic polynomial fitting, in which the collection amount climbs with the increase of the height of the collection monomer, the operating current frequency of the fan and the elevation angle of the nozzle increases, but descends with the increase of the length of the collection monomer. The determination coefficients were 0.9773, 0.9985, 0.9682 and 0.9686, respectively. So if the distribution of the whole machine's power permits, a possibly high power fan with optimized layout of piping and structure and parameters of the monomer and the nozzle should be adopted in order to ensure adequate airflow field intensity and scope, obtaining a proper collecting effect of the falling rape seeds. This paper lays a research base for further study on the collection of falling rape seeds by positive pressure airflow under the conditions with stationary stalks or moving stalks.