Simulation of rice threshing performance with concentric and non-concentric threshing gaps

The gap between concave grid and drum, the threshing gap, is one of the important operating parameters that affects the performance of threshing devices. The different methods currently adopted on combine harvesters to adjust both the drum and the concave, results in concentric and non-concentric threshing gaps that have different influence one threshing performance. The threshing process is complex, therefore, in order to analyse the influence of the threshing gap on performance, flexible rice straw models were built using the discrete element method to simulate the threshing processes of the two adjustment methods. Their respective movements, separation status and the distribution of the mixture of the threshed output were examined. Simulation results indicated that over the same time, drum adjustment produced better material separation and transportation capabilities and more evenly distributed output mixture in the reception box, compared with the concave adjustment. A threshing experiment on a combine harvester was performed in order to verify the simulation result and the output mixture distribution status was found to be consistent with the results of the simulations. The experimental results showed that threshing was more effectively improved by changing the threshing drum diameter although the threshing gap was more complicated to adjust. (C) 2020 IAgrE. Published by Elsevier Ltd. All rights reserved.