Particle size and distribution play an important role in ignition. The size and distribution of the cyclotetramethylene tetranitramine (HMX) particles were investigated by Laser Particle Size Analyzer Malvern MS2000 before experiment and calculation. The mean size of particles is 161 mu m. Minimum and maximum sizes are 80 mu m and 263 mu m, respectively. The distribution function is like a quadratic function. Based on the distribution of micron scale explosive particles, a microscopic model is established to describe the process of ignition of HMX particles under drop weight. Both temperature of contact zones and ignition probability of powder explosive can be predicted. Thecalculated results show that the temperature of the contact zones between the particles and the drop weight surface increases faster and higher than that of the contact zones between two neighboring particles. For HMX particles, with all other conditions being kept constant, if the drop height is less than 0.1 m, ignition probability will be close to 0. When the drop heights are 0.2m and 0.3 m, the ignition probability is 0.27 and 0.64, respectively, whereas when the drop height is more than 0.4m, ignition probability will be close to 0.82. In comparison with experimental results, the two curves are reasonably close to each other, which indicates our model has a certain degree of rationality.
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