The porosity change with spontaneous combustion development of coal and its influence on spontaneous combustion were studied in this paper. On the basis of activation energy theory, the equation of porosity change with the combustion process of coal was deduced. A simplified small-scale experiment and its numerical simulation were preceded. By comparing the results of experiment with those of the numerical simulation, the equation of porosity deduced was validated. At the same time, the porosity change influenced the development of spontaneous combustion of coal from two aspects. One side, the porosity added could increase the reaction area and then accelerated the reaction speed directly. On the other side, the porosity added strengthened the heat convection between gases with high temperature and solid skeleton, and then the reaction speed was increased indirectly. Thus, the porosity change accelerated the spontaneous combustion development of coal. In coal feld outcrop, the acceleration action of porosity change appeared as that the coalfield spontaneous combustion was anisotropic under the action together porosity change with seepage velocity.
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