Abstract: For the shake of studying the spontaneous combustion temperature of upscale low rank coal piles, experiments were made by means of a constant temperature heating system and a gas detection and analysis system among others. Based on the Frank-Kamenetskii boundary condition theory and the critical self-ignition temperature analysis method, the internal temperature, effect of water evaporation and energy conversion of coal pile were described. Then, the relationships between ambient temperature, oxidizing gas and coal spontaneous combustion tendency were examined. The results show that the water content of coal pile is an important factor leading to the appearing of a decreasing stage in the self-heating curve, and the duration of temperature decreasing depends on the position of the measuring point in the coal pile, that there is a positive correlation between the concentrations of gases produced by the oxidation reaction and the coal temperature, that under the condition of non self-ignition, the strongest stage of oxidation is the later stage of temperature rising process, that both natural convection and low temperature oxidation result in the reduction of coal pile volume, that the higher the ambient temperature, the greater the reduction will be, and that the critical self-ignition temperature theory can be effectively applied to the prediction of large volume coal pile spontaneous combustion.

Key words: critical self-ignition temperature, Frank-Kamenetskii boundary theory, natural convection, water evaporation, environment temperature, gas detection