Coal is an important energy resource for meeting the future demand for electricity, as coal reserves are much more abundant than those of other fossil fuels. In this study, the percolation model, which can account for swelling due to devolatilization and ash agglomeration, is applied to particulate matter formation process in coal combustion, and the effects of coal properties, ambient temperature, ambient pressure and initial coal size on the characteristics of a burning coal particle are studied. The devolatilization rate of coal is given by the first-order reaction model with FLASHCHAIN (R) model [Niksa, S., Combust. Flame, 100, (1995) 384-394.]. The characteristics of a burning coal particle are investigated under the atmospheric and high pressure conditions. The results show that in the atmospheric pressure condition, the characteristics of the burning coal particle obtained by the percolation model are in general agreement with the experimental data. The particle diameter of Newlands coal with higher fuel ratio and ash content is larger than that of Plateau coal in the char-combustion-dominant process. As the ambient temperature increases, the particle diameter becomes small in the early stage of the char-cornbustion-dornmant process, but becomes large afterward. The porosity in the char-combustion-dominant process decreases with decreasing the initial coal size. It is also observed that the effect of ambient pressure is prominent in the char-combustion-dominant process. The particle diameter and porosity in the pressurized condition are greater than those in the atmospheric pressure condition. These behaviors can be explained by the interaction between char reaction and ash agglomeration. (c) 2006 Elsevier B.V. All rights reserved.