Experimental observation of solid particles and their volatile flames was performed to present the characteristic combustion behavior of solid fuels used in energy-production industries, i.e. coal, biomass, and petro-chemical polymers. In a hot gas stream at similar to 1240 K and a rapid heating rate of similar to 100 K/ms, time-resolved visualization of a sub-millimeter fuel particle at high magnification showed patterns of flame development of the particle, demonstrating the sub-processes of particle heat-up, devolatilization, and char combustion. The shadow images of moving particle and its surrounding volatile flame could be visualized at the same time. Repeatable experiments were able to present volatile flame patterns, which were unique in accordance with the fuel type in the corresponding combustion environment. Among the different formation patterns, a concentric and spherical volatile flame was chosen as a reference. The parameters, particle size (75-200 mu m) and O-2 concentration (21.1-40.2 vol %), which affected the patterns were considered for understanding influence on them. Visible appearance was quantified by using a length scale that measured the apparent flame diameter and a set of newly-defined time scales that described its chronological variation. Using quantitative identifiers and feature descriptions, the observed flame behaviors were discussed as unique signatures for characterizing the combustion process of burning fuel particle. (C) 2017 Elsevier B.V. All rights reserved.