Volatile flame visualization of single pulverized fuel particles

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 ~1240 K and a rapid heating rate of ~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 μm) and O2 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. [Display omitted] •Direct observation of single solid particles and their volatile flames was performed.•Apparent form of the particle flame was revealed as characteristic progress of each fuel.•High-speed images of associated flame were clearly identified in high magnification.•All volatile flames were not typical envelope flames surrounding the particle.•Time-wise patterns of the particle and its flame were quantified in time and length scales.