New ignition phenomenon in coal combustion

A new ignition phenomenon has been observed during studies of coal combustion. The experiment, which was described in a recent publication [1], injects coal particles suspended in a roomtemperature carrier gas as a jet into a flowing preheated air stream. The new phenomenon is shown in Fig. 1, which is a photograph of several ignited particles traveling upward. The particles of interest are at the edge of the cold particle stream and have first contact with the surrounding hot preheated gas stream. They ignite and appear to burn on the particle's surface, as indicated by the fact that the width of the luminosity is roughly that of the particle diameter. The particles become hotter with increasing distance. The new ignition phenomenon occurs after the particles have burned for a short time. Under these conditions there is often a secondary ignition event. To the unaided eye, it looks like a bright flash of light at the end of a long luminous trajectory. When viewed through a microscope, this event has the following characteristics.