An experimental study on ignition of single coal particles at low oxygen concentrations
An experimental study on the ignition of single coal particles at low oxygen concentrations ( <21%) was conducted using a tube furnace. The surface temperature ( ) and the center temperature ( ) of the coal particles were obtained from the images taken by an infrared camera and thermocouples respectively. The ignition processes were recorded by a high-speed camera at different values and furnace temperatures . Compared with literature experimental data obtained at a high value, the ignition delay time decreases more rapidly as increases at the low region. The responses of and to the variation of are different: decreases while remains nearly constant with increasing at a low value. In addition, is less sensitive to while the ignition temperature is more sensitive to at a low value than in air. Observations of the position of flame front evolution illustrate that the ignition of a coal particle may change from a homogeneous mode to a heterogeneous or combined ignition mode as decreases. At a low value, buoyancy plays a more significant role in sweeping away the released volatiles during the ignition process.