An experimental study on the ignition of single coal particles at low oxygen concentrations(XO2＜21％)was conducted using a tube furnace.The surface temperature(Ts)and the center temperature(Tc)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 XO2 values and furnace temperatures Tw.Compared with literature experimental data obtained at a high XO2 value,the ignition delay time τi decreases more rapidly as XO2 increases at the low XO2 region.The responses of Ts and Tc to the variation of XO2 are different:Ts decreases while Tc remains nearly constant with increasing XO2 at a low XO2 value.In addition,τi is less sensitive to Tw while the ignition temperature Ti is more sensitive to Tw at a low XO2 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 XO2 decreases.At a low XO2 value,buoyancy plays a more significant role in sweeping away the released volatiles during the ignition process.