An elementary analysis of ignition mechanism governing three types of coal-powder burners used for oilless direct ignition has been made

and a torch expanding theory in the process of oilless direct ignition being suggested. The said theory can distinctly reflect the process of catching fire. The factors influencing upon torch expanding are: the energy intensity B of initial torch; expanding factor （α）1

（x） due to torch’s rolling suction; and expanding factor （α）2

（x） caused by diffusion. In the expanding process

the coal powder torch’s expanding form is varying with the change of time

space

and air flow field. The performance of coal-powder burners for three said types is different

an appropriate direct ignition style should be determined on the basis of fuel coal properties etc..