Abstract: Systems, methods, and devices are provided herein for burners. In one aspect, a burner is provided comprising at least one air pipe; at least one fuel pipe; a plurality of groups of mixing units disposed at a downstream end of the burner, wherein each of the plurality of groups of mixing units is arranged coaxially and adjacent to one another, and each group of mixing units comprises at least one fuel channel connected to the at least one fuel pipe and at least one air channel connected to the at least one air pipe, wherein an outlet of the at least one fuel channel and an outlet of the at least one air channel are angled at a certain degree relative to one another such that the fuel flowing out of the outlet of the at least one fuel channel is mixed with the air flowing out of the outlet of the at least one air channel, thereby achieving multiple-stage mixing of the air and fuel.