A fuel injection nozzle includes: a nozzle body having a plurality of injection holes; and a needle accommodated in the nozzle body to inject a DME fuel containing dimethyl ether as a main component. The nozzle body has a seat part to which the needle seated or from which the needle separated, and a tip end chamber arranged downstream of the seat part in a flow of the DME fuel to communicate with the plurality of injection holes. The DME fuel in the tip end chamber is heated with combustion heat in a combustion chamber of an internal combustion engine to have a supercritical state.

A method of using a throttle body fuel injection system including a throttle body with at least one air intake, an electronic fuel injector coupled to the throttle body at a fuel port and an annular ring coupled to the cylindrical inner wall of the air intake. The annular ring includes a fuel discharge orifices arranged radially around the annular ring for spraying atomized fuel into the air intake, in order to operate an internal combustion engine.