Warp injector was the collective term for the matter and antimatter injectors, part of the matter-antimatter reaction assembly of a warp drive. A component of this system were warp injector casings.
Cleaning the warp injectors of plasma residue was part of routine maintenance. In 2152, Zobral's ship deliberately neglected this maintenance, so the engines would fail and the ship could send out a distress signal to attract the attention of Jonathan Archer. (ENT: "Desert Crossing")
In September 2152, Commander Tucker shut down the warp injector system so the crew of Enterprise NX-01 could seek shelter in the catwalk. (ENT: "The Catwalk")
While testing modifications to the warp engine of Enterprise in 2153, chief engineer Tucker watched a display on a monitor in engineering, that displayed an injector while a particle stream ran through it. (ENT: "Similitude")
The representation of an injector in this diagram is not identified on screen; its designation as an injector comes from the final draft script of "Similitude".