A time engine was a type of space-time vessel akin to a TARDIS, (TV: The Lodger) or in some cases a component of a time vessel.
Arborecc used a time engine as part of his converter on Beltros Station which allowed the Space Security Service to mutated wounded soldiers into fake Daleks for enemy infiltration. The Tenth Doctor removed the engine (AUDIO: The Trojan Dalek) and used it as he and Anya Kingdom piloted a ship through the Gruad Confusion before crashing into the realm of the Lost. (AUDIO: The Lost)
79B Aickman Road was a time engine which the Eleventh Doctor descrbied as "someone's attempt to build a TARDIS," (TV: The Lodger) later finding a similar, if not the same, time engine in 1969. (TV: Day of the Moon)
Arianda's spaceship had time engines that leaked time energy and particles, contaminating the HMS Nemesis and aging anyone who made contact. (AUDIO: Storm of the Horofax)