The Hydrogen Injected ICE is an engine type used by the UNSC, and is featured in the M274 Mongoose Ultra-Light All-Terrain Vehicle and M12 Warthog vehicles [1].
Background
The AMG 12.0 liter version used in the warthog makes a kind of whiny hum, and produces a significant amount of power (enough to propel 3 and one-quarter tons of 'Hog to 78 MPH).
The 1000cc 4-stroke used in the Mongoose ULATV has a rough growl to it, especially when starting up.
Trivia
- It is unclear exactly how the HI ICE works, but it presumably includes an internal combustion engine (Or ICE abbreviated).