An internal combustion engine (also called the combustion engine) was a type of motor that used the burning of a fuel to create mechanical energy that would propel various vehicles.
One superstition that Montgomery Scott had developed a belief in was that of gremlins. By all indications, Scott succeeded in trapping such a being in 2286 after the USS Enterprise-A was plagued by a series of equipment failures. Scott placed a well-tuned internal combustion engine in an empty torpedo casing, and when the engine began to fail, Scott launched the torpedo towards an out-of-service space buoy in order to keep the being occupied while the ship moved away. Because of the mechanical failures, no records of the nature of the being were made. (TOS novel: The Better Man)