gas engine - internal combustion engine, either two or four-stroke cycle, powered by natural gas or LPG. Commonly used to drive compressors on gas pipelines, utilizing as fuel a portion of the gas being compressed. Gas engine combustion chamber temperatures are typically hotter than in gasoline or diesel engines and thus have a greater tendency toward nitration (formation of nitrogen oxides, which can degrade the crankcase oil) and piston deposits (which can impair engine performance and damage engine parts). Gas engine oils are specially formulated to control these tendencies. See engine deposits.