turbine - device that converts the force of a gas or liquid moving across a set of rotor and fixed blades into motion. There are three basic types of turbines: gas, steam, and hydraulic. Gas turbines are powered by the expansion of compressed gases gene rated by the combustion of a fuel. (See internal combustion engine). Some of the power thus produced is used to drive an air compressor, which provides the air necessary for combustion of the fuel. In a turbo-jet aircraft engine, the turbine's only function is to drive the compressor: the plane is propelled by the force of the expanding gases escaping from the rear of the engine. In other applications, however, the rotor shaft provides the driving thrust to some other mechanism, such as a propeller or generator. Thus, gas turbines power not only turbo-jet aircraft, but also turbo-prop aircraft, locomotives, ships, compressors, and small-to-medium-size electric utility generators. Gas turbine-powered aircraft present severe lubrication demands that are best met with a synthetic turbo oil. Steam turbines employ steam that enters the turbine at high temperature and pressure and expands across both rotating and fixed blades (the latter serving to direct the steam). Steam turbines, which power large electric generators, produce most of the world's electricity. Only the highest-quality lubricants are able to with stand the wet conditions and high temperatures associated with steam turbine operation. The term turbine oil has thus become synonymous with quality. Hydraulic turbines (water turbines) are either impulse type, in which falling water hits blades for buckets on the periphery of a wheel that turns a shaft, or reaction type, where water under pressure emerges from nozzles on the wheel, causing it to turn. Hydraulic turbines can be used to produce electric power near reservoirs or river dams.