External combustion steam engine

In ancient Greece, Archimedes invented a device that directed steam outward in opposing directions, causing the device to rotate. Itwould be known later as an external combustion steam engine. 

An external combustion engine that has been widely supported as a low-emission power source is the Rankine cycle steam engine. Many different types of expanders can be used to convert the energy in the working fluid... 

The driver is a prime mover capable of developing the required torque at a constant speed or over a range of speeds. The driver s energy source can be either electrical or mechanical. Electrical energy is used by motors, either of the induction or synchronous type, while the mechanical covers a multitude of sources. It may be a fuel, as in internal or external combustion engines, or it may be a gas, such as steam or process gas used in a turbine or expander. 

Because the steam engine described is a heat engine of the external-combustion type, the cycle experienced by the working medium can be executed without combustion. In some steam engines, for example, the required input heat is supplied by a nuclear reactor. Stirling engines have been operated on radiant energy supplied by the sun. 

The first widely used industrial steam engine, the Watt Steam Engine, invented in 1765, used evaporation and condensation to efficiently create energy. Fire was used to boil water in an enclosed space to produce steam. The Watt Steam Engine was an external combustion engine because of the external source of fuel. In this case, the fire burned outside of the engine itself. 

A commercial combustion turbine with the provision to inject, at any point upstream of the combustor, the externally supplied humidified and preheated supplementary compressed air. Engineering and mechanical aspects of the air injection for the compressed air injection plant concepts are similar to the steam injection for the power augmentation, which has accumulated significant operating experience. 

For most of the rotary compressors in process service, the driver is an electric motor. Compressors in portable service, however, particularly the helical-lobe compressor, use internal combustion engines. Many of the rotary compressors require the high speed that can be obtained from a direct-connected motor. The dry type helical-lobe compressor is probably the main exception as the smaller units operate above motor speed and require a speed increasing gear which may be either internal or external (see Figure 4-1). The helical-lobe compressor is the most likely candidate for a driver other than the electric motor. Aside from the portables already mentioned, engines are used extensively as drivers for rotaries located in the field in gas-gathering service. Steam turbines, while not common, probably comprise most of process service alternate drive applications. 

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