External Combustion Engines: Steam Engines and Turbines

External Combustion Engine

Steam Engine

The main elements of the steam engine and the functions they perform are:

• Hearth: This is an element external to the machine where burning occurs.
• Boiler: A vessel where steam is generated. A water pump driven by a boiler enters the liquid state at high pressure and a temperature close to ambient. In the boiler, the water heats and vaporizes. It goes on to a superheater where the temperature gets higher, but keeping the pressure of the boiler. Finally, the superheated steam enters the cylinder.
• Cylinder Engine: It consists of the distribution box, the slide, and the plunger. Inside the cylinder, the vapor expands and causes the piston reciprocation to be transmitted to the transforming elements of movement. The slide function is to direct the steam into the cylinder to achieve the reciprocating plunger. Moreover, to expand the steam, pressure and temperature decrease, and some of it condenses. Then, passing the mixture of liquid and saturated steam to a condenser, where the rest of the vapor condenses, releasing heat to a coolant. Finally, the condensed liquid is sent back to the boiler by a pump, completing the cycle.

Steam Turbine

Steam turbines are another alternative mechanism for the use of steam expansion. In them, the vapor is distributed by four jets acting directly on the blades of a wheel, rotating at speeds of about 10,000 rev/min. Passing through the steam jet loses pressure and gains speed, while the flow is oriented so that it impinges tangentially on the blades.

This device has the advantage of lacking a processing cylinder and organs of movement, so its performance is higher. The basic scheme of operation and the Rankine cycle for the turbine are the same as for the steam engine. Basic-cycle changes are usually performed in order to improve overall performance. Two of the most important changes are the overheating of the steam back into work by expansion of steam produced and warm water at the entrance to the boiler by extraction from the steam before their full expansion. The turbines are currently used in plants producing electric power, in the propulsion of ships, in blast furnaces, and cogeneration systems.