Steam engine
A steam engine is a mechanical device that converts thermal energy from steam into mechanical energy, typically to drive machinery or vehicles. The process begins with burning fossil fuels to create steam in a boiler, which then powers a piston connected to a rotating shaft. The history of the steam engine dates back to early efforts by Hero of Alexandria around 60 C.E., but it was Thomas Newcomen's steam engine, built in 1712, that marked a significant advancement for practical use, particularly in pumping water from coal mines. James Watt later improved upon Newcomen's design in the 1760s by introducing a separate condenser, enhancing efficiency and fuel consumption.
Steam engines played a crucial role in the Industrial Revolution, facilitating advancements in transportation, such as steam-powered ships and locomotives, as well as innovations in the textile industry. Though many applications of steam engines have been replaced by electric motors and internal combustion engines today, their foundational impact on technology and industry remains significant. Their design principles continue to influence modern engineering, showcasing the steam engine's lasting legacy.
Subject Terms
Steam engine
A steam boiler converts the chemical energy in fuel into the thermal energy of steam. A steam engine converts this thermal energy into the mechanical energy of a rotating shaft. This shaft can drive an electric generator or pump.
Background
The chemical energy that is contained within fossil fuels such as oil and coal can be converted into thermal energy (heat) by burning the fuel. This thermal energy can be used to create steam in a boiler. A steam engine converts the thermal energy of steam into the mechanical energy of a rotating shaft, and this shaft can drive a pump, a ventilating fan, a ship’s propeller, and many other devices.
History
Although there were attempts to use steam to drive mechanical devices as early as 60 c.e. by Hero of Alexandria, the first real steam engine was designed and built by Thomas Newcomen in 1712. That year Newcomen successfully used a steam engine to pump water from a coal mine near Dudley Castle, England. In 1765, as he walked across Glasgow Green in the city of Glasgow, Scotland, James Watt conceived the idea of connecting the steam engine to a separate condenser. The first full-size engines based on this concept were built in 1776: one at John Wilkinson’s blast furnace near Broseley, England, and the other at Bloomfield coal mine near Tipton, England. Newcomen’s design and Watt’s early designs used steam at constant pressure. Over the course of his life, Watt invented many improvements to the steam engine, including rotary engines, a device for measuring engine performance, and engines in which the steam expanded during the piston stroke. Expanding steam engines soon drove the earlier type off the market, because the fuel consumption associated with the boiler of an expanding steam engine is far less than that of a constant pressure engine. While modern steam engines operate at much higher pressure than Watt’s, they are similar in design.
Principles of Operation
Early steam engines would be considered upside-down by modern standards. The piston was connected to a rod that emerged from the top of the engine, and steam was fed into the cylinder below the piston. A chain connected the piston rod to one end of a pivoted beam suspended above the engine, and the other end of the beam was connected to a pump that drew water up from the bottom of a mine. The weight of the pump rod was sufficient to pull the pump end of the pivoted beam downward, which caused the other end of the beam to rise and lift the piston upward. As the piston rose, steam at just above atmospheric pressure flowed from the boiler into the growing space below the piston. When the piston reached the top of its stroke, the valve between boiler and cylinder closed, and in Newcomen’s engine water was sprayed into the cylinder. As the water absorbed heat from the steam, the steam condensed, which created a partial vacuum. This vacuum, combined with atmospheric pressure acting on the upper side of the piston, caused the piston to move downward. When the piston reached the bottom of its stroke, the steam valve opened again. The steam pressure balanced the atmospheric pressure on the other side of the piston, and the weight of the pump rod again raised the piston to the top of its stroke.
Watt recognized that spraying cold water directly into the cylinder not only condensed the steam but also cooled off the cylinder itself. On the next stroke some incoming steam was wasted in reheating the cylinder. The separate condenser in Watt’s engine condensed the steam without chilling the cylinder. This resulted in a dramatic improvement in fuel consumption. Watt also closed off the upper side of the piston and provided a hole just big enough for the piston rod to pass out. Constant-pressure steam was admitted to the space above the piston, and this steam provided the pressure previously supplied by the atmosphere. Watt’s original purpose here was to eliminate the cooling effect of the atmosphere, but he soon realized that there was another benefit. Instead of continuing to admit steam at constant pressure during the entire downward stroke, the steam valve could be closed and the steam could be allowed to expand. This further reduced fuel consumption and paved the way for modern expansion steam engines.
Applications of the Steam Engine
The first applications were to drive dewatering pumps in mines and to supply pressurized air for blast furnaces that produced cast iron. It was soon realized that rotary steam engines could be used to drive all kinds of machinery. Without the invention of the steam engine, the Industrial Revolution would not have occurred in the time and place that it did. Steam engines drove spinning and weaving machines in the textile industry. Ships and railroad locomotives powered by steam engines revolutionized transportation. There were steam-powered farm tractors, automobiles, and construction machines. Early electric generators were also driven by steam engines. Many of these applications are now powered by electric motors, gasoline and diesel engines, and steam turbines, but it was the steam engine that showed the way.
Bibliography
Barton, D. B. The Cornish Beam Engine: A Survey of Its History and Development in the Mines of Cornwall and Devon from Before 1800 to the Present Day, with Something of Its Use Elsewhere in Britain and Abroad. New ed. Truro, Cornwall, England: Author, 1966.
Bray, Stan. Making Simple Model Steam Engines. Ramsbury, England: Crowood, 2005.
Briggs, Asa. The Power of Steam: An Illustrated History of the World’s Steam Age. Chicago: University of Chicago Press, 1982.
Crump, Thomas. A Brief History of the Age of Steam: The Power That Drove the Industrial Revolution. New York: Carroll & Graf, 2007.
Marsden, Ben. Watt’s Perfect Engine: Steam and the Age of Invention. New York: Columbia University Press, 2002.
Rose, Joshua. Modern Steam Engines. Philadelphia: H.C. Baird, 1886. Reprint. Mendham, N.J.: Astragal Press, 2003.
Steingress, Frederick M., Harold J. Frost, and Daryl R. Walker. Stationary Engineering. 3d ed. Homewood, Ill.: American Technical, 2003.
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