steam engine

Engine that uses the power of steam to produce useful work. The first successful steam engine was built in 1712 by English inventor Thomas Newcomen at Dudley, West Midlands; it was developed further by Scottish instrument maker James Watt from 1769 and by English mining engineer Richard Trevithick, whose high-pressure steam engine of 1802 led to the development of the steam locomotive.

In Newcomen's engine, steam was admitted to a cylinder as a piston moved up, and was then condensed by a spray of water, allowing air pressure to force the piston downwards. James Watt improved Newcomen's engine in 1769 by condensing the steam outside the cylinder (thus saving energy formerly used to reheat the cylinder) and by using steam to move the piston. Watt also introduced the double-acting engine, in which steam is alternately sent to each side of the piston forcing it up and down. The compound engine (1781) uses the exhaust from one cylinder to drive the piston of another. A later development was the steam turbine, still used today to power ships and generators in power stations. In other contexts, the steam engine was superseded by the internal-combustion engine or the electric motor.