<P> Uniflow engines attempt to remedy the difficulties arising from the usual counterflow cycle where, during each stroke, the port and the cylinder walls will be cooled by the passing exhaust steam, whilst the hotter incoming admission steam will waste some of its energy in restoring working temperature . The aim of the uniflow is to remedy this defect and improve efficiency by providing an additional port uncovered by the piston at the end of each stroke making the steam flow only in one direction . By this means, the simple - expansion uniflow engine gives efficiency equivalent to that of classic compound systems with the added advantage of superior part - load performance, and comparable efficiency to turbines for smaller engines below one thousand horsepower . However, the thermal expansion gradient uniflow engines produce along the cylinder wall gives practical difficulties. . The Quasiturbine is a uniflow rotary steam engine where steam intakes in hot areas, while exhausting in cold areas . </P> <P> A steam turbine consists of one or more rotors (rotating discs) mounted on a drive shaft, alternating with a series of stators (static discs) fixed to the turbine casing . The rotors have a propeller - like arrangement of blades at the outer edge . Steam acts upon these blades, producing rotary motion . The stator consists of a similar, but fixed, series of blades that serve to redirect the steam flow onto the next rotor stage . A steam turbine often exhausts into a surface condenser that provides a vacuum . The stages of a steam turbine are typically arranged to extract the maximum potential work from a specific velocity and pressure of steam, giving rise to a series of variably sized high - and low - pressure stages . Turbines are only efficient if they rotate at relatively high speed, therefore they are usually connected to reduction gearing to drive lower speed applications, such as a ship's propeller . In the vast majority of large electric generating stations, turbines are directly connected to generators with no reduction gearing . Typical speeds are 3600 revolutions per minute (RPM) in the USA with 60 Hertz power, and 3000 RPM in Europe and other countries with 50 Hertz electric power systems . In nuclear power applications the turbines typically run at half these speeds, 1800 RPM and 1500 RPM . A turbine rotor is also only capable of providing power when rotating in one direction . Therefore, a reversing stage or gearbox is usually required where power is required in the opposite direction . </P> <P> Steam turbines provide direct rotational force and therefore do not require a linkage mechanism to convert reciprocating to rotary motion . Thus, they produce smoother rotational forces on the output shaft . This contributes to a lower maintenance requirement and less wear on the machinery they power than a comparable reciprocating engine . </P> <P> The main use for steam turbines is in electricity generation (in the 1990s about 90% of the world's electric production was by use of steam turbines) however the recent widespread application of large gas turbine units and typical combined cycle power plants has resulted in reduction of this percentage to the 80% regime for steam turbines . In electricity production, the high speed of turbine rotation matches well with the speed of modern electric generators, which are typically direct connected to their driving turbines . In marine service, (pioneered on the Turbinia), steam turbines with reduction gearing (although the Turbinia has direct turbines to propellers with no reduction gearbox) dominated large ship propulsion throughout the late 20th century, being more efficient (and requiring far less maintenance) than reciprocating steam engines . In recent decades, reciprocating Diesel engines, and gas turbines, have almost entirely supplanted steam propulsion for marine applications . </P>

Who designed a steam engine that was 40 more efficient