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The term steam engine may also refer to an entire power plant, including boiler/steam generator.
A steam engine is a heat engine that converts heat energy to mechanical work using steam as the working fluid.
Many, but not all, steam engines are external combustion engines. Steam engines in general allow the use of very many heat sources to produce the steam. Some for example, are powered by geothermal or nuclear power and employ no combustion at all.E.C.E.
There are two common forms of steam engine: reciprocating (piston engine) and rotary (the steam turbine). In common usage, "steam engine" often refers specifically to the reciprocating type. However, both are steam-engines and both use the Rankine cycle.
Steam engines may be either "closed cycle" or "open cycle". Open cycle dump the low temperature steam to the environment, closed cycle engines cool and recirculate it. Open cycle engines are typically simpler and have lower weight and initial cost, but can frequently be less efficient.
Brief history Edit
Steam engines were the power source that made the Industrial Revolution possible. From 1712, when the Newcomen steam engine was first introduced to pump water from mines, continued development allowed the use of more advanced engines in a wider variety of applications. Steam engines saw widespread commercial use powering machinery in factories and mills and powering industrial utilities such as water and sewage pumping stations. In the 19th century, following Richard Trevithick's successful use of high-pressure steam, steam engines were developed as the prime mover for transportation in railway locomotives, steam ships, traction engines, and road vehicles such as the steam car and steam wagon.
They remained the primary source of mechanical power well into the 20th century, until technological improvements in the design of internal combustion engines and electric motors rendered most small engines 'uneconomical' for most applications. However, with new energy issues of the 21st century, steam engines are being used for "micro combined heat and power." Large Steam engines (in the form of turbines) are still vitally important, generating about 86% of all electric power used throughout the world.
As steam expands in a high pressure engine its temperature drops; because no heat is released from the system, this is known as adiabatic expansion and results in steam entering the cylinder at high temperature and leaving at low temperature. This causes a cycle of heating and cooling of the cylinder with every stroke which is a source of inefficiency.
A method to lessen the magnitude of this heating and cooling was invented in 1804 by British engineer Arthur Woolf, who patented his Woolf high pressure compound engine in 1805. In the compound engine, high pressure steam from the boiler expands in a high pressure (HP) cylinder and then enters one or more subsequent lower pressure (LP) cylinders. The complete expansion of the steam now occurs across multiple cylinders and as less expansion now occurs in each cylinder so less heat is lost by the steam in each. This reduces the magnitude of cylinder heating and cooling, increasing the efficiency of the engine. To derive equal work from lower pressure steam requires a larger cylinder volume as this steam occupies a greater volume. Therefore the bore, and often the stroke, are increased in low pressure cylinders resulting in larger cylinders.
Double expansion (usually known as compound) engines expanded the steam in two stages. The pairs may be duplicated or the work of the large LP cylinder can be split with one HP cylinder exhausting into one or the other, giving a 3-cylinder layout where cylinder and piston diameter are about the same making the reciprocating masses easier to balance.
Two-cylinder compounds can be arranged as:
- Cross compounds - The cylinders are side by side.
- Tandem compounds - The cylinders are end to end, driving a common connecting rod
- Angle compounds - The cylinders are arranged in a vee (usually at a 90° angle) and drive a common crank.
With two-cylinder compounds used in railway work, the pistons are connected to the cranks as with a two-cylinder simple at 90° out of phase with each other (quartered). When the double expansion group is duplicated, producing a 4-cylinder compound, the individual pistons within the group are usually balanced at 180°, the groups being set at 90° to each other. In one case (the first type of Vauclain compound), the pistons worked in the same phase driving a common crosshead and crank, again set at 90° as for a two-cylinder engine. With the 3-cylinder compound arrangement, the LP cranks were either set at 90° with the HP one at 135° to the other two, or in some cases all three cranks were set at 120°.
The adoption of compounding was common for industrial units, for road engines and almost universal for marine engines after 1880; it was not universally popular in railway locomotives where it was often perceived as complicated. This is partly due to the harsh railway operating environment and limited space afforded by the loading gauge (particularly in Britain, where compounding was never common and not employed after 1930). However although never in the majority it was popular in many other countries
An animation of a simplified triple-expansion engine.High-pressure steam (red) enters from the boiler and passes through the engine, exhausting as low-pressure steam (blue) to the condenser. An animation of a simplified triple-expansion engine. High-pressure steam (red) enters from the boiler and passes through the engine, exhausting as low-pressure steam (blue) to the condenser. 1890s vintage triple-expansion (three cylinders of 26, 42 and 70 inch diameters in a common frame with a 42 inch stroke) marine engine that powered the SS Christopher Columbus 1890s vintage triple-expansion (three cylinders of 26, 42 and 70 inch diameters in a common frame with a 42 inch stroke) marine engine that powered the SS Christopher Columbus
It is a logical extension of the compound engine (described above) to split the expansion into yet more stages to increase efficiency. The result is the multiple expansion engine. Such engines use either three or four expansion stages and are known as triple and quadruple expansion engines respectively. These engines use a series of double-acting cylinders of progressively increasing diameter and/or stroke and hence volume. These cylinders are designed to divide the work into three or four, as appropriate, equal portions for each expansion stage. As with the double expansion engine, where space is at a premium, two smaller cylinders of a large sum volume may be used for the low pressure stage. Multiple expansion engines typically had the cylinders arranged inline, but various other formations were used. In the late 19th century, the Yarrow-Tweedy balancing 'system' was used on triple expansion engines. Such engines divided the low pressure expansion stages between two cylinders, one at each end of the engine. This allowed the crankshaft to be better balanced, resulting in a smoother, faster-responding engine which ran with less vibration. This made the 4-cylinder triple-expansion engine popular with large passenger liners (such as the Olympic class), but was ultimately replaced by the virtually vibration-free turbine (see below).
The development of this type of engine was important for its use in steamships as by exhausting to a condenser the water can be reclaimed to feed the boiler, which is unable to use seawater. Land-based steam engines could exhaust much of their steam, as feed water was usually readily available. Prior to and during World War II, the expansion engine dominated marine applications where high vessel speed was not essential. It was however superseded by the British invention steam turbine where speed was required, for instance in warships, such as the pre-dreadnought battleships, and ocean liners. HMS Dreadnought of 1905 was the first major warship to replace the proven technology of the reciprocating engine with the then-novel steam turbine.
Steam engines can generally be classified by their application:
Stationary steam engines can be classified into two main types:
- Winding engines, rolling mill engines, steam donkeys, (marine engines) and similar applications which need to frequently stop and reverse.
- Engines providing power, which stop rarely and do not need to reverse. These include engines used in thermal power stations and those that were used in mills, factories and to power cable railways and cable tramways before the widespread use of electric power. Very low power engines are used to power model ships and speciality applications such as the steam clock.
The steam donkey is technically a stationary engine but is mounted on skids to be semi-portable. It is designed for logging use and can drag itself to a new location. Having secured the winch cable to a sturdy tree at the desired destination, the machine will move towards the anchor point as the cable is winched in.
Steam engines have been used to power a wide array of vehicles:
- Steam aircraft
- Steamboat and steamship
- Steam car
- Steam locomotive - generally Railway engines.
- Steam roller
- Steam shovel
- Steam rockets
- Traction engine often referred to as a steam engine in general speech.
- Main article: wikipedia:thermodynamic efficiency
- Carter's Steam Fair - touring vintage fairground, including several rides powered by steam engines
- Great Dorset Steam Fair - 5-day annual show in England - specialises in showing engines being used in their original context: heavy haulage, threshing, ploughing, sawing, road making, etc
- Antique Gas & Steam Engine Museum - Bi-Annual show in Vista, CA, Specializing in farm equipment, engines, and machinery from 1850-1950
- See also: List of pumping stations, many of which are, or were, steam-powered.
- Bancroft Mill Engine.
- Black Country Living Museum in Dudley, Staffs UK: full-size working replica of the first Newcomen atmospheric engine of 1712.
- Bolton Steam Museum - Mill engines
- Crofton Beam Engines (Movie of Crofton engines operating)
- Hollycombe Steam Collection
- Kempton Park Steam Engines - Steam pumping station museum
- Kew Bridge Steam Museum - Pumping station
- Newcomen Engine House, Dartmouth, Devon, England, UK
- Sherborne Steam and Waterwheel Centre
- Shows and Meets - list of the various events in the UK (Expansion required, add any missing ones please)
- List of Steam Machinery Manufacturers
- Museums List
- Show Reports
- Old Glory Magazine - Steam based preservation Magazine
Wikipedia for initial article
|This page uses some content from Wikipedia. The original article was at Steam engine. The list of authors can be seen in the page history. As with Tractor & Construction Plant Wiki, the text of Wikipedia is available under the Creative Commons by Attribution License and/or GNU Free Documentation License. Please check page history for when the original article was copied to Wikia|