Engine
From Wikipedia, the free encyclopedia
An engine in the broadest sense, is something that produces an output effect from a given input. The origin of engineering however, came from the design, building and working of (military "engines") because before such devices came to be employed in battles there were very few mechanical devices used. Military engines included siege engines, large catapults, trebuchets, battering rams etc. So the first engineers were military engineers, then later as engineering developed, there came Civil engineers. These were engineers who dealt with designing, building and commissioning roads, bridges, docks and wharves, large public and private buildings etc. There also exists an overlap in English between two meanings of the word "engineer": "those who operate engines" and "those who design and construct new items."
An engine whose purpose is to produce kinetic energy output from a fuel source is called a prime mover; alternatively, a motor is a device which produces kinetic energy from a preprocessed "fuel" (such as electricity, a flow of hydraulic fluid or compressed air). Unfortunately some everyday English language confusion exists about this terminology demarcation that sometimes leads to expensive errors. For example, a service specialist (an electrical engineer) might be called upon to travel some way to examine a faulty "motor" - to find on arrival at the site that the so-called "motor", is in fact, a rather large diesel engine that he has no knowledge of, as its operating principles lie outside his area of specialisation.
An ordinary car (up to the present time: 2007) has a starter motor, a windscreen wiper motor, windscreen washer motor, a fuel pump motor and motors to adjust the wing mirrors from within the car and a (motorised) radio antenna - but the power plant that propels the car is an engine. Again an aircraft will have many motors installed for operation of its many auxiliary operations and services, but aircraft are propelled by engines, in this case, jet engines.
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[edit] Usage of the term
Originally, early at the beginning of the Industrial Revolution in everyday language [English] an engine was any sort of mechanical device that converted some form of energy into mechanical or motion force. The term "gin" as in cotton gin is recognised as originating from the Old French word 'engin' as a short form of its usage. Practically every device from the industrial revolution was referred to as an engine, and this is where the steam engine gained its name. The term has more recently become popular in computer science in terms like "search engine", "3-D graphics game engine", "rendering engine" and "text-to-speech engine", even though these "engines" are not mechanical and cause no mechanical action (this usage may have been inspired by the "difference engine", and early mechanical computing device). Military devices such as catapults are referred to as siege engines.
In more recent usage, the term is used to describe devices that perform mechanical work, follow-ons to the original steam engine. In most cases the work is supplied by exerting a torque, which is used to operate other machinery, generate electricity, pump water or compress gas.
In the context of propulsion systems, an air breathing engine is one that uses atmospheric air to oxidise the fuel carried, rather than carrying an oxidiser, as in Engines using human power, animal power, water power, wind power and even steam power date back to antiquity.
Human power was focused by the use of simple engines, such as the capstan, windlass or treadmill, and with ropes, pulleys, and block and tackle arrangements, this power was transmitted and multiplied. These were used in cranes and aboard ships during Ancient Greece, and in mines, water pumps and siege engines in Ancient Rome. Early oared warships used human power augmented by the simple engine of the lever -- the oar itself. The writers of those times, including Vitruvius, Frontinus and Pliny the Elder, treat these engines as commonplace, so their invention may be far more ancient.
By the 1st century AD, various breeds of cattle and horses were used in mills, using machines similar to those powered by humans in earlier times.
According to Strabo, a water powered mill was built in Kaberia in the kingdom of Mithridates in the 1st century BC. Use of water wheels in mills spread through Europe over the next few centuries. Some were quite complex, with aqueducts, dams, and sluices to maintain and channel the water, and systems of gears, or toothed-wheels made of wood with metal, used to regulate the speed of rotation. In a poem by Ausonius in the 4th century, he mentions a stone-cutting saw powered by water.
Hero of Alexandria demonstrated both wind and steam powered machines in the 1st century, although it is not known if these were put to any practical use.
[edit] Modern
English inventor Sir Samuel Morland allegedly used gunpowder to drive water pumps in the 17th century. For more conventional, reciprocating internal combustion engines the fundamental theory for two-stroke engines was established by Sadi Carnot, France, 1824, whilst the American Samuel Morey received a patent on April 1, 1826. (Dugald Clark) Sir Dugald Clark (1854 – 1932) designed the first two-stroke engine in 1878 and patented it in England in 1881.
Automotive production has used a range of energy-conversion systems. These include electric, steam, solar, turbine, rotary, and piston-type internal combustion engines. The petrol internal combustion engine, operating on a four-stroke Otto cycle, has been the most successful for automobiles, while diesel engines are used for trucks and buses.
Karl Benz was one of the leaders in the development of new engines. In 1878 he began to work on new designs. He concentrated his efforts on creating a reliable gas two-stroke engine that was more powerful, based on Nikolaus Otto's design of the four-stroke engine. Karl Benz showed his real genius, however, through his successive inventions registered while designing what would become the production standard for his two-stroke engine. Benz finished his engine on New Year's Eve and was granted a patent for it in 1879.
In 1896, Karl Benz was granted a patent for his design of the first engine with horizontally-opposed pistons. Many BMW motorcycles use this engine type. His design created an engine in which the corresponding pistons move in horizontal cylinders and reach top dead centre simultaneously, thus automatically balancing each other with respect to momentum. Engines of this design are often referred to as flat engines because of their shape and lower profile. They must have an even number of cylinders and six, four or two cylinder flat engines have all been common. The most well-known engine of this type is probably the Volkswagen beetle engine. Engines of this type continue to be a common design principle for high performance aero engines (for propellor driven aircraft) and, engines used by automobile producers such Porsche and Subaru.
Continuance of the use of the internal combustion engine for automobiles is partly due to the improvement of engine control systems (onboard computers providing engine management processes, and electronically controlled fuel injection). Forced air induction by turbocharging and supercharging have increased power outputs and efficiencies available. Similar changes have been applied to smaller diesel engines giving them almost the same power characteristics as petrol engines. This is especially evident with the popularity of smaller diesel engine propelled cars in Europe. Larger diesel engines are still often used in trucks and heavy machinery. They don't burn as clean as gasoline engines, however they're far more powerful.
The internal combustion engine was originally selected for the automobile due to its flexibility over a wide range of speeds. Also, the power developed for a given weight engine was reasonable; it could be produced by economical mass-production methods; and it used a readily available, moderately priced fuel - petrol.
In today’s world, there has been a growing emphasis on the pollution producing features of automotive power systems. This has created new interest in alternate power sources and internal-combustion engine refinements that were not economically feasible in prior years. Although a few limited-production battery-powered electric vehicles have appeared, they have not proved to be competitive owing to costs and operating characteristics. In the twenty-first century the diesel engine has been increasing in popularity with automobile owners. However, the gasoline engine, with its new emission-control devices to improve emission performance, has not yet been challenged significantly.
The first half of the twentieth century saw a trend to increase engine power, particularly in the American models. Design changes incorporated all known methods of raising engine capacity, including increasing the pressure in the cylinders to improve efficiency, increasing the size of the engine, and increasing the speed at which power is generated. The higher forces and pressures created by these changes created engine vibration and size problems that led to stiffer, more compact engines with V and opposed cylinder layouts replacing longer straight-line arrangements. In passenger cars, V-8 layouts were adopted for all piston displacements greater than 250 cubic inches (4 litres).
The design principles favoured in Europe, because of economic and other restraints, leant toward smaller cars and corresponding design principles that concentrated on increasing the the combustion efficiency of smaller engines. This produced more economical engines with earlier four-cylinder designs rated at 40 horsepower (30 kW) and six-cylinder designs rated as low as 80 horsepower (60 kW), compared with the large volume V-8 American engines with power ratings in the range from 250 to 350 hp (190 to 260 kW).
Earlier automobile engine development produced a much larger range of engines than is in common use today. Engines have ranged from 1 to 12 cylinder designs with corresponding differences in overall size, weight, piston displacement, and cylinder bores. Four cylinders and power ratings from 19 to 120 hp (14 to 90 kW) were followed in a majority of the models. Several three-cylinder, two-stroke-cycle models were built while most engines had straight or in-line cylinders. There were several V-type models and horizontally opposed two- and four-cylinder makes too. Overhead camshafts were frequently employed. The smaller engines were commonly air-cooled and located at the rear of the vehicle; compression ratios were relatively low. The 1970s and '80s saw an increased interest in improved fuel economy which brought in a return to smaller V-6 and four-cylinder layouts, with as many as five valves per cylinder to improve efficiency.
The largest internal combustion engine ever built is the Wärtsilä-Sulzer RTA96-C - a 14 cylinder, 2 stroke, turbocharged diesel engine that was designed to power the Emma Maersk, the largest container ship in the world. This engine weighs 2300 tonnes, and when running at 102 r/min produces 109000bhp (8314 kW) consuming some 13.7 tonnes of fuel each hour.
[edit] Air-breathing engines
Air-breathing engines use atmospheric air to oxidise the fuel carried, rather than carrying an oxidiser, as in a rocket. Theoretically, this should result in a better specific impulse than for rocket engines.
Air-breathing engines include:
- Internal combustion engine
- Jet engine
- Ramjet
- Scramjet
- Pulse detonation engine
- Pulse jet
- Liquid air cycle engine/SABRE