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An engine is something that produces an effect from a given input. The origin of engineering was "the working of engines". There is an overlap in English between two meanings of the word "engineer": 'those who operate engines' and 'those who design and construct new items'.


Usage of the term "Engine"

In original usage, an engine was any sort of mechanical device. The term "gin" in cotton gin is a short form of this usage. Practically every device from the industrial revolution was referred to as an engine, and this is where the steam engine gained its name. This form of the term has recently come into use once again in computer science, where terms like "search engine", "3-D graphics game engine", "rendering engine" and "text-to-speech engine" are common. The earliest mechanical computing device was called the difference engine; Military devices such as catapults are referred to as siege engines. In more recent usage, the term is typically 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 a rocket. Theoretically, this should result in a better specific impulse than for rocket engines.

Types of engines

An engine is a device that converts things. In computer science, a software engine is the functional core of a computer program. This can be a search engine (term to results), game engine (input to display), layout engine (markup to display), or a core of a text to speech system.

More often it referes to motors. Here it is related to motor cars or automobile, motor vehicle, motor systems (the physiological system that is responsible for physical movement), or motor neuron (neurons that originate in the spinal cord and synapse with muscle fibers). When used in the context of poert and energy, it is usually meant to signify a "Electric motor" (a machine that converts electricity into a mechanical motion), Thermodynamic motor (or heat engine; a machine that converts heat into mechanical motion), Molecular motors, (the essential agents of movement in living organisms), Pneumatic motor, (a machine that converts the energy of compressed air into mechanical motion), Hydraulic motor (a machine that converts the energy of pressurized liquid flow into mechanical motion), Synthetic molecular motors (or nanomotors),

An electric motor converts electrical energy into kinetic energy. The reverse task, that of converting kinetic energy into electrical energy, is accomplished by a generator or dynamo. In many cases the two devices differ only in their application and minor construction details, and some applications use a single device to fill both roles. For example, traction motors used on locomotives often perform both tasks if the locomotive is equipped with dynamic brakes.

In engineering and thermodynamics, a heat engine performs the conversion of heat energy to mechanical work by exploiting the temperature gradient between a hot "source" and a cold "sink". Heat is transferred from the source, through the "working body" of the engine, to the sink, and in this process some of the heat is converted into work by exploiting the properties of a working substance (usually a gas or liquid).

A pneumatic motor is a machine which converts energy of compressed air into mechanical motion; for example a pneumatic vane motor, a pneumatic piston motor, or pneumatic artificial muscles.In industrial applications linear motion can come from either a diaphragm or piston actuator. For rotary motion a vane type air motor is used. Hydraulic machinery are machines and tools which use fluid power to do work. Heavy equipment is a common example. In this type of machine, hydraulic fluid is pumped to a high pressure and transmitted throughout the machine to various actuators. The hydraulic pumps are powered by engines or electric motors. Pressurized fluid is controlled by the operator with control valves and distributed through hoses and tubes. The popularity of hydraulic machinery is due to the very large amount of power that can be transferred through small tubes and flexible hoses; and the high power density and wide array of actuators that can make use of this power.

Molecular motors are biological "nanomachines" and are the essential agents of movement in living organisms. Generally speaking, a motor is defined as a device that consumes energy in one form and converts it into motion or mechanical power; many protein-based molecular motors convert the chemical energy present in ATP into mechanical energy. In terms of energetic efficiency, these types of motors are often superior to currently available man-made motors. One important difference between molecular motors and macroscopic motors is that molecular motors operate in the thermal bath, an environment where thermal noise is significant relative to the motor's energy consumption.

Recently, chemists and those involved in nanotechnology efforts have begun to explore the possibility of creating molecular motors de novo. These synthetic molecular motors currently suffer many limitations that limit their adoption to only experimental use. It should be expected, however, that many of these limitations will soon be overcome, as understanding of chemistry and physics at the nanoscale increases. In particular, there are many examples of molecular machines that operate in solution or when attached to solid surfaces, such as the nanocar. Such systems are paving the way towards synthetic motors.

Synthetic molecular motors are nanoscale devices capable of rotation under energy input. Although the term "molecular motor" has traditionally referred to a naturally occurring protein that induces motion, some groups also use the term when referring to non-biological, non-peptide synthetic motors. Many chemists are pursuing the synthesis of such molecular motors. The prospect of synthetic molecular motors was first raised by the nanotechnology pioneer Richard Feynman in 1959 in his classic talk There's Plenty of Room at the Bottom.

The basic requirements for a synthetic motor are repetitive 360° motion, the consumption of energy and unidirectional rotation. Two efforts in this direction were published in 1999 in the same issue of Nature. For the two reports below, it is unknown whether these molecules are capable of generating torque. It is expected that reports of more efforts in this field will increase, as understanding of chemistry and physics at the nanoscale improves.

History of engines


While chemical and electrical engines of enormous power dominate the modern world, engines themselves are not new. 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 commonly 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 slowly 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's not known if these were put to any practical use until much later.


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.

Automotive production down the ages has required a wide range of energy-conversion systems. These include electric, steam, solar, turbine, rotary, and different types of piston-type internal combustion engines. The gasoline internal combustion engine, operating on a four-stroke Otto cycle, has traditionally been the most successful for automobiles, while diesel engines are widely used for trucks and buses. The patent on the design by Otto had been declared void. Karl Benz led in the development of new engines. In 1878 he began to work on new patents. First, he concentrated all his efforts on creating a reliable gas two-stroke engine, 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 boxer engine with horizontally-opposed pistons. His design created an engine in which the corresponding pistons reach top dead centre simultaneously, thus balancing each other with respect to momentum. Flat engines with four or fewer cylinders are most commonly boxer engines and are also known as, horizontally-opposed engines. This continues to be the design principle for high performance, automobile racing engines such as Porsches. Continuance of the use of the internal combustion engine for automobiles is partially due to the improvement of engine control systems (computers) and forced induction (turbos and superchargers), giving modern diesel engines the same power characteristics as gasoline engines. This is especially evident with the popularity of diesel engines in Europe.

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--gasoline.

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 from time to time, 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).

Smaller cars brought about a return a to smaller engines, the four- and six-cylinder designs rated as low as 80 horsepower (60 kW), compared with the standard-size V-8 of large cylinder bore and relatively short piston stroke with power ratings in the range from 250 to 350 hp (190 to 260 kW).

The automobile motor had a bigger range, varying from 1-12 cylinders 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.

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:

Engine design

Engine design is the making of the engine mostly through computers. Once it is designed it is made in real life and tested. Alternative propulsion systems have experimental and more advanced designs. You must have a degree in engineering to design engines. You must know all the main components and make sure it is up to date and meets the government standards (safety/emissions inspection).

Related concepts

External articles and references

Sites on Engines
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Images of Engines
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Newsgroups with Engines
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News of Engines
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See also

- PowerPedia main index
- PESWiki home page

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