An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.[ Dictionary.com: (World heritage) "3. any device that converts another form of energy into mechanical energy so as to produce motion"]
Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power generation), heat energy (e.g. geothermal), chemical energy, electric potential and nuclear energy (from nuclear fission or nuclear fusion). Many of these processes generate heat as an intermediate energy form; thus have special importance. Some natural processes, such as atmospheric convert environmental heat into motion (e.g. in the form of rising air currents). Mechanical energy is of particular importance in transportation, but also plays a role in many industrial processes such as cutting, grinding, crushing, and mixing.
Mechanical heat engines convert heat into work via various thermodynamic processes. The internal combustion engine is perhaps the most common example of a mechanical heat engine in which heat from the combustion of a fuel causes rapid pressurisation of the gaseous combustion products in the combustion chamber, causing them to expand and drive a piston, which turns a crankshaft. Unlike internal combustion engines, a reaction engine (such as a jet engine) produces thrust by expelling reaction mass, in accordance with Newton's third law of motion.
Apart from heat engines, convert electrical energy into mechanical motion, use compressed air, and in use elastic energy. In biological systems, , like in , use chemical energy to create forces and ultimately motion (a chemical engine, but not a heat engine).
Chemical heat engines which employ air (ambient atmospheric gas) as a part of the fuel reaction are regarded as airbreathing engines. Chemical heat engines designed to operate outside of Earth's atmosphere (e.g. , deeply submerged ) need to carry an additional fuel component called the oxidizer (although there exist Superoxidant suitable for use in rockets, such as fluorine, a more powerful oxidant than oxygen itself); or the application needs to obtain heat by non-chemical means, such as by means of .
Emission/Byproducts
All chemically fueled heat engines emit exhaust gases. The cleanest engines emit water only. Strict
zero-emissions generally means zero emissions other than water and water vapour. Only heat engines which combust pure hydrogen (fuel) and pure oxygen (oxidizer) achieve zero-emission by a strict definition (in practice, one type of rocket engine). If hydrogen is burnt in combination with air (all airbreathing engines), a side reaction occurs between atmospheric oxygen and atmospheric
nitrogen resulting in small emissions of . If a
hydrocarbon (such as
Alcohol fuel or gasoline) is burnt as fuel, , a
greenhouse gas, is emitted. Hydrogen and oxygen from air can be reacted into water by a
fuel cell without side production of , but this is an electrochemical engine not a heat engine.
Terminology
The word
engine derives from
Old French , from the
Latin ingenium–the root of the word . Pre-industrial weapons of war, such as
,
and
, were called
, and knowledge of how to construct them was often treated as a military secret. The word
gin, as in
cotton gin, is short for
engine. Most mechanical devices invented during the Industrial Revolution were described as engines—the steam engine being a notable example. However, the original steam engines, such as those by
Thomas Savery, were not mechanical engines but pumps. In this manner, a
fire engine in its original form was merely a water pump, with the engine being transported to the fire by horses.
In modern usage, the term engine typically describes devices, like steam engines and internal combustion engines, that burn or otherwise consume fuel to perform mechanical work by exerting a torque or linear force (usually in the form of thrust). Devices converting heat energy into motion are commonly referred to simply as engines.
When the internal combustion engine was invented, the term motor was initially used to distinguish it from the steam engine—which was in wide use at the time, powering locomotives and other vehicles such as steamroller. The term derives from the Latin verb which means 'to set in motion', or 'maintain motion'. Thus a motor is a device that imparts motion.
Motor and engine are interchangeable in standard English.[Dictionary definitions:
] In some engineering jargons, the two words have different meanings, in which is a device that combustion or otherwise consumes fuel, changing its chemical composition, and a motor is a device driven by Electric motor, pneumatic motor, or hydraulic motor pressure, which does not change the chemical composition of its energy source.["Engine", McGraw-Hill Concise Encyclopedia of Science and Technology, Third Edition, Sybil P. Parker, ed. McGraw-Hill, Inc., 1994, p. 714.]
A heat engine may also serve as a —a component that transforms the flow or changes in pressure of a Fluid mechanics into mechanical energy.["Prime mover", McGraw-Hill Concise Encyclopedia of Science and Technology, Third Edition, Sybil P. Parker, ed. McGraw-Hill, Inc., 1994, p. 1498.] An automobile powered by an internal combustion engine may make use of various motors and pumps, but ultimately all such devices derive their power from the engine. Another way of looking at it is that a motor receives power from an external source, and then converts it into mechanical energy, while an engine creates power from pressure (derived directly from the explosive force of combustion or other chemical reaction, or secondarily from the action of some such force on other substances such as air, water, or steam).
History
Antiquity
, such as the club and
oar (examples of the
lever), are
Prehistory. More complex engines using
human power,
Working animals,
Water wheel,
Windmill and even steam power date back to antiquity. Human power was focused by the use of simple engines, such as the capstan,
windlass or
Treadwheel, and with
,
, and block and tackle arrangements; this power was transmitted usually with the forces multiplied and the speed
gear reduction. These were used in cranes and aboard
in
Ancient Greece, as well as in
Mining,
Pump and
siege engines in
Ancient Rome. The writers of those times, including
Vitruvius,
Frontinus and Pliny the Elder, treat these engines as commonplace, so their invention may be more ancient. By the 1st century AD,
cattle and
were used in mills, driving machines similar to those powered by humans in earlier times.
According to Strabo, a water-powered mill was built in Kaberia of the Parthian Empire during the 1st century BC. Use of in mills spread throughout the Roman Empire over the next few centuries. Some were quite complex, with aqueducts, , and to maintain and channel the water, along with systems of gears, or toothed-wheels made of wood and metal to regulate the speed of rotation. More sophisticated small devices, such as the Antikythera Mechanism used complex trains of gears and dials to act as calendars or predict astronomical events. In a poem by Ausonius in the 4th century AD, he mentions a stone-cutting saw powered by water. Hero of Alexandria is credited with many such wind and steam powered machines in the 1st century AD, including the Aeolipile and the vending machine, often these machines were associated with worship, such as animated altars and automated temple doors.
Medieval
Medieval Muslim engineers employed
in mills and water-raising machines, and used
as a source of water power to provide additional power to watermills and water-raising machines.
In the medieval Islamic world, such advances made it possible to
Mechanization many industrial tasks previously carried out by
manual labour.
In 1206, al-Jazari employed a crank-conrod system for two of his water-raising machines. A rudimentary steam turbine device was described by Taqi al-Din[Hassan, Ahmad Y. (1976). Taqi al-Din and Arabic Mechanical Engineering, pp. 34–35. Institute for the History of Arabic Science, University of Aleppo.] in 1551 and by Giovanni Branca
In the 13th century, the solid rocket motor was invented in China. Driven by gunpowder, this simplest form of internal combustion engine was unable to deliver sustained power, but was useful for propelling weaponry at high speeds towards enemies in battle and for fireworks. After invention, this innovation spread throughout Europe.
Industrial Revolution
The Watt steam engine was the first type of steam engine to make use of steam at a pressure just above atmospheric to drive the piston helped by a partial vacuum. Improving on the design of the 1712 Newcomen steam engine, the Watt steam engine, developed sporadically from 1763 to 1775, was a great step in the development of the steam engine. Offering a dramatic increase in
fuel efficiency,
James Watt's design became synonymous with steam engines, due in no small part to his business partner,
Matthew Boulton. It enabled rapid development of efficient semi-automated factories on a previously unimaginable scale in places where waterpower was not available. Later development led to
and great expansion of
Rail transport.
As for internal combustion , these were tested in France in 1807 by de Rivaz and independently, by the Niépce brothers. They were theoretically advanced by Carnot in 1824. In 1853–57 Eugenio Barsanti and Felice Matteucci invented and patented an engine using the free-piston principle that was possibly the first 4-cycle engine.
The invention of an internal combustion engine which was later commercially successful was made during 1860 by Etienne Lenoir.[Victor Albert Walter Hillier, Peter Coombes – Hillier's Fundamentals of Motor Vehicle Technology, Book 1 Nelson Thornes, 2004 Retrieved]
In 1877, the Otto cycle was capable of giving a far higher power-to-weight ratio than steam engines and worked much better for many transportation applications such as cars and aircraft.
Automobiles
The first commercially successful automobile, created by
Karl Benz, added to the interest in light and powerful engines. The lightweight gasoline internal combustion engine, operating on a four-stroke Otto cycle, has been the most successful for light automobiles, while the thermally more-efficient
Diesel engine is used for trucks and buses. However, in recent years,
turbocharged Diesel engines have become increasingly popular in automobiles, especially outside of the United States, even for quite small cars.
Horizontally-opposed pistons
In 1896, Karl Benz was granted a patent for his design of the first engine with horizontally opposed pistons. His design created an engine in which the corresponding pistons move in horizontal cylinders and reach top dead center simultaneously, thus automatically balancing each other with respect to their individual momentum. Engines of this design are often referred to as “flat” or “boxer” engines due to their shape and low profile. They were used in the Volkswagen Beetle, the Citroën 2CV, some Porsche and Subaru cars, many
BMW and
Honda . Opposed four- and six-cylinder engines continue to be used as
aircraft engine in small, propeller-driven
aircraft.
Advancement
The continued use of internal combustion engines in automobiles is partly due to the improvement of engine control systems, such as on-board computers providing engine management processes, and electronically controlled fuel injection. Forced air induction by turbocharging and supercharging have increased the power output of smaller displacement engines that are lighter in weight and more fuel-efficient at normal cruise power. Similar changes have been applied to smaller Diesel engines, giving them almost the same performance characteristics as gasoline engines. This is especially evident with the popularity of smaller diesel engine-propelled cars in Europe. Diesel engines produce lower
hydrocarbon and emissions, but greater particulate and pollution, than gasoline engines.
Diesel engines are also 40% more fuel efficient than comparable gasoline engines.
[
]
Increasing power
In the first half of the 20th century, a trend of increasing engine power occurred, particularly in the U.S. models. Design changes incorporated all known methods of increasing engine capacity, including increasing the pressure in the cylinders to improve efficiency, increasing the size of the engine, and increasing the rate at which the engine produces work. 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.
Combustion efficiency
Optimal combustion efficiency in passenger vehicles is reached with a coolant temperature of around .
Engine configuration
Earlier automobile engine development produced a much larger range of engines than is in common use today. Engines have ranged from 1- to 16-cylinder designs with corresponding differences in overall size, weight, engine 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 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 1980s saw an increased interest in improved fuel economy, which caused a return to smaller V-6 and four-cylinder layouts, with as many as five valves per cylinder to improve efficiency. The Bugatti Veyron 16.4 operates with a W16 engine, meaning that two V8 cylinder layouts are positioned next to each other to create the W shape sharing the same crankshaft.
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 Mærsk, the largest container ship in the world when launched in 2006. This engine has a mass of 2,300 tonnes, and when running at 102 rpm (1.7 Hz) produces over 80 MW, and can use up to 250 tonnes of fuel per day.
Types
An engine can be put into a category according to two criteria: the form of energy it accepts in order to create motion, and the type of motion it outputs.
Heat engine
Combustion engine
Combustion engines are driven by the heat of a combustion process.
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel (generally, fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine the expansion of the high temperature and high pressure gases, which are produced by the combustion, directly applies force to components of the engine, such as the or or a nozzle, and by moving it over a distance, generates mechanical work.
External combustion engine
An external combustion engine (EC engine) is a heat engine where an internal working fluid is heated by combustion of an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine produces motion and usable Mechanical work.
"Combustion" refers to burning fuel with an oxidizer, to supply the heat. Engines of similar (or even identical) configuration and operation may use a supply of heat from other sources such as nuclear, solar, geothermal or exothermic reactions not involving combustion; but are not then strictly classed as external combustion engines, but as external thermal engines.
The working fluid can be a gas as in a Stirling engine, or steam as in a steam engine or an organic liquid such as n-pentane in an Organic Rankine cycle. The fluid can be of any composition; gas is by far the most common, although even single-phase liquid is sometimes used. In the case of the steam engine, the fluid changes phases between liquid and gas.
Air-breathing combustion engines
Air-breathing combustion engines are combustion engines that use the oxygen in atmospheric air to oxidise ('burn') the fuel, rather than carrying an oxidiser, as in a rocket. Theoretically, this should result in a better specific impulse than for rocket engines.
A continuous stream of air flows through the air-breathing engine. This air is compressed, mixed with fuel, ignited and expelled as the exhaust gas. In , the majority of the combustion energy (heat) exits the engine as exhaust gas, which provides thrust directly.
- Examples
Typical air-breathing engines include:
Environmental effects
The operation of engines typically has a negative impact upon air quality and ambient noise pollution. 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. Though a few limited-production battery-powered electric vehicles have appeared, they have not proved competitive owing to costs and operating characteristics. In the 21st century the diesel engine has been increasing in popularity with automobile owners. However, the gasoline engine and the Diesel engine, with their new emission-control devices to improve emission performance, have not yet been significantly challenged. A number of manufacturers have introduced hybrid engines, mainly involving a small gasoline engine coupled with an electric motor and with a large battery bank, these are starting to become a popular option because of their environment awareness.
Air quality
Exhaust gas from a spark ignition engine consists of the following: nitrogen 70 to 75% (by volume), water vapor 10 to 12%, carbon dioxide 10 to 13.5%, hydrogen 0.5 to 2%, oxygen 0.2 to 2%, carbon monoxide: 0.1 to 6%, unburnt hydrocarbons and partial oxidation products (e.g. ) 0.5 to 1%, nitrogen monoxide 0.01 to 0.4%, nitrous oxide <100 ppm, sulfur dioxide 15 to 60 ppm, traces of other compounds such as fuel additives and lubricants, also halogen and metallic compounds, and other particles.[Paul Degobert, Society of Automotive Engineers (1995), Automobiles and Pollution] Carbon monoxide is highly toxic, and can cause carbon monoxide poisoning, so it is important to avoid any build-up of the gas in a confined space. Catalytic converters can reduce toxic emissions, but not eliminate them. Also, resulting greenhouse gas emissions, chiefly carbon dioxide, from the widespread use of engines in the modern industrialized world is contributing to the global greenhouse effect – a primary concern regarding global warming.
Non-combusting heat engines
Some engines convert heat from noncombustive processes into mechanical work, for example a nuclear power plant uses the heat from the nuclear reaction to produce steam and drive a steam engine, or a gas turbine in a rocket engine may be driven by decomposing hydrogen peroxide. Apart from the different energy source, the engine is often engineered much the same as an internal or external combustion engine.
Another group of noncombustive engines includes thermoacoustic heat engines (sometimes called "TA engines") which are thermoacoustic devices that use high-amplitude sound waves to pump heat from one place to another, or conversely use a heat difference to induce high-amplitude sound waves. In general, thermoacoustic engines can be divided into standing wave and travelling wave devices.
Stirling engines can be another form of non-combustive heat engine. They use the Stirling thermodynamic cycle to convert heat into work. An example is the alpha type Stirling engine, whereby gas flows, via a recuperator, between a hot cylinder and a cold cylinder, which are attached to reciprocating pistons 90° out of phase. The gas receives heat at the hot cylinder and expands, driving the piston that turns the crankshaft. After expanding and flowing through the recuperator, the gas rejects heat at the cold cylinder and the ensuing pressure drop leads to its compression by the other (displacement) piston, which forces it back to the hot cylinder.
Non-thermal chemically powered motor
Non-thermal motors usually are powered by a chemical reaction, but are not heat engines. Examples include:
Electric motor
An electric motor uses electrical energy to produce mechanical energy, usually through the interaction of magnetic fields and current-carrying conductors. The reverse process, producing electrical energy from mechanical energy, is accomplished by a generator or dynamo. used on vehicles often perform both tasks. Electric motors can be run as generators and vice versa, although this is not always practical.
Electric motors are ubiquitous, being found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances, power tools, and hard drive. They may be powered by direct current (for example a battery powered portable device or motor vehicle), or by alternating current from a central electrical distribution grid. The smallest motors may be found in electric wristwatches. Medium-size motors of highly standardized dimensions and characteristics provide convenient mechanical power for industrial uses. The very largest electric motors are used for propulsion of large ships, and for such purposes as pipeline compressors, with ratings in the thousands of kilowatts. Electric motors may be classified by the source of electric power, by their internal construction, and by their application.
The physical principle of production of mechanical force by the interactions of an electric current and a magnetic field was known as early as 1821. Electric motors of increasing efficiency were constructed throughout the 19th century, but commercial exploitation of electric motors on a large scale required efficient electrical generators and electrical distribution networks.
To reduce the electric energy consumption from motors and their associated , various regulatory authorities in many countries have introduced and implemented legislation to encourage the manufacture and use of higher efficiency electric motors. A well-designed motor can convert over 90% of its input energy into useful power for decades.
By convention, electric engine refers to a railroad electric locomotive, rather than an electric motor.
Physically powered motor
Some motors are powered by potential or kinetic energy, for example some , gravity plane and have used the energy from moving water or rocks, and some clocks have a weight that falls under gravity. Other forms of potential energy include compressed gases (such as ), springs () and elastic bands.
Historic military siege engines included large , , and (to some extent) were powered by potential energy.
Pneumatic motor
A pneumatic motor is a machine that converts potential energy in the form of compressed air into mechanical work. Pneumatic motors generally convert the compressed air to mechanical work through either linear or rotary motion. Linear motion can come from either a diaphragm or a piston actuator, while rotary motion is supplied by either a vane type air motor or piston air motor. Pneumatic motors have found widespread success in the hand-held tool industry and continual attempts are being made to expand their use to the transportation industry. However, pneumatic motors must overcome efficiency deficiencies before being seen as a viable option in the transportation industry.
Hydraulic motor
A hydraulic motor derives its power from a pressure liquid. This type of engine is used to move heavy loads and drive machinery.
Hybrid
Some motor units can have multiple sources of energy. For example, a plug-in hybrid electric vehicle's electric motor could source electricity from either a battery or from fossil fuels inputs via an internal combustion engine and a generator.
Performance
The following are used in the assessment of the performance of an engine.
Speed
Speed refers to crankshaft rotation in piston engines and the speed of compressor/turbine rotors and electric motor rotors. It is typically measured in revolutions per minute (rpm).
Thrust
Thrust is the force exerted on an airplane as a consequence of its propeller or jet engine accelerating the air passing through it. It is also the force exerted on a ship as a consequence of its propeller accelerating the water passing through it.
Torque
Torque is a turning moment on a shaft and is calculated by multiplying the force causing the moment by its distance from the shaft.
Power
Power is the measure of how fast work is done.
Efficiency
Efficiency is a proportion of useful energy output compared to total input.
Sound levels
Vehicle noise is predominantly from the engine at low vehicle speeds and from tires and the air flowing past the vehicle at higher speeds.
Engines by use
Particularly notable kinds of engines include:
See also
Citations
Sources
External links
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