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An engine or motor is a
machine A machine is a physical system using Power (physics), power to apply Force, forces and control Motion, movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to na ...
designed to convert one or more forms of energy into mechanical energy. Available energy sources include
potential energy In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors. Common types of potential energy include the gravitational potentia ...
(e.g. energy of the Earth's
gravitational field In physics, a gravitational field is a model used to explain the influences that a massive body extends into the space around itself, producing a force on another massive body. Thus, a gravitational field is used to explain gravitational phenome ...
as exploited in
hydroelectric power generation Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined and ...
), heat energy (e.g. geothermal),
chemical energy Chemical energy is the energy of chemical substances that is released when they undergo a chemical reaction and transform into other substances. Some examples of storage media of chemical energy include batteries, Schmidt-Rohr, K. (2018). "How ...
, electric potential and nuclear energy (from
nuclear fission Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radio ...
or nuclear fusion). Many of these processes generate heat as an intermediate energy form, so heat engines have special importance. Some natural processes, such as atmospheric
convection cell In the field of fluid dynamics, a convection cell is the phenomenon that occurs when density differences exist within a body of liquid or gas. These density differences result in rising and/or falling currents, which are the key characteristics ...
s 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 A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but ...
causes rapid pressurisation of the gaseous combustion products in the combustion chamber, causing them to expand and drive a
piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...
, which turns a
crankshaft A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecting ...
. Unlike internal combustion engines, a reaction engine (such as a
jet engine A jet engine is a type of reaction engine discharging a fast-moving jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include rocket, Pump-jet, water jet, and hybrid propulsion, the term ...
) produces thrust by expelling reaction mass, in accordance with Newton's third law of motion. Apart from heat engines, electric motors convert electrical energy into
mechanical Mechanical may refer to: Machine * Machine (mechanical), a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement * Mechanical calculator, a device used to perform the basic operations of ...
motion, pneumatic motors use
compressed air Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and o ...
, and clockwork motors in wind-up toys use
elastic energy Elastic energy is the mechanical potential energy stored in the configuration of a material or physical system as it is subjected to elastic deformation by work performed upon it. Elastic energy occurs when objects are impermanently compressed, ...
. In biological systems,
molecular motor Molecular motors are natural (biological) or artificial molecular machines that are the essential agents of movement in living organisms. In general terms, a motor is a device that consumes energy in one form and converts it into motion or mecha ...
s, like
myosin Myosins () are a superfamily of motor proteins best known for their roles in muscle contraction and in a wide range of other motility processes in eukaryotes. They are ATP-dependent and responsible for actin-based motility. The first myosin ...
s in
muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
s, use
chemical energy Chemical energy is the energy of chemical substances that is released when they undergo a chemical reaction and transform into other substances. Some examples of storage media of chemical energy include batteries, Schmidt-Rohr, K. (2018). "How ...
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. rockets, deeply submerged
submarine A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
s) need to carry an additional fuel component called the oxidizer (although there exist super-oxidizers suitable for use in rockets, such as
fluorine Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reacti ...
, a more powerful oxidant than oxygen itself); or the application needs to obtain heat by non-chemical means, such as by means of nuclear reactions.


Emission/By products

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 , which is adverse even in small quantities. If a hydrocarbon (such as
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
or gasoline) is burnt as fuel, large quantities of are emitted, a potent
greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
. Hydrogen and oxygen from air can be reacted into water by a
fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...
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 –the root of the word . Pre-industrial weapons of war, such as
catapult A catapult is a ballistic device used to launch a projectile a great distance without the aid of gunpowder or other propellants – particularly various types of ancient and medieval siege engines. A catapult uses the sudden release of stored p ...
s, trebuchets and battering rams, were called '' siege engines'', and knowledge of how to construct them was often treated as a military secret. The word ''gin'', as in ''
cotton gin A cotton gin—meaning "cotton engine"—is a machine that quickly and easily separates cotton fibers from their seeds, enabling much greater productivity than manual cotton separation.. Reprinted by McGraw-Hill, New York and London, 1926 (); a ...
'', 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 In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...
(usually in the form of thrust). Devices converting heat energy into motion are commonly referred to simply as ''engines''. Examples of engines which exert a torque include the familiar automobile gasoline and diesel engines, as well as turboshafts. Examples of engines which produce thrust include turbofans and rockets. 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 steam rollers. The term '' motor'' 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. In some engineering jargons, the two words have different meanings, in which '' engine'' is a device that
burns Burns may refer to: * Burn, an injury (plural) People: * Burns (surname), includes list of people and characters Business: * Burns London, a British guitar maker Places: ;In the United States * Burns, Colorado, unincorporated community in Eagle ...
or otherwise consumes fuel, changing its chemical composition, and a motor is a device driven by electricity, air, or hydraulic pressure, which does not change the chemical composition of its energy source. However,
rocketry Rocketry may refer to: Science and technology * The design and construction of rockets ** The hobbyist or (semi-)professional use of model rockets * Aerospace engineering, also known as rocket science * Amateur rocketry, a hobby in which partici ...
uses the term rocket motor, even though they consume fuel. A heat engine may also serve as a '' prime mover''—a component that transforms the flow or changes in pressure of a
fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
into mechanical energy. 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

Simple machines, such as the club and oar (examples of the lever), are
prehistoric Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use of ...
. More complex engines using human power,
animal power A working animal is an animal, usually domesticated, that is kept by humans and trained to perform tasks instead of being slaughtered to harvest animal products. Some are used for their physical strength (e.g. oxen and draft horses) or for tr ...
, 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 The windlass is an apparatus for moving heavy weights. Typically, a windlass consists of a horizontal cylinder (barrel), which is rotated by the turn of a crank or belt. A winch is affixed to one or both ends, and a cable or rope is wound arou ...
or treadmill, and with ropes,
pulley A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and cable or belt. In the case of a pulley supported by a frame or shell that ...
s, and block and tackle arrangements; this power was transmitted usually with the forces multiplied and the speed reduced. These were used in
cranes Crane or cranes may refer to: Common meanings * Crane (bird), a large, long-necked bird * Crane (machine), industrial machinery for lifting ** Crane (rail), a crane suited for use on railroads People and fictional characters * Crane (surname), ...
and aboard ships in Ancient Greece, as well as in mines,
water pumps A pump is a device that moves fluids ( liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they ...
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 horses were used in mills, driving machines similar to those powered by humans in earlier times. According to
Strabo Strabo''Strabo'' (meaning "squinty", as in strabismus) was a term employed by the Romans for anyone whose eyes were distorted or deformed. The father of Pompey was called "Pompeius Strabo". A native of Sicily so clear-sighted that he could see ...
, a water-powered mill was built in Kaberia of the kingdom of Mithridates during the 1st century BC. Use of water wheels in mills spread throughout the Roman Empire over the next few centuries. Some were quite complex, with aqueducts, dams, and
sluice Sluice ( ) is a word for a channel controlled at its head by a movable gate which is called a sluice gate. A sluice gate is traditionally a wood or metal barrier sliding in grooves that are set in the sides of the waterway and can be considered ...
s 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 Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization ...
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 gears in mills and water-raising machines, and used dams as a source of water power to provide additional power to watermills and water-raising machines. In the
medieval Islamic world The Islamic Golden Age was a period of cultural, economic, and scientific flourishing in the history of Islam, traditionally dated from the 8th century to the 14th century. This period is traditionally understood to have begun during the reign ...
, such advances made it possible to
mechanize ''Mechanize'' is the seventh studio album by American heavy metal band Fear Factory. It is the only album to feature Gene Hoglan on drums and the first since 2001's '' Digimortal'' to include original guitarist and founding member Dino Cazares, ...
many industrial tasks previously carried out by manual labour. In 1206,
al-Jazari Badīʿ az-Zaman Abu l-ʿIzz ibn Ismāʿīl ibn ar-Razāz al-Jazarī (1136–1206, ar, بديع الزمان أَبُ اَلْعِزِ إبْنُ إسْماعِيلِ إبْنُ الرِّزاز الجزري, ) was a polymath: a scholar, ...
employed a
crank Crank may refer to: Mechanisms * Crank (mechanism), in mechanical engineering, a bent portion of an axle or shaft, or an arm keyed at right angles to the end of a shaft, by which motion is imparted to or received from it * Crankset, the compone ...
- conrod system for two of his water-raising machines. A rudimentary
steam turbine A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam turbin ...
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 1629. 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 An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
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 Fuel efficiency is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical potential energy contained in a carrier (fuel) into kinetic energy or work. Overall fuel efficiency may vary per device, wh ...
,
James Watt James Watt (; 30 January 1736 (19 January 1736 OS) – 25 August 1819) was a Scottish inventor, mechanical engineer, and chemist who improved on Thomas Newcomen's 1712 Newcomen steam engine with his Watt steam engine in 1776, which was fun ...
'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
steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the locomot ...
s and great expansion of railway transportation. As for internal combustion
piston engine A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common featu ...
s, 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. 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 more efficient Diesel engine is used for trucks and buses. However, in recent years, turbo Diesel engines have become increasingly popular, 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 engines because of their shape and lower profile. They were used in the Volkswagen Beetle, the Citroën 2CV, some Porsche and Subaru cars, many BMW and Honda motorcycles, and propeller
aircraft engine An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many ...
s.


Advancement

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 engine efficiencies. Similar changes have been applied to smaller diesel engines giving them almost the same power characteristics as gasoline 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, although they require special machining not available in most factories. 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
camshaft A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition systems ...
s 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 A W16 engine is a sixteen-cylinder piston engine with four banks of four cylinders in a W configuration. W16 engines are rarely produced, with the notable exception of the Volkswagen Group 8.0 WR16 engine, which has been used since 2005 in the ...
, 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 ''Emma Mærsk'' is the first container ship in the of eight owned by the A. P. Moller-Maersk Group. When launched in 2006, she was the largest container ship ever built, and in 2010 she and her seven sister ships were among the longest ...
'', 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 heat engines 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 A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels m ...
) 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 In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...
to components of the engine, such as the
piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...
s or turbine blades or a
nozzle A nozzle is a device designed to control the direction or characteristics of a fluid flow (specially to increase velocity) as it exits (or enters) an enclosed chamber or pipe. A nozzle is often a pipe or tube of varying cross sectional area, a ...
, 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 In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
is heated by combustion of an external source, through the engine wall or a heat exchanger. The
fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
then, by expanding and acting on the
mechanism Mechanism may refer to: *Mechanism (engineering), rigid bodies connected by joints in order to accomplish a desired force and/or motion transmission *Mechanism (biology), explaining how a feature is created *Mechanism (philosophy), a theory that a ...
of the engine produces motion and usable work. The fluid is then cooled, compressed and reused (closed cycle), or (less commonly) dumped, and cool fluid pulled in (open cycle air engine). " Combustion" refers to
burning Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...
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 Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization ...
as in a steam engine or an organic liquid such as n-pentane in an
Organic Rankine cycle In thermal engineering, the Organic Rankine Cycle (ORC) is a type of thermodynamic cycle. It is a variation of the Rankine cycle named for its use of an organic, high-molecular-mass fluid whose vaporization temperature is lower than that of wat ...
. The fluid can be of any composition; gas is by far the most common, although even single-phase
liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...
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 Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
('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 reaction engines, the majority of the combustion energy (heat) exits the engine as exhaust gas, which provides thrust directly. ;Examples Typical air-breathing engines include: * Reciprocating engine *
Steam engine A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be trans ...
* Gas turbine * Airbreathing jet engine * Turbo-propeller engine * Pulse detonation engine * Pulse jet * Ramjet * Scramjet * Liquid air cycle engine/ Reaction Engines SABRE.


Environmental effects

The operation of engines typically has a negative impact upon air quality and ambient sound levels. 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. aldehydes) 0.5 to 1%, nitrogen monoxide 0.01 to 0.4%, nitrous oxide <100 ppm,
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...
15 to 60 ppm, traces of other compounds such as fuel additives and lubricants, also halogen and metallic compounds, and other particles. 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 A Stirling engine is a heat engine that is operated by the cyclic compression and expansion of air or other gas (the ''working fluid'') between different temperatures, resulting in a net conversion of heat energy to mechanical work. More specif ...
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 A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecting ...
. 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: *
Molecular motor Molecular motors are natural (biological) or artificial molecular machines that are the essential agents of movement in living organisms. In general terms, a motor is a device that consumes energy in one form and converts it into motion or mecha ...
– motors found in living things *
Synthetic molecular motor Synthetic molecular motors are molecular machines capable of continuous directional rotation under an energy input. Although the term "molecular motor" has traditionally referred to a naturally occurring protein that induces motion (via protein ...
.


Electric motor

An ''electric motor'' uses
electrical energy Electrical energy is energy related to forces on electrically charged particles and the movement of electrically charged particles (often electrons in wires, but not always). This energy is supplied by the combination of electric current and electr ...
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 Generator may refer to: * Signal generator, electronic devices that generate repeating or non-repeating electronic signals * Electric generator, a device that converts mechanical energy to electrical energy. * Generator (circuit theory), an eleme ...
or dynamo. Traction motors 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 A power tool is a tool that is actuated by an additional power source and mechanism other than the solely manual labor used with hand tools. The most common types of power tools use electric motors. Internal combustion engines and compressed air ...
, and disk drives. They may be powered by direct current (for example a
battery Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...
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 Energy consumption is the amount of energy used. Biology In the body, energy consumption is part of energy homeostasis. It derived from food energy. Energy consumption in the body is a product of the basal metabolic rate and the physical activity ...
from motors and their associated
carbon footprint A carbon footprint is the total greenhouse gas (GHG) emissions caused by an individual, event, organization, service, place or product, expressed as carbon dioxide equivalent (CO2e). Greenhouse gases, including the carbon-containing gases carbo ...
s, 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. When the efficiency of a motor is raised by even a few percentage points, the savings, in
kilowatt hour A kilowatt-hour (unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common bil ...
s (and therefore in cost), are enormous. The electrical energy efficiency of a typical industrial
induction motor An induction motor or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding. An induction mot ...
can be improved by: 1) reducing the electrical losses in the
stator The stator is the stationary part of a rotary system, found in electric generators, electric motors, sirens, mud motors or biological rotors. Energy flows through a stator to or from the rotating component of the system. In an electric mot ...
windings (e.g., by increasing the cross-sectional area of the
conductor Conductor or conduction may refer to: Music * Conductor (music), a person who leads a musical ensemble, such as an orchestra. * ''Conductor'' (album), an album by indie rock band The Comas * Conduction, a type of structured free improvisation ...
, improving the winding technique, and using materials with higher electrical conductivities, such as copper), 2) reducing the electrical losses in the rotor coil or casting (e.g., by using materials with higher electrical conductivities, such as copper), 3) reducing magnetic losses by using better quality magnetic
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
, 4) improving the aerodynamics of motors to reduce mechanical windage losses, 5) improving bearings to reduce friction losses, and 6) minimizing manufacturing
tolerances Engineering tolerance is the permissible limit or limits of variation in: # a physical dimension; # a measured value or physical property of a material, manufacturing, manufactured object, system, or service; # other measured values (such as t ...
. ''For further discussion on this subject, see
Premium efficiency Premium efficiency, when used in reference to specific types of Electric Motors (with a rotating shaft), is a class of motor efficiency. As part of a concerted effort worldwide to reduce energy consumption, CO2 emissions and the impact of indust ...
.)'' 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 funiculars,
gravity plane A funicular (, , ) is a type of cable railway system that connects points along a railway track laid on a steep slope. The system is characterized by two counterbalanced carriages (also called cars or trains) permanently attached to opposite en ...
and ropeway conveyors 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 pneumatic motors), springs ( clockwork motors) and elastic bands. Historic military siege engines included large
catapult A catapult is a ballistic device used to launch a projectile a great distance without the aid of gunpowder or other propellants – particularly various types of ancient and medieval siege engines. A catapult uses the sudden release of stored p ...
s, trebuchets, and (to some extent) battering rams were powered by potential energy.


Pneumatic motor

A ''pneumatic motor'' is a machine that converts potential energy in the form of
compressed air Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and o ...
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 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 pressurized
liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...
. 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 A plug-in hybrid electric vehicle (PHEV) is a hybrid electric vehicle whose battery pack can be recharged by plugging a charging cable into an external electric power source, in addition to internally by its on-board internal combustion engine ...
'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 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 measure of how much fuel is wasted in producing power.


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. Electric motors are quieter than internal combustion engines. Thrust-producing engines, such as turbofans, turbojets and rockets emit the greatest amount of noise due to the way their thrust-producing, high-velocity exhaust streams interact with the surrounding stationary air. Noise reduction technology includes intake and exhaust system mufflers (silencers) on gasoline and diesel engines and noise attenuation liners in turbofan inlets.


Engines by use

Particularly notable kinds of engines include: *
Aircraft engine An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many ...
*
Automobile engine , there were a wide variety of propulsion systems available or potentially available for automobiles and other vehicles. Options included internal combustion engines fueled by petrol, diesel, propane, or natural gas; hybrid vehicles, plug-in hybri ...
* Model engine * Motorcycle engine * Marine propulsion engines such as Outboard motor * Non-road engine is the term used to define engines that are not used by vehicles on roadways. * Railway locomotive engine *
Spacecraft propulsion Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. In-space propulsion exclusively deals with propulsion systems used in the vacuum of space and should not be confused with space launch or atmospheric e ...
engines such as Rocket engine * Traction engine


See also

*
Aircraft engine An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many ...
* Automobile engine replacement * Electric motor * Engine cooling * Engine swap * Gasoline engine * HCCI engine *
Hesselman engine The Hesselman engine is a hybrid between a petrol engine and a Diesel engine. It was designed and introduced in 1925 by Sweden, Swedish engineer Jonas Hesselman (1877-1957). It represented the first use of direct Gasoline direct injection, gaso ...
* Hot bulb engine *
IRIS engine The IRIS Engine is a design for a new type of internal combustion engine. Its inventors say that engines constructed using this design can be smaller, lighter and significantly more efficient than traditional engines of comparable horsepower and d ...
*
Micromotor Micromotors are very small particles (measured in microns) that can move themselves. The term is often used interchangeably with "nanomotor," despite the implicit size difference. These micromotors actually propel themselves in a specific directio ...
**
Flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...
– biological motor used by some microorganisms ** Nanomotor **
Molecular motor Molecular motors are natural (biological) or artificial molecular machines that are the essential agents of movement in living organisms. In general terms, a motor is a device that consumes energy in one form and converts it into motion or mecha ...
**
Synthetic molecular motor Synthetic molecular motors are molecular machines capable of continuous directional rotation under an energy input. Although the term "molecular motor" has traditionally referred to a naturally occurring protein that induces motion (via protein ...
** Adiabatic quantum motor * Multifuel * Reaction engine *
Solid-state engine A Johnson thermoelectric energy converter or JTEC is a type of solid-state heat engine that uses the electrochemical oxidation and reduction of hydrogen in a two-cell, thermal cycle that approximates the Ericsson cycle. It is under investigation ...
* Timeline of heat engine technology * Timeline of motor and engine technology


References


Citations


Sources

* J.G. Landels, ''Engineering in the Ancient World'',


External links

*
Detailed Engine Animations



Animated illustrations of various engines

5 Ways to Redesign the Internal Combustion Engine

Article on Small SI Engines.

Article on Compact Diesel Engines.


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