An engine or motor is a machine designed to convert one form of energy
into mechanical energy.
Heat engines burn a fuel to create heat
which is then used to do work. Electric motors convert electrical
energy into mechanical motion; pneumatic motors use compressed air;
and clockwork motors in wind-up toys use elastic energy. In biological
systems, molecular motors, like myosins in muscles, use chemical
energy to create forces and eventually motion.
2.3 Industrial Revolution
2.4.1 Horizontally opposed pistons
2.4.3 Increasing power
Internal combustion engine
External combustion engine
188.8.131.52 Air-breathing combustion engines
184.108.40.206 Environmental effects
220.127.116.11 Air quality
3.1.2 Non-combusting heat engines
3.2 Non-thermal chemically powered motor
3.3 Electric motor
3.4 Physically powered motor
3.4.1 Pneumatic motor
3.4.2 Hydraulic motor
4.6 Sound levels
5 Engines by use
6 See also
9 External links
The word engine derives from
Old French engin, from the Latin
ingenium–the root of the word ingenious. Pre-industrial weapons of
war, such as catapults, 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, 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. 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 moto which
means to set in motion, or maintain motion. Thus a motor is a device
that imparts motion.
Motor and engine later came to be used largely interchangeably in
casual discourse. However, technically, the two words have different
meanings. An engine is a device that burns or otherwise consumes fuel,
changing its chemical composition, whereas 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
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 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).
Simple machines, such as the club and oar (examples of the lever), are
prehistoric. More complex 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 usually with the
forces multiplied and the speed reduced. These were used in cranes and
aboard ships in Ancient Greece, as well as in mines, water pumps and
siege engines in Ancient Rome. The writers of those times, including
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, 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 sluices
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 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, such advances made it possible to mechanize
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 in 1551 and by Giovanni Branca in
In the 13th century, the solid rocket motor was invented in China.
Driven by gunpowder, this, the 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.
Boulton & Watt engine of 1788
Watt steam engine
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
steam locomotives and great expansion of railway transportation.
As for internal combustion piston engines, 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
Eugenio Barsanti and
Felice Matteucci invented and patented an
engine using the free-piston principle that was possibly the first
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.
The first commercially successful automobile, created by Karl Benz,
added to the interest in light and powerful engines. The lightweight
petrol internal combustion engine, operating on a four-stroke Otto
cycle, has been the most successful for light automobiles, while the
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
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 engines.
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
petrol engines. This is especially evident with the popularity of
smaller diesel engine propelled cars in Europe. Larger diesel engines
are still often used in trucks and heavy machinery, although they
require special machining not available in most factories. Diesel
engines produce lower hydrocarbon and CO2 emissions, but greater
NOx pollution, than gasoline engines. Diesel
engines are also 40% more fuel efficient than comparable gasoline
In the first half of the 20th century, a trend of increasing engine
power occurred, particularly in the American models.[clarification
needed] 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 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.
The design principles favoured in Europe, because of economic and
other restraints such as smaller and twistier roads, leant toward
smaller cars and corresponding to the design principles that
concentrated on increasing the combustion efficiency of smaller
engines. This produced more economical engines with earlier
four-cylinder designs rated at 40 horsepower (30 kW) and
six-cylinder designs rated as low as 80 horsepower (60 kW),
compared with the large volume V-8 American engines with power ratings
in the range from 250 to 350 hp, some even over 400 hp (190
to 260 kW).[clarification needed]
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 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 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. This engine weighs 2,300 tons, and when
running at 102 RPM produces 109,000 bhp (80,080 kW)
consuming some 13.7 tons of fuel each hour.
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.
Main article: heat engine
Combustion engines are heat engines driven by the heat of a combustion
Internal combustion engine
Internal combustion engine
Animation showing the four stages of the four-stroke combustion engine
Fuel is burnt)
Emission (Exhaust out)
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 pistons or turbine blades or a nozzle, and by
moving it over a distance, generates useful mechanical
External combustion engine
Main article: 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 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 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
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
Typical air-breathing engines include:
airbreathing jet engine
Pulse detonation engine
Liquid air cycle engine/Reaction Engines SABRE.
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, but these too have yet to make much of an inroad into
the market shares of gasoline and Diesel engines.
Exhaust 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 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 completely 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
Main article: heat engine
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 which
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.
Non-thermal chemically powered motor
Non-thermal motors usually are powered by a chemical reaction, but are
not heat engines. Examples include:
Molecular motor - motors found in living things
Synthetic molecular motor.
Main articles: electric motor and electric vehicle
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. 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, and disk drives.
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 carbon footprints, 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 hours (and
therefore in cost), are enormous. The electrical energy efficiency of
a typical industrial induction motor can be improved by: 1) reducing
the electrical losses in the stator windings (e.g., by increasing the
cross-sectional area of the conductor, 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, 4) improving the aerodynamics of motors
to reduce mechanical windage losses, 5) improving bearings to reduce
friction losses, and 6) minimizing manufacturing tolerances. For
further discussion on this subject, see Premium efficiency.)
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 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 catapults, trebuchets,
and (to some extent) battering rams were powered by potential energy.
Main article: 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 though 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
Main article: Hydraulic motor
A hydraulic motor is one that derives its power from a pressurized
fluid. This type of engine can be used to move heavy loads or produce
Given that the majority of engines for which a speed is defined
rotate, engine speed is measured in revolutions per minute (RPM).
Engines may be classified as low-speed, medium-speed or high-speed,
but these terms are always relative and depend on the type of engine
being described. Generally, diesel engines operate at lower speeds
(~1500-2000 RPM for an automotive diesel) compared to gasoline engines
(~2200-3400 RPM for an automotive gasoline engine). Electric motors
and turboshafts are capable of very high speeds (~10,000 RPM or more),
generally constrained only by the bulk modulus and intended service
life of the parts constituting the rotor, which must bear the brunt of
the centrifugal force.
Thrust is the force arising from the interaction between two masses
which exert equal but opposite forces on each other due to their
speed. The force F can be measured either in newtons (N, SI units) or
in pounds-thrust (lbf, imperial units).
Torque is the force being exerted on a theoretical lever connected to
the output shaft of an engine. This is expressed by the formula:
displaystyle tau = mathbf r times mathbf F =rFsin( mathbf
r , mathbf F )
where r is the length of the lever, F is the force applied on it, and
r×F is the vector cross product.
Torque is measured typically either
in newton-metres (N·m, SI units) or in foot-pounds (ft·lb, imperial
Power is the amount of work being done, or energy being produced, per
unit of time. This is expressed by the formula:
displaystyle P= frac mathrm d W mathrm d t
With a quick demonstration, it can be shown that:
displaystyle P= mathbf F cdot mathbf v
This formula with linear forces and speeds can be used equally well
for both engines outputting thrust and engines exerting torque.
When considering propulsive engines, typically only the raw force of
the core mass flow is considered, leading to such engines having their
'power' rated in any of the units discussed above for forces.
If the engine in question outputs its power on a shaft, then:
displaystyle P=tau omega
This is the reason why any engine outputting its power on a rotating
shaft is usually quoted, along with its rated power, the rotational
speed at which that rated power is developed.
Depending on the type of engine employed, different rates of
efficiency are attained.
For heat engines, efficiency cannot be greater than the Carnot
In the case of sound levels, engine operation is of greatest impact
with respect to mobile sources such as automobiles and trucks. Engine
noise is a particularly large component of mobile source noise for
vehicles operating at lower speeds, where aerodynamic and tire noise
is less significant. Generally speaking, petrol (gasoline) and
diesel engines emit less noise than turboshafts of equivalent power
output; electric motors very often emit less noise than their fossil
fuel-powered equivalents. Thrust-outputting engines, such as
turbofans, turbojets and rockets emit the greatest amount of noise
because their method of producing thrust is directly related to the
production of sound. Various methods have been devised to reduce
noise. Petrol and diesel engines are fitted with mufflers (silencers);
newer turbofans often have outsized fans (the so-called high-bypass
technology) in order to reduce the proportion of noisy, hot exhaust
from the integrated turboshaft in the exhaust stream, and hushkits
exist for older, low-bypass turbofans. No known methods exist for
reducing the noise output of rockets without a corresponding reduction
Engines by use
Particularly notable kinds of engines include:
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 engines such as
Timeline of motor and engine technology
Timeline of heat engine technology
Hot bulb engine
Automobile engine replacement
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Wikimedia Commons has media related to Engines.
Look up engine in Wiktionary, the free dictionary.
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U.S. Patent 194,047
Video from inside a four-stroke engine cylinder.
Engine - Animation
Animated illustrations of various engines
5 Ways to Redesign the Internal
Timeline of heat engine technology
Without phase change
(hot air engines)
Brayton / Joule
Stirling (pseudo / adiabatic)
With phase change
Rankine (Organic Rankine)
Brayton / Joule
Homogeneous charge compression ignition
Mixed / Dual