An
engine is a
machine that
produces mechanical force and motion from another form of energy
(e.g. a
fuel source, compressed air, or
electricity). It is also referred to
as a
prime mover. An
automobile makes use of several motors to start
the car and drive the car's various pumps – but the
power plant that propels the car is
called an engine. The term
motor was originally
used to distinguish the new
internal combustion
engine-powered vehicles from earlier vehicles powered by a
steam engine, such as the
steam roller and
motor
roller; but can be used to refer to any engine that creates
motion.
Historic
military siege engines included large
catapults,
trebuchets, and
battering rams.
Usage of the term "Engine"
Originally an engine was a mechanical device that converted force
into motion. Military devices such as
catapults are referred to as
siege engines. The term "gin" as in
cotton gin is recognised as a short form
of the
Old French word
engin, in turn from the
Latin ingenium, related to
ingenious. Most devices used in the
industrial revolution were
referred to as an engine, and this is where the
steam engine gained its name.
In more modern usage, the term is used to describe devices that
perform
mechanical work, follow-ons
to the original steam engine. In most cases the work is supplied by
exerting a
torque or linear force, which is
used to operate other machinery which can generate
electricity,
pump water, or
compress gas. In the context of
propulsion systems, an air-breathing engine is one that uses
atmospheric air to oxidise the
fuel carried
rather than supplying an independent oxidizer, as in a
rocket.
Classical utilization of engines
Antiquity
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
mine,
water 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 far more ancient. By the 1st century AD, various breeds of
cattle and
horses were
used in
mill, 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. In a poem by
Ausonius in the 4th century, 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, but it is not known if any of these
were put to practical use.
Medieval
During the
Muslim
Agricultural Revolution from the 9th to 13th centuries,
Muslim engineers
developed numerous innovative
industrial
uses of
hydropower, early industrial uses
of
tidal power,
wind power, and
fossil
fuels such as
petroleum, together with
the earliest large
factory complexes
(
tiraz in Arabic). The industrial uses of
watermills in the Islamic world date back to the
7th century, whereas horizontal-
wheeled
and vertical-wheeled water mills were both in widespread use since
at least the 9th century. A variety of industrial mills were
invented in the Islamic world, including
fulling mills,
gristmills,
hullers,
paper
mills,
stamp mills,
steel mills,
sugar
refineries, and
windmills.
By the 11th century,
every province throughout the Islamic world had these industrial
mills in operation, from the Middle East
and Central Asia to al-Andalus
and North
Africa.
Muslim engineers also invented
water
turbines, employed
gears in mills and
water-raising
machines, and pioneered the
use of
dams as a source of water power to
provide additional power to watermills and water-raising machines.
Such advances made it possible for many industrial tasks that were
previously driven by
manual labour to
be
mechanized and driven by
machinery to some extent in the
medieval Islamic world.
In 1206,
al-Jazari employed a
crank-connecting rod system for two of his water-raising machines.
A similar steam turbine later appeared in Europe a century later,
which eventually led to the
steam
engine and Industrial Revolution in 18th century Europe.
Heat engine
Combustion engine
Combustion engines are
heat engines
driven by the heat of a
combustion
process.
Internal combustion engine
English
inventor Sir
Samuel Morland allegedly used
gunpowder to drive water pumps in the 17th
century. For more conventional, reciprocating internal combustion engines, the
fundamental theory for two-stroke
engines was established by Sadi Carnot, France
, 1824,
whilst the American Samuel Morey
received a patent on April 1, 1826.
Sir Dugald Clark (1854 – 1932) designed the first two-stroke engine
in 1878 and patented it in England in 1881. Automotive production
has used a range of energy-conversion systems. These include
electric,
steam,
solar,
turbine, rotary,
and piston-type internal combustion engines.
Engine cycles
The petrol internal combustion engine, operating on a four-stroke
Otto cycle, has been the most successful for
automobiles, while diesel engines are used for
trucks and buses.
Karl Benz was one of the
leaders in the development of new engines. In 1878 he began to work
on new designs. He concentrated his efforts on creating a reliable
gas two-stroke engine that was more powerful, based on
Nikolaus Otto's design of the four-stroke
engine. Karl Benz showed his real genius, however, through his
successive inventions registered while designing what would become
the production standard for his two-stroke engine.Benz was granted
a patent for it in 1879.
Horizontally-opposed pistons
In 1896, Karl Benz was granted a patent for his design of the first
engine with horizontally-opposed pistons. Many BMW motorcycles use
this engine type. His design created an engine in which the
corresponding pistons move in horizontal cylinders and reach top
dead center simultaneously, thus automatically balancing each other
with respect to their individual momentums. Engines of this design
are often referred to as flat engines because of their shape and
lower profile. They must have an even number of cylinders and six,
four or two cylinder flat engines have all been common. The most
well-known engine of this type is probably the Volkswagen Beetle
engine. Engines of this type continue to be a common design
principle for high performance
aero
engines (for propellor driven aircraft) and, engines used by
automobile producers such as Porsche and Subaru.
Advancement
Mercedes V6 engine in 1996
[[Image:Model Engine Luc Viatour.jpg|thumb|right|School model
ofengine]][[Image:Model Engine B Luc Viatour.jpg|thumb|right|School
modelof an engine]]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. They do not burn as clean as
gasoline engines, however they have far more
torque. The internal combustion engine was originally
selected for the automobile due to its flexibility over a wide
range of speeds. Also, the power developed for a given weight
engine was reasonable; it could be produced by economical
mass-production methods; and it used a readily available,
moderately priced fuel - petrol.
Increasing power
The first half of the twentieth century saw a trend to increasing
engine power, particularly in the American models. Design changes
incorporated all known methods of raising engine capacity,
including increasing the pressure in the cylinders to improve
efficiency, increasing the size of the engine, and increasing the
speed at which power is generated. The higher forces and pressures
created by these changes created engine vibration and size problems
that led to stiffer, more compact engines with V and opposed
cylinder layouts replacing longer straight-line arrangements.
Combustion efficiency
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 to350 hp (190 to
260 kW).
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, piston displacement, and cylinder bores. Four
cylinders and power ratings from 19 to 120 hp (14 to
90 kW) were followed in a majority of the models. Several
three-cylinder, two-stroke-cycle models were built while most
engines had straight or in-line cylinders. There were several
V-type models and horizontally opposed two- and four-cylinder makes
too. Overhead camshafts were frequently employed. The smaller
engines were commonly air-cooled and located at the rear of the
vehicle; compression ratios were relatively low. The 1970s and '80s
saw an increased interest in improved fuel economy which brought in
a return to smaller V-6 and four-cylinder layouts, with as many as
five valves per cylinder to improve efficiency. The
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.
The largest internal combustion engine ever built is the
Wärtsilä-Sulzer RTA96-C, a
14-cylinder, 2-stroke turbocharged diesel engine that was designed
to power the
Emma Maersk, the largest
container ship in the world. This engine weighs 2300 tons, and when
running at 102 RPM produces 109,000 bhp (80,080 kW)
consuming some 13.7 tons of fuel each hour.
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
engineor 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
phase
between liquid and gas.
Air-breathing combustion engines
Air-breathing engines are
combustion engines that use the
oxygen in
atmospheric air to
oxidise ('burn') the fuel
carried, rather than carrying an
oxidiser,
as in a
rocket. Theoretically, this should
result in a better
specific impulse
than for rocket engines.
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. Thrust produced by a typical air-breathing engine is about
eight times greater than its weight. The maximum velocity of
Air-breathing engines is
limited to 1–3 km/s due to extreme temperature and
dissociation of the exhaust gas; however, the maximum velocity of a
hydrogen-breathing engine of the same design is about 4 times
higher.
Examples
Typical air-breathing engines include:
- duct jet engine
- Turbo-propeller engine
Environmental effects
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. Although a few
limited-production battery-powered electric vehicles have appeared,
they have not proved to be competitive owing to costs and operating
characteristics. In the twenty-first century the diesel engine has
been increasing in popularity with automobile owners. However, the
gasoline engine, with its new emission-control devices to improve
emission performance, has not yet been significantly
challenged.
Air quality
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,
widespread use of engines in the modern industrialized world has
led to an escalation in the
Greenhouse
Effect. This has led to
Global
Warming, and scientists the world over have recognized
Carbon Dioxide as a
pollutant to the
atmosphere.
Non combustive heat engines
Some engines convert heat from non combustive 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.
Non thermal chemically powered engine
Non thermal engines usually are powered by a chemical reaction, but
are not heat engines.
Muscles
Muscle (from
Latin
musculus, diminutive of
mus "mouse") is the
contractile tissue of animals and is derived from the
mesodermal layer of embryonic germ cells.
Muscle cells contain contractile filaments that move past each
other and change the shape of the cell.
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.
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
kilowatt. 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.
By convention,
electric engine refers to a railroad
electric locomotive, rather than
an electric motor.
Physically powered engine
Some engines are powered by potential energy, for example some
clocks have a weight that falls under gravity. Other forms of
potential energy include compressed gases (such as
pneumatic motors) and springs.
Historic
military siege engines included large
catapults,
trebuchets, and
(to some extent)
battering rams were
powered by potential energy.
Sound levels
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 tyre noise is less
significant. Petrol and diesel engines are fitted with
mufflers (silencers) to reduce noise.
See also
References
- J. G. Landels, Engineering in the Ancient World, ISBN
0-520-04127-5
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