An engine is a machine that can convert some form of energy
(obtained from a fuel) into useful mechanical power or motion. If the
engine produces kinetic energy (energy of motion) from a fuel source, it
is called a prime mover; if it produces kinetic energy from a
preprocessed "fuel" (such as electricity, a flow of hydraulic fluid, or
compressed air), it is called a motor. Thus, the main device that powers
an automobile is called an engine. A locomotive is also loosely
referred to as an engine.
Usage of the term "engine"
Originally, an engine was a mechanical device that converted force into
motion. Military devices such as catapults, trebuchets, and battering
rams were referred to as "siege engines." The term "gin" as in cotton
gin is recognized 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
engines, and this is where the steam engine gained its name.
In more modern usage, the term "engine" 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, which is used to
operate other machinery, generate electricity, or pump water or
compressed gas. In the context of propulsion systems, an air-breathing
engine is one that uses atmospheric air to oxidize the fuel carried,
rather than carrying an oxidizer, as in a rocket.
The term is used in computer science in "search engine," "3-D graphics
game engine," "rendering engine," and "text-to-speech engine." Although
these "engines" are not mechanical and perform no mechanical action,
they generate useful output.
Engines in antiquity
Simple machines, such as 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 connected to the use of simple engines, such as the
capstan, windlass, or treadmill, and with ropes, pulleys, and block and
tackle arrangements, this power was transmitted and multiplied. These
were used in cranes and aboard ships in Ancient Greece, and in mines,
water pumps 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 first century C.E., various breeds of cattle and horses were used
for mills, with machines similar to those powered by humans in earlier
times.
According to Strabo, a water-powered mill was built in Kaberia in the
kingdom of Mithridates in the first century B.C.E. 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, and systems of gears, or toothed-wheels made of
wood with metal, used to regulate the speed of rotation. In a fourth
century poem, Ausonius mentions a stone-cutting saw powered by water.
Hero of Alexandria demonstrated both wind and steam-powered machines in
the first century, although it is not known if these were put to any
use.
Medieval engines
During the Muslim Agricultural Revolution from the seventh to thirteenth
centuries, Muslim engineers developed numerous innovative industrial
uses of hydropower, early industrial uses of tidal power, wind power,
and fossil fuels (such as petroleum), and the earliest large factory
complexes (tiraz in Arabic). The industrial uses of watermills in
the Islamic world date back to the seventh century, and both
horizontal-wheeled and vertical-wheeled water mills were in widespread
use since at least the ninth century.
A variety of industrial mills were invented in the Islamic world,
including fulling mills, gristmills, hullers, paper mills, sawmills,
ship mills, stamp mills, steel mills, sugar refineries, tide mills, and
windmills. By the eleventh 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 crankshafts and 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 labor in ancient
times to be mechanized and driven by machinery to some extent in the
medieval Islamic world. The transfer of these technologies to medieval
Europe later laid the foundations for the Industrial Revolution in
eighteenth-century Europe.
In 1206, al-Jazari invented the crankshaft and connecting rod, and he
employed them in a crank-connecting rod system for two of his
water-raising machines. His invention of the crankshaft is considered
one of the most important mechanical inventions after the wheel, as it
transforms continuous rotary motion into a linear reciprocating motion,
and is central to modern machinery such as the steam engine and the
internal combustion engine. In 1551, Taqi al-Din invented a practical
steam turbine as a prime mover for rotating a spit. A similar steam
turbine later appeared in Europe a century later, which eventually led
to the steam engine and Industrial Revolution in Europe.
Modern engines
English inventor Sir Samuel Morland allegedly used gunpowder to drive
water pumps in the seventeenth century. For more conventional,
reciprocating internal combustion engines, the fundamental theory for
two-stroke engines was established by Sadi Carnot in France in 1824, and
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. The gasoline (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 Nicolaus 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.
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
propeller-driven aircraft) and engines used by automobile producers such
as Porsche and Subaru.
Continued 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 efficiencies available.
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 cleanly as gasoline
engines, but 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 gasoline, a
readily available fuel that was moderately priced.
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.
The first half of the twentieth century saw a trend to increasing engine
power, particularly in American models. Design changes incorporated all
known methods of raising engine capacity, including increasing the
pressure in the cylinders to improve efficiency, increasing the size of
the engine, and increasing the speed at which power is generated. The
higher forces and pressures created by these changes created engine
vibration and size problems that led to stiffer, more compact engines
with V and opposed cylinder layouts replacing longer straight-line
arrangements. In passenger cars, V-8 layouts were adopted for all piston
displacements greater than 250 cubic inches (4 liters).
In Europe, because of economic and other restraints (such as narrower
and twisty roads), the design principles leaned toward smaller cars with
the higher 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 ranging from 250 to 350 hp (190 to 260 kW).
Earlier automobile engine development produced a much larger range of
engines than those 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 1980s saw an increased interest in improved fuel economy,
leading to 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. Thus
the Veyron has the largest number of cylinders to appear in a production
car.
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 metric tons, and when running at 102 RPM
produces 109,000 bhp (80,080 kW) consuming some 13.7 metric tons of fuel
per hour.
Air-breathing engines
Air-breathing engines use atmospheric air to oxidize the fuel carried,
rather than carrying an oxidizer, as a rocket would. Theoretically, this
should provide a better specific impulse than rocket engines.
Air-breathing engines include:
- Internal combustion engine
- Jet engine
- Ramjet
- Scramjet
- IRIS engine
- Pulse detonation engine
- Pulse jet
- Liquid air cycle engine/SABRE
Environmental effects
Operation of engines typically has a negative impact upon air quality
and ambient sound levels. Although, exhaust contains mostly harmless
nitrogen, water vapor, and carbon dioxide; unwanted gases such as carbon
monoxide, hydrocarbons, and nitrogen oxides make up only a small part
of engine exhaust. 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.