10-11-2012, 04:50 PM
Internal combustion engine
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The internal combustion engine is an engine in which the combustion of a fuel (normally a 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 produced by combustion apply direct force to some component of
the engine. This force is applied typically to pistons, turbine blades, or a nozzle. This force moves the
component over a distance, transforming chemical energy into useful mechanical energy. The first internal
combustion engine was created by Étienne Lenoir.[1][2][3][4]
The term internal combustion engine usually refers to an engine in which combustion is intermittent, such as
the more familiar four-strokeand two-stroke piston engines, along with variants, such as the six-stroke piston
engine and the Wankel rotary engine. A second class of internal combustion engines use continuous
combustion: gas turbines, jet engines and most rocket engines, each of which are internal combustion engines
on the same principle as previously described.
Nomenclature
At one time, the word, "Engine" (from Latin, via Old French, ingenium, "ability") meant any piece ofmachinery—
a sense that persists in expressions such as siege engine. A "motor" (from Latinmotor, "mover") is any machine
that produces mechanical power. Traditionally, electric motors are not referred to as "Engines"; however,
combustion engines are often referred to as "motors." (Anelectric engine refers to a locomotive operated by
electricity.)
Types of internal combustion engine
Engines can be classified in many different ways: By the engine cycle used, the layout of the engine, source of
energy, the use of the engine, or by the cooling system employed.
Combustion
All internal combustion engines depend on the combustion of a chemical fuel, typically with oxygen from the
air (though it is possible to inject nitrous oxide in order to do more of the same thing and gain a power boost).
The combustion process typically results in the production of a great quantity of heat, as well as the production
of steam and carbon dioxide and other chemicals at very high temperature; the temperature reached is
determined by the chemical make up of the fuel and oxidisers (see stoichiometry), as well as by the
compression and other factors.
The most common modern fuels are made up of hydrocarbons and are derived mostly from fossil
fuels (petroleum). Fossil fuels include diesel fuel, gasoline and petroleum gas, and the rarer use of propane.
Except for the fuel delivery components, most internal combustion engines that are designed for gasoline use
can run on natural gas or liquefied petroleum gases without major modifications. Large diesels can run with air
mixed with gases and a pilot diesel fuel ignition injection. Liquid and gaseous biofuels, such
as ethanol and biodiesel (a form of diesel fuel that is produced from crops that yield triglycerides such
as soybean oil), can also be used. Engines with appropriate modifications can also run on hydrogen gas, wood
gas, or charcoal gas, as well as from so-called producer gas made from other convenient biomass. Recently,
experiments have been made with using powdered solid fuels, such as the magnesium injection cycle.
Internal combustion engines require ignition of the mixture, either by spark ignition (SI) or compression
ignition (CI). Before the invention of reliable electrical methods, hot tube and flame methods were used.
Experimental engines with laser ignition have been built.[5]
Gasoline Ignition Process
Gasoline engine ignition systems generally rely on a combination of a lead–acid battery and an induction coil to
provide a high-voltage electric spark to ignite the air-fuel mix in the engine's cylinders. This battery is recharged
during operation using an electricity-generating device such as an alternator or generator driven by the engine.
Gasoline engines take in a mixture of air and gasoline and compress it to not more than 12.8 bar (1.28 MPa),
then use a spark plug to ignite the mixture when it is compressed by the piston head in each cylinder.
Diesel Ignition Process
Diesel engines and HCCI (Homogeneous charge compression ignition) engines, rely solely on heat and
pressure created by the engine in its compression process for ignition. The compression level that occurs is
usually twice or more than a gasoline engine.