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The purpose of a gasoline car engine is to convert
gasoline into motion so that your car can move. Currently the
easiest way to create motion from gasoline is to burn the
gasoline inside an engine. Therefore, a car engine is an
internal combustion engine -- combustion takes place
internally. Two things to note:
There are different kinds of internal combustion engines.
Diesel engines are one form and gas turbine engines are
another. See also the articles on HEMI engines, rotary engines
and two-stroke engines. Each has its own advantages and
disadvantages.
There is such a thing as an external combustion engine. A steam engine in
old-fashioned trains and steam boats is the best example of an
external combustion engine. The fuel (coal, wood, oil,
whatever) in a steam engine burns outside the engine to create
steam, and the steam creates motion inside the engine.
Internal combustion is a lot more efficient (takes less fuel
per mile) than external combustion, plus an internal
combustion engine is a lot smaller than an equivalent external
combustion engine. This explains why we don't see any cars
from Ford and GM using steam engines.
Almost all cars currently use what is called a four-stroke
combustion cycle to convert gasoline into motion. The
four-stroke approach is also known as the Otto cycle, in honor
of Nikolaus Otto, who invented it in 1867. They are:
Intake stroke
Compression stroke
Combustion stroke
Exhaust stroke
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