Internal Combustion Engines

Powerful Essays
Internal Combustion Engines

An internal-combustion engine is a heat engine that burns fuel and air

inside a combustion chamber located within the engine proper. Simply stated, a

heat engine is an engine that converts heat energy to mechanical energy. The

internal- combustion engine should be distinguished from the external-

combustion engine, for example, the steam engine and the Stirling engine, which

burns fuel outside the prime mover, that is, the device that actually produces

mechanical motion. Both basic types produce hot, expanding gases, which may then

be employed to move pistons, turn turbine rotors, or cause locomotion through

the reaction principle as they escape through the nozzle.

Most people are familiar with the internal-combustion reciprocating engine,

which is used to power most automobiles, boats, lawn mowers, and home generators.

Based on the means of ignition, two types of internal-combustion reciprocating

engines can be distinguished: spark-ignition engines and compression-ignition

engines. In the former, a spark ignites a combustible mixture of air and fuel;

in the latter, high compression raises the temperature of the air in the chamber

and ignites the injected fuel without a spark. The diesel engine is a

compression-ignition engine. This article emphasizes the spark-ignition engine.

The invention and early development of internal-combustion engines are

usually credited to three Germans. Nikolaus Otto patented and built (1876) the

first such engine; Karl Benz built the first automobile to be powered by such an

engine (1885); and Gottlieb Daimler designed the first high-speed internal-

combustion engine (1885) and carburetor. Rudolf Diesel invented a successful

compression-ignition engine (the diesel engine) in 1892.

The operation of the internal-combustion reciprocating engine employs

either a four-stroke cycle or a two-stroke cycle. A stroke is one continuous

movement of the piston within the cylinder.

In the four-stroke cycle, also known as the Otto cycle, the downward

movement of a piston located within a cylinder creates a partial vacuum. Valves

located inside the combustion chamber are controlled by the motion of a camshaft

connected to the crankshaft. The four strokes are called, in order of sequence,

intake, compression, power, and exhaust. On the first stroke the intake valve is

opened w...

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... energy within the

muffler before the exhaust gases are permitted to escape.

The power capacity of an engine depends on a number of characteristics,

including the volume of the combustion chamber. The volume can be increased by

increasing the size of the piston and cylinder and by increasing the number of

cylinders. The cylinder configuration, or arrangement of cylinders, can be

straight, or in-line (one cylinder located behind the other); radial (cylinders

located around a circle); in a V (cylinders located in a V configuration); or

opposed (cylinders located opposite each other). Another type of internal-

combustion engine, the Wankel engine, has no cylinders; instead, it has a rotor

that moves through a combustion chamber.

An internal-combustion engine must also have some kind of transmission

system to control and direct the mechanical energy where it is needed; for

example, in an automobile the energy must be directed to the driving wheels.

Since these engines are not able to start under a load, a transmission system

must be used to "disengage" the engine from the load during starting and then to

apply the load when the engine reaches its operating speed.
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