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How an engine
works
The
Otto cycle is characterized by four strokes, or straight movements
alternately, back and forth, of a piston inside a cylinder:
1. intake (induction) stroke
2. compression stroke
3. power (combustion) stroke
4. exhaust stroke
The cycle begins at top dead centre (TDC), when the piston is furthest
away from the crankshaft. On the first stroke (intake) of the piston,
a mixture of fuel and air is drawn into the cylinder through the
intake (inlet) port. The intake (inlet) valve (or valves) then close(s)
and the following stroke (compression) compresses the fuel-air mixture.
Four-stroke cycle (or Otto cycle)The air-fuel mixture is then ignited,
usually by a spark plug for a gasoline or Otto cycle engine or by
the heat and pressure of compression for a Diesel |
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cycle
or compression ignition engine, at approximately the top of the compression
stroke. The resulting expansion of burning gases then forces the piston
downward for the third stroke (power) and the fourth and final stroke
(exhaust) evacuates the spent exhaust gases from the cylinder past the
then-open exhaust valve or valves, through the exhaust port.
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