Lesson 2/Learning Event 2
The compression ratio for any engine is constant. The greater the pressure at the beginning of the
compression stroke, the greater will be the pressure at the end of the stroke. Higher compression increases
the power output of the engine, because the burning temperature of the gases is higher; therefore, more
energy is released per stroke of the engine.
SUPERCHARGER SYSTEMS AND PUMPS
Types of drives
Two means of driving supercharger pumps are used. In one system, escaping exhaust gas is used to drive a
turbine that is coupled to a supercharger impeller pump; this is called a turbosupercharger. The second
method is a mechanical drive, powered by a gear train from the engine.
Types of pumps (compressors).
There are four basic types of compressors: diaphragm, reciprocating, rotary, and centrifugal.
Diaphragm and reciprocating types are not used in supercharging because of the limited amount of air that
they can handle. Rotary and centrifugal compressors have no reciprocating parts, and large volumes of air
can be handled per unit of time. For this reason, only rotating compressors (rotary and centrifugal) can be
used for supercharging.
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