Lesson 2/Learning Event 1
Many four-stroke-cycle diesel engines use the turbosupercharger. The turbosupercharger is driven by exhaust
gases, thereby using some of the energy that is normally wasted. An example would be the M915-series
vehicles.
A turbosupercharger consists of two impellers mounted on the same shaft. The compressor impeller is on one
end of the shaft and the turbine impeller on the other. Each impeller works or spins in separate sections of the
housing, with seals between to prevent leakage from one housing to the other. The impellers have a series of
straight or curved vanes that act much like a fan. The turbine impeller and housing is mounted in the engine
exhaust system and is driven by the pressure from the escaping exhaust gases. The compressor impeller is
mounted in the air intake system and turns with the turbine, forcing air into the cylinders.
The blower increases normal air pressure and aids in forcing air into the cylinder and the burned gases from
the cylinder. It is lubricated by the engine lubrication system.
Most high-speed diesel engines use the full-force oil feed system. An oil pump mounted in the crankcase is
driven by gears and shafts. The pump picks up oil from the sump (oil pan) and forces it under pressure
through drilled passages to all the working parts of the engine.
Most compression-ignition engines use an oil cooler. The oil cooler is a series of tubes mounted in a water
passage of the engine cooling system. As the hot lubricating oil passes through these tubes, the heat is
transferred into the cooling water.
Compression-ignition engines have fuel injection systems. Although many types of fuel injection systems are
used, they must all perform the same functions. These functions are first, to put the fuel under very high
pressure (or to pressurize); second, meter or measure an exact amount of fuel for delivery; and third, to inject
this fuel into the combustion chamber at the proper time.
Most compression-ignition engines use a governor with the fuel injection pump. The governor controls the
maximum (top) engine speed and aids in maintaining a constant operating speed. The operating speeds and
power output of the engine are controlled by changing the amount of fuel that is injected into the combustion
chamber.
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