4.4.2. General descriptions
The engine output is determined by the fuel delivery volume and engine efficiency.
To burn the supplied fuel completely to change into effective power for the engine, the volume
of air enough to burn the fuel completely should be supplied into the cylinders.
Therefore, the engine output is determined substantially by the cylinder capacity, and the
greater volume of compressed air is charged into the cylinders of given capacity, the greater
engine output can be obtained as a greater volume of air charged into the cylinders burns so
much more fuel.
As explained, the compressing of air to supply into the cylinders is called "Supercharging" and
the making use of the energy of exhaust gas discharged from the combustion chamber to
charge the compressed air into the cylinders is called "Turbocharging".
4.4.3. Functions
1) Turbine
Exhaust gas discharged from the combustion chamber distributes its own energy to the turbine
blades while passing the inside of the turbine housing, with the result that the turbine shaft can
get rotating force. This is the working principle of 'turbine', which is mounted with seal rings and
heat protector to prevent exhaust gas from affecting the bearings adversely.
2) Compressor
The compressor, which is connected to the turbine over the one and same shaft to form a rotat-
ing body, takes in and compresses ambient air with rotating force transmitted from the turbine
shaft. Then, the compressed air is delivered to the intake pipe. This is the working principle of
the compressor.
3) Bearings
(1) Thrust bearing
The turbine wheel creates thrust force. Therefore, exercise care so that the shaft is not
deviated from its original position due to this thrust.
(2) Journal bearing
This journal bearing of floating type forms a dual oil film on both the inside and outside of
the bearing so that the bearing can rotate independently. As the dual oil film plays a role
as a damper, the sliding speed of the bearing surface becomes lower than the rotating
speed of the shaft, resulting in assurance of stability in its movement.
4) Sealing-Compressor shaft
The compressor is of a dual construction type composed of seal plate and seal ring to prevent
the leak of compressed air or lubricating oil.
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