THEORY OF OPERATION
The diesel engine is an internal compression combustion power unit where the heat of the fuel and air is
compressed and burned, thereby converting it into work in the cylinders of the engine.
In the diesel engine, air is compressed creating heat in the cylinder. The fuel is then injected into the compressed
air igniting the diesel fuel which starts the power stroke or work.
The two-cycle engine has two strokes, the motion of the piston in one direction or one rotation of the crankshaft
for each cycle of the engine. In contrast, the four-cycle engine has four strokes or two rotations of the crankshaft
for each cycle of the engine.
How the Two-Cycle Principle Works
The diesel engine is provided with a blower to force air into the cylinders to provide fresh air for combustion and to
expel exhaust gases. The cylinder liner contains a row of ports which are above the piston when it is at the bottom
of its stroke. These ports allow air to enter from the blower as soon as the rim of the piston begins to uncover the
ports. At the same time, the exhaust valves are open and a unidirectional flow of air from the liner ports to the
exhaust valves accomplishes two vital processes. First, the exhaust gases are expelled from the cylinder and
second, the cylinder is filled with fresh air for combustion.
The piston travels upward, covering and sealing the liner ports. As the piston continues upward it then
compresses the air therefore creating heat. Just before the piston reaches the top of the stroke, fuel is then
injected into the heated compressed air in the cylinder. The intense heat of the compressed air immediately
ignites the fuel. The resulting combustion will continue until all of the fuel and air are depleted.
The resulting pressure forces the piston downward starting the power stroke. The resulting energy is converted
from linear motion to rotating motion by the crankshaft. As the piston travels downward it will again uncover the
liner ports and the exhaust valves will open allowing the incoming air to push the exhaust gases out starting the
process over again. This entire process is completed in all eight cylinders once every rotation of the crankshaft.