TROUBLESHOOTING THE HMMWV - OD1616 - LESSON 1/TASK 1
The air is compressed to about one-twentieth of its original volume
in a diesel engine.
In contrast, the fuel and air mixture in a
volume. The diesel engine must compress the air tightly to generate
enough heat to ignite the fuel when it is injected into the cylinder.
The gasoline engine mixes the fuel and air before it reaches the
A diesel engine takes in air only through the
in, it mixes with the air and ignites because of the heat.
The engine speed and power output of the diesel engine are controlled
amount of air remains constant.
This contrasts with the gasoline
engine where the speed and power output are regulated by limiting the
air entering the engine.
In the paragraphs that follow, the operation of
the engine will be followed through each of the four strokes that
When the intake stroke begins, the piston is at
top dead center (TDC).
As the piston moves downward, the intake
valve opens and the downward movement of the piston creates a vacuum
that sucks the air into the cylinder. When the piston reaches bottom
dead center (BDC), the intake valve closes and the intake stroke is
piston travels upward toward TDC, the air that was drawn into the
cylinder is compressed to a ratio of nearly 20 to 1, almost three
ends when the piston reaches TDC.
When the piston reaches TDC, the fuel injector sprays a precisely
measured amount of fuel into the precombustion chamber.
superheated air in the combustion chamber ignites the fuel as it is
This ultra-high compression causes the air to superheat,
making it hot enough to ignite the diesel fuel.
This is where the
term compression ignition comes from. This very high