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 TM 5-685/NAVFAC MO-912
Figure 3-4. Typical diesel power plant on transportable frame base.
The "V" configuration is favored when there is a
port (or the exhaust valve closes), then the scaveng-
lack of space because "V" engines are shorter and
ing air port is closed. The piston now compresses
more compact than in-line engines. Most engines in
the air to heat it to a temperature required for
use are liquid-cooled. Air cooling is sometimes used
ignition as the piston nears top dead center (TDC).
with single-cylinder and other small engines (driv-
As the piston nears TDC, a metered amount of fuel
ing generators with up to 10 kW output). Air-cooled
is injected at a certain rate. Injection atomizes the
engines usually reach operating temperature
fuel, which is ignited by the high temperature, and
quickly but are relatively noisy during operation.
combustion starts. Combustion causes the tempera-
a. Two cycle. The series of events that take place
ture and pressure to rise further.
in a two-cycle diesel engine are: compression, com-
(2) Power: As the piston reaches and passes
bustion, expansion, exhaust, scavenging, and air in-
TDC, the pressure of the hot gas forces and acceler-
take. Two strokes of the piston during one revolu-
ates the piston downward. This turns the crank-
tion of the crankshaft complete the cycle.
shaft against the load connected to the shaft. The
(1) Compression. The cycle begins with the pis-
fuel/air mixture continues to burn. As the piston
ton in its bottom dead center (BDC) position. The
passes eighty percent (80%) to eighty-five percent
exhaust valve is open permitting burned gases to
(85%) of the stroke travel towards BDC, it uncovers
escape the cylinder, and the scavenging air port is
the exhaust port (or the exhaust valve is opened).
uncovered, permitting new air to sweep into the
This allows exhaust gas to escape from the cylinder.
cylinder. With new air in the cylinder, the piston
As the piston continues downward, it uncovers the
moves upward. The piston first covers the exhaust
scavenging air port, allowing scavenging air (fresh
3-4
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