TM 9-2815-202-34
1-11. PRINCIPLES OF OPERATION (Cont)
The engine has a turbocharger and a blower to force air into the cylinders (called supercharging) for
both the intake and the exhaust functions. When the piston is halfway down, the exhaust valves open.
Shortly thereafter, the piston drops below a row of inlet ports in the cylinder liner wall. Pressurized air
is then forced through the cylinder. During this process, all of the exhaust gases are removed (or
scavenged) from the cylinder. When the exhaust valves close, during the pistons upward stroke, fresh
air is trapped in the cylinder for compression.
Fuel injection into the cylinder begins with the piston near its highest point and continues into the
power stroke. The intense heat created by the high compression of the air immediately ignites the fine
fuel spray. The combustion continues until the injected fuel has burned. The resulting pressure forces
the piston downward on its power stroke. When the piston is about halfway down, the exhaust valves
open. Shortly thereafter, the piston drops below the ports, and the cylinder is again swept with clean
scavenging air. This entire combustion cycle is completed in each cylinder for each revolution of the
crankshaft.
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