TM-9-2815-205-24

TM-9-2815-205-24 - Page 63 of 856

ENGINE SYSTEMS

being one stroke and down being the return stroke. The air intake and exhaust functions are accomplished during

the compression and power strokes as explained below.

Scavenging

The blower, which is an air pump that is gear driven from the crankshaft, forces air into the air box. Each cylinder

has a row of ports in the cylinder wall opening to the air box and located at the bottom of the piston stroke. When

the top of the piston moves down and uncovers the ports, air in the air box is forced through the ports. The air

then flows toward the exhaust valves and produces a scavenging effect, leaving the cylinder full of fresh air when

the piston returns and covers the ports.

Compression

As the piston continues the upward stroke, the exhaust valves close and the piston compresses the charge of

fresh air. The fuel injector injects the required amount of fuel into the cylinder shortly before the piston reaches its

highest point and continues into the power stroke.

Power

The heat generated from compression ignites the fine fuel spray to start combustion. Combustion continues until

the injected fuel has all burned. The resulting pressure forces the piston downward on its power stroke.

Exhaust

When the piston is approximately halfway down, the exhaust valves open and most of the high pressure exhaust

gases escape. Shortly thereafter, the piston drops below the inlet ports in the cylinder wall. Pressurized air is then

forced through the cylinder. During this process, the remaining exhaust gases are removed (or scavenged) from

the cylinder.

END OF WORK PACKAGE

TM 9-2815-205-24

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