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 TM 55-1905-22'3-24-3
(1) Intake Stroke. During intake stroke, the piston travels downward, intake valves are open, and
exhaust valve are closed. The downward travel of the piston allows air from the atmosphere to enter the
cylinder. On turbocharged engines the intake manifold is pressurized as the turbocharger forces more air into
the cylinder through the intake manifold. The intake charge consists of air only, with no fuel mixture.
(2) Compression Stroke. At the end of the intake stroke, intake valves close and piston starts upward
on compression stroke. The exhaust valves remain closed. At end of compression stroke, air in combustion
chamber has been forced by the piston to occupy a smaller space than it occupied at the beginning of stroke.
Thus, compression ratio is the direct proportion in the amount of air in the combustion chamber before and
after being compressed. Compressing air into a small space causes temperature of that air to rise to a point
high enough for ignition of fuel. During last part of compression stroke and early part of power stroke, a small
metered charge of fuel is injected into the combustion chamber. Almost immediately after fuel charge is
injected into combustion chamber, fuel is ignited by the existing hot compressed air.
(3) Power Stroke. During the beginning of the power stroke, the piston is pushed downward by the
burning and expanding gases. Both intake and exhaust valves are closed. As more fuel is added and burns,
gases get hotter and expand more to further force piston downward. Thus adds driving force to crankshaft
rotation.
(4) Exhaust Stroke. During exhaust stroke, intake valves are closed, exhaust valves are open, and
piston is on the upstroke. Upward travel of the piston forces burned gases out of the combustion chamber
through open exhaust valve ports and into the exhaust manifold.
b. Fuel System. The "Pressure Time" (PT) Fuel System used on this engine consists of the fuel pump,
supply lines, drain lines, fuel passages, and injectors.
(1) Fuel Pump. The fuel pump is coupled to the fuel pump drive which is driven from the engine gear
train. Fuel pump main shaft in turn drives the gear pump.
(a) Gear Pump and Pulsation Damper. The gear pump is driven by the pump main shaft and
contains a single set of gears to pick up and deliver fuel throughout the fuel system. Inlet is at the rear of the
gear pump. A pulsation damper mounted to the gear pump contains a steel diaphragm which absorbs
pulsations and smooths fuel flow through the fuel system. From gear pump, fuel flows through the filter screen.
(b) Electric Fuel Control (EFC) Governor/Actuator. The EFC governor contains a magnetic pickup,
a remote automatic governor control, and an actuator. The magnetic pickup senses the flywheel rotation and
sends an electrical signal to the remote governor control. The governor control compares the electrical signal,
or pulse, from the magnetic pickup with a preset reference point. The control then changes the current going to
the actuator on the fuel pump. When the control current changes, the actuator shaft turns. When the shaft
turns, the engine speed changes.
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