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 TM 55-1905-223-24-5
FIGURE 1-5. Diesel Engine Cycles.
(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 the piston downward and add driving force to crankshaft
rotation.
(4) Exhaust Stroke. During the 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 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, governor, and tachometer shaft assemblies. The PT
(type G) fuel pump is made up of three main units: the gear pump, standard governor, and throttle.
(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.
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