TM10-4320-226-14
1.14.2.4
Fuel System. The fuel system is connected to the fuel tank and provides fuel to the engine. Figure 1-4
provides a functional diagram of the fuel system. When the engine is cranked or operating, the fuel feed pump draws
fuel through the filter/separator that filters solid contaminants larger than one micron in size from the fuel.
In addition,
filter/separator removes water from the fuel. After the filter/separator, fuel is drawn to the fuel feed pump The fuel feed
pump is a diaphragm type pump actuated by a cam in the fuel injection pump. When activated, the fuel feed pump provides
a positive head of pressure to the fuel injection pump via a fuel filter. The fuel filter provides additional filtering of the fuel
before it enters the fuel injector pump. The fuel injection pump is a high pressure fuel delivery pump driven by a timing
gear in the engine. The main shaft in the injection pump has cams which operate plungers. Plungers pump fuel into the
injector nozzles. The amount of fuel injected into the nozzles is controlled mechanically. The fuel injector nozzles are
single inlet, four outlet, high pressure injectors. High pressure injectors spray fuel directly into the engine cylinders.
Overflow lines are provided to carry excess fuel that is not needed for combustion. The excess fuel is carried to the fuel
tank and injection pump. Fuel is returned to the fuel tank by way of an overflow return fitting on the fuel tank.
1.14.2.4.1 Cold Start Systems.
a. The cold start system (figure 1-5) on all models except model 350 PAWN is stricly a mechanical system and
operates as follows: The reservoir is filled with starting fluid by first opening the cover, setting the ether bottle on the
reservoir and pushing down to penetrate the seal, This allows fluid to gravity feed into the reservoir. The bottle is removed
when the reservoir is full to the MAXI line. The handpump is operated just prior to initiating the start sequence to inject
starting fluid into the intake manifold of the engine through the nozzle.
b. The start system on Model 350 PAWN is an electrical system and consists of the components illustrated in
figure 1-5.1. Its operation is covered in conjunction with the electrical system in paragraph 1.14.2.3.1.
1.14.2.5
Engine Assembly. The engine assembly (figure 1-6) is started as described in paragraph 1.14.2.3 and
1.14.2.3.1 and provides the drive for the 350 GPM pumping assembly. When the engine is started, starter motor B1 turns
the crankshaft. When the crankshaft is turned, the pistons and valves move up and down. While one of the pistons is
moving upward, fuel is injected into the combustion chamber and mixed with air at a controlled rate. The temperature
inside the combustion chamber causes the fuel and air to burn (combustion). This combustion forces the piston
downward, which causes the crankshaft to rotate and the engine to start. The starter motor B1 is then disengaged. The
up and down movement of the pistons continues with fuel being injected into selected cylinders. The rotation of the
crankshaft also turns the camshaft and timing gears. The timing gears turn the oil pump and the fuel pump. Oil is pumped
through the lubrication system and fuel is pumped to the fuel injectors. In addition, the drive pulley rotates and drives the
V-belts. The V-belts operate the cooling fan and alternator, The cooling fan keeps the oil and engine cool to prevent
overheating. The alternator provides 14 V dc. The following paragraphs provide a more detailed description of diesel
engine operation.
1.14.2.5.1 Engine Operation Overview. The 350GPM Pumping Assembly used
engine with three
cylinders. The complete cycle for a fout-stroke engine occurs in four events for each pistion. Two revolutions of the
crankshaft are required to complete one cycle. The four events are as follows:
Intake stroke
Compression stroke
Power stroke
Exhaust stroke
When the intake stroke begins the piston is pulled down into the cylinder by the crankshaft and connecting rod. When
the piston is at the lowest point possible, it is at bottom dead center (BDC). During this time the intake valve is held open
by the camshaft. Since the piston has moved down in the cylinder to BDC, a vacuum is created and air is forced past
the intake valve into the cylinder’s combustion chamber.
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