PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
(a) The fuel supply pump and the fuel filter provide a low-
pressure supply of fuel to the multiple unit injection pump.
Pressure
usually is regulated to approximately 15 psi.
(b) The multiple unit injection pump contains an individual
injection pump for each engine cylinder.
Fuel is delivered from the
multiple unit injection pump to the injectors at each cylinder in a timed
sequence and a regulated amount, based on accelerator pedal position and
engine speed.
(c) The injectors receive fuel charges from their respective
injection pumps and spray it into the combustion chambers in a spray pattern
that is tailored to provide the best overall performance for their
particular application.
(2) The Multiple Unit Injection Pump.
(a) The multiple unit injection pump contains an individual
plunger-type injector pump for each cylinder. These pumps are arranged in a
line so that they may be driven by a common camshaft.
The lobes of the
camshaft are arranged so that they operate the injection pumps in a sequence
that coincides with the firing order of the engine. This camshaft is driven
by the engine, through gears, at a speed of exactly one-half that of the
crankshaft. This exact speed is maintained so that the injectors will each
deliver their fuel charge at the beginning of their respective cylinder's
power stroke. Power strokes occur during every other crankshaft revolution
in a four-stroke cycle diesel engine.
(b) Excess fuel flows from the injection pump through the relief
valve and back to the fuel tank. The relief valve usually is adjusted to
open at approximately 15 psi.
(c) The pumps consist of a finely fitted plunger that is actuated
by the camshaft against the force of the plunger spring. The bore that the
plunger rides in has two passages machined into it. One of these passages
is the delivery port, through which the pump is filled. The other passage
is the spill port, through which excess fuel is discharged.
When the
plunger is fully in its return position, fuel flows into the pump cavity
through the uncovered delivery port and out of the pump cavity through the
uncovered spill port. The
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