Fuel injector nozzle (typical example)
(1) Fuel inlet
(4) Fuel injector nozzle
(2) Fuel return line
(5) Seat washer
(3) Fuel injector holder
Each fuel injection nozzle is fastened to the cylinder head by a
gland nut on the fuel injector holder (3). Fuel injection nozzles
are not serviceable except for removal of the fuel injector
nozzle (4) in order to clean the orifice (6).
The operating pressure of the fuel injection nozzle is set and
tested at the factory. Refer to the Specifications, "Fuel Injector
Nozzles" for the pressure settings of the fuel injector nozzles.
The fuel injection pump forces the fuel to flow under high
pressure to the hole in the fuel inlet (1). The fuel then flows
around a needle valve within the fuel injector holder (3) which
causes the fuel injection nozzle (4) to fill with fuel. The
pressure of the fuel pushes the needle valve and a spring.
When the force of the fuel pressure is greater than the force of
the spring, the needle valve will lift up.
When the needle valve opens, fuel under high pressure will
flow through the nozzle orifices (6) into the cylinder. The fuel is
injected into the cylinder through the orifices in the nozzle end
as a very fine spray. When the fuel is injected into the cylinder,
the force of the fuel pressure in the nozzle body will decrease.
The force of the spring will then be greater than the force of the
fuel pressure that is in the nozzle body. The needle valve will
move quickly to the closed position.
The needle valve has a close fit with the inside of the nozzle.
This makes a positive seal for the valve.
When the fuel flows to the cylinder, a small quantity of fuel will
leak by the valve guide. This fuel lubricates the moving parts
of the fuel injection nozzle. This fuel then goes through a
passage in the fuel injector holder (3) to the fuel return line (2).
This excess fuel is then returned to the fuel tank.
Fuel Injection Pump
The fuel injection pump is a pressurized system that is totally
enclosed. The pump sends the correct amount of fuel under
high pressure at the correct time through the fuel injection
nozzles to the individual cylinders. The correct timing occurs
near the end of the compression stroke. The fuel injection
pump regulates the amount of fuel that is delivered to the fuel
injection nozzles. This action controls the engine rpm by the
governor setting or the position of the throttle control.
The fuel lines to the fuel injection nozzles are equal lengths.
This ensures even pressure and correct injection timing at
each fuel injection nozzle.
During operation, extra fuel is used as coolant and lubricant for
pump parts that move. The extra fuel is circulated through the
pump housing. The extra fuel is then returned to the fuel tank.
Return lines also carry away any air that is trapped in the fuel
injection nozzles or of the fuel injection pump housing.