PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
pressure adjusting spring, the nozzle valve will be lifted off of its seat
resulting in the injection of fuel into the cylinder.
The valve usually
requires a fuel pressure of 1,000 to 40,000 psi to open, depending on the
engine combustion chamber requirements.
(c) A controlled seepage exists between the lapped surfaces of the
nozzle valve and its body to provide for lubrication.
The leakage or
overflow passes around the spindle and into the pressure adjusting spring
chamber.
From here, the fuel leaves the injector through the overflow
outlet and finally to the overflow lines, which lead back to the low-
pressure fuel supply.
(4) Injector Nozzles (figure 45 on the following page). Because of
the widely differing requirements in the shapes of the fuel spray for
various chamber designs, and the wide range of engine power demands, there
is a large variety of injector nozzles in use. The spray nozzles are put
into two basic groups: pintle nozzles and hole nozzles.
Pintle nozzles
generally are used in engines having precombustion or turbulence chambers,
whereas the hole nozzles generally are used in open chamber engines.
(a) In pintle nozzles, the nozzle valve carries an extension at
its lower end in the form of a pin (pintle) which protrudes through the hole
in the nozzle bottom. This requires the injected fuel to pass through an
annular orifice, producing a hollow, cone-shaped spray, the nominal included
angle of which may be from 0 to 60, depending on the combustion chamber
requirement.
The projection of the pintle through the nozzle orifice
includes a self-cleaning effect, discouraging the accumulation of carbon at
this point.
(b) A specific type of pintle nozzle used extensively in small
bore high-speed diesel engines is the throttling nozzle.
It differs from
the standard pintle nozzle in that the pintle projects from the nozzle for a
much greater distance, and the orifice in the bottom of the nozzle body is
much longer.
The outstanding feature of the throttling nozzle is its
control of the rate at which fuel is injected into the combustion chamber.
When no fuel is being injected, the pintle extends through the nozzle
orifice. At the beginning of the injection period, only a small quantity of
fuel
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