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 TM 9-8000
down to the pressure chamber above the valve seat.
nozzle orifice. At the beginning of the injection period,
only a small quantity of fuel is injected into the chamber
(2) At the moment that the pressure developed
because the straight section of the pintle is in the nozzle
by the injection pump exceeds the force exerted by the
orifice. The volume of the fuel spray then increases
pressure adjusting spring, the nozzle valve will be lifted
progressively as the pintle is lifted higher, because the
off of its seat, resulting in the injection of fuel into the
straight section leaves the nozzle orifice and the tapered
cylinder. The valve usually requires a fuel pressure of
tip of the pintie in the orifice provides a larger opening for
1000 to 4000 psi (6895 to 27580 kPa) to open,
the flow of fuel.
depending on the engine combustion chamber
requirements.
(3) Another type of throttling nozzle has its
pintle flush with the nozzle-body tip for no-fuel delivery
(3) A controlled seepage exists between the
and extended through the body for maximum fuel
lapped surfaces of the nozzle valve and its body to
delivery. In this type, fuel under high pressure from the
provide for lubrication. The leakage or overflow passes
injection pump acts on the seat area of the pintle, forcing
around the spindle and into the pressure adjusting spring
it outward against a preloaded spring. This spring,
chamber. From here, the fuel leaves the injector through
through its action on a spring hanger, also returns the
the overflow outlet and finally to the overflow lines, which
pintle to its seat, sealing the nozzle against further
lead back to the low-pressure fuel supply.
injections or dribble when the line pressure is relieved at
the pump. When the pintle moves outward due to fuel
d.
Injector Nozzles (Fig. 5-9). Because of the
pressure, an increasingly larger orifice area is opened
widely differing requirements in the shapes of the fuel
around the flow angle of the pintle.
spray for various chamber designs and the wide range of
engine power demands, there is a large variety of
(4) The hole nozzles have no pintle but
injector nozzles in use. The spray nozzles are put into
basically are similar in construction to the pintle type.
two basic groups: pintle nozzles and hole nozzles. Pintle
They have one or more spray orifices that are straight,
nozzles generally are used in engines having
round passages through the tip of the nozzle body
precombustion or turbulence chambers, whereas the
beneath the valve seat. The spray from each orifice is
hole nozzles generally are used in open chamber
relatively dense and compact, and the general spray
engines.
pattern is determined by the number and the
arrangement of the holes. As many as 18 holes are
(1) In pintle nozzles, the nozzle valve carries
provided in larger nozzles, and the diameter of these
an extension at its lower end in the form of a pin (pintle),
drilled orifices may be as small as 0.006 in. (0.152 mm).
which protrudes through the hole in the nozzle bottom.
The spray pattern may not be symmetrical, as in the
This requires the injected fuel to pass through an annular
case of the multifuel engine, where the spray pattern is
orifice, producing a hollow, cone-shaped spray, the
off to one side so as to deposit the fuel properly in the
nominal included angle of which may be from 0 to 60
spherical combustion chamber (para 5-12). The size of
degrees, depending on the combustion chamber
the holes determines the degree of atomization attained.
requirement. The projection of the pintle through the
The smaller the holes, the greater the atomization; but if
nozzle orifice includes a self-cleaning effect,
the hole is too small, it will be impossible to get enough
discouraging the accumulation of carbon at this point.
fuel into the chamber during the short time allowed for
injection. If the hole is too large, there will be an overrich
(2) A specific type of pintle nozzle that is used
mixture near the nozzle tip and a lean mixture at a
extensively in small bore high-speed diesel engines is
distance from it. Using multiple holes in the Injector tips
the throttling nozzle. It differs from the standard pintle
usually overcomes both difficulties because the holes
nozzle in that the pintle projects from the nozzle for a
can be drilled small enough to provide proper
much greater distance, and the orifice in the bottom of
atomization and a sufficient number can be provided to
the nozzle body is much longer. The outstanding feature
allow the proper amount of fuel to enter during the
of the throttling nozzle is its control of the rate at which
injection period.
fuel is injected into the combustion chamber. When no
fuel is being injected, the pintle extends through the
5-12
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