PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
(c) Another type of throttling nozzle has its pintle flush with
the nozzlebody tip for nofuel delivery and extended through the body for
maximum fuel delivery. In this type, fuel under high pressure from the
injection pump acts on the seat area of the pintle, forcing it outward
against a preloaded spring. This spring, through its action on a spring
hanger, also returns the pintle to its seat, sealing the nozzle against
further injections or dribble when the line pressure is relieved at the
pump. When the pintle moves outward due to fuel pressure, an increasingly
larger orifice area is opened around the flow angle of the pintle.
(d) The hole nozzles have no pintle but basically are similar in
construction to the pintle type. They have one or more spray orifices that
are straight, round passages through the tip of the nozzle body beneath the
valve seat. The spray from each orifice is relatively dense and compact,
and the general spray pattern is determined by the number and the
arrangement of the holes. As many as 18 holes are provided in larger
nozzles, and the diameter of these drilled orifices may be as small as 0.006
in. The spray pattern may not be symmetrical, as in the case of the
multifuel engine, where the spray pattern is off to one side so as to
deposit the fuel properly in the spherical combustion chamber. The size of
the holes determines the degree of atomization attained. The smaller the
holes, the greater the atomization; but if the hole is too small, it will be
impossible to get enough fuel into the chamber during the short time allowed
for injection. If the hole is too large, there will be an overrich mixture
near the nozzle tip and a lean mixture at a distance from it. Using
multiple holes in the injector tips usually overcomes both difficulties
because the holes can be drilled small enough to provide proper atomization
and in a sufficient number to allow the proper amount of fuel to enter
during the injection period.
c. Wobble Plate Pump System (figure 46 on the following page).
(1) General System Operation. The wobble plate pump system basically
is the same as the multiple unit injection system. The difference in the
systems lies in the injection pump. In a wobble plate pump, all of the pump
plungers are actuated by a single wobble plate instead of a camshaft that
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