PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
percentage of the air between the piston and the cylinder head is forced
into the turbulence chamber during the compression stroke. The chamber
usually is spherical, and the opening through which the air must pass
becomes smaller as the piston reaches the top of the stroke, thereby
increasing the velocity of the air in the chamber. This turbulence speed is
approximately 50 times crankshaft speed. The fuel injection is timed to
occur when the turbulence in the chamber is the greatest. This ensures a
thorough mixing of the fuel and the air, with the result that the greater
part of combustion takes place in the turbulence chamber itself. The
pressure created by the expansion of the burning gases is the force that
drives the piston downward on the power stroke.
d. Spherical Combustion Chamber. The spherical combustion chamber is
designed principally for use in the multifuel engine. The chamber consists
of a basic opentype chamber with a sphericalshaped relief in the top of
the piston head. The chamber works in conjunction with a strategically
positioned injector, and an intake port which produces a swirling effect on
the intake air as it enters the chamber. Operation of the chamber is as
follows:
(1) As the air enters the combustion chamber, a swirl effect is
introduced to it by the shape of the intake port (figure 42, view A, on the
following page).
(2) During the compression stroke, the swirling motion of the air
continues as the temperature in the chamber increases (figure 42, view B, on
the following page).
(3) As the fuel is injected, approximately 95 percent of it is
deposited on the head of the piston and the remainder mixes with the air in
the spherical combustion chamber (figure 42, view C, on the following page).
(4) As combustion begins, the main portion of the fuel is swept off
of the piston head by the high velocity swirl that was created by the intake
and the compression strokes. As the fuel is swept off of the head, it burns
through the power stroke, maintaining even combustion and eliminating
detonation (figure 42, view D and E, on the following page).
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