Open Combustion Chamber
The open combustion chamber (fig. 4-27) is the
PRECOMBUSTION
simplest form of chamber. Due to the design of the
CHAMBER
piston crown, turbulence is generated as the piston
comes up on the compression stroke. The injector is
mounted in the cylinder head so that the end extends
slightly below the bottom. The fuel is injected directly
into the combustion space formed by the top of the
piston and the cylinder head. The open chamber
requires higher injection pressures and a greater degree
of atomization to obtain the proper fuel-air mixture
than the other types of combustion chambers. To
equalize combustion in the combustion chamber, it uses
a multiple orifice-type injector tip for effective
penetration and angle of spray.
PISTON
Precombustion Chamber
ASf04028
Figure 4-28.--Diesel engine precombustion chamber.
Figure 4-28 shows a diagram of a precombustion
chamber. This chamber is usually separate from the
precombustion chamber as ignition begins. This
cylinder head, but is screwed or pressed into the
pressure causes the remaining fuel to vaporize and, at
opening provided in the cylinder head. The
the same time, move into the main combustion space.
precombustion chamber is water-cooled because it
extends through the water jacket and into the bottom of
Turbulence Chamber
the cylinder head. It must be sealed at both ends to
prevent water leakage. As the piston moves up on the
The turbulence chamber (fig. 4-29) is similar in
compression stroke, a small part of the compressed air
appearance to the precombustion chamber, but its
enters the precombustion chamber, where it swirls
function is different. There is very little clearance
rapidly within a small space. The fuel nozzle is of the
between the top of the piston and the head, so that a
single-hole type and is mounted into the precombustion
high percentage of the air between the piston and the
chamber. As it is injected from a single-hole nozzle, the
cylinder head is forced into the turbulence chamber
fuel is only slightly atomized and depends on this
during the compression stroke. The chamber is usually
highly turbulent air for further atomization and
spherical, and the small opening through which the air
ignition. High pressure builds up inside the
must pass causes an increase in air velocity as it enters
TURBULENCE
CHAMBER
ASf04027
ASf04029
Figure 4-27.--Diesel engine open combustion chamber.
Figure 4-29.--Diesel engine turbulence combustion chamber.
4-21
