Figure 5-2.Open combustion chamber.
distributed as evenly as possible throughout the
chamber if the engine is to function at maximum
efficiency and exhibit maximum drivabilty. A well-
designed engine uses a combustion chamber that is
designed for the intended usage of the engine. The
injects used should compliment the combustion
chamber. The combustion chambers described on the
following pages are the most common and cover
Figure 5-3.Precombustion chamber.
virtually all of the designs that are currently in use.
These are the open chamber, precombustion chamber,
turbulence chamber, and spherical (hypercycle)
Open Combustion Chamber
The open combustion chamber (fig. 5-2) is the
simplest form of chamber. It is suitable for only slow-
speed, four-stroke cycle engines, but is widely used in
two-stroke cycle diesel engines. In the open chamber,
the fuel is injected directly into the space on top of the
cylinder. The combustion space, formed by the top of
the piston and the cylinder head, usually is shaped to
provide s swirling action of the air, as the piston comes
up on the compression stroke. There are no special
pockets, cells, or passages to aid the mixing of the fuel
and air. This type of chamber requires a higher injection
pressure and a greater degree of fuel atomization than is
required by other combustion chambers to obtain an
acceptable level of fuel mixing.
combustion in the combustion chamber, use a multiple
orifice-type injector tip for effective penetration. This
chamber design is very susceptible to ignition lag.
The precombustion chamber (fig. 5-3) is an
auxiliary chamber at the top of the cylinder. It is
connected to the main combustion chamber by a
restricted throat or passage. The precombustion
chamber conditions the fuel for final combustion in the
cylinder. A hollowed-out portion of the piston top