DIESEL ENGINE COMPRESSION STROKE.
The piston is at bottom dead center at the beginning of
the compression stroke, and, as the piston moves
upward, the air compresses. As the piston reaches top
dead center, the compression stroke ends (fig. 1-10,
DIESEL ENGINE POWER STROKE. The
piston begins the power stroke at top dead center. The
air is compressed to as much as 500 psi and at a
compressed temperature of approximately 1000°F. At
this point, fuel is injected into the combustion chamber
and is ignited by the heat of the compression. This
begins the power stroke. The expanding force of the
burning gases pushes the piston downward, providing
power to the crankshaft. The diesel fuel will continue to
bum through the entire power stroke (a more complete
burning of the fuel) (fig. 1-10, view C). The gasoline
engine has a power stroke with rapid combustion in the
beginning, but little to no combustion at the end.
DIESEL ENGINE EXHAUST STROKE. As
the piston reaches bottom dead center on the power
stroke, the power stroke ends and the exhaust stroke
begins (fig. 1-10, view D). The exhaust valve opens,
and, as the piston rises towards top dead center, the burnt
gases are pushed out through the exhaust port. As the
piston reaches top dead center, the exhaust valve closes
and the intake valve opens. The engine is now ready to
begin another operating cycle.
The multifuel engine (fig. 1-11) is basically a
four-stroke cycle diesel engine with the capability of
operating on a wide variety of fuel oils without
adjustment or modification. The fuel injection system is
equipped with a device called a fuel density
compensator that varies the amount of fuel to keep the
power output constant regardless of the type fuel being
used. The multifuel engine uses a spherical combustion
chamber (fig. 1-12) that aids in thorough fuel and air
mixing, complete combustion, and minimizes knocks.
NOTE: Because of environmental pollution
controls and the development of more efficient diesel
engines, the multifuel engine is being phased out.
Figure 1-11.Multifuel engine.