dispersed in the combustion space. Since penetration
requirements of the type of combustion chamber in use.
and atomization tend to oppose each other, a
Some chambers require very fine atomization; others
compromise in the degree of each is necessary in the
function with coarser atomization. Proper atomization
design of fuel injection equipment, particularly if
makes it easier to start the burning process, and ensures
uniform distribution of fuel within the combustion
that each minute particle of fuel is surrounded by
chamber is to be obtained.
particles of oxygen with which it can combine.
Atomization is generally obtained when the liquid
Methods of Fuel Injection
fuel, under high pressure, passes through the small
opening (or openings) in the injector or nozzle. As the
There are several types of fuel injection systems
fuel enters the combustion space, high velocity is
used in today's SE diesel engines. Some engine
developed because the pressure in the cylinder is lower
manufacturers make and install their own fuel injection
than the fuel pressure. The created friction, resulting
equipment. Others rely on manufacturers who
from the fuel passing through the air at high velocity,
specialize in fuel injection equipment and who design
causes the fuel to break up into small particles.
or modify their product to meet the requirements of the
engine manufacturer.
Creating Pressure
ROOSA MASTER FUEL INJECTION
A fuel injection system must increase the pressure
PUMP.--The Roosa Master fuel injection pump
of the fuel enough to overcome compression pressures
commonly used is the opposed plunger, inlet metering,
and to ensure proper dispersion of the fuel injected into
twin cylinder (Model DC), distributor type pump. The
the combustion space. Proper dispersion is essential if
main components are the drive shaft, distributor rotor,
the fuel is to mix thoroughly with the air and burn
transfer pump, pumping plungers, internal cam ring,
efficiently. While pressure is a chief contributing factor,
hydraulic head, end plate, governor, and the pump
the dispersion of the fuel is influenced, in part, by
housing with an integral advance mechanism. Early
atomization and penetration of the fuel. (Penetration is
advance mechanisms are attached to the pump housing
the distance through which the fuel particles are carried
and can be removed from the housing as a unit for
by the motion given them as they leave the injector or
servicing.
nozzle.)
The rotating members that revolve on a common
If the atomization process reduces the size of the
axis include the drive shaft, distributor rotor, and
fuel particles too much, they will lack penetration. Too
transfer pump.
little penetration results in the small particles of fuel
In the Model DC pump (fig. 4-37), the driving
igniting before they have been properly distributed or
member is the drive shaft that rotates inside a pilot tube
HYDRAULIC HEAD
DRIVE SHAFT
GOVERNOR
WEIGHT RETAINER
END PLATE
PLUNGERS
ROTOR
CAM RING
ASf04037
Figure 4-37.--Roosa Master fuel injection pump (Model DC).
4-30
