Figure 5-21.Spring-loaded ball-check valve.
maintained by a spring-loaded ball-check return fitting
(fig. 5-21) in the governor cover of the pump.
The injector nozzle, used with the DB2 fuel
injection pump, is opened outward by high fuel pressure
and closed by spring tension (fig. 5-22). It has a unique
feature in that it is screwed directly into the cylinder
head An outward opening valve creates a narrow spray
that is evenly distributed into the precombustion
chamber. Both engine compression and combustion
pressure forces assist the nozzle spring in closing an
outward opening valve.
These factors allow the
opening pressure settings of the nozzle to be lower than
those of conventional injectors.
During injection, a degree of swirl is imparted to the
fuel before it actually emerges around the head of the
nozzle. This forms a closely controlled annular orifice
with the nozzle valve seat, which produces a high-
velocity atomized fuel spray, forming a narrow cone
suitable for efficient burning of the fuel in the
Figure 5-22.Injector nozzle.
The nozzle has been designed as basically a
throwaway item. After a period of service, the
functional performance may not meet test
specifications. Nozzle testing is comprised of the
Nozzle opening pressure
Each test is done independently of the others (for
example, when checking the opening pressure, do not
check for leakage). If all the tests are satisfied, the
nozzle can be reused. If any one of the tests is not
satisfied, replace the nozzle. For testing procedures,
consult the manufacturers service manual.
When testing nozzles, do not place your
hand or arms near the top of the nozzle. The
high-pressure atomized fuel spray from the
nozzle has sufficient penetrating power to
puncture flesh and destroy tissue and may
result in blood poisoning. The nozzle tip
should always be enclosed in a receptacle,
preferably transparent, to contain the spray.
DETROIT DIESEL UNIT INJECTION
The fuel system used by Detroit diesel is known as a
low-pressure fuel system, owing to the fact that fuel
delivered to the unit injectors averages 45 to 70 psi.
This is much lower than the average 2,500 to 300 psi
that passes through the fuel line from the injection pump
and nozzles used in other systems.
The four main functions of the fuel system used
with a Detroit diesel engine are as follows:
1. To supply clean, cool fuel to the system by
passing it through at least a primary and
secondary filter before the pump and injectors.
2. To cool and lubricate the injectors, as the fuel
flows through them, and return to the tank
3. To maintain sufficient pressure at all times
through the action of the positive displacement