6-
2-4
INJECTION
TIMING
AND EFFECTIVE
STARTlNG
When the plunger closes suction port
of
the barrel, forced delivery
of
fuel starts.
But fuel
is
not injected from the nozzle
at once because of contraction
of
fuel, etc.
Injection timing of this engine is fixed
constant
(23"
before
TDC)
irrespective
of
engine rpm. On the other hand, in starting,
a proper delay from the timing for high
speed running and increased fuel injection
is
indispensable for effective starting.
For
this
purpose a notch
is
made at the
plunger head, which reserves
to
delay the
injection timing by nearly
8"
to facilitate
starting. (See Fig.
65.)
FIG.
65
6-
2-5
FUNCTION OF THE DELIVERY VALVE
By
the plunger stroke, fuel pressure is raised. And when it becomes higher than the
,-
pressure remained in the high pressure pipe, the delivery valve spring is pushed down
and the valve opens.
As
the result, the fuel in the high pressure pipe
is
delivered forcibly.
When the plunger lead meets suction port
of
the plunger barrel, delivery
of
fuel ends,
and the delivery valve is closed by the spring tension
of
the valve.
At
this time, delivery
valve prevents reverse flow of the fuel. Also suction back motion around the upper
part
of
the plunger sucks back the fuel in the equal amount of the stroke
[A]
and decreases
remaining pressure in the high pressure pipe. The nozzle jets the fuel clearly off and
prevents after dripping. (See Fig.
66.)
DELIVERY
DELIVERY
VALVE
VALVE
SPRING
BACK
STROKE
FIG.
66
-
42
-
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