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FLOW DIVIDER
Fuel from the FCU passes through a flow di-
vider enroute to the fuel manifolds (Figure 7-
1 5 ) . O n e h a l f o f t h e f l ow d iv i d e r i s a
spring-loaded closed valve. The flow divider
allows fuel to flow unrestricted to the primary
fuel manifold, but fuel pressure must reach a
certain point to open the other half of the
valve, and allow fuel to flow to the secondary
fuel manifold.
During engine start, fuel flows through the
flow divider to the primary manifold provid-
ing the correct volume of fuel for light-off
and initial engine acceleration. As the engine
and engine-driven fuel pump gain speed, fuel
pressure increases to the point (approximately
150 PPH) where the flow divider opens al-
lowing fuel to flow to the secondary mani-
fold and nozzles. After engine start the flow
divider normally remains open allowing fuel
to flow to both the primary and secondary
manifolds.
FUEL MANIFOLDS/NOZZLES
Fuel flows from the flow divider into the pri-
mary and secondary manifolds (Figure 7-15).
Twelve duplex spray nozzles are mounted be-
tween the primary and secondary manifolds al-
l ow i n g f u e l f r o m b o t h m a n i f o l d s t o b e
discharged through each nozzle (atomizer).
The atomizers are designed to provide a cone-
shaped spray of finely atomized fuel into the
combustion chamber.
ENGINE SUB-SYSTEMS
IGNITION
The ignition is a dual system utilizing aircraft
DC power from the essential busses. There
are two circuit breakers, (CH A and CH B) lo-
cated within the left and right engine group on
each side. The engine mounted system in-
cludes an ignition unit, a dual channel capac-
itive discharge unit, two ignition plugs and two
high voltage output cables.
The DEEC activates the ignition during three
automatic modes of operation. (1) The first is
normal engine start when the thrust lever is
moved to the idle detent and the START switch
is depressed. Ignition is commanded on at 6.8%
N2 and turned off at approximately 45% N2.
The thrust lever must be at IDLE position for
automatic activation of ignition during start. (2)
The second mode is for uncommanded engine
deceleration. If N1 is below a set point and N2
is not accelerating, the ignition system is acti-
vated. (3) The last automatic mode is for ex-
cessive engine deceleration. If the physical
deceleration of the engine exceeds the decel-
eration commanded through the power levers,
the ignition is turned on for at least one second
to protect the engine against possible flameout.
Ignition may be manually turned on with
switches on the engine/fuel control panel
(Figure 7-17). The switches are labeled L/R
IGN and are the push-on and push-off type. A
white “ON” will annunciate in the switch when
selected to the on position. The “ON” does not
illuminate however, when ignition is activated
by the DEEC.
The “IGN” annunciator(s) will be displayed
on the EICAS when ignition is being called for
by the DEEC or through the switch(es). The
IGN annunciators are located outboard of each
ITT indicator (Figure 7-18). One or both may
be illuminated since they operate indepen-
dently. The color of the IGN annunciators will
be green, white or amber (Table 7-3).
(1) The IGN annunciator is green if the switch
is on or if auto-ignition has been activated by
the DEEC and both ignitors are active. (2) It is
white if ignition is being called for and one ig-
nitor plug is not firing, and (3) it is amber if ig-
nition is being called for and neither plug is
firing.
When the ignition is manually selected ON
with the corresponding engine DEEC selected
to the OFF position, the IGN E/I will be amber
even though the ignition may be firing nor-
mally.
L E A R J E T 4 5
P I L O T T R A I N I N G M A N U A L
7-24
FOR TRAINING PURPOSES ONLY
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