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engine start, electric igniters create sparks that
ignite the mixture. After each engine start, the
flame in the combustion chamber continues
burning as long as fuel and air are supplied.
The burning fuel/air mixture creates hot, highpressure
exhaust, which expands rapidly and
moves aft through the engine.
Exhaust
As the hot, high-pressure exhaust moves aft
through the engine, it turns the high-pressure
turbine. The high-pressure turbine is connected
to the compressors through a short,
CITATION MUSTANG OPERATING MANUAL
510OM-00 7-3
Figure 7-3. Engine Schematic/Cutaway
hollow shaft. The high-pressure rotors (turbine,
shaft, and compressors) are referred to
as the “high-pressure (HP) spool.” Its rate of
rotation is referred to as “N2 rpm” or simply
“N2.” N2 rotation keeps the airflow entering
the engine and maintains the intake/compression/
combustion/exhaust cycle.
A thermocouple harness at engine Station 6
measures exhaust stream temperature. This information
is processed by the FADEC and
converted to an equivalent interstage turbine
temperature (ITT) for use by the pilot.
After exiting the HP turbine, the exhaust (now
at lower pressure and temperature, but at higher
speed) continues through the LP turbine, turning
it. The LP turbine turns a long, narrow,
inner shaft (which passes through the hollow
HP spool) to directly drive the fan. The LP rotors
(LP turbine, inner shaft, and fan) are
referred to as the “LP spool.” Its rate of rotation
is referred to as “N1 rpm” or simply “N1.”
The exhaust loses some heat as it turns the turbines,
and then mixes with the fan bypass air
before exiting aft through the engine exhaust
nozzle. As the engine moves the exhaust aft
and out, it produces jet propulsion thrust. Jet
propulsion thrust and fan bypass thrust combine
to produce total engine thrust.
COMPONENTS
ENGINE SYSTEMS AND
ACCESSORIES
On the bottom of the engine is an accessory
gearbox (AGB) with an integral oil reservoir,
pump, and mechanical power connections for
engine-driven accessories. The AGB is driven
by the HP spool (N2) through a gear-driven
shaft. The AGB drives the engine fuel pump
and its associated alternator. The AGB also
connects the starter-generator to the engine.
CITATION MUSTANG OPERATING MANUAL
7-4 510OM-00
FAN BYPASS DUCT
LEGEND
AMBIENT-AIR AND FAN-BYPASS AIR
LOW-PRESSURE COMPRESSED AIR
HIGH-PRESSURE COMPRESSED AIR
BURNING FUEL
HOT, SLOW, HIGH-PRESSURE EXHAUST
HOT, FAST, LOW-PRESSURE EXHAUST
LOW-PRESSURE
COMBUSTION CHAMBER TURBINE
FAN
HIGH-PRESSURE
TURBINE
HIGH-PRESSURE COMPRESSOR
(CENTRIFUGAL-FLOW, SINGLE-STAGE)
LOW-PRESSURE COMPRESSOR
MIXED-FLOW ROTOR
Figure 7-4. Turbofan Engine Basics
Two ports on the outside of the front bypass
duct allow for “bleed off” of HP P3 air. This
air is used in conjunction with the environmental
and ice-protection systems.
To prevent engine surge, a bleed valve actuator
(BVA) controls pressure in the compressor
section of the engine. Compressor surge is
managed by bleeding off pressure as required
during the different phases of operation to the
fan bypass duct. This process is controlled by
the FADEC throughout the engine operating
envelope.
Nacelles and Covers
The engine nacelles (cowlings) are aluminum
and consist of the inlet, upper, and lower nacelle
doors, and the aft nacelle assembly. The leading
edge of the inlet is heated with engine bleed
air for anti-icing purposes (see Figure 7-1).
When engine anti-ice is operated, and
for some time after, the nacelle leading
edge and starter-generator cooling
inlet may be extremely hot and cause
burns to skin. Avoid direct contact.
The upper and lower nacelle doors are attached
using quarter-turn fasteners, which
allow for quick access to the engines for maintenance
or inspection (Figure 7-5).
On the lower outboard side of each of the
lower nacelles is an oil door, which provides
the crew with easy access to the oil level sight
glass (Figure 7-6).
A spring-loaded closed door is provided on
each lower nacelle (outboard on the right nacelle
and inboard on the left nacelle), allowing
for a visual inspection of the oil filter bypass
indicator.
Engine contamination is possible from many
sources and may cause engine damage. These
sources include:
• Hail
• Condensation and freezing
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