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pressure is applied to all internal tanks with WoffW. Pressurization is terminated for inflight refueling
(PROBE switch in EXTEND) and for arrested landing (both HOOK and LDG GEAR handles down).
The vent system provides over-pressure and over-fill relief for the internal tanks. Bleed air pressure
is applied to the vent lines in the two fuselage vent tanks. The vent lines connect all internal tanks and
are ported through the fuselage and vertical tail vent tanks to outlets located on the side of the vertical
tail. Normally, the vent lines contain only pressurized air; however, if a refuel valve failure overfills an
internal tank, fuel flows through the vent lines to the fuselage vent tanks. Two motive flow powered
vent tank scavenge pumps return this fuel from the fuselage vent tanks to the feed tanks.
Additionally, the vent system provides pressure relief of the internal fuel tanks during climbs and
vacuum relief during descents, if the pressurization system fails.
2.2.4 Thermal Management System. The hot fuel recirculation system uses fuel from the motive
flow/boost pump to cool the FADECs, liquid coolant, and AMAD and hydraulic oils. The output of the
motive flow/boost pump on each AMAD has four branches.
The first branch is used to run motive flow powered pumps and valves in the fuel system. The second
branch directs cooling flow to the FADEC and exits into the recirculation return line.
The third branch runs through the liquid cooling system (LCS)/fuel heat exchanger and the
combined AMAD oil and hydraulic oil/fuel heat exchanger in order to cool those fluids. A hot fuel
diverter valve in the third branch either directs fuel away from the engine and into the recirculation
return line or directs fuel to the engines where it is combined with fuel feed from the motive flow/boost
pump and burned.
Recirculated fuel first passes through a fuel/air heat exchanger bypass valve, which either directs the
fuel through or around the fuel/air heat exchanger. Then, the fuel passes through a diverter valve,
located in Tank 3, which either directs the fuel to the wing tanks or the feed tanks. Fuel directed to the
wing tanks then flows to Tank 4 for additional cooling. When Tank 4 is below 300 lb, recirculation fuel
is returned to the feed tanks by the Tank 4 scavenge pumps.
The fourth branch runs to the cross cooling valve which opens following a motive flow failure,
allowing one motive flow system to cool both FADECs and both engines' accessories.
A1-F18EA-NFM-000
I-2-16 ORIGINAL
When the system determines that more cooling is required (typically due to hot weather or low fuel
levels), the engine thermal control valve (TCV), located in the engine fuel control unit opens, directing
feed fuel into the recirculation return line. With the TCV open, greater cooling flow is induced through
the FADEC and the accessory heat exchangers, ultimately reducing system temperatures.
When sufficient recirculation fuel flow is present, the SDC opens the heat exchanger bypass valve
(Mach greater than approximately 0.35) to direct hot fuel through the fuel/air heat exchanger. At
normal operating temperatures, the TCVs are closed, and the fuel/air heat exchangers are bypassed.
When LCS fluid is cooler than recirculation fuel (extended ground operations at low fuel levels), the
LCS/fuel heat exchanger is used to remove heat from the fuel. With WonW, feed tank fuel
temperatures in excess of 40°C, ambient temperatures approximately 10°C cooler than feed tank
temperatures, and total fuel quantity less than 5,000 lb, the thermal management system activates the
radar coolant pump and the radar ground cooling fan (if not already on). With hot feed tank
temperatures, placing the RADAR switch OFF removes the radar as a heat source and aids LCS/fuel
cooling.
2.2.4.1 Fuel/Air Heat Exchanger. A fuel/air heat exchanger is located above each engine inlet, near
the leading edge. When the heat exchanger bypass valve is open, the heat exchanger uses inlet air to
provide additional fuel cooling. Air is drawn from the inlet through several banks of small pin holes
(bleed plates) and is exhausted through the spoiler opening on the upper surface of the LEX/fuselage.
2.2.4.2 Fuel/Air Heat Exchanger Leak Detection. Since a leak in the fuel/air heat exchanger can
result in engine fuel ingestion through the bleed plates, a leak detection system is incorporated. If a fuel
leak is detected during fuel/air heat exchanger operation, the SDC closes the heat exchanger bypass
valve and isolates the heat exchanger.
Leak detection logic is only capable of detecting a leak greater than approximately 400 pph. To
prevent an undetectable leak from being ingested, heat exchanger operation is inhibited when inlet
airflow is insufficient to keep this fuel out of the engine (Mach below approximately 0.35).
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本文链接地址：
NATOPS Flight Manual 飞行手册 1(38)
