Vaporization of JP-8 Jet Fuel in a Simulated Aircraft Fuel Tank ...

since jet fuel is typically not flammable under 100°F [13]. On the ground, the top wing
surfaces can be heated by sunlight. However, this is generally not a critical condition
because the liquid fuel is on the bottom fuel tank surface, and significant time is required
to heat the liquid to create a flammable mixture. The extra fuel required for larger
aircraft, such as a Boeing 747, is carried in the center wing tank, which is located in the
structural wing box within the fuselage and beneath the cabin. Figure 1.2 shows a
schematic of a Boeing 747 center wing tank. On flights where the fuel in the wing tanks
is sufficient to reach the destination, the CWT is left empty to save weight and increase
fuel efficiency [13].
In the case of TWA 800, the CWT had a fuel capacity of 12,890 gallons, but
contained only 50 gallons of fuel [2]. This small amount of fuel in the tank formed a
very thin liquid layer across the bottom surface, and any heat input into this fuel layer
could rapidly raise its temperature to above the flash point of the fuel, thus forming
combustible vapors in the ullage space. In some large commercial airliners with CWT’s,
environmental control system air conditioning packs (ECS packs) are located underneath
the CWT. These ECS packs “reduce the temperature and pressure of hot bleed air from
one or more of the airplane’s engines, the APU (auxiliary power unit), or the high-
pressure ground power carts during ground operations, to provide environmental control
(pressurization, ventilation, and temperature) to the cockpit and the main cabin” [13].
These packs remove heat from the hot bleed air and essentially use the CWT and
surrounding areas as a heat sink to dissipate the heat, thus raising the temperature of the
liquid fuel in the CWT.
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