Cold Ambient Temperature Effects on Heated Fuel Tank Vapor Concentrations

摘要

Experiments were conducted within a simulated aircraft center wing fuel tank(CWT) to qualitatively analyze the effects of decreased ambient temperatures, such as might occur at increased altitudes, on the vapor concentrations found in a typical CWT ullage. A small quantity of fuel in the CWT test article was heated to 125 deg. F for two hours, corresponding to a temperature of approximately 10 deg. F above the flashpoint of the fuel. The tests were conducted at sea level (14.7 psia), however, the wall temperature of the tank was cooled to a temperature corresponding to a given altitude. The following real-life scenarios were simulated: (1) Baseline Test: The environmental conditioning system (ECS) packs are run for two hours while the aircraft is on the ground. After some time, the packs are turned off, and the aircraft remains on the ground. (2) Low-Altitude Test: The aircraft, after running its ECS packs, takes off and climbs to a low altitude, of approximately 9,000 ft, cooling the CWT to approximately 55 deg. F; (3) Intermediate-Altitude Test: The aircraft, after running its ECS packs, takes off and climbs to an intermediate altitude of approximately 22,000 ft, cooling the CWT to 15 deg. F; (4) High-Altitude Test: The aircraft, after running its ECS packs, takes off and climbs to a full altitude of approximately 30,000 ft, cooling the CWT to -20 deg. F. From these tests, it was determined that the ambient temperature does indeed have a significant effect on the vapor concentrations formed in the fuel tank ullage at small fuel mass loadings. When allowed to cool naturally to the room's ambient temperature (-75 deg. F), the fuel-air ratio decreased at an average rate of 1.07 x 10(sup -5) min(sup -1) for the low-altitude test, it decreased at an average rate of 7.50 x 10(sup -5) min,