- Author
- Summer, S. M.
- Title
- Limiting Oxygen Concentration Required to Inert Jet Fuel Vapors Existing at Reduced Fuel Tank Pressures. Final Phase.
- Coporate
- Federal Aviation Administration, Atlantic City International Airport, NJ
- Report
- DOT/FAA/AR-04/8, August 2004, 43 p.
- Keywords
- fuel tanks | oxygen index | jet fuels | flammability | inerting | nitrogen | fuels | vapors | ignition | JP-1 jet fuel | JP-8 jet fuel
- Identifiers
- ignition inert; limiting oxygen concentration; spark/arc energy calculation method and results; long-durabion oil burner transformer tests; engine spark igniter tests; hort-duration oil burner transformer tests; four hundred-cycle short to ground ignition tests; hot-surface vapor ignition tests
- Abstract
- Aircraft fuel tank protection has become of great importance within the aviation community since the fatal accident of TWA flight 800, a Boeing 747, over East Moriches, NY, in July 1996. The National Transportation Safety Board determined that the "probable cause of the TWA flight 800 accident was an explosion of the center wing fuel tank (CWT), resulting from ignition of the flammable fuel-air mixture in the tank." As a result, the Federal Aviation Administration (FAA) is conducting research aimed at reducing or eliminating the flammability exposure time of such heated CWTs. Much consideration is being given to the design and optimization of a system using nitrogen inerting. In this process, nitrogen or nitrogen-enriched air is used to reduce oxygen concentration within the fuel tank to a level that prevents the ignition of flammable ullage vapors. This type of system has been implemented in several military aircraft; however, the high cost and weight combined with low reliability make those designs impractical for transport category aircraft. Recent advances in gas separation technologies may make it possible to design an economic and reliable means of inerting commercial aircraft fuel tanks. However, to optimize such a system, more data on fuel flammability and inerting gas requirements are needed. The goal of the research effort discussed herein is to determine the oxygen concentration necessary to render the fuel tank ullage inert. This value is termed the limiting oxygen concentration (LOC). The tests were conducted at the FAA William J. Hughes Technical Center, Atlantic City International Airport, NJ, in a facility capable of creating pressures corresponding to altitudes ranging from 0 to 38,000 ft. From these tests, it was determined that the LOC at sea level through 10,000 ft is approximately 12% O2, with a linear increase from 12% at 10,000 ft to approximately 14.5% at 40,000 ft. Tests with various sparks and arcs as ignition sources at sea level showed little variation in results with the LOC ranging from 11.9% to 12.8%. In addition, a heated surface capable of igniting a fuel-air mixture proved insufficient for ignition in a tank inerted to just 14%. Peak pressures resulting from ignition at oxygen concentrations 1% to 1.5% above LOC values decreased as the altitude was increased to 30,000 ft, while the duration to reach the peak pressure increased. Further experiments to examine the rise in peak pressure as a function of both altitude and oxygen concentration are needed. The results contained in this report should be useful in the design, sizing, and optimization of future aircraft inerting systems and add to the overall knowledge base of jet fuel flammability characteristics.