Aviation Fuels with Improved Fire Safety A Proceedings (1997) / Chapter Skim
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II. Presented Papers: Fuel and Additive Technologies
II. Presented Papers: Fuel and Additive Technologies
Pages 17-58
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ll PRESENTED PAPERS FUEL AND ADDITIVE TECHNOLOGIES
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Army Fuels & Lubricants Laboratory in San Antonio, Texas, to consider problems involving fuel fires in military vehicles. This is a substantial problem because many military vehicles, tanks and the Bradley vehicle, for example, are run by diesel engines where the fuel doubles as engine coolant.
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Since the utility of the emulsion as a fuel depends on its ability to burn, it is obvious that this clue must be employed with some caution. All of the papers I consulted in preparing this presentation on the use of surface-active agents have included very AVIATION FUELS WITH IMPROVED FIRE SAFETY: A PROCEEDINGS conventional surfactants in the formulations.
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Candidate "fire-safe" fuels should have the availability, reasonable cost, and suitable physical and chemical properties for direct utilization in operational aircraft without extensive fuel system modifications or serious degradation of aircraft performance. Because of these stringent requirements, most of the successful efforts to reduce the aircraft fire hazard have been inprovement in prevention and protection areas rather than development of TABLE 5-1 Comparison of the Properties of Aviation Fuels f~re-safe fuel.
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The study team reported that: The second approach to the search for fire-safe fuel involves modifying the fuel to reduce the ignition and flame propagation of mists and sprays normally associated with neat fuels in a crash situation. This approach has few fire safety benefits for neat fuels with high vapor pressures, i.e., for low flash point fuels (Gandee and Clodfelter, 19741.
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It is possible that an AMK-type fire-safe fuel could be developed in the distant future. Against this backdrop, a brief discussion of jet fuels, fuel flammability, the fire problem (including fire prevention and protection techniques)
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AVIATION FUELS WITH IMPROVED FIRE SAFETY: A PROCEEDINGS Heater (a) Stirrer FIGURE 5-4 Autoign~uon temperature (AIT)
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flash point test involves downward flame propagation Can the number of aviation fatalities and injuries be re whereas the lower flammability limit test involves upward flame propagation. Because upward flame propagation is easier to achieve than downward flame propagation, it re quires fewer fuel vapors at a lower temperature.
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. · terrorist achv~t~es AVIATION FUELS WITH IMPROVED FIRE SAFETY: A PROCEEDINGS Figure 5-6 illustrates the relative rate of fuel-vapor generation and the flammability volume associated with a fuel spill at ambient conditions for kerosene, JP-4, and gasoline.
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As a result of the recent TWA 800 accident, fuel tank inerting systems will be conscientiously reconsidered for commercial aircraft. -80 -40 0 40 80 120 160 200 240 280 COST~ENEFIT ANALYSIS Liquid Fuel Temperature, OF FIGURE 5-9 Flame spread across a jet fuel spill.
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I · flight safety (fuel tanks, dry bays, engine compart ments) FIGURE 5-10 Fire problem associated with projectiles piercing the fuel · safety hazards tank.
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of a system is the total cost at the end of its lifetime, including all expenses for research and development, production, modification, transportation, introduction of the item/system into the inventory, new facilities, training, performance, operations, support, maintenance, disposal, and any other TABLE 5-5 Effects of Fuel Properties on Aircraft Performance and Fire Safety Fuel Property Best for Operations Best for Fire Safer Heat of Combustion high Flash Point depends Viscosity Density Atom~zanon Vapor Pressure Freeze Point Thermal Stability Resisuvity low high high depends low high unknown low high high low low low 29 costs of ownership penalties, less any salvage revenue at the end of its lifetime. LCC by itself is useful only when two or more competing items/systems provide the same total benefits or the same performance.
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The "+100" denotes an increase in the upper limit for the fuel at the combustor nozzles from 325°F to 425°F. In terms of hire safety, these trends mean a higher probability of flammable mixtures in fuel tanks with the current fuels, a higher probability of hot surface ignition, a faster buildup of flammable zones, and larger flammable zones associated with fuel release into aircraft compartments or on the ground.
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Such complex behavior cannot be characterized purely in terms of simple parameters, such as the material viscosity or elastic modulus. One of the objectives of this paper is to indicate the possible applications of rheology towards designing improved aviation fuels.
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. If the same experiment is run in a container of polymeric fluid, the flow changes directions and moves toward AVIATION FUELS WITH IMPROVED FIRE SAFETY: A PROCEEDINGS (b)
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STEADY SHEAR RHEOLOGY Simple steady-shear flow is the easiest flow to generate and is, therefore, of central importance in rheology. Most of the theological data reported in the literature is for steadyshear material functions.
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In the simplest case, the sample shows Newtonian behavior at low shear rates and shear thinning at higher shear rates (Figure 6-4b)
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shear stress and shear rate; and (d) shear thickening.
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The above analysis assumes that the measurements are AVIATION FUELS WITH IMPROVED FIRE SAFETY: A PROCEEDINGS made in the "linear viscoelastic" (LYE) regime of the sample under consideration (Ferry, 19804.
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in the network. In steady shear, a gel will show a yield stress at low shear, followed by shear thinning at higher shear rates.
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`~log G' log G" log G' log G" log G' log G" G.. lo/ ~ / G' it- /2 109 co 109 co 109 co FIGURE 6-6 Dynamic rheology and microstructure of colloidal dispersions.
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As the molecular weight increases, shear thinning begins to set in at lower shear rates. From a microstructural point of view, shear thinning reflects a decrease in the density of entanglement with increasing shear because of progressive stretching and uncoiling of polymer chains (Ferguson and Kemblowski, 1991~.
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AVIATION FUELS WITH IMPROVED FIRE SAFE7-Y: A PROCEEDINGS cone and a flat plate. The cone angle is denoted to be a, and the radius of the cone/plate is R
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Consider the rheology of a polymeric melt under steady-shear as well as extension, as represented schematically in Figure 6-10. The steady-shear viscosity ~ is constant at low shear rates and decreases at higher shear rates (shear thinning behavior)
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Its corresponding dispersion shows shear thinning over the entire range of shear-rates, and the viscosity at low shear rates is significantly higher than for the A200 silica dispersion. In order to study the at-rest microstructures, we resort to dynamic theological measurements.
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At low concentrations, the initial Newtonian plateau is followed by an intermediate range of mild shear thickening and then a region of drastic shear thinning. At high concentrations, the shear thickening is no longer observed but a viscosity plateau exists at intermediate stresses.
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Note that the molecular structure of the surfactant is crucial to its behavior; other types of surfactants can produce the reverse effect, i.e., they can reduce the elastic character of the system. RHEOLOGY OF AVIATION FUELS Currently, the fuels used in the gas-turbine engines of commercial aircraft are kerosene-based jet fuels (Hutchinson, 19951.
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Future research on aviation fuels might involve designing new additives and considering alternate fuels to prevent fire in "survivable" crashes. Possible additives are combinations of associative polymers and surfactants to produce materials with "tunable" properties.
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Chemistry of Materials 6:2359-2363. AVIATION FUELS WITH IMPROVED FIRE SAFETY: A PROCEEDINGS Kroes, M.J., and T.W.
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Most civil and military jet fuels are kerosene-based and are predominantly straight-run distillates. Processing and finishing steps can vary considerably and include both chemical treatment and catalytic treatment with hydrogen.
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Unlike other transportation fuels, aviation fuel specification requirements are deemed absolute in ASTM D 1655. Every batch of jet fuel is tested to prove its conformance to all specification requirements, and test results are not subject AVIATION FUELS WITH IMPROVED FIRE SAFETY: A PROCEEDINGS to correction for tolerance of test methods.
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Clay treatment using attapulgus clay is employed to remove trace levels of sodium carboxylate salts left in the fuel and/or other trace polar compounds. If the fuel blending stock contains excess odorous mercaptan sulfur compounds but acceptable total sulfur levels, it can be treated by a sweetening process (example 21.
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AVIATION FUELS WITH IMPROVED FIRE SAFETY: A PROCEEDINGS and phenols are also present and are limited by the acid number specification. A typical acid number specification limit of 0.015 mg KOH/g by ASTM D 3242 suggests an upper limit of approximately 60 ppm monocarboxylic acids in the jet fuel boiling range.
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~ 1 ::: :3 ~ ~ - .:: :.:.: :.:.:.: 1 ~] I_ FIGURE 7-3 Typical aviation fuel dishibudon system.
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3,917,466. AVIATION FUELS WITH IMPROVED FIRE SAFETY: A PROCEEDINGS Lieberman, M., and W
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A coannular fuel tank, with an inner space containing fuel and an outer space containing halon, has been demonstrated using halon 2402 but has not been implemented. A less vulnerable fuel has been developed using a high molecular weight polymer as an antimisting agent.
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The Purdue University study of 1950 AVIATION FUELS WITH IMPROVED FIRE SAFETY: A PROCEEDINGS also demonstrated that several agents were even more effective fire suppressants than halon 1301, namely C2F4I2 (5.0 percent) , C2F5I (5.3 percent)
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Because the fuel surface provides the vapor for a fire, enhancing the effectiveness of the agent at the fuel surface will enhance agent efficiency and improve its fire prevention potential. So, one idea is to provide surface-enhancement for halon replacements or alternatives.
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The agent would be concentrated where the fire was initiated with heat from the fire and hot surfaces releasing the fire prevention chemical. Self-Activating Powder Extinguishment Technology Dry chemical powders have been used as fire fighting agents for many years.
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1994. Evaluation of Alternative In-Flight Fire Suppressants for Full-Scale Testing in Simulated Aircraft Engine Nacelles and Dry Bays.
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