Aviation Fuels with Improved Fire Safety A Proceedings (1997) / Chapter Skim
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I. Summary of Workshop
I. Summary of Workshop
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Chapter 1 provides information on the history of fuel fire-safety research and practices, and places the problem in a policy context. Chapter 2 presents workshop discussions on fuel and additive technologies, aircraft fuel system requirements, the characterization of fuel fires, and fuel fire-safety strategies.
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Current designers of commercial and military aircraft incorporate a broad array of fire safety features, such as firewalls, shrouded and break-away fuel lines, flame arrestors, fuel-line isolation, explosion-proof electromechanical equipment, detectors and extinguishing systems, and fire-resistant materials, into their designs. In the last decade, a range of new requirements have imposed stringent fire safety standards on civil aircraft.
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. Similarities between diesel fuel and low-volatility aviation kerosenes have created a synergism between fire safety research on Army tanks and research on aircraft fuel safety.
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The Aviation Safety Research Act of 1988 required that the FAA undertake research on low-flammability aircraft fuels. In his 1988 congressional testimony on fuel safety, then FAA Administrator T
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Workshop discussions are summarized in this chapter according to topic- fuel and additive technologies, requirements for aircraft fuel systems, the characterization of fuel fires, and fire inerting and suppression technologies. FUEL AND ADDITIVE TECHNOLOGIES Aviation kerosene consists mostly of hydrocarbon molecules with eight to sixteen carbon atoms arranged in various molecular configurations.
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Fire-safe fuel additives must not be adversely reactive either with existing aircraft fuels or with additives already in use, such as antistatic compounds, antioxidants, corrosion inhibitors, and metal deactivators. A viable fire safety additive has to be an integral chemical component of the kerosene formulation and must have predictable, measurable, and consistent characteristics.
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Altering fuels to add fire safety features for the case of an aircraft crash may very well cause problems with fuel performance during normal operation. Workshop participants discussed barriers to the implementation of fire-safe fuels and additives presented by interrelations among fuel specifications, fuel system requirements, and the operational requirements of existing aircraft.
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Fuel tank capacity and sensor circuits are designed with electrical power requirements an order of magnitude lower than the minimum spark ignition energy of 0.2 mJ Fuel vent ports from aircraft surge tanks are located inboard of the lightning strike zone, and tank structure is designed to prevent internal sparking in case of a lightning strike. Additional fire safety design features include the strategic placement of fuel drain masts, shrouded fuel lines within the aircraft pressure hull, flame arrestors in vent lines, fireproof hose assemblies in engine nacelles, the separation of fuel lines from electrical wiring, and the ventilation of compartments and bays where fuel vapor can accumulate.
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These computational tools were presented to the workshop as a cohesive engineering framework based on laminar diffusion flamelet concepts and classical turbulence models. Universal state relationships can be used to correlate various fluid properties with the degree of mixing predicted by turbulence models.
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Some participants felt that the type of fuel safety research done in the past could not be contemplated in today's climate because the private sector would be unlikely to invest resources in a long-term fuel safety research program without AVIATION FUELS WITH IMPROVED FIRE SAFETY: A PROCEEDINGS government support, and the government would be unlikely to commit large resources for an engineering demonstration of an industry sample product without a substantial systems analysis of the costs, benefits, and likelihood of success. Hence, for economic reasons, as well as for technical reasons, a future fuel safety research program will have to be grounded in fundamental research and subscribed to by all stakeholders.
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Advances in the understanding of polymer rheology complement the technical advances in the petroleum industry described above. Workshop participants discussed several advances that could help in the development of fuel additives, including: · molecular modeling techniques that allow for designing and tailoring polymer and surfactant systems with specified characteristics at the microstructural level advances in measuring extensional viscosity that can identify composition effects for very dilute polymer systems and for solutions of association polymers techniques for making dynamic theological measurements that can characterize polymer-solvent interaction at the microstructural level theological modeling methods that provide means for relating non-Newtonian flow behavior to the microstructure of polymer systems In principle, the capability exists of employing theological methods and molecular design techniques to develop polymer and surfactant additives that would thermally self-degrade prior to injection into the combustor, rather than requiring a mechanical degrader to restore acceptable fuel flow characteristics.
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Fuel performance specifications have evolved in the areas of combustion performance, fuel thermal behavior, flow characteristics, and materials compatibility. The workshop participants discussed several fire-safe design features already used in aircraft systems: · preventing the ignition of fuel vapor by electrical sources using several methods including electrical bonding of components to the airframe to prevent discharges of static electricity and discharges induced by electromagnetic-fields, the use of explosion-proof electromechanical equipment, the use of low power fuel tank capacity and sensor circuits, locating fuel vent ports from aircraft surge tanks inboard of the lightning strike zone, and designing the tank structure to prevent internal sparking during a lightning strike the strategic placement of fuel drain masts shrouded fuel lines within the aircraft pressure hull flame arrestors in vent lines fireproof hose assemblies in engine nacelles separating fuel lines from electrical wiring ventilating compartments and bays where fuel vapor can accumulate · preventing fuel leaks by fuel line stretch flexibility, fuel shutoff capability outside the engine fire zone, and duplicate wiring to the shutoff valve actuator Military and civil aircraft vary widely in terms of age and technologies.
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can delay aircraft fuselage burnthrough as a result of external fuel fires. RESEARCH OPPORTUNITIES Workshop participants discussed six primary areas of opportunity for long-term research to establish performance goals, evaluate potential fuel additives and modifications, and develop fundamental capabilities to model the complex phenomena that need to be considered in the development of fuels with improved fire safety.
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. combination · extending methods for analyzing the atomization and combustion of fuel sprays to fuel systems with nonNewtonian flow characteristics
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