William M. Cavage

Recent Federal Aviation Administration research has illustrated that fuel tank inerting could be practical in the commercial fleet for the protection of center wing or body style tanks. The effect of pressure differences on the release of dissolved oxygen in a fuel load on an inert fuel tank ullage was studied. A test article was constructed and experiments were conducted to quantify the potential increase in oxygen concentration in an adjacent inert ullage as a result of gases in fuel during sea level stimulation, as well as at reduced atmospheric pressure. Different methods of stimulating the release of gases from the fuel were examined during laboratory experiments in an attempt to quantify the increase in oxygen concentration in an inert aircraft fuel tank ullage. This data was compared with flight test data in an attempt to gage the ability of laboratory tests and simple calculations to predict the resulting change in oxygen concentration of an inert commercial airplane fuel tank during a flight cycle.

The oxygen evolution from different fuel loads was measured to determine the resulting oxygen concentration on an adjacent ullage. At sea level, the increase in oxygen concentration can be as great as 7 percent for an ullage inerted to 6 percent with an 80 percent fuel load that was stimulated. Increasing altitude allows for an additional increase in the oxygen concentration of the ullage even if the ullage was at equilibrium at sea level. Inerting the ullage through fuel has the effect of scrubbing the fuel to some rudimentary level of protection that reduces or eliminates the increase in oxygen concentration due to fuel air evolution, depending upon fuel load. Flight test data illustrated a relatively small amount of oxygen evolving from fuel compared to the theoretical amount available. Any effect of oxygen concentration increase due to fuel tended to be obscured by the more dominant effect of air entering the vent due to fuel consumption. Oxygen concentration flight test data with consumed fuel loads and inert ullages were best duplicated in laboratory experiments by not stimulating the fuel. Calculations of oxygen concentration increase have poor agreement with flight test data, but the flight test oxygen concentrations results fall within the band of 0 and 100 percent oxygen evolution.

John W. Reinhardt

This technical note presents the second update to the minimum performance standards that a Halon 1301 replacement or alternate system for aircraft cargo compartment must meet as part of the aircraft certification procedures. This document replaces report number DOT/FAA/AR-TN03/6. This standard considers gaseous and nongaseous fire suppression systems for full-scale fire testing. This report update includes the corrections made to the aerosol can simulator specifications, acceptance criteria section, and the new criteria for the aerosol can explosion test. In addition, some sections were added to the test requirements to clarify some testing procedures.

Richard E. Lyon and Marc L. Janssens

This report provides an overview of polymer flammability from a materials science perspective and describes currently accepted test methods to quantify burning behavior. Simplifying assumptions about the gas and condensed phase processes of flaming combustion provide mathematical relationships between polymer properties, chemical structure, flame resistance, and fire behavior that can be used to design fire-resistant plastics.

Richard E. Lyon Ph.D & David Blake

The heat release rate of objects burning in a relatively large, simply ventilated cargo compartment is reconstructed from the oxygen consumption history of the exiting gas stream, assuming perfect mixing of the combustion gases in the compartment. The model was calibrated using a premixed propane gas burner to generate a variety of well-defined heating histories. Qualitative agreement between actual and computed heat release rate histories is obtained when the duration of the burning is on the order of 1/2 of the mixing time of the compartment. This research supports efforts by the Federal Aviation Administration to develop new certification requirements for aircraft cargo compartment fire detectors.

Michael Burns, William M. Cavage, Robert Morrison, & Steven Summer

Extensive development and analysis has illustrated that fuel tank inerting could, potentially, be cost-effective if air separation modules, based on hollow-fiber membrane technology, could be packaged and used in an efficient way. To illustrate this, the Federal Aviation Administration (FAA) has developed a prototype onboard inert gas generation system that uses aircraft bleed air to generate nitrogen-enriched air (NEA) at varying flows and purities during a commercial airplane flight cycle. A series of ground and flight tests were performed, in conjunction with National Aeronautics and Space Administration (NASA) aircraft operations personnel, designed to evaluate the FAA inerting system used in conjunction with a compartmentalized center wing tank (CWT). Additionally, the flammability of both the CWT and one inboard wing fuel tank was measured. The system was mounted on a Boeing 747, operated by NASA, and used to inert the aircraft CWT during testing. The inerting system, CWT, and the number 2 main wing tanks were instrumented to analyze the system performance, fuel tank inerting, and flammability.

The results of the testing indicated that the FAA prototype inerting system operated as expected. Using a variable-flow methodology allowed a greater amount of NEA to be generated on descent when compared to the simple dual-flow methodology, but it had no measurable effect on the resulting average ullage oxygen concentration after each test, while improving inert gas distribution by decreasing the worst bay oxygen concentration when three similar tests were compared. The highest average ullage oxygen concentration observed on any flight test correlates directly with the worst bay oxygen concentration, illustrating the importance of maintaining a low average ullage oxygen concentration in good inert gas distribution. Oxygen diffusion between the bays of the tank was relatively rapid, and overnight dispersion of the ullage oxygen concentration was measured to be very small. Flammability measurements showed trends very similar to what was expected based on both experimental and computer model data. The equilibrium data agreed favorably with data from both the Fuel Air Ratio Calculator and the Condensation Model, while transient data trends matched closely with the Condensation Model with some discrepancies in total hydrocarbon concentration magnitude at altitude.