Steven M. Summer

This report discusses experiments to determine the reduction in oxygen concentration required to prevent a fuel tank explosion. A simulated aircraft fuel tank containing JP-8 fuel of an amount equivalent to a mass loading of approximately 4.5 kg/m3 was used to determine the limiting oxygen concentration (LOC) at pressures corresponding to altitudes ranging from 0 to 38,000 ft. In addition, the peak pressure rise was measured at various altitudes (pressures) due to ignition occurring at O2 levels approximately 1% to 1.5% above the LOC.

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/arcs as ignition sources at sea level showed little variation in results, with the LOC ranging from 11.9% to 12.8%. The single ignition event falling below 12% O2 is attributed to inherent error in the oxygen measurement system, whose sensitivity is stated to be ±1% of the full-scale value (25% O2). In addition, a heated surface capable of igniting a flammable 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.

Harry Webster

This report documents the findings of a series of tests conducted to determine the flammability characteristics of primary lithium batteries and the dangers associated with shipping them in bulk form on commercial transport category aircraft.

Michael Burns, William M. Cavage, Richard Hill, & Robert Morrison

Extensive development and analysis has illustrated that fuel tank inerting could potentially be cost-effective if air separation modules (ASM), based on hollow-fiber membrane technology, could be used in an efficient way. To illustrate this, the Federal Aviation Administration has developed an onboard inert gas generation system that uses aircraft bleed air to generate nitrogen-enriched air (NEA) at varying flow and purity (oxygen concentration) during a commercial airplane flight cycle. A series of ground and flight tests were performed, in conjunction with Airbus, designed to prove the simplified inerting concept. The system was mounted in the cargo bay of an A320 operated by Airbus for the purposes of research and development and used to inert the aircraft center wing fuel tank during testing. The system and center wing fuel tank were instrumented to allow for the analysis of the system performance and inerting capability.

The results of the tests indicated that the concept of the simplified inerting system is valid and that the air separation module dynamic characteristics were as expected. ASM pressure had the expected effect on flow rate and purity; however, bleed air consumption was greater than expected during cruise. The fuel tank inerting results illustrated that no stratification or heterogeneous oxygen concentrations occurred in the tank. The measured average tank ullage oxygen concentration data agreed well with a simple analytical model applied to the flight test data. The measured effect of the high-flow mode was significant, allowing the single-membrane configuration to maintain an inert ullage during the entire flight cycle, even with the very high rate of descent employed for the flight tests. Fuel had virtually no effect on the resulting oxygen concentrations observed in all the tests.

Cesar Gomez

There is a need to clarify the wire flammability compliance requirements specified in the latest amendments of Title 14 Code of Federal Regulations and the Airworthiness Manual (CFR/AWM) for the detailed specification sheet MIL-W-22759/16. CFR requirements prescribe a 60 degree flammability test for the MIL-W-22759 specification sheet, while MIL-W-22759/16 calls for a vertical flammability test. Confusion lies as to which of the requirements should be followed. This technical note will show how the MIL-W-22759/16 specification sheet satisfies both flammability requirements.

John W. Reinhardt

This technical note presents the data from simulated aerosol can explosion tests while using bromotrifluoropropene (BTP) and pentafluoroethane (HFC-125) as fire suppression agents for aircraft cargo compartments. These explosion tests were conducted at below inert volumetric concentrations to determine the agent’s explosion attenuation performance. The tests were conducted inside a 402-ft3 pressure vessel. The collected data showed that BTP and HFC-125, at these below inert concentrations, enhanced the explosion (acted as fuel) instead of mitigating it.