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Fuel Tank Ignition Experiments at Reduced Oxygen Concentrations. Steve Summer Project Engineer Federal Aviation Administration Fire Safety Section, AAR-422. International Aircraft Systems Fire Protection Working Group Seattle, WA March 12 – 13, 2002. Where’s the final report?.
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Fuel Tank Ignition Experiments at Reduced Oxygen Concentrations Steve Summer Project Engineer Federal Aviation Administration Fire Safety Section, AAR-422 International Aircraft Systems Fire Protection Working Group Seattle, WA March 12 – 13, 2002 IASFPWG – Seattle, WA
Where’s the final report? IASFPWG – Seattle, WA
Where’s the final report? After October conference, the decision was made to run some more experiments at a near-stoichiometric concentration, as well as some other test sets. IASFPWG – Seattle, WA
Objectives • Determine the Lower Oxygen Content (LOC) at altitudes ranging from 0 – 40 kft. • What is the O2 concentration, below which ignition of the ullage fuel vapors will not occur? • How does this effect fuel tank inerting requirements? • Measure ignition pressure at several ‘key’ test points. • Determine the Lower Explosion Limit (LEL) of JP-8 vapors at 0 and 38 kft. IASFPWG – Seattle, WA
Facilities – Pressure Chamber IASFPWG – Seattle, WA
Facilities – Pressure Chamber • 353 ft3 pressure vessel • Working pressure of 650 psi. • Attached vacuum pump used to evacuate chamber to reduced pressures seen at altitude. • Not capable of simulating temperatures seen at altitude. IASFPWG – Seattle, WA
Facilities - LOC Test Article • 9 ft3 simulated fuel tank placed inside of vessel equipped with: • Bottom surface heaters. • 12 thermocouples. • 2 piezoresistive pressure transducers mounted behind sintered porous metal discs. • Interchangeable pressure relief mechanism. • ¼-in. aluminum plate. • Foil diaphragm. • Ignition source. • 2 tungsten electrodes powered by 10 kV transformer operating at ~20 mA, providing 200 J/s IASFPWG – Seattle, WA
Apparatus – LOC Testing IASFPWG – Seattle, WA
Apparatus – LOC Testing IASFPWG – Seattle, WA
Ullage Vapor Sampling IASFPWG – Seattle, WA
Ullage Vapor Sampling IASFPWG – Seattle, WA
Test Program • JP-8 LOC Tests • Mass Loading ~ 4.5 kg/m3 • Ambient pressure corresponding to altitudes of 0, 10, 20, 30 and 38 kft • Ullage oxygen concentrations ranging from 21% to below the determined LOC • Tests conducted with two different pressure relief mechanisms • ¼-in. aluminum plate • Ignition = movement of plate • Foil diaphragm • Ignition = rupture of foil IASFPWG – Seattle, WA
Results – LOC Tests (Al. Plate) IASFPWG – Seattle, WA
Results – LOC Tests (Foil Diaphragm) IASFPWG – Seattle, WA
Results – LOC Tests (Foil Diaphragm) IASFPWG – Seattle, WA
Test Program • Ignition Pressure Tests • Tests with pressure relief (i.e. foil diaphragm) • Piezoresistive transducer placed behind sintered porous metal discs. • O2 concentrations 1 – 1.5% above LOC. • Pressure corresponding to 0, 10, 20 & 30 kft. • Tests without pressure relief (i.e. full vessel) • Diaphragm type transducer placed behind flash arrestor. • O2 concentrations ~1.5% above LOC. • Pressure corresponding to 20 & 38 kft. IASFPWG – Seattle, WA
Results – Pressure Tests with Pressure Relief IASFPWG – Seattle, WA
Results – Pressure Tests with Pressure Relief IASFPWG – Seattle, WA
Results – Pressure Tests without Pressure Relief IASFPWG – Seattle, WA
Test Program • LEL Tests • Oxygen Concentration of 21% • Altitudes of 0 and 38 kft • THC concentration varied to the point of non-ignition (LEL) IASFPWG – Seattle, WA
LEL Tests - Results IASFPWG – Seattle, WA
Conclusions • LOC is a linear function of altitude, going from ~12% at 0 kft to ~16% at 38 kft. • Peak pressure rise decreases in an exponential trend as a function of altitude. • Oxygen concentration has a slight effect on ignition pressure. • Time duration to reach peak pressure increases in an exponential trend as a function of altitude. • LEL shifted slightly to the right as altitude was increased from 0 to 38 kft. IASFPWG – Seattle, WA
Future Plans • Conduct ignition pressure tests without pressure relief at lower altitudes. • Conduct a thorough investigation of the LEL dependence on O2 concentration and altitude. • A paper detailing the LOC tests will be composed and published shortly. IASFPWG – Seattle, WA