Fuel Tank Ignition Experiments at Reduced Oxygen Concentrations

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Fuel Tank Ignition Experiments at Reduced Oxygen
Concentrations

• International Aircraft Systems Fire Protection
  Working Group
• Seattle, WA
• March 12 13, 2002

Steve Summer Project Engineer Federal Aviation
Administration Fire Safety Section, AAR-422
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Wheres the final report?
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Wheres 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.
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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.

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Facilities Pressure Chamber
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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.

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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

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Apparatus LOC Testing
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Apparatus LOC Testing
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Ullage Vapor Sampling
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Ullage Vapor Sampling
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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

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Results LOC Tests (Al. Plate)
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Results LOC Tests (Foil Diaphragm)
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Results LOC Tests (Foil Diaphragm)
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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.

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Results Pressure Tests with Pressure Relief
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Results Pressure Tests with Pressure Relief
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Results Pressure Tests without Pressure Relief
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Test Program

• LEL Tests
• Oxygen Concentration of 21
• Altitudes of 0 and 38 kft
• THC concentration varied to the point of
  non-ignition (LEL)

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LEL Tests - Results
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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.

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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.