Limiting Oxygen Concentration LOC Work Update

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Limiting Oxygen Concentration (LOC) Work Update

• International Aircraft Systems Fire Protection
  Working Group
• Atlantic City, NJ
• November 5 - 6, 2003

Steve Summer Project Engineer Federal Aviation
Administration Fire Safety Branch, AAR-440
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LOC Testing Work Update

• Technical Note consisting of all data except 400
  cycle short tests published and placed on website
  (AR-02/79)
• 400 cycle short spark energy has been measured
  and testing has been completed
• Final report currently being put together

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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.
• Spark gap.
• 2 tungsten electrodes with controllable gap
  alignment and spacing

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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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LOC Testing Apparatus

• Ignition Sources
• 10 kV Oil burner transformer operating at 30 mA
  provided both long (1 second) and short (0.1
  second) arcs
• J-57 Engine spark igniter provided a very short
  (175 msecond) spark
• 3" x 6" x 1" metal block heated by two cartridge
  heaters to temperature in excess of 1400F
• 400 cycle, 120 V hard short to ground provided
  high energy/current, short duration spark
• Energy Measurements
• Voltage and current traces were taken using a HV
  and current probe at the spark gap connected to
  oscilloscope

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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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Test Program (cont.)

• Tests conducted initially at all altitudes with
  long duration oil burner transformer arc (0.5 J,
  1 s)
• Subsequent tests conducted with various ignition
  sources at sea level in effort to determine any
  variation of LOC with ignition source
• Short duration oil burner transformer arc (0.08
  J, 0.1 s)
• J-57 Engine igniter spark (0.5 J, 175 ms)
• Hot surface vapor ignition (HSVI)
• 400 cycle, 120 V hard short to ground

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400 Cycle Hard Short Tests
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Spark Energy Measurements
Energy 2.8 J Duration .01 s
Energy 2.2 J Duration .006 s
Energy 1.75 J Duration .01 s
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400 Cycle Short Test Results
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Summary

• 2 J spark from 400 cycle short did not cause a
  change in the LOC at sea level
• Of all ignition sources used (oil burner arc,
  engine ignitor spark, hot surface, 400 cycle
  short), none have caused an ignition with ullage
  above 12 O2
• Testing is complete and final report will be
  published and available on website ASAP