# Presentation: 658339

## 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

## Where’s the final report?

## 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.

## 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.

## Facilities – Pressure Chamber

## 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.

## 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.
- 1⁄4-in. aluminum plate.
- Foil diaphragm.
- Ignition source.
- 2 tungsten electrodes powered by 10 kV transformer operating at ~20 mA, providing 200 J/s

## Apparatus – LOC Testing

## Apparatus – LOC Testing

## Ullage Vapor Sampling

## Ullage Vapor Sampling

## 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
- 1⁄4-in. aluminum plate
-  Ignition = movement of plate
- Foil diaphragm
- Ignition = rupture of foil

## Results – LOC Tests (Al. Plate)

## Results – LOC Tests (Foil Diaphragm)

## Results – LOC Tests (Foil Diaphragm)

## 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.

## Results – Pressure Tests with Pressure Relief

## Results – Pressure Tests with Pressure Relief

## Results – Pressure Tests without Pressure Relief

## Test Program

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

## LEL Tests - Results

## 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.

## 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.