03-12-02IASFPWG – Seattle, WA

Fuel Tank Ignition Experiments at Reduced Oxygen Concentrations

International Aircraft Systems Fire Protection Working GroupSeattle, WAMarch 12 – 13, 2002

Steve SummerProject EngineerFederal Aviation AdministrationFire Safety Section, AAR-422

03-12-02IASFPWG – Seattle, WA

Where’s the final report?

03-12-02IASFPWG – 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.

03-12-02IASFPWG – 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.

03-12-02IASFPWG – Seattle, WA

Facilities – Pressure Chamber

03-12-02IASFPWG – Seattle, WA

Facilities – Pressure Chamber353 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.

03-12-02IASFPWG – 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

03-12-02IASFPWG – Seattle, WA

Apparatus – LOC Testing

TH C A nalyzer

R igh t Test Track

Left Test Track

1 0 m P ressu re Vesse l

3 Ana lyze r Byp a ss

Sa m p le Line O A nalyzer

2

H eaterH eater

Spark Source

Fan

= Therm ocouple Feed through

N L ines2

H ouse A ir L ine

03-12-02IASFPWG – Seattle, WA

Apparatus – LOC Testing

R ig h t T /C T re eL e ft T /C T re e

L iq u id J P -8 F u e lF u e l P a n

= T h e rm o c o u p le B e a d

6.0"

6.0"

03-12-02IASFPWG – Seattle, WA

Ullage Vapor Sampling

03-12-02IASFPWG – Seattle, WA

Ullage Vapor Sampling

03-12-02IASFPWG – 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

03-12-02IASFPWG – Seattle, WA

Results – LOC Tests (Al. Plate)

03-12-02IASFPWG – Seattle, WA

Results – LOC Tests (Foil Diaphragm)

03-12-02IASFPWG – Seattle, WA

Results – LOC Tests (Foil Diaphragm)

03-12-02IASFPWG – Seattle, WA

Test ProgramIgnition 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.

03-12-02IASFPWG – Seattle, WA

Results – Pressure Tests with Pressure Relief

03-12-02IASFPWG – Seattle, WA

Results – Pressure Tests with Pressure Relief

03-12-02IASFPWG – Seattle, WA

Results – Pressure Tests without Pressure Relief

03-12-02IASFPWG – 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)

03-12-02IASFPWG – Seattle, WA

LEL Tests - Results

03-12-02IASFPWG – 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.

03-12-02IASFPWG – 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.