Federal Aviation Measuring Oxygen Concentration in a Fuel Tank Ullage · Measuring Ullage Oxygen...

0Federal AviationAdministration

Measuring Ullage Oxygen ConcentrationNovember 17-18, 2009

MeasuringOxygen Concentration in a Fuel Tank Ullage

Federal AviationAdministration

ISFPWG Meeting

Atlantic City, NJ

November 17 - 18, 2009

William CavageAJP-6320 Fire Safety TeamWm. J. Hughes Technical CenterFederal Aviation Administration



• Background

• FAA Method

• Light Absorption Gas Sample

• Optical Fluorescence In Situ

• Status

Outline



• FAA has been seeking to improve fuel tank safety in the wake of TWA Flight 800 in July of 1996− Rule published requiring extensive flammability reduction on

both future built and existing aircraft on present types

• The measurement of ullage oxygen concentration is important to the fuel tank inerting community when researching methods, validating models, and certifying systems− FAA method for measuring ullage oxygen concentration at

reduced ullage pressures has been successful but can be cumbersome

− Emerging products have the potential to simplify and improve upon R&D / Certification work for fuel tank inerting

Background



FAA Method• FAA method involves an extensive controlled gas sample

system using lab based galvanic cell oxygen sensors− Method used extensively in the lab and on several flight tests with

great success− Consistently duplicates calibrations gases up to 40K feet within +/-

0.1% oxygen

• Improved FAA gas sampling method− Made design changes to OBOAS regulated sample train and

packaging based on lessons learned during FAA flight testing − New system is lighter, smaller, quieter, and takes less power to

start and operate− Gas sample lag time better but not proven to have equivalent level

of safety− Questions remains if it is more reliable and maintainable



FAA Oxygen Concentration Measurement Method

c

XX.XO2Analyzers

Cal Gas In

Sample Return

Sample Containment Box

c

c

cMotor

Motor

Motive In

Motive Out/Dump

Ventilation Air

XX.X XX.X XX.X XX.X

Ch4

Aux4

Ch3

Aux3

Ch2

Aux2

Ch1

Aux1

PressureController

Electronics ShroudPower InterfaceSignal Interface

- Flash Arrestor

- Check Valve

- Pump

- Bulkhead Fitting

- Pressure Controller

- Filter

- Sensor

- Selector Valve

- Flow Meter

Key

- Needle Valvec

- Pressure Regulator

- Air Inductor

- Flow Indicator



FAA Method Flight Test Results Compared with Lab and Analytical Calculation

0

2

4

6

8

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12

14

16

18

65 70 75 80 85 90 95 100 105 110 115

Time (mins)

Oxy

gen

Con

cent

ratio

n (%

vol

)

A320 Flight Test [O2]

Analytical Model [O2]

Scale Model [O2]

Comparison of Model Data - Average Ullage [O2]Airbus Test v1972 - Dual Flow System



4-Bay Cascading Inerting Data Comparison of FAA Method Compared with Analytical Calculation

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5

10

15

20

25

0 5 10 15 20 25 30 35 40

Time (mins)

Oxy

gen

Con

cent

ratio

n (%

vol

)

Bay 1 Bay 1 Bay 2 Bay 2 Bay 3 Bay 3 Bay 4 Bay 4

Comparison of Cascading Inerting Test with Model Data

Analytical Model Measured Data

Increasing Altitude

StableCruise

Decreasing Altitude



Light Absorption Gas Sample• Oxigraf makes a light absorption sensor which has been

applied to an unregulated gas sample train− Unregulated sample train uses an integrated sensor board that

measures infrared light absorption using a tunable laser diode (TLD technology)

− Proprietary software used to interpret spectral data

• System has been packaged for flight test− System has very fast response time, given short enough gas

sample lines and has been shown to duplicate calibration gases as well as FAA method up to 35K feet sample altitude.

− System packaging has potential to be significantly smaller and lighter than the FAA method and system requires less power.

− System speed has yet to illustrate usefulness and there are significant limitations to gas sample, and return locations



Light Absorption Method using TLD

Oxigraf O2N2 Flight TestOxygen Analyzer



Results – Airplane Fuel Tank Simulation• Measured fuel tank test article ullage [O2] with both the

FAA method and the light absorption method (Oxigraf) − Results of

Oxigraf and FAA method very close

− The inertingof test tank erratic due to problems, but this illustrates the small advantage of rapid response

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4

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10

12

14

0 20 40 60 80 100 120 140 160 180 200

Time (mins)

Oxy

gen

Con

cent

ratio

n (%

vol)

-20

0

20

40

60

80

100

120

Alti

tude

(kFt

) / T

empe

ratu

re (d

eg F

)

FAA Method OxigrafAltitude Ullage Temp

Commercial Transport AirplaneMission Simulation



Optical Fluorescence• Optical fluorescence using in situ probe (ASF)

− Small fiber optic probe uses spectrometer to interpret coherent light signal which is highly dependent on temperature/pressure

− Used in situ (in place) which has many advantages (low power, small size/weight, rapid response) but also has limitations

• Applying an in situ probe has been be very problematic− Not practical to calibrate on a daily basis− Requires simultaneous/co-located accurate temperature and

pressure measurement to compensate signal− As applied today, does not have faster response than FAA

• Recent work performed has illustrated marked improvement of the probe to duplicate calibration gases− Still struggle with good results at high altitudes− Probe has passed rigorous DO-160 E testing



Latest Optical Fluorescence (ASF) In Situ Probe



ASF Oxygen Sensor Data with Varying Temperature



• Both the FAA method and the light absorption (Oxigraf) method duplicate calibration gases well at a variety of conditions and both agree on oxygen concentration measurements made during a simulation of an inert commercial transport airplane fuel tank flight cycle− Oxigraf system has faster response time but appears to be of

little advantage− Oxigraf system already performed some flight testing and is

slated for more with several OEMs / Operators

• Optical fluorescence making progress but still working out problems− Slated for more chamber examinations in December

Status

Federal Aviation Measuring Oxygen Concentration in a Fuel Tank Ullage · Measuring Ullage Oxygen...

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