Development and Testing of the FAA Simplified Fuel Tank Inerting System William Cavage & Robert...

Development and Testing of the FAA Simplified Fuel Tank Inerting System

William Cavage & Robert MorrisonAAR-440 Fire Safety Branch

Wm. J. Hughes Technical Center Federal Aviation Administration

International Fire and Cabin Safety Research Conference

Parque das Nações Conference Center Lisbon, Portugal

November 15-18, 2004

AAR-440 Fire Safety R&D

FAA Fuel Tank Inerting System____________________________________

Outline• Background

– Inerting theory

– Inerting History

– ASM theory of Operation

• System Architecture

• Test articles– Boeing 747SP Ground

Test Article

– Airbus A320 Flight Test Aircraft

– NASA 747 SCA

• Results– Initial Ground Testing– Single ASM Flight

Test Data– Complete System

Flight Test Data

• Summary



Background• Fuel tank explosion accident history highlighted by TWA800

disaster– Past Certification of fuel systems based on ignition source elimination,

not flammability control/reduction

• FAA Certification Office has been seeking flammability elimination/reduction rule since 1997– Multiple industry rule making advisory working groups (ARAC HWGs)

yielded no solutions palatable to FAA and industry

• Previous research illustrated potentially most efficient fuel tank inerting method is OBIGGS – Needed to do detail study of onboard inert gas generation systems

(OBIGGS) specifically for commercial applications



Inerting Background• Inerting refers to rendering the ullage (air above fuel) unable

to propagate a reaction given flammable conditions and ignition source– In this case Refers specifically to reducing tank oxygen concentration

– Other methods of compliance possible

• Fire Triangle must be satisfied to have a reaction (explosion) in the ullage of a fuel tank– Ignition Source

– Correct ratio of fuel and air



Fuel Tank Inerting History• Inerting has been studied since 1950s

• Stored gas inerting used by military in 1970s– FAA built and tested demo cryogenic nitrogen system on DC-9

• DOD did OBIGGS research using PSA and ASMs– Found HFM technology made ASMs very cost effective for OBIGGS

• FAA research illustrated fuel tank inerting could be practical if applied in a cost effective manner– Initially focused on ASM performance for fire suppression capabilities

– After second ARAC, focused on using ASMs to generate inert gas on an aircraft from bleed air during the flight cycle

– FAA experiments agree with previous experiments and indicated that a tank oxygen concentration below 12% will render tank inert



• Hollow fiber membrane technology uses the selective permeation properties of certain materials to separate air into two streams, one nitrogen rich and the other oxygen rich (compared to air). – Materials are woven into hair-sized fibers and bundled by the

thousands into a canister called an air separation module (ASM)

– Pressurized air is forced through the membrane fibers, allowing fast gases to escape through the membrane wall and the nitrogen rich stream to pass through

Hollow Fiber Membrane



System Architecture• A simplified inerting system conceived by Ivor Thomas

(CSTA for Fuel Systems) illustrated feasibility

• Concept utilizes HFMs in a two flow methodology– Uses low flow mode during taxi, takeoff, ascent, and cruise to

deplete CWT of oxygen almost completely

– Uses high flow mode during descent to offset (but not eliminate) the air entering the fuel tank vent system resulting in a net inert fuel tank oxygen concentration

• Does not need to run on ground or store NEA, eliminates need for compressors or ground service equipment

• System only needing to reduce the oxygen concentration below 12% makes sizing more realistic



FAA Simplified Inerting System Block Diagram

HeatExchanger

Cool Air Source

Exi

stin

g A

ircr

aft B

leed

air

Supp

ly

Filter

Heater

Shut-OffValve

Variable/High Flow Valve

Fuel Tank

ThrottlingValve

AS

MSystem Controller

TemperatureSensor

AS

M

AS

M

Air

craf

tP

ower

Oxygen RichWaste Gas

Waste StreamDiscarded

Nitrogen RichProduct Gas

Low Flow Orifice



System Construction• Uses 3 ASMs based on HFM technology

– Excepts 350 degree F air from aircraft bleed system through an SOV

– Uses a H/x to cool air to 180˚F +/- 10˚F and a filter to condition air

– Air is separated ASMs and NEA is plumbed to output valves to control flow, OEA is dumped overboard with H/X cooling air

– System flow control is presently configured with low flow orifice and high flow control valve

• System controlled by control box in cabin that is connected to system with cable

• System built on aluminum pallet for ease of construction and to support a wide variety of installation methods


FAA Fuel Tank Inerting System____________________________________CAD Rendering of FAA Inerting System



Test Articles – 747 SP• Boeing 747SP with fully functioning systems

– Decommissioned from airline service and purchased by the FAA for Ground Testing Only

• All major systems fully operational

• Has independent power for test equipment and instrumentation

• Designed inerting system to mount in empty pack bay

– Full Complement of Ground Service Equipment

• Instrumentation– Aircraft is Fully Instrumented

• Oxygen sampling, pressure taps, and thermocouples on system for OBIGGS performance

• Thermocouples in Pack Bay

• Some Weather Data Available



Test Article - Airbus A320• Airbus A320 Flight Test Vehicle

– Original A320 from production start operated by Airbus for the purposes of research and development

• Fully Instrumented with extensive DAS capabilities

• Was modified to accommodate an inerting system in the cargo bay

– Operated out of Airbus, France Flight Test

• World class mod and test center


• Oxygen Sampling for OBIGGS performance

• Pressure Transducers and Thermocouples on System.

• All flight parameters performed



Test Article – NASA 747 SCA• Highly modified Boeing 747-100

– Reengineered and modified by NASA for the purposes of carrying a Space Shuttle Orbiter for operations and maintenance

• Fully operational, standard, fuel system with unmodified pack bay

– Operated out of Ellington field - Houston, Texas• Operated by excellent group of test pilots at a top notch operations facility in

and maintained by dedicated group of ground service personnel


• Oxygen sampling, pressure taps, and thermocouples on system for OBIGGS performance

• Thermocouples in Pack Bay Area

• Pressure altitude measured



• Mounted and tested system in the 747 SP ground test article– Operated OBIGGS with static conditions (best as possible) for the

purposes of validating the system performance

– Focused on the volume flow of 5% and 11% NEA that could be generated with varying ASM pressure

• Testing Illustrated– Stable system performance is

difficult to achieve in a dynamic aircraft environment

– Manufactures data based on general properties not specific ASM

– Different measurement techniques gave different results

Measured Results – Ground Testing

0

5

10

15

20

25

30

35

40

45

10 15 20 25 30 35 40 45 50

ASM Inlet Pressure (psig)

NE

A F

low

(S

CF

M)

Manufacturers Data

Validation Data - Oct 28

Validation Data - Oct 25

3 ASM Performance at Sea Level - 5% NEA



• Compared dynamic ASM performance with static measurements – through out flight cycle on A320 flight test and compared to static lab

data

• Data comparison generally good with some large discrepancies– Illustrates the difficulty in obtaining stable temperature and pressure during flight test

– 180 degree F ASM temp frequently unattainable during Airbus testing

– Fixed orifice gives variable flow

Measured Results – Single ASM

0

2

4

6

8

10

12

14

16

18

20

0 20 40 60 80 100 120

Time (min)

[O2]

(% v

ol)

/ F

low

(sc

fm)

0

10

20

30

40

50

60

70

80

Alt

itu

de

(k

ft)

/ Pre

ss

ure

(p

sig

)

NEA Flow NEA Flow NEA [O2] NEA [O2] ASM Pressure ASM Pressure Altitude Altitude

Single Membrane Test

Switch to HighFlow Mode

Flight Test Data Static Data



• Calculated bleed air consumption for the A320 flight cycle

– Used equation in terms of NEA flow, NEA [O2], and OEA [O2]

• Amount of bleed air consumed large but makes sense– Much higher cruise bleed pressure than expected

– Stable NEA flow observed is not from stable ASM performance characteristics

– Illustrates the relationship between permeability, selectivity, and altitude


0

10

20

30

40

50

60

0 20 40 60 80 100 120

Time (min)

Flo

w R

ate

(SC

FM

)

NEA Flow (SCFM)

Bleedair Flow (SCFM)

Permeate Flow (SCFM)

Single Membrane Data

)][21.0(

)][]([

2

22

Perm

PermNEANEABleed O

OOQQ



• Correlated ASM pressure with NEA flow– Compared data for selected parts of A320 testing flight cycle

• Not a true correlation because ASM performance is changing– Ascent and Descent

cause large variations in ASM performance due to change in altitude / ASM pressure

– Cruise data shows a true correlation in the low flow mode


0

2

4

6

8

10

12

14

0 5 10 15 20 25 30 35 40 45 50

ASM Pressure (psig)

NE

A F

low

(S

CF

M)

Ascent Cruise Descent

Correlation of Single ASM Pressure and Flow



• Measured static system flow and purity on the 747 SCA test bed at selected altitudes and somewhat stable ASM pressures– Used variable flow valve to vary flow and purity in flight

– Some data did not follow trend

– Highlights the difficulty in obtaining stable ASM conditions on a flight test aircraft

– Stable ASM temperatures a constant battle

Measured Results – Complete System

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12 14 16 18

Flow (SCFM)

Ox

yge

n C

on

ce

ntr

atio

n (

% v

ol)

Sea Level

30,000 Feet

20,000 Feet

15 Psig ASM Pressure



• Dynamic performance during takeoff/ascent and descent/landing portion of flight cycle is least predictable

• Analyzed this portion of flight cycle for 3 different tests– Similar ASM pressure observed

– Varying but similar ascent and descent profiles

• On ascent flow and purity vary for different tests although input conditions are similar– Attributed to unstable ASM temperature due to different warm ups

– No adverse effect on system capabilities

• On descent flow and purity vary for different tests as expected because of different variable/high flow orifice settings– Bleed air flow nearly constant

Measured Results – Complete System



NEA Purity Data

0

2

4

6

8

10

12

14

16

18

20

15 20 25 30 35 40 45

Adjusted Time (mins)

Ox

yg

en

Co

nc

en

tra

tio

n (

vo

l %)

0

5

10

15

20

25

30

35

40

Alt

itu

de

(k

Ft)

Test 1 NEA [O2]Test 2 NEA [O2]Test 4 NEA [O2]Test 1 AltitudeTest 2 AltitudeTest 4 Altitude

NEA [O2] Comparison

0

5

10

15

20

25

30

35

15 20 25 30 35 40 45


Flo

w (

scfm

)

0

5

10

15

20

25

30

35

40

Alt

itu

de

(kF

t)

Test 1 NEA Flow

Test 2 NEA Flow

Test 4 NEA Flow

Test 1 Altitude

Test 2 Altitude

Test 4 Altitude

NEA Flow Comparison

Comparison of System Performance During Takeoff

NEA flow Data



NEA Purity Data

Comparison of System Performance During Landing

NEA flow Data

0

2

4

6

8

10

12

14

16

18

20

105 110 115 120 125 130 135 140 145 150 155


Oxy

gen

Co

nce

ntr

atio

n (

% v

ol)

0

5

10

15

20

25

30

35

40

Alt

itu

de

(kF

t)

Test 1 NEA [O2]

Test 2 NEA [O2]

Test 3 NEA [O2]

Test 1 Altitude

Test 2 Altitude

Test 3 Altitude

NEA [O2] Comparison

0

10

20

30

40

50

60

70

80

105 110 115 120 125 130 135 140 145 150 155


Alt

itu

de

(kft

) /

Flo

w (

scfm

)

0

5

10

15

20

25

30

35

40

Alt

itu

de

(kF

t)

Test 1 NEA Flow

Test 2 NEA Flow

Test 3 NEA Flow

Test 1 Altitude

Test 2 Altitude

Test 3 Altitude

NEA Flow Comparison


FAA Fuel Tank Inerting System____________________________________Comparison of System Bleed air Flow During Landing

0

50

100

150

200

250

300

105 110 115 120 125 130 135 140 145 150 155


Flo

w (

scfm

)

0

5

10

15

20

25

30

35

40

Alt

itu

de

(kF

t)

Test 1 Bleedair Flow



Test 1 Altitude

Test 2 Altitude

Test 3 Altitude

Bleedair Flow Comparison



• FAA used existing technology in an innovative way to develop a near term, simple, solution to fuel tank flammability control

• Duplicating static OBIGGS performance data on an aircraft could be problematic, but the system performed as expected

• Bleed air consumption should be studied further to examine the penalty associated with high bleed air consumption and potential methods of reducing bleed air consumption

• Measurable performance variations observed at the start of system attributed to different warm-up times did not hamper system from reducing ullage oxygen concentration

• Bleed air consumption remained constant after the system was sufficiently warmed-up even when varying flow and purity

Summary



The Fourth Triennial The Fourth Triennial International Aircraft Fire and Cabin Safety International Aircraft Fire and Cabin Safety Research ConferenceResearch Conference

The Fourth Triennial The Fourth Triennial International Aircraft Fire and Cabin Safety International Aircraft Fire and Cabin Safety Research ConferenceResearch Conference

Development and Testing of the FAA Simplified Fuel Tank Inerting System William Cavage & Robert...

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