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
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
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
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
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
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
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
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
• 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
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
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
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
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
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FAA Fuel Tank Inerting System____________________________________
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
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FAA Fuel Tank Inerting System____________________________________CAD Rendering of FAA Inerting System
AAR-440 Fire Safety R&D
FAA Fuel Tank 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
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
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
• Instrumentation– Aircraft is Fully Instrumented
• Oxygen Sampling for OBIGGS performance
• Pressure Transducers and Thermocouples on System.
• All flight parameters performed
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
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
• Instrumentation– Aircraft is Fully Instrumented
• Oxygen sampling, pressure taps, and thermocouples on system for OBIGGS performance
• Thermocouples in Pack Bay Area
• Pressure altitude measured
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
• 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
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
• 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
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FAA Fuel Tank Inerting System____________________________________
• 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
Measured Results – Single ASM
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
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
• 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
Measured Results – Single ASM
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
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
• 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
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
• 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
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting 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
Adjusted Time (mins)
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
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FAA Fuel Tank Inerting System____________________________________
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
Adjusted Time (mins)
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
Adjusted Time (mins)
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
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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
Adjusted Time (mins)
Flo
w (
scfm
)
0
5
10
15
20
25
30
35
40
Alt
itu
de
(kF
t)
Test 1 Bleedair Flow
Test 2 Bleedair Flow
Test 3 Bleedair Flow
Test 1 Altitude
Test 2 Altitude
Test 3 Altitude
Bleedair Flow Comparison
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
• 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
AAR-440 Fire Safety R&D
FAA Fuel Tank Inerting System____________________________________
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