View
214
Download
0
Category
Tags:
Preview:
Citation preview
Modeling of Fuel Tank Inerting for FAA OBIGGS Research
William CavageAAR-440 Fire Safety Branch
Wm. J. Hughes Technical CenterFederal 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
Modeling of Fuel Tank Inerting____________________________________
Outline• Background
– Goals and Objectives
– Previous Work• Analytical (calculation) Models
• Physical (scale) Models
• Modeling Methods– Scale A320 Tank in Altitude
Chamber
– Calculation Model
– Scale 747 Tank in Altitude Chamber
• Summary
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________
Background• FAA has been developing and testing an OBIGGS for fuel
tank inerting to illustrate the feasibility of light weight, simplified inerting systems to reduce flammability in commercial transport airplanes
• Modeling inert gas effects and distribution in commercial transport fuel tanks could assist in the development process and allow for cost effective systems analysis and trade studies– Capitalize on previous FAA modeling work done in support of ground
based inerting research (sea level inerting only)– Models have to be simple to be useful in a cost analysis study or rulemaking
exercise
– FAA has a relatively large amount of flight test data to validate any developed models
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________
Previous Work – Ullage [O2] Calculation Model• Uses perfect mixing assumption and calculates the volume
of oxygen in and out of tank at every time stepTankONEANEAOO VttVQtIGOFQtVtV /)1()1()(
222
Tank
O
V
tVtOTank
)()]([ 2
2
– Uses a basic spreadsheet iterating calculation and runs immediately given the volume of the tank, the flow rate and purity of the NEA
– Constant inerting only
0
5
10
15
20
25
0 500 1000 1500 2000 2500
Time (seconds)
Oxy
gen
Co
nce
ntr
atio
n (
%)
94% NEA Model 94% NEA Data
96% NEA Model 96% NEA Data
6 CFM Flow Rate - Data vs Model
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________
Previous Work – Multi-Bay Inerting Model• Engineering model that calculates inert gas distribution in 6-
bay tank, in terms of oxygen concentration evolution, given NEA purity and bay deposit flow rates– Based on calculation method previously discussed and tracks oxygen
in and out of each bay assuming perfect mixing
– Designed for “localized deposit” methods and assumes an “outward” flow pattern, splitting flow to adjacent bays based on flow area relationships
– Data agreed fairly well with full-scale data
Bay 1Flow Out
Bay 2
Flow InBay 3 Bay 4
Bay 5 Bay 6FlowOut
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________Engineering Model Inerting Data Comparison
0
5
10
15
20
25
5 10 15 20 25 30 35
Time (mins)
Oxy
gen
Co
nce
ntr
atio
n (
% v
ol)
Bay 1 Bay 1
Bay 2 Bay 2
Bay 3 Bay 3
Bay 4 Bay 4
Bay 5 Bay 5
Bay 6 Bay 6
CWT Inerting, Single Bay Deposit in Bay 3Comparison with Engineering Model Data
B-747 Data Engineering Model
140 CFM Flow Rate95% NEA (5% O2)
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________
Previous Work – Scale 747SP CWT • FAA built and performed tests in 24% scale 747SP (classic
type) center-wing fuel tank– Made from plywood using NTSB Shepherd report drawings
– Scaled all penetrations (holes) between bays and vent system
– Variable NEA deposit capability to allow for inerting of tank with scaled flows in each bay
– Oxygen concentration measured in each bay
– Model data duplicated full-scale results very well for localized deposit method studied
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________Scale Model Inerting Data Comparison
0
5
10
15
20
25
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Overall VTE
Oxy
gen
Co
nce
ntr
atio
n (
% v
ol)
Bay 1 Bay 1
Bay 2 Bay 2
Bay 3 Bay 3
Bay 4 Bay 4
Bay 5 Bay 5
Bay 6 Bay 6
CWT Inerting, Single Bay Deposit in Bay 3Comparison with Scale Tank Data
B-747 Data Scale Tank
20 Minute Inerting Rate95% NEA (5% O2)
VolumeTankFuel
RateFlowVolumeTimeExchangeTankVolumetric
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________
• Regardless of methodology, all modeling methods predict bulk ullage oxygen concentration well
Previous Work – Average [O2] Predictions
0
5
10
15
20
25
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
Volumetric Tank Exchange
Ave
rag
e O
xyg
en C
on
cen
trat
ion
(%
vo
l) Full-Scale Test Article
24% Scale Tank
Engineering Model
747 CWT GBI Weighted Average Inerting DataSingle Bay Deposit, 95% NEA, 20-Minute Inerting
8% Line
VolumeTankFuel
RateFlowVolumeTimeExchangeTankVolumetric
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________
Modeling Method – Altitude Calculation Model• A calculation model of average ullage oxygen concentration
based on inert gas added and altitude change was developed based on existing model– Model changed to calculate mass of oxygen added and removed at each
time step, assuming perfect mixing, in a single bay tank given a tank volume and starting oxygen concentration
– Must input system performance (NEA flow and purity) in terms of time and altitude
– Calculates ullage gas removed from tank due to increase in altitude (decrease in pressure) to calculate mass of oxygen decrease in tank
– Calculates air entering tank due to decrease in altitude (increase pressure) to calculate mass of oxygen increase
– The model is a relatively simple time step spreadsheet that calculates instantaneously
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________
Modeling Method – Altitude Calculation Model– Basic equation governing modeling method
21.*)*()1()*(
)1()1()(22
TankTank
OO
VtUGOFV
tUGOFmIGOFmtmtm
With: = Mass of oxygen in tank at time t = Mass flow rate of inerting gas (in terms of t)
IGOF = Fraction of oxygen in inerting gasΔρ = Change in Ullage Density due to Altitude ChangeVTank = Volume of Tank UllagemTank = Mass of Gas in Tankmair = Mass of air entering tank
Ullage Gas Oxygen Fraction (UGOF) is given as:
)(2tmO
m
TankO mtmtUGOF /)1()1(2
– Simple effective model for predicting resulting ullage oxygen concentration given a system performance and mission profile
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________Altitude Inerting Calculation Model Data Comparison
0
5
10
15
20
25
0 20 40 60 80 100 120
Time (mins)
Oxy
gen
Co
nce
ntr
atio
n (
% v
ol)
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
45,000
50,000
Alt
itu
de
(ft)
)
Calculation Model
Flight Test Data
Altitude
A320 Flight Test - Single ASM Data
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________
Modeling Method – Scale A320 CWT • FAA built and performed tests in 50% scale Airbus A320
center-wing fuel tank– Made from plywood using drawings given to us by Airbus in support
of joint inerting flight test
– Scaled all structural members of tank inside down to the smallest detail– Mass flow controller and NEA mixer used to inert the tank in altitude chamber
– Altitude oxygen analyzer used to track ullage with additional basic instrumentation
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________Block Diagram of Scale A320 CWT Experiment
Altitude ChamberN
EA
Mix
er
OxygenAnalyzer
Flow Controller
DAS
Nitr
ogen
CompressedAir
NEA Generator
Com
pute
r
T
AltitudeOxygen
Analyzer
PressureTransducer
Sample Return
Scale Tank Model
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________
• Results indicate that duplication of the flight cycle with the system performance in the altitude chamber was accomplished with coordination of test personnel
• Measured scale tank oxygen concentration data illustrated good agreement with flight test results considering the large differences in measurement systems sample lag
• Localized oxygen concentration dynamics illustrated some fidelity when specific sample location data were compared with similar locations in the flight test aircraft
Modeling Method – Scale A320 CWT
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________Full-Scale Data Compared with Scale System Performance
0
5
10
15
20
25
65 70 75 80 85 90 95 100 105 110 115
Time (min)
Oxy
gen
Co
nce
ntr
atio
n (
% v
ol)
0
20
40
60
80
100
120
140
160
Flo
w (
scfh
)
Scale Test NEA Purity
Flight Test NEA Purity
Scale Test NEA Flow
Flight Test NEA Flow (scaled)
Comparison of Model Data - Single ASM TestMeasured System Performance Data
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________Full-Scale Data Compared with Scale Model [O2] Results
0
2
4
6
8
10
12
14
16
18
65 70 75 80 85 90 95 100 105 110 115
Time (mins)
Ox
yg
en
Co
nc
en
tra
tio
n (
% v
ol)
A320 Flight Test [O2]
Analytical Model [O2]
Scale Model [O2]
Comparison of Model Data - Average Ullage [O2]Airbus Test v1972 - Dual Flow System
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________Full-Scale Data Compared with Modeling Methods
0
5
10
15
20
25
65 70 75 80 85 90 95 100 105 110 115
Time (mins)
Oxy
gen
Co
nce
ntr
atio
n (
% v
ol)
0
5
10
15
20
25
30
35
40
45
Alt
itu
de
(kft
)
Scale Model [O2]
Flight Test [O2]
Flight Test Altitude
Scale Model Altitude
Comparison of Model Data - Single ASM TestUllage Sample Near Vent
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________Comparison of Modeling Methods
0
2
4
6
8
10
12
14
16
18
65 70 75 80 85 90 95 100 105 110
Time (mins)
Oxy
gen
Co
nce
ntr
atio
n (
% v
ol)
Single ASM Performance Single ASM Performance
75% System Performance 75% System Performance
50% System Performance 50% System Performance
Analytical Model Data for System Size ComparisonUllage [O2] Airbus v1972 Descent - Dual Flow System
Analytical Model Scale Tank Model
Modeling Data for System Size ComparisonUllage [O2] for Airbus v1972 Test Descent
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________
Modeling Method – Scale 747SP CWT • FAA performed tests in 24% scale Boeing 747 (classic type) CWT
built for GBI inert gas distribution study– Used scale model in altitude chamber with NEA mixer and mass flow
controller and simulated potential 747 missions with predicted system performance
– OBOAS used to track bay [O2]
– Single deposit in bay 6
– Results appear to make sense but have no flight test data to make valid comparisons 0
2
4
6
8
10
12
14
16
18
0 10 20 30 40 50 60
Time (mins)
Oxy
gen
Co
nce
ntr
atio
n (
% V
ol)
Bay 1 Bay 2 Bay 3
Bay 4 Bay 5 Bay 6
Descent Inerting Data - 39K FeetStarting [O2] 2%, 10 Min Hold at 5K Feet
AAR-440 Fire Safety R&D
Modeling of Fuel Tank Inerting____________________________________
• Simple calculation models of average ullage oxygen concentration have been developed and can duplicate flight test data in a fairly accurate manner– Requires no unique engineering skills
– Very easy to develop and modify for a wide variety of flight cycles, OBIGGS capabilities and ullage conditions
• Scale models can be tested with an altitude facility in a relatively cost effective manner to give good agreement with flight test data– Some specialized instrumentation and facilities needed
– Provides some ability to analyze internal flow dynamics
– More work is needed to validate this method for compartmentalized tanks
Summary
Recommended