11-16-2004aircraft fire and cabin safety research – lisbon, portugal in-flight fuel tank...
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11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
In-Flight Fuel Tank Flammability Testing
The 4th Triennial Int’l Aircraft Fire and Cabin Safety Research ConferenceLisbon, PortugalNovember 15 – 18, 2004
Steve SummerProject EngineerFederal Aviation AdministrationFire Safety Branch
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
Background To date, real-time flammability (hydrocarbon) data in
flight has yet to be obtained from aircraft fuel tanks (CWT or wing)
Lab-based instruments in use at the FAA are based on a flame-ionization detection (FID) technique, and are unsuitable for in flight use
Such a system must maximize safety and data reliability while being able to handle the rigors of a flight environment (vibration, pressure & temperature changes, etc…)
The FAA developed such a system for real-time monitoring of the CWT and wing tank flammability during flight tests on NASA’s 747 SCA
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
FAS System Overview
System uses a Non-Dispersive Infrared Analyzer (NDIR) to measure fuel tank flammability in the form of total hydrocarbons (THC)
Sample stream must be heated at all points leading to the NDIR to prevent condensation of fuel vapors
Overall system consists of two units• Pallet Mounted NDIR Analyzer
• Rack Mounted Sampling System
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
FAS System Overview
Pallet Mounted NDIR Analyzer:• Custom built by Rosemount
Analytical specifically for this application
• Dual sample capability
• Separated into two sections – electronics and sample stream
• Sample stream section temperature controlled to 200°F
• Entire unit continuously purged
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
FAS System Overview Rack Mounted Sampling System:
• Supplies a temperature, pressure and flow controlled sample to the NDIR utilizing four components: Quad head (2 heads/channel)
diaphragm pump pulls sample from CWT/WT
Sampling conditioning unit actively controls pressure and flow of sample supplied to NDIR
Heated box maintains a 200°F sample
Electronics panel houses all pressure/temperature electronic control units
• Components containing sample lines are continuously purged
Heated Sample Box
Sample Flow/Pressure Conditioning Unit
Controller Electronics Panel
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
FAS – Safety Features
System safety features include:• Diaphragm pump is safe for explosive atmosphere
and pump motor has failure containment standard
• Pump motor and all electronics kept separated from sample stream where possible
• All enclosures that sample passes through are continuously purged
• Float valve, fluid trap and flash arrestor on sample inlets
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
FAS Block Diagram
Heated Line
Heated Line
Sample Backpressure
Regulated
Sample Flow Regulated
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
FAS – Performance
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
THC Sample Point Locations
ThermocoupleBundle 1
ThermocoupleBundle 2
Heated Line
Fastener 1
Fastener 2Fastener 3 Fastener 4
Solid PartitionRib
Fairing Area
Sample point penetrations are located at ‘fastener 1’ (STA 1098) and ‘fastener 2’ (STA 630, ~40 ft from fuselage)
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
Peak CWT THC reading on all flights corresponded closely with the start of cruise
CWT THC readings rise slowly, but steadily on the ground prior to take-off
CWT THC readings rise rapidly on ascent as hydrocarbons evolve faster at the reduced pressures, overcoming the corresponding condensation effect due to reduced temperatures.
Once level flight is reached, temperature effects are what drive the THC readings
General Flammability Trends Seen In Flight
On descent, incoming air causes THC to drop at a slightly higher rate
WT THC readings follow similar trends, except that condensation effects are always what drive THC
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
A Closer Look at Temperature Effects
Effect of pressure overpowers condensation
Once condensation effects take over, as temperatures change, so does the THC reading
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
A Closer Look at Temperature Effects
In this test, CWT temperatures don’t change much in flight…therefore, THC readings don’t change much either
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
Effect of Cross-Venting on Flammability
As seen in previous slides, CWT THC readings drop off steadily due to condensation
Sampling system shut down
This test was ran with no OBIGGS and with one side of the vent capped (i.e. no cross-venting). The data is spotty as the system was turned off at various points during test…a trendline is added in black.
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
Effect of Cross-Venting on Flammability
This test was ran with no OBIGGS and with both sides of the vent open (i.e. with cross-venting).
We again see the CWT THC drop off, but at a much higher rate, despite similar temperature trends and flight profiles
All pressure readings were lost, but cruise was at 31 kft
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
Comparison of Data with Models
Fuel Air Ratio Calculator• Developed by Ivor Thomas• Predicts FAR for a wide range of fuels over a wide
range of altitudes, temperatures and mass loadings• Assumes isothermal conditions => conservative
estimate Vapor Generation Model
• Developed by Prof. Polymeropolous of Rutgers University
• Uses free convection and heat transfer correlations to predict total mass of vapor generated and vapor masses of the component species over time.
• User must input fuel, wall and ambient temperatures and pressures
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
Model Comparisons – Equilibrium Values
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
Vapor Generation Model Comparison – Ground Test
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
Time (s)
TH
C (
% P
rop
an
e)
Measured
Computed - 130 FP
Computed - 135 FP
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
Vapor Generation Model Comparison – Flight Test
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
Vapor Generation Model Comparison Flight Test (25% Fuel Load)
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
Vapor Generation Model Comparison – Flight Test
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
Summary
The FAS has been shown to accurately measure a sample of 2% propane from sea level to ~40 kft with an accuracy of 0.02%
The FAS gave consistent readings when compared to a typical FID
The FAS worked as expected during flight test except for a few minor issues such as condensation within flowmeters which were overcome during testing
11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal
Summary Data shows the strong correlation of flammability
with tank temperature trends
Cross-venting through the CWT greatly increases the rate at which flammability decreases in flight (given the limited scope of the data).
Equilibrium and transient model data agreed favorably
Vapor Generation model tends to overestimate the peak THC reading
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