In-Flight Fuel Tank Flammability Testing

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In-Flight Fuel Tank Flammability Testing
The 4th Triennial Intl Aircraft Fire and Cabin
Safety Research Conference Lisbon,
Portugal November 15 18, 2004
Steve Summer Project Engineer Federal Aviation
Administration Fire Safety Branch
2
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 NASAs 747 SCA

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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

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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
  200F
• Entire unit continuously purged

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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 200F sample
• Electronics panel houses all pressure/temperature
  electronic control units
• Components containing sample lines are
  continuously purged

Controller Electronics Panel
Sample Flow/Pressure Conditioning Unit
Heated Sample Box
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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

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FAS Block Diagram
Heated Line
Sample Flow Regulated
Sample Backpressure Regulated
Heated Line
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FAS Performance
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THC Sample Point Locations
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General Flammability Trends Seen In Flight
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A Closer Look at Temperature Effects
Once condensation effects take over, as
temperatures change, so does the THC reading
Effect of pressure overpowers condensation
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A Closer Look at Temperature Effects
In this test, CWT temperatures dont change much
in flighttherefore, THC readings dont change
much either
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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 testa trendline is
added in black.
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Effect of Cross-Venting on Flammability
We again see the CWT THC drop off, but at a much
higher rate, despite similar temperature trends
and flight profiles
This test was ran with no OBIGGS and with both
sides of the vent open (i.e. with cross-venting).

All pressure readings were lost, but cruise was
at 31 kft
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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 gt 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

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Model Comparisons Equilibrium Values
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Vapor Generation Model Comparison Ground Test
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Vapor Generation Model Comparison Flight Test
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Vapor Generation Model Comparison Flight Test
(25 Fuel Load)
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Vapor Generation Model Comparison Flight Test
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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

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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