In flight fuel tank flammability testing
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In-Flight Fuel Tank Flammability Testing. Steve Summer Project Engineer Federal Aviation Administration Fire Safety Branch. The 4th Triennial Int’l Aircraft Fire and Cabin Safety Research Conference Lisbon, Portugal November 15 – 18, 2004. Background.

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In-Flight Fuel Tank Flammability Testing

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In flight fuel tank flammability testing

In-Flight Fuel Tank Flammability Testing

Steve Summer

Project Engineer

Federal Aviation Administration

Fire Safety Branch

The 4th Triennial Int’l Aircraft Fire and Cabin Safety Research Conference

Lisbon, Portugal

November 15 – 18, 2004

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


Background

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

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


In flight fuel tank flammability testing

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

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


In flight fuel tank flammability testing

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

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


In flight fuel tank flammability testing

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

Controller Electronics Panel

Sample Flow/Pressure Conditioning Unit

Heated Sample Box

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


In flight fuel tank flammability testing

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

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


In flight fuel tank flammability testing

FAS Block Diagram

Heated Line

Sample Flow Regulated

Sample Backpressure Regulated

Heated Line

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


Fas performance

FAS – Performance

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


Thc sample point locations

Sample point penetrations are located at ‘fastener 1’ (STA 1098) and ‘fastener 2’ (STA 630, ~40 ft from fuselage)

THC Sample Point Locations

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


General flammability trends seen in flight

CWT THC readings rise rapidly on ascent as hydrocarbons evolve faster at the reduced pressures, overcoming the corresponding condensation effect due to reduced temperatures.

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

Once level flight is reached, temperature effects are what drive the THC readings

WT THC readings follow similar trends, except that condensation effects are always what drive THC

On descent, incoming air causes THC to drop at a slightly higher rate

General Flammability Trends Seen In Flight

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


In flight fuel tank flammability testing

A Closer Look at Temperature Effects

Once condensation effects take over, as temperatures change, so does the THC reading

Effect of pressure overpowers condensation

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


In flight fuel tank flammability testing

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

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


In flight fuel tank flammability testing

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.

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


In flight fuel tank flammability testing

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

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


Comparison of data with models

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

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


Model comparisons equilibrium values

Model Comparisons – Equilibrium Values

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


Vapor generation model comparison ground test

Vapor Generation Model Comparison – Ground Test

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


Vapor generation model comparison flight test

Vapor Generation Model Comparison – Flight Test

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


Vapor generation model comparison flight test 25 fuel load

Vapor Generation Model Comparison Flight Test (25% Fuel Load)

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


Vapor generation model comparison flight test1

Vapor Generation Model Comparison – Flight Test

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


Summary

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

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


Summary1

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

Aircraft Fire and Cabin Safety Research – Lisbon, Portugal


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