11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal In-Flight Fuel Tank Flammability Testing The 4th Triennial Int’l Aircraft Fire and

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


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


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


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


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


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


FAS Block Diagram

Heated Line

Heated Line

Sample Backpressure

Regulated

Sample Flow Regulated


FAS – Performance


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)


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


A Closer Look at Temperature Effects

Effect of pressure overpowers condensation

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


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


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.


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


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


Model Comparisons – Equilibrium Values


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


Vapor Generation Model Comparison – Flight Test


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


Vapor Generation Model Comparison – Flight Test


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


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

Documents

11-16-2004Aircraft Fire and Cabin Safety Research – Lisbon, Portugal In-Flight Fuel Tank Flammability Testing The 4th Triennial Int’l Aircraft Fire and