# Presentation: 066141

## An Update on FAA Fuel Tank Ullage Modeling

- William Cavage, Steven Summer, and Robert Ochs AAR-440 Fire Safety BranchWm. J. Hughes Technical CenterFederal Aviation Administration

- International Systems Fire Protection Working Group CAA  London, England UK April 19-20, 2006

## Outline

- Background
- Models Employed
- Flight Test Results Comparison
- Representative Flight Modeling

## Background

- FAA developed a proof of concept inerting system to inert the CWT of classic style Boeing model 747
- FAA intends to make a rule requiring flammability control of some or all CWTS with an emphasis on inerting system technologies
- Fire Safety research has been working to expand modeling capabilities to allow for systems analysis, trade studies, etc.
- Used lab research and flight test data to develop, expand, and validate a multiple bay fuel tank inerting model and an ullage flammability model
- Performed analysis of a single fictitious flight to examine the SOA of our modeling capability
- Developed a more typical 747 flight profile with a bigger OBIGGS than the NASA flight test system

## Models Employed

- Multiple bay inerting model same as model discussed in AIAA paper (see web site) with some small improvements
- Tracks mass of oxygen in and out of each bay knowing NEA flow and given a set of generic flow splits between bays with no back pressure
- Tracks mass of ullage knowing the change in density (given altitude changes) with no mass storage in tank
- Model does these calculations in a time step process
- Ullage flammability model is the evaporation/condensation model by Polymeropoulos & Ochs and discussed in Lisbon
- Uses a generic fuel species model based on flash point developed by Sagebiel
- Calculates the equilibrium state of the ullage given fuel temperature and then determines condensation effect from walls/ceiling in time

## Results from Flight Test Comparison

- Inerting model illustrated excellent agreement with measured flight test data with some exception
- Good agreement is expected since a similar test was used to develop the bay to bay flow split ratios
- Bay 4 trends look good but value is considerably off (the problem bay)
- Resulting ullage average time values very consistent
- Flammability model data trend results very good
- Magnitude of data peaks and troughs illustrate significant deviation although measured data has some uncertainty so it is unclear how well the model duplicates flight test results
- Models uses no empirical relationships to obtain results

## Comparison of Flight Test Results with FAA Model

## Comparison of Flight Test Results with FAA Model

## Results – Representative Flight

- Developed flight profile, OBIGGS performance, and temperature profile from existing flight test data taking into account a typical 747 flight profile
- Difficult to determine precise temperature peaks and troughs but did best to approximate
- OBIGGS was assumed to 33% bigger (1 more ASM)
- Data trends as expected but very little we can do to validate the magnitude of the results
- Regardless of peak oxygen concentration in single bay, tank remained nonflammable during entire flight
- Tank flammability dropped below LEL during peak oxygen concentration rise in bay 1

## Input Data for 747 Modeling Exercise

## Results of Modeling Exercise

## Summary

- Analysis of FAA Fire Safety model capabilities illustrates good fidelity for this single aircraft type
- Remains to be seen how this work could translate to other multiple bay CWT aircraft types
- Need additional work to be able to simulate different deposit and venting schemes
- No additional modeling work planned to date