An Update on FAA Fuel Tank Ullage Modeling

1. 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

2. Outline • Background • Models Employed • Flight Test Results Comparison • Representative Flight Modeling AAR-440 Fire Safety R&D

3. 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 AAR-440 Fire Safety R&D

4. 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 AAR-440 Fire Safety R&D

5. 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 AAR-440 Fire Safety R&D

6. Comparison of Flight Test Results with FAA Model AAR-440 Fire Safety R&D

7. Comparison of Flight Test Results with FAA Model AAR-440 Fire Safety R&D

8. 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 AAR-440 Fire Safety R&D

9. Input Data for 747 Modeling Exercise AAR-440 Fire Safety R&D

10. Results of Modeling Exercise AAR-440 Fire Safety R&D

11. 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 AAR-440 Fire Safety R&D