International Aircraft Fire and Cabin Safety Conference Fuel Tank Inerting Modeling Ivor Thomas Consultant to FAA

International Aircraft Fire and Cabin Safety Conference Background Following TWA 800 the FAA undertook to examine fuel tank inerting to determine if a system could be made practical. –Two ARAC studies –FAA lab, ground and flight test programs –Computer simulations of system performance

International Aircraft Fire and Cabin Safety Conference Computer simulations of system performance Initial model to verify system performance in a single bay tank, using FAA Technical Center tests to confirm model. Flight simulation model to look at performance of an inerting system throughout a flight Air Separation Module (ASM) performance in flight (effects of available bleed air, system pressure drop etc.) Multi-bay simulations to examine in-tank performance (potential for one or more high oxygen bays when the tank average is satisfactory)

International Aircraft Fire and Cabin Safety Conference Initial Model Model Features: –Simple one bay tank, –Single source of Nitrogen Enriched Air, at a fixed level of O2 –Single vent overboard –Sea level conditions only

International Aircraft Fire and Cabin Safety Conference Initial Model Model Results: –Mixing was very rapid, and could be assumed to be instantaneous –Starting from 21 % O2 model would predict test results accurately

International Aircraft Fire and Cabin Safety Conference

Flight Model Model Features: –Simple one bay tank, –Single source of Nitrogen Enriched Air, at a variable level of O2 and flow rate Changeable for different flight conditions Could add results of ASM performance for given airplane/engine combination –Single vent overboard –Ground and Flight profiles can be simulated. –Fuel O2 Evolution and Fuel consumption included

International Aircraft Fire and Cabin Safety Conference Flight Model Model Results: –Very useful in determining effectiveness of inerting options Ground based inerting Various sizes of ASM and flow modes Substantiated concept of variable flow technique, low flow in climb and cruise, high flow in descent

International Aircraft Fire and Cabin Safety Conference Ground Based Inerting

International Aircraft Fire and Cabin Safety Conference Ground Based Inerting

International Aircraft Fire and Cabin Safety Conference Dual-Flow On Board Inerting

International Aircraft Fire and Cabin Safety Conference Dual Flow On board Inerting

International Aircraft Fire and Cabin Safety Conference Air Separation Module (ASM) ASM performance strongly affected by available pressure and temperature Airplane bleed flow affected by airplane flight conditions. Model combined airplane/engine bleed data with ASM performance data to predict ASM performance in flight, which could then be used in the inerting flight model.

International Aircraft Fire and Cabin Safety Conference Screen Dump of ASM Model

International Aircraft Fire and Cabin Safety Conference Typical Single ASM Performance

International Aircraft Fire and Cabin Safety Conference Multi-bay simulations Background: The performance of an inerting system can be estimated with the inerting flight model at a gross tank level. In-tank effects needed to be examined to understand the potential for bays of a tank to be left at a high O2 state even though the tank average O2 was acceptable.

International Aircraft Fire and Cabin Safety Conference Multi-bay simulations Model Features: –Specific airplane /tank set-up Bay sizes Interconnect flow areas vent geometry, –Multiple NEA insertion points –Ground and Flight Operation –Leakage

International Aircraft Fire and Cabin Safety Conference Multi-bay simulations Model Approach: –Establish bay to bay flow paths, vent flow paths and any leakage flows –Determine mass changes in each bay for each time increment, based on NEA flow and altitude change and temperature change –Solve for flows between bays and compute resultant O2 level in each bay –Iterate along flight path

International Aircraft Fire and Cabin Safety Conference

Current Status FAA Multi-bay model developed for specific tanks NOT available to public as the model uses specific airplane data Specific model allows examination of different distribution techniques to minimize bay-to-bay O2 variation, particularly at Landing.

International Aircraft Fire and Cabin Safety Conference Conclusions FAA computer models, together with a large amount of testing to verify the assumptions in the models have allowed the FAA to understand the potential for On-board inerting systems and has allowed FAA to go forward towards an NPRM to address high flammability fuel tanks.