Development and Testing of the FAA Simplified Fuel

Development and Testing of the FAA Simplified Fuel Tank Inerting System William Cavage & Robert Morrison AAR-440 Fire Safety Branch Wm. J. Hughes Technical Center Federal Aviation Administration International Fire and Cabin Safety Research Conference Parque das Nações Conference Center Lisbon, Portugal November 15 -18, 2004

__________________ FAA Fuel Tank Inerting System Outline • Background – Inerting theory – Inerting History – ASM theory of Operation • System Architecture • Test articles – Boeing 747 SP Ground Test Article – Airbus A 320 Flight Test Aircraft – NASA 747 SCA • Results – Initial Ground Testing – Single ASM Flight Test Data – Complete System Flight Test Data • Summary AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Background • Fuel tank explosion accident history highlighted by TWA 800 disaster – Past Certification of fuel systems based on ignition source elimination, not flammability control/reduction • FAA Certification Office has been seeking flammability elimination/reduction rule since 1997 – Multiple industry rule making advisory working groups (ARAC HWGs) yielded no solutions palatable to FAA and industry • Previous research illustrated potentially most efficient fuel tank inerting method is OBIGGS – Needed to do detail study of onboard inert gas generation systems (OBIGGS) specifically for commercial applications AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Inerting Background • Inerting refers to rendering the ullage (air above fuel) unable to propagate a reaction given flammable conditions and ignition source – In this case Refers specifically to reducing tank oxygen concentration – Other methods of compliance possible • Fire Triangle must be satisfied to have a reaction (explosion) in the ullage of a fuel tank – Ignition Source – Correct ratio of fuel and air AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Fuel Tank Inerting History • Inerting has been studied since 1950 s • Stored gas inerting used by military in 1970 s – FAA built and tested demo cryogenic nitrogen system on DC-9 • DOD did OBIGGS research using PSA and ASMs – Found HFM technology made ASMs very cost effective for OBIGGS • FAA research illustrated fuel tank inerting could be practical if applied in a cost effective manner – Initially focused on ASM performance for fire suppression capabilities – After second ARAC, focused on using ASMs to generate inert gas on an aircraft from bleed air during the flight cycle – FAA experiments agree with previous experiments and indicated that a tank oxygen concentration below 12% will render tank inert AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Hollow Fiber Membrane • Hollow fiber membrane technology uses the selective permeation properties of certain materials to separate air into two streams, one nitrogen rich and the other oxygen rich (compared to air). – Materials are woven into hair-sized fibers and bundled by the thousands into a canister called an air separation module (ASM) – Pressurized air is forced through the membrane fibers, allowing fast gases to escape through the membrane wall and the nitrogen rich stream to pass through AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Architecture • A simplified inerting system conceived by Ivor Thomas (CSTA for Fuel Systems) illustrated feasibility • Concept utilizes HFMs in a two flow methodology – Uses low flow mode during taxi, takeoff, ascent, and cruise to deplete CWT of oxygen almost completely – Uses high flow mode during descent to offset (but not eliminate) the air entering the fuel tank vent system resulting in a net inert fuel tank oxygen concentration • Does not need to run on ground or store NEA, eliminates need for compressors or ground service equipment • System only needing to reduce the oxygen concentration below 12% makes sizing more realistic AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System FAA Simplified Inerting System Block Diagram AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Construction • Uses 3 ASMs based on HFM technology – Excepts 350 degree F air from aircraft bleed system through an SOV – Uses a H/x to cool air to 180˚F +/- 10˚F and a filter to condition air – Air is separated ASMs and NEA is plumbed to output valves to control flow, OEA is dumped overboard with H/X cooling air – System flow control is presently configured with low flow orifice and high flow control valve • System controlled by control box in cabin that is connected to system with cable • System built on aluminum pallet for ease of construction and to support a wide variety of installation methods AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System CAD Rendering of FAA Inerting System AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Test Articles – 747 SP • Boeing 747 SP with fully functioning systems – Decommissioned from airline service and purchased by the FAA for Ground Testing Only • All major systems fully operational • Has independent power for test equipment and instrumentation • Designed inerting system to mount in empty pack bay – Full Complement of Ground Service Equipment • Instrumentation – Aircraft is Fully Instrumented • Oxygen sampling, pressure taps, and thermocouples on system for OBIGGS performance • Thermocouples in Pack Bay • Some Weather Data Available AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Test Article - Airbus A 320 • Airbus A 320 Flight Test Vehicle – Original A 320 from production start operated by Airbus for the purposes of research and development • Fully Instrumented with extensive DAS capabilities • Was modified to accommodate an inerting system in the cargo bay – Operated out of Airbus, France Flight Test • World class mod and test center • Instrumentation – Aircraft is Fully Instrumented • Oxygen Sampling for OBIGGS performance • Pressure Transducers and Thermocouples on System. • All flight parameters performed AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Test Article – NASA 747 SCA • Highly modified Boeing 747 -100 – Reengineered and modified by NASA for the purposes of carrying a Space Shuttle Orbiter for operations and maintenance • Fully operational, standard, fuel system with unmodified pack bay – Operated out of Ellington field - Houston, Texas • Operated by excellent group of test pilots at a top notch operations facility in and maintained by dedicated group of ground service personnel • Instrumentation – Aircraft is Fully Instrumented • Oxygen sampling, pressure taps, and thermocouples on system for OBIGGS performance • Thermocouples in Pack Bay Area • Pressure altitude measured AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Measured Results – Ground Testing • Mounted and tested system in the 747 SP ground test article – Operated OBIGGS with static conditions (best as possible) for the purposes of validating the system performance – Focused on the volume flow of 5% and 11% NEA that could be generated with varying ASM pressure • Testing Illustrated – Stable system performance is difficult to achieve in a dynamic aircraft environment – Manufactures data based on general properties not specific ASM – Different measurement techniques gave different results AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Measured Results – Single ASM • Compared dynamic ASM performance with static measurements – through out flight cycle on A 320 flight test and compared to static lab data • Data comparison generally good with some large discrepancies – Illustrates the difficulty in obtaining stable temperature and pressure during flight test – 180 degree F ASM temp frequently unattainable during Airbus testing – Fixed orifice gives variable flow AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Measured Results – Single ASM • Calculated bleed air consumption for the A 320 flight cycle – Used equation in terms of NEA flow, NEA [O 2], and OEA [O 2] • Amount of bleed air consumed large but makes sense – Much higher cruise bleed pressure than expected – Stable NEA flow observed is not from stable ASM performance characteristics – Illustrates the relationship between permeability, selectivity, and altitude AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Measured Results – Single ASM • Correlated ASM pressure with NEA flow – Compared data for selected parts of A 320 testing flight cycle • Not a true correlation because ASM performance is changing – Ascent and Descent cause large variations in ASM performance due to change in altitude / ASM pressure – Cruise data shows a true correlation in the low flow mode AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Measured Results – Complete System • Measured static system flow and purity on the 747 SCA test bed at selected altitudes and somewhat stable ASM pressures – Used variable flow valve to vary flow and purity in flight – Some data did not follow trend – Highlights the difficulty in obtaining stable ASM conditions on a flight test aircraft – Stable ASM temperatures a constant battle AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Measured Results – Complete System • Dynamic performance during takeoff/ascent and descent/landing portion of flight cycle is least predictable • Analyzed this portion of flight cycle for 3 different tests – Similar ASM pressure observed – Varying but similar ascent and descent profiles • On ascent flow and purity vary for different tests although input conditions are similar – Attributed to unstable ASM temperature due to different warm ups – No adverse effect on system capabilities • On descent flow and purity vary for different tests as expected because of different variable/high flow orifice settings – Bleed air flow nearly constant AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Comparison of System Performance During Takeoff NEA Purity Data AAR-440 Fire Safety R&D NEA flow Data

__________________ FAA Fuel Tank Inerting System Comparison of System Performance During Landing NEA Purity Data AAR-440 Fire Safety R&D NEA flow Data

__________________ FAA Fuel Tank Inerting System Comparison of System Bleed air Flow During Landing AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System Summary • FAA used existing technology in an innovative way to develop a near term, simple, solution to fuel tank flammability control • Duplicating static OBIGGS performance data on an aircraft could be problematic, but the system performed as expected • Bleed air consumption should be studied further to examine the penalty associated with high bleed air consumption and potential methods of reducing bleed air consumption • Measurable performance variations observed at the start of system attributed to different warm-up times did not hamper system from reducing ullage oxygen concentration • Bleed air consumption remained constant after the system was sufficiently warmed-up even when varying flow and purity AAR-440 Fire Safety R&D

__________________ FAA Fuel Tank Inerting System The Fourth Triennial International Aircraft Fire and Cabin Safety Research Conference AAR-440 Fire Safety R&D