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Topic Discussion NFPA World Safety Conference & Exposition Minneapolis, MN May 19-23, 2002

An Overview of Commercial Transport Airplane Fuel Tank Inerting Research. William M Cavage Lead Engineer - Fuel Tank Inerting FAA AAR-440, Fire Safety R&D Branch. Topic Discussion NFPA World Safety Conference & Exposition Minneapolis, MN May 19-23, 2002. Outline. Background

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Topic Discussion NFPA World Safety Conference & Exposition Minneapolis, MN May 19-23, 2002

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  1. An Overview of Commercial Transport Airplane Fuel Tank Inerting Research William M CavageLead Engineer - Fuel Tank Inerting FAA AAR-440, Fire Safety R&D Branch Topic DiscussionNFPA World SafetyConference & Exposition Minneapolis, MN May 19-23, 2002

  2. Outline • Background • Previous Research • Preliminary Research • Full-Scale Fuel Tank Inerting • Inert Gas Distribution Modeling • Onboard Inert Gas Generation AAR-422 Fire Safety R&D

  3. Background - Accident History • Three Accidents in Recent History • 1990: 737-300 - Manila, Philippines • 1996: 747-100 - New York, United States • 2001: 737-400 - Bangkok, Thailand (Investigation Pending) • All Accidents had Explosions in Center Wing-Tank • Explosions Occurred During/Just After Long Ground Operations on Hot Days with Empty (Residual Fuel) Center Wing Tanks • Exact Ignition Source Not Found During Any Investigation AAR-422 Fire Safety R&D

  4. Background - Recent Regulatory Activity • Inspections Required • 737, 747 Fuel Tank Wiring, 747 CWT Terminal Blocks, FQIS • Scavenge Pump Inspections, Related Equipment • Airworthiness Directives Issued • Various Fuel Pump Wiring/Connectors Inspect/Replace • Scavenge Pump and Surge Tank Flame Arrestor Installation • FQIS Wiring, Terminals, and Connectors Inspect/Replace • Special Addition to FARs (SFAR 88) • Requires Re-Validation of all Fuel Tank Safety Analysis for Existing Large Commercial Transport Category Airplanes • New Type Certificate Airplanes Must Minimize Flammability of Center-Wing Type Fuel Tanks to Be Equivalent to Wing Tanks AAR-422 Fire Safety R&D

  5. Background - Proposed Flammability Rule • FAA Issued Rule-Making Project Letter • Wrote Tasking Statement and Coordinated with JAA and ARAC and Published Notice in Federal Registry • ARAC Committee Formed Working Group • Congressionally Sanctioned Industry Oversight Committee that Advises FAA on Rulemaking • ARAC Working Group is made up of Industry Experts, Government Regulators, and Consumer Advocates • Focused on Analyzing Inerting Methods that could be Potentially Cost-Effective for the Commercial Fleet • Performed Extensive Cost Benefit Analysis • Report Pending Industry/Government Consensus AAR-422 Fire Safety R&D

  6. Previous Research - Methods • Macdonald and Wyeth - Fire and Explosion Protection of Fuel Tank Ullage, Circa 1950s • Compares Different Methods of Reducing Flammability including Nitrogen Inerting • Emphasized Requirements for Low Weight and Reliability • Klueg, McAdoo, and Neese - Performance of a DC-9 Aircraft Liquid Nitrogen Fuel Tank Inerting System, 1972 • FAA Developed and Tested an Inerting System Using Stored LN2 • System was Big, Heavy, and Required Extensive Ground Support • Yagle, et al. - Performance Tests of Two Inert Gas Generator Concepts for Airplane Fuel Tank Inerting, 1983 • Compared Pressure Swing Absorption (PSA) with Hollow Fiber Membrane (HFM) AAR-422 Fire Safety R&D

  7. Previous Research - Requirements • Stewart and Starkman - Inerting Conditions for Aircraft Fuel Tanks, 1955 • Most Comprehensive Work to Date on Flammability Limits and Oxygen Concentration Requirements • Pre-Dates JP-8 (Jet A) • Much of the Work is Theoretical with Limited Validation Points • Kuchta - Oxygen Dilution Requirements for Inerting Aircraft Fuel Tanks, 1970 • Presents Minimum Oxygen Requirements for CO2 and N2 From a Large body of Spark Ignition Data • No JP-8 Data (some Kerosene), Very Little Altitude Data AAR-422 Fire Safety R&D

  8. Previous Research - Requirements (cont’d) • Hill and Johnson - Investigation of Aircraft Fuel Tank Explosions and Nitrogen Inerting Requirements During Ground Fires, 1975 • Extensive Work on Ground Fires (Post Crash Scenarios) Causing Wing Fuel Tank Explosions • Largely Destructive Work had Older Test Articles AAR-422 Fire Safety R&D

  9. Preliminary Research • Ullage Washing Experiments (Inerting) • Quantitatively Determined Amount of Nitrogen Enriched Air (NEA) Required to Inert a Fuel Tank Test Article • Simple Rectangular Tank with Single Deposit Nozzle and Single Vent • Examined Different NEA % (Residual O2 Concentration) and Flow Rates as well as Examined Effects of Fuel Vapor and Temperature • Ullage Washing is Term Describing Inerting by Ventilation • Developed Nondimensional Relationships, Empirical Equation, and a Theoretical “Perfect Mixing” Solution • Data Illustrated that a VTE of 1.5 to 1.6 is Needed to Inert an Ullage to 8% Oxygen by Volume with 95% NEA (5% [O2]) • Published Report DOT/FAA/AR-01/6 AAR-422 Fire Safety R&D

  10. Rectangular Fuel Tank Inerting Data AAR-422 Fire Safety R&D

  11. Preliminary Research • Fuel Effects on an Inert Ullage • Quantitatively Determined the Effect an Unscrubbed Fuel Load Can Have on an Adjacent Inert Ullage • Simple Rectangular Tank with Single Deposit Nozzle and Single Vent • Examined Fuel Loads of 20, 40, 60, and 80 Percent Full at Sea Level and Two Altitudes; Inerted to 6, 8, and 10 Percent • Measured the Increase in Ullage [O2] due to Air Evolving from Fuel • Circulated the Ullage Through the Fuel to Bring Tank to Equilibrium Quickly - Represents Maximum Fuel Effect on Ullage • Study of Time Effects Showed Unless You Stimulate the Fuel, The Excess Air in Fuel had Small Effect on Ullage • Report Pending Publication AAR-422 Fire Safety R&D

  12. Inert Ullage Fuel Effects Data Max Increase in Ullage [O2] Due to Adjacent Fuel Load AAR-422 Fire Safety R&D

  13. Preliminary Research • GBI Proof of Concept Ground/Flight Testing • Joint Project with Boeing that Evaluated the Concept of Ground-Based Inerting • GBI is Inerting on Ground, Perform Ground Operations, and Fly • Examined the Effects of Wind and Flight Conditions on Ullage Oxygen Concentration of a model 737-700 • Inerted Tank with Ground Supplied NEA to Approximately 8% • Measured Oxygen Concentration at 8 Locations in CWT During “Normal” Ground and Flight Conditions • Testing Illustrated that the Benefit from Inerting was Substantial • Must Eliminate/Reduce CWT Cross Venting with Vent System Mod • Some Benefit Even With Small Fuel Loads • Published Report DOT/FAA/AR-01/63 AAR-422 Fire Safety R&D

  14. GBI Flight Test Data AAR-422 Fire Safety R&D

  15. Preliminary Research • Scale Boeing 747SP Tank Inerting • Quarter-Scale Model of Boeing 747SP CWT was Built from Three Quarter Inch Plywood By Scaling Drawings from Shepherd Report (24% Length Scale) • Variable Deposit Manifold Allowed for NEA to be Deposited at Any Rate in any Bay(s) Desired • Measured Oxygen Concentration in Each of the 6 Bays • Testing Illustrated that Equally Deposit NEA 95 will Allow for Comparable Results to the Simple Tank (VTE of 1.5-1.6 to 8%) • More Importantly, Uneven Deposit of Inert Gas Resulted in More Efficient Inerting (Less Gas to Inert the Same), Particularly when Half the Vent System Was Blocked • Published Report DOT/FAA/AR-02/51 AAR-422 Fire Safety R&D

  16. Boeing 747SP Scale CWT Model Inerting AAR-422 Fire Safety R&D

  17. Preliminary Research • Lower Oxygen Content Study • Performed Ignition Experiments with Model Fuel Tank in Pressure Chamber with both Propane and JP-8 at Reduced Oxygen Concentration • Tank Instrumented with Thermocouples and Sample Lines for Hydrocarbon and Oxygen Concentration Measurement. • Heaters Placed Underneath the Tank Control the Liquid Fuel Temperature (Flammability). • Used Single High Power Spark to Ensure a Reaction if Probable • Study at Sea Level and Altitude to 38K Feet • Follow on Tests Validated Previous Testing that the Critical Oxygen Concentration is Approximately 12% at Sea Level • Report Pending Publication AAR-422 Fire Safety R&D

  18. Lower Oxygen Content Study Data AAR-422 Fire Safety R&D

  19. Full-Scale Fuel Tank Inerting • Boeing 747SP Test Article • 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 • Center-Wing Tank Fully Instrumented • Gas Sample Tubing for Oxygen and Total Hydrocarbon Analysis • 32 Thermocouples in Tank (Ullage, Fuel, Walls, Floor, and Ceiling) • Other Instrumentation • Additional Thermocouples in Pack Bay, NEA Deposit, Cabin etc. • 4 User Specified Oxygen Analysis Channels (Vent Channel, Dry Bay, etc.) • Some Weather Data Acquired • Full Complement of Ground Service Equipment AAR-422 Fire Safety R&D

  20. Boeing 747SP in Photo AAR-422 Fire Safety R&D

  21. 747SP Center Wing Tank Top Diagram AAR-422 Fire Safety R&D

  22. Full-Scale Fuel Tank Inerting • Validation of Assumptions / Localized Deposit • 747SP is Plumbed with a Single Deposit Manifold in Bay 3 Which was the Optimal Case (most efficient inerting), Developed from the Scale Tank Testing, with Half the Vent System Blocked • Inerted Tank with Different NEA Purities and Different Flow Rates in an Attempt to Validate Existing Knowledge Base and Assumptions • Limited Amount of Data to Date • Preliminary Data Shows Deposit Methodology and Modeling Work was Sound and Productive • Preliminary Data Looks Good as long as Mixing is Promoted by Operating the ACMs AAR-422 Fire Safety R&D

  23. 747SP Center Wing Tank Inerting Data AAR-422 Fire Safety R&D

  24. 747SP Center Wing Tank Inerting Data AAR-422 Fire Safety R&D

  25. Full-Scale Fuel Tank Inerting • Vertical Mixing / Temperature Effects • Quiescent Full-Scale Testing has Indicated that Inerting of the 747SP in the Optimal Deposit Method Developed with the Plywood Model can be Problematic (No ACMs Operating) • Inerting Efficiency Different from Test to Test • Measured Strong “Vertical Effects” in one Full Length Bay • Bottom of Bay [O2] Lags Behind Top of Bay on Quiescent Tests • Complicated by the Fact that Sample System only Samples from Top • Preliminary Data Shows Effect is Not NEA Temperature Dependant but is Effected by the NEA Temperature • Developed Inerting Efficiency Coefficient to Compare Tests • Back Calculate VTEs between 1.2 and 2.0 to reach 8% [O2] with 95% NEA AAR-422 Fire Safety R&D

  26. 747SP Inerting Data with Different Vertical Mixing AAR-422 Fire Safety R&D

  27. 747SP Calculated Inerting Curves with Different Vertical Mixing AAR-422 Fire Safety R&D

  28. Inert Gas Distribution Modeling • Preliminary Models • Original Simple Inerting Model Developed by Ivor Thomas (FAA CSTA for Fuel Systems) • Tracks the Volume of Oxygen In and Out of a Tank and Calculates Oxygen Concentration Given the Tank Volume • Uses a Basic Spreadsheet Layout and Runs Instantaneously Given the Volume of the Tank, The Flow Rate and Purity of the NEA • Basic Formula for Model • Model Results Compared Well with Ullage Washing Data AAR-422 Fire Safety R&D

  29. Simple Inerting Model Results Compared with Ullage Washing Data AAR-422 Fire Safety R&D

  30. Inert Gas Distribution Modeling • Scale CWT Model • Original Plywood Model Results Encouraging, But NEA Distribution Did Not Compare Well with Full-Scale Data • Made Several Improvements to Model • Better Modeling of Vent System Cross Sectional Flow Areas • Ensured Lid Did Not Leak Around Bay Tops which Would Alter Flow Pattern • Performed Additional Testing • Scale Tank Inert Gas Distribution Results Compared Very Well to Data Acquired on 747SP full-scale test article • Additional Testing Planned for Different Deposit Methods (Onboard System) AAR-422 Fire Safety R&D

  31. Scale Plywood CWT Model AAR-422 Fire Safety R&D

  32. Scale Plywood CWT Model Data Comparison AAR-422 Fire Safety R&D

  33. Inerting Model Development • Multiple-Bay Inerting Engineering Model • Model Calculates Inert Gas Distribution in 6 Bay Tank, in terms of Oxygen Concentration Evolution, Given NEA Purity and Bay Deposit Flow Rates • Based on Original Inerting Model by Ivor Thomas which Tracks Oxygen In and Out of Each Bay Assuming Perfect Mixing During the Time Step • Assumes an “Outward” Flow Pattern and Splits Flow into a Bay to Adjacent Bays Using Out Flow Area Relationships • Presently Does Half Blocked Venting Case Only • Compared with Full-Scale Test Article • Must Run ACMs to Obtain Data that Agrees with Engineering Model (Which Assumes Perfect Mixing) • Agrees Best for Single Deposit Case Compared with Scale Tank Data AAR-422 Fire Safety R&D

  34. Engineering Model Assumed Flow Pattern Bay 1 Flow Out Bay 2 Flow In Bay 3 Bay 4 Bay 5 Bay 6 Flow Out AAR-422 Fire Safety R&D

  35. Engineering Model Data Comparison AAR-422 Fire Safety R&D

  36. Full-Scale Data Compared with Modeling Methods AAR-422 Fire Safety R&D

  37. Onboard Inert Gas Generation System • Popular Methods of Generating NEA or N2 • Pressure Swing Absorption (PSA) • System Pressurizes a Separation Bed with Air and Allows to Dwell • Can Generate High Purity N2 and O2 (OBIGGs/OBOGs) • Systems can be Designed to Have High Output Volumes • Needs High Pressure Bleed Air / Many Complex Moving Parts • Hollow Fiber Membrane Gas Separation • Hollow Polymeric Membranes Are Wove and Bundled in Canisters -Pressurized Bundle Ends Separates Fast and Slow Gases in Air • Can Operate at Low Pressures and Systems Have very Few Moving Parts • Can Not Generate O2, Inefficient at Producing NEA above 99% Nitrogen • Distillation / Cryogenic • New Technology Allows for Small Scale Liquefaction of Air Components • Low Output so Storage is Needed AAR-422 Fire Safety R&D

  38. Onboard Inert Gas Generation System • Commercial Transport Onboard System Development • Optimized a System for Inerting Boeing 747SP CWT on Ground • System Designed to Inert Empty CWT below 12% in less then 90 Minutes with Compressor. Can Inert in Half that time with Bleed Air • System Installed in Pack Bay Area with Crashworthy Mounting • System Weight Approx. 240 lbs Plus Deposit Plumbing and Vent Modification • System Designed to Provide Some Cargo Bay Fire Protection • Replace a Bleed System for 747SP • Specified all Airworthy, Commercially Available Parts • Some Parts will be for Ground Test Only • Compressor is Modification of Existing Design AAR-422 Fire Safety R&D

  39. OBGI System Block Diagram AAR-422 Fire Safety R&D

  40. 3-D Rendering of System Installation AAR-422 Fire Safety R&D

  41. Closing Remarks • Addition Information • Contact Me @ AAR-440 Fire Safety Branch, Building 204 Wm. J Hughes Technical Center Atlantic City Int’l Airport, NJ 08405 (609) 485 - 4993 william.m.cavage@faa.gov • Fire Safety Web Site @ www.fire.tc.faa.gov • Inerting Work is Under Systems Fire Group / Fuel Tank Safety • More Information on Projects and Facilities • Download Reports and Presentations (Including This One!!!) • International Systems Fire Protection Working Group • Open Forum to Discuss FAA/Industry R&D in Area of Aviation Fire Protection (Including Fuel Tank Safety) - Register on Web Site AAR-422 Fire Safety R&D

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