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Topic Discussion NFPA World Safety Conference & Exposition Minneapolis, MN May 19-23, 2002 PowerPoint Presentation
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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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Presentation Transcript
slide1

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

slide2

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

slide3

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

slide4

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

slide5

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

slide6

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

slide7

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

slide8

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

slide9

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

slide11

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

slide12

Inert Ullage Fuel Effects Data

Max Increase in Ullage [O2]

Due to Adjacent Fuel Load

AAR-422 Fire Safety R&D

slide13

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

slide14

GBI Flight Test Data

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slide15

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

slide17

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

slide18

Lower Oxygen Content Study Data

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slide19

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

slide20

Boeing 747SP in Photo

AAR-422 Fire Safety R&D

slide21

747SP Center Wing Tank Top Diagram

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slide22

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

slide25

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

slide28

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

slide30

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

slide31

Scale Plywood CWT Model

AAR-422 Fire Safety R&D

slide33

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

slide34

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

slide35

Engineering Model Data Comparison

AAR-422 Fire Safety R&D

slide37

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

slide38

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

slide39

OBGI System Block Diagram

AAR-422 Fire Safety R&D

slide41

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