Ground Based Fuel Tank Inerting

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Ground-Based Inerting of a Boeing 737 Center Wing
Fuel Tank
William M CavageAdvances in Aviation Safety
ConferenceSAE Aerospace Congress Exhibition
September 10-14, 2001 Seattle, WA
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Outline

• Background
• Work Distribution
• Instrumentation
• Inerting Data
• Ground Testing
• Flight Testing

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Background

• FAA is Seeking to Improve Upon Existing Fuel Tank
  Safety in Fleet in the wake of TWA800 Air
  Disaster
• 1998 ARAC FTHWG Stated GBI is a Potentially
  Cost-Effective Method of Providing Fuel Tank
  Protection
• Report Also States CWTs More Susceptible to
  Mishaps
• Focus of the testing is to determine if the
  Existing Fleet Vented Fuel Tanks Will Maintain
  NEA Benefit for a Significant Amount of Time
• Some CWTs in Fleet are Cross Vented
• Also Attempted to Gage Practicality

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Testing Work Distribution

• FAA Certification Office Proposed Testing to
  Examine Certain Key Assumptions. Formulated Test
  Plan
• Boeing Offered Use a Boeing B-737NG as the Test
  Aircraft
• Air Liquide Provided an NEA Generator with
  Delivery Equipment at Low Cost
• Boeing also Provided Aircraft NEA Distribution
  System, Support Personnel, Data Acquisition, and
  Most Instrumentation
• FAA Fire Safety RD Provided Integrated Ullage
  Sample System with Oxygen Analyzers

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Aircraft Instrumentation

• Oxygen Analysis System Provides 8 Channels of
  Continuous Oxygen Concentration Data
• Actively Controls Sample Inlet and Outlet
  Pressure
• Flow Through Sensor Design
• Fluid Traps, Ejector/Evacuator, Flame Suppressors
  for Safety
• Other Instrumentation
• CWT Thermocouples
• Flight Data (air speed, altitude, attitude)
• Fuel Load
• Wind Data

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System Block Diagram
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Sample Port Location Diagram
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Data Presentation

• Calculated Average Oxygen Concentration in the
  Three Primary Areas in CWT Center Section, Left
  Cheek, and Right Cheek
• Marked Some Critical Events
• Data Plotted Every 1/Second for Inerting Data,
  1/Minute for Ground and Flight Tests
• Inerting Data Nondimensionalized for Comparison

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Data Nondimensional Scheme

• Want to Express Time in Terms of Volume Delivered
  or Volumetric Tank Exchange (VTE)
• VTE Time Volume Flow Rate / Total Tank
  Volume
• Want to Express Oxygen Concentration in Terms of
  Purity Delivered. Consider that Inerting Gas is
  Slowly Changing the Ullage Oxygen Concentration
  to that of the Gas (Purity) Call this the Tank
  Inerting Ratio
• Inerting Ratio AirO2 - TankO2 /
  AirO2 - NEAO2

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Fuel Tank Inerting

• Only Inerted the CWT with Properly Operating
  Manifold 3 Times
• Fuel Clogged Lines and Prevented Equal
  Distribution at Different Times
• Data Looks Consistent with Lab Observations
• Manifold not Balanced for Optimal Delivery
  Distribution
• Performed Non-Dimensional Analysis and Compared
  with Existing Models
• Volumetric Tank Exchange Measured at
  Approximately 1.8 Tank Volumes

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Fuel Tank Inerting Data
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Nondimensional Data Comparison
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Ground Testing Data

• In Calm Conditions, Tank Oxygen Concentration
  Rose Very Little During Ground Operations, But
  some Wind Conditions Caused Sharp Increases in
  Local Oxygen Concentrations having an Overall
  Detrimental Effect
• Did Not Quantify Wind Effects
• Some Wind Conditions Generated, Some Natural
• Fueling had a Notable Effect, but Did Not Cause
  the Oxygen Concentration to Rise Above 10

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Ground Testing Data
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Ground Testing Data
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Comparison Data
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Ground Testing Data
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Ground Testing Data
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Flight Testing Data

• Due to Profound Effect of Ground Winds and some
  Flight Conditions, Vent System was Modified to
  Prevent Cross Flow After First Flight Test
• Effect of Cross-Flow Very Profound Over a Two
  Hour Flight
• Plotted Altitude with Average Bay Oxygen
  Concentrations to Illustrate Effect of Flight
• With Cross-Flow Eliminated The CWT Retained the
  Oxygen Concentration Fairly Well.

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Flight Testing Data
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Flight Testing Data
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Comparison Data
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Flight Testing Data
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Flight Testing Data
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Flight Testing Data
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Flight Testing Data Comparison

• Compare Overall Fuel Tank Oxygen Concentration
  Average to Illustrate Effect of Certain
  Parameters
• Fuel Load Effect Less Profound Then Predicted
• Effect of Fuel Burn Appears to be the Primary
  Effect on CWT O2
• Effect of Altitude Difficult to Discern

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Comparison Data
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Comparison Data
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Comparison Data
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Summary

• GBI Was Easily Accomplished by Distributing NEA
  into a CWT with a Basic Distribution Manifold
  with Amount of NEA Consistent with Lab Tests
• Fuel had a Small but Measurable Effect During
  Ground Operations
• Wind Conditions Could Have A Profound Effect on
  the Ability of a Cross Vented Aircraft fuel Tank
  Staying Inert as do Some Flight Conditions
• GBI Provided Significant Protection Through
  Takeoff and Most of Cruise to a Vented CWT
  Provided Cross Venting was Eliminated Even with
  Some Fuel Loads