Ground Based Fuel Tank Inerting

1
Modeling of Inert Gas Distribution in
Commercial Transport Fuel Tanks
William M CavageProject Manager - Fuel Tank
Inerting FAA AAR-440, Fire Safety RD Branch
June 13th-14th, 2002International Systems Fire
ProtectionWorking Group CAA House - London, UK
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Outline

• Background
• Preliminary Model Methods
• Scale Tank Testing
• Engineering Model
• Summary

3
Background

• FAA Would Like to Develop Cost Effective Methods
  of Modeling Inert Gas Distribution in Commercial
  Transport Fuel Tanks
• Developed a Scale Tank Model of the 747SP CWT
• Made From Plywood Using NTSP Shepard Report
  Drawings
• Variable NEA Deposit Capabilities, Oxygen
  Analyzer in Each Bay
• Preliminary Results Didnt Model Gas Distribution
  Well
• Developed Multiple Bay Inert Gas Distribution
  Engineering Model of 747SP CWT
• Models 6 Bay Tank in Test Article Venting Config.
  (half blocked)
• Based on Ullage Washing Model

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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

5
Simple Inerting Model Results Compared with
Ullage Washing Data
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Scale CWT Tests

• Original Plywood Model Results Encouraging, But
  NEA Distribution Did Not Compare Well with
  Full-Scale Data
• Made Several Improvements to Scale Tank
• 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)

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Scale Plywood CWT Model
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Scale Plywood CWT Model Data Comparison
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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

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Engineering Model Assumed Flow Pattern
Bay 1
Flow Out
Bay 2
Flow In
Bay 3
Bay 4
Bay 5
Bay 6
Flow Out
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Engineering Model Data Comparison
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Full-Scale Data Compared with Modeling Methods
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Summary

• Scale Tank Testing Produced Good Results when
  Compared with the Good Mixing Full-Scale
  Testing
• Cost Effective Modeling Method
• Simple Engineering Modeling Methods Can Produce
  Fair Results in a Very Cost Effective Way
• Additional Work Needed to Improve Model for
  Multiple Deposits
• Both Methods Predict VTE Required (Amount of NEA)
  Very Well, Given a Highly Localized Deposit