June 13th-14th, 2002 International Systems Fire Protection Working Group CAA House - London, UK Modeling of Inert Gas Distribution in Commercial Transport Fuel Tanks William M Cavage Project Manager - Fuel Tank Inerting FAA AAR-440, Fire Safety R&D Branch

Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Outline Background Preliminary Model Methods Scale Tank Testing Engineering Model Summary

Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D 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 Didn’t 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

Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D 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

Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Simple Inerting Model Results Compared with Ullage Washing Data

Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D 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)

Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Scale Plywood CWT Model

Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Scale Plywood CWT Model Data Comparison

Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D 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

Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Engineering Model Assumed Flow Pattern Bay 1 Flow Out Bay 2 Flow InBay 3Bay 4 Bay 5Bay 6 Flow Out

Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Engineering Model Data Comparison

Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D Full-Scale Data Compared with Modeling Methods

Inert Gas Distribution Modeling ___________________________________ AAR-422 Fire Safety R&D 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