Fuel Tank Protection Research at NASA GRC

1. Fuel Tank Protection Research at NASA GRC Clarence T. ChangNASA Glenn Research CenterCleveland, Ohio 44135USAINTERNATIONAL AIRCRAFT SYSTEMS FIRE PROTECTION WORKING GROUP MEETINGNovember 1-2, 2005Atlantic City, New JerseyUSA

2. The Problem The Outcomes The Inputs Ignition sources Fuel tank constraints Always FATAL Ullage detonation Fuel Ignitable fuel tank ullage mixture Detonation transition Mostly FATAL May be survivable Outside air Tank over- pressure Limited ignition Survivable Damage Corrective responses No Problem No ignition CTC 9-15-2005 O2 sensor Inert gas Inert gas generation Ullage ignition model Ullage flammability sensors Adaptive OBIGGS

3. n-Octane iso-Octane MTBE Fuel Modification Reduces Ignition Overpressure Vapor Pressure Increases With Branching Ignition Energy Increases with Branching Energy Density Increases with Branching Vapor Phase iso-Octane Concentration is 3 Times That of n-Octane at 40oC, MIE is a Factor of 6 Higher Substitution of Branched for Linear Alkanes Reduces Pressure Impulse Thus Reducing Structural Failure Branched Alkanes Increase Ignition Delay That Decreases Reaction Rates and Leads to Flame Extinction Linear Species (n-Octane) Form Reactive Ethylene While Branched Species (iso-Octane, MTBE) Form Reaction Quenching Isobutylene

4. 103 n-Octane, 35.9 ºC, Φ=2 102 n-Octane, 18.3 ºC, Φ=1 n-Octane, 17 ºC, Φ=0.95 Spark Energy ,mJ 101 n-Octane, 19.8 ºC, Φ=1.06 n-Octane, 19.8 ºC (no spark) 100 10-1 100 101 102 103 104 Spark Duration, μs Ignition Sensitization: Minimum Ignition Energy Dependent on Spark Duration! n-Octane MIE vs. Spark Duration

5. Ullage gas Detonation Deflagration Unspecified Ignition Source Liquid fuel at bottom C B A Fuel tank Protection -Deflagration-to-Detonation Transition • Ignition in compartment A results in constant-volume combustion • Constant volume combustion results in over-pressure in A maximum 8x • Pressurized gas jets into compartment B at sonic speed. • Jet poses 4-10 order of magnitude stronger ignition energy than the MIE • Jet ignites ullage gas in B, transition from deflagration to detonation wave. Some deflagration over-pressure may be survivable. Detonation is not survivable.

6. 100 98 150 ºF 180 ºF 96 ASM, N2 only CDI, Φ = 0.70, N2 only 94 CDI, Φ = 0.70, N2+CO2 92 90 Inert-Gas Purity, % 88 86 84 82 80 Φ = 0.70 Dry Combustion Products and Air at 150 ºF and 180 ºF at 40 psig 0 10 20 30 40 50 60 70 80 90 100 Inert-Gas Recovery Fraction, % Improved Inert-Gas Recovery from Combustion Derived Inerting 1/3 More N2 Recovery or ¼ less Bleed Air Needed

7. Gas Inlet Low-Volume Gas Sampling Chamber (or Fuel Tank Ullage) Real-Time Fiber Optic Gas Analyzer Fiber Optic Sensor Probe Advantages Gas Outlet • Real-Time: 5 second update interval for feedback control, and critical time-dependent process monitoring • Multi-Species Analysis: N2, O2, CO2, H2O, CO, CH4, other HC’s, H2, H2S, NO, SO2,… • Precise: currently has 1% precision in 5 seconds for N2; future versions will require < 1 second for same precision • Rugged and Reliable: system has no moving parts to go out of alignment or consumables to wear out • Intrinsically-Safe: No electrical penetration into measurement volume • Cost-Effective: Monitor multiple locations simultaneously with multiple fiber sensors and one base unit Respiration Gas Monitoring Example In-Tank Real-Time Multi-Species Fiber Optic Flammability Sensor

8. Contact Information at NASA Glenn Research Center CDI-OBIGGS & Ignition Mitigation Clarence Chang, Ph.D. Clarence.T.Chang@nasa.gov Deflagration-to-Detonation Transition Science Nan-Suey Liu, Dr.-Ing. Nan-Suey.Liu@nasa.gov In-Tank Real-Time Flammability Sensor Quang-Viet Nguyen, Ph.D. Quang-Viet.Nguyen@nasa.gov Fuel & Ignition Science Marty Rabinowitz, Ph.D. Martin.J.Rabinowitz@nasa.gov