In-Flight Fuel Tank Flammability Testing

1. In-Flight Fuel Tank Flammability Testing Steve Summer Project Engineer Federal Aviation Administration Fire Safety Branch The 4th Triennial Int’l Aircraft Fire and Cabin Safety Research Conference Lisbon, Portugal November 15 – 18, 2004 Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

2. Background • To date, real-time flammability (hydrocarbon) data in flight has yet to be obtained from aircraft fuel tanks (CWT or wing) • Lab-based instruments in use at the FAA are based on a flame-ionization detection (FID) technique, and are unsuitable for in flight use • Such a system must maximize safety and data reliability while being able to handle the rigors of a flight environment (vibration, pressure & temperature changes, etc…) • The FAA developed such a system for real-time monitoring of the CWT and wing tank flammability during flight tests on NASA’s 747 SCA Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

3. FAS System Overview • System uses a Non-Dispersive Infrared Analyzer (NDIR) to measure fuel tank flammability in the form of total hydrocarbons (THC) • Sample stream must be heated at all points leading to the NDIR to prevent condensation of fuel vapors • Overall system consists of two units • Pallet Mounted NDIR Analyzer • Rack Mounted Sampling System Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

4. FAS System Overview • Pallet Mounted NDIR Analyzer: • Custom built by Rosemount Analytical specifically for this application • Dual sample capability • Separated into two sections – electronics and sample stream • Sample stream section temperature controlled to 200°F • Entire unit continuously purged Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

5. FAS System Overview • Rack Mounted Sampling System: • Supplies a temperature, pressure and flow controlled sample to the NDIR utilizing four components: • Quad head (2 heads/channel) diaphragm pump pulls sample from CWT/WT • Sampling conditioning unit actively controls pressure and flow of sample supplied to NDIR • Heated box maintains a 200°F sample • Electronics panel houses all pressure/temperature electronic control units • Components containing sample lines are continuously purged Controller Electronics Panel Sample Flow/Pressure Conditioning Unit Heated Sample Box Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

6. FAS – Safety Features • System safety features include: • Diaphragm pump is safe for explosive atmosphere and pump motor has failure containment standard • Pump motor and all electronics kept separated from sample stream where possible • All enclosures that sample passes through are continuously purged • Float valve, fluid trap and flash arrestor on sample inlets Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

7. FAS Block Diagram Heated Line Sample Flow Regulated Sample Backpressure Regulated Heated Line Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

8. FAS – Performance Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

9. Sample point penetrations are located at ‘fastener 1’ (STA 1098) and ‘fastener 2’ (STA 630, ~40 ft from fuselage) THC Sample Point Locations Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

10. CWT THC readings rise rapidly on ascent as hydrocarbons evolve faster at the reduced pressures, overcoming the corresponding condensation effect due to reduced temperatures. Peak CWT THC reading on all flights corresponded closely with the start of cruise CWT THC readings rise slowly, but steadily on the ground prior to take-off Once level flight is reached, temperature effects are what drive the THC readings WT THC readings follow similar trends, except that condensation effects are always what drive THC On descent, incoming air causes THC to drop at a slightly higher rate General Flammability Trends Seen In Flight Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

11. A Closer Look at Temperature Effects Once condensation effects take over, as temperatures change, so does the THC reading Effect of pressure overpowers condensation Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

12. A Closer Look at Temperature Effects In this test, CWT temperatures don’t change much in flight…therefore, THC readings don’t change much either Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

13. Effect of Cross-Venting on Flammability As seen in previous slides, CWT THC readings drop off steadily due to condensation Sampling system shut down This test was ran with no OBIGGS and with one side of the vent capped (i.e. no cross-venting). The data is spotty as the system was turned off at various points during test…a trendline is added in black. Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

14. Effect of Cross-Venting on Flammability We again see the CWT THC drop off, but at a much higher rate, despite similar temperature trends and flight profiles This test was ran with no OBIGGS and with both sides of the vent open (i.e. with cross-venting). All pressure readings were lost, but cruise was at 31 kft Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

15. Comparison of Data with Models • Fuel Air Ratio Calculator • Developed by Ivor Thomas • Predicts FAR for a wide range of fuels over a wide range of altitudes, temperatures and mass loadings • Assumes isothermal conditions => conservative estimate • Vapor Generation Model • Developed by Prof. Polymeropolous of Rutgers University • Uses free convection and heat transfer correlations to predict total mass of vapor generated and vapor masses of the component species over time. • User must input fuel, wall and ambient temperatures and pressures Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

16. Model Comparisons – Equilibrium Values Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

17. Vapor Generation Model Comparison – Ground Test Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

18. Vapor Generation Model Comparison – Flight Test Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

19. Vapor Generation Model Comparison Flight Test (25% Fuel Load) Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

20. Vapor Generation Model Comparison – Flight Test Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

21. Summary • The FAS has been shown to accurately measure a sample of 2% propane from sea level to ~40 kft with an accuracy of 0.02% • The FAS gave consistent readings when compared to a typical FID • The FAS worked as expected during flight test except for a few minor issues such as condensation within flowmeters which were overcome during testing Aircraft Fire and Cabin Safety Research – Lisbon, Portugal

22. Summary • Data shows the strong correlation of flammability with tank temperature trends • Cross-venting through the CWT greatly increases the rate at which flammability decreases in flight (given the limited scope of the data). • Equilibrium and transient model data agreed favorably • Vapor Generation model tends to overestimate the peak THC reading Aircraft Fire and Cabin Safety Research – Lisbon, Portugal