IASFPWG – Ottawa, Canada In-Flight Fuel Tank Flammability Testing Steve Summer Project Engineer Federal Aviation Administration Fire Safety Branch International Aircraft Systems Fire Protection Working Group Ottawa, Canada February 15 – 16, 2005

IASFPWG – Ottawa, Canada 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

IASFPWG – Ottawa, Canada 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

IASFPWG – Ottawa, Canada 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

IASFPWG – Ottawa, Canada 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 Heated Sample Box Sample Flow/Pressure Conditioning Unit Controller Electronics Panel

IASFPWG – Ottawa, Canada 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

IASFPWG – Ottawa, Canada FAS Block Diagram Heated Line Sample Backpressure Regulated Sample Flow Regulated

IASFPWG – Ottawa, Canada THC Sample Point Locations Sample point penetrations are located at ‘fastener 1’ (STA 1098) and ‘fastener 2’ (STA 630, ~40 ft from fuselage)

IASFPWG – Ottawa, Canada 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 CWT THC readings rise rapidly on ascent as hydrocarbons evolve faster at the reduced pressures, overcoming the corresponding condensation effect due to reduced temperatures. Once level flight is reached, temperature effects are what drive the THC readings General Flammability Trends Seen In Flight On descent, incoming air causes THC to drop at a slightly higher rate WT THC readings follow similar trends, except that condensation effects are always what drive THC

IASFPWG – Ottawa, Canada A Closer Look at Temperature Effects Effect of pressure overpowers condensation Once condensation effects take over, as temperatures change, so does the THC reading

IASFPWG – Ottawa, Canada 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

IASFPWG – Ottawa, Canada 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.

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

IASFPWG – Ottawa, Canada 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

IASFPWG – Ottawa, Canada Model Comparisons – Equilibrium Values

IASFPWG – Ottawa, Canada Vapor Generation Model Comparison – Ground Test

IASFPWG – Ottawa, Canada Vapor Generation Model Comparison – Flight Test

IASFPWG – Ottawa, Canada Vapor Generation Model Comparison Flight Test (25% Fuel Load)

IASFPWG – Ottawa, Canada Vapor Generation Model Comparison – Flight Test

IASFPWG – Ottawa, Canada 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

IASFPWG – Ottawa, Canada 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