# Presentation: 267662

## Development and Testing of the FAA Simplified Fuel Tank Inerting System

- William Cavage & Robert MorrisonAAR-440 Fire Safety Branch Wm. J. Hughes Technical Center Federal Aviation Administration

- International Fire and Cabin Safety Research ConferenceParque das Nações Conference Center Lisbon, Portugal November 15-18, 2004

## Outline

- Background
- Inerting theory
- Inerting History
- ASM theory of Operation
- System Architecture
- Test articles
- Boeing 747SP Ground Test Article
- Airbus A320 Flight Test Aircraft
- NASA 747 SCA

- Results
- Initial Ground Testing
- Single ASM Flight Test Data
- Complete System Flight Test Data
- Summary

## Background

- Fuel tank explosion accident history highlighted by TWA800 disaster
- Past Certification of fuel systems based on ignition source elimination, not flammability control/reduction
- FAA Certification Office has been seeking flammability elimination/reduction rule since 1997
- Multiple industry rule making advisory working groups (ARAC HWGs) yielded no solutions palatable to FAA and industry
- Previous research illustrated potentially most efficient fuel tank inerting method is OBIGGS
- Needed to do detail study of onboard inert gas generation systems (OBIGGS) specifically for commercial applications

## Inerting Background

- Inerting refers to rendering the ullage (air above fuel) unable to propagate a reaction given flammable conditions and ignition source
- In this case Refers specifically to reducing tank oxygen concentration
- Other methods of compliance possible

- Fire Triangle must be satisfied to have a reaction (explosion) in the ullage of a fuel tank
- Ignition Source
- Correct ratio of fuel and air

## Fuel Tank Inerting History

- Inerting has been studied since 1950s
- Stored gas inerting used by military in 1970s
- FAA built and tested demo cryogenic nitrogen system on DC-9
- DOD did OBIGGS research using PSA and ASMs
- Found HFM technology made ASMs very cost effective for OBIGGS
- FAA research illustrated fuel tank inerting could be practical if applied in a cost effective manner
- Initially focused on ASM performance for fire suppression capabilities
- After second ARAC, focused on using ASMs to generate inert gas on an aircraft from bleed air during the flight cycle
- FAA experiments agree with previous experiments and indicated that a tank oxygen concentration below 12% will render tank inert

## Hollow Fiber Membrane

- Materials are woven into hair-sized fibers and bundled by the thousands into a canister called an air separation module (ASM)

- Pressurized air is forced through the  membrane fibers, allowing fast gases to escape through the membrane wall and the nitrogen rich stream to pass through

## System Architecture

- A simplified inerting system conceived by Ivor Thomas (CSTA for Fuel Systems) illustrated feasibility
- Concept utilizes HFMs in a two flow methodology
- Uses low flow mode during taxi, takeoff, ascent, and cruise to deplete CWT of oxygen almost completely
- Uses high flow mode during descent to offset (but not eliminate) the air entering the fuel tank vent system resulting in a net inert fuel tank oxygen concentration
- Does not need to run on ground or store NEA, eliminates need for compressors or ground service equipment
- System only needing to reduce the oxygen concentration below 12% makes sizing more realistic

## FAA Simplified Inerting System Block Diagram

## System Construction

- Uses 3 ASMs based on HFM technology
- Excepts 350 degree F air from aircraft bleed system through an SOV
- Uses a H/x to cool air to 180 ̊F +/- 10 ̊F and a filter to condition air
- Air is separated ASMs and NEA is plumbed to output valves to control flow, OEA is dumped overboard with H/X cooling air
- System flow control is presently configured with low flow orifice and high flow control valve
- System controlled by control box in cabin that is connected to system with cable
- System built on aluminum pallet for ease of construction and to support a wide variety of installation methods

## CAD Rendering of FAA Inerting System

## Test Articles – 747 SP

- Boeing 747SP with fully functioning systems
- Decommissioned from airline service and purchased by the FAA for **Ground Testing Only**
- All major systems fully operational
- Has independent power for test equipment and instrumentation
- Designed inerting system to mount in empty pack bay
- Full Complement of Ground Service Equipment

- Instrumentation
- Aircraft is Fully Instrumented
- Oxygen sampling, pressure taps, and thermocouples on system for OBIGGS performance
- Thermocouples in Pack Bay
- Some Weather Data Available

## Test Article - Airbus A320

- Airbus A320 Flight Test Vehicle
- Original A320 from production start operated by Airbus for the purposes of research and development
- Fully Instrumented with extensive DAS capabilities
- Was modified to accommodate an inerting system in the cargo bay
- Operated out of Airbus, France Flight Test
- World class mod and test center

- Instrumentation
- Aircraft is Fully Instrumented
- Oxygen Sampling for OBIGGS performance
- Pressure Transducers and Thermocouples on System.
- All flight parameters recorded

## Test Article – NASA 747 SCA

- Highly modified Boeing 747-100
- Reengineered and modified by NASA for the purposes of carrying a Space Shuttle Orbiter for operations and maintenance
- Fully operational, standard, fuel system with unmodified pack bay
- Operated out of Ellington field - Houston, Texas
- Operated by excellent group of test pilots at a top notch operations facility in and maintained by dedicated group of ground service personnel

- Instrumentation
- Aircraft is Fully Instrumented
- Oxygen sampling, pressure taps, and thermocouples on system for OBIGGS performance
- Thermocouples in Pack Bay Area
- Pressure altitude measured

## Measured Results – Ground Testing

- Operated OBIGGS with static conditions (best as possible) for the purposes of validating the system performance
- Focused on the volume flow of 5% and 11% NEA that could be generated with varying ASM pressure

- Testing Illustrated
- Stable system performance is difficult to achieve in a dynamic aircraft environment
- Manufactures data based on single ASM
- Different measurement techniques gave different results

## Measured Results – Single ASM

- Operated on A320 flight test and compared to static lab data
- Data comparison generally good with some large discrepancies

- Illustrates the difficulty in obtaining stable temperature and pressure during flight test
- 180 degree F ASM temp frequently unattainable during Airbus testing
- Fixed orifice gives variable flow

## Measured Results – Single ASM

- Used equation in terms of NEA flow, NEA [O2], and OEA [O2]
- Amount of bleed air consumed large but makes sense
- Much higher cruise bleed pressure than expected

- Stable NEA flow observed is not from stable ASM performance characteristics
- Illustrates the relationship between permeability, selectivity, and altitude

## Measured Results – Single ASM

- Compared data for selected parts of A320 testing flight cycle
- Not a true correlation because ASM performance is changing

- Ascent and Descent cause large variations in ASM performance due to change in altitude / ASM pressure
- Cruise data shows a true correlation in the low flow mode

## Measured Results – Complete System

- Used variable flow valve to vary flow and purity in flight

- Some data did not follow trend
- Highlights the difficulty in obtaining stable ASM conditions on a flight test aircraft
- Stable ASM temperatures a constant battle

## Measured Results – Complete System

- Analyzed this portion of flight cycle for 3 different tests
- Similar ASM pressure observed
- Varying but similar ascent and descent profiles
- On ascent flow and purity vary for different tests although input conditions are similar
- Attributed to unstable ASM temperature due to different warm ups
- No adverse effect on system capabilities
- On descent flow and purity vary for different tests as expected because of different variable/high flow orifice settings
- Bleed air flow nearly constant

## Comparison of System Performance During Takeoff

- NEA flow Data

## Comparison of System Performance During Landing

- NEA flow Data

## Comparison of System Bleed air Flow During Landing

## Summary

- Duplicating static OBIGGS performance data on an aircraft could be problematic, but the system performed as expected
- Bleed air consumption should be studied further to examine the penalty associated with high bleed air consumption and potential methods of reducing bleed air consumption
- Measurable performance variations observed at the start of system attributed to different warm-up times did not hamper system from reducing ullage oxygen concentration
- Bleed air consumption remained constant after the system was sufficiently warmed-up even when varying flow and purity