# Presentation: 927614

## Background: 

- Inerting History

**AAR-440 Fire Safety Branch****Wm. J. Hughes Technical Center****Federal Aviation Administration**

## 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
- FAA demo Post Crash effectiveness
- DOD did OBIGGS research using PSA and ASMs
- C-5,  C-17,  C-130, Fighter Aircraft
- Found HFM technology made ASMs cost effective for OBIGGS

## Fuel Tank Inerting History

- 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 for Air Separation

- As air is forced through the fibers, fast gases escape through the fiber wall and the nitrogen rich stream to pass through the fiber core

- The separation is not direct as some oxygen passes through the core and some nitrogen ventilates from the fiber
- As flow through the core is slowed (back pressure), more fast gases escape (and N2) making the core stream  (product) more pure (less O2)

**Hollow Fiber Membrane for Air Separation**

## HFM Air Separation Module Construction

- Fibers are generally potted into an epoxy sheet at each end with some structure for strength
- The epoxy sheet is machined flat, to expose the fibers to the pressurized air source
- The ASM is mounted in a canister to facilitate pressurized air feed, gather the product (NEA), and collect the ventilated waste gas (OEA)

**HFM Air Separation Module Construction**

**Air In**

**NEA **
**Out**

**OEA Vent**

## ASM Performance

- Permeability describes how much air flows into the ASM
- Selectivity describes what percentage of that air becomes NEA
- These performance parameters are a function of ASM feed pressure, OEA vent pressure, and system back pressure
- Given these three parameters the ASM will flow a specific NEA volume and purity (residual O2 concentration)
- This is only valid at a given operational temperature
- Specific flow and purity is described by the manufacturer in terms of the above two stated parameters

**ASM Performance**

## Simplified Inert Gas Generation System Concept

- Concept utilizes ASMs 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% (by FAA research) makes sizing more realistic

## FAA Simplified Inerting System Block Diagram

## FAA Inerting 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 by ASMs and NEA is plumbed to output valves to control flow, OEA is dumped overboard with H/x cooling air
- System flow control is accomplished with low flow orifice and high flow control valve
- System controlled by control box in cabin that is connected to system with cable
- Prototype built on aluminum pallet for ease of construction and to support a wide variety of installation methods

## CAD Rendering of FAA Inerting System Prototype

**CAD Rendering of FAA Inerting System Prototype**