Why do we have NGS (Nitrogen-Generation System) and What Is It?
A NGS or nitrogen-generation system removes oxygen from the ambient air and blows it into the center fuel tank. The nitrogen is not actually “negated” rather it is separated from all other elements; there is no actual nitrogen generation.
The history of ATA Chapter 47, Inert Gas System or nitrogen generation system (NGS) for commercial use comes from the accident of TWA flight 800. Trans World Airlines Flight 800 (TWA 800) was a "Boeing 747-100 that exploded and crashed into the Atlantic Ocean near East Moriches, New York on July 17, 1996, 12 minutes after takeoff from John F. Kennedy International airport. All 230 people on board died in the third-deadliest aviation accident in U.S. history." The four-year NTSB investigation concluded that the probable cause of the accident was an explosion of flammable fuel vapors in the center fuel tank. Although it could not be determined with certainty, the likely ignition source was a short circuit. Problems with the aircraft's wiring were found, including evidence of arcing in the Fuel Quantity Indication System (FQIS) wiring that enters the tank.
Inert Gas System was not developed for the crash, rather FAA did not consider lightweight inerting systems for commercial jets until the 1996 TWA 800 Cash. The current-day inerting system uses a hollow fiber membrane material that separates supplied air into nitrogen-enriched air. The inerting system runs continuously to reduce fuel vapor flammability whenever the aircraft's engines are running; and its goal is to reduce oxygen content within the fuel tank to 12%, lower than normal atmospheric oxygen content of 21%. This is accomplished by ventilating fuel vapor laden ullage gas out of the tank and into the atmosphere.
- Ozone (O3) converter: Basically a catalytic converter that converts triatomic oxygen (ozone) to biatomic ("regular") oxygen to protect other elements in the system from oxidation.
- Heat exchanger: Cools the bleed air (which is really hot when it comes off the engine), again to protect other elements of the system and increase their effectiveness.
- Air separation module: Physically removes almost everything but the dinitrogen (N2) in the air. This separation is accomplished by running the air through semipermeable fibrous tubes; because almost all the non-N2 molecules present are smaller than the N2 molecules, those smaller molecules pass through the membranes and are exhausted overboard, leaving only the nitrogen to exit into the fuel tank.
- Other: There are various filters to protect components from particulate matter, valves to control the timing and rate of flows, controllers to control the valves, and sensors to inform the controllers.
The 787 system
The 787 is a no-bleed airplane, which means that instead there is an electric-driven compressor to supply the NGS rather than bleed air. This setup requires a slightly different heat-exchanging architecture, but the overall function and operation of the primary system components are similar.
The video and the unit we have in stock is the no-bleed electric driven compressor part number 2222254-1. Manufactured by Honeywell.
Sr Operations Manager - General Dynamics OTS, DeFuniak Springs, Fl
5 年Great article Jimmy! My first job out of the Navy was at Sundstrand Pneumatics Systems in San Diego building OBIGGS for (at that time the new) C-17. Thanks!