Oxygen Concentration and Wavelength Agile Spectral Harmonic Sensors
Mitigation of some potential aircraft explosion possibilities in flight is possible by eliminating the ability of combustion to initiate and propagate in the aircraft fuel system. On-Board Inert Gas Generation Systems (OBIGGS) are used to control the gaseous environment in the fuel tank ullage and minimize this combustion hazard. This system currently utilizes the injection of nitrogen enriched air (NEA) in the the fuel tank. Current technology has the OBIGGS system operating in an open loop manner, injecting sufficient nitrogen to dilute the air present in the open volume of the tank several times. The current systems do not have reliable sensors to use in feedback controllers. As such, an accurate oxygen sensor would allow the system to inject only as much NEA as necessary and offer more fault-proof operation of the system.
APRI has developed a compact, robust, optically-based sensor for measuring local oxygen concentration in aircraft fuel tanks. This system utilizes absorption of a rapidly scanned Vertical Cavity Surface Emitting Diode Lasers (VCSELs) by molecular oxygen. The system can accurately measure oxygen concentration over a wide range of ambient conditions from below sea level to high altitudes utilizing a spectroscopic frequency domain detection scheme known as the wavelength agile spectral-harmonic (WASH) technique. WASH is self referencing and does not require periodic calibration, it is able to withstand immersion into liquid fuels, and has a response time greater than 10Hz.
The flight-weight sensor has been tested in a relevant environment under the environmental conditions found in an aircraft fuel tank. The sensor has passed shock and vibration test, electro-magnetic interference (EMI) test, electro magnetic compatibility (EMC) test and the explosive atmosphere test. Interface to the host aircraft is accomplished through flexible digital or analog data paths.
Inquiries concerning APRI's Oxygen Sensor program should be directed to Dr. Thomas Sobota at Thomas.Sobota@apri.com