We propose to engineer a compact, robust, optically-based sensor for measuring local oxygen concentration in aircraft fuel tanks. This system will utilize absorption of rapidly scanned Vertical Cavity Surface Emitting Diode Lasers (VCSELs) by molecular oxygen. This proposed system can measure 100 ppm to 100% oxygen in ambient temperatures from -100 to 300 F utilizing a new spectroscopic frequency domain detection scheme known as the wavelength agile spectral-harmonic (WASH) technique. The wavelength agile aspect of the laser source allows for temperature insensitive measurements of oxygen concentration over a wide range of pressures (0.1 atm to 50 atm). The system will also possess auto-calibration capabilities, the ability to withstand temporary immersion in all liquid fuels, fast time response (~100 msec), and long operating life (> 10,000 hrs). POTENTIAL COMMERCIAL APPLICATIONS There are many commercial and military applications for an accurate and rugged fuel tank oxygen concentration sensor. The fuel tank oxygen sensor could be used in both new and retrofit commercial aircraft as a control sensor for fuel tank protection systems. The reliable and precise instrument can be used to control onboard inert gas generation systems (OBIGGS) for cargo compartment fire suppression, fuel tank inerting, and emergency breathing oxygen systems (OBOGS) for passengers and crew. The key to the commercial viability of this product is the accuracy of the sensor, its ability to handle harsh environments including highly variable temperatures and pressures, and its reliability and lifetime, which we propose to engineer into the system. The long operating lifetime and stability of this measurement system in challenging operating environments are superior to existing oxygen measurement strategies.
