Detection of Explosive Mixtures in the Ullage of Aircraft Fuel Tanks

Abstract

Sensors for detecting explosive mixtures in the ullage of aircraft fuel tanks along with inerting systems are of paramount importance for preventing fires and explosions during ground and flight operations of both commercial and military aircraft. A diode laser-based oxygen sensing system is designed and tested to assess its ruggedness and performance in simulated flight conditions and fuel tank environment. This sensor system incorporates recent innovations in microelectronics such as digital signal processors, new vertical surface cavity lasers, high sensitivity absorption spectroscopy, and mechanisms for preventing liquid interferences on optical surfaces. Metal foams and sintered metals of different porosities were tested and found to prevent liquid interferences as a result of liquid sloshing/splashing and immersion without compromising the sensor’s time response. Liquid droplets on optical surfaces can interfere with the sensor’s performance. Gravity-driven flow on surfaces can remove most of the liquid. Kerosene fuel tends to form a thin liquid film on optical surfaces. The sensor’s performance was not adversely affected by this thin film. However, coatings and motions encountered during flight could further enhance the removal of liquid off optical surfaces.