Fuel tank combustible mixtures-new lessons learned

The mission was to identify the environmental conditions of atmospheric pressure and ambient temperature under which a so-called empty fuel tank, containing residual fuel, could contain combustible air/fuel mixtures. The issues are limited to two applications: explosion safety concerns in aerospace and automotive vehicles; and terrestrial vehicle emissions reduction. In general, the authors concluded that flammable mixtures, under certain conditions, may exist in an empty fuel tank containing residual fuel, at ambient temperatures ranging from below -18°C (0°F) to above 38°C (100°F), at atmospheric pressure and higher altitudes. Furthermore, it is certain that an over-rich mixture normally exists in an automotive fuel tank and this fact permits the fuel rich vapor to be applied to reduce cold-start portion of exhaust emissions by diluting with air in the intake manifold. On the other hand, it is unlikely that a combustible mixture would normally exist in a jet aircraft fuel tank, because jet fuels have lean limit flash point temperatures above 38°C (100°F). Nevertheless, this study identified three highly unlikely, but rationally possible scenarios which may permit a combustible mixture to exist within a jet aircraft fuel tank and pose a potential hazard