IGNITION CHARACTERISTICS OF FUELS AND LUBRICANTS

Abstract

Abstract : The combustibles included n-hexane, n-octane, n-decane, JP-6 jet fuel, aircraft engine oil MIL-L-7808, and other hydrocarbon materials. Expressions based on thermal ignition theory are given which correlate minimum autoignition and wire ignition temperatures of the combustible vapor-oxidant mixtures as a function of the heat source dimensions, oxygen concentration, ignition delay, and initial mixture temperature (in wire ignitions). The ignition temperatures increased consistently with decreasing heat source diameter or surface area. Hot gas ignition temperatures determined for the combustibles with various size jets of hot air also varied with heat source diameter; they tended to approximate the hot surface ignition temperatures when the size of the heat source and ignition criterion were the same. Jet temperatures required to produce hot flames and luminous or cool flame reactions were also compared. In oxidation rate studies at reduced pressures with JP-6 and n-octane vapor-oxygen-nitrogen mixtures, the critical pressures for cool flame reactions increased with decreasing vessel size, temperature, oxygen concentration, and fuel concentration. In flammability studies with hydrocarbon fuel vapor-air mixtures, the upper limits of flammability are shown to increase markedly with increasing temperature, particularly in the case of the high molecular weight paraffins which display a greater tendency to form cool flames. (Author)