Laminar hot air jets of 1/8- to 3/4-inch diameter were used to determine the hot gas ignition temperatures of various combustible vapor-air mixtures. The combustibles were n-hexane, n-octane, n-decane, a hydrocarbon jet fuel (JP-6), and an adipate ester aircraft engine oil (MIL-L-7808). Minimum ignition temperatures occurred at a fuel to air weight ratio of about 0.5 and were not greatly sensitive to variations of fuel concentration. Moderate variations of jet velocity also had little influence on these ignition temperatures. However, these temperatures decreased with increase in heat source dimensions (jet diameter). The hot gas ignition temperatures of the combustibles were not necessarily much greater than corresponding autoignition and wire ignition temperatures when the size of the heat source and the ignition criterion were the same. (Author).

Hot surface ignition temperature data are presented for n-hexane, n-octane, n-decane, JP-6 jet fuel and aircraft engine oils MIL-L-7808 (0-60-18) and H-1026 in various oxygen-nitrogen atmospheres (2.5 to 100 volume percent oxygen) under stagnant or near-stagnant flow conditions. Minimum ignition temperatures were found to increase with decreasing oxygen concentration. In vessel ignitions, these temperatures increased with decrease in fuel contact time and with increase in surface area/volume ratio. In wire ignitions, the minimum ignition temperatures increased with decrease in wire diameter, length/diameter ratio, and initial mixture temperature. Expressions were developed to define the ignition temperatures as a function of the above pertinent variables. Hot gas ignition temperatures of the above combustibles were also found to vary with the heat source diameter, for 1/8, 3/8 and 1/2-inch diameter jets. In oxidation studies with n-octane vapor air-mixtures, rates of pressure rise were found to vary as the 0.38 power of the fuel concentration (5 to 30 volume percent) and as the 1.4 power of the initial total pressure (0.6 to 13 psia) at temperatures between 428 and 536F. (Author).