At high temperatures, the vapor pressure of kerosene-type hydrocarbons is difficult to measure accurately with laboratory apparatus. Because of the inherent difficulties in direct measurement of vapor pressure-temperature relationships at high temperatures, the vapor pressure is being determined through calculation techniques. The purposes of this report are to compare the difficulty and accuracy of five techniques, of which three were basic calculation techniques and two were experimental techniques. In an effort to com-pare the techniques and to determine the precision of a calculation technique, four independent workers calculated the vapor pressure-temperature relationship for one high-quality jet fuel and for one synthetic blend of seven pure hydrocarbons. The results demonstrate that the method of assuming segments of the true boiling point curve to be pure compounds and finding the total vapor pressure as the sum of the component partial pressures in precise to ±5 percent. The empirical technique developed by Demister is less accurate (based on the comparison with experimental results) and less precise than the more laborious true boiling point curve technique. An empirical curve relating the 20-percent point to vapor pressure was found to be within ±10 percent of experimental results when applied to fuels with a Reid Vapor Pressure of less than 0.1 psia and a 5 per-cent to 95 percent ASTM distillation range of less than 200° F.
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