Prediction of the influence of pressure on flash points of liquid fuels at sub-atmospheric pressure

Abstract

Aircraft fuel tanks experience sub-atmospheric pressure during flight, and so do fuels during storage and transportation at high altitudes. Additionally, chemical processes commonly operate at non-atmospheric pressure. Flash points measured at sub-atmospheric pressure are lower than those measured at the standard atmospheric pressure of 101.3 kPa, signifying that ignitable liquids at sub-atmospheric pressure are more hazardous than those at 101.3 kPa. This study developed a model for predicting the influence of pressure on flash points on the basis of basic thermodynamic characteristics; this model was validated against experimental data obtained from the literature for six single-component and multiple-component liquid fuels at sub-atmospheric pressure. The proposed model effectively predicts closed-cup flash points, with small deviations in the range 0.18 °C–1.25 °C. However, because the model's assumption of vapor–liquid equilibrium was violated in the experiments, the predicted open-cup flash points did not agree well with their experimental counterparts, with the deviations in the range 1.11 °C–12.55 °C. Nevertheless, the trends predicted by the model agreed with those in the experimental data. Furthermore, standard flash point test method (such as ASTM D56-22, ASTM D93-20, and ASTM D7094-17) are based on a linear formula for correcting flash points measured at pressures other than 101.3 kPa. When the ambient pressure is approximately 101.3 kPa during flash point testing, the slope value of the correction formula should be changed from 0.25 to 0.20.