Spectroscopic studies on thermal-oxidation stability of hydrocarbon fuels

The enhanced autoxidation experiments of hydrocarbon fuels were performed simultaneously. The concentration of hydroperoxides in each fuel oxidized at temperatures from 120 to 180 °C was effectively quantified by measuring the absorption spectra of the iodine–starch solutions using ultraviolet–visible spectrometry. It can be observed that the hydroperoxide concentration increases, passes through a maximum value and then decreases to a low steady state at each temperature with the oxidation time going. The maximum values under various oxidation temperatures appear at obviously different times. The higher the temperature is, the earlier the maximum value of hydroperoxide concentration appears and the lower value it has. The thermal-oxidation stabilities for these fuels under different conditions are compared by the ultraviolet–visible spectrometry measurements and the infrared spectra. The results verify that the hydroperoxides, as the main intermediates, can transform themselves into various oxygenated species and that the hydroperoxide concentrations convey information concerning the thermal-oxidation stability of a particular fuel.