Improved Kinetic Model of the Low-Temperature Oxidation of <i>n</i>‑Heptane

The low- and high-temperature oxidation mechanisms of <i>n</i>-heptane have been extensively studied in recent and past literature because of its importance as a primary reference fuel. Recent advanced analytical methods allowed for the identification of several intermediate oxygenated species at very low-temperature conditions in jet-stirred reactors. On these bases, new classes of successive reactions involving hydroperoxide species, already discussed for propane and <i>n</i>-butane oxidation, were included in the low-temperature oxidation mechanism of <i>n</i>-heptane. These new reactions allowed for the improvement of the overall mechanism, not only obtaining a satisfactorily agreement with reaction products, such as organic acids, diones, and ketones, but also in terms of system reactivity. Moreover, deeper attention was also paid to the formation of ketohydroperoxides, rarely experimentally measured. Because of <i>n</i>-heptane importance as a primary reference fuel, the overall POLIMI kinetic mechanism is validated in a wide range of conditions, in both the high- and low-temperature regimes. Moreover, the reliability of the updated oxidation mechanism is further proven in a couple of more complex applications, such as the autoignition of <i>n</i>-heptane droplets in microgravity conditions and the oxidation of lean <i>n</i>-heptane/air mixtures in homogeneous charge compression ignition (HCCI) engines