Wide Range Experimental and Kinetic Modeling Study of Chain Length Impact on n‑Alkanes Autoxidation

The control of deposit precursors formation resulting from the oxidative degradation of alternative fuels relies strongly on the understanding of the underlying chemical pathways. Although C8–C16 n-alkanes are major constituents of commercial fuels and well-documented solvents, their respective reactivities and selectivities in autoxidation are poorly understood. This study experimentally investigates the influence of chain length, temperature (393–433 K), purity, and blending on n-alkanes autoxidation kinetics under concentrated oxygen conditions, using both Induction Period (IP) and speciation analysis. It also numerically constructs new detailed liquid-phase chemical mechanisms for n-C8–C14 obtained with an automated mechanism generator. Macroscopic reactivity descriptors such as IP, combined to microscopic ones, obtained from GC-MS analyses, are herein used to emphasize similarities and discrepancies in n-alkanes autoxidation processes. Experimental results highlight a nonlinear IP evolution with n-alkanes chain length, a linear IP variation for two component paraffinic blends, and similarities among oxidation product families. Experimental data from the present study and from the literature are used to evaluate n-C8–C14 mechanisms on IP and on monohydroperoxides (ROOH) concentrations. Under pure O2 conditions, mechanisms generally predict IPs within a factor of 3 for intermediate and high temperature and even lower when air is used instead of pure oxygen. In addition, the chain length impact is also well reproduced, with a reactivity increase from C8 to C12 and a plateau for higher chain length. Rate of Consumption (RoC) analyses of n-C8 and n-C12 mechanisms evidenced the main role of peroxy radicals in autoxidation through fuel consumption, and ROOH and polyhydroperoxides (R­(OOH)2) formation.