The Influence of Raw Materials for Fatty Acid Methyl Ester Production on the Aging Rate of Diesel Fuel Blends with Biocomponents

We present a rapid screening method to assess the aging of diesel blends containing fatty acid methyl esters (FAME) produced from two contrasting feedstocks: refined sunflower oil (SFME) and used cooking oil (UCO). Diesel–FAME blends at several biocomponent concentrations (0–50% v/v) were subjected to accelerated thermal aging at 90, 120 and 150 °C and monitored by peroxide value (PV), anisidine value (AV) and acid value measurements. Kinetic analysis of PV and AV trends, supported by Arrhenius plots, reveals feedstock-dependent oxidation pathways: UCO-FAME exhibits higher initial PV and AV and a faster progression to secondary oxidation products, whereas SFME accumulates hydroperoxides more at moderate temperatures and decomposes more slowly. The method distinguishes formation-dominated and decomposition-dominated regimes, quantifies apparent rate constants as functions of temperature and FAME content, and identifies an inflection in apparent activation behavior for UCO blends near 120 °C. The novelty of this work lies in the direct comparison of blend oxidation kinetics for refined versus waste-derived FAME and in proposing a practical, rapid protocol for identifying unstable feedstocks to support improved quality control of diesel–FAME blends.