Experimental study of the impact of alcohols on the oxidation stability of a surrogate jet-fuel

Abstract

The addition of biofuel in jet fuels can be seen as a promising answer to reduce the carbon footprint of the aviation transport sector. In this work, the impact of the addition of alcohols on the oxidation stability of a jet fuel surrogate was investigated. Different chemical structures of bioalcohols were considered and blended with n-decane used as the surrogate. The thermal oxidation stability of the mixtures was measured in a standard PetroOxy apparatus, which measures an induction period (IP). In addition to this global indicator of the fuel thermal stability, we quantified the total hydroperoxide concentration at the end of the test by iodometric titration. The influence of the length of the carbon chain in alcohols (1-butanol to 1-decanol) and the isomeric structure of butanols on the IPs of pure n-decane have been quantified. We show that the addition of a low percentage by volume of alcohols in the fuel increases its oxidation stability. This effect is non-linear, and the IP value increases with the volume percentage of alcohol in the fuel up to 10%. Beyond this value, a decrease in the stability of the mixture is observed. The influence of the length of the carbon chain is shown to be negligible. In contrast, the structure of butanol isomers strongly impacts the stabilization efficiency of the alcohol in the fuel. Conclusions on the fundamental chemical mechanism are drawn from ab initio calculations and highlight the central role of the low bond dissociation energy of the H-atoms linked to the carbon atom bearing the OH group in the liquid phase and the fate of the formed radical which ultimately yields HO2 and an aldehyde upon its reaction with O2. This mechanism is specific to linear alcohols and differs from the classic mechanism of autooxidation of alkanes.