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Comparison of the Effects of Different Biofuel on the Oxidation Stability of a Hydrocarbon Fuel
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on September 15, 2020 by SAE International in United States
Oxidation stability of fuels is a major issue in the fields of transport and energy. It is indeed crucial that fuels remain stable over their entire chain of use, from storage to combustion. The oxidation of liquid fuels leads to a fundamental modification of their chemical and physical structures, which leads to safety issues and engine malfunction. Understanding and controlling the auto-oxidation of fuels is therefore a crucial issue in the petroleum, automotive and aeronautical industries. The increase in the share of biofuels in the transport sector leads to many questions about their impact on the oxidation stability of conventional fuels. A large number of molecules from different biomass sources are proposed in the literature. If the impact of biodiesel and ethanol on diesel and gasoline fuels oxidation stability has been probed in the literature, the effect of other types of biofuels on conventional fuels remains unexplored. In this work, the effects of the addition of biofuels belonging to different chemical families on the oxidation stability of a conventional fuel surrogate (n-decane) have been determined. Experiments have been performed in a PetroOxy apparatus, which is one of the reference Rapid Small Scale Oxidation Test of the ASTM 7545 methods. In these experiments, a 5 ml sample of liquid fuel is placed in a cell, which is pressurized with pure O2. The cell is then heated at 140 °C and the evolution of the pressure is measured as a function of time. When the pressure decreases by 10% of the maximum pressure recorded, the time measured to reach this target value defines the Induction Period (IP), which constitutes a quantitative measure of the oxidation stability of the fuel. In addition to the IP measurements for each biofuel / hydrocarbon fuel blend, organic peroxides produced in the liquid sample were quantified at the IP, using iodometric titration and ultraviolet–visible spectrophotometry. Different biofuel molecules that are representative of different types of biofuel have been studied in this work: diethyl ether, n-butanol, and cyclopentanone. Cyclohexane addition has also been considered to probe the effects of a non-oxygenated additive. For each type of biofuel, its proportion added to the hydrocarbon fuel surrogate was varied from 0.2 to 20%vol. For each blend, the IP and the total peroxide content in the liquid have been systematically measured. The experimental results show that the variation in the proportion of biofuel added to the conventional fuel surrogate leads to non-linear variations in the measured IPs. This study also demonstrates that n-butanol strongly enhance the oxidation stability of the fuel surrogate (up to a factor of 6) while diethyl ether and cyclopentanone decrease the fuel surrogate stability. Organic peroxide measurements confirmed that a similar reaction mechanism underpins the oxidation of all the biofuel/fuel surrogate blends.