Impact of Biofuels on the Aging of Conventional Fuels – BioACe

The growing pressure on energy produced from the combustion of liquid fossil fuels and its adverse effects on the biosphere has intensified research efforts in biomass conversion into liquid fuels. Expectations are high for second-generation biofuels, produced from non-edible biomass, that would ideally be renewable, home-produced, operational in current motor engine, and carbon neutral, i.e., carbon dioxide is consumed by biomass during growth and emitted during combustion. European Union regulations will inevitably lead to an increased share of biofuels, that will be blended with conventional transportation fuels (gasoline, Diesel). In depth scientific studies are therefore crucial to assess the performance and environmental consequences of their use as fuels. In the literature a large number of studies are dedicated to the consequences of the use of next-generation biofuels in internal combustion engines but almost no work has been done on their impact on the aging of liquid fuels. This is surprising as it will be possible to use these biofuels only if their resistance to aging is high enough to guarantee their stability throughout their chain of use. Liquid fuels are subjected to various stresses during their storage, transport and use. During these operations, the fuels are in contact with air and oxidation of the liquid phase occurs (also called autoxidation), which cause aging. This phenomenon induces fundamental changes in the fuel chemical and physical structures, yielding oxidation products that are responsible for the formation of soluble and insoluble solids which can form deposit in the vehicle fuel system, from the tank to the combustion chamber, wich ultimately affects engine efficiency and performance, degrading pollutants emissions and engine longivity.
This proposal aims to study the impact of next-generation biofuel additions in a conventional fuel on its oxidation stability (aging).
The chemistry underlying gas-phase oxidation (combustion) and liquid-phase oxidation are both rules by a similar free radical chain reaction mechanism that involves thousands of elementary reactions. If the simulation of combustion is well defined in the literature, through the use of detailed kinetic models, their development for the liquid phase has long been an unrealizable challenge. In the gas phase, the thermo-kinetic data of the thousands of elementary reactions contained in the kinetic models are independent of the reaction environment in which they occur (ideal gas approximation). In the liquid phase, this approximation is no longer valid and these data become solvent dependent which leads to an explosion of the number of
thermo-kinetic parameters. This BioACe project aims to adapt combustion kinetic model to the liquid phase through the use of solvation corrections, applied to the gas phase thermo-kinetic data, based on theoretical chemistry tools.
The validation of the liquid phase detailed kinetic models relies on the acquisition of data in well-defined reactors.In this project, experimental studies of the auto-oxidation mechanisms of fuel surrogate / biofuel mixtures will be conducted in a standardized autoclave, to establish the kinetics of aging. A sampling system will be coupled to the autoclave to measure the evolution of hydroperoxides concentrations. The latter molecules are crucial intermediates of the oxidation processes and are considered as the initiators of the aging process. Different types and proportions of next-generation biofuels will be blended with a petroleum surrogate fuel to quantify their impact on its oxidation stability. The experimental data will be systematically simulated using the kinetic models developed for the autoxidation of these mixtures.
This project will yield a decisive understanding on the consequences of the use of this next-generation biofuels as additives in current conventional fuels and shed a new light on their impact on the fuel oxidation stability.