Thesis of Carolina Sampaio Mergulhao

Amphithéâtre Pierre Glorieux (CERLA) Thesis defense of Carolina Sampaio Mergulhao - laboratory PC2A PhD supervisor : Guillaume Vanhove Abstract : In 2019, nearly 30% of the CO₂ emissions in the EU coming from the transport sector. Electrification is one of the possible and stringent alternatives towards reducing CO₂ emissions from the mobility; nevertheless, its popularizing would cost an enormous budget and decades to replace more than 300 million passenger cars powered by internal combustion engines. Moreover, some domains such as aviation and marine transport are still far from adopting electrification due to the comparably lower energy density of the batteries and carbon-free energy provision. Considering these situations and limitations, renewable biofuels emerge as a promising way to decarbonize the transport sector promptly. Biofuels are currently blended as additives, and it can be produced by transformation of lignocellulosic biomass; inedible and renewable feedstock utilized for second-generation biofuel production. The newly introduced biofuels would demonstrate different combustion characteristics than the conventional fossil-based fuels, which needs to be investigated in detail. The implementation of such substances requires appropriate engine design modification and precise operation strategy to avoid engine knock from spark-ignition (SI) engines, which is a major obstacle against increasing the thermal efficiency in highly turbocharged engines. Taking into account that the engine knock, or in general the autoignition of the unburned end-gas under lower temperature conditions, is governed by the autoignition chemistry of fuel, it is, therefore, necessary to ensure their compatibility with the new engines by looking into their reaction pathways and kinetic studies. This study aims, therefore, to present a benchmark of potential new biofuels and/or additives to be used in (SI) engines, as well as provide useful discussions from a kinetics perspective on the co-oxidation of these compounds along with conventional fuels. Four oxygenated lignocellulosic derived compounds (LDCs) were investigated; anisole, o-cresol, prenol, and cyclopentanone (CPN), which are either potential automotive fuels or additives. Isooctane, which has often been used as the reference gasoline surrogate, was also tested to compare the acquired data with literature and validate the methodology used in this study. Ignition delay times (IDTs) were measured using ULille Rapid Compression Machine (RCM), and the mixtures of isooctane/LDC/O₂/inert were evaluated at stoichiometric fuel-in-air conditions. The composition effect was investigated, varying the amount of LDC within isooctane mixtures and also varying the compression pressure from 14 to 25 bar. The effect of temperature on the IDT was investigated at 20 bar, and core gas temperatures from 665 to 870 K. The surrogates were formulated at stoichiometric conditions and prepared until the LDC fraction reached the maximum allowed value within the mixture preparation bench, considering the saturated vapor pressure of the LDCs. The limits were 20% for o-cresol, 40% for anisole and CPN, and 50% for prenol. All surrogates exhibited an Arrhenius behavior except prenol. Overall, the LDC addition inhibits the isooctane reactivity, which can be ranked in descending order for reactivity: pure isooctane, o-cresol, anisole, and cyclopentanone. On the other hand, prenol surrogate was the only one to show limited reactivity at low temperatures and promote the isooctane reactivity at high temperatures, i.e., from 800 to 870 K.