Corrosion of automotive components in biofuel environments

The global transition toward sustainable mobility necessitates a concurrent paradigm shift in automotive engineering: the reduction of vehicular weight through lightweight metal alloys and the replacement of fossil fuels with renewable alternatives, such as bioethanol, biodiesel, and Hydrotreated Vegetable Oils (HVO). While these advanced biofuels are critical for reducing anthropogenic CO2 emissions, their distinct chemical compositions introduce severe compatibility challenges when interacting with standard automotive fuel system components. Conducted within the framework of the Italian National Center for Sustainable Mobility (M.O.S.T.), this doctoral dissertation systematically investigates the corrosion and degradation mechanisms occurring at the biofuel-alloy interface. The research is structured around three primary industrially relevant case studies. The first investigates the severe localized corrosion observed in AA1050 aluminum fuel tanks utilized by Stellantis when exposed to an E27 bioethanol blend. The second case study provides a comparative analysis of the corrosion behavior of copper (Cu) and stainless steel (AISI 304) exposed to commercial biodiesel (B7) and advanced HVO. Finally, the third phase focuses on 5000-series aluminum alloys (AA5052 and AA5754), typically employed in heavy transport vehicles, interacting with a wide spectrum of bioethanol blends (E5, E27, E85, and E100). Crucially, a unified and aggressive experimental methodology was applied across all three studies to establish the functional limits of the materials: the specimens were subjected to autoclave immersion tests at 100 °C for varying durations under a nitrogen-flushed atmosphere. A dual-analytical methodology was employed throughout the investigation. The structural and compositional evolution of the metallic substrates was characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and Optical Microscopy. Simultaneously, the degradation of the fuel and the quantification of water content were monitored via chromatographic techniques. To establish predictive models for material lifespan, advanced electrochemical techniques, including Cyclic Polarization (CP), Linear Polarization (LP), and Electrochemical Impedance Spectroscopy (EIS), were utilized to determine the corrosion rates. The findings reveal that bioethanol environments are exceptionally detrimental to aluminum alloys. The inherent presence and formation of acetic acid in ethanol blends rapidly compromise the passivation layer, leading to near-complete structural degradation under extreme thermal conditions. Furthermore, the dual role of water contentacting as either a corrosion inhibitor or promoter depending on the specific thermodynamic conditions is elucidated. The role of the absence of oxygen in promoting an alcoholate-mediated reaction was also investigated. Conversely, the investigation 4 into B7 and HVO demonstrates that these specific biofuels exhibit negligible corrosivity toward copper and stainless steel, primarily due to their inherently low electrical conductivity and distinct chemical matrix.This work was strengthened by strategic industrial and academic partnerships, specifically through a collaboration with Stellantis for the opportunity to analyze their fuel system failures, and with the National Centre for Metallurgical Research (CENIM-CSIC) in Madrid for advanced electrochemical characterization. Ultimately, this thesis provides critical predictive data and methodological frameworks essential for the selection and protection of lightweight alloys in the next generation of green automotive design