Influence of synthetic ethanol-to-gasoline fuel use on engine oil composition and properties

The transition toward synthetic renewable transportation fuels requires a thorough understanding of their effects on engine behavior, especially on the engine-lubrication system. This study evaluates oil dilution and changes in oil properties through driving tests using four Ethanol-to-Gasoline (ETG) fuels with varying compositions. Commercial (Super 95) and alkylate-based gasolines were used as benchmarks. Tests included cold‑start short‑distance, cold‑start real driving emissions procedure, and mixed cold–warm high‑load driving. Key findings are: (1) ETG-based fuels produced higher oil-dilution rates than reference fuels; (2) this led to reduced viscosity and flash point; (3) viscosity index and density remained stable or improved; (4) accumulation of heavy aromatics in the oil. Comprehensive oil analysis revealed a strong link between oil dilution and the presence of heavy (C 10+ ) aromatics in ETG fuels. Modified ETG contained ∼75% less C 11+ aromatics, resulting in lower oil dilution than the standard one, but still about double that of commercial gasoline. The presence of fuel residues (predominantly aromatics) in the engine oil interestingly increased the viscosity index, although aromatics are generally considered undesirable constituents of lubricating oils. The findings were, however, validated and confirmed via an analysis of model oil samples containing C 10 aromatics. These findings identified a critical gap in current gasoline specifications. Distillation criteria, designed to prevent engine oil dilution, do not capture the behavior of new synthetic fuel components. Possible solutions include tightening currently used limits for some distillation parameters (e.g., E150), introducing new ones (e.g., E180), further reducing heavy‑aromatic fractions in ETG production, or using ETG only as a blending component at 30–50% concentration. Overall, the study highlights the need for updated fuel‑quality frameworks to ensure compatibility of advanced synthetic fuels with current engine lubrication systems.