A comprehensive review of C1–C6 alcohol-diesel blends: physicochemical properties, combustion characteristics, and advanced optimization techniques

This systematic review provides a multi-dimensional synthesis of research conducted between 2015 and 2025 concerning the integration of C1 – C6 alcohols (ranging from methanol to hexanol) into compression ignition engines. By analyzing 130 high-impact studies, this work evaluates the intricate interplay between alcohol molecular structure, physicochemical properties, and combustion dynamics. The outcome reveals a clear ‘Carbon Number Hierarchy": while short-chain alcohols (C1–C2) offer the highest potential for soot reduction (up to 80%), they require significant hardware modifications due to extended ignition delays and stability issues. In contrast, higher alcohols (C4–C6) serve as effective ‘drop-in’ candidates, delivering a balanced trade-off between emission benefits and engine performance. Furthermore, this review highlights that traditional ‘soot-NOx’ trade-offs can be effectively bypassed through the synergistic application of nanoparticle additives and advanced optimization techniques, such as Response Surface Methodology (RSM) and Artificial Neural Networks (ANN). The paper concludes with application-oriented recommendations, positioning specific alcohol families for maritime, stationary, and long-haul transport sectors based on their unique energetic and environmental profiles.