Boosting the energy transition in the transport sector through the use of sustainable alcohol–diesel blends

The transition to a cleaner energy matrix requires the assessment of renewable alternatives to fossil fuels, such as alcohol-based biofuels, which can be produced from different sustainable processes and raw materials, including agricultural and industrial wastes. Each bioalcohol has specific physical and chemical properties, such as cetane number, oxygen content, and enthalpy of vaporization, which grant unique characteristics to blends with diesel fuel, directly affecting engine performance and emissions profiles. In this study, short-, long- and branched-chain alcohols have been blended with diesel fuel in a Euro 6 compression-ignition engine under the WLTC cycle. The results showed that all blends significantly reduced particulate matter and carbon monoxide emissions compared to diesel fuel. This positive effect is associated with the oxygen content of the alcohols, which favored a more complete combustion. However, the combination of a lower cetane number and oxygen contributed to increased peak temperatures during combustion, increasing nitrogen oxide emissions. Unburned hydrocarbon emissions were more sensitive to vaporization behavior: short-chain alcohols with high enthalpy of vaporization (such as ethanol and propanol) caused a drop in the in-cylinder temperature and a significant increase in these emissions. However, long-chain alcohols (such as hexanol and octanol) showed more moderate increases, thanks to their less significant cooling effect. It can be concluded that the use of alcohol-diesel blends in diesel engines has real potential for mitigating critical pollutants, but requires optimization of engine parameters to maximize environmental gains without compromising performance. • Renewable alcohols from biomass are reviewed as diesel blending components. • Biological and catalytic routes enable production of sustainable alcohols. • Alcohol molecular structure governs ignition and combustion behavior in CI engines. • Real-driving WLTC evaluation demonstrates the feasibility of biomass-derived fuels. • Higher alcohols show strong potential for drop-in diesel substitution strategies.