Advanced Bioethanol as a Transition Fuel in Transportation: Performance in Internal Combustion Engines, Environmental Impacts, and Technological Challenges

Transport decarbonization cannot rely exclusively on electrification, particularly in regions where charging infrastructure, vehicle affordability, and fleet renewal remain constrained. This review critically assesses advanced bioethanol as a complementary transition fuel for road transportation, integrating evidence on lignocellulosic and residual biomass conversion, ethanol–gasoline blend behavior in spark-ignition (SI) engines, regulated and unregulated emissions, life cycle assessment (LCA), and scalability barriers. A critical narrative and integrative approach were applied, using literature retrieved from Scopus and Web of Science and organized across production pathways, engine performance, environmental impacts, technological challenges, and Latin American deployment conditions. The evidence indicates that advanced bioethanol can valorize agricultural and agro-industrial residues, reduce fossil-carbon dependence, and lower carbon monoxide (CO) and unburned hydrocarbon (HC) emissions in suitable SI engines. However, large-scale implementation remains strongly influenced by pretreatment performance and enzymatic hydrolysis efficiency, together with feedstock logistics, fermentation robustness, ethanol recovery energy demand, and overall biorefinery economics. Life-cycle performance remains pathway-dependent, with potential trade-offs in land use, water demand, toxicity, acidification, and eutrophication. Overall, advanced bioethanol should be understood as a realistic short- to medium-term complement to electrification rather than a universal carbon-neutral solution.