Butanol–Diesel Blends in Compression Ignition Engines: A Comprehensive Review of Fuel Properties, Combustion, Performance, Emissions, and Optimization

The growing concerns regarding fossil fuel depletion, volatile petroleum prices, and increasingly stringent emission regulations have intensified research on renewable fuels for compression ignition (CI) engines. Among alcohol‐based biofuels, butanol has emerged as a promising alternative because of its favorable physicochemical properties, including higher energy density, lower hygroscopicity, and better compatibility with diesel compared with lower‐chain alcohols such as methanol and ethanol. This review critically examines the application of butanol in CI engines by consolidating recent experimental and numerical investigations. The review covers fuel properties, blending strategies, combustion characteristics, engine performance, engine parameters, and dual‐fuel operating modes. Particular attention is given to the influence of butanol concentration and operating conditions on brake thermal efficiency, fuel consumption, nitrogen oxides, soot, carbon monoxide, and unburned hydrocarbon emissions. The analysis reveals that butanol–diesel blends can provide a favorable balance between combustion efficiency and emission reduction, although the extent of improvement depends strongly on engine configuration and optimization of operating parameters. By integrating findings from diverse studies, this work identifies current research trends, highlights unresolved challenges related to ignition behavior and fuel economy, and outlines future directions for the effective utilization of butanol in CI engines. The review demonstrates that butanol is a viable renewable fuel candidate capable of supporting cleaner and more efficient diesel‐engine operation.