Evaluation of Performance and Emissions of Methanol, Ethanol, and n-Butanol Blends in a Common-Rail Diesel Engine

Present study experimentally investigates performance and emission behaviors of various al¬cohol (methanol, ethanol, and n-butanol) mixing with diesel fuel in a common-rail direct injection (CRDI) engine. Alcohol/diesel blends containing 5%, 10%, and 15% alcohol by volume were prepared. The experiments were performed at four different loads corresponding to 20%, 30%, 40%, and 50% of the gas rack levels under a constant speed of 1500 rpm. The results demonstrated increasing load levels led to richer air/fuel mixtures, which enhanced brake power (BP) and exhaust gas temperature (EGT) for all tests. However, the presence of alcohols, particularly methanol, generally reduced BP due to their lesser lower heating value (LHV) and cetane numbers. Among the blends, ethanol/diesel showed relatively better BP results. In terms of brake specific fuel consumption (BSFC), all alcohol blends showed higher fuel consumption compared to conventional diesel, especially at higher alcohol addition and load, owing to lower energy content and viscosity of the alcohols. Notably, the 5% alcohol blends (E5, M5, B5) yielded favorable BSFC results to pure diesel, suggesting this ratio as optimal. Emission analysis revealed that unburned hydrocarbon (HC) emissions decreased with rising load. Methanol and n-butanol blends effectively reduced HC emissions, while ethanol blends increased them in the range of 4.3–27.17%. CO2 emissions increased slightly with the engine load but were decreased by alcohol/diesel blends, particularly by addition of the ethanol. Soot emissions enhanced at the low load but then decreased at higher loads with the alcohol addition due to better atomization and oxygen content. Lastly, O2 emissions declined with higher loads but were higher with alcohol blends, especially with methanol, suggesting incomplete combustion under certain conditions. Overall, while alcohol addition affects variably fuel economy and emissions in this study, lower alcohol percentages appear a favorable balance between performance and environmental impact.