This study presents a three-dimensional CFD investigation of the combustion and emission characteristics of diesel/n-butanol blended fuels (B5, B10, and B20, corresponding to 5%, 10%, and 20% n-butanol by volume, respectively) in a four-cylinder, 1.9 L Turbo-Direct Injection (TDI) diesel engine using CONVERGE CFD software. A detailed in-cylinder simulation was performed under engine loads of 25%, 50%, 75%, and 100% at a constant speed of 3000 rpm. The computational model incorporated spray breakup, turbulence, combustion, and emission sub-models, and was validated against experimental in-cylinder pressure and heat release rate data for conventional diesel (D2). In relation to experimental data, strong agreement, with maximum deviations below 8% was observed. Simulation results revealed that an increase in the n-butanol content has a direct influence on ignition delay, in-cylinder temperature, and heat release behavior due to enhanced oxygen availability and altered fuel atomization. Among the blends, B10 exhibited combustion characteristics most comparable to diesel, particularly at higher loads, while also demonstrating improved atomization and blend stability. Emission analysis showed that n-butanol blends tend to reduce CO, HC, and soot emissions across all loads, with B10 achieving up to 6% and 9% reductions in CO and HC, and an 8.4% reduction in soot at full load. Nevertheless, due to elevated oxygen content, a marginal increase in NOx (1.9%) was observed (for B10). Overall, the results indicate that moderate n-butanol blending offers a promising pathway for improving diesel engine combustion efficiency and emission performance without major modifications to engine operation.
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