This research aims to investigate, experiment with, and assess the practical application and efficacy of butanol and pentanol as alternative fuels for internal combustion engines. A primary focus is analyzing how these two higher alcohols affect soot formation in diffusion flames when mixed with diesel. This study employs the smoke point method for an indirect assessment of the blend’s soot formation tendency, combined with the Light Extinction Method (LEM) and Beer-Lambert Law to measure the volume of generated soot via the attenuation of light passing through the flame. Fuel samples were prepared with various blend ratios, specifically 100D-0Bu, 95D-5Bu, 90D-10Bu, 85D-15Bu, 80D-20Bu, 50D-50Bu, along with 100D-0Pe, 95D-5Pe, 90D-10Pe, 85D-15Pe, 80D-20Pe, and 50D-50Pe. These mixtures were combusted in a rigorously controlled laboratory setting utilizing a co-flow diffusion flame model. During combustion, flame morphology, color, and brightness were observed. The study’s results reveal an inverse relationship between the generated soot volume and the concentration of butanol or pentanol in the fuel mixture. The soot volume notably declined from 0.000554 mm3 (pure diesel, 100D-0), reducing to 0.000270 mm3 for the 50D-50Pe blend, and ultimately reaching its minimum value of 0.000196 mm3 with the 50D-50Bu mixture. Conspicuously, at the same blending ratios, diesel–pentanol mixtures tended to produced higher soot emissions than diesel–butanol mixtures. This phenomenon is likely due to the lower oxygen content and longer carbon chain length of pentanol, both of which contribute to an increased propensity for forming soot precursors during the pyrolysis phase.