This study investigates the effects of oxygenated fuels, specifically long-chain alcohols, impact fuel atomization and combustion behavior in CI engines. The objective is to examine how higher n-butanol blending ratios in diesel fuel influence spray dynamics and combustion performance under varying engine conditions using an advanced combustion strategy. Experiments were conducted using a constant volume chamber (CVC) and a rapid compression-expansion machine (RCEM), both designed to replicate CI engine conditions. N-butanol was blended with diesel at ratios ranging from 70% to 90% with 10% increments, and key parameters such as spray formation, cone angle, penetration length, in-cylinder pressure, combustion performance, and efficiency were analyzed. The study also evaluated the effects of varying injection pressures on spray behavior. The results demonstrate that increasing n-butanol content significantly alters spray and combustion characteristics. Higher n-butanol proportions lead to longer spray tip penetration and larger spray areas at higher injection pressures, while the cone angle remains relatively unchanged. The 90% n-butanol blend exhibited the most distinct differences from pure diesel. However, due to n-butanol’s high latent heat of vaporization, in-cylinder temperatures decreased, resulting in longer ignition delays. To mitigate this, a spark-assisted compression ignition (SACI) strategy was employed, with adjustable spark duration to assess its impact. Compared to pure diesel, SACI-applied n-butanol/diesel blends exhibited higher peak in-cylinder pressure and heat release rates, improving indicated thermal efficiency. Additionally, ringing intensity (RI) assessments confirmed that all tested conditions remained below the 5 MW/m² threshold, ensuring acceptable combustion stability. This study provides a comprehensive analysis of n-butanol/diesel blends under SACI conditions, demonstrating their potential to enhance spray and combustion characteristics. The findings underscore n-butanol’s promise as a sustainable alternative fuel, addressing key challenges in dual-fuel combustion strategies.