LTC was researched by introducing an 80% mass fraction of n-butanol in reactivity controlled compression ignition (RCCI) mode. A 60% mass fraction of n-butanol was port fuel injected (PFI) and the additional 20% was directly injected through a blend of n-butanol (Bu) with Fischer-Tropsch gas to liquid synthetic paraffinic kerosene (GTL) or ULSD as reference. The blended fuels GTL20-Bu80 and ULSD20-Bu80 have reduced cetane for improved combustion phasing control compared to the reference RCCI mode with direct injection of neat ULSD and n-Butanol PFI (ULSD40-Bu60). RCCI strategies delayed ignition and increased peak heat release rates due to prolonged mixing time and reactivity stratification, inducing faster flame speeds. In RCCI mode, the ringing intensity (RI) increased up to 85% higher than in CDC. NOx and soot were reduced up to 90% with ULSD40-Bu60 compared to CDC. The butanol blends decreased CO by 25% compared to ULSD RCCI. CO levels overlayed each other for GTL20-Bu80 and ULSD20-Bu80 across loads, suggesting that the butanol was the influencing factor. ULSD and ULSD20-Bu80 RCCI increased mechanical efficiencies compared to CDC by 3–4% across loads. ULSD20-Bu80 had the lowest cetane and displayed the greatest improvement in the overall emissions and efficiencies in RCCI compared to CDC.