The characteristics of combustion, emissions, and thermal efficiency of a diesel engine with direct injection (DI) neat n-butanol were investigated. The engine ran at a load of 6.5–8.0 bar indicated mean effective pressure (IMEP) at 1500 rpm engine speed and the injection pressure was controlled to 900 bar. The intake boost pressure, injection timing, and EGR rate were adjusted to investigate the engine performance. The tests demonstrated that neat n-butanol had the potential to achieve ultralow emissions. However, challenges related to reducing the pressure rise rate and improving the ignition controllability were identified.