A very competitive alcohol for use in diesel engines is butanol. Butanol is of particular interest as a renewable bio-fuel, as it is less hydrophilic and it possesses higher heating value, higher cetane number, lower vapor pressure, and higher miscibility than ethanol or methanol. These properties make butanol preferable to ethanol or methanol for blending with conventional diesel or gasoline fuel. In this paper, the spray and combustion characteristics of pure n-butanol fuel was experimentally investigated in a constant volume combustion chamber. The ambient temperatures were set to 1000 K, and three different oxygen concentrations were set to 21%, 16%, and 10.5%. The results indicate that the penetration length reduces with the increase of ambient oxygen concentration. The combustion pressure and heat release rate demonstrate the auto-ignition delay becomes longer with decreasing of oxygen concentrations. With decreasing of oxygen concentrations, the peak of heat release rate reduces and the combustion duration increases. Compared to the 21% oxygen concentration, the premixed combustion fraction is a little larger at 16% oxygen concentration, while the premixed combustion fraction is nearly unobservable at 10.5% oxygen concentration. Compared to the 21% oxygen concentration, the flame luminosity is lower, and more combustion occurs at the near wall region at 16% oxygen concentration. The soot emission increases compared to the 21% oxygen concentration. The soot distribution is also at the downstream of the spray jet, like the soot emissions at 21% oxygen concentration. At 10.5% oxygen concentration, nearly all the combustion occurs in the near wall region and the flame distribution is the widest. The soot emission increases further compared to 16% oxygen concentration, and soot distribution is mainly near the chamber wall.