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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.

Biodiesel is a widely used biofuel in diesel engines, which is of particular interest as a renewable fuel because it possesses the similar properties as the diesel fuel. The pure soybean biodiesel was tested in an optical constant volume combustion chamber using natural flame luminosity and forward illumination light extinction (FILE) methods to explore the combustion process and soot distribution at various ambient temperatures (800 K and 1000 K) and oxygen concentrations (21%, 16%, 10.5%). Results indicated that, with a lower ambient temperature, the autoignition delay became longer for all three oxygen concentrations and more ambient air was entrained by spray jet and more fuel was burnt by premixed combustion. With less ambient oxygen concentration, the heat release rate showed not only a longer ignition delay but also longer combustion duration.