Combustion Characteristics and Soot Distributions of Neat Butanol and Neat Soybean Biodiesel

The combustion characteristics and soot distributions of neat butanol and neat soybean biodiesel were explored in an optical constant-volume combustion chamber using natural flame luminosity and forward illumination light extinction methods under various ambient temperatures (800 and 1000 K) and oxygen concentrations (21%, 16%, 10.5%). Results demonstrated that butanol had a higher normalized peak pressure compared with the biodiesel. Soybean biodiesel autoignited earlier than butanol at 21% and 16% oxygen, while a reverse trend was found at 10.5% oxygen. The oxygen concentration had little effect on the autoignition timing for butanol when it was between 16% and 10.5% at 800-1000 K. The natural flame luminosity reduced with lowered oxygen concentration and the flame distribution was notably increased at 10.5% oxygen. At 800 K ambient temperature, there was no soot formation detected for butanol, while the net soot release for soybean biodiesel was reduced with the decrease of oxygen concentration. At 1000 K ambient temperature, the net soot release increased for both butanol and soybean biodiesel with the decrease of oxygen concentration. Compared with butanol, soybean biodiesel had a higher value of normalized time integrated soot mass (NTISM) under all conditions. The value of NTISM increased about 16 times from 800 to 1000 K for the soybean biodiesel at 10.5% oxygen, indicating that low oxygen concentration will deteriorate combustion and increase the difficulty of soot emissions control for the soybean biodiesel under a higher ambient temperature.