This work focuses on understanding the formation and oxidation of soot when adding
n-butanol, an oxygenated fuel, to n-dodecane. A two-stage burner was used to characterize
the oxidation of soot from different n-butanol blends, 10%, 30%, and 60 mol% in n-dodecane.
The two-stage burner isolates the soot oxidation process from the formation process.
Soot is formed in a first-stage premixed burner under fuel-rich conditions, while
in a second stage, the soot is oxidized under slightly fuel-rich conditions. A scanning
mobility particle sizer (SMPS) was used to measure the soot particle size distributions
in the flame at different heights during oxidation. Results showed a decrease in particle
mass concentration (g/cm(3)) as the fraction of n-butanol increased, which indicates
the capability of n-butanol to reduce soot particle number and mass. On the other
hand, the results demonstrated that the increasing n-butanol reduces the difference
between initial mass of soot particles entering and the final mass of soot particles
leaving the second burner. This result implies that increasing the n-butanol concentration
decreases the rate of soot oxidation. Two different fuel quality indicators are used
to quantify our observations. The first one, "sooting tendency", is calculated to
show how the amount of soot formed in the flame is affected by using different n-butanol
percentages. The second one, "sooting stability", is defined for quantifying the stability
of soot particles against oxidation. The results demonstrated that by increasing the
n-butanol percentage, soot formation was suppressed. However, sooting stability increased
with higher concentrations of n-butanol. The soot nanostructure was quantified by
high-resolution electron microscopy and digital image processing. Image analysis revealed
layer arrangement is in correlation with sooting stability. The results of interlayer
spacing showed a decrease by increasing n-butanol at the same sampling height. (C)
2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved.