Sooting behaviors of n-butanol and n-dodecane blends

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/cm3) 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.