Analyzing the robustness of the yield sooting index as a measure of sooting tendency

Soot formation from combustion is linked with many issues, ranging from global warming to human health complications. To tackle these problems, measures of sooting tendency that are accurate and robust with respect to flame conditions are needed to facilitate the development of cleaner fuels and combustion technologies. The objective of this research is to analyze the accuracy and robustness of the Yield Sooting Index (YSI), a measure of sooting tendency, under different temperatures and air-to-fuel equivalence ratios (λ). In this work, the YSI of various cyclic hydrocarbons and jet fuels were measured in several methane/air coflow flames doped with small quantities (0.85% by mass of total fuel) of each test compound using two soot diagnostic techniques, color-ratio pyrometry and line-of-sight spectral radiance. The flame temperature and λ values of these doped coflow flames were varied by premixing the base methane fuel with varying amounts of nitrogen and/or air. The sensitivity of the measured YSI for the test compounds to the various temperature and λ conditions for each base flame was analyzed. Our results show that the YSI values of the cyclic hydrocarbons and test fuels were invariant across all the investigated flame conditions, suggesting that the YSI as a measure of sooting tendency is robust across a wide range of premixed air levels and temperatures relevant to soot formation.