Sensitivity of soot formation to strain rates in counterflow diffusion flames of various C3-C5 alkanes and alcohols

Abstract

In this work, the sensitivities of soot formation to the variations of strain rates have been studied both experimentally and numerically in counterflow diffusion flames of fourteen C3-C5 alkanes and alcohols. The results showed that an increase in strain rate would lead to a decrease of soot volume fraction in all the tested flames. Except for tert-butanol and tert-pentanol, the sensitivity of soot volume fraction to strain rate was observed to be lower for fuels with a higher sooting tendency. When the soot loadings in flames of the different fuels were matched at a reference strain rate by adjusting oxygen mole fraction, their dependence on strain rate became comparable, except that there was a more substantial reduction in soot volume fraction for tert-butanol and tert-pentanol flames. Kinetic pathway analysis found that the main reason for the faster decline of soot loading in tert-butanol flame has to with the unique molecular structure of tert-alcohols which led to a unique pathway for the formation of molecular soot precursors. The present work served as a first test in alcoholic fuels of the general trend that was previously observed in experiments with aliphatic fuels regarding the sensitivities of soot formation to strain rate. The present data identified tert-alcohols as outliers; corresponding numerical simulation helped to explain the observed peculiarities in flames of tert-alcohols.