Effect of alkyl substituent for cyclohexane on pyrolysis towards sooting tendency from theoretical principle

Abstract

The fuel structure is an important controlling factor during the process of soot formation. Alkylated cyclohexane is a typical surrogate fuel with more complex structure than alkanes or aromatic fuels. Five alkylated cyclohexanes (i.e., cyclohexane, methylcyclohexane, ethylcyclohexane, 1,3-dimethylcyclohexane, 1,3,5-trimethylcyclohexane) and the n-alkane were selected to investigate the effect of the alkyl substituent on sooting tendency during the pyrolysis process from the theoretical principle. The reaction energy barriers profiles of alkylated cyclohexanes obtained by the density functional theory (DFT) illustrate the length and number of the alkyl substituent will affect the production of alkenes fragments which finally decompose to C2H2 and C3H3 species. The molecular dynamics simulations show the abundance of C2H2 and C3H3 fragments from the initial pyrolysis of fuels will accelerate the sooting tendency, which follow the trend of cyclohexane < methylcyclohexane < ethylcyclohexane ≈ 1,3-dimethylcyclohexane < 1,3,5-trimethylcyclohexane, in agreement with experimental findings. We hope this study can provide a more comprehensive understanding of the effect of fuel structure on sooting tendency and ideas for soot inhibition.