The effects of 1-methylnaphthalene addition to n-dodecane on the formation of soot and polycyclic aromatic hydrocarbons in laminar coflow diffusion flames

1-Methylnaphthalene (1-MN) is a typical diaromatic component in petroleum-based fuels and has been widely chosen to represent aromatic fractions in surrogate fuels of diesel and jet fuels. In this study, experimental and modeling studies were performed to investigate the formation of typical polycyclic aromatic hydrocarbons (PAHs) and soot in coflow methane/air diffusion flames doped with 1-methylnaphthalene/n-dodecane mixtures, and explore chemical effects of 1-methylnaphthalen on key soot formation steps. The laser-induced incandes-cence (LII) and laser-induced fluorescence (LIF) techniques were used to obtained the soot volume fraction and relative concentration of typical PAHs along the flame centerline, respectively. A novel apparatus-independent indicator, yield aromatic index (YAI), was first proposed to quantify the formation tendency of a specific aro-matic product in a flame. It can be found that the addition of 1-methylnaphthalene in the fuel mixtures has a significantly promoting effect on soot formation processes. The correlation between the mass fraction of 1-meth-ylnaphthalene and sooting tendency shows a strong linear relationship. As to the PAH formation tendency, YAI(A2R5) have the smaller deviations from corresponding YSIs than YAI(A2 & A3) and YAI(A4), which indicating that A2R5 can be a type of important species leading to soot inception and have strong contribution to soot formation. Through the chemical kinetic analysis, A2R5 is proved to be a key coupling point of two A4 formation pathways, which start from n-dodecane and 1-methylnaphthalene, respectively. As a small amount of 1-methylnaphthalene is introduced into the fuel, the dominant approach to A2R5 rapidly shifts to a more efficient pathway, and is continually enhanced with increasing 1-methylnaphthalene at a moderate trend. The results reveal that 1-meth-ylnaphthalene in the fuel can stride over the rate limiting step of the soot formation process of non-aromatic fuels, eventually leading to an obviously increasing sooting tendency. This study aims to provide useful infor-mation for the development of soot nucleation mechanisms and the control of soot formation processes.

Automated summary

This study investigates the influence of 1-methylnaphthalene (1-MN) on the formation of polycyclic aromatic hydrocarbons (PAHs) and soot in flames. Experimental and modeling studies were conducted using methane/air diffusion flames doped with 1-MN/n-dodecane mixtures. The results show that the addition of 1-MN significantly promotes soot formation processes and has a strong linear relationship with the sooting tendency. A novel indicator, yield aromatic index (YAI), is proposed to quantify the formation tendency of specific aromatic products in flames. Chemical kinetic analysis reveals that A2R5 is a key species contributing to soot formation. The findings provide useful information for the development of soot nucleation mechanisms and the control of soot formation processes.