<p>Aromatic hydrocarbons represent an important fraction of diesel and kerosene and their soot emissions contribute major soot emissions of diesel and kerosene. The current study analyzed the soot precursor of the large alkylbenzene n-butylbenzene found in diesel and kerosene in laminar flame, and integrated the corresponding poly-aromatic hydrocarbon (PAH) growth mechanism with the popular n-butylbenzene oxidation mechanisms to improve the soot formation prediction for n-butylbenzene. The size of soot precursor was determined by the fringe length in the core of soot particle. The first reason is that the fringe length of soot particle is a strong function of the number of carbon atoms in the molecules. The second reason is that the core of soot particle is the consequence of soot precursor molecules nucleation process. The fringe length in the core of soot particle can be used to determine the number of carbon atoms of soot precursor molecules. At dimensionless height DH=0.25 of n-butylbenzene of flame, the geometric mean fringe length in the core of soot particles of n-butylbenzene was measured to be 0.67 nm. The molecule with the size that equals to the geometric mean fringe length of 0.67 nm was estimated to have an atomic carbon count of 20.8 atoms, which approximates to the size of the five-ringed poly-aromatic hydrocarbon (A5). An A5 growth mechanism was then added on a popular n-butylbenzene oxidation mechanism. The combined mechanism including A5 growth was further reduced from 2414 reactions to 904 reactions by directed relation graph error propagation (DREGEP) method to support more practical three-dimension combustion simulation. The base n-butylbenzene oxidation mechanism only contains the phenanthrene formation and phenanthrene was treated as soot precursor in simulation. The combined mechanism contains A5 growth and A5 was treated as soot precursor in simulation. After validation by the ignition delay time in literature, the combined mechanism was then used to simulate the soot property and validated by the measured primary particle diameter. The simulation results suggested that the computed soot precursor concentration of the combined mechanism is smaller than that of the base mechanism. The combined mechanism weakens the soot growth process which decreases the soot volume fraction prediction for n-butylbenzene. Eventually, the proposed combined mechanism including the large PAH growth provides a better agreement with the measured primary particle diameter. This study provides certain support for further detailed investigation of soot formation of n-butylbenzene and practical fuels like diesel and kerosene.</p>

A Numerical and Experimental Study of Soot Precursor and Primary Particle Size of N-Butylbenzene in Laminar Flame

Paper Proceedings: https://asmedigitalcollection.asme.org/ICEF/ICEF2021/volume/85512

ASME 2021 Internal Combustion Engine Division Fall Technical Conference (ICEF2021)

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