by Iavarone Salvatore, Pascazio Laura, Sirignano Mariano, De Candia Antonio, Fierro Annalisa, DE ARCANGELIS Lucilla, D’Anna Andrea
Abstract:
Particle nucleation remains one of the most intriguing steps in the process of particle formation in flames. Although stacking/clustering of polycyclic aromatic hydrocarbons (PAHs) has been identified as a key step in the nucleation process, uncertainties remain about the size of the PAHs undergoing clustering, the organisation of the PAHs in the forming clusters and the factors affecting the relative amounts of order and disorder present in the texture organisation. A molecular dynamics approach is presented to study the influence of the molecular weight and structure of PAHs on the nucleation and coagulation processes and on the morphology of the formed clusters. Two different types of macromolecules have been analysed: pericondensed aromatic hydrocarbons (PCAHs) and aromatic aliphatic linked hydrocarbons (AALHs), known to be present in flame environments depending on flame temperature, equivalence ratio and fuel chemical structure. Clustering of six organic molecules has been analysed at two extreme temperatures, namely 500 K and 1500 K. The six molecules have been chosen on the basis of their molecular weight (pyrene and coronene) and molecular structure (single molecules, covalent-bonded dimers and covalent-bonded trimers). Nucleation of single pyrene molecules is negligible at low temperature and practically absent at high temperature. Conversely, nucleation of single coronene molecules involves 33\% of the initial molecules at low temperature. Molecules within the clusters are highly mobile at flame temperatures and just 5\% of the initial molecules are in clusters. The presence of covalent bonds among the aromatic sub-units improves clustering and growth, both for pyrene and coronene sub-units. Looking at the structure and the fractal dimensionality of the formed clusters, an enhancement of the disorder of the clusters is observed in the case of the AALHs (dimers and trimers) with an increased number of molecules not arranged in parallel planes. The same behaviour is found for the higher temperature.
Reference:
Molecular dynamics simulations of incipient carbonaceous nanoparticle formation at flame conditions (Iavarone Salvatore, Pascazio Laura, Sirignano Mariano, De Candia Antonio, Fierro Annalisa, DE ARCANGELIS Lucilla, D’Anna Andrea), In COMBUSTION THEORY AND MODELLING, volume 20, 2016. (Articolo in rivista)
Bibtex Entry:
@article{iav16,
author = {Iavarone Salvatore, and Pascazio Laura, and Sirignano Mariano, and De Candia Antonio, and Fierro Annalisa, and DE ARCANGELIS Lucilla, and D’Anna Andrea,},
title = {Molecular dynamics simulations of incipient carbonaceous nanoparticle formation at flame conditions},
volume = {20},
note = {Articolo in rivista},
issn = {1364-7830},
journal = {COMBUSTION THEORY AND MODELLING},
doi = {10.1080/13647830.2016.1242156},
year = {2016},
wosId = {WOS:000398056600005},
abstract = {Particle nucleation remains one of the most intriguing steps in the process of particle
formation in flames. Although stacking/clustering of polycyclic aromatic hydrocarbons
(PAHs) has been identified as a key step in the nucleation process, uncertainties remain
about the size of the PAHs undergoing clustering, the organisation of the PAHs in the
forming clusters and the factors affecting the relative amounts of order and disorder
present in the texture organisation. A molecular dynamics approach is presented to
study the influence of the molecular weight and structure of PAHs on the nucleation
and coagulation processes and on the morphology of the formed clusters. Two different
types of macromolecules have been analysed: pericondensed aromatic hydrocarbons
(PCAHs) and aromatic aliphatic linked hydrocarbons (AALHs), known to be present
in flame environments depending on flame temperature, equivalence ratio and fuel
chemical structure. Clustering of six organic molecules has been analysed at two extreme
temperatures, namely 500 K and 1500 K. The six molecules have been chosen on
the basis of their molecular weight (pyrene and coronene) and molecular structure
(single molecules, covalent-bonded dimers and covalent-bonded trimers). Nucleation of
single pyrene molecules is negligible at low temperature and practically absent at high
temperature. Conversely, nucleation of single coronene molecules involves 33\% of the
initial molecules at low temperature. Molecules within the clusters are highly mobile at
flame temperatures and just 5\% of the initial molecules are in clusters. The presence of
covalent bonds among the aromatic sub-units improves clustering and growth, both for
pyrene and coronene sub-units. Looking at the structure and the fractal dimensionality
of the formed clusters, an enhancement of the disorder of the clusters is observed in the
case of the AALHs (dimers and trimers) with an increased number of molecules not
arranged in parallel planes. The same behaviour is found for the higher temperature.}
}