Nucleation of soot: Molecular dynamics simulations of pyrene dimerization

Schuetz, Charles A.; Frenklach, Michael

doi:10.1016/s1540-7489(02)80281-4

Cited by 196 publications

(148 citation statements)

References 35 publications

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“…Currently, there are three conceptual pathways leading to soot nucleation [3,[33][34][35][36] : 1) the dimerization of two pyrene molecules [36] , 2) the formation of fullerene-like structures from large PAHs via a HACA pathway [33] , 3) the chemical coalescence of moderate-sized PAHs into crosslinked three-dimensional structures via the addition reaction of PAHs and PAH radicals [37,38] as shown in Fig. 5 (a)-(c).…”

Section: Implications For Soot Nucleation and Surface Growthmentioning

confidence: 99%

The growth of PAHs and soot in the post-flame region

Liu

Roberts

2019

Proceedings of the Combustion Institute

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The PAHs-C 2 H 2 pathway (PAHs + C 2 H 2 → intermediate → product + H 2 ) has been shown, in theory, to be the important contributor to the growth of polycyclic aromatic hydrocarbons (PAHs) and soot in the post-flame region where H atoms are rare. Calculations of the potential energy surface (PES) using the DFT B3LYP 6-311 + G(d,p) method, and the reaction rate coefficients using the RRKM theory, reveal that armchair and bridge surface sites share similar kinetic characteristics, and are more likely to be the targets of C 2 H 2 molecules in flames compared to zig-zag and 5-membered ring surface sites. Results show that the energy barrier of a 2-H elimination reaction (14-23.8 kcal/mol) is much lower than that of a 1-H elimination (typically 30-40 kcal/mol) for some molecules. The formation of pyrene from phenanthrene via HACA (PAHs + H → PAHs radical ( + C 2 H 2 ) → intermediate → product + H) and PAHs-C 2 H 2 pathways is investigated using a closed homogeneous zero-dimensional reactor with combustion parameters abstracted from the premixed stagnation C 2 H 4 /O 2 /Ar sooting flame. Results show that the HACA pathway is the dominant pathway for the formation of PAHs and soot surface growth in the main-flame region where H atoms are abundant, but that the PAHs-C 2 H 2 pathway is the preferred pathway in the post-flame region. Our study also suggests that the soot nucleation involving a chemical coalescence of moderate-sized PAHs into a crosslinked three-dimensional structure via the addition reactions of PAHs and PAH radicals in the main-flame region should be considered for inclusion in any soot modeling.

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Section: Implications For Soot Nucleation and Surface Growthmentioning

confidence: 99%

The growth of PAHs and soot in the post-flame region

Liu

Roberts

2019

Proceedings of the Combustion Institute

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“…Frenklach 24 calculated the lifetimes of its dimer at combustion-relevant temperatures and suggested that it survives long enough for subsequent growth and compound stabilization to occur at pressures relevant to, for example, diesel combustion. This result is supported by the study of Herdman and Miller.…”

Section: Schuetz Andmentioning

confidence: 99%

Critical Assessment of Photoionization Efficiency Measurements for Characterization of Soot-Precursor Species

et al. 2017

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We present a critical evaluation of photoionization efficiency (PIE) measurements coupled with aerosol mass spectrometry for the identification of condensed soot-precursor species extracted from a premixed atmospheric-pressure ethylene/oxygen/nitrogen flame. Definitive identification of isomers by any means is complicated by the large number of potential isomers at masses likely to comprise particles at flame temperatures. This problem is compounded using PIE measurements by the similarity in ionization energies and PIE-curve shapes among many of these isomers. Nevertheless, PIE analysis can provide important chemical information. For example, our PIE curves show that neither pyrene nor fluoranthene alone can describe the signal from C16H10 isomers and that coronene alone cannot describe the PIE signal from C24H12 species.A linear combination of the reference PIE curves for pyrene and fluoranthene yields good agreement with flame-PIE curves measured at 202 u, which is consistent with pyrene and fluoranthene being the two major C16H10 isomers in the flame samples, but does not provide definite proof. The suggested ratio between fluoranthene and pyrene depends on the sampling conditions. We calculated the values of the adiabatic-ionization energy (AIE) of twenty-four C16H10 isomers. Despite the small number of isomers considered, the calculations show that the differences in AIEs between several of the isomers can be smaller than the average thermal energy at room temperature. The calculations also show that PIE analysis can sometimes be used to separate hydrocarbon species into those that contain mainly aromatic rings and those that contain significant aliphatic content for species sizes investigated in this study. Our calculations suggest an inverse relationship between AIE and the number of aromatic rings. We have demonstrated that further characterization of precursors can be facilitated by measurements that test species volatility.3

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“…Miller [14] calculated that sticking PAH collisions are only important for PAHs with masses larger than 800 u. Schuetz and Frenklach [15] calculated lifetimes for pyrene dimers, however, and found that they are stabilized by internal rotational and vibrational motion of the cluster and may survive long enough for subsequent growth to occur. Such a kinetically controlled process requires reversibility, and Eaves et al [16] recently presented a nucleation study that accounts for reversibility.…”

Section: Introductionmentioning

confidence: 99%

Radical–radical reactions, pyrene nucleation, and incipient soot formation in combustion

Johansson

Dillstrom

Elvati

et al. 2017

Proceedings of the Combustion Institute

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We present a combined experimental and probabilistic simulation study of soot-precursor. The experiments were conducted using aerosol mass spectrometry coupled with tunable vacuum ultraviolet radiation from the Advanced Light Source at Lawrence Berkeley National Laboratory. Mass spectra and photoionization efficiency (PIE) curves of soot precursor species were measured at different heights in a premixed flat flame and in a counter-flow diffusion flame fueled by ethylene and oxygen. The PIE curves at the pyrene mass from these flames were compared with reference PIE scans recorded for pyrene. The results demonstrate that other C 16 H 10 isomers than pyrene are major components among species condensed onto incipient soot in this study, which is in agreement with the simulations. Species with mass 202 u only have a high prevalence in incipient soot particles drawn from the premixed flame, but hydrocarbon species with sizes in the range 200-400 u are important to incipient-soot formation in both flames. The simulations predict that some species form through combination reactions involving relatively large radicals and bypass traditional molecular-growth pathways through addition of small hydrocarbon species. The experimental results support this prediction; they demonstrate that these species have higher relative abundances in particles formed close to the fuel outlet than smaller, lighter molecular species and indicate that these species are important to early formation of incipient-soot precursors. The results also imply that a leading role in incipient-soot precursor formation * Corresponding author. Johansson et al. / Proceedings of the Combustion Institute 36 (2017) [799][800][801][802][803][804][805][806] is played by species with lower thermal stability than the even-carbon numbered, unsubstituted polycyclic aromatic hydrocarbons known as "stabilomers".

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Nucleation of soot: Molecular dynamics simulations of pyrene dimerization

Cited by 196 publications

References 35 publications

The growth of PAHs and soot in the post-flame region

The growth of PAHs and soot in the post-flame region

Critical Assessment of Photoionization Efficiency Measurements for Characterization of Soot-Precursor Species

Radical–radical reactions, pyrene nucleation, and incipient soot formation in combustion

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