Detailed, sterically-resolved modeling of soot oxidation: Role of O atoms, interplay with particle nanostructure, and emergence of inner particle burning

Frenklach, Michael; Liu, Zhenyuan; Singh, Ravi I.; Galimova, Galiya R.; Azyazov, Valeriy N.; Mebel, Alexander M.

doi:10.1016/j.combustflame.2017.10.012

Cited by 91 publications

(50 citation statements)

References 133 publications

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“…The distribution of the small particles is unimodal showing one accumulation mode of primary particles and is shifted to slightly smaller CMD of 9.2 nm when passing the reactor at an oven temperature of 1123 K (Figure 3(a)). This shift is also observed at lower oven temperatures as seen in Figure 3(b) for a temperature of 773 K. Oxidation of soot particles by O 2 cannot be observed at this temperature and oxidation by H 2 O or CO 2 , which are sampled from the flame but are in comparison to O 2 only of minor importance in soot oxidation (Frenklach et al, 2018;Neoh et al, 1981), is also rather unlikely to contribute to the observed size reduction of soot particles in our experiment. Therefore, thermal effects seem to alter the mobility diameter of the particles.…”

Section: Characterization Of Particles Without Any Oxidation Processsupporting

confidence: 71%

“…Other effects which may influence the soot oxidation in our experiments, e.g., oxidation by other oxidants formed during the oxidation of sampled flame species like the OH radical or competitive particle growth, are not considered herein. Recently, Frenklach et al (2018) have modeled the low-temperature oxidation results of nascent soot by Camacho et al (2015). They even had to consider catalytic decomposition of water vapor on the reactor walls to provide additional H and OH radicals to match the experimental values of Camacho et al (2015) with their model.…”

Section: Particle Size Distributions During the Oxidation Process Andmentioning

confidence: 99%

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Experimental Investigation of Soot Oxidation under Well-Controlled Conditions in a High-Temperature Flow Reactor

Bierkandt

Oßwald

Schripp

et al. 2019

Combustion Science and Technology

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Oxidation by molecular oxygen of freshly-produced soot from a flat ethylene-air-flame is investigated under well-controlled conditions in a flow reactor at 773-1273 K and atmospheric pressure. Soot particles are characterized before and after oxidation by electrical mobility technique. In addition to the size-classified soot number density, the molecular gasphase species are obtained simultaneously by molecular-beam mass spectrometry. Oxidation behavior of soot particles as well as some hydrocarbon species sampled from the soot source was determined quantitatively. Oxygenated species are formed as molecular intermediates during the oxidation process inside the reactor. Different particle size distributions have been investigated by varying the sampling position and equivalence ratio of the flame. Oxidation of soot starts at different temperatures, but is clearly separated from oxidation of flame species starting earlier at lower temperatures. Soot oxidation rates were calculated and comparison with the Nagle-Strickland-Constable model indicates that the investigated flamesampled soot is more reactive than graphite under the investigated conditions. The presented dataset may help to validate existing soot models.

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Section: Characterization Of Particles Without Any Oxidation Processsupporting

confidence: 71%

Section: Particle Size Distributions During the Oxidation Process Andmentioning

confidence: 99%

Experimental Investigation of Soot Oxidation under Well-Controlled Conditions in a High-Temperature Flow Reactor

Bierkandt

Oßwald

Schripp

et al. 2019

Combustion Science and Technology

View full text Add to dashboard Cite

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“…Comparisons of reaction rates for the PAHs + C 2 H 2 pathway, the rate coefficients of A 1 -+ C 2 H 2 → A 1 C 2 H 2 and A 1 C 2 H 2 → A 1 C 2 H + H come from [26] . the HACA pathway, as the active site on PAHs (soot) is available for H and O 2 before being targeted by C 2 H 2 [28,29] . The specific reactions and corresponding reaction rate coefficients used in the simulation of PAHs and soot surface growth along HACA pathway are listed in Table S4 and Table S5 respectively.…”

Section: Simulation For Pyrene Formationmentioning

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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“…Furthermore, it is notable that phenyl radical only consists of free edges, but larger PAH radicals contain free edge and zig-zag surface sites at least. Therefore, the accuracy of the analogy treatment of reaction rates from phenyl+C4H4 reaction to PAH radical + C4H4 reactions requires further investigation, as the kinetics are highly sensitive to the type of targeted surface site instead of the size of PAHs in growth and oxidation processes [35][36][37][38][39]. Thus, obtaining reliable reaction rate coefficients and yield distribution of products in PAH radical + C4H4 reaction system is crucial to better understand PAH formation in flames and materials production.…”

Section: Introductionmentioning

confidence: 99%

Computational study of polycyclic aromatic hydrocarbons growth by vinylacetylene addition

Liu

Zhang

et al. 2019

Combustion and Flame

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The growth of polycyclic aromatic hydrocarbons (PAH) can proceed via multiple chemical mechanisms. The mechanism of naphthyl radical and vinylacetylene (C4H4) addition reaction has been systematically investigated in this computational study. A combination of DFT/B3LYP/6-311+G(d,p), CCSD/6-311+G(d,p) and CBS-QB3 methods were performed to calculate the potential energy surfaces. It revealed that the products, including phenanthrene, anthracene, a PAH with a five-membered ring structure, and PAH with a C4H3 radical substitution, can be formed in A2-1 (1-naphthyl)+C4H4 and A2-2 (2-naphthyl) +C4H4 reaction networks. The reaction rate constants at 0.1-100 atm were evaluated by RRKM theory by solving the master equation in the temperature range of 800-2500 K, which showed that the rate constants of reactions A2-1 (A2-2)+C4H4→product+H are highly temperature-dependent but nearly pressure-independent. The distribution of products was investigated in a 0-D batch reactor, wherein the initial reactant concentrations were taken from experimental measurements. The results showed that adduct intermediates were the main products at low temperature (T < 1000 K), and the phenanthrene and PAH with C4H3 radical substitution became the dominant products at temperatures where PAHs and soot form in flames (T > 1000 K). It was observed that a significant amount of phenanthrene is formed from PAH with a C4H3 radical substitution with the assistance of H atom. Reaction pathway sensitivity analysis for the PAH radical+C4H4 reaction system was performed and showed that the new benzene rings are more likely to be generated near the zigzag edge surface site instead of the free edge. For the development of a PAH mechanism, the analogous treatment of rate constants for larger PAH radical + C4H4 reaction system are discussed. The formation rate of naphthalene from the reaction of phenyl+C4H4 was found to be very close to that of phenanthrene from the reaction of naphthyl+C4H4, suggesting that the analogous treatment of the rates is reasonable in PAH mechanisms.

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Detailed, sterically-resolved modeling of soot oxidation: Role of O atoms, interplay with particle nanostructure, and emergence of inner particle burning

Cited by 91 publications

References 133 publications

Experimental Investigation of Soot Oxidation under Well-Controlled Conditions in a High-Temperature Flow Reactor

Experimental Investigation of Soot Oxidation under Well-Controlled Conditions in a High-Temperature Flow Reactor

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

Computational study of polycyclic aromatic hydrocarbons growth by vinylacetylene addition

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