Reconciliation of carbon oxidation rates and activation energies based on changing nanostructure

Gaddam, Chethan K.; Wal, Randy L. Vander; Chen, Xu; Yezerets, Aleksey; Kamasamudram, Krishna

doi:10.1016/j.carbon.2015.11.035

Cited by 60 publications

(29 citation statements)

References 55 publications

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“…Additionally, as a result of a better accessibility of C atoms on the edge sites, an amorphous structure shows higher reactivity. 13 Moreover, it is known that the chemical composition of the particles, as well as the particle size, does plays a role on health, 14 although the precise relationship is not well understood. 15 Accounting for these phenomena is challenging, as the step from the gas-phase towards the particle phase during combustion, the so-called soot inception, is poorly understood.…”

Section: Introductionmentioning

confidence: 99%

A Theoretical Multiscale Approach to Study the Initial Steps Involved in the Chemical Reactivity of Soot Precursors

et al. 2019

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In the present study bond formation reactions between soot precursors and their role in the soot inception process is investigated. The soot precursors were generated in macroscopic detailed gas-phase kinetic calculations and according to certain criteria introduced in simulation boxes to model bond formation between soot precursor molecules with reactive force field molecular dynamics modeling. The impacts of temperature, fuel mixture and equivalence ratio have been investigated on the rate and structure of the newly formed molecules. The resulting structures compare well to previously reported experimental results. Furthermore, the bond formation rate between PAH is found to be linearly correlated with the temperature at which the PAH precursors are generated, while fuel and equivalence ratio do not have a direct impact on the reaction rate. The generated growth structures are lumped in: 1) directly linked, 2) aliphatically linked and 3) pericondensed polycyclic hydrocarbons. It is found that the amount of aliphatically linked PAH increases with the amount of aliphatic content of fuel mixture. Finally, a reaction scheme is presented displaying the most representative reaction pathways to form growth structures in each lumping class and their eventual interconversion. The present work -that applies a combined approach of macroscopic gas-phase kinetic calculations and atomistic reactive force field simulations -offers a good alternative to obtain structural differences of nascent soot for a broad range of thermodynamic conditions and detailed reaction mechanisms for soot inception process.

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Section: Introductionmentioning

confidence: 99%

A Theoretical Multiscale Approach to Study the Initial Steps Involved in the Chemical Reactivity of Soot Precursors

et al. 2019

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“…Pahalagedara et al 14 provide a detailed statistical study of the influence of particle structure on soot oxidation activity. A central point from this work is that soot activity toward oxidation decreases with the increased organization of structure in the soot, making it less reactive to further oxidative attack, as shown in our prior studies, 5,6,17,18 and as mechanistically described in terms of basal to edge-site carbons. 6,18 Such comparative knowledge for oxidation by NO 2 -O 2 gas mixtures is still limited, having received little attention until recently.…”

Section: Introductionmentioning

confidence: 72%

“…To summarize, as inferred by the difference plots, longer and flatter lamellae remain after oxidation by NO 2 + O 2 . For reference, by our prior studies, 5,6,17,32 lamellae with higher curvature are preferentially attacked in O 2 oxidation. Added NO 2 appears to accentuate this, accelerating the preferential loss of short and more curved lamellae.…”

Section: Oxidation In 10% Omentioning

confidence: 85%

“…A linked study by the same group 10 showed that soot oxidative reactivity was qualitatively related to its morphology and subsequently to its nanostructure as the primary factor regulating oxidative reactivity. In contrast, several notable works have identified soot ''structure,'' 10,[13][14][15] either understood or named as nanostructure 1,3,16,17 as an essential metric governing soot oxidative reactivity and as consequence, nanostructure has been studied across a variety of fuels and fuel blends under different oxidation conditions. Yet absent from present literature is a study showing comparative nanostructure evolution for conditions of passive DPF regeneration with and without NO 2 at typical exhaust temperatures, as detailed in this article.…”

Section: Introductionmentioning

confidence: 99%

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Nanostructure changes in diesel soot during NO₂–O₂ oxidation under diesel particulate filter-like conditions toward filter regeneration

Singh

Srilomsak

Wang

et al. 2018

International Journal of Engine Research

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Development of the regeneration process on diesel particulate filters requires a better understanding of soot oxidation phenomena, especially its relation to soot nanostructure. Nitrogen dioxide (NO2) is known to play an essential role in passive regeneration by oxidizing soot at low temperatures, especially in the presence of oxygen (O2) in the exhaust. However, change in soot nanostructure due to oxidation by NO2–O2 mixtures has not received much attention. This work focuses on nanostructure evolution during passive regeneration of the diesel particulate filter by oxidation of soot at normal exhaust gas temperatures (300°C–400°C). High-resolution transmission electron microscopy of partially oxidized model carbons (R250, M1300, arc-generated soot) and diesel soot under NO2–O2 mixtures is used to investigate physical changes in nanostructure correlating with the material’s behavior during oxidation. Microscopy reveals the changing nanostructure of model carbons during oxidation while fringe analysis of the images points to the differences in the structural metrics of fringe length and tortuosity of the resultant structures. The variation in oxidation rates highlights the inter-dependence of the material’s reactivity with its structure. NO2 preferentially oxidizes edge-site carbon, promotes surface oxidation by altering the particle’s burning mode with increased overall reactivity of NO2+O2 resulting in inhibition of internal burning, typically observed by O2 at exhaust gas temperatures.

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“…Thermal oxidation of carbon is a complex solid-gas reaction because of the intrinsic heterogeneity of the reaction, as has been studied in detail for the oxidation reaction of graphite [18][19][20][21][22][23][24][25][26][27][28] and in many solid-state and solid-gas reactions [29][30][31][32]. In carbon/carbon composites, the situation is more complex because of the additional heterogeneity introduced by the compositional and structural factors of the composites [4,[6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Kinetic characterization of multistep thermal oxidation of carbon/carbon composite in flowing air

Nishikawa

Ueta

Hara

et al. 2016

J Therm Anal Calorim

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Thermal oxidation of carbon/carbon composites in an oxidizing atmosphere is a multistep process regulated by the intrinsic heterogeneity of the solid-gas reaction, the additional heterogeneity of the compositional and structural characteristics of the composite, and how these two properties change as the reaction progresses. By focusing on the overlapping features of the component reaction steps, the kinetic characterization of the multistep kinetic process was studied to reveal the correlation between the thermal oxidation behavior and the compositional and structural characteristics of carbon/carbon composites. Using commercially available mechanical pencil leads as a typical model system for a carbon/carbon composite, the thermal behaviors of two different leads manufactured by different companies were investigated comparatively via thermoanalytical techniques and morphological observations. On the basis of a reaction model considering the different reactivities of the main (graphite) and secondary (carbonized polymer) carbon components, the kinetic features of two partially overlapping reaction steps were revealed via a kinetic deconvolution analysis of the thermoanalytical data for the thermal oxidation process. The kinetic results were correlated with the compositional and structural characteristics of carbon/carbon composites using morphological observations of the partially reacted samples. Herein, the practical usefulness of the kinetic analysis in characterizing carbon/carbon composites is discussed.

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Reconciliation of carbon oxidation rates and activation energies based on changing nanostructure

Cited by 60 publications

References 55 publications

A Theoretical Multiscale Approach to Study the Initial Steps Involved in the Chemical Reactivity of Soot Precursors

A Theoretical Multiscale Approach to Study the Initial Steps Involved in the Chemical Reactivity of Soot Precursors

Nanostructure changes in diesel soot during NO₂–O₂ oxidation under diesel particulate filter-like conditions toward filter regeneration

Kinetic characterization of multistep thermal oxidation of carbon/carbon composite in flowing air

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Reconciliation of carbon oxidation rates and activation energies based on changing nanostructure

Cited by 60 publications

References 55 publications

A Theoretical Multiscale Approach to Study the Initial Steps Involved in the Chemical Reactivity of Soot Precursors

A Theoretical Multiscale Approach to Study the Initial Steps Involved in the Chemical Reactivity of Soot Precursors

Nanostructure changes in diesel soot during NO2–O2 oxidation under diesel particulate filter-like conditions toward filter regeneration

Kinetic characterization of multistep thermal oxidation of carbon/carbon composite in flowing air

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Product

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Nanostructure changes in diesel soot during NO₂–O₂ oxidation under diesel particulate filter-like conditions toward filter regeneration