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Combustion of an Illinois No. 6 coal char simulated using an atomistic char representation and the ReaxFF reactive force field

Evidence and attribution

Authority of statements

Prose sections below (Summary, Methods, Findings, etc.) are curated summaries of the publication identified by doi, title, and pdf_path in the front matter above. They are not new primary claims by this wiki.

For definitive numerical values, reaction schemes, and interpretations, use the peer-reviewed article (and optional records under normalized/papers/ when present)—not this page alone.

Summary

Coal char is a disordered polyaromatic solid whose combustion chemistry is hard to probe atomistically. This work builds a devolatilized Illinois No. 6 char atomistic model using Fringe3D (from HRTEM lattice-fringe statistics) plus Perl scripts to place heteroatoms and aliphatic motifs with reduced investigator bias, constrained by elemental and NMR literature targets. ReaxFF for hydrocarbon combustion drives reactive MD at very high temperature (3000–4000 K) under stoichiometric, fuel-lean, and fuel-rich conditions to force chemistry to complete on accessible simulation times. Oxidation initiates by thermal fragmentation of aromatic moieties and/or H abstraction by O\(_2\), O, and OH; fuel-lean conditions yield faster oxidation of polyaromatic frameworks than fuel-rich. Ring transformations include 6-membered rings converting to 5- and 7-membered rings that further react or decompose.

Methods

1 — MD application (atomistic dynamics)

Reactive MD uses ReaxFF for hydrocarbon combustion chemistry applied to an atomistic devolatilized Illinois No. 6 coal char model (pdf_path; normalized/extracts/2012castro-marcano-combustion-a-combustion-illinois_p1-2.txt).

  • Engine / code: ReaxFF reactive molecular dynamics (abstract/Introduction class wording on extract); N/A — MD engine/package not named on the indexed excerpt pages.
  • System size & composition: Coal char structural model built via Fringe3D (HRTEM fringe statistics) plus Perl scripts adding heteroatoms and aliphatic motifs with reduced investigator bias, constrained to literature elemental and NMR targets (abstract framing on extract).
  • Boundaries / periodicity: N/A — not stated on the indexed excerpt pages.
  • Ensemble / timestep / duration / thermostat / barostat: N/A — NVT/NPT/NVE labels, timestep sizes, production run segment reporting, and thermostat/barostat algorithms are not stated on the indexed excerpt pages.
  • Temperature: 3000–4000 K window stated for the high-temperature combustion MD campaign (indexed excerpt; verify exact sub-ranges per condition in pdf_path).
  • Pressure / stress: N/A — not stated on the indexed excerpt pages.
  • Electric field: N/A — not stated on the indexed excerpt pages.
  • Replica / enhanced sampling: N/A — not stated on the indexed excerpt pages.

Oxygen stoichiometry conditions: Stoichiometric, fuel-lean (oxygen-rich), and fuel-rich environments are used to accelerate chemistry to completable timescales at these temperatures (abstract, extract).

2 — Force-field training

N/A — the study uses an established ReaxFF hydrocarbon combustion parameterization associated with the van Duin-group ecosystem rather than reporting a new fit in the indexed excerpt.

3 — Static QM / DFT-only

N/A — not the primary methodology beyond structural model construction context (verify pdf_path for any DFT benchmarks).

Findings

The analyses indicate char oxidation initiates either by thermal fragmentation of aromatic moieties into smaller pieces that subsequently oxidize, or by H abstraction by O₂, atomic O, and OH. Fuel-lean (oxygen-rich) conditions produce faster oxidation/consumption of polyaromatic frameworks than fuel-rich runs in their comparison. Six-membered aromatic rings transform into five- and seven-membered rings that further react or decompose, predominantly with O and OH. The work is presented as demonstrating integration of a representative char structural model with ReaxFF for high-temperature combustion chemistry (with inorganics/ash explicitly deferred as future work in the abstract framing).

Limitations

  • Inorganics/ash omitted in this “initial work”; temperatures are far above practical burners but chosen for ReaxFF timescale accessibility.
  • Extrapolation to engineering burners requires bridging scales and lower-temperature kinetics not directly sampled.

Relevance to group

van Duin-group ReaxFF on coal char combustion with PSU coal modeling collaborators—key corpus link between reactive MD and energy carbonaceous solids.

Citations and evidence anchors