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ReaxFF-based molecular dynamics study of bio-derived polycyclic alkanes as potential alternative jet fuels

Summary

ReaxFF reactive molecular dynamics is used to study the initial stages of pyrolysis of two bio-derived head-to-head polycyclic alkanes (HtH-1 and HtH-2) proposed as high energy-density aviation fuels, including mixture effects and comparison to conventional jet-fuel chemistry. The work examines thermal decomposition of HtH-1 (C18H32) and HtH-2 (C18H34) with ReaxFF MD. Global Arrhenius parameters characterize overall kinetics; a systematic reaction-analysis framework extracts temperature-dependent pathways. HtH-1 decomposes faster than HtH-2 under matched temperature and density, and faster than JP-10 in the same framework. Dominant bond-breaking channels shift from central inter-ring C–C scission at lower temperature toward C–CH3 cleavage at higher temperature. Major product distributions differ between fuels and are discussed in relation to sooting tendency and experiments. Binary mixtures show largely unimolecular chemistry with weak cross-talk between components.

Corpus note

The corpus holds an uncorrected proof PDF. For the version-of-record file path, see 2020kwon-fuel-279-202-reaxff-based-molecular.

Methods

Note: pdf_path is the Elsevier galley; for final tables, use 2020kwon-fuel-279-202-reaxff-based-molecular if values differ.

1 — MD application (ReaxFF pyrolysis). Engine / code: ReaxFF reactive MD in LAMMPS (as in the Fuel galley / VOR). System size & composition: 3D periodic vapor boxes with 40 fuel molecules per single--component case at mass densities 0.1–0.3 kg dm⁻³; binary mixtures keep 40 molecules total with HtH-1 mole fractions α = 0.9, 0.7, 0.5. Boundaries / PBC: 3D periodic. Ensemble: NVT at fixed box volume (ρ set by loading)— N/A for NPT 1 atm barostat-style pressure servicing (constant--V heating of vapor). Timestep: 0.1 fs production; 0.05 fs at 3000 K for convergence checks (article / SI). Duration / stages: equilibration NVT 1500 K for 2.5 ps (designed to limit decomposition); production NVT 1500–3000 K (full ns-scale windows in source). Thermostat: Berendsen with 100 fs damping. Barostat / hydrostatic pressure: N/A (NVT only in the cited stages). Temperature (K): 1500–3000 K as above; 1500 K also used with CVHD (below). Electric field / shock / shear: N/A. Replica / enhanced sampling: control--variable-driven hyperdynamics (CVHD) at 1500 K to accelerate rare reaction events (per article); umbrella / metadynamics: N/A (not stated in the galley bullets used here). Analysis: in--house reaction-analysis code on trajectories; global Arrhenius fits; optional ReaxFF PES sampling for selected channels (see article)**.

2 — Force-field training. N/A—uses a published C/H ReaxFF (cited in the article), not a de novo fit in this manuscript.

3 — Static QM / DFT-only. N/A—ReaxFF MD is the sampling method for the reported kinetics (QM only as reference, if any, per VOR).

Findings

  • HtH-1 shows faster decomposition than HtH-2 at the same conditions and faster kinetics than JP-10 in the same simulation setup.
  • Mechanisms are temperature-dependent: central C–C inter-ring breaking dominates at lower temperature; C–CH3 bond breaking becomes increasingly important at higher temperature due to entropic effects.
  • Major products reported include C5H8 and C4H8 from HtH-1 and C4H8 and C2H4 from HtH-2; the authors relate product slate to sooting tendency, consistent with measurements for HtH-1 vs HtH-2.
  • In binary mixtures, HtH-1 and HtH-2 react primarily through unimolecular channels with little mutual interaction during pyrolysis at the conditions sampled.
  • The study is framed as demonstrating ReaxFF-MD plus automated reaction analysis for complex fuel chemistries without pre-specified reaction networks.

Limitations

Proof-stage PDF; kinetic parameters and product statistics are simulation-level and depend on the ReaxFF parameterization and the elevated temperatures used to sample reactions in nanosecond-scale MD.

Relevance to group

Penn State co-authorship (van Duin, Kwon, Lele, Xuan); extends ReaxFF pyrolysis workflows to new bio-derived polycyclic fuels.

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