(39h) Automated Discovery of Reaction Pathways for the Combustion of Alternative Fuel Candidates

A primary culprit of emission-related health issues is the soot produced via the combustion of common fuels. This soot, often formed from polyaromatic compounds, has been observed to irritate tissue, and can also be a carrier for mutagenic and carcinogenic organics.^4,7 Because of the severity of this problem, accurate and detailed analysis of these combustion byproducts and how they are formed has become increasingly necessary.

We use reactive molecular dynamics to examine soot formation pathways starting with anisole, C₇H₈O, and toluene, C₇H₈.^2,3 Fuel and oxygen molecules are studied at different ratios, temperatures between 2000 K and 2400 K, and pressures between 187 atm and 224 atm. The system is simulated using LAMMPS with the ReaxFF force field developed for hydrocarbons by Chenoweth et al.¹ Thermodynamic and positional data is recorded throughout the length of the trials, and can then be passed to the ChemTraYzer software package for analysis of reaction pathways and pertinent reaction data.³ The output of this analysis is a reaction network that can be visualized from the parent fuel through various radical pathways to the final product of the reaction, thereby allowing for accounting of all molecules in the reaction chain through various physical conditions and constraints.

References

(1) Chenoweth, K.; van Duin, A.C.T.; Goddard III, A.; ReaxFF Reactive Force Field for Molecular Dynamics Simulations of Hydrocarbon Oxidation. J. Phys. Chem. 2008 112 (5), pp 1040-1053

(2) Döntgen, M.; ChemTraYzer – Reaction Models from Molecular Dynamics Simulations.

(3) Döntgen, M.; et al,; Automated Discovery of Reaction Pathways, Rate Constants, and Transition States Using Reactive Molecular Dynamics Simulations. J. Chem. Theory Comput 2015, 11 (6), pp 2517–2524

(4) Lighty, J.; Veranth, J.; Sarofim, A.; Combustion Aerosols: Factors Governing Their Size and Composition and Implications to Human Health. J. Air and Waste Management Association 2000, 50 (9), pp 1565-1618

(5) Plimpton, S.; Fast Parallel Algorithms for Short-Range Molecular Dynamics. J Comp Phys 1995 117, pp 1-19 (http://lammps.sandia.gov)

(6) Richter, H.; Howard, J.B.; Formation of polycyclic aromatic hydrocarbons and their growth to soot—a review of chemical reaction pathways. Progress in Energy and Combustion Science 2000, 26, pp 565–608