Chain reactions with heat release: Continuum and molecular modeling

The effect of violation of thermodynamic equilibrium and deviation of reaction rates from their equilibrium expressions during chain chemical reactions with heat release was studied. Single reactions, chain linear and cyclic mechanisms, as well as an example of the hydrogen combustion mechanism are considered sequentially. For this purpose, the event-driven molecular dynamics (EDMD) simulation method was used, which does not require the assumption of thermodynamic equilibrium of the mixture. A nonequilibrium mechanism for activating one of the stages of a chain reaction has been discovered, which is realized if the product of an exothermic stage with a small molar mass is a reagent in a stage with an activation barrier. In this case, the use of the traditional continuum approach to describe chemical kinetics can lead to a significant distortion of the results both in product composition and in thermodynamic parameters. A method for correcting the continuum approach was proposed, which allows taking into account the discovered nonequilibrium mechanism and does not require any changes in the continuum solvers used in engineering practice.