(315b) Direct Dissociation of Small Combustion Radicals Impact Flame Propagation

In combustion chemistry, the decompositions of radicals (formed by either unimolecular or bimolecular reactions) are almost always assumed to be characterized by thermal kinetics; i.e. reactants are in thermal equilibrium. However, recent theoretical studies indicate that non-equilibrium effects persist for the formyl (HCO) radical such that it undergoes direct dissociation to H + CO under combustion conditions (T > 1000 K). Simulations using detailed kinetics models reveal that laminar flame speeds for hydrocarbon and oxygenated fuels are influenced when incorporating these non-equilibrium effects for HCO. We expect that similar weakly bound radicals should undergo significant direct dissociation at high temperatures. In this present work, we have computed non-equilibrium factors and corresponding direct dissociation probabilities for small hydrocarbon and oxygenated radicals (C₂H₃, C₂H₅, CH₂OH, and CH₃O). These direct dissociation probabilities were then incorporated into detailed kinetics models describing the combustion of hydrocarbon fuels. Simulations using these detailed combustion models indicate that flame propagation is enhanced when non-equilibrium effects for these small radicals are accounted for. The present preliminary results have also highlighted the need for detailed dynamics studies for key reactions forming these small radicals.  

Acknowledgements

This work was supported by the U. S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, under Contract No. DE-AC02-06CH11357. Support for R. S., S. J. K., and J. A. M. was provided as part of the Argonne-Sandia Consortium on High-Pressure Combustion Chemistry, FWP# 2009 ANL 59044.