title: Weakly Bound Free Radicals in Combustion: "Prompt" Dissociation of Formyl Radicals and Its Effect on Laminar Flame Speeds.
abstract: Weakly bound free radicals have low-dissociation thresholds such that at high temperatures, time scales for dissociation and collisional relaxation become comparable, leading to significant dissociation during the vibrational-rotational relaxation process. Here we characterize this "prompt" dissociation of formyl (HCO), an important combustion radical, using direct dynamics calculations for OH + CH2O and H + CH2O (key HCO-forming reactions). For all other HCO-forming reactions, presumption of a thermal incipient HCO distribution was used to derive prompt dissociation fractions. Inclusion of these theoretically derived HCO prompt dissociation fractions into combustion kinetics models provides an additional source for H-atoms that feeds chain-branching reactions. Simulations using these updated combustion models are therefore shown to enhance flame propagation in 1,3,5-trioxane and acetylene. The present results suggest that HCO prompt dissociation should be included when simulating flames of hydrocarbons and oxygenated molecules and that prompt dissociations of other weakly bound radicals may also impact combustion simulations.
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Nicole J
authors.initials: NJ
authors.lastname: Labbe
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Raghu
authors.initials: R
authors.lastname: Sivaramakrishnan
authors.affiliation: School of Engineering, Brown University , Providence, Rhode Island 02912, United States.
authors.forename: C Franklin
authors.initials: CF
authors.lastname: Goldsmith
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Georgievskii
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: James A
authors.initials: JA
authors.lastname: Miller
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Klippenstein
keywords: combustion simulations; formyl; free radical; prompt dissociation