The National Institute of Standards and Technology provides an online database of rate constants for gas phase reactions, but as the database is not evaluated, it often takes a trained kineticists to extract useful rate constants. Our goal is to create computer programs that can evaluate this data and output evaluated rate constants. As an initial step, we found evaluated rate constants for the reaction of i-butane with CH3 and H (870 K to 1130 K and 140 kPa to 360 kPa) with the Method of Uncertainty Minimization using Polynomial Chaos Expansions (MUM-PCE) – pioneered by David Sheen and Hai Wang – which constrains a kinetics model to the experimental data using Bayes theorem. The model was constrained both to literature rate constants from the NIST kinetics database – including early experiments at low temperatures, measurements of the total rate constant, and measurement from ethane for the rate constant for primary carbons – and new shock tube experiments quantifying the branching ratio of H-abstraction from the primary and tertiary carbons. A comprehensive Cantera kinetics model based on JetSurF 2.0 was optimized to these experimental measurements and the literature data using MUM-PCE. For both H and CH3, the optimization increased the rate of H-abstraction from the tertiary carbon relative to the primary carbon. We combine our primary and tertiary rate constants with previous results from our group on n-butane to derive a self-consistent set of site-specific rate constants for the abstraction of H by hydrogen atoms and CH3 from generic primary, secondary and tertiary carbon.

Initial steps towards computer-generated rate constants: Rate constants for the reactions of isobutane with H and CH3 with shock tube experiments and the method of uncertainty minimization using polynomial chaos expansions (MUM-PCE)

256th National Meeting (2018)

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