Deviations from the linear mixture rule in nonequilibrium chemical kinetics

Dove, John E.; Halperin, Stephen; Raynor, Susanne

doi:10.1063/1.447713

Cited by 18 publications

(14 citation statements)

References 23 publications

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“…For example, in the case of non‐Boltzmann reactant distributions, constraints imposed on theoretical kinetics parameters by experimental data under conditions where non‐Boltzmann reactant distributions are insignificant can still be used to constrain model predictions under conditions where non‐Boltzmann reactant distributions are significant through substitution of the elementary kinetics model. Similar situations may also arise in many realistic combustion environments, where comparable concentrations of species with different collision efficiencies might require more accurate mixture rules for pressure‐dependent reactions (e.g., ).…”

Section: Consideration Of Relevant Parametric and Structural Uncertaimentioning

confidence: 85%

“…In addition to the uncertainties in the calculation of molecular properties discussed above, there are additional uncertainties that can arise in some situations from inadequacy of the employed elementary kinetics model, e.g., the breakdown of standard assumptions in cases where non‐Boltzmann reactant distributions , non‐RRKM , nonadiabatic , coupled torsions , multidimensional tunneling , weak‐collision‐in‐ J energy transfer , or nonlinear mixture rules are important. For example, in previous implementations of the multiscale informatics approach for Cl‐initiated C 3 H 8 oxidation , the structural uncertainty parameter describing uncertainty due to non‐Boltzmann reactant distributions was identified to play a key role in the interpretation of some of the experimental data (γ n‐B in Fig.…”

Section: Consideration Of Relevant Parametric and Structural Uncertaimentioning

confidence: 99%

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Harnessing the Combined Power of Theoretical and Experimental Data through Multiscale Informatics

Burke

2016

Int J of Chemical Kinetics

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Monumental, recent and rapidly continuing, improvements in the capabilities of ab initio theoretical kinetics calculations provides reason to believe that progress in the field of chemical kinetics can be accelerated through a corresponding evolution of the role of theory in kinetic modeling and its relationship with experiment. The present article reviews and provides additional demonstrations of the unique advantages that arise when theoretical and experimental data across multiple scales are considered on equal footing, including the relevant uncertainties of both, within a single mathematical framework. Namely, the multiscale informatics framework simultaneously integrates information from a wide variety of sources and scales: ab initio electronic structure calculations of molecular properties, rate constant determinations for individual reactions, and measured global observables of multireaction systems. The resulting model representation consists of a set of theoretical kinetics parameters (with constrained uncertainties) that are related through elementary kinetics models to rate constants (with propagated uncertainties) that in turn are related through physical models to global observables (with propagated uncertainties). An overview of the approach and typical implementation is provided along with a brief discussion of the major uncertainties (parametric and structural) in theoretical kinetics calculations, kinetic models for complex chemical mechanisms, and physical models for experiments. Higher levels of automation in all aspects, including closed‐loop autonomous mixed‐experimental‐and‐computational model improvement, are advocated for facilitating scalability of the approach to larger systems with reasonable human effort and computational cost. The unique advantages of combining theoretical and experimental data across multiple scales are illustrated through a series of examples. Previous results demonstrating the utility of simultaneous interpretation of theoretical and experimental data for assessing consistency in complex systems and for reliable, physics‐based extrapolation of limited data are briefly summarized. New results are presented to demonstrate the high predictive accuracy of multiscale informed models for both small (molecular properties) and large (global observables) scales. These new results provide examples where the optimization yields physically realistic parameter adjustments and where physical model uncertainties in experiments are larger than kinetic model uncertainties. New results are also presented to demonstrate the utility of the multiscale informatics approach for design of experiments and theoretical calculations, accounting for both theoretical and experimental existing knowledge as well as relevant parametric and structural uncertainties in interpreting potential new data. These new results provide examples where neglecting structural uncertainties in design of experiments results in failure to identify the most worthwhile experiment. Further progress in the c...

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Section: Consideration Of Relevant Parametric and Structural Uncertaimentioning

confidence: 85%

Section: Consideration Of Relevant Parametric and Structural Uncertaimentioning

confidence: 99%

Harnessing the Combined Power of Theoretical and Experimental Data through Multiscale Informatics

Burke

2016

Int J of Chemical Kinetics

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“…The nonlinear behavior can be attributed to the fact that the rovibrational energy distribution of the reactant in bath gases composed of colliders with varied energy transferred per collision, E , will vary with composition. Master equation solutions by Dove et al [37] show that the rate constant in a multicomponent bath gas is always higher than that predicted by the linear mixture rule. Analytical solutions of the master equation by Troe [36] indicate that deviations are higher when components have greater differences in E values and the stronger collider is present in mole fractions of 5-10%.…”

Section: H + O 2 (+M)=ho 2 (+M) (R9)mentioning

confidence: 93%

“…While the above-mentioned mixture rules differ in terms of their description of the falloff regime, all of them assume a linear mixture rule in the low-pressure limit. However, previous theoretical studies have indicated deviations from the linear mixture rule in the low-pressure limit if one of the bath-gas components is a weak collider with an average energy transferred per collision, E , that differs from the other colliders in the mixture [36,37]. The nonlinear behavior can be attributed to the fact that the rovibrational energy distribution of the reactant in bath gases composed of colliders with varied energy transferred per collision, E , will vary with composition.…”

Section: H + O 2 (+M)=ho 2 (+M) (R9)mentioning

confidence: 99%

Comprehensive H₂/O₂ kinetic model for high‐pressure combustion

Burke¹,

Chaos²,

Ju³

et al. 2011

Int J of Chemical Kinetics

773

447

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An updated H 2 /O 2 kinetic model based on that of Li et al. (Int J Chem Kinet 36, 2004, 566-575) is presented and tested against a wide range of combustion targets. The primary motivations of the model revision are to incorporate recent improvements in rate constant treatment and resolve discrepancies between experimental data and predictions using recently published kinetic models in dilute, high-pressure flames. Attempts are made to identify major remaining sources of uncertainties, in both the reaction rate parameters and the assumptions of the kinetic model, affecting predictions of relevant combustion behavior. With regard to model parameters, present uncertainties in the temperature and pressure dependence of rate constants for HO 2 formation and consumption reactions are demonstrated to substantially affect predictive capabilities at high-pressure, low-temperature conditions. With regard to model assumptions, calculations are performed to investigate several reactions/processes that have not received much attention previously. Results from ab initio calculations and modeling studies imply that inclusion of H + HO 2 = H 2 O + O in the kinetic model might be warranted, though further studies are necessary to ascertain its role in combustion modeling. In addition, it appears that characterization of nonlinear bath-gas mixture rule behavior for H + O 2 (+ M) = HO 2 (+ M) in multicomponent bath gases might be necessary to predict high-pressure flame speeds within ∼15%. The updated model is tested against all of the previous validation targets considered by Li et al. as well as new targets from a number of recent studies. Special attention is devoted to establishing a context for evaluating model performance against experimental data by careful consideration of uncertainties in measurements, initial conditions, and physical modelCorrespondence to: Michael P. Burke;

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“…29,30 Second, the classic linear mixture rule (cf. LMR,P in Table 2) always underestimates the rate constant in the mixture, 30 i.e., any nonzero deviations from the classic linear mixture rule are always positive. Third, deviations from the classic linear mixture rule are generally larger when mixture components have greater differences in their energy transfer characteristics.…”

Section: ■ Introductionmentioning

confidence: 99%

Bath Gas Mixture Effects on Multichannel Reactions: Insights and Representations for Systems beyond Single-Channel Reactions

Lei

Burke

2018

J. Phys. Chem. A

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Nearly all studies of and available data for pressure-dependent reactions focus on pure bath gases. Of the comparatively fewer studies on bath gas mixtures, important to combustion and planetary atmospheres, nearly all focus on single-channel reactions. The present study explores, and seeks reliable representations of, bath gas mixture effects on multichannel reactions. Analytical and numerical solutions of the master equation here reveal several unique manifestations of mixture effects for multichannel reactions, including behavior completely opposite to trends observed for single-channel reactions. The most common way of evaluating mixture rate constants from data for pure components, the classic linear mixture rule, is found to yield errors exceeding a factor of ∼10. A new linear mixture rule based on the reduced pressure, instead of the absolute pressure, is found to be accurate within ∼30% for rate constants (and ∼50% for the branching ratio). A new nonlinear mixture rule that additionally incorporates analytically derived activity coefficients is found to be accurate within ∼10% for rate constants and branching ratios. These new mixture rules are therefore recommended for use in fundamental and applied chemical kinetics investigations of reacting mixtures, including reacting flow codes and experimental interpretations of third-body efficiencies.

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Deviations from the linear mixture rule in nonequilibrium chemical kinetics

Cited by 18 publications

References 23 publications

Harnessing the Combined Power of Theoretical and Experimental Data through Multiscale Informatics

Harnessing the Combined Power of Theoretical and Experimental Data through Multiscale Informatics

Comprehensive H₂/O₂ kinetic model for high‐pressure combustion

Bath Gas Mixture Effects on Multichannel Reactions: Insights and Representations for Systems beyond Single-Channel Reactions

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Deviations from the linear mixture rule in nonequilibrium chemical kinetics

Cited by 18 publications

References 23 publications

Harnessing the Combined Power of Theoretical and Experimental Data through Multiscale Informatics

Harnessing the Combined Power of Theoretical and Experimental Data through Multiscale Informatics

Comprehensive H2/O2 kinetic model for high‐pressure combustion

Bath Gas Mixture Effects on Multichannel Reactions: Insights and Representations for Systems beyond Single-Channel Reactions

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Product

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Comprehensive H₂/O₂ kinetic model for high‐pressure combustion