Understanding kinetic interactions between NOx and C2-C5 alkanes and alkenes: The rate rules and influences of H-atom abstractions by NO2

TL;DR

This paper investigates the H atom abstraction reactions by NO2 from C2-C5 alkanes and alkenes using high-level quantum chemistry and kinetic modeling, providing new rate rules and insights into their impact on hydrocarbon oxidation.

Contribution

It offers the first comprehensive quantum chemical and kinetic analysis of NO2 H atom abstractions from C2-C5 hydrocarbons, establishing accurate rate rules for modeling.

Findings

Updated rate parameters significantly influence ignition delay predictions.

Branching ratios reveal key reaction pathways and similarities among species.

Sensitivity analysis underscores the importance of these reactions in combustion models.

Abstract

This study aims to reveal the important role and the respective rate rules of H atom abstractions by NO2 for better understanding NOX hydrocarbon interactions. To this end, H atom abstractions from C2 to C5 alkanes and alkenes 15 species by NO2, leading to the formation of three HNO2 isomers (TRANS HONO, HNO2, and CIS HONO) and their respective products 45 reactions, are first characterized through high-level quantum chemistry computation, where electronic structures, single point energies, C H bond dissociation energies and 1 D hindered rotor potentials are determined at DLPNO CCSD T cc pVDZ M06 2X 6 311 plus plus g(d,p). The rate coefficients for all studied reactions, over a temperature range from 298.15 to 2000 K, are computed using Transition State Theory with the Master Equation System Solver program. Comprehensive analysis of branching ratios elucidates the diversity and similarities between different species, HNO2 isomers, and abstraction site, from which accurate rate rules are determined. Incorporating the updated rate parameters into a detailed chemical kinetic model reveals the significant influences of this type of reaction on model prediction results, where the simulated ignition delay times are either prolonged or reduced, depending on the original rate parameters presented in the selected model. Sensitivity and flux analysis further highlight the critical role of this type of reaction in affecting system reactivity and reaction pathways, emphasizing the need for adequately representing these kinetics in existing chemistry models. This can now be sufficiently achieved for alkanes and alkenes through the results from this study.