Bimolecular Peroxy Radical (RO2) Reactions and Their Relevance in Radical Initiated Oxidation of Hydrocarbons

Cho, Jaeyoung; Mulvihill, Clayton R.; Klippenstein, Stephen J.; Sivaramakrishnan, Raghu

doi:10.1021/acs.jpca.2c06960

Title: Bimolecular Peroxy Radical (RO₂) Reactions and Their Relevance in Radical Initiated Oxidation of Hydrocarbons

Journal Article · Fri Dec 23 00:00:00 EST 2022 · Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory

DOI:https://doi.org/10.1021/acs.jpca.2c06960· OSTI ID:2324611

Cho, Jaeyoung ^[1];

^[1];

^[1]

Argonne National Laboratory (ANL), Argonne, IL (United States)

The kinetics of peroxy radical (RO₂) reactions have been of long-standing interest in atmospheric and combustion chemistry. Nevertheless, the lack of kinetic studies at higher temperatures for their reactions with other radicals such as OH has precluded the inclusion of this class of reactions in detailed kinetics models developed for combustion applications. In this work, guided by the limited room temperature experimental studies on selected alkyl-peroxy radicals and literature theoretical kinetics on the prototypical CH₃O₂ + OH system, we have performed parametric studies on the effect of uncertainties in the rate coefficients and branching ratios to potential product channels for RO₂ + OH reactions at higher temperatures. Literature kinetics models were used to simulate autoignition delays, laminar flame speeds, and speciation profiles in flow and stirred reactors for a variety of common combustion-relevant fuels. Inclusion of RO₂ + OH reactions was found to retard autoignition in fuel-lean (φ = 0.5) mixtures of ethane and dimethyl ether in air. The observed effects were noticeably more pronounced in ozone-enriched combustion of ethane and dimethyl ether. The simulations also examined the influence of ozone doping levels, pressures, and equivalence ratios for both ethane and dimethyl ether oxidation. Sensitivity and flux analyses revealed that the RO₂ + OH reaction is a significant sink of RO₂ radicals at the early stage of autoignition, affecting fuel oxidation through RO₂ ↔ QOOH, RO₂ ↔ alkene + HO₂, or RO₂ + HO₂ ↔ ROOH + O₂. Additionally, the kinetic stability of the trioxide formed from RO₂ + OH reactions was investigated using master equation analyses. Last, we discuss other bimolecular reactions that are missing in literature kinetics models but are relevant to hydrocarbon oxidation initiated by external radical sources (plasma-enhanced, ozone-enriched combustion, etc.). In conclusion, the present simulations provide a strong motivation for better characterizing the bimolecular kinetics of peroxy radicals.

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Research Organization:: Argonne National Laboratory (ANL), Argonne, IL (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division (CSGB)

Grant/Contract Number:: AC02-06CH11357

OSTI ID:: 2324611

Journal Information:: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory, Vol. 127, Issue 1; ISSN 1089-5639

Publisher:: American Chemical SocietyCopyright Statement

Country of Publication:: United States

Language:: English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Atmospheric Chemistry
Autoignition
Chemical Kinetics
Ozone-enriched combustion
RO2 + OH reactions

Title: Bimolecular Peroxy Radical (RO2) Reactions and Their Relevance in Radical Initiated Oxidation of Hydrocarbons

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Title: Bimolecular Peroxy Radical (RO₂) Reactions and Their Relevance in Radical Initiated Oxidation of Hydrocarbons