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Results for “carbonyl peroxy radicals”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Aldehyde cool-flame chemistry explains a missing source of organic acids

Combustion emission is a significant source of organic acids, impacting atmospheric chemistry and climate. Their formation mechanisms, however, remain poorly understood, leading to underestimation in kinetic models. We investigate the cool-flame oxidation of key combustion intermediates—C 1 –C 4 aldehydes and benzaldehyde. Using in-situ synchrotron vacuum ultraviolet photoionization mass spectrometry, we observe the direct conversion of aldehydes to organic acids, a process enhanced by HO 2 radicals. Quantum chemistry calculations reveal that the reaction of RC(O)O 2 with HO 2 on the singlet potential energy surface contributes to organic acids. Incorporating this pathway into a kinetic model significantly improves organic acid prediction. Despite the high-temperature nature of engine combustion, significant spatial and temporal inhomogeneities (e.g., near-wall regions and crevice volumes) lead to localized cool-flame conditions, facilitating organic acid formation and emission. Elucidating the acid formation under cool-flame conditions provides a critical mechanism for accurately modelling anthropogenic organic acid emissions and developing mitigation strategies.

SVUV-PIMS↗
DOE OSTI2020

Experimental Evidence of Dioxole Unimolecular Decay Pathway for Isoprene-Derived Criegee Intermediates

Ozonolysis of isoprene, one of the most abundant volatile organic compounds emitted into the Earth’s atmosphere, generates two four-carbon unsaturated Criegee intermediates, methyl vinyl ketone oxide (MVK-oxide) and methacrolein oxide (MACR-oxide). The extended conjugation between the vinyl substituent and carbonyl oxide groups of these Criegee intermediates facilitates rapid electrocyclic ring closures that form 5-membered cyclic peroxides, known as dioxoles. This research discusses the first experimental evidence of this novel decay pathway, which is predicted to be the dominant atmospheric sink for specific conformational forms of MVK-oxide (anti) and MACR-oxide (syn) with the vinyl substituent adjacent to the terminal O atom. The resulting dioxoles are predicted to undergo rapid unimolecular decay to oxygenated hydrocarbon radical products, including acetyl, vinoxy, formyl, and 2-methyl-vinoxy radicals. In the presence of O 2 , these radicals rapidly react to form peroxy radicals (ROO), which quickly decay via carbon-centered radical intermediates (QOOH) to stable carbonyl products that are identified in this work. The carbonyl products are detected under thermal conditions (298 K, 10 torr He) using multiplexed photoionization mass spectrometry (MPIMS). The main products (and associated relative abundances) originating from unimolecular decay of anti-MVK-oxide and subsequent reaction with O 2 are formaldehyde (88 ± 5%), ketene (9 ± 1%) and glyoxal (3 ± 1%). Those identified from the unimolecular decay of syn-MACR-oxide and subsequent reaction of O 2 are acetaldehyde (37 ± 7%), vinyl alcohol (9 ± 1%), methylketene (2 ± 1%), and acrolein (52 ± 5%). In addition to the stable carbonyl products, the secondary peroxy chemistry also generates OH or HO 2 radical co-products.

09 BIOMASS FUELS↗
NASA NTRS1990

An assessment of potential degradation products in the gas-phase reactions of alternative fluorocarbons in the troposphere

Tropospheric chemical transformations of alternative hydrofluorocarbons (HCF's) and hydrochlorofluorocarbons (HCFC's) are governed by hydroxyl radical initiated oxidation processes, which are likely to be analogous to those known for alkanes and chloroalkanes. A schematic diagram is used to illustrate plausible reaction mechanisms for their atmospheric degradation, where R, R', and R'' denote the F- and/or Cl-substituted alkyl groups derived from HCF's and HCFC's subsequent th the initial H atom abstraction by HO radicals. At present, virtually no kinetic data exist for the majority of these reactions, particularly for those involving RO. Potential degradation intermediates and final products include a large variety of fluorine- and/or chlorine-containing carbonyls, acids, peroxy acids, alcohols, hydrogen peroxides, nitrates and peroxy nitrates, as summarized in the attached table. Probably atmospheric lifetimes of these compounds were also estimated. For some carbonyl and nitrate products shown in this table, there seem to be no significant gas-phase removal mechanisms. Further chemical kinetics and photochemical data are needed to quantitatively assess the atmospheric fate of HCF's and HCFC's, and of the degradation products postulated in this report.

Niki, Hiromi↗
DOE OSTI2025

Coupling of Lipid Peroxidation and Criegee Intermediate Mediated Autoxidation in the Heterogeneous Oxidation of Linoleic Acid Aerosols

Autoxidation is an established mechanism for the degradation of organic molecules, which is relevant in the atmosphere, combustion processes, the environment, and the rancidification of lipids (commonly known as lipid peroxidation). Autoxidation proceeds via radical chain reactions involving hydroxyl (•OH), peroxy (RO2•), and alkoxy radicals, which are also prominent oxidants in the atmosphere. Recent reports have provided evidence for an alternative autoxidation mechanism driven instead by Criegee intermediates (CIs), which are produced from the reaction of β-hydroxy peroxy radicals (β-OH-RO2•). This work evaluates the contributions of these two mechanisms in the •OH initiated heterogeneous oxidation of linoleic acid (LA) aerosols. Reaction kinetics and product distributions are monitored using a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer. To explain the observed kinetics, a kinetic model is developed that incorporates both the conventional peroxidation and alternative CI-mediated autoxidation mechanisms. We observe that the CI-mediated autoxidation pathways enhance the heterogeneous autoxidation rate, while the peroxidation reactions, although present, contributes less to the overall oxidation rate. α-Acyloxyalkyl hydroperoxides (AAHPs) are identified as key indicators for bimolecular reactions of CI with LA, highlighting the role of LA as a CI scavenger. Moreover, the measured functionalized LA products with hydroxyl or carbonyl group(s), serve as markers for the peroxidation reactions. In summary, this work presents a quantitative framework to understand the coupled reaction network of •OH, RO2•, β-OH-RO2• radicals, and CI in driving heterogeneous autoxidation, which is crucial for understanding degradation mechanisms of organic molecules in the environment and atmosphere.

Criegee intermediate↗
DOE OSTI2026

An experimental and kinetic modeling study of the ignition of 2-methyl decane

Ignition delay times (IDTs) of 2-methyl decane (C 11 H 24 -2) are measured in a high-pressure shock tube and in a rapid compression machine at equivalence ratios in the range 0.5–2.0 at 90 % dilution, at temperatures in the range 600–1430 K and at pressures of 15 and 30 bar. To clarify the effect of the branched methyl group on fuel oxidation, IDTs of n-undecane (nC 11 H 24 ) are also measured at similar conditions to those measured for C 11 H 24 -2. A new chemical kinetic mechanism, using C3MechV4.0.1 as the core chemistry, is developed and validated against the new experimental data. The thermodynamic properties of the fuel (RH), alkyl (Ṙ), alkyl peroxy (RȮ 2 ), hydroperoxy-alkyl (Q̇OOH), and peroxy hydroperoxy alkyl (Ȯ 2 QOOH) radicals are updated in both the C 11 H 24 -2 and nC 11 H24 models using THERM25. A reaction path flux analysis for C 11 H 24 -2 at different temperatures was conducted. Compared to nC 11 H 24 , C 11 H 24 -2 shows slower reactivity. At low and intermediate temperatures, the chain propagation pathway Q̇OOH ↔ C 11 cyclic ether + ȮH is favored for C 11 H 24 -2, while the chain branching pathway Q̇OOH ↔ Ȯ 2 QOOH ↔ C 11 carbonyl hydroperoxide (KHP) + ȮH is suppressed, leading to lower reactivity compared to nC 11 H 24 . At high temperatures, the presence of the branched methyl group inhibits the direct decomposition of the fuel, resulting in reduced C 2 H 4 formation, which in turn suppresses the reactivity of the fuel.

2-methyl decane↗