6 research outputs found
Ab Initio Investigation of the Thermal Decomposition of <i>n</i>‑Butylcyclohexane
Environmental
and energy security concerns have motivated an increased
focus on developing clean, efficient combustors, which increasingly
relies on insight into the combustion chemistry of fuels. In particular,
naphthenes (cycloalkanes and alkylcycloalkanes) are important chemical
components of distillate fuels, such as diesel and jet fuels. As such,
there is a growing interest in describing napthene reactivity with
kinetic mechanisms. Use of these mechanisms in predictive combustion
models aids in the development of combustors. This study focuses on
the pyrolysis of <i>n</i>-butylcyclohexane (<i>n</i>-BCH), an important representative of naphthenes in jet fuels. Seven
different unimolecular decomposition pathways of C–C bond fission
were explored utilizing ab initio/DFT methods. Accurate reaction energies
were computed using the high-level quantum composite G3B3 method.
Variational transition state theory, Rice–Ramsperger–Kassel–Marcus/master
equation simulations provided temperature- and pressure-dependent
rate constants. Implementation of these pathways into an existing
chemical kinetic mechanism improved the prediction of experimental
OH radical and H<sub>2</sub>O speciation in shock tube oxidation.
Simulations of this combustion showed a change in the expected decomposition
chemistry of <i>n</i>-BCH, predicting increased production
of cyclic alkyl radicals instead of straight-chain alkenes. The most
prominent reaction pathway for the decomposition of <i>n</i>-BCH is <i>n</i>-BCH = C<sub>3</sub>H<sub>7</sub> + C<sub>7</sub>H<sub>13</sub>. The results of this study provide insight
into the combustion of <i>n</i>-BCH and will aid in the
future development of naphthene kinetic mechanisms
Formation and emission of large furans and oxygenated hydrocarbons from flames.
Many oxygenated hydrocarbon species formed during combustion, such as furans, are highly toxic and detrimental to human health and the environment. These species may also increase the hygroscopicity of soot and strongly influence the effects of soot on regional and global climate. However, large furans and associated oxygenated species have not previously been observed in flames, and their formation mechanism and interplay with polycyclic aromatic hydrocarbons (PAHs) are poorly understood. We report on a synergistic computational and experimental effort that elucidates the formation of oxygen-embedded compounds, such as furans and other oxygenated hydrocarbons, during the combustion of hydrocarbon fuels. We used ab initio and probabilistic computational techniques to identify low-barrier reaction mechanisms for the formation of large furans and other oxygenated hydrocarbons. We used vacuum-UV photoionization aerosol mass spectrometry and X-ray photoelectron spectroscopy to confirm these predictions. We show that furans are produced in the high-temperature regions of hydrocarbon flames, where they remarkably survive and become the main functional group of oxygenates that incorporate into incipient soot. In controlled flame studies, we discovered ∼100 oxygenated species previously unaccounted for. We found that large alcohols and enols act as precursors to furans, leading to incorporation of oxygen into the carbon skeletons of PAHs. Our results depart dramatically from the crude chemistry of carbon- and oxygen-containing molecules previously considered in hydrocarbon formation and oxidation models and spearhead the emerging understanding of the oxidation chemistry that is critical, for example, to control emissions of toxic and carcinogenic combustion by-products, which also greatly affect global warming
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Formation and emission of large furans and oxygenated hydrocarbons from flames.
Many oxygenated hydrocarbon species formed during combustion, such as furans, are highly toxic and detrimental to human health and the environment. These species may also increase the hygroscopicity of soot and strongly influence the effects of soot on regional and global climate. However, large furans and associated oxygenated species have not previously been observed in flames, and their formation mechanism and interplay with polycyclic aromatic hydrocarbons (PAHs) are poorly understood. We report on a synergistic computational and experimental effort that elucidates the formation of oxygen-embedded compounds, such as furans and other oxygenated hydrocarbons, during the combustion of hydrocarbon fuels. We used ab initio and probabilistic computational techniques to identify low-barrier reaction mechanisms for the formation of large furans and other oxygenated hydrocarbons. We used vacuum-UV photoionization aerosol mass spectrometry and X-ray photoelectron spectroscopy to confirm these predictions. We show that furans are produced in the high-temperature regions of hydrocarbon flames, where they remarkably survive and become the main functional group of oxygenates that incorporate into incipient soot. In controlled flame studies, we discovered ∼100 oxygenated species previously unaccounted for. We found that large alcohols and enols act as precursors to furans, leading to incorporation of oxygen into the carbon skeletons of PAHs. Our results depart dramatically from the crude chemistry of carbon- and oxygen-containing molecules previously considered in hydrocarbon formation and oxidation models and spearhead the emerging understanding of the oxidation chemistry that is critical, for example, to control emissions of toxic and carcinogenic combustion by-products, which also greatly affect global warming
Formation and emission of large furans and oxygenated hydrocarbons from flames
Many oxygenated hydrocarbon species formed during combustion, such as furans, are highly toxic and detrimental to human health and the environment. These species may also increase the hygroscopicity of soot and strongly influence the effects of soot on regional and global climate. However, large furans and associated oxygenated species have not previously been observed in flames, and their formation mechanism and interplay with polycyclic aromatic hydrocarbons (PAHs) are poorly understood. We report on a synergistic computational and experimental effort that elucidates the formation of oxygen-embedded compounds, such as furans and other oxygenated hydrocarbons, during the combustion of hydrocarbon fuels. We used ab initio and probabilistic computational techniques to identify low-barrier reaction mechanisms for the formation of large furans and other oxygenated hydrocarbons. We used vacuum-UV photoionization aerosol mass spectrometry and X-ray photoelectron spectroscopy to confirm these predictions. We show that furans are produced in the high-temperature regions of hydrocarbon flames, where they remarkably survive and become the main functional group of oxygenates that incorporate into incipient soot. In controlled flame studies, we discovered ∼100 oxygenated species previously unaccounted for. We found that large alcohols and enols act as precursors to furans, leading to incorporation of oxygen into the carbon skeletons of PAHs. Our results depart dramatically from the crude chemistry of carbon- and oxygen-containing molecules previously considered in hydrocarbon formation and oxidation models and spearhead the emerging understanding of the oxidation chemistry that is critical, for example, to control emissions of toxic and carcinogenic combustion by-products, which also greatly affect global warming