Oxidation In Jet-stirred Reactor Research Articles

Exploring low-temperature oxidation chemistry of 2- and 3-pentanone

The low-temperature oxidation chemistry of 2- and 3-pentanone was investigated over a wide range of conditions using a jet-stirred reactor (JSR) and a rapid compression machine (RCM). The JSR oxidation experiment was performed at the pressure of 93.3 kPa over a temperature range of 600-1000 K. Detailed speciation information was obtained using synchrotron vacuum ultraviolet photoionization mass spectrometry. Ignition delay times (IDTs) of 2- and 3-pentanone were measured in an RCM from 640 to 820 K at pressures of 15 and 25 bar and an equivalence ratio of 1.0. The two C5 ketones showed NTC behavior and two-stage ignition phenomena. Mole fraction time histories of intermediate species during the two-stage ignition process of both ketones were obtained using a fast-sampling system coupled with gas chromatography. There are distinct differences between 2- and 3-pentanone in species concentration profiles and IDTs. A kinetic mechanism for the low-temperature oxidation of 2- and 3-pentanone was developed, which can satisfactorily predict all available measurements. The reaction path analyses indicate that the intramolecular hydrogen migration reaction of ROO radicals tends to produce resonance-stabilized QOOH radical structures. The secondary oxygen addition reaction of resonance-stabilized QOOH radicals thus is the most important source of OH radicals in the low-temperature oxidation of ketone fuels. The intramolecular hydrogen migration reactions are slowed down in the presence of the carbonyl functional group, which makes the low-temperature reactivity of the two C5 ketones lower than that of n-pentane. The position of the carbonyl functional group affects the species pools during the oxidation of the two ketones to a great extent. Larger production of CH4, C3H6, CH3COCH3, and C2H5CHO were observed in 2-pentanone oxidation, while the production of CH3CHO was favored during 3-pentanone oxidation both in the JSR and RCM experiments. The different lengths of the carbon chain on both sides of the carbonyl group in 2- and 3-pentanone resulted in the difference in the species distribution.

Experimental and kinetic modeling studies on oxidation of n-heptane under oxygen enrichment in a jet-stirred reactor

Oxygen-enriched combustion can improve thermal efficiency and reduce CO, unburned hydrocarbons and soot emissions in internal combustion engines. There are significant differences in the combustion process and pollutant emissions between oxygen-enriched and air condition. In order to develop an improved understanding of the effect of oxygen concentration on n-heptane oxidation, the jet-stirred reactor oxidation characteristics of n-heptane were experimentally tested at temperatures of 450–950 K and pressures of 1.03 atm with the residence time (τ) of 2 s, under the condition of oxygen mole fractions from 0.055 to 0.6. Meantime, the simulations were performed on CHEMKIN. Results show that, firstly, with the increase of oxygen concentration, the NTC (Negative Temperature Coefficient) effect is weakened, mainly due to the strengthening of low-temperature reaction path, which is also the reason for the improvement of ignition stability in cold-start condition of engines. Secondly, the activity of the reaction system improves with the increase of oxygen concentration. Within 500–750 K, it is due to enhancement of the low-temperature reaction path. When the temperature is higher than 750 K, the improvement is due to the enhancement of decomposition of H2O2 and addition reaction of H and O2. Thirdly, with the increase of oxygen concentration, both the generation and consumption of CO are strengthened, which leads to the tip of the diesel spray flame changing from soot area under air condition to the CO chemiluminescence.

Low temperature oxidation of toluene in an n-heptane/toluene mixture

As an important component of transportation fuels, toluene has little reactivity in the low temperature regime. However, the low temperature reactivity of toluene may be enhanced by the reaction of other reactive components (e.g., n-heptane) in fuel mixtures. This work examines low temperature oxidation of toluene in jet stirred reactor oxidation of an n-heptane/toluene mixture (1:1 in mole, 500–800 K, ϕ=0.5, τ=2.0 s, p = 1 bar). Two measurement techniques, time of flight molecular beam mass spectrometry using synchrotron vacuum ultraviolet radiation as the photon ionization source and gas chromatography mass spectrometry, were applied to identify and measure 32 species, including four polycyclic aromatic hydrocarbons (PAH) and oxygenated PAH (OPAH). Numerical simulations using the latest kinetic model from Lawrence Livermore National Laboratory predicted the mole fractions of fuel molecules and small intermediates well, but under-predicted the mole fractions of oxygenated aromatics (phenol, benzyl alcohol, and cresol). The identification of benzyl peroxide–an important intermediate–supported the proposed formation pathways for the identified aromatics. Model analysis highlighted the influence of H-atom abstraction, OH/H radical ipso substitution, and OH addition reactions of toluene on the formation of phenol, benzyl alcohol, and cresol, which may further grow to OPAH molecules by the addition of benzyl radical from H-atom abstraction of toluene.

Experimental and kinetic modeling studies on oxidation of n-heptane under oxygen enrichment in a jet-stirred reactor

Oxygen-enriched combustion can improve thermal efficiency and reduce CO, unburned hydrocarbons and soot emissions in internal combustion engines. There are significant differences in the combustion process and pollutant emissions between oxygen-enriched and air condition. In order to develop an improved understanding of the effect of oxygen concentration on n-heptane oxidation, the jet-stirred reactor oxidation characteristics of n-heptane were experimentally tested at temperatures of 450-950 K and pressures of 1.03 atm with the residence time (τ) of 2 s, under the condition of oxygen mole fractions from 0.055 to 0.6. Meantime, the simulations were performed on CHEMKIN. Results show that, firstly, with the increase of oxygen concentration, the NTC (Negative Temperature Coefficient) effect is weakened, mainly due to the strengthening of low-temperature reaction path, which is also the reason for the improvement of ignition stability in cold-start condition of engines. Secondly, the activity of the reaction system improves with the increase of oxygen concentration. Within 500-750 K, it is due to enhancement of the low-temperature reaction path. When the temperature is higher than 750 K, the improvement is due to the enhancement of decomposition of H2O2 and addition reaction of H and O2. Thirdly, with the increase of oxygen concentration, both the generation and consumption of CO are strengthened, which leads to the tip of the diesel spray flame changing from soot area under air condition to the CO chemiluminescence.

Ammonia and ammonia/hydrogen blends oxidation in a jet-stirred reactor: Experimental and numerical study

One of the most important problems of modern energy industry is the transition to carbon free fuels, which can mitigate the negative environmental effects. This paper presents experimental data on ammonia and ammonia/hydrogen blends oxidation in an isothermal jet-stirred reactor over the temperature of range 800–1300 K. Experiments were performed under atmospheric pressure, residence time of 1 s, various equivalence ratios, and with argon dilution at ≈0.99. It was revealed that hydrogen addition shifts the onset temperature of ammonia oxidation by about 250 K towards the lower region. A detailed chemical kinetic model which showed the best predictive capability was used to understand the effect of hydrogen addition on ammonia reactivity. It was shown that hydrogen presence results into higher concentrations of H, O and OH radicals. Moreover, these radicals start to form at lower temperatures when hydrogen is present. However, the change of the equivalence ratio has only slight effect on the temperature range of ammonia conversion.

Low-temperature oxidation chemistry of 2,4,4-trimethyl-1-pentene (diisobutylene) triggered by dimethyl ether (DME): A jet-stirred reactor oxidation and kinetic modeling investigation

This paper explores the low-temperature (low-T) oxidation chemistry of 2,4,4-trimethyl-1-pentene (IC8D4, diisobutylene) by using jet-stirred reactor (JSR) experiments of both IC8D4/dimethyl ether (DME) mixture and pure IC8D4 at near atmospheric pressure and low temperatures. Oxidation species are measured using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS), gas chromatography (GC) and GC combined with mass spectrometry (GC/MS). It is found that the oxidation of pure IC8D4 at atmospheric pressure presents negligible low-T reactivity and negative temperature coefficient (NTC) behavior, and that the oxidation reactivity of IC8D4/DME mixture is lower than that of butene/DME mixtures previously studied. A kinetic model for low-T IC8D4/DME oxidation is developed from recent oxidation models of IC8D4 and DME. Thermodynamic data of IC8D4 and key species in its sub-mechanism are obtained from theoretical calculations in this work, while rate constants of critical reactions are updated from recent theoretical calculation studies in literature. Based on the modeling analysis, four main pathways are found to be responsible for the consumption of IC8D4 at low temperatures. Among them, the first three pathways initiated by H addition, OH addition and H abstraction on allylic carbon sites are similar to those in 1-butene/DME and isobutene/DME oxidation. These three pathways are mainly responsible for promoting or retaining OH formation. The fourth pathway initiated by H abstraction on the alkyl carbon site differs from the other three in that it is only important in IC8D4/DME oxidation while not important in butenes/DME oxidation. This fourth pathway incorporates stepwise O2 addition and cycloaddition reaction sequences, which can promote and inhibit OH formation, respectively. The increasing contribution of this fourth pathway in IC8D4/DME oxidation reduces its reactivity compared to that of butenes/DME oxidation.

Exploring pyrolysis and oxidation chemistry of o-xylene at various pressures with special concerns on PAH formation

This work reports an experimental and kinetic modelling investigation on flow reactor pyrolysis and jet-stirred reactor oxidation of o-xylene. The flow reactor pyrolysis experiments were conducted over 1050–1600 K at 0.04 and 1.0 atm. Key products related to fuel decomposition such as o-xylyl radical, o-xylylene, benzocyclobutene and styrene, as well as polycyclic aromatic hydrocarbons (PAHs), were detected by using synchrotron vacuum ultraviolet photoionization mass spectrometry. The jet-stirred reactor oxidation experiments were performed at 10 atm, 800–1200 K, a residence time of 0.5 s and equivalence ratios of 0.5, 1.0 and 2.0. Speciation were conducted by using gas chromatography and Fourier transform infrared spectrometry. A kinetic model of o-xylene was developed from our previous models of aromatic fuels and validated against both present data and experimental data in literature. Styrene is observed as the dominant product in the pyrolysis of o-xylene and it is mainly produced from the isomerization of o-xylylene directly or via benzocyclobutene as an intermediate species. C9 PAHs (indenyl, indene and indane), phenanthrene and its methyl derivatives were observed as the abundantly produced bicyclic and tricyclic PAHs. The main formation pathways of bicyclic and tricyclic PAHs are found to be different at low and atmospheric pressures, depending on the major precursors produced. Particularly, the self-combination reactions of o-xylyl and the addition reaction of o-xylyl with benzyl and subsequent stepwise H-loss/cyclization reactions are found to be the main sources of methylphenanthrene and dimethylphenanthrene. In the JSR oxidation of o-xylene, toluene and benzene were observed as the abundantly produced aromatic products, while o-methylbenzaldehyde was among the most abundantly produced oxygenated aromatics. modelling analysis reveals that o-xylyl radical is also the dominant fuel consumption product. Its consumption mainly proceeds through the oxidation by HO2 and finally produces o-methylbenzaldehyde. Further decomposition reactions of o-methylbenzaldehyde contribute to the formation of other major oxygenated aromatics such as cresol and benzofuran. Indene and naphthalene were also observed in the oxidation of o-xylene, which are mainly produced from the stepwise H-loss/cyclization reaction sequence of o-methylethylbenzene and decomposition of dibenzofuran, respectively.

Oxygenated PAH Formation Chemistry Investigation in Anisole Jet Stirred Reactor Oxidation by a Thermodynamic Approach

Oxygenated poly aromatic hydrocarbons (OPAH) are widely produced in biomass combustion. Recent studies suggest significantly higher toxicity for OPAH in comparison to PAH and soot. However, the pre...

Experimental and kinetic modeling study on 1,3-cyclopentadiene oxidation and pyrolysis

The oxidation of 1,3-cyclopentadiene (c-C5H6), a key intermediate formed in the combustion of aromatic and cyclic hydrocarbon fuels and formation of polycyclic aromatic hydrocarbons (PAHs), was studied in a jet-stirred reactor (JSR) under the pressure of 0.1 MPa and temperatures from 623 to 1073 K with three equivalence ratios (φ = 0.5, 1.0 and 1.8). The mole fraction profiles of 25 oxidation products including light hydrocarbons, oxygenated and aromatic species were identified and quantified using online synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) with uncertainties of C, H, and O molar balances about 24%, 20% and 14%, respectively. A detailed kinetic model with 245 species and 1638 reactions was constructed based on the theoretical calculation and reported models in literature and validated with the new JSR oxidation data in this work. The dominant consumption channels of 1,3-cyclopentadiene are through H-atom abstraction reactions by OH, HO2 and CH3 radicals to produce cyclopentadienyl radical (c-C5H5) under all equivalence ratios and the contribution of CH3 attacking increases from φ = 0.5 to 1.8. Subsequently, the c-C5H5 is consumed via the reactions with HO2 and O2 to form small molecule and the recombination reaction with c-C5H6 to yield PAHs. Furthermore, the current model was also validated with a wide range of experimental data in literature of 1,3-cyclopentadiene combustion, including the species concentration profiles in flow reactors pyrolysis and oxidation.

Surrogate Fuels Formulation for FACE Gasoline Using the Nuclear Magnetic Resonance Spectroscopy

An efficient surrogate fuel formulation methodology, which directly uses the chemical structure information from nuclear magnetic resonance (NMR) spectroscopy analysis, has been proposed. Five functional groups, paraffinic CH2, paraffinic CH3, aromatic C-CH, olefinic CH-CH2, and cycloparaffin CH2, have been selected to show the basic molecular structure of the fuels for the advanced combustion engines (FACE) fuels. A palette that contains six candidate components, n-heptane, iso-octane, toluene, 2,5-dimethylhexane, methylcyclohexane, and 1-hexene, is chosen for different FACE fuels, based on the consideration that surrogate mixtures should provide the representative functional groups and comparable molecular sizes. The kinetic mechanisms of these six candidate components are chosen to assemble a detailed mechanism of each surrogate fuel for FACE gasoline. Whereafter, the accuracy of FACE A and F surrogate models was demonstrated by comparing the model predictions against experimental data in homogeneous ignition, jet stirred reactor oxidation, and premixed flame.

An experimental and modeling study on the low temperature oxidation of surrogate for JP-8 part II: Comparison between neat 1,3,5-trimethylbenzene and its mixture with n-decane

The low temperature oxidation of neat 1,3,5-trimethylbenzene (T135MB) and n-decane/T135MB mixture as a surrogate for JP-8 has been investigated in a jet-stirred reactor over the temperature range of 500–1100 K at atmospheric pressure under fuel-rich condition with residence time from 2.33 to 1.06 s. Mole fraction profiles of 29 intermediates including light hydrocarbons, oxygenated and aromatic compounds were identified by gas chromatographic techniques. In general, the concentrations of intermediates tend to increase progressively with temperature from 925 K in neat T135MB oxidation, while these species exhibit bimodal distributions from 550 K in the oxidation of n-decane/T135MB mixture (surrogate). By considering the calculated rate constants of T135MB and analogous coupling reactions between T135MB and n-decane, a detailed kinetic mechanism involving 910 species and 5329 reactions was established with a reasonable agreement with the experimental results. The low temperature chemistry of T135MB and surrogate was analyzed including the NTC behavior below 800 K. The oxidation process of T135MB is occurring mainly by H-abstraction with OH radical and subsequent reactions. The difference is that in the NTC region H-abstraction by OH radicals is the major consumption pathway for T135MB in the surrogate. But for neat T135MB, the dominant channels change to the H-abstractions by H-atoms, OH and CH3 radicals. Addition of n-decane can promote the oxidation of T135MB by providing OH radicals in the low temperature oxidation of surrogate fuel. Moreover, the model was also validated against the experimental data on n-decane and JP-8 combustion, including species profiles in low temperature jet-stirred reactor oxidation and high temperature flow reactor pyrolysis as well as ignition delay times. These extended results yielded overall satisfactory agreement, and will benefit for further application of practical JP-8 fuels, particularly for their combustion properties at wide temperature range.

Experimental and kinetic modeling investigation on pyrolysis and combustion of n-butane and i-butane at various pressures

Butane is the smallest alkane with normal and branched isomers. To obtain insight into the effects of fuel structure and pressure on its intermediate-to-high temperature combustion chemistry, flow reactor pyrolysis and laminar burning velocities of the butane isomers were investigated at various pressures. In the pyrolysis experiments, species profiles were measured as function of the heating temperature at 0.04, 0.2 and 1 atm using synchrotron vacuum ultraviolet photoionization mass spectrometry. Laminar burning velocities of both n-butane/air and i-butane/air mixtures were measured at 298 K and 1–10 atm using spherically expanding flames. It was observed that both the pyrolysis and combustion behaviors of the butane isomers were influenced by the fuel structures. A detailed kinetic model of butane isomers was developed and validated against the new experimental data. Both rate of production analysis and sensitivity analysis were performed to give insight into the chemistry of butane pyrolysis and combustion. In the flow reactor pyrolysis, the weaker primary-tertiary CC bond than the primary-secondary and secondary-secondary CC bonds leads to lower initial decomposition temperatures of i-butane than n-butane. Under both pyrolysis and combustion conditions, the reaction pathways towards C2 and C3 species pool are emphasized for the decomposition of n-butane and i-butane, respectively. The more abundant production of C3 precursors explains the higher concentrations of benzene in the i-butane pyrolysis, while the higher laminar burning velocities of n-butane/air mixtures at all investigated pressures are mainly attributed to the easy production of H atom from n-butane decomposition and the dominance of the reactive C2 chemistry. Moreover, the i-butane/air flames exhibit stronger pressure dependence than the n-butane/air flames. The model was further validated against a wide range of experimental data in the literature, including ignition delay times and species profiles in flow reactor pyrolysis and oxidation, shock tube pyrolysis and oxidation, jet-stirred reactor oxidation and laminar premixed flames.

N-Heptane cool flame chemistry: Unraveling intermediate species measured in a stirred reactor and motored engine

This work identifies classes of cool flame intermediates from n-heptane low-temperature oxidation in a jet-stirred reactor (JSR) and a motored cooperative fuel research (CFR) engine. The sampled species from the JSR oxidation of a mixture of n-heptane/O2/Ar (0.01/0.11/0.88) were analyzed using a synchrotron vacuum ultraviolet radiation photoionization (SVUV-PI) time-of-flight molecular-beam mass spectrometer (MBMS) and an atmospheric pressure chemical ionization (APCI) Orbitrap mass spectrometer (OTMS). The OTMS was also used to analyze the sampled species from a CFR engine exhaust. Approximately 70 intermediates were detected by the SVUV-PI-MBMS, and their assigned molecular formulae are in good agreement with those detected by the APCI-OTMS, which has ultra-high mass resolving power and provides an accurate elemental C/H/O composition of the intermediate species. Furthermore, the results show that the species formed during the partial oxidation of n-heptane in the CFR engine are very similar to those produced in an ideal reactor, i.e., a JSR.The products can be classified by species with molecular formulae of C7H14Ox (x = 0–5), C7H12Ox (x = 0–4), C7H10Ox (x = 0–4), CnH2n (n = 2–6), CnH2n−2 (n = 4–6), CnH2n+2O (n = 1–4), CnH2nO (n = 1–6), CnH2n−2O (n = 2–6), CnH2n−4O (n = 4–6), CnH2n+2O2 (n = 0–4, 7), CnH2nO2 (n = 1–6), CnH2n−2O2 (n = 2–6), CnH2n−4O2 (n = 4–6), and CnH2nO3 (n = 3–6). The identified intermediate species include alkenes, dienes, aldehyde/keto compounds, olefinic aldehyde/keto compounds, diones, cyclic ethers, peroxides, acids, and alcohols/ethers. Reaction pathways forming these intermediates are proposed and discussed herein. These experimental results are important in the development of more accurate kinetic models for n-heptane and longer-chain alkanes.

A comprehensive experimental and kinetic modeling study of n-propylbenzene combustion

This work presents a comprehensive experimental and kinetic modeling study on the combustion of n-propylbenzene. Flow reactor pyrolysis of n-propylbenzene at 0.04, 0.2 and 1 atm and laminar premixed flames of n-propylbenzene at 0.04 atm with equivalence ratios of 0.75 and 1.00 were investigated with synchrotron vacuum ultraviolet photoionization mass spectrometry. Jet stirred reactor (JSR) oxidation of n-propylbenzene at 10 atm with equivalence ratios of 0.5, 1.0, 1.5 and 2.0 was investigated with gas chromatography. A detailed kinetic model for n-propylbenzene combustion with 340 species and 2069 reactions was developed and validated against the data measured in this work. Model analyses such as rate of production analysis and sensitivity analysis were also performed to reveal the key pathways in the consumption of fuel and formation of polycyclic aromatic hydrocarbons (PAHs). The analysis results demonstrate that the benzylic CC bond dissociation reaction is crucial for the decomposition of n-propylbenzene in the pyrolysis and rich flame. Low temperature oxidation reactions play important roles in the high pressure JSR oxidation of n-propylbenzene. In addition, the formation pathways of PAHs are strongly related to the fuel structure, especially for the formation of bicyclic PAHs such as indene and naphthalene. Furthermore, the present model was also validated against previous experimental data of n-propylbenzene combustion under a wide range of conditions, including ignition delay times, laminar flame speeds, extinction strain rates, speciation profiles in atmospheric pressure JSR oxidation, flow reactor oxidation and high pressure shock tube pyrolysis and oxidation.

Quantities of Interest in Jet Stirred Reactor Oxidation of a High-Octane Gasoline

This work examines the oxidation of a well-characterized, high-octane-number FACE (fuel for advanced combustion engines) F gasoline. Oxidation experiments were performed in a jet-stirred reactor (JSR) for FACE F gasoline under the following conditions: pressure, 10 bar; temperature, 530–1250 K; residence time, 0.7s; equivalence ratios, 0.5, 1.0, and 2.0. Detailed species profiles were achieved by identification and quantification from gas chromatography with mass spectrometry (GC-MS) and Fourier transform infrared spectrometry (FTIR). Four surrogates, with physical and chemical properties that mimic the real fuel properties, were used for simulations, with a detailed gasoline surrogate kinetic model. Fuel and species profiles were well-captured and -predicted by comparisons between experimental results and surrogate simulations. Further analysis was performed using a quantities of interest (QoI) approach to show the differences between experimental and simulation results and to evaluate the gasoline surro...

A comprehensive iso-octane combustion model with improved thermochemistry and chemical kinetics

Iso-Octane (2,2,4-trimethylpentane) is a primary reference fuel and an important component of gasoline fuels. Moreover, it is a key component used in surrogates to study the ignition and burning characteristics of gasoline fuels. This paper presents an updated chemical kinetic model for iso-octane combustion. Specifically, the thermodynamic data and reaction kinetics of iso-octane have been re-assessed based on new thermodynamic group values and recently evaluated rate coefficients from the literature. The adopted rate coefficients were either experimentally measured or determined by analogy to theoretically calculated values. Furthermore, new alternative isomerization pathways for peroxy-alkyl hydroperoxide (ȮOQOOH) radicals were added to the reaction mechanism. The updated kinetic model was compared against new ignition delay data measured in rapid compression machines (RCM) and a high-pressure shock tube. These experiments were conducted at pressures of 20 and 40 atm, at equivalence ratios of 0.4 and 1.0, and at temperatures in the range of 632–1060K. The updated model was further compared against shock tube ignition delay times, jet-stirred reactor oxidation speciation data, premixed laminar flame speeds, counterflow diffusion flame ignition, and shock tube pyrolysis speciation data available in the literature. Finally, the updated model was used to investigate the importance of alternative isomerization pathways in the low temperature oxidation of highly branched alkanes. When compared to available models in the literature, the present model represents the current state-of-the-art in fundamental thermochemistry and reaction kinetics of iso-octane; and thus provides the best prediction of wide ranging experimental data and fundamental insights into iso-octane combustion chemistry.

Experimental and kinetic modeling study of 1-hexene combustion at various pressures

The pyrolysis of 1-hexene was studied in a flow reactor by synchrotron vacuum ultraviolet photoionization mass spectrometry and gas chromatography combined with mass spectrometry at 0.04, 0.2, and 1atm. Laminar flame speeds of 1-hexene/air mixtures at various pressures (1, 2, 5, and 10atm) were measured at an initial temperature of 373K and equivalence ratios from 0.7 to 1.5. A kinetic model of 1-hexene combustion with 122 species and 919 reactions was developed to investigate the key pathways in the decomposition of 1-hexene and the formation and consumption of products, as well as the chemical kinetic effects on the laminar flame propagation. The presence of double bond in 1-hexene molecule leads to the enhanced formation of resonantly stabilized radicals and unsaturated intermediates. The model was also validated against the experimental data of 1-hexene combustion from literature, including ignition delay times and species profiles in jet-stirred reactor oxidation and laminar premixed flames. The extensive validations demonstrate the applicability of the present model over a wide range of conditions, such as low to high pressures, intermediate to high temperatures, and pyrolysis to oxidation circumstances.

Measuring hydroperoxide chain-branching agents during n-pentane low-temperature oxidation

The reactions of chain-branching agents, such as H2O2 and hydroperoxides, have a decisive role in the occurrence of autoignition. The formation of these agents has been investigated in an atmospheric-pressure jet-stirred reactor during the low-temperature oxidation of n-pentane (initial fuel mole fraction of 0.01, residence time of 2s) using three different diagnostics: time-of-flight mass spectrometry combined with tunable synchrotron photoionization, time-of-flight mass spectrometry combined with laser photoionization, and cw-cavity ring-down spectroscopy. These three diagnostics enable a combined analysis of H2O2, C1–C2, and C5 alkylhydroperoxides, C3–C5 alkenylhydroperoxides, and C5 alkylhydroperoxides including a carbonyl function (ketohydroperoxides). Results using both types of mass spectrometry are compared for the stoichiometric mixture. Formation data are presented at equivalence ratios from 0.5 to 2 for these peroxides and of two oxygenated products, ketene and pentanediones, which are not usually analyzed during jet-stirred reactor oxidation. The formation of alkenylhydroperoxides during alkane oxidation is followed for the first time. A recently developed model of n-pentane oxidation aids discussion of the kinetics of these products and of proposed pathways for C3–C5 alkenylhydroperoxides and the pentanediones.

Burning velocities and jet-stirred reactor oxidation of diethyl carbonate

There is current interest in utilizing oxygenated biofuels such as carbonates in blends with conventional oil-derived liquid fuels. Carbonates, commonly used as electrolyte solvents in Li-ion cells, could ignite after abusive operating conditions. Improving the kinetic modeling of the oxidation of these bio-derived oxygenates requires further investigation under well-controlled conditions. An experimental and detailed chemical kinetic modeling study of diethyl carbonate (DEC) oxidation and combustion was performed. Experiments were carried out in a jet stirred reactor over a wide range of equivalence ratios, temperatures, and pressure. Mole fractions of stable species were measured in the jet stirred reactor at atmospheric pressure. Burning velocities of DEC/air mixtures were determined at elevated temperature over a range of pressures and equivalence ratios. A detailed chemical kinetic modeling was performed using the present experimental results and existing literature data and model. The model represents fairly well the present data. Sensitivity and reaction paths analyses were used to rationalize the results.

Experimental and kinetic modeling study of laminar premixed decalin flames

Laminar premixed flames of decalin with equivalence ratios of 0.75, 1.0 and 1.8 were studied using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Dozens of flame species were identified and their mole fraction profiles were evaluated, including a series of free radicals. A detailed kinetic model of decalin combustion consisting of 538 species and 3218 reactions was developed and validated on the new flame data. The rate of production analysis at different equivalence ratios were performed to help understand the kinetics in the decompostion of decalin and the formation of some key intermediates. The H-atom abstraction reactions play an overwhelming role in the primary decomposition of decalin at flame conditions. Monocyclic aromatic hydrocarbons (MAHs) are mainly produced from the decomposition of decalin, while polycyclic aromatic hydrocarbons (PAHs) originate from mass growth process of PAH precursors. In addition, some oxygenated intermediates have important contributions to the formation of key MAHs and PAHs such as benzene (A1) and indene (C9H8). The direct production of PAH precursors in fuel decomposition process explains the higher sooting tendency of decalin than n-alkanes and benzene. Furthermore, the model was used to simulate literature data of decalin combustion, such as species profiles in jet stirred reactor oxidation of decalin and ignition delay times of decalin.