Experimental and Modeling Study of Premixed Laminar Flames of Ethanol and Methane

To better understand the chemistry of the combustion of ethanol, the structure of five low pressure laminar premixed flames has been investigated: a pure methane flame (φ = 1), three pure ethanol flames (φ = 0.7, 1.0, and 1.3), and an ethanol/methane mixture flame (φ = 1). The flames have been stabilized on a burner at a pressure of 6.7 kPa using argon as a dilutant, with a gas velocity at the burner of 64.3 cm/s at 333 K. The results consist of mole fraction profiles of 20 species measured as a function of the height above the burner by probe sampling followed by online gas chromatography analyses. A mechanism for the oxidation of ethanol was proposed. The reactions of ethanol and acetaldehyde were updated and include recent theoretical calculations while that of ethenol, dimethyl ether, acetone, and propanal were added in the mechanism. This mechanism was also tested against experimental results available in the literature for laminar burning velocities and laminar premixed flame where ethenol was detected. The main reaction pathways of consumption of ethanol are analyzed. The effect of the branching ratios of reaction C₂H₅OH + OH → Products + H₂O is also discussed

Kinetic Modeling of the Thermal Destruction of Nitrogen Mustard Gas

The destruction of stockpiles or unexploded ammunitions of nitrogen mustard (tris­(2-chloroethyl)­amine, HN-3) requires the development of safe processes. The thermal destruction of this kind of compound is one of the most efficient method of destruction. Because of the high-level of toxicity of this chemical, there is a considerable lack of knowledge on the chemical kinetics at high temperatures. In this study, a detailed chemical kinetic model for the pyrolysis of nitrogen mustard gas is developed based on a large number of thermokinetic parameters calculated with theoretical chemistry. The thermal decomposition of HN-3 is shown to mainly proceed through stepwise dechlorination with Cl-atom being the principal chain carrier. The successive losses of chlorine atom mainly lead to unsaturated amines without chlorine groups. Theoretical calculations demonstrated that the thermal decomposition of these compounds ultimately lead to the formation of pyrrole, which can accumulate at low temperature. At higher temperatures, pyrrole yields HCN and acetylene. Simulations also predict that about 52% of the total flux of decomposition of HN-3 leads to the formation of <i>N</i>,<i>N</i>-diethenyl-2-chloroethylamine (P29), which acts as a chain branching agent because its unimolecular decomposition is preponderant and produces one chlorine and one hydrogen atoms. Comparisons with the simulated reactivity of sulfur mustard gas are also performed and show that HN-3 is more reactive that the former toxic. The higher number of chlorine atoms in HN-3 compared to sulfur mustard (3 vs 2) and the formation of the chain branching intermediate P29 during its decomposition explain this behavior

Measurements of Laminar Burning Velocities above Atmospheric Pressure Using the Heat Flux MethodApplication to the Case of <i>n-</i>Pentane

A new adiabatic burner allowing the measurement of burning velocities at high pressure with the heat flux method has been developed. Experimental measurements of laminar burning velocities of methane and <i>n-</i>pentane were performed for pressures up to 6 atm at 298 K and at atmospheric pressure for temperatures from 298 to 398 K. Equivalence ratios varied from 0.6 to 1.9. The results for methane flames are in good agreement with the only results of literature obtained above atmospheric pressure using the heat flux method; those for <i>n-</i>pentane are to our knowledge the first application of this method to a flame of a liquid fuel above atmospheric pressure. Based on these measurements, empirical correlations of the variation of the measured laminar flame velocities with pressure and temperature have been proposed for methane and <i>n-</i>pentane. In the case of methane, these correlations lead to a satisfactory prediction of literature measurements made using constant volume bombs

Thermal Decomposition of Phosgene and Diphosgene

Phosgene (COCl₂) is a toxic compound used or formed in a wide range of applications. The understanding of its thermal decomposition for destruction processes or in the event of accidental fire of stored reserves is a major safety issue. In this study, a detailed chemical kinetic model for the thermal decomposition and combustion of phosgene and diphosgene is proposed for the first time. A large number of thermo-kinetic parameters were calculated using quantum chemistry and reaction rate theory. The model was validated against experimental pyrolysis data from the literature. It is predicted that the degradation of diphosgene is mainly ruled by a pericyclic reaction producing two molecules of phosgene and, to a lesser extent, by a roaming radical reaction yielding CO₂ and CCl₄. Phosgene is much more stable than diphosgene under high-temperature conditions, and its decomposition starts at higher temperatures. Decomposition products are CO and Cl₂. An equimolar mixture of the latter molecules can be considered as a surrogate of phosgene from the kinetic point of view, but the important endothermic effect of the decomposition reaction can lead to different behaviors, for instance, in the case of autoignition under high pressure and high temperature

Quantification of Hydrogen Peroxide during the Low-Temperature Oxidation of Alkanes

The first reliable quantification of hydrogen peroxide (H₂O₂) formed during the low-temperature oxidation of an organic compound has been achieved thanks to a new system that couples a jet stirred reactor to a detection by continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near-infrared. The quantification of this key compound for hydrocarbon low-temperature oxidation regime has been obtained under conditions close to those actually observed before the autoignition. The studied hydrocarbon was <i>n</i>-butane, the smallest alkane which has an oxidation behavior close to that of the species present in gasoline and diesel fuels

Experimental Study of Tetrahydrofuran Oxidation and Ignition in Low-Temperature Conditions

The chemistry associated with low-temperature oxidation and ignition of tetrahydrofuran (THF) has been probed through experimental work in two distinct devices: a rapid compression machine (RCM) and a jet-stirred reactor (JSR). Ignition delays of stoichiometric THF/O₂/inert mixtures have been measured for pressures ranging from 0.5 to 1.0 MPa and core gas temperatures from 640 to 900 K. Two-stage ignition is visible up to 810 K, and the evolution of the ignition delay with the temperature shows a clear deviation from Arrhenius behavior between 680 and 750 K. Sampling of the reactive mixture during the ignition delay provided evidence of the formation of C₁–C₄ aldehydes and alkenes, a variety of oxygenated heterocycles, including oxirane, methyloxirane, oxetane, furan, both isomers of dihydrofuran, and 1,4-dioxene, as well as cyclopropanecarboxaldehyde and formic acid-2-propenyl ester. JSR experiments have been performed under pressure close to 1 atm, at temperatures from 500 to 1000 K, and at equivalence ratios from 0.5 to 2, with detailed analysis of the low-temperature intermediate products. Major products include carbon monoxide, carbon dioxide, C₁–C₂ hydrocarbons, and aldehydes, 1-butene, ethylene oxide, methylvinylether, acrolein, propanal, both isomers of dihydrofuran, furan, 2-butenal, cyclopropanecarboxaldehyde, 1,4-dioxene, and unsaturated dihydrofuranols. The obtained mole fraction profiles indicate a significant low-temperature reactivity of THF beginning at temperatures around 550 K, with a marked negative temperature coefficient zone. The results from both experimental devices are put in perspective and allow for the identification of the major formation pathways of the observed species

Shock Tube and Chemical Kinetic Modeling Study of the Oxidation of 2,5-Dimethylfuran

A detailed kinetic model describing the oxidation of 2,5-dimethylfuran (DMF), a potential second-generation biofuel, is proposed. The kinetic model is based upon quantum chemical calculations for the initial DMF consumption reactions and important reactions of intermediates. The model is validated by comparison to new DMF shock tube ignition delay time measurements (over the temperature range 1300–1831 K and at nominal pressures of 1 and 4 bar) and the DMF pyrolysis speciation measurements of Lifshitz et al. [J. Phys. Chem. A 1998, 102 (52), 10655–10670]. Globally, modeling predictions are in good agreement with the considered experimental targets. In particular, ignition delay times are predicted well by the new model, with model–experiment deviations of at most a factor of 2, and DMF pyrolysis conversion is predicted well, to within experimental scatter of the Lifshitz et al. data. Additionally, comparisons of measured and model predicted pyrolysis speciation provides validation of theoretically calculated channels for the oxidation of DMF. Sensitivity and reaction flux analyses highlight important reactions as well as the primary reaction pathways responsible for the decomposition of DMF and formation and destruction of key intermediate and product species

Measurements of Laminar Flame Velocity for Components of Natural Gas

This paper presents new experimental measurements of the laminar flame velocity of components of natural gas, methane, ethane, propane, and <i>n</i>-butane as well as of binary and tertiary mixtures of these compounds proposed as surrogates for natural gas. These measurements have been performed by the heat flux method using a newly built flat flame adiabatic burner at atmospheric pressure. The composition of the investigated air/hydrocarbon mixtures covers a wide range of equivalence ratios, from 0.6 to 2.1, for which it is possible to sufficiently stabilize the flame. Other measurements involving the enrichment of methane by hydrogen (up to 68%) and the enrichment of air by oxygen (oxycombustion techniques) were also performed. Both empirical correlations and a detailed chemical mechanism have been proposed, the predictions being satisfactorily compared with the newly obtained experimental data under a wide range of conditions

Products from the Oxidation of Linear Isomers of Hexene

The experimental study of the oxidation of the three linear isomers of hexene was performed in a quartz isothermal jet-stirred reactor (JSR) at temperatures ranging from 500 to 1100 K including the negative temperature coefficient (NTC) zone, at quasi-atmospheric pressure (1.07 bar), at a residence time of 2 s and with dilute stoichiometric mixtures. The fuel and reaction product mole fractions were measured using online gas chromatography. In the case of 1-hexene, the JSR has also been coupled through a molecular-beam sampling system to a reflectron time-of-flight mass spectrometer combined with tunable synchrotron vacuum ultraviolet photoionization. A difference of reactivity between the three fuels, which varies with the temperature range has been observed and is discussed according to the changes in the possible reaction pathways when the double bond is displaced. An enhanced importance of the reactions via the Waddington mechanism and of those of allylic radicals with HO₂ radicals can be noted for 2- and 3-hexenes compared to 1-hexene

Experimental and Kinetic Modeling Study of 2‑Methyl-2-Butene: Allylic Hydrocarbon Kinetics

Two experimental studies have been carried out on the oxidation of 2-methyl-2-butene, one measuring ignition delay times behind reflected shock waves in a stainless steel shock tube, and the other measuring fuel, intermediate, and product species mole fractions in a jet-stirred reactor (JSR). The shock tube ignition experiments were carried out at three different pressures, approximately 1.7, 11.2, and 31 atm, and at each pressure, fuel-lean (ϕ = 0.5), stoichiometric (ϕ = 1.0), and fuel-rich (ϕ = 2.0) mixtures were examined, with each fuel/oxygen mixture diluted in 99% Ar, for initial postshock temperatures between 1330 and 1730 K. The JSR experiments were performed at nearly atmospheric pressure (800 Torr), with stoichiometric fuel/oxygen mixtures with 0.01 mole fraction of 2M2B fuel, a residence time in the reactor of 1.5 s, and mole fractions of 36 different chemical species were measured over a temperature range from 600 to 1150 K. These JSR experiments represent the first such study reporting detailed species measurements for an unsaturated, branched hydrocarbon fuel larger than iso-butene. A detailed chemical kinetic reaction mechanism was developed to study the important reaction pathways in these experiments, with particular attention on the role played by allylic C–H bonds and allylic pentenyl radicals. The results show that, at high temperatures, this olefinic fuel reacts rapidly, similar to related alkane fuels, but the pronounced thermal stability of the allylic pentenyl species inhibits low temperature reactivity, so 2M2B does not produce “cool flames” or negative temperature coefficient behavior. The connections between olefin hydrocarbon fuels, resulting allylic fuel radicals, the resulting lack of low-temperature reactivity, and the gasoline engine concept of octane sensitivity are discussed