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Ethylene plays a crucial role as an intermediate component in the cracking and combustion processes of large molecular alkane and olefins. In this article, the laminar flame speed of ethylene–air mixtures was measured using the heat flux method. The mechanism of ethylene was simplified by utilizing the error propagation directed relationship graph (DRGEP) and sensitivity analysis (SA), and the Arrhenius pre‐exponential factors for 20 selected reactions in the skeletal mechanism were optimized using the particle swarm optimization (PSO) algorithm. Finally, an ethylene optimization mechanism including 39 species and 85 reactions was obtained. The prediction results for flame speed, ignition delay time, and species concentration were compared with experimental data and other mechanisms, covering a wide range of temperatures (298–1725 K), pressures (1–22.8 atm), and equivalence ratios (0.5–2.0). The findings demonstrate that the optimization mechanism not only improves the prediction results of laminar flame speed in the rich combustion zone and low oxygen environment but also enhances the prediction accuracy of the ignition delay time at high pressure and in the lean combustion zone, as well as the prediction accuracy of C2H4 and H2O radicals. In conclusion, the optimized mechanism exhibits higher accuracy and broader applicability. [ABSTRACT FROM AUTHOR]

Unsaturated hydrocarbons are major components of transportation fuels, combustion intermediates, and unburnt exhaust emissions. Conversely, NOx species are minor species present in the residual and exhaust gases of gasoline-fueled engines and gas turbines. Their co-existence in transportation engines is quite common, particularly with exhaust gas recirculation, which can greatly influence engine combustion characteristics. Therefore, this paper presents a review on the combustion chemistry of unsaturated hydrocarbons and NOx mixtures, with a focus on their chemical kinetic interactions. First, a comprehensive overview of fundamental combustion experiments is provided, covering mixtures of C2–C5 unsaturated/oxygenated species (namely alkenes, alkynes, dienes, alcohols, ethers, ketones, and furans) and three major NOx species (namely NO, NO2, and N2O), as well as reactors including jet-stirred reactors, flow reactors, burners, shock tubes, and rapid compression machines. Then, two widely adopted nitrogen chemistry models are evaluated in conjunction with a core chemistry model (i.e., NUIGMech1.1) via detailed chemical kinetic modeling, and the model similarities and differences across broad temperature ranges are highlighted. Thereafter, the unique interconversions between the three major NOx species are presented. In particular, the controversy regarding the pathways governing NO and NO2 conversion is discussed. Following this, the key direct interaction reactions between unsaturated species and NOx species are overviewed. Finally, the distinguishing features of the combustion chemistry for unsaturated hydrocarbon and NOx mixtures are summarized, and recommendations for future research on this topic are highlighted. [ABSTRACT FROM AUTHOR]

The ethylene inverse diffusion sooting flame chemistry was studied for the first time experimentally and numerically in detail. Effects of oxygen index on flame major species and important small intermediate species formation were analyzed. Inverse diffusion flames were detected by online gas chromatograph to quantitatively measure the mole fraction distributions of major and important intermediate species. With the increase of oxygen index, More C 2 H 4 is consumed and most of intermediate species are promoted. However, the formation of CO 2 on the centerline, C 2 H 6 in the radial direction, and C 3 H 6 in both directions are inhibited. The modified inverse diffusion flame model can successfully reproduce the main variation trend of species mole fraction using the KM2 mechanism. The predicted results by the inverse diffusion flame simulation with the KM2 mechanism were used for further discussion of the combustion chemistry in detail. Two-dimensional predictions indicate that the O 2 oxidant is completely depleted in the reaction zone, and peak mole fractions of most species appear on the fuel side of the flame front or the centerline of the flame. According to the analysis of the reaction path for species formation under different oxygen indexes, A1 formation process is mostly dominated by the even carbon atom path, and the odd carbon atom path only contributes to the formation of A1 at a lower height. [ABSTRACT FROM AUTHOR]

[Display omitted] • An axial local dilution (ALD) inverse diffusion flame (IDF) burner is manufactured. • The model structure in the CoFlame code is modified based on the ALD-IDF burner. • The concentrations of radial species are quantitatively measured. • The impact of various injection rates and locations on flame structure is studied. • The inhibitory effects of CO 2 on key species vary with injection rate and height. To investigate the combustion chemistry of methane inverse diffusion sooting flames with local CO 2 injection, this study designs an axial local dilution (ALD) inverse diffusion flame (IDF) burner capable of precisely controlling the diluent injection rate and location along the flame centerline using a diluent injection pipe. Then the flame generated by the ALD-IDF burner is simulated by a modified model based on the CoFlame code. The distributions of flame temperature and major species mole fractions are measured using a thermocouple and online gas chromatography, and the measurements are compared with numerical results. The impact of different injection flow rates and locations on the flame structure is studied. Results show that injecting CO 2 close to the high-temperature region significantly affects the oxidizer flow field. The predictions of the main trends of species mole fractions show good agreement with experimental results. The oxidizer stream structure variety caused by CO 2 injection is the main reason for affecting the spatial distribution of species in the flame. The local CO 2 injection inhibits the formation of some small molecules and radicals (H 2 , H, OH) as well as intermediate species (C 2 H 2 , C 2 H 4 , C 4 H 2 , A1) close to the flame centerline region. In addition, the inhibitory effect of CO 2 on the aforementioned species increases with higher injection flow rates and heights. However, injecting CO 2 at different heights results in moderate differences in the inhibition of A1 formation. Kinetic analysis of the A1 formation pathways indicates that this phenomenon is due to the varying degrees of suppression on the main A1 formation reaction (2C 3 H 3 = A1) at different injection heights. This study presents a novel method for adding diluents within the flame and analyzes the underlying regulatory mechanisms. The obtained insights are expected to expand the existing pollutant control technologies. [ABSTRACT FROM AUTHOR]

The diversity of reactivities, intermediates, and pathways associated with the low-temperature (low-T) oxidation of various component classes that constitute real fuels is perhaps the most challenging aspect of modeling their combustion chemistry. Unlike high-temperature oxidation (T > 1100 K), where the combustion properties of multicomponent fuels are relatively insensitive to compositional variations, reactions governing low-T oxidation exhibit pronounced sensitivity to fuel composition. Despite the fuel specificity, intermediate formation during low-T oxidation exhibits characteristic behaviors. Combining such observations and the already mature Hy brid Chem istry (HyChem) methodology for high-temperature oxidation of real fuels [ 1 ], we propose a framework to develop simplified, physics-based chemical kinetic models for low-T oxidation of real fuels. The proposed model captures the complexity of low-T oxidation through concise, fuel-specific reactions whose stoichiometric parameters and rate constants are experimentally constrained. Shock tube experiments needed for constraining model parameters are identified and plausible validation targets are discussed. The present paper outlines the model's description, its underlying physical principles, and an initial application to a simple, multi-component mixture, TPRF-60. Detailed uncertainty analyses and application to three real fuels will be presented in a companion paper. [ABSTRACT FROM AUTHOR]

The study of fuel chemistry and soot inception in non-premixed combustion can be advanced by characterizing flame configurations in which the advection and diffusion transport can be finely controlled, with the ability to decouple pyrolysis from oxidation. Also, the ideal flames to be investigated should be perturbed minimally by probes and thick enough for sampling techniques to yield spatially resolved measurements of their structure. The Planar Mixing Layer Flame (PMLF) configuration introduced herein is established between a fuel and an oxidizer slot jet adjacent to each other and shielded from the ambient air by annularly co-flowing inert nitrogen. The PMLF flow is kept laminar and steady by an impinging flat plate equipped with a rectangular exhaust slit opening which anchors the position of the hot combustion products via buoyancy. The PMLF is accessible to sampling and its flow stability is preserved when using any tested probe. The experiments are complemented with 2D- Computational Fluid Dynamics (CFD) modeling with detailed chemical kinetics. The results demonstrate that the PMLF has a self-similar boundary layer structure whose horizontal cross-sections are equivalent to properly selected and equally thick 1D- Counterflow Flames (CFs). The equivalence allows for excellent predictions of the PMLF thermochemical structure characterized experimentally but at a small fraction of the 2D-CFD computational cost. The 1D-CF equivalence affects even aromatics less than twofold despite their kinetics being known to be very sensitive to the temperature field. Importantly, the PMLF thickness is several millimeters and grows at increasing HABs so that the equivalent 1D-CFs have strain rates as small as 7.0 /s which cannot be studied in CF experiments. As a result, the PMLF emerges as a promising canonical non-premixed flame configuration for studying flame chemistry and soot inception on time scales of tens of milliseconds typical of many combustion applications. [ABSTRACT FROM AUTHOR]

The extinction limits of non-premixed counterflow flames of methane (CH 4)/ammonia (NH 3)/nitrogen (N 2) versus high-temperature air (T Air = 700 K and 1000 K) were investigated both experimentally and numerically. Extinction stretch rates of non-premixed counterflow flames of CH 4 /NH 3 mixtures decreased greatly as the ammonia mixing ratio increased. Recent chemical kinetic models could well predict measured extinction limits of non-premixed counterflow flames of CH 4 /NH 3 mixtures, especially for T Air = 1000 K. Chemical kinetic analyses indicated that the nature of NH 3 consuming active radicals but not regenerating them through its oxidation is the primary reason for the drastic decreases in extinction stretch rates of non-premixed counterflow flames of CH 4 /NH 3 mixtures. Furthermore, the combined metric of the transport weighted enthalpy (TWE) and the radical index (RI) is introduced for non-premixed counterflow flames of CH 4 /NH 3 mixtures. The OH-radical index (RI OH), previously used in the combined metric for extinction limits of non-premixed counterflow flames of large hydrocarbons, expresses linear relationships with extinction limits for both T Air conditions. According to further investigations on heat releases from individual reactions, the contribution to heat releases from a reaction involving O radicals, i.e., CH 3 + O ⇄ CH 2 O + H, becomes large in addition to reactions involving OH radicals, i.e., CO + OH ⇄ CO 2 + H and H 2 + OH ⇄ H + H 2 O. Based on the analyses, a new radical index based on the combination of OH and O radicals (RI OH&O) is proposed. The RI OH&O better expresses the linear relationship between extinction limits and the combined metric of RI OH&O and TWE. [ABSTRACT FROM AUTHOR]

As an alternative fuel, dimethyl ether (DME) has attracted much attention due to its high efficiency and low emission. In this study, first, a skeletal mechanism of DME is obtained using a directed relation graph with error propagation (DRGEP) and sensitivity analysis (SA). Then the Arrhenius preexponential factors of the selected reactions in the skeletal mechanism are adjusted by the particle swarm optimization (PSO) algorithm to improve the prediction accuracy. Finally, an optimized mechanism with 30 species and 65 elementary reactions is proposed to describe the combustion of DME–air mixtures. This reaction mechanism is validated against the experimental data of ignition delay time, species concentration, and laminar flame speed, covering a wide range of initial temperatures (298–1600 K), pressures (1.0–60 bar), and equivalence ratios (0.5–2.0). Comparing the previous skeletal mechanisms, the optimized mechanism can excellently reproduce the experiment results, especially in the prediction of the ignition delay time of low‐temperature zone and laminar flame speed of high‐pressure conditions. It means that this mechanism corresponds to higher precision and more extensive applicability. [ABSTRACT FROM AUTHOR]

We report a first attempt to investigate the reaction mechanisms of hydroborate iron compound (HIC), a promising candidate for combustion catalyst, in AP/HTPB/Al composite solid propellants using ammonium perchlorate (AP) as the oxidizer and aluminum as the metal fuel. The effects of HIC on the combustion properties of propellants were experimentally examined to determine burning rates, combustion flame structures and flame temperature distribution. The combustion residues were collected and examined; the mechanical sensitivity of propellant samples were tested. It was found that the addition of HIC particles can increase the burning rates with only minor changes of the pressure exponent. When 5.0 wt% of Al is replaced by HIC, the pressure exponent increases from 0.31 to 0.35 over the pressure range 1–12 MPa while the burning rate increases from 33 mm s−1 to 40 mm s−1 at 7 MPa. The combustion flame images of burning propellants surface loaded with HIC at various pressures present multi-flame structures, and the flame brightness increases with increasing the pressure. Many sparks are observed near the burning surface during the propellant combustion, due to burning aluminum particles in gas phase. With 5.0 wt% HIC included, the propellant produces very different condensed combustion products (CCPs) with a variety of morphologies, and the most typical ones are "porous" shape, large alveolate and loose structures. The relative combustion residue mass decreases with increasing pressure (1–5 MPa) and HIC mass fraction in the formulation (0–5%); While HIC powder is insensitive to friction and impact stimuli (0% at height is higher than 125 cm), the tested propellant formulations containing different mass fraction of HIC particles result sensitive to impact and friction a bit more than the reference formulation without HIC particles. [ABSTRACT FROM AUTHOR]

The present work quantifies the impact of fuel chemistry on burning modes using premixed dimethyl ether (DME), ethanol (EtOH) and methane flames in a back-to-burnt opposed jet configuration. The study considers equivalence ratios 0 ≤ Φ ≤ 1, resulting in a Damköhler (Da) number range 0.06 ≤ Da ≤ 5.1. Multi-scale turbulence (Re ≃ 19,550 and Re t ≃ 360) is generated by means of a cross fractal grid and kept constant along with the enthalpy of the hot combustion products (T HCP = 1700 K) of the counterflow stream. The mean turbulent rate of strain exceeds the laminar extinction rate for all flames. Simultaneous Mie scattering, OH-PLIF and PIV are used to identify reactants, mixing, weakly reacting, strongly reacting and product fluids. The relative balance between conventional flame propagation and auto-ignition based combustion is highlighted using suitably defined Da numbers and a more rapid transition towards self-sustained (e.g. flamelet type) combustion is observed for DME. The strain rate distribution on the reactant fluid surface for methane remains similar to the (non-reactive) mixing layer (Φ = 0), while DME and EtOH flames gradually detach from the stagnation plane with increasing Φ leading to stabilisation in regions with lower compressive rates of strain. The study further provides information on the conditions leading to burning mode transitions via (i) multi-fluid probabilities, (ii) structural flow field information and turbulence-flame interactions delineated by means of conditional (iii) velocity statistics and (iv) the rate of strain along fluid iso-contours. [ABSTRACT FROM AUTHOR]

The formulation of reactive flow problems can be both quite challenging and important to the efficiency and robustness of solution algorithms. In this article, we focus on the choice of the thermochemical state vector as it relates to recently-developed computational techniques for complex combustion chemistry problems. We identify over-specification of the state vector as a source of both ambiguity and error in the partial derivatives used in forming analytical forms of the chemical source Jacobian matrix. We review and compare several approaches taken to increase sparsity of the Jacobian matrix, as it relates to the use of Newton–Krylov methods for implicit time integration, and identify proper techniques for achieving sparsity that do not rely on ad-hoc choice of state variables with inconsistent Jacobians. Chemical explosive mode analysis and linearly-implicit methods, such as Rosenbrock methods, are identified as areas where Jacobian accuracy may be critical. The distinction between how Jacobian exactness impacts Rosenbrock and Newton–Krylov methods is demonstrated with a simple example. We demonstrate the errors in conservation obtained from over-specification of the state vector with auto-ignition calculations for hydrogen, ethylene, and n-heptane chemistry with a high-order implicit Runge–Kutta method. [ABSTRACT FROM AUTHOR]

Aromatic hydrocarbons are important components of petroleum-based transportation fuels, biomass, coal, and solid waste, etc. The reaction kinetics of aromatic hydrocarbons largely determine the combustion characteristics and pollutant emission of vehicle/jet engines, power plants, and industrial reactors. While a few reviews have recently focused on aromatic hydrocarbons in gasoline surrogate fuels, thermochemical conversion of biomass/coal/solid waste, and combustion soot formation, a dedicated overview of research on the combustion chemistry of aromatic hydrocarbons is still lacking. In the last decades, valuable investigations addressing the reaction kinetics were reported based on the measurements from pyrolysis, oxidation, flames, shock tubes, and rapid compression machines, complemented by quantum chemistry and detailed kinetic modeling. Significant advances have allowed a better understanding of such physicochemical reacting system, from aromatic decomposition, oxidation, to pollutants formation. In the present review, aromatic hydrocarbons are systematically categorized to five common classes: basic, mono-substituted, multi-substituted, hydrogenated, and polycyclic aromatics. Fundamental aromatic combustion chemistry consists of the reactions of basic aromatic molecular structures. Then the aryl group strongly influences the reaction kinetics of aromatic derivates, which leads to very different combustion performance from those ordinary paraffins, olefins, and naphthenes. This paper seeks to provide an introduction to the knowledge gathered in the recent research, highlight pertinent aspects of this rapidly enriching information, and outlook the challenges towards fundamentally comprehensive aromatic combustion chemistry and practically efficient aromatic combustion model. [ABSTRACT FROM AUTHOR]

Macroscopic transition processes of soot formation for 1-butene, isobutene, n-butane and isobutane counterflow diffusion flames from sooting-free to heavy-sooting were studied by varying fuel concentration (X F) in the fuel stream. A novel optical diagnostic algorithm was proposed to classify different sooting transition stages in flames. Effects of saturated/unsaturated bonds and linear/branched structures of fuel molecules on the sooting transition were investigated in details. Flame species were detected and quantified by on-line gas chromatography and also kinetic analysis was performed. KL factor was obtained by optical diagnostics to qualitatively compare soot concentrations. Results showed that X F required for 1-butene flame to reach the critical state of macroscopic sooting transition was the lowest, followed by isobutene, isobutane and n-butane flames. Fuels with higher sooting tendencies could achieve entire sooting transition process with a narrower range of X F. Linear butane was more difficult to achieve the sooting transition than branched butane, while linear 1-butene was easier to form soot than branched butene, reflecting the difference between isomeric structures acting on C4 alkenes and alkanes. These might be largely due to the close association of allyl (C 3 H 5 -A) with 1-butene. Higher C3 species content in isobutane flame made it have higher sooting tendency than n-butane. • Novel optical method was developed to identify flame sooting transition stages. • Close association with allyl brought the highest sooting tendency of 1-butene. • Linear/branched butanes performed opposite order of sooting tendencies to butenes. • Benzene formation mechanism in different sooting transition stages was revealed. [ABSTRACT FROM AUTHOR]

Simultaneously reducing smoke and oxides of nitrogen to meet the stringent emission standards received considerable attention in diesel combustion chemistry. The Zeldovich kinetics depends on the temperature during the combustion, to reduce the NOx formation in the combustion duration. Modifications of the combustion system designs are used to control NOx emissions in the compression ignition engines. In the present investigation improvement in performance, combustion and emission characteristics of a direct injection diesel engine by achieving better fuel air mixing by turbulence inducement through internal jet arrangement. The experimental results of modified combustion chambers having the two, three and four internal jets are compared with that of the base engine performance. These results show that, decrease in peak pressure and smoke and a marginal increase in the oxides of nitrogen at part load conditions. [ABSTRACT FROM AUTHOR]

Oxy-fuel combustion of pulverized fuels (PF), as a promising technology for CO 2 capture from power plants, has gained a lot of concerns and also advanced considerable research, development and demonstration in the past years worldwide. The use of CO 2 or the mixture of CO 2 and H 2 O vapor as the diluent in oxy-fuel combustion, instead of N 2 in conventional air–fuel combustion, induces significant changes to the combustion fundamentals, because of the great differences in the physical properties and chemical effects of the different diluents. Therefore, some fundamental issues and technological challenges need to be properly addressed to develop oxy-fuel combustion into an enabled technology. Computational Fluid Dynamics (CFD) modeling, which has been proven to be a very useful and cost-effective tool in research and development of conventional air–fuel combustion, is expected to play a similarly vital role in future development of oxy-fuel combustion technology. The paper presents a state-of-the-art review and an in-depth discussion of PF oxy-fuel combustion fundamentals and their modeling, which underpin the development of this promising technology. The focus is placed on the key issues in combustion physics (e.g., turbulent gas–solid flow, heat and mass transfer) and combustion chemistry (e.g., pyrolysis, gas phase combustion and char reactions), mainly on how they are affected in oxy-fuel conditions and how they are modeled and implemented into CFD simulations. The system performance of PF oxy-fuel combustion is also reviewed. Finally, the current status of PF oxy-fuel combustion fundamentals and modeling is concluded and the research needs in these regards are suggested. [ABSTRACT FROM AUTHOR]

Considering the important effect of coal volatiles combustion on coal-fired organic pollutants formation, coal pyrolysis gas was selected as fuel in this work. Spatial profiles of light hydrocarbons and aromatic hydrocarbons in counterflow diffusion flames (CDFs) were detected by gas chromatography and gas chromatography-mass spectrometer, combined with chemical reaction kinetic analysis. As the main component of exhaust gas, CO 2 could significantly affect hydrocarbons formation in flames. By adding CO 2 to the oxidizer of CDF, the regulation of CO 2 addition on organic products during coal pyrolysis gas combustion was studied. The results showed that the dilution/thermal and chemical effects of CO 2 all decreased the mole fractions of H, thereby inhibiting the formation of acetylene (C 2 H 2), propargyl (C 3 H 3), propyne (PC 3 H 4), 1,3-butadiene, vinylacetylene, diacetylene, benzene (C 6 H 6), toluene and naphthalene in the flame. With CO 2 addition, the path from C 2 H 2 to PC 3 H 4 was inhibited, and less C 3 H 3 formed C 6 H 6 through self-recombination, while more favored to form C 6 H 6 through fulvene. Decrease in the concentration of above-mentioned soot precursors indicated that adding CO 2 could effectively inhibit the emission of organic pollutants during coal combustion process. • Effects of CO 2 addition on coal volatiles flame chemistry was revealed. •Light and aromatic hydrocarbons in coal pyrolysis gas flames were analyzed. •Kinetic analysis was performed to explore pollutants formation mechanisms. •Results can serve for future coal volatiles combustion mechanisms optimization. [ABSTRACT FROM AUTHOR]

The pyrotechnic flames of Ba(NO3)2, NH4ClO4, and shellac compositions have been analyzed spectrophotometrically. The oxidizer ratio and oxygen balance were varied in a series of compositions to investigate how this ratio influences the flame emission spectra and burning properties of pyrotechnic compositions. The burning rate, emission spectra, and chromaticity data and their analysis are presented. [ABSTRACT FROM AUTHOR]

The pyrotechnic flames of Ba(NO3)2, NH4ClO4, and shellac compositions have been analyzed spectrophotometrically. The oxidizer ratio and oxygen balance were varied in a series of compositions to investigate how this ratio influences the flame emission spectra and burning properties of pyrotechnic compositions. The burning rate, emission spectra, and chromaticity data and their analysis are presented. [ABSTRACT FROM AUTHOR]

The combustion chemistry of formaldehyde in fuel-rich flames has been studied by numerical modeling and sensitivity analysis. It has been shown that the wide flammability limits of CHO/air mixtures are due to features of the combustion chemistry of formaldehyde at high equivalence ratios rather than to the superadiabatic temperature effect. In this case, the thermal decomposition reaction of hydrogen peroxide HO plays a key role in the conventional branching reactions. [ABSTRACT FROM AUTHOR]

Products formed in the reaction of C 2 H radicals with 1,3-butadiene at 4 Torr and 298 K are probed using photoionization time-of-flight mass spectrometry. The reaction takes place in a slow-flow reactor, and products are ionized by tunable vacuum-ultraviolet light from the Advanced Light Source. The principal reaction channel involves addition of the radical to one of the unsaturated sites of 1,3-butadiene, followed by H-loss to give isomers of C 6 H 6 . The photoionization spectrum of the C 6 H 6 product indicates that fulvene is formed with a branching fraction of (57 ± 30)%. At least one more isomer is formed, which is likely to be one or more of 3,4-dimethylenecyclobut-1-ene, 3-methylene-1-penten-4-yne or 3-methyl-1,2-pentadien-4-yne. An experimental photoionization spectrum of 3,4-dimethylenecyclobut-1-ene and simulated photoionization spectra of 3-methylene-1-penten-4-yne and 3-methyl-1,2-pentadien-4-yne are used to fit the measured data and obtain maximum branching fractions of 74%, 24% and 31%, respectively, for these isomers. An upper limit of 45% is placed on the branching fraction for the sum of benzene and 1,3-hexadien-5-yne. The reactive potential energy surface is also investigated computationally. Minima and first-order saddle-points on several possible reaction pathways to fulvene + H and 3,4-dimethylenecyclobut-1-ene + H products are calculated. [ABSTRACT FROM AUTHOR]

Recent progress in molecular combustion chemistry allows for detailed investigation of the intermediate species pool even for complex chemical fuel compositions, as occur for technical fuels. This study provides detailed investigation of a comprehensive set of complex alternative gasoline fuels obtained from laminar flow reactors equipped with molecular-beam sampling techniques for observation of the combustion intermediate species pool in homogeneous gas phase reactions. The combination of ionization techniques including double-imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy enables deeper mechanistic insights into the underlying reaction network relevant to technical fuels. The selected fuels focus on contemporary automotive engine application as drop-in fuels compliant to European EN 228 specification for gasoline. Therefore, potential alternative gasoline blends containing oxygenated hydrocarbons as octane improvers obtainable from bio-technological production routes, e.g., ethanol, iso -butanol, methyl tert ‑butyl ether (MTBE), and ethyl tert ‑butyl ether (ETBE), as well as a Fischer-Tropsch surrogate were investigated. The fuel set is completed by two synthetic naphtha fractions obtained from Fischer-Tropsch and methanol-to-gasoline processes alongside with a fossil reference gasoline. In total, speciation data for 11 technical fuels from two atmospheric flow reactor setups are presented. Detailed main and intermediate species profiles are provided for slightly rich (ϕ = 1.2) and lean (ϕ = 0.8) conditions for intermediate to high temperatures. Complementary, the isomer distribution on different mass channels, like m/z = 78 u fulvene/benzene, of four gasolines was investigated. Experimental findings are analyzed in terms of the detailed fuel composition and literature findings for molecular combustion chemistry. Influences of oxygenated fuel components as well as composition of the hydrocarbon fractions are examined with a particular focus on the soot precursor chemistry. This dataset is available for validation of chemical kinetic mechanisms for realistic gasolines containing oxygenated hydrocarbons. [ABSTRACT FROM AUTHOR]

Alternative transportation fuels, preferably from renewable sources, include alcohols with up to five or even more carbon atoms. They are considered promising because they can be derived from biological matter via established and new processes. In addition, many of their physical-chemical properties are compatible with the requirements of modern engines, which make them attractive either as replacements for fossil fuels or as fuel additives. Indeed, alcohol fuels have been used since the early years of automobile production, particularly in Brazil, where ethanol has a long history of use as an automobile fuel. Recently, increasing attention has been paid to the use of non-petroleum-based fuels made from biological sources, including alcohols (predominantly ethanol), as important liquid biofuels. Today, the ethanol fuel that is offered in the market is mainly made from sugar cane or corn. Its production as a first-generation biofuel, especially in North America, has been associated with publicly discussed drawbacks, such as reduction in the food supply, need for fertilization, extensive water usage, and other ecological concerns. More environmentally friendly processes are being considered to produce alcohols from inedible plants or plant parts on wasteland. While biofuel production and its use (especially ethanol and biodiesel) in internal combustion engines have been the focus of several recent reviews, a dedicated overview and summary of research on alcohol combustion chemistry is still lacking. Besides ethanol, many linear and branched members of the alcohol family, from methanol to hexanols, have been studied, with a particular emphasis on butanols. These fuels and their combustion properties, including their ignition, flame propagation, and extinction characteristics, their pyrolysis and oxidation reactions, and their potential to produce pollutant emissions have been intensively investigated in dedicated experiments on the laboratory and the engine scale, also emphasizing advanced engine concepts. Research results addressing combustion reaction mechanisms have been reported based on results from pyrolysis and oxidation reactors, shock tubes, rapid compression machines, and research engines. This work is complemented by the development of detailed combustion models with the support of chemical kinetics and quantum chemistry. This paper seeks to provide an introduction to and overview of recent results on alcohol combustion by highlighting pertinent aspects of this rich and rapidly increasing body of information. As such, this paper provides an initial source of references and guidance regarding the present status of combustion experiments on alcohols and models of alcohol combustion. [ABSTRACT FROM AUTHOR]

Abstract: The state of the art and the further challenges of combustion chemistry research in laminar flames are reviewed. Laminar flames constitute an essential part of kinetic model development as the rates of elementary reactions are studied and/or validated in the presence of temperature and species concentration gradients. The various methods considered in this review are the flat, low-pressure, burner-stabilized premixed flame for chemical speciation studies, and the stagnation, spherically expanding, and burner-stabilized flames for determining the global flame properties. The data derived using these methods are considered at present as the most reliable ones for three decades of pressures ranging from about 50 mbar to over 50 bar. Furthermore, the attendant initial and/or boundary conditions and physics are in principle well characterized, allowing for the isolation of various physical parameters that could affect the flame structure and thus the reported data. The merits of each approach and the advances that have been made are outlined and the uncertainties of the reported data are discussed. At the same time, the potential sources of uncertainties associated with the experimental methods and the hypotheses for data extraction using each method are discussed. These uncertainties include unquantified physical effects, inherent instrument limitations, data processing, and data interpretation. Recommendations to reduce experimental uncertainties and increase data fidelity, essential for accurate kinetic model development, are given. [Copyright &y& Elsevier]

The reaction of methanol and ozone on the singlet potential energy surface has been carried out using the RMP2 theoretical approach in connection with the 6-311++G(d, p) basis set. To obtain a more reliable energy, single point calculations were performed for all species at the CCSD(T) level. One pre-reactive complex C1 is formed between the reactants. From a variety of the complexes, five types of product are obtained, of which four types have enough thermodynamic stability at the RMP2 level. In the thermodynamic approach, the most favoured route begins with the formation of a pre-reactive complex C1 and gives H2CO+H2O+3O2 as the final adducts. This process is exothermic by -73.243 kcal mol-1 in standard enthalpy and exergonic by -83.382 kcal mol-1. [ABSTRACT FROM AUTHOR]

Dicarbon (C2), the simplest bare carbon molecule, is ubiquitous in the interstellar medium and in combustion flames. A gas-phase synthesis is presented of the benzyl radical (C6H5CH2) by the crossed molecular beam reaction of dicarbon, C2(X1Σg+, a3Πu), with 2-methyl-1,3-butadiene (isoprene; C5H8; X1A′) accessing the triplet and singlet C7H8 potential energy surfaces (PESs) under single collision conditions. The experimental data combined with ab initio and statistical calculations reveal the underlying reaction mechanism and chemical dynamics. On the singlet and triplet surfaces, the reactions involve indirect scattering dynamics and are initiated by the barrierless addition of dicarbon to the carbon-carbon double bond of the 2-methyl-1,3-butadiene molecule. These initial addition complexes rearrange via multiple isomerization steps, leading eventually to the formation of C7H7 radical species through atomic hydrogen elimination. The benzyl radical (C6H5CH2), the thermodynamically most stable C7H7 isomer, is determined as the major product. [ABSTRACT FROM AUTHOR]

Abstract: Molecular dynamics simulations are applied to model fuel droplet surrounded by air in a spatially and temporally evolving environment. A numerical procedure is developed to include chemical reactions into molecular dynamics. The model reaction is chosen to allow investigation of the position of chemical reactions (gas phase, surface, liquid phase) and the behavior of typical products (alcohols and aldehydes). A liquid droplet at molecular scale is seen as a network of fuel molecules interacting with oxygen, nitrogen, and products of chemical fuel breakdown. A molecule is evaporating when it loosens from the network and diffuses into the air. Naturally, fuel molecules from the gas phase, oxygen and nitrogen molecules can also be adsorbed in the reverse process into the liquid phase. Thus, in the presented simulations the time and length scales of transport processes – oxygen adsorption, diffusion, and fuel evaporation are directly determined by molecular level processes and not by model constants. In addition, using ab initio calculations it is proven that the reaction barriers in liquid and gas phases are similar. [Copyright &y& Elsevier]

Abstract: Biofuels are considered as potentially attractive alternative fuels that can reduce greenhouse gas and pollutant emissions. iso-Pentanol is one of several next-generation biofuels that can be used as an alternative fuel in combustion engines. In the present study, new experimental data for iso-pentanol in shock tube, rapid compression machine, jet stirred reactor, and counterflow diffusion flame are presented. Shock tube ignition delay times were measured for iso-pentanol/air mixtures at three equivalence ratios, temperatures ranging from 819 to 1252K, and at nominal pressures near 40 and 60bar. Jet stirred reactor experiments are reported at 5atm and five equivalence ratios. Rapid compression machine ignition delay data was obtained near 40bar, for three equivalence ratios, and temperatures below 800K. Laminar flame speed data and non-premixed extinction strain rates were obtained using the counterflow configuration. A detailed chemical kinetic model for iso-pentanol oxidation was developed including high- and low-temperature chemistry for a better understanding of the combustion characteristics of higher alcohols. First, bond dissociation energies were calculated using ab initio methods, and the proposed rate constants were based on a previously presented model for butanol isomers and n-pentanol. The model was validated against new and existing experimental data at pressures of 1–60atm, temperatures of 650–1500K, equivalence ratios of 0.25–4.0, and covering both premixed and non-premixed environments. The method of direct relation graph (DRG) with expert knowledge (DRGX) was employed to eliminate unimportant species and reactions in the detailed mechanism, and the resulting skeletal mechanism was used to predict non-premixed flames. In addition, reaction path and temperature A-factor sensitivity analyses were conducted for identifying key reactions at various combustion conditions. [Copyright &y& Elsevier]

The complex triplet potential energy surface for the reaction of the triplet oxygen atom O(P) with cis-2-butene is investigated at the CBS-QB3 level of theory. The different possible isomerization and dissociation pathways, including both O-additions and H-abstractions, are thoroughly studied. Our calculations show that as found for the trans-2-butene reaction, in the high-pressure limit, the major product is CHCHC(O)H + CH (P1), whereas in the low-pressure limit the most thermodynamically stable product forms CHCO + CHCH (P4). The experimental negative activation energy reported for the addition step is very well reproduced at the CBS-QB3 level of theory. Various thermodynamic and kinetic values of interest for these reactions are predicted for the first time. A discussion on the negative activation energy for the addition step of the trans- and cis-2-butene reactions with O(P) focussing on the addition reactant complexes is presented. [ABSTRACT FROM AUTHOR]

Reaction dynamics: Crossed molecular beam experiments and ab initio electronic structure calculations on the reaction of the ethynyl radical with isoprene are reported. The picture shows a flux contour map of the reaction of [D1]ethynyl with isoprene forming [D1]toluene and atomic hydrogen at a collision energy of 51.3 kJ mol−1. [ABSTRACT FROM AUTHOR]

Abstract: Oxy-fuel combustion technique is a viable option to reduce several types of greenhouse gases (GHGs) emissions from the pulverized coal (PC) combustion systems. In this paper, a computational fluid dynamics (CFD) modelling study has been developed in order to investigate the Victorian brown coal combustion in a 550MW utility boiler under the air-fired (reference case) and three oxy-fuel-fired scenarios. The reference firing case was modelled based on the operating conditions of Loy Yang A power plant located in the state of Victoria, Australia. While Chalmers’ oxy-fuel combustion approach was selected for the present oxy-fuel combustion simulations, which referred to as OF25 (25vol.% O2), OF27 (27vol.% O2), and OF29 (29vol.% O2). User-defined functions (UDFs) were written and incorporated into the CFD code to calculate the following mathematical models: the PC devolatilization, char burnout, multi-step chemical reactions, mass and heat transfer, carbon in fly-ash, and NO x formation/destruction. A level of confidence of the CFD model was achieved validating four different parameters of the conventional combustion case, as well as the previous preliminary CFD studies that conducted on a 100kW unit firing propane and lignite under oxy-fuel combustion environments. The numerical results of OF29 combustion condition were considerably similar to the reference firing results in terms of gas temperature levels and radiative heat transfer relative to the OF25 and OF27 combustion cases. This similarity was due to increasing the residence time of PC in the combustion zone and O2-enriched in feed oxidizer gases. A significant increase in the CO2 concentrations and a noticeable decrease in the NO x formation were observed under all oxy-fuel combustion scenarios. The combustion chemistry was adopted in these investigations in order to capture the effects of O2 concentrations and gas temperatures on the CO/CO2 production rate and equilibrium between H2 and H2O in the combustion zone. Also, the use of O2-enriched atmospheres during oxy-fuel-fired cases was slightly enhanced the carbon burnout rate. These predicted results were reasonably consistent with the experimental investigations and numerical modelling found in the literature. This study of Victorian brown coal oxy-fuel combustion in a large-scale tangentially-fired boiler is important prior to its implementation in real-life. [Copyright &y& Elsevier]

The most likely reaction pathways and reaction products in the Al-CH4-O2-N2 system are investigated using density functional theory and ab initio calculations. The B3LYP functional with extended 6–311+G(3df,2p) basis set as well as the CBS-QB3 composite method are mainly utilised. Theoretical analysis of corresponding reaction rate constants is also performed with the use of simple theoretical models. A critical overview of current knowledge on combustion-relevant reactions with aluminium compounds is given. On the basis of critical comparison of available experimental kinetic data with theoretical calculations, the approximations for rate constants for 44 reversible elementary reactions involving Al-containing species are recommended for use in combustion issues. [ABSTRACT FROM PUBLISHER]

Abstract: The capabilities of the crossed molecular beam (CMB) method with mass spectrometric detection in the study of multi-channel elementary reactions of relevance in combustion chemistry are illustrated by several examples of reactions involving atomic oxygen and unsaturated hydrocarbons (acetylene, ethylene and allene), as well as hydrocarbon radicals (methyl and allyl). These systems have been investigated in our laboratory by resorting to soft electron impact ionization. Important information on the nature of the primary products and their branching ratio is reported and the implications for the modeling of combustion chemistry commented on. [Copyright &y& Elsevier]

Abstract: Near-threshold absolute photoionization and dissociative photoionization cross-sections for photon energies from 9.7 to 11.75eV are presented for 30 combustion intermediates including hydrocarbons, oxygenates and nitrogenous compounds (trans-2-butene, 2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene, trans-2-hexene, 1-hexene, allene, 1,3-butadiene, 1,3-pentadiene, 1,4-pentadiene, 3-methyl-1,2-butadiene, 1,5-hexadiene, isobutane, methylcyclohexane, furan, 2,3-dihydrofuran, 2,5-dihydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, n-butanal, isobutanal, 2-butenal, 3-methyl-2-butenal, ketene, allyl alcohol, methyl vinyl ketone, dimethoxymethane, methylamine, ethylamine, piperidine). Because allene is one of the most important intermediates in hydrocarbon combustion and pyrolysis processes, very accurate cross-sections for allene are desired to enable the measurement of its mole fractions in flames and to determine relative concentration ratios of allene to its isomer propyne. The cross-sections for allene have thus been re-measured with high precision using an apparatus of improved signal/noise ratio. Furthermore, these allene cross-sections yield accurate previously unmeasured cross-sections for ketene, another key combustion intermediate. [Copyright &y& Elsevier]

Abstract: In order to investigate the role of combustion chemistry and radiation heat transfer in oxy-fuel combustion modeling, a computational fluid dynamics (CFD) modeling study has been performed for two different oxy-fuel furnaces. One is a lab-scale 0.8MW oxy-natural gas flame furnace whose detailed in-flame measurement data are available; the other is a conventional 609MW utility boiler which is assumed to be operating under oxy-fuel combustion condition with dry flue gas recycle. A new model for gaseous radiative properties is developed, validated, and then implemented in the CFD simulations. The CFD results are compared to those based on the widely used model in literature, as well as the in-flame measurement data. The importance and advantage of the new model for gaseous radiative properties have been well demonstrated. Different combustion mechanisms are also implemented and compared in the CFD simulations, from which significant difference in the predicted flame temperature and species is observed. This difference is consistent with those expected from the equilibrium calculation results. As a conclusion, the appropriate combustion mechanisms applicable to oxy-fuel combustion modeling are identified. Among the key issues in combustion modeling, e.g., mixing, radiation and chemistry, this paper derives useful guidelines on radiation and chemistry implementation for reliable CFD analyses of oxy-fuel combustion, particularly for industrial applications. [Copyright &y& Elsevier]

Abstract: The formation of propellant dark zone (DZ) structures in the gaseous flames above many solid propellants has been a subject of recurrent interest to us for about 20years. The DZ structure is controlled by small molecule chemistry. The DZ chemistry is very important in controlling both the flame structure at low pressure (10–100atm) and burning rates at high pressure (above ∼500atm), even though DZs collapse at higher pressures. We developed a detailed, frequently updated mechanism to model it. This report reviews prior work, introduces our most recent modeling results, and documents the first quantitative tests of several key assumptions. All relevant experimental literature is critically assessed to identify datasets for testing our model. Comparison of predictions and experimental results shows reasonable agreement, and thus we advocate use of our mechanism. But the precision of both experiments and predictions is not tight, nor are there many test datasets. Further experimentation is needed, and types of study that would be of greatest benefit are suggested. A detailed discussion of the chemistry that controls DZ structure is presented. [Copyright &y& Elsevier]

Abstract: The first measurements of absolute cross-sections for near-threshold molecular and dissociative photoionization are presented for 11 small esters (methyl formate, ethyl formate, vinyl acetate, methyl propanoate, ethyl propanoate, methyl butanoate, methyl isobutanoate, methyl propenoate, ethyl propenoate, methyl crotonate, and methyl methacrylate). Photoionization mass spectrometry (PIMS) is employed with an energy resolution of 40meV (fwhm) using a monochromated VUV synchrotron light source. An extensive literature exploring isomerization/dissociation mechanisms is available for six of these molecules. There are, however, no previous observations of dissociative ionization for four simple monounsaturated esters (methyl propenoate, ethyl propenoate, methyl crotonate, and methyl methacrylate), and dissociative ionization of ethyl propanoate has received scant attention. Appearance energies for dissociative photofragment ions of these five molecules are presented. [Copyright &y& Elsevier]

Abstract: In parallel calculations of combustion processes with realistic chemistry, the serial in situ adaptive tabulation (ISAT) algorithm [S.B. Pope, Computationally efficient implementation of combustion chemistry using in situ adaptive tabulation, Combustion Theory and Modelling, 1 (1997) 41–63; L. Lu, S.B. Pope, An improved algorithm for in situ adaptive tabulation, Journal of Computational Physics 228 (2009) 361–386] substantially speeds up the chemistry calculations on each processor. To improve the parallel efficiency of large ensembles of such calculations in parallel computations, in this work, the ISAT algorithm is extended to the multi-processor environment, with the aim of minimizing the wall clock time required for the whole ensemble. Parallel ISAT strategies are developed by combining the existing serial ISAT algorithm with different distribution strategies, namely purely local processing (PLP), uniformly random distribution (URAN), and preferential distribution (PREF). The distribution strategies enable the queued load redistribution of chemistry calculations among processors using message passing. They are implemented in the software , which is a Fortran 95 library for facilitating many parallel evaluations of a general vector function. The relative performance of the parallel ISAT strategies is investigated in different computational regimes via the PDF calculations of multiple partially stirred reactors burning methane/air mixtures. The results show that the performance of ISAT with a fixed distribution strategy strongly depends on certain computational regimes, based on how much memory is available and how much overlap exists between tabulated information on different processors. No one fixed strategy consistently achieves good performance in all the regimes. Therefore, an adaptive distribution strategy, which blends PLP, URAN and PREF, is devised and implemented. It yields consistently good performance in all regimes. In the adaptive parallel ISAT strategy, the type and extent of redistribution is determined “on the fly” based on the prediction of future simulation time. Compared to the PLP/ISAT strategy where chemistry calculations are essentially serial, a speed-up factor of up to 30 is achieved. The study also demonstrates that the adaptive strategy has acceptable parallel scalability. [Copyright &y& Elsevier]

Abstract: Flame-sampling molecular-beam mass spectrometry of premixed, laminar, low-pressure flat flames has been demonstrated to be an efficient tool to study combustion chemistry. In this technique, flame gases are sampled through a small opening in a quartz probe, and after formation of a molecular beam, all flame species are separated using mass spectrometry. The present review focuses on critical aspects of the experimental approach including probe sampling effects, different ionization processes, and mass separation procedures. The capability for isomer-resolved flame species measurements, achievable by employing tunable vacuum-ultraviolet radiation for single-photon ionization, has greatly benefited flame-sampling molecular-beam mass spectrometry. This review also offers an overview of recent combustion chemistry studies of flames fueled by hydrocarbons and oxygenates. The identity of a variety of intermediates in hydrocarbon flames, including resonantly stabilized radicals and closed-shell intermediates, is described, thus establishing a more detailed understanding of the fundamentals of molecular-weight growth processes. Finally, molecular-beam mass-spectrometric studies of reaction paths in flames of alcohols, ethers, and esters, which have been performed to support the development and validation of kinetic models for bio-derived alternative fuels, are reviewed. [Copyright &y& Elsevier]

The HSOH, H2SO and H2OS isomers have been investigated employing the CCSD(T) methodology and the cc-pV(X + d)Z X = 3,4,5,6 basis sets. The anharmonic force fields have been calculated to predict the fundamental vibrational frequencies, rotational constants, vibration-rotation corrections, anharmonic corrections to zero-point energies, and structural parameters. In addition to this, a spectroscopic characterization of the deuterated isomers D2SO and D2OS was performed. At the CCSD(T)/CBS limit and including corrections for scalar relativistic, spin orbit and core-valence correlation effects, the estimated enthalpies of formation are -28.1 ± 1, -12.3 ± 1, and 10.1 ± 1 kcal/mol for HSOH, H2SO and H2OS, respectively. Finally, we discuss the problems faced during the extrapolation to the CBS limit of the properties investigated. [ABSTRACT FROM AUTHOR]

Abstract: Density functional theory quantum chemical calculations corrected with empirical atomic increments have been used to examine Ce:glyph name="sbnd" />O, and (CO)ission enthalpies in gas-phase fatty acid methyl esters (FAMEs) present in biodiesel derived from rapeseed oil methyl ester and soybean oil methyl ester. Mechanistic information, currently not available elsewhere for these large species, is obtained based on thermochemical considerations and compared to thermochemical considerations reported for methyl butanoate, a small methyl ester sometimes used as a model for FAMEs. These results are compared to previously reported Ce:glyph name="sbnd" />H bond scissions in these FAMEs, derived using this same protocol. [Copyright &y& Elsevier]

The thermochemistry of 35 diatomic, triatomic and tetratomic, sulphur-containing molecules was investigated. For each molecule, we have estimated its enthalpy of formation at the CCSD(T)/CBS level, including corrections for, scalar relativistic, core-valence and spin-orbit effects. When experimental data was available we also included a correction for anharmonicities in Zero point energies. The molecules investigated are involved in several areas, atmospherical chemistry, astrochemsitry, nanotechnology, and biology. The present results demonstrate that from the previous landmark review of Benson, published in 1978, we had advanced only a little and much work must be done to have sulfur thermochemistry well established. It was very difficult to obtain a meaningful mean absolute deviation (MAD) because of the reduced number of accurate enthalpies of formation available. For a selected set of eight molecules the MAD=0.4 kcal/mol. For the 27 remaining molecules we discussed the available experimental and theoretical data and suggested new values. The consistency of our propositions has been double checked employing homodesmic and isodesmic reactions. In all cases, except one that involved S2, the results were perfectly consistent. We expect that the present work motivates new theoretical and experimental investigations of these fascinating species that contain sulfur. [ABSTRACT FROM AUTHOR]

Abstract: The use of photoionization mass spectrometry for the development of quantitative kinetic models for the complex combustion chemistry of both conventional hydrocarbon fuels and oxygenated biofuels requires near-threshold measurements of absolute photoionization cross-sections for numerous reaction intermediates. Near-threshold absolute cross-sections for molecular and dissociative photoionization for 20 stable reaction intermediates (methane, ethane, propane, n-butane, cyclopropane, methylcyclopentane, 1-butene, cis-2-butene, isobutene, 1-pentene, cyclohexene, 3,3-dimethyl-1-butene, 1,3-hexadiene, 1,3-cyclohexadiene, methyl acetate, ethyl acetate, tetrahydrofuran, propanal, 1-butyne, 2-butyne) are presented. Previously measured total photoionization cross-sections for 9 of these molecules are in good agreement with the present results. The measurements are performed with photoionization mass spectrometry (PIMS) using a monochromated VUV synchrotron light source with an energy resolution of 40meV (fwhm) comparable to that used for flame-sampling molecular beam PIMS studies of flame chemistry and reaction kinetics. [Copyright &y& Elsevier]

A reduced in situ adaptive tabulation (RISAT) method, which was originally proposed by Pope (Combustion Theory and Modelling, 1997, 1, 41-36), is developed for the applications of multidimensional transient reactive flow computations. The RISAT method, which based on the storage/retrieval operation processes of data, employs the constant approximation of chemical reactions and the dynamic deletion of a data table to limit the table size during the computations. It is incorporated in the computations of two-dimensional detonation of CH4/O2 premixed gas induced by shock waves focusing to enhance the computational performance of combustion chemistry. The effects of query tolerance and table size on the computational efficiency are examined. A maximum chemical speedup factor of 17.88 can be obtained by using the RISAT, without losing the computational accuracy. It is concluded from the computational results that the RISAT method is strongly dependent on the table size, tolerance and physics of transient reactive flow problems. [ABSTRACT FROM AUTHOR]

Abstract: The chemical dynamics of the formation of the i-C4H3(X2A′) radical together with its partially deuterated isotopomers were investigated in eight crossed molecular beams experiments of dicarbon molecules in their electronic ground and in first excited a3Πu state with (partially deuterated) ethylene at collision energies between 12.1 and 40.9kJmol−1. The center-of-mass angular distributions suggest that the reaction dynamics on the singlet and triplet surfaces are indirect and involve butatriene reaction intermediates. In case of the C2/C2H4 reaction, the ‘symmetric’ singlet butatriene intermediate would lead solely to a symmetric center-of-mass angular distribution; however, in combination with isotopically labeled reactants, we deduced that triplet butatriene intermediates excited to B/C like rotations likely account for the observed asymmetries in the center-of-mass angular distributions at higher collision energies. The translational energy distributions are also indicative of the involvement of both the triplet and singlet surfaces which lead both to the i-C4H3(X2A′) radicals through lose (singlet) and tight (triplet) exit transitions states. Also, our experiments helped to determine the enthalpy of formation of the i-C4H3(X2A′) radical to be about 504±10kJmol−1 in good agreement with previous computational studies suggesting 498–499kJmol−1. The explicit identification of the resonance-stabilized i-C4H3(X2A′) radical proposes that the reaction of dicarbon with ethylene can lead to formation of i-C4H3(X2A′) in combustion flames; the n-C4H3(X2A′) isomer is not formed in this reaction. This conclusion correlates nicely with Hansen’s et al. flame experiments at the advanced light source observing only the i-C4H3(X2A′) radical in hydrocarbon flames. [Copyright &y& Elsevier]

Risk assessment studies for hazardous material packages require fire response prediction tools that are both accurate and rapid. This article describes the theoretically based, semiempirical reaction chemistry and radiation heat transfer models for large, optically dense pool fires incorporated in the ISIS-3D CFD software. The chemistry model employs four separate reactions (two produce radiating soot). The heat transfer model divides the computational domain into the diffusely radiative fire and its nonparticipating environment. ISIS-3D simulations are performed on a 6-m square JP8 pool fire experiment in which the soot temperature and volume fraction are measured. The reaction rate and soot formation parameters of the chemistry model are determined based on a comparison of the simulation with the measured data. Simulations are then performed on an experiment that measures the temperature of a pipe calorimeter suspended over the leeside of a 19-m-diameter JP8 fuel pool fire with a 9.5m/s crosswind. The soot volume fraction that the heat transfer model uses to define the edge of the diffusely radiating fire is determined based on a comparison with the measured average temperature of the calorimeter. That simulation accurately predicts the calorimeter spatial temperature variation without further adjustment. ISIS-3D is not fully predictive, should not be used far outside the range of conditions in which its parameters are determined (JP8 pool fires larger than 2m), and is not intended to replace the fundamental fire physics software. However, it demonstrates highly accurate results with rapid turnaround times for a range of conditions that are relevant to large hazardous material transport packages in severe fire conditions. [ABSTRACT FROM AUTHOR]

Abstract: The reactions of HCO and DCO with NO have been measured by the laser photolysis/continuous-wave (CW) laser-induced fluorescence (LIF) method from 296 to 623K, probing the () HCO (DCO) system. The HCO+NO rate coefficient is (1.81±0.10)×10−11 cm3 molecule−1 s−1 and the DCO+NO rate coefficient is (1.61±0.12)×10−11 cm3 molecule−1 s−1 at 296K. Both rate coefficients decrease with increasing temperature between 296 and 623K. The kinetic isotope effect is k H/k D =1.12±0.09 at 296K and increases to 1.25±0.15 at 623K. The normal kinetic isotope effect supports abstraction as the principal mechanism for the reaction, in agreement with recent computational results. [Copyright &y& Elsevier]

Abstract: Previously unmeasured absolute photoionization cross sections are presented for eight common reaction intermediates found in the combustion of many simple hydrocarbons. Total photoionization cross sections recorded for 11 additional hydrocarbons are in good agreement with previous studies. The measurements are performed with photoionization mass spectrometry (PIMS), using VUV synchrotron radiation. Absolute cross sections for molecular and dissociative photoionization are determined by comparison of the photoionization efficiencies for each intermediate with that of propene, used as a calibration standard, for photon energies from 9.7 to 11.75eV, recorded with a photon energy resolution of 50meV(fwhm). [Copyright &y& Elsevier]

Combustion mechanisms of higher hydrocarbons are governed by a hierarchical structure. This structure is reflected in reduced mechanisms based on intrinsic low dimensional manifolds (ILDM). Based on the mathematical analysis we present in this work a hierarchical concept where the ILDMs of higher hydrocarbons are generated on the basis of existing ILDMs of simpler reaction mechanisms. It is based on a numerical method which allows to estimate, how well an ILDM can be represented by an ILDM of a simpler subsystem. If the conditions for a good representation of the ILDM by the simpler subsystem are met, then the ILDM of the simpler system can be used directly. If not, then the ILDM of the simpler subsystem is used as a starting estimate for the generation of the ILDM which reduces the computational effort considerably. The example of a syngas ILDM which is used as a generic ILDM for n-heptane combustion validates the approach. [Copyright &y& Elsevier]

Experimental reaction rate data for the Al/HCl system are very scarce. Such data are needed for the comprehension and for the numerical simulation of the combustion of aluminum particles as encountered in solid segmented motors. Toward this end, we have examined the homogeneous chemistry of this system, computed rate parameters for important reactions using conventional Transition State Theory (TST) and RRKM/master equation simulations, and estimated rate parameters for reactions where rigorous computations are not presently feasible. The reaction mechanism presented in this study consists of 15 species participating in 39 reversible elementary reactions for which rate parameters have been estimated or computed. [Copyright &y& Elsevier]

• Master equation-based chemical lumping (MEL) of potential energy surfaces (PESs). • MEL allows greater than 90% reduction of species and reactions for a complex C10H10/C10H9 PES. • An open-source software implementing MEL is provided for interested users. • MEL connects theoretical chemistry and the development of complex kinetic models. Ab initio transition state theory-based master equation methodologies for the calculation of rate constants have gained enormous popularity in the past decades. Nevertheless, introducing these rate constants into large kinetic schemes is a non-trivial task when large potential energy surfaces (PESs) are investigated. To determine proper phenomenological rate constants it is in fact necessary to account for the formation of all the thermodynamically stable wells considered in the master equation (ME), even if most wells do not exhibit significant secondary reactivity. Moreover, reactions involving intermediates with lifetimes comparable to the rovibrational relaxation timescale can exhibit discontinuities both in the rate constants and in the number of thermodynamically stable wells across the investigated temperature and pressure ranges. In this work, we address these problems with a "master equation-based lumping" (MEL) approach specifically designed to process the output of ME calculations of multi-well PESs. Simple kinetic simulations allow identifying both intermediate wells with limited lifetime and isomers with similar reactivity. Then, equivalent rate constants for a smaller set of pseudospecies are derived so as to reproduce the kinetics of the detailed mechanism. Our methodology is independent of any experimental data or experience-based assumptions. The power of MEL is demonstrated with three case studies of increasing complexity, namely the PES for CH 3 COOH decomposition, and the portions of the C 5 H 5 OH and C 10 H 10 /C 10 H 9 PESs accessed from C 5 H 5 + OH and C 5 H 5 + C 5 H 5 recombination. This work constitutes the first systematic step addressing the robust integration of rate constants derived from ME simulations into global kinetic schemes and provides a useful approach for the entire chemical kinetics community filling the gap between detailed theoretical investigations of complex PESs and the development of detailed kinetic models. [ABSTRACT FROM AUTHOR]