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Showing papers on "Diffusion flame published in 2010"


Journal ArticleDOI
TL;DR: In this article, the laminar flame speeds and extinction strain rates of premixed methanol, ethanol, and n-butanol flames were determined experimentally in the counterflow configuration at atmospheric pressure and elevated unburned mixture temperatures.

351 citations


Journal ArticleDOI
TL;DR: In this article, the thermal and kinetic effects of O(sub 3) on flame propagation were investigated experimentally and numerically by using C{sub 3}H{sub 8}/O(sub 2}/N{sub 2}) laminar lifted flames.

332 citations


Journal ArticleDOI
TL;DR: In this article, a hierarchical approach is employed to describe combustion of isomers of butanol, and the complete set of the primary propagation reactions for butanol isomers proceeds from the extension of the kinetic parameters.

247 citations


Journal ArticleDOI
TL;DR: In this article, a projection of the full set of mass conservation species balance equations into a restricted subset of the composition space was derived from first principles, under given hypotheses, for partially premixed combustion, where the tangential strain rate of scalar isosurfaces is expressed in the form of the scalar dissipation rates of the control parameters.

224 citations


Journal ArticleDOI
TL;DR: In this paper, the dynamics and properties of a turbulent flame, formed in the presence of subsonic, high-speed, homogeneous, isotropic Kolmogorov-type turbulence in an unconfined system, were studied.

212 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used time resolved chemiluminescence imaging along with simultaneous particle image velocimetry and OH planar laser-induced fluorescence to determine the sequence of events leading to blowoff and provide a quantitative analysis of the experimental results.

211 citations


Journal ArticleDOI
TL;DR: In this paper, the stabilisation region of turbulent non-premixed flames of natural gas mixtures burning in a hot and diluted coflow was studied by recording the flame luminescence with an intensified high-speed camera.

191 citations


Journal ArticleDOI
TL;DR: In this article, colorless distributed combustion (CDC) is characterized by distributed reaction zone of combustion which leads to uniform thermal field and avoidance of hot spot regions to provide significant improvement in pattern factor, lower sound levels and reduced NOx emission.

190 citations


Journal ArticleDOI
TL;DR: In this paper, the laminar flame characteristics from a quiescent homogeneous air−fuel mixture were examined using high speed schlieren visualization, and the flame speed was determined by measurement of the flame growth following ignition.
Abstract: The 2,5-dimethylfuran (DMF) has attracted renewed global interest since its improved production methods were published in Nature and Science in 2007. Its high energy density makes it a promising biofuel and a possible alternative to gasoline. Consequently, a series of studies, led by the University of Birmingham, aims to assess the potential of DMF as an automotive energy carrier. These studies will include an analysis of the spray properties, the laminar flame characteristics, the engine performance, and the subsequent emissions. This paper examines the laminar flame characteristics from a quiescent homogeneous air−fuel mixture. The experiments were conducted using a constant volume vessel and were recorded by high speed schlieren visualization. By measurement of the flame growth following ignition, the laminar flame speed was determined. The calculation of flame stretch yielded the Markstein lengths and the laminar burning velocities. This paper presents the results of DMF combustion for a range of equi...

178 citations


Journal ArticleDOI
TL;DR: In this paper, the potential of burning and reforming ammonia as a carbon-free fuel in production of hydrogen, fundamental unstretched laminar burning velocities, and flame response to stretch were studied both experimentally and computationally.

166 citations


Journal ArticleDOI
Zhongshan Li1, Bo Li1, Zhiwei Sun1, Xue-Song Bai1, Marcus Aldén1 
TL;DR: In this article, high-resolution planar laser-induced fluorescence (PLIF) was applied to investigate the local flame front structures of turbulent premixed methane/air jet flames in order to reveal details about turbulence and flame interaction.

Journal ArticleDOI
TL;DR: In this article, the authors describe a mechanism for the stabilization of ultra lean premixed methane/air flames by pulsed nonequilibrium plasma enhancement and demonstrate that the pulsed discharge plasma produces a cool stream of relatively stable intermediate species including hydrogen (H{sub 2}) and carbon monoxide (CO), which play a central role in enhancing flame stability.

Journal ArticleDOI
TL;DR: In this article, a detailed chemical kinetic model has been constructed, validated against, and used to interpret these experimental data, showing that methyl formate oxidation proceeds through concerted elimination reactions, principally forming methanol and carbon monoxide.
Abstract: The oxidation of methyl formate (CH3OCHO) has been studied in three experimental environments over a range of applied combustion relevant conditions: 1.A variable-pressure flow reactor has been used to quantify reactant, major intermediate and product species as a function of residence time at 3 atm and 0.5% fuel concentration for oxygen/fuel stoichiometries of 0.5, 1.0, and 1.5 at 900 K, and for pyrolysis at 975 K. 2.Shock tube ignition delays have been determined for CH3OCHO/O2/Ar mixtures at pressures of ≈ 2.7, 5.4, and 9.2 atm and temperatures of 1275–1935 K for mixture compositions of 0.5% fuel (at equivalence ratios of 1.0, 2.0, and 0.5) and 2.5% fuel (at an equivalence ratio of 1.0). 3.Laminar burning velocities of outwardly propagating spherical CH3OCHO/air flames have been determined for stoichiometries ranging from 0.8–1.6, at atmospheric pressure using a pressure-release-type high-pressure chamber. A detailed chemical kinetic model has been constructed, validated against, and used to interpret these experimental data. The kinetic model shows that methyl formate oxidation proceeds through concerted elimination reactions, principally forming methanol and carbon monoxide as well as through bimolecular hydrogen abstraction reactions. The relative importance of elimination versus abstraction was found to depend on the particular environment. In general, methyl formate is consumed exclusively through molecular decomposition in shock tube environments, while at flow reactor and freely propagating premixed flame conditions, there is significant competition between hydrogen abstraction and concerted elimination channels. It is suspected that in diffusion flame configurations the elimination channels contribute more significantly than in premixed environments. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 527–549, 2010

Journal ArticleDOI
TL;DR: In this paper, the effects of premixed ratio of diethyl ether (DEE) on combustion and exhaust emissions of a single-cylinder, HCCI-DI engine were investigated.

Journal ArticleDOI
TL;DR: In this article, the effect of hydrogen content of fuel on flame structure for two co-flow oxygen levels is studied by considering three fuel mixtures, 5%H 2 +95% CH 4, 10% H 2 +90%CH 4 and 20% H2 +80% CH4 (by mass), by using the EDC model, to describe turbulence-chemistry interaction, and the DRM-22 reduced mechanism and the GRI2.11 full mechanism.

Journal ArticleDOI
TL;DR: In this article, a simplified modeling approach is proposed to describe combustion in the presence of electric body forces, and the sensitivity of the flame lift-off height to the applied voltage is studied and the modification of the velocity field induced by the electric volume forces is highlighted.

Journal ArticleDOI
TL;DR: In this paper, chemical and morphological characterization of the products generated in ethylene and benzene inverse diffusion flames (IDF) using different analytical techniques is presented, which indicates that the soot precursor material and soot particles generated in the benzene IDF have a higher degree of complexity than the samples obtained in the ethylene IDF, which is reflected by an increase in the aromaticity of the chloroform extracts observed by {sup 1}H NMR and FT-IR.

Journal ArticleDOI
TL;DR: In this article, detailed scalar structure measurements of highly sheared turbulent premixed flames stabilized on the piloted premixed jet burner (PPJB) are reported together with corresponding numerical calculations using a particle based probability density function (PDF) method.
Abstract: Detailed scalar structure measurements of highly sheared turbulent premixed flames stabilized on the piloted premixed jet burner (PPJB) are reported together with corresponding numerical calculations using a particle based probability density function (PDF) method. The PPJB is capable of stabilizing highly turbulent premixed jet flames through the use of a small stoichiometric pilot that ensures initial ignition of the jet and a large shielding coflow of hot combustion products. Four lean premixed methane-air flames with a constant jet equivalence ratio are studied over a wide range of jet velocities. The scalar structure of the flames are examined through high resolution imaging of temperature and OH mole fraction, whilst the reaction rate structure is examined using simultaneous imaging of temperature and mole fractions of OH and CH2O. Measurements of temperature and mole fractions of CO and OH using the Raman–Rayleigh–LIF-crossed plane OH technique are used to examine the flame thickening and flame reaction rates. It is found that as the shear rates increase, finite-rate chemistry effects manifest through a gradual decrease in reactedness, rather than the abrupt localized extinction observed in non-premixed flames when approaching blow-off. This gradual decrease in reactedness is accompanied by a broadening in the reaction zone which is consistent with the view that turbulence structures become embedded within the instantaneous flame front. Numerical predictions using a particle-based PDF model are shown to be able to predict the measured flames with significant finite-rate chemistry effects, albeit with the use of a modified mixing frequency.

Journal ArticleDOI
TL;DR: In this paper, the authors extended these analyses to include stretch and non-quasi-steady effects on the linear flame dynamics, as well as analysis of nonlinearities in flame response characteristics.
Abstract: This paper studies the heat-release oscillation response of premixed flames to oscillations in reactant stream fuel/air ratio. Prior analyses have studied this problem in the linear regime and have shown that heat release dynamics are controlled by the superposition of three processes: flame speed, heat of reaction, and flame surface area oscillations. Each contribution has somewhat different dynamics, leading to complex frequency and mean fuel/air ratio dependencies. The present work extends these analyses to include stretch and non quasi-steady effects on the linear flame dynamics, as well as analysis of nonlinearities in flame response characteristics. Because the flame response is controlled by a superposition of multiple processes, each with a highly nonlinear dependence upon fuel/air ratio, the results are quite rich and the key nonlinearity mechanism varies with mean fuel/air ratio, frequency, and amplitude of excitation. In the quasi-steady framework, two key mechanisms leading to heat-release sat...

Journal ArticleDOI
TL;DR: In this article, the stabilization characteristics of nonpremixed laminar jet flames in a coflow have been investigated experimentally for propane fuel by applying AC and DC electric fields to the fuel nozzle with a single-electrode configuration.

Journal ArticleDOI
TL;DR: In this paper, the impact of toluene addition in n-decane on OH concentrations, maximum heat release rates, and extinction limits were studied experimentally and computationally by using counterflow diffusion flames with laser induced fluorescence imaging.

Journal ArticleDOI
TL;DR: In this paper, a parametric study of forced ignition at the mixing layer between air and air carrying fine monosized fuel droplets is done through one-step chemistry direct numerical simulations to determine the influence of the size and volatility of the droplets, the spark location, the droplet-air mixing layer initial thickness and the turbulence intensity on the ignition success and subsequent flame propagation.

Journal ArticleDOI
TL;DR: Simultaneous 10-kHz OH-PLIF and 20-kHz two-component PIV were made in conjunction with wide-field 20kHz flame luminescence imaging of an unconfined, swirling, lean premixed, bluff-body stabilized flame during flashback.
Abstract: Simultaneous 10-kHz OH-PLIF and 20-kHz two-component PIV were made in conjunction with wide-field 20-kHz flame luminescence imaging of an unconfined, swirling, lean premixed, bluff-body stabilized flame during flashback. Flashback was induced by increasing the stoichiometry or swirl number or reducing the Reynolds number. A detailed stability regime was prepared and compared to predictions. Analysis of the time-correlated flame history inside the exit nozzle during flashback and non-flashback flame events led to a new hypothesis for the flashback mechanism.

Journal ArticleDOI
TL;DR: In this paper, the authors used a 1-m free-fall spherical combustion chamber to eliminate the effect of buoyancy, enabling accurate measurements of near-limit burning velocities and flammability limits.

Journal ArticleDOI
TL;DR: In this paper, the fractal characteristics of carbon nanoparticle aggregates produced by an ethylene diffusion flame and sampled by means of four commonly used techniques were compared using a TEM grid.
Abstract: The aim of this work was to compare the fractal characteristics, Df and kf, the primary particle diameter, Dpp, the gyration diameter of aggregates, Dg, and the overlap coefficient, Cov, of carbon nanoparticle aggregates produced by an ethylene diffusion flame and sampled by means of four commonly used techniques. The first method involves a thermophoretic piston probe (TPP) which inserts a TEM grid into the flame. Three other methods were applied at the outlet of a dilution device, also inserted in the flame. The first of these used a nuclepore filtration sampler (NFS), and is based on filtration of particles onto a polycarbonate membrane. The second, post dilution method, the insertion particle sampler (IPS), inserts a TEM grid, perpendicular to the aerosol flow. Similar to TPP, the last method is a thermophoretic particle sampler (TPS) sampling directly onto a TEM grid. After collection, the samples are stored in the dark either, (1) in a nitrogen filled cell at low humidity or, (2) in ambient air for ...

Journal ArticleDOI
TL;DR: In this paper, a new soot formation model for gas turbine combustor simulations is presented, where a sectional approach for the description of polycyclic aromatic hydrocarbons (PAHs) and a two-equation model for soot particle dynamics are introduced.

Journal ArticleDOI
TL;DR: In this paper, the effect of hydrogen addition on flame stability, flame length, flame structure, exhaust species concentration and pollutant emissions was investigated in a free jet turbulent diffusion flame flowing into a slow co-flowing air stream.

Journal ArticleDOI
TL;DR: In this paper, the authors examined the dynamics of premixed propane-air flame in a meso-scale ceramic combustor by measuring the acoustic emissions and preheat temperatures together with high-speed cinematography.

Journal ArticleDOI
TL;DR: In this paper, the separate and combined effects of Soret diffusion of the hydrogen molecule (H 2 ) and radical (H) on the structure and propagation speed of the freely-propagating planar premixed flames, and the strain-induced extinction response of premixed and non-premixed counterflow flames, were computationally studied for hydrogen-air mixtures using a detailed reaction mechanism and transport properties.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the combustion dynamics of methane-air flames in both premixed and non-premixed configurations using a transient arc dc plasmatron and obtained planar laser-induced fluorescence images of hydroxyl (OH) and carbon monoxide (CO) radicals.
Abstract: Combustion dynamics are investigated for plasma-enhanced methane-air flames in premixed and nonpremixed configurations using a transient arc dc plasmatron. Planar laser-induced fluorescence images of hydroxyl (OH) and carbon monoxide (CO) radicals are obtained over a range of equivalence ratios (φ = 0.7 - 1.3), flow rates (6-18 LPM), and plasma powers (100-900 mA) to monitor radical propagation and in situ fuel reforming. The flow rates presented here are outside the range of normal flame stability. In the nonpremixed mode, the fuel is injected separately as a coflow around the plasma discharge, resulting in a unique two-cone flame front geometry, and the flame stability is mainly dependent on the flow dynamics. For premixed flames, partial oxidation occurs inside the chamber, resulting in higher energy conversion efficiencies, and stability is shown to be sensitive to the combustion chemistry. Both configurations are significantly influenced by in situ fuel reforming at higher plasma powers.