Showing papers on "Laminar flame speed published in 2010"
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
TL;DR: In this paper, the extinction strain rates of premixed C5-C12 n-alkane flames were determined at atmospheric pressure and elevated unburned mixture temperatures, over a wide range of equivalence ratios.
305 citations
TL;DR: In this article, a reduced two-step scheme for kerosene-air premixed flames is presented in the context of Large Eddy Simulation of reacting turbulent flows in industrial applications.
239 citations
TL;DR: In this paper, the error in the laminar burning speed evaluation induced by using the traditional linear methodology is evaluated, taking the non-linear methodology as the reference, and it is observed that the use of the linear methodology starts to induce substantial errors after an equivalence ratio of 1.1 for methane/air mixtures and before an equivalency ratio of 0.5 for iso-octane/air mixture.
226 citations
TL;DR: In this paper, the effect of molecular structure on laminar burning velocities of the isomers of butanol is analyzed from the aspect of C H bond dissociation energy.
216 citations
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
TL;DR: In this article, a new modeling strategy called F-TACLES (Filtered Tabulated Chemistry for Large Eddy Simulation) is developed to introduce tabulated chemistry methods in large eddy simulation (LES) of turbulent premixed combustion.
212 citations
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
TL;DR: In this article, a single-step reaction mechanism was used to simulate flame acceleration and deflagration-to-detonation transitions in large obstructed channels filled with a stoichiometric methane-air mixture.
210 citations
TL;DR: In this paper, a 10kW partially pre-mixed, swirl-stabilized methane-air flame exhibiting self-excited thermo-acoustic oscillations is analyzed.
203 citations
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...
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.
TL;DR: In this paper, a computational study is performed for propagating spherical flames of lean methane/air mixtures in different spherical chambers using different radiation models and the emphasis is focused on the effects of radiation and compression.
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.
TL;DR: In this paper, the authors used an improved version of the kinetics model that the authors have been developing over the past few years, including experiments performed at elevated pressures, up to 10-atm initial pressure, and investigated the fuels in a pure form as well as in binary blends.
Abstract: Alkanes such as methane, ethane, and propane make up a large portion of most natural gas fuels. Natural gas is the primary fuel used in industrial gas turbines for power generation. Because of this, a fundamental understanding of the physical characteristics such as the laminar flame speed is necessary. Most importantly, this information is needed at elevated pressures to have the most relevance to the gas turbine industry for engine design. This study includes experiments performed at elevated pressures, up to 10-atm initial pressure, and investigates the fuels in a pure form as well as in binary blends. Flame speed modeling was done using an improved version of the kinetics model that the authors have been developing over the past few years. Modeling was performed for a wide range of conditions, including elevated pressures. Experimental conditions include pure methane, pure ethane, 80/20 mixtures of methane/ethane, and 60/40 mixtures of methane/ethane at initial pressures of 1, 5, and 10 atm. Also included in this study are pure propane and 80/20 methane/propane mixtures at 1 and 5 atm. The laminar flame speed and Markstein Length measurements were obtained from a high-pressure flame speed facility using a constant-volume vessel. The facility includes optical access, a high-speed camera, a schlieren optical setup, a mixing manifold, and an isolated control room. The experiments were performed at room temperature, and the resulting images were analyzed using linear regression. The experimental and modeling results are presented and compared to previously published data. The data herein agree well with the published data. In addition, a hybrid correlation was created to perform a rigorous uncertainty analysis. This correlation gives the total uncertainty of the experiment with respect to the true value rather than reporting the standard deviation of a repeated experiment. Included in the data set are high-pressure results at conditions where in many cases for the single-component fuels few data existed and for the binary blends no data existed prior to this study. Overall, the agreement between the model and data is excellent.Copyright © 2010 by Rolls-Royce Canada Ltd.
TL;DR: In this paper, the authors describe a methodology to improve the accuracy of prediction of the eigenfrequencies and growth rates of self-induced instabilities and demonstrate its application to a laboratory-scale, swirl-stabilized, lean-premixed, gas turbine combustor.
01 Feb 2010
TL;DR: In this article, microwave energy is deposited directly into the reaction zone through coupling to the weakly ionized gas in that region, resulting in an increase in flame speed of up to 20%.
Abstract: : Microwave induced flame speed enhancement is quantified in a laminar, premixed CH4/air wall stagnation flat flame. Experiments were performed in a high Q microwave cavity with the cavity tuned so that the maximum microwave field is located in the vicinity of a flat flame front. Equivalence ratios were varied between 0.6 and 0.8. When the flame is radiated by a continuous wave microwave field of approximately 5 kV/cm, the flame front is observed to move towards the burner exit and stabilize at a standoff distance corresponding to a flame speed increase of up to 20%. No microwave discharge is observed, indicating that the enhanced flame speed arises from microwave energy deposited directly into the reaction zone through coupling to the weakly ionized gas in that region. Laser diagnostics were performed to quantify temperature increase, the laminar flame speed enhancement, and changes in the OH radical concentration through filtered Rayleigh scattering, particle image velocimetry, and planar laser induced fluorescence, respectively.
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.
TL;DR: In this article, the forced response of a swirl-stabilized partially premixed flame when it is subjected to acoustic velocity and equivalence ratio fluctuations is analyzed using phase-resolved CH* chemiluminescence images and flame transfer function (FTF) measurements.
TL;DR: In this paper, the impact of oxy-fuel combustion on flame characteristics through the application of digital imaging and image processing techniques is investigated, and the characteristic parameters of the flame are derived from flame images that are captured using a vision-based flame monitoring system.
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...
TL;DR: In this article, the formation and propagation of the hot plasma kernel has been simulated for inert gas mixtures using a thermodynamic model, and the effects of various parameters including the discharge energy, radiation losses, initial temperature and initial volume of the plasma have been studied in detail.
TL;DR: In this paper, three typical mixtures of H 2, CO, CH 4, CO 2 and N 2 have been considered as representative of the producer gas coming from wood gasification.
TL;DR: In this article, the effect of the presence of singlet delta oxygen molecules in a CH4-air mixture on the speed of laminar flame propagation is considered. But the main reason for such an acceleration of flame propagation was the intensification of chain reactions due to addition of delta oxygen.
TL;DR: In this article, a flame speed expression has been studied in detail and extensively validated in a wide range of experimental data of S T from various flame configurations and conditions, with the same values of the model constants.
Abstract: A flame speed expression proposed recently is studied in detail and extensively validated in this study. This expression has no adjustable parameters, and its constants are closely tied to the physics of scalar mixing at small scales. In the weak turbulence limit, the flame speed expression recovers a linear dependence of the turbulent to laminar flame speed ratio, , on the normalized turbulence rms velocity, , in accordance with Damkohler's classical result. However, in the limit of intense turbulence, Damkohler's result gives a square-root dependence, while the new expression gives a combination of linear and square-root terms. Predictions of the new expression are compared to a wide range of experimental data of S T from various flame configurations and conditions, with the same values of the model constants. The quantitative comparisons are found to be very good with experimental data beyond the usually restricted range of of existing models. Predictions of S T for high-pressure turbulent flames, up t...
TL;DR: In this paper, the structure of a methane-air edge flame stabilized against an incoming mixing layer is computed using detailed chemical kinetics, and the analysis is based on computational singular perturbation theory.
Abstract: We study the structure of a methane–air edge flame stabilized against an incoming mixing layer. The flame is computed using detailed chemical kinetics, and the analysis is based on computational singular perturbation theory. We focus on examination of the dynamical fast/slow structure of the flame, exploring the distribution of time-scales, the composition of the related specific modes and the effective low-dimensional structure. We also study the importance of chemical/transport processes for both major species and radicals in the flame, analyzing the information available from slow/fast importance indices as compared to reaction flux analysis. Results provide enhanced understanding of the flame, outlining the role of different chemical and transport processes in its observed structure.
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.
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.
TL;DR: In this article, the burning speed of laminar flames of JP-8/air was measured and its flame structure was studied at high temperatures and pressures using a high-speed camera.
TL;DR: In this article, a constant volume combustion chamber and high-speed schlieren imaging system were used to calculate the laminar burning velocities of 2,5-dimethylfuran (DMF)-air premixed mixtures at different initial temperatures and equivalence ratios.
Abstract: Laminar burning velocities and Markstein lengths of 2,5-dimethylfuran (DMF)-air premixed mixtures at different initial temperatures and equivalence ratios were obtained using a constant volume combustion chamber and high-speed schlieren imaging system. The results indicate that both unstretched flame propagation speed and laminar burning velocity peak near the equivalence ratio of 1.2, and increase with increasing initial temperature. The peak unstretched flame propagation speed moves to the rich mixture side as the initial temperature increases, whereas the peak laminar burning velocity is unaffected by the variation of initial temperature. The Markstein length decreases with increasing equivalence ratio and increases with the increasing initial temperature. Based on the experimental data, a formula to calculate the laminar burning velocities of 2,5-DMF-air mixtures is provided.