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1
Sun, Y., N. Liu i W. Gao. "Experimental Study on Geometrical Characteristics of a Square Turbulent Buoyant Jet Flame". Journal of Physics: Conference Series 2442, nr 1 (1.02.2023): 012020. http://dx.doi.org/10.1088/1742-6596/2442/1/012020.
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Abstract This paper gives the experimental results for the buoyant jet diffusion flame in square burners. The flame height and lift-off were measured and discussed. The results show that the normalized flame height and lift-off height of square flames are lower than that of round flames with the same experimental conditions, which indicates enhanced air entrainment in square flames. The model of flame height based on the flame Froude-number, which integrates a correction factor to account for the enhancement of air entrainment, reasonably collapses the square flame data under different experimental cases. The critical Froude number for the transition from buoyancy to momentum controlled regime of a square jet flame is highly dependent on the fuel type and burner size. The lift-off height of the square jet flames increases linearly when the initial velocity increases, but also depends on the fuel type and burner size. A unified correlation using a dimensionless flow number derived from the mixedness-reactedness flamelet model is established, which reasonably predicts the lift-off distances of square jet flames.
2
Villani, Manfredi, i Phillip Aquino. "Turbulent Flame Geometry Measurements in a Mass-Production Gasoline Direct Injection Engine". Energies 13, nr 1 (1.01.2020): 189. http://dx.doi.org/10.3390/en13010189.
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Direct optical access to the combustion chamber of a gasoline direct injection (GDI) engine provides extremely valuable information about the combustion process. Experimental measurements of the geometric characteristics of the turbulent flame—such as the flame radius, flame center, flame edges and flame brush thickness—are of fundamental interest in support of the development and validation of any combustion model. To determine the macroscopic properties of sprays and flames, visualization and digital image processing techniques are typically used in controlled experimental setups like single-cylinder optical engines or closed vessels, while optical measurements on mass-production engines are more uncommon. In this paper the optical experimental setup (consisting of a high-speed camera, a laser light source and a data acquisition system) used to characterize the planar turbulent flame propagation in the cylinder of a 3.5 L GDI V6 mass-production engine, is described. The image acquisition process and the image processing that is necessary to evaluate the geometric characteristics of the propagating flame front, which are usually omitted in the referenced literature, are reported in detail to provide a useful guideline to other researchers. The results show that the step-by-step algorithm and the calculation formulae proposed allow to retrieve clear visualizations of the propagating flame front and measurements of its geometrical properties.
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Hicks, E. P. "Rayleigh–Taylor unstable flames at higher Reynolds number". Monthly Notices of the Royal Astronomical Society 489, nr 1 (30.07.2019): 36–51. http://dx.doi.org/10.1093/mnras/stz2080.
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ABSTRACT Rayleigh–Taylor (RT) unstable flames are a key component of Type Ia and Iax supernovae explosions, but their complex hydrodynamics is still not well understood. These flames are affected not only by the RT instability, but also by the turbulence it generates. Both processes can increase the flame speed by stretching and wrinkling the flame. This makes it hard to choose a subgrid model for the flame speed in full star Type Ia or Iax simulations. Commonly used subgrid models get around this difficulty by assuming that either the RT instability or turbulence is dominant and sets the flame speed. In previous work, we evaluated the physical assumptions and predictive abilities of these two types of models by analysing a large parameter study of 3D direct numerical simulations of RT unstable flames. Surprisingly, we found that the flame dynamics is dominated by the RT instability and that RT unstable flames are very different from turbulent flames. In particular, RT unstable flames are thinner rather than thicker when turbulence is strong. In addition, none of the turbulent flame speed models adequately predicted the flame speed. We also showed that the RT flame speed model failed when the RT instability was strong, suggesting that geometrical burning effects also influence the flame speed. However, these results depended on simulations with Re ≲ 720. In this paper, we extend the parameter study to higher Reynolds number and show that the basic conclusions of our previous study still hold when the RT-generated turbulence is stronger.
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Thiesset, F., F. Halter, C. Bariki, C. Lapeyre, C. Chauveau, I. Gökalp, L. Selle i T. Poinsot. "Isolating strain and curvature effects in premixed flame/vortex interactions". Journal of Fluid Mechanics 831 (13.10.2017): 618–54. http://dx.doi.org/10.1017/jfm.2017.641.
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This study focuses on the response of premixed flames to a transient hydrodynamic perturbation in an intermediate situation between laminar stretched flames and turbulent flames: an axisymmetric vortex interacting with a flame. The reasons motivating this choice are discussed in the framework of turbulent combustion models and flame response to the stretch rate. We experimentally quantify the dependence of the flame kinematic properties (displacement and consumption speeds) to geometrical scalars (stretch rate and curvature) in flames characterized by different effective Lewis numbers. Whilst the displacement speed can be readily measured using particle image velocimetry and tomographic diagnostics, providing a reliable estimate of the consumption speed from experiments remains particularly challenging. In the present work, a method based on a budget of fuel on a well chosen domain is proposed and validated both experimentally and numerically using two-dimensional direct numerical simulations of flame/vortex interactions. It is demonstrated that the Lewis number impact neither the geometrical nor the kinematic features of the flames, these quantities being much more influenced by the vortex intensity. While interacting with the vortex, the flame displacement (at an isotherm close to the leading edge) and consumption speeds are found to increase almost independently of the type of fuel. We show that the total stretch rate is not the only scalar quantity impacting the flame displacement and consumption speeds and that curvature has a significant influence. Experimental data are interpreted in the light of asymptotic theories revealing the existence of two distinct Markstein numbers, one characterizing the dependence of flame speed to curvature, the other to the total stretch rate. This theory appears to be well suited for representing the evolution of the displacement speed with respect to either the total stretch rate, curvature or strain rate. It also explains the limited dependence of the flame displacement speed to Lewis number and the strong correlation with curvature observed in the experiments. An explicit relationship between displacement and consumption speeds is also given, indicating that the fuel consumption rate is likely to be altered by both the total stretch rate and curvature.
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Smyth, N. F. "Propagation of flame fronts". Journal of the Australian Mathematical Society. Series B. Applied Mathematics 31, nr 4 (kwiecień 1990): 385–96. http://dx.doi.org/10.1017/s0334270000006743.
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AbstractThe propagation of a flame front in a combusting gas is considered in the limit in which the width of the reaction-zone is small compared with some overall flow dimension. In this approximation, the front propagates along its normals at a speed dependent on the local curvature of the front and is governed by a nonlinear equivalent of the geometric optics equations. Some exact solutions of this equation are found and a numerical scheme is developed to solve the equation for more complicated geometries.
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Adebiyi, Abdulafeez, Olatunde Abidakun i V’yacheslav Akkerman. "Acceleration of Premixed Flames in Obstructed Pipes with Both Extremes Open". Energies 13, nr 16 (7.08.2020): 4094. http://dx.doi.org/10.3390/en13164094.
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Premixed flame propagation in obstructed channels with both extremes open is studied by means of computational simulations of the reacting flow equations with a fully-compressible hydrodynamics, transport properties (heat conduction, diffusion and viscosity) and an Arrhenius chemical kinetics. The aim of this paper is to distinguish and scrutinize various regimes of flame propagation in this configuration depending on the geometrical and thermal-chemical parameters. The parametric study includes various channel widths, blockage ratios, and thermal expansion ratios. It is found that the interplay of these three critical parameters determines a regime of flame propagation. Specifically, either a flame propagates quasi-steady, without acceleration, or it experiences three consecutive distinctive phases (quasi-steady propagation, acceleration and saturation). This study is mainly focused on the flame acceleration regime. The accelerating phase is exponential in nature, which correlates well with the theoretical prediction from the literature. The accelerating trend also qualitatively resembles that from semi-open channels, but acceleration is substantially weaker when both extremes are open. Likewise, the identified regime of quasi-steady propagation fits the regime of flame oscillations, found for the low Reynolds number flames. In addition, the machine learning logistic regression algorithm is employed to characterize and differentiate the parametric domains of accelerating and non-accelerating flames.
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Chien, Yu-Chien, i Derek Dunn-Rankin. "Combustion Characteristics of Methane Hydrate Flames". Energies 12, nr 10 (21.05.2019): 1939. http://dx.doi.org/10.3390/en12101939.
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This research studies the structure of flames that use laboratory-produced methane hydrates as fuel, specifically for the purpose of identifying their key combustion characteristics. Combustion of a methane hydrate involves multiple phase changes, as large quantities of solid clathrate transform into fuel gas, water vapor, and liquid water during burning. With its unique and stable fuel energy storage capability, studies in combustion are focused on the potential usage of hydrates as an alternative fuel source or on their fire safety. Considering methane hydrate as a conventional combustion energy resource and studying hydrate combustion using canonical experimental configurations or methodology are challenges. This paper presents methane hydrate flame geometries from the time they can be ignited through their extinguishment. Ignition and burning behavior depend on the hydrate initial temperature and whether the clathrates are chunks or monolithic shapes. These behaviors are the subject of this research. Physical properties that affect methane hydrate in burning can include packing density, clathrate fraction, and surface area. Each of these modifies the time or the temperature needed to ignite the hydrate flames as well as their subsequent burning rate, thus every effort is made to keep consistent samples. Visualization methods used in combustion help identify flame characteristics, including pure flame images that give reaction zone size and shape and hydrate flame spectra to identify important species. The results help describe links between hydrate fuel characteristics and their resulting flames.
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Abam, D. P. S. "Methane Combustion in Laminar Diffusion Flames". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power Engineering 203, nr 1 (luty 1989): 65–72. http://dx.doi.org/10.1243/pime_proc_1989_203_008_02.
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This paper is concerned with methane combustion in laminar diffusion flames. Data on methane concentration distributions in different diffusion flame geometries are correlated against a conserved scalar called mixture fraction. The correlation is used to determine a global methane combustion rate applicable in the rich to stoichiometric regions of laminar diffusion flames. The global rate is consistent with methane disappearance through the forward kinetic step: CH4 + H → CH3 + H2 with [H] equilibrated according to [Formula: see text] on the rich side. This equilibration results from the three-body reaction [Formula: see text] which is equilibrated in the region 1.1 ≤ φ ≤ 2.74, 1300 K ≤ T ≤ 2000 K. These results indicate that initial radical attack on the fuel molecule provides the rate-controlling step for methane combustion.
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Sattelmayer, T., W. Polifke, D. Winkler i K. Do¨bbeling. "NOx-Abatement Potential of Lean-Premixed GT Combustors". Journal of Engineering for Gas Turbines and Power 120, nr 1 (1.01.1998): 48–59. http://dx.doi.org/10.1115/1.2818087.
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The influence of the structure of perfectly premixed flames on NOx formation is investigated theoretically. Since a network of reaction kinetics modules and model flames is used for this purpose, the results obtained are independent of specific burner geometries. Calculations are presented for a mixture temperature of 630 K, an adiabatic flame temperature of 1840 K, and 1 and 15 bars combustor pressure. In particular, the following effects are studied separately from each other: • molecular diffusion of temperature and species; • flame strain; • local quench in highly strained flames and subsequent reignition; • turbulent diffusion (no preferential diffusion); • small scale mixing (stirring) in the flame front. Either no relevant influence or an increase in NOx production over that of the one-dimensional laminar flame is found. As a consequence, besides the improvement of mixing quality, a future target for the development of low-NOx burners is to avoid excessive turbulent stirring in the flame front. Turbulent flames that exhibit locally and instantaneously near laminar structures (“flamelets”) appear to be optimal. Using the same methodology, the scope of the investigation is extended to lean-lean staging, since a higher NOx-abatement potential can be expected in principle. As long as the chemical reactions of the second stage take place in the boundary between the fresh mixture of the second stage and the combustion products from upstream, no advantage can be expected from lean-lean staging. Only if the primary burner exhibits much poorer mixing than the second stage can lean-lean staging be beneficial. In contrast, if full mixing between the two stages prior to afterburning can be achieved (lean-mix-lean technique), the combustor outlet temperature can in principle be increased somewhat without NO penalty. However, the complexity of such a system with a larger flame tube area to be cooled will increase the reaction zone temperatures, so that the full advantage cannot be realized in an engine. Of greater technical relevance is the potential of a lean-mixlean combustion system within an improved thermodynamic cycle. A reheat process with sequential combustion is perfectly suited for this purpose, since, first, the required low inlet temperature of the second stage is automatically generated after partial expansion in the high pressure turbine, second, the efficiency of the thermodynamic cycle has its maximum and, third, high exhaust temperatures are generated, which can drive a powerful Rankine cycle. The higher thermodynamic efficiency of this technique leads to an additional drop in NOx emissions per power produced.
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Winkler, Dieter, Weiqun Geng, Geoffrey Engelbrecht, Peter Stuber, Klaus Knapp i Timothy Griffin. "Staged combustion concept for gas turbines". Journal of the Global Power and Propulsion Society 1 (27.09.2017): CVLCX0. http://dx.doi.org/10.22261/cvlcx0.
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AbstractGas turbine power plants with high load flexibility are particularly suitable to compensate power fluctuations of wind and solar plants. Conventional gas turbines suffer from higher emissions at low load operation. With the objective of improving this situation a staged combustion system has been investigated. At low gas turbine load an upstream stage (first stage) provides stable combustion at low emissions while at higher loads the downstream stage (second stage) is started to supplement the power. Three injection geometries have been studied by means of computational fluid dynamics (CFD) simulations and atmospheric tests. The investigated geometries were a simple annular gap, a jet-in-cross-flow configuration and a lobe mixer. With CFD simulations the quality of mixing of second stage fresh gas with first stage exhaust gas was assessed. The lobe mixer showed the best mixing quality and hence was expected to also be the best variant in terms of combustion. However atmospheric combustion tests showed lower emissions for the jet-in-cross-flow configuration. Comparing flame photos in the visible and ultraviolet (UV) range suggest that the flame might be lifted off for the lobe mixer, leading to insufficient time for carbon monoxide (CO) burnout. CFD analysis of turbulent flame speed, turbulence and strain rates support the hypotheses of lifted off flame. Overall the staged concept was found to show very promising results not only with natural gas but also with natural gas enriched with propane or hydrogen. The investigations showed that apart from having an efficient and compact mixing of the two stages it is also very important to design the flow field such that the second flame can be anchored properly in order to achieve compact flames with sufficient time for CO burnout.
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Sheen, Sowon, Jeonghoon Lee i Chang Gyu Woo. "Application of coflow premixed flame for generating aggregate silica particles and its limitation". AIP Advances 12, nr 9 (1.09.2022): 095007. http://dx.doi.org/10.1063/5.0082172.
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This paper reports the geometrical characteristics and the growth of aggregate silica particles generated in a premixed flame using thermophoretic sampling, a light scattering technique, and aggregate dynamics modeling only for a premixed flat flame condition. The area equivalent size and the morphology of thermophoretically collected silica aggregate particles were analyzed through images taken from a transmission electron microscope. The particle stream in flames was visualized through a planar light scattering technique. Light scattering intensity at 90° using an Ar-ion laser (wavelength, 514 nm) was monitored for various flame conditions. The results of aggregate dynamics modeling under a one-dimensional assumption indicated that the silica particles grew as the height above the burner increased. Aggregate particles produced at various equivalence ratios showed different levels of OH-species. The OH-related species increased as the equivalence ratio decreased, which implies that a high equivalence ratio is recommended to produce pure silica particles. In this study, the purest silica aggregate particles were produced at the equivalence ratio of 11.4, among others. Our study helps to determine which flame condition is best in terms of the quality and/or quantity of silica aggregate particles generated by a coflow burner.
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Lv, Jiang, Qiang Wang, Fei Tang i Xiepeng Sun. "The evolution of flame geometrical characteristics and air entrainment of inclined jet flames". Process Safety and Environmental Protection 178 (październik 2023): 414–22. http://dx.doi.org/10.1016/j.psep.2023.08.053.
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Kuban, Łukasz, Jakub Stempka i Artur Tyliszczak. "Numerical Analysis of the Combustion Dynamics of Passively Controlled Jets Issuing from Polygonal Nozzles". Energies 14, nr 3 (22.01.2021): 554. http://dx.doi.org/10.3390/en14030554.
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In the present work, the combustion of vitiated hydrogen jets issuing from differently shaped nozzles is modelled using the LES method. We investigate the impact of nozzle cross-sectional geometries (circular, square, triangular, hexagonal and hexagram) and the jet Reynolds numbers (Re= 18,000, 20,000 and 23,600) on the flame lift-off height, its structure, the locations of the temperature maxima and species distributions. The triangular nozzle yields the highest mixing rate and therefore the fastest decay of axial velocity and the fastest growth of the average temperature along the flame axis. It was found that for the largest Re, the zone of intense mixing and the reaction zone occur in distinct regions, while for the lower Re, these regions combine into an indistinguishable zone. Finally, it is shown that the lift-off height of the flames and the mean temperature field are non-linearly correlated with Re and strongly dependent on the nozzle shape.
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Ahmed, E., i H. Yong. "Prediction of lean blowout performance of gas turbine combustor based on flow structures". Aeronautical Journal 122, nr 1248 (21.12.2017): 238–59. http://dx.doi.org/10.1017/aer.2017.131.
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ABSTRACTThe insufficient depth of modelling to capture the flow physics within primary combustion zone is the prime reason behind limited accuracy of semi-empirical correlations. Flame volume concept establishes a better connection between LBO performance and flame parameters, which improves the modelling depth and hence the prediction accuracy. Nonetheless, estimation of flame parameters is a challenging task. In addition, the iterative loop to approach convergence for a single geometry demands several numerical simulation runs. In this study, the association of LBO performance has been extended to flow structures, they are uniquely associated with the geometric features and can efficiently relate global LBO performance with primary zone geometry. The lean blowout phenomenon was presented as a contest between igniting and extinction forces within Reverse Flow Zone. These forces were quantified by four performance parameters including area, minimum axial velocity, average temperature, and average velocity. Selected parameters provide valuable information regarding the size of recirculation bubble, the intensity of flow reversal and the amount of entrained hot gases. For the purpose of validation, 11 combustor geometries were selected. The RANS simulation was carried out to estimate performance parameters, and predicted performance was compared against experimental data. The excellent agreement highlights the efficiency and promising future for the proposed methodology. Moreover, the association of prediction process with flow structure, instead of geometric features/dimension, makes it universal prediction methodology for wide range of combustor configurations.
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Giusti, A., i E. Mastorakos. "Turbulent Combustion Modelling and Experiments: Recent Trends and Developments". Flow, Turbulence and Combustion 103, nr 4 (listopad 2019): 847–69. http://dx.doi.org/10.1007/s10494-019-00072-6.
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AbstractThe development of better laser-based experimental methods and the fast rise in computer power has created an unprecedented shift in turbulent combustion research. The range of species and quantities measured and the advent of kHz-level planar diagnostics are now providing great insights in important phenomena and applications such as local and global extinction, pollutants, and spray combustion that were hitherto unavailable. In simulations, the shift to LES allows better representation of the turbulent flow in complex geometries, but despite the fact that the grid size is smaller than in RANS, the push towards realistic conditions and the need to include more detailed chemistry that includes very fast species and thin reaction zones emphasize the necessity of a sub-grid turbulent combustion model. The paper discusses examples from current research with experiments and modelling that focus on flame transients (self-excited oscillations, local extinction), sprays, soot emissions, and on practical applications. These demonstrate how current models are being validated by experimental data and the concerted efforts the community is taking to promote the modelling tools to industry. In addition, the various coordinated International Workshops on non-premixed, premixed, and spray flames, and on soot are discussed and some of their target flames are explored. These comprise flames that are relatively simple to describe from a fluid mechanics perspective but contain difficult-to-model combustion problems such as extinction, pollutants and multi-mode reaction zones. Recently, swirl spray flames, which are more representative of industrial devices, have been added to the target flames. Typically, good agreement is found with LES and some combustion models such as the progress variable - mixture fraction flamelet model, the Conditional Moment Closure, and the Transported PDF method, but predicting soot emissions and the condition of complete extinction in complex geometries is still elusive.
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Pokharel, Sunita, Mohsen Ayoobi i V’yacheslav Akkerman. "Computational Analysis of Premixed Syngas/Air Combustion in Micro-channels: Impacts of Flow Rate and Fuel Composition". Energies 14, nr 14 (11.07.2021): 4190. http://dx.doi.org/10.3390/en14144190.
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Due to increasing demand for clean and green energy, a need exists for fuels with low emissions, such as synthetic gas (syngas), which exhibits excellent combustion properties and has demonstrated promise in low-emission energy production, especially at microscales. However, due to complicated flame properties in microscale systems, it is of utmost importance to describe syngas combustion and comprehend its properties with respect to its boundary and inlet conditions, and its geometric characteristics. The present work studied premixed syngas combustion in a two-dimensional channel, with a length of 20 mm and a half-width of 1 mm, using computational approaches. Specifically, a fixed temperature gradient was imposed at the upper wall, from 300 K at the inlet to 1500 K at the outlet, to preheat the mixture, accounting for the conjugate heat transfer through the walls. The detailed chemistry of the ignition process was imitated using the San Diego mechanism involving 46 species and 235 reactions. For the given boundary conditions, stoichiometric premixed syngas containing various compositions of carbon monoxide, methane, and hydrogen, over a range of inlet velocities, was simulated, and various combustion phenomena, such as ignition, flame stabilization, and flames with repeated extinction and ignition (FREI), were analyzed using different metrics. The flame stability and the ignition time were found to correlate with the inlet velocity for a given syngas mixture composition. Similarly, for a given inlet velocity, the correlation of the flame properties with respect to the syngas composition was further scrutinized.
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Ingason, Haukur, i John de Ris. "Flame heat transfer in storage geometries". Fire Safety Journal 31, nr 1 (lipiec 1998): 39–60. http://dx.doi.org/10.1016/s0379-7112(97)00062-3.
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Józsa, Viktor, i Gergely Novotni. "Wavelet analysis of flame blowout of a liquid-fueled swirl burner with quarls". Noise Control Engineering Journal 67, nr 5 (1.09.2019): 394–403. http://dx.doi.org/10.3397/1/376734.
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Lean swirl combustion is the leading burner concept today, used in several steadyoperating applications to ensure awide operating range and low pollutant emissions. Approaching lean blowout is highly desired by design to achieve the lowest possible NOX emission. It was shown earlier that quarls could significantly extend the operating regime of liquid-fueled swirl burners. In the present study, the accompanying acoustic noise is evaluated by continuous wavelet transformation to show the effect of various quarl geometries on lean flame blowout. However, the desired flame shape of swirl burners is V, first, and a straight flame, and then a transitory regime can be observed before the developed V-shaped flame through increasing the swirl number. If the axial thrust is excessive, blowout might occur in earlier stages. Presently, the characteristic bands before blowout were analyzed and evaluated at various quarl geometries, swirl numbers, and atomizing pressures. The latter parameter also acts as an axial thrust control to adjust the swirl number. firstly, a straight flame, then a transitory regime can be observed before the developed V-shaped flame through increasing the swirl number. If the axial thrust is excessive, blowout might occur in earlier stages. Presently, the characteristic bands before blowout were analyzed and evaluated at various quarl geometries, swirl numbers, and atomizing pressures. The latter parameter also acts as an axial thrust control to adjust the swirl number.
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Durox, D., T. Schuller, N. Noiray i S. Candel. "Experimental analysis of nonlinear flame transfer functions for different flame geometries". Proceedings of the Combustion Institute 32, nr 1 (2009): 1391–98. http://dx.doi.org/10.1016/j.proci.2008.06.204.
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Dunstan, Thomas D., Nedunchezhian Swaminathan, Ken N. C. Bray i R. Stewart Cant. "Geometrical Properties and Turbulent Flame Speed Measurements in Stationary Premixed V-flames Using Direct Numerical Simulation". Flow, Turbulence and Combustion 87, nr 2-3 (27.07.2010): 237–59. http://dx.doi.org/10.1007/s10494-010-9284-1.
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Cecere, Giovanni, Adrian Irimescu, Simona Silvia Merola, Luciano Rolando i Federico Millo. "Lean Burn Flame Kernel Characterization for Different Spark Plug Designs and Orientations in an Optical GDI Engine". Energies 15, nr 9 (6.05.2022): 3393. http://dx.doi.org/10.3390/en15093393.
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Lean burn spark ignition (SI) engines represent an effective solution for improving fuel economy and reducing exhaust emissions and can be implemented both in conventional and hybrid powertrains. On the other hand, lean operation increases cyclic variability with negative impact on power output, engine efficiency, roughness, and operating stability. Although this phenomenon has been widely investigated, the effects of flow field on the inception and development of flames in direct injection spark ignition (DISI) engines under lean burn conditions is not yet completely understood. In particular, the effect of spark plug geometry and electrode orientation with respect to tumble motion has been minimally investigated. For these reasons, two different spark-plug geometries (i.e., single- and double-ground electrode) and three different orientations (i.e., cross-, counter-, and uni-flow with respect to the direction of tumble motion) were investigated in an optically accessible DISI engine for understanding their influence on the initial phase of combustion. The relative air–fuel ratio (AFRrel) was changed from stoichiometric to lean burn (1.00 to 1.30) for different spark timings around the maximum brake torque setting at fixed engine speed (2000 rpm). An image processing procedure was developed for evaluating the morphological parameters of flame kernels and studying the effects of spark plug design on engine operating stability. With a focus on the correlation between the position where ignition occurs with the subsequent locations of the flame kernel during the first phases of the combustion process, the analysis allowed the gathering of a better understanding of the influence that the electrodes’ geometries and orientation can have on the first stages of combustion development.
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Ren, Ze-tian, Su-hui Li i Min Zhu. "Dynamic responses of anchored ducted flames to harmonic velocity forcing". International Journal of Spray and Combustion Dynamics 10, nr 1 (13.10.2017): 72–85. http://dx.doi.org/10.1177/1756827717735301.
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This paper aims at developing a computationally inexpensive method to investigate the premixed flame instabilities. The kinematic G-equation is combined with a two-dimensional discrete vortex method, and the conformal mapping is applied to make calculations for complicated geometries more efficiently. The vortex dynamics and flame response to harmonic velocity forcing of an anchored ducted V-flame are investigated, and the effects of harmonic forcing, Reynolds number, and bluff body geometry are examined. Results show that the vortex structures, flow instability, and flame response are closely coupled with each other. The unsteady vortex structures generate instabilities at the flame base, and the convection of the flame wrinkles then influences the flame dynamics downstream. The flame heat release fluctuates with larger amplitude under low-frequency forcings, while the phase of the flame transfer function is quasi-linear with increasing forcing frequency. Both higher inflow velocity and sharper bluff body corners can result in more unsteady large-scale vortex structures and hence influence the flame responses.
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Huang, Youbo, Bin Wang, Bingyan Dong, Ying Tang i Wenhe Wang. "Experimental study on flame geometric of horizontal jet fire inpinging a facing wall and side wall". Thermal Science, nr 00 (2023): 148. http://dx.doi.org/10.2298/tsci230328148h.
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This work focuses on investigating the characteristics of restricted horizontal jet fire caused by fuel leakage as a pipeline or tank fracture. The study aims to quantify the effect of the exit velocity and nozzle-facing wall distance on the flame height and width, as well as developing a new non-dimensional heat release rate Qn* to better characterize the flame geometry. The study conducted three nozzle-facing wall distances (0.05, 0.10, and 0.15 m) with varying fuel ejection speeds from 1.04 to 6.25 m/s. Results show that the flame height and width increase with both the nozzle-facing wall distance and fuel ejection speed. The side wall constrains the air entering into the fire plume, which pushes the flame closer to the side wall. A new non-dimensional heat release rate Qn* was proposed on the basis of plate-nozzle distance, that the flame height and width fit well with the 1/4 and 2/5 power of Qn*, respectively. The global model was developed for flame size under multiple restrictions. The findings of this study are crucial in improving our understanding of the restricted horizontal jet fire accidents caused by fuel leakage and can aid in developing measures to minimize potential casualties and economic losses.
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Morgan, Michael D., S. A. (Raj) Mehta, T. J. Al-Himyary i R. G. (Gord) Moore. "Propagation of Turbulent Natural Gas/Air Flames in Tubing With 90° Bends". Journal of Energy Resources Technology 125, nr 4 (18.11.2003): 304–10. http://dx.doi.org/10.1115/1.1619431.
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Anytime flammable gas mixtures are handled, there is a risk of combustion. This is particularly true in many industrial applications where space is limited and equipment is located near sources of ignition. Unfortunately, there is a lack of understanding of combustion phenomena within process equipment such as mufflers, rotating blowout preventers, liquid traps, and dry gas seal assemblies. These vessels have small internal volumes, complex internal geometries, and are connected using small diameter piping. This paper discusses the results of a parametric study which was carried out to establish the nature of combustion within such vessels and tubing. The test vessel had an internal volume of 7 in3 (115 ml) and the tubing had a nominal diameter of 0.5 in (1.27 mm). Flowing, turbulent, pre-mixed natural gas/air mixtures were used. The study did not attempt to increase turbulence using devices such as mesh screens or attempt to stabilize the flame. The results from a representative sample of 76 tests, from the 5,000+ tests that have been completed, are discussed herein. Typical pressure and temperature responses are presented and analyzed. It is demonstrated that flames can be remotely detected using only high speed pressure data. Turbulent flames were formed whose velocity was found to be linearly dependant on Reynolds number.
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HAYAKAWA, Akihiro, Toshihiko KUBO, Yukito MIKI, Yukihide NAGANO i Toshiaki KITAGAWA. "J054013 Geometric Characteristics of Flame Front Shape of Spherically Propagating Premixed Turbulent Flame". Proceedings of Mechanical Engineering Congress, Japan 2012 (2012): _J054013–1—_J054013–5. http://dx.doi.org/10.1299/jsmemecj.2012._j054013-1.
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Abou-Arab, T. W., M. M. Enayet i M. M. Kamel. "Recent measurements of flame acceleration in semiconfined geometries". Journal of Loss Prevention in the Process Industries 4, nr 3 (kwiecień 1991): 202–6. http://dx.doi.org/10.1016/0950-4230(91)80037-u.
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Ni, Jian, i Hong Xia Liu. "Research on Flame Simulation Based on Improved Particle System and the Texture Mapping". Applied Mechanics and Materials 44-47 (grudzień 2010): 3601–5. http://dx.doi.org/10.4028/www.scientific.net/amm.44-47.3601.
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Flame simulation in computer graphics has been the most challenging problems. According to the key problem of real time and reality in flame simulation based on particle system, a new flame model based on improved particle system and the texture mapping is proposed in this paper. This article uses specific geometric shape as the elementary particles and combines treatment of derivatives based on the flame of the original particle system to simplify some of the dynamic equation, to reduce the difficulty of computational modeling and improve rendering speed; Through texture mapping and particle mixing effects to achieve flame changes color in different regions and reflect the temperature difference between them; In addition, the method also reflects the dynamic field of the particle system.
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Торба, Юрий Иванович, Дмитрий Викторович Павленко i Ярослав Викторович Двирник. "ОПТИМІЗАЦІЯ КОНСТРУКЦІЇ ФАКЕЛЬНОГО ЗАПАЛЬНИКА ГТД ЧИСЕЛЬНИМ МЕТОДОМ". Aerospace technic and technology, nr 5 (29.08.2020): 83–95. http://dx.doi.org/10.32620/aktt.2020.5.11.
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Solved the problem of gas-turbine engine combustion chamber flame igniter efficiency increasing by increasing the flame temperature via optimizing the body design. To determine the influence of the igniter body various geometric parameters, affecting the formation and combustion of the fuel-air mixture, a parametric model was developed. This model together with the developed project in the ANSYS Workbench software package made it possible to automate the modeling process. The influence of the geometric parameters of the igniter body and external factors on the average flame temperature has been studied via a numerical model of the stationary combustion process of the air-fuel mixture formed inside the igniter of the combustion chamber of a gas turbine engine by evaporation and spraying particles of aviation kerosene in the air stream. The adequacy of the numerical simulation results was confirmed by the implementation of a series of full-scale experiments using the Fisher criterion.The uniformity of temperature and adequacy of the average temperature estimation algorithm was established using the correlation analysis of the results of measured temperature at various points of the flame. To determine the degree and nature of their influence, sequentially screening (fractional), as well as full-factor experiments with varying factors at two and three levels were implemented. Based on the results of the analysis of variance, the most statistically significant factors were selected. A regression dependence was established that relates the diameter of the air inlet orifice and the air pressure drop to the flame temperature. A qualitative and quantitative assessment of the influence of the considered factors on the process of formation of a hot air mixture and its combustion has been performed. The optimal values of the geometric parameters of the igniter body and its operating conditions are determined under which the maximum flame temperature at the stationary combustion stage is ensured. Relationships between design features, igniter operation mode, and the temperature of the flame are established. This allows expanding the range of stable ignition of gas turbine engine combustion chambers in accordance with the design of the igniter, the starting fuel supply mode, and the air pressure drop.
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Dunstan, Thomas D., Nedunchezhian Swaminathan, Ken N. C. Bray i R. Stewart Cant. "Erratum to: Geometrical Properties and Turbulent Flame Speed Measurements in Stationary Premixed V-flames Using Direct Numerical Simulation". Flow, Turbulence and Combustion 87, nr 4 (5.10.2010): 725–28. http://dx.doi.org/10.1007/s10494-010-9304-1.
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Silva, R. L. da, L. S. Azevedo, B. V. Sant´Anna, J. R. Patelli Jr i M. M. Vieira. "THERMAL PERFORMANCE AND FLAME TEMPERATURES ON LPG RADIAL BURNERS IN DOMESTIC COOKERS". Revista de Engenharia Térmica 18, nr 2 (16.12.2019): 38. http://dx.doi.org/10.5380/reterm.v18i2.70787.
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The objective is to investigate radial burners through experimental tests, looking for its thermal performance behavior. Gas burners in domestic cookers operate on LPG, typically with two different geometries and five thermal power conditions. Usually, those thermal equipment lacks information on its whole operating conditions range for higher energy conversion efficiency and lower fuel consumption; it is not pointed out by the manufacturer or by energy efficiency labeling, what could result in a recommendation for widely effective performance. Appropriate instrumentation was used to carry out the measurements and methodology used as a guideline regulations from INMETRO/CONPET, ABNT - Brazilian Technical Standards Normative, and ANP - National Agency of Petroleum, Natural Gas and Biofuels. Experimental measurements and uncertainties are for the following parameters: fuel mass consumption (kg.s-1), test time elapsed (s), temperature (°C), water mass (kg) and flame temperature by K-type thermocouples (quantitative) and a thermal camera (qualitative). Main conclusions are: a) Operating domestic cookers with handle position selector on middle position (TP3) provides almost the same temperature rise as maximum fuel consumption (TP5), i.e., ΔT in the water container; b) Heat is better transferred (Qgas → Qwater) with the handle position selector fully opened (TP5@B1) and just before fully opening (TP4@B2); c) A non-linear behavior occurs for ηThermal, when moving forward the handle position selector; maximum efficiency occurs at fully open (TP5@B2) and middle opening (TP3@B1); d) Higher values for TPexperimental occurs for B2, in comparison to B1, in whole operational condition ranges; differences are mainly due to geometric parameters (ARB2/ARB1~0.82). In general, B2 has a better geometric design; e) Uncertainty analysis indicate values lower than ±3%, proving to be a suitable methodology for the experimental results in this work; f) Flame temperatures are entirely consistent with both, ηThermal and heat energy delivered, reaching higher temperature values at TP4 for both burners; 751.5°C (B1) and 830.7°C (B2).
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Yan, Zhuo, Shengli Guo, Shujie Yuan i Chaomin Mu. "Influence of Chamber Geometrical Parameters on Suppressing Explosion Propagation". Shock and Vibration 2021 (30.08.2021): 1–11. http://dx.doi.org/10.1155/2021/6377887.
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In this article, the effect of a chamber’s geometrical parameters on suppressing gas explosion propagation was studied. Three rectangular chambers were used in the study, with a constant length of 0.5 m, a constant height of 0.2 m, and a variable width of 0.3 m, 0.5 m, and 0.8 m; each chamber was installed in a pipeline system for experimental research. The experimental results showed that when the chamber length and height were fixed at 0.5 m and 0.2 m, respectively, the suppression effect of the chamber on the explosion shockwave improves with the increase in the chamber width; when the chamber width increases to 0.8 m, the chamber has suppressive effect on explosion shockwave propagation. It was also found that the suppression effect of the chambers on the explosion flame improves with the increase in the chamber width; when the width of the chamber is 0.5 m, the chamber effectively suppresses explosion flames. Based on the experimental results, a numerical model was established to simulate the suppression effect of five types of chambers with a length, width, and height of 0.5 m × 0.3 m × 0.2 m, 0.3 m × 0.5 m × 0.2 m, 0.5 m × 0.5 m × 0.2 m, 0.5 m × 0.8 m × 0.2 m, and 0.8 m × 0.5 m × 0.2 m, respectively. The numerical simulation results indicated that when the chamber length and height are constant at 0.5 m and 0.2 m, respectively, the suppressive effect of the chamber on the shockwave improves as the chamber width increases; when the chamber width increases to 0.8 m, the shockwave overpressure at the chamber outlet is attenuated by 10.61%, indicating that the chamber suppresses the propagation of explosion shockwave, which is consistent with the experimental results obtained in the study. It was also found that when the chamber width and height were constant at 0.5 m and 0.2 m, respectively, as the chamber length increases, the overpressure increases first and then weakens. When the chamber length increases to 0.8 m, the overpressure at the chamber outlet is attenuated by −14.16%, indicating that the chamber is not able to suppress the propagation of explosion shockwave. Finally, a numerical simulation of the propagation process of a methane-air mixture and explosion flames in different chambers was performed to analyse the effect of chamber geometrical parameters on explosion suppression effect.
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Blondé, Audrey, Bruno Schuermans i Nicolas Noiray. "Experiments and Modelling on the Effect of an Adjustable Boundary on Thermoacoustic Stability". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 265, nr 3 (1.02.2023): 4590–98. http://dx.doi.org/10.3397/in_2022_0661.
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Predicting the existence of thermoacoustic instabilities is a key step in the design of modern gas turbines and the choice of their operating conditions. The stability of a combustion system crucially depends on the acoustic boundary conditions. To systematically investigate the influence of these boundary conditions, a test facility with variable inlet and outlet geometries has been developed. Cold flow tests confirmed that the acoustic terminations allow for a change of the reflection coefficient from close to open end to anechoic to almost closed end over a large frequency range. In the present work, we present the design of an adjustable exit boundary enabling a change in the thermoacoustic stability without modifying the flame operating conditions. Experiments have been conducted in a turbulent axial atmospheric combustor. The acoustic reflection coefficients in hot condition of the exit boundary are measured for different boundary geometries and the impact of these geometries on the flame stability is assessed. A parametrized model is derived and reproduces the experiments well.
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Yang, Yang, i Zhijian Yu. "Design and Decomposition Analysis of Mixing Zone Structures on Flame Dynamics for a Swirl Burner". Energies 13, nr 24 (21.12.2020): 6744. http://dx.doi.org/10.3390/en13246744.
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The recirculation zone and the swirl flame behavior can be influenced by the burner exit shape, and few studies have been made into this structure. Large eddy simulation was carried out on 16 cases to distinguish critical geometry factors. The time series of the heat release rate were decomposed using seasonal-trend decomposition procedure to exclude the effect of short physical time. Dynamic mode decomposition (DMD) was performed to separate flame structures. The frequency characteristics extracted from the DMD modes were compared with those from the flame transfer functions. Results show that the flame cases can be categorized into three types, all of which are controlled by a specific geometric parameter. Except one type of flame, they show nonstationary behavior by the Kwiatkowski–Phillips–Schmidt–Shin test. The frequency bands corresponding to the coherent structures are identified. The flame transfer function indicates that the flame can respond to external excitation in the frequency range 100–300 Hz. The DMD modes capture the detailed flame structures. The higher frequency bands can be interpolated as the streamwise vortices and shedding vortices. The DMD modes, which correspond to the bands of flame transfer functions, can be estimated as streamwise vortices at the edges.
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Hasalová, Lucie, Petr Vaněk i Milan Jahoda. "Temperature Field Evolution in Wood Samples During the Flame Spread Experiments". TRANSACTIONS of the VŠB – Technical University of Ostrava, Safety Engineering Series 9, nr 1 (29.09.2014): 16–24. http://dx.doi.org/10.2478/tvsbses-2014-0003.
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Abstract Vertical, horizontal and 45° upward flame spread experiments over the small scale beech and pine wood samples were performed. Wood samples were of two geometries - square cross section prisms (15 x 15 mm) and a thin rectangular cross section prisms (5 x 40 mm) - and of three different lengths - 10, 15 and 30 cm. Samples were ignited by a heptane source fire extinguished immediately when the wood samples ignited. During the flame spread an internal temperature profiles along the centreline of the samples were measured by a set of thermocouples. Flame spread was observed in all sample positions except the horizontal orientation of the beech and pine square prism samples. Experimental data will serve for a validation of the pyrolysis models in the Computational Fluid Dynamics (CFD) flame spread models.
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Sathyan, P., S. Srikanth, I. Dheepan, M. Arun, C. Aswin i V. R. Sanal Kumar. "Studies on Aerodynamic Characteristics of Dump Diffusers for Modern Aircraft Engines". Applied Mechanics and Materials 232 (listopad 2012): 246–51. http://dx.doi.org/10.4028/www.scientific.net/amm.232.246.
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The geometrical optimization of dump diffusers are extremely demanding as the flow fields and stress fields are very complex and must be well understood to achieve the required design efficiencies. In this paper parametric analytical studies have been carried out for examining the aerodynamics characteristics of different dump diffusers for modern aircraft engines. Numerical studies have been carried out using SST K- ω turbulence model. This code solves SST k- ω turbulence equations using the coupled second order implicit unsteady formulation. In the numerical study, a fully implicit finite volume scheme of the compressible, Reynolds-Averaged, Navier-Stokes equations is employed. We concluded that in addition to the dump gap ratio, the aerodynamic shape of the flame tube case and the other geometric variables are also need to be optimized judiciously after considering the fluid dynamic constraints for controlling the pressure recovery and the losses.
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Filipi, Z. S., i D. N. Assanis. "The effect of the stroke-to-bore ratio on combustion, heat transfer and efficiency of a homogeneous charge spark ignition engine of given displacement". International Journal of Engine Research 1, nr 2 (1.04.2000): 191–208. http://dx.doi.org/10.1243/1468087001545137.
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This study investigates how the selection of the stroke-to-bore (S/B) ratio affects combustion, heat transfer and overall efficiency in a homogeneous charge spark ignition (SI) engine of a given displacement. Initially, flame front area maps and wall areas in contact with burned gases are examined from a purely geometric point of view, for S/B ratios of 0.7, 1.0 and 1.3. Subsequently, a quasi-dimensional turbulent flame entrainment model is used to quantify the extent to which turbulence versus geometric factors are responsible for the observed combustion, heat transfer and cycle efficiency behaviour, as the S/B ratio varies. Calculations are performed for a range of engine speeds and loads, as well as for operation with 15 per cent exhaust gas recirculation (EGR). Results show that the S/B ratio has a significant effect on both turbulence levels and the geometric interaction of the flame front with the combustion chamber walls. In general, a longer stroke leads to higher thermal efficiency through faster burning and lower overall chamber heat loss. These effects are non-linear, being more dramatic when the S/B ratio is increased from below unity than from above unity. The potential of the long-stroke engine for brake fuel economy improvement can be exploited to the fullest at low speeds, while friction losses gradually diminish it at higher speeds.
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Borille, Anderson Vicente, Jefferson de Oliveira Gomes i Daniel Lopes. "Geometrical analysis and tensile behaviour of parts manufactured with flame retardant polymers by additive manufacturing". Rapid Prototyping Journal 23, nr 1 (16.01.2017): 169–80. http://dx.doi.org/10.1108/rpj-09-2015-0130.
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Purpose Flame-retardant plastics are used in critical applications, such as aircraft interior parts, when the occurrence of fire can lead to serious injury to people. However, there is a lack of related publications. The purpose of this study is to present experimental data regarding geometrical analysis, such as dimensional accuracy and surface roughness, tensile strength and elongation of parts manufactured with flame-retardant materials by additive manufacturing. Design/methodology/approach Two additive manufacturing processes, selective laser sintering (SLS) and fused deposition modeling (FDM), were selected to manufacture the parts to be evaluated. Each process used its respective polymer, that is polyamide with flame-retardant additive (PA) for SLS and polyphenylsulfone (PPSF) for FDM. The samples consist of tensile specimens and representative parts of different products. Tensile tests were performed using standard tensile test machines, and geometrical analyses were performed using coordinate measuring machine as well as surface roughness tester. Findings As each material can be, in commercial machines, produced by only one process, the material selection for final products has to consider the manufacturing process as well. In general, although the FDM/PPSF process provided specimens with the highest ultimate strength, because of its strong influence by the building direction, FDM/PPSF also provided the lowest strength. SLS/PA was able to provide average strength with less dependency on the build-up direction. The geometrical analysis showed that SLS/PA presents a much smoother surface, but FDM/PPSF presented slightly better dimensional accuracy. Originality/value There is still lack of publications on polymers with flame resistance or flame-retardant polymers. Thus, this paper brings new technical information about processing such materials.
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De Soete, G. G. "Effects of geometrical and aerodynamic induced flame stretch on the propagation of spark fired premixed flames in early stages". Symposium (International) on Combustion 20, nr 1 (styczeń 1985): 161–68. http://dx.doi.org/10.1016/s0082-0784(85)80499-9.
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Jiang, Yan-Huan, Guo-Xiu Li, Hong-Meng Li, Lei Li i Guo-Peng Zhang. "Effect of flame inherent instabilities on the flame geometric structure characteristics based on wavelet transform". International Journal of Hydrogen Energy 43, nr 18 (maj 2018): 9022–35. http://dx.doi.org/10.1016/j.ijhydene.2018.03.141.
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Kiverin, Alexey D., i Ivan S. Yakovenko. "Estimation of critical conditions for deflagration-to-detonation transition in obstructed channels filled with gaseous mixtures". Mathematical Modelling of Natural Phenomena 13, nr 6 (2018): 54. http://dx.doi.org/10.1051/mmnp/2018071.
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The paper considers the peculiarities of deflagration-to-detonation transition (DDT) in obstructed channels filled with gaseous mixtures. The necessary stage in flame evolution prior to DDT is the stage of flame propagation in so-called “chocked flame” regime. The structure of the chocked flame is studied numerically in details that allows formulating the criterion of its stability. In turn, the stability of chocked flame determines the possibility of further flame acceleration and subsequent DDT. Such a criterion is of purely chemical nature and can be estimated using the parametric study involving simple one-dimensional calculations. It should be however noted that to get the prediction of DDT in real complex geometry one should additionally estimate the particular conditions of chocked flame formation in the given geometry. Moreover, the particular mechanisms of detonation onset should be analyzed. Such a complex analysis involving both chemical criterion and analysis of geometrical conditions is applied to the estimation of DDT possibility in obstructed channels. The obtained results are in a good agreement with available experimental data.
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Antonescu, Nicolae, i Paul-Dan Stanescu. "High Stability and Low Emissions Burners Using Karlowitz Effect in Conical Burners". Mathematical Modelling in Civil Engineering 10, nr 3 (1.09.2014): 1–11. http://dx.doi.org/10.2478/mmce-2014-0011.
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Abstract The conical tunnel burner is an improvement of the cylindrical tunnel burner because, by maintaining all its advantages by means of burning intensification, it may also insure the flame stabilization in a wide range of regulation with considerable diminished pressure losses. Technical applications for the conical furnace burner can vary due to the limited dimensions required by the system, as well as the important thermal loads, and also because of the burning stability characteristic that spreads over an important range of regulation. The low costs required by the burner, generated mainly by its simple construction, also raise the interest for this technical solution. A physical model is proposed for the ignition and flame front stabilization. The flame front stabilization contains different steps from the ignition moment to final flame front stabilization, with specific flame front geometries and specific locations along the burner axis. The installation realised by the authors allowed the experimental study of the burning process in conical furnaces, in order to determine the temperature fields and the flame profiles. The physical model developed for this new type of application and the experimental data sets obtained (along with their interpretation) make the subject of this paper.
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Ahmed, E., i Y. Huang. "Flame volume prediction and validation for lean blow-out of gas turbine combustor". Aeronautical Journal 121, nr 1236 (12.01.2017): 237–62. http://dx.doi.org/10.1017/aer.2016.125.
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ABSTRACTLean Blow-Out (LBO) limits are critically important in the operation of aero engines. Previously, Lefebvre's LBO empirical correlation has been extended to the flame volume concept by the authors. Flame volume takes into account the effects of geometric configuration, spatial interaction of mixing jets, turbulence, heat transfer and combustion processes inside the gas turbine combustion chamber. For these reasons, LBO predictions based on flame volume are more accurate. Although LBO prediction accuracy has improved, it poses a challenge associated with Vfestimation in real gas turbine combustors. This work extends the approach of flame volume prediction based on fuel iterative approximation with cold flow simulations to reactive flow simulations. Flame volume for 11 combustor configurations were simulated and validated against experimental data. To make prediction methodology robust, as required in preliminary design stage, reactive flow simulations were carried out with the combination of presumed Probability Density Function (PDF) and discrete phase model (DPM) in Fluent 15.0 The criterion for flame identification was defined. Two important parameters—critical injection diameter (Dp,crit) and critical temperature (Tcrit)—were identified and their influence on reactive flow simulation was studied for Vfestimation. Results exhibit ±15% error in Vf estimation with experimental data.
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Pashchenko, Serhii, Oleksandr Kharchenko, Artem Shulhin i Yevheniy Chemerys. "The Peculiarities of Applying CAD/CAE Systems for the Primary Combustion Chamber Flame Tube Cycle Life Prolongation of the Tactical Military Aircraft Afterburning Turbofan Jet Engine". Journal of KONBiN 52, nr 4 (1.12.2022): 167–76. http://dx.doi.org/10.2478/jok-2022-0048.
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Abstract In this article, the computational simulation of the workflow in the primary combustion chamber flame tube of the afterburning turbofan jet engine (ATJE) on the tactical military aircraft was carried out. The geometric model of a flame tube was created and adapted to perform the interrelated calculation of the thermal and stress-strain behaviour of the walls of the flame tube influenced by the operational loads during the computational simulation of the workflow. Quantitative and qualitative analysis of the simulation results was conducted, and the connection between the peculiarities of the workflow and the characteristic damage of the flame tubes, detected during the operation, was established. The possibility of using modern CAD/CAE systems to solve the scientific tasks towards maximizing the cycle life potential of the main and primarily important components of the ATJE on the assessment basis of their damage exhaustion degree was determined.
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Agafontsev, M. V., i V. V. Reyno. "Effect of low-frequency vibrations on the characteristics of the diffusion flame". Journal of Physics: Conference Series 2389, nr 1 (1.12.2022): 012004. http://dx.doi.org/10.1088/1742-6596/2389/1/012004.
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Abstract The paper considers the effect of low-amplitude acoustic oscillations on the temperature field in the flame formed during the combustion of kerosene gasoline. As a result of using the IRT-method, sets of thermograms of the combustion process were obtained. For the obtained thermograms, the distribution of high-temperature inhomogeneities in the flame plume was analyzed. As a result, it was obtained that the effect of acoustic oscillations on the flame plume causes a change in the height of the plume, a change in the combustion rate. When analyzing the spectra of temperature changes, characteristic pulsations, which are different, depending on the flame zone, were observed. Analysis of the distribution of temperature inhomogeneities under different modes of exposure to pressure pulsations, allowed to identify the characteristic modes in which there is a change in the geometric dimensions of the temperature inhomogeneity distribution zone.
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Meng, Nan, i Feng Li. "Large-Eddy Simulations of Unsteady Reaction Flow Characteristics Using Four Geometrical Combustor Models". Aerospace 10, nr 2 (6.02.2023): 147. http://dx.doi.org/10.3390/aerospace10020147.
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Combustion instability constitutes the primary loss source of combustion chambers, gas turbines, and aero engines, and it affects combustion performance or results in a sudden local oscillation. Therefore, this study investigated the factors affecting flame fluctuation on unsteady combustion flow fields through large-eddy simulations. The effects of primary and secondary holes in a triple swirler staged combustor on flame propagation and pressure fluctuation in a combustion field were studied. Moreover, the energy oscillations and dominant frequencies in the combustion field were obtained using the power spectral density technique. The results revealed a variation in the vortex structure and Kelvin–Helmholtz instability in the combustion field, along with a variation in the pressure pulsation during flame propagation under the influence of the primary and secondary hole structures. Additionally, the spatial distributions of pressure oscillation and heat release rate amplitude were obtained, revealing that the foregoing increased owing to the primary and secondary holes in the combustion field, reaching a peak in the shear layer and vortex structure regions.
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Lamioni, Rachele, Sebastiano Cinnirella, Cristiana Bronzoni, Marco Folli, Leonardo Tognotti i Chiara Galletti. "Impact of hydrogen admixture on interacting premixed flames in domestic boilers". E3S Web of Conferences 238 (2021): 04001. http://dx.doi.org/10.1051/e3sconf/202123804001.
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The injection of hydrogen into the natural gas network can contribute to the large-scale integration of renewables, as hydrogen can be easily produced through electrolysis from wind or solar energy. However, the addition of hydrogen to natural gas influences fuel properties, asking for the assessment of the safe and efficient operation of existing end-user equipment, such as domestic burners and boilers. In this work, 3-dimensional resolved numerical simulations based on Computational Fluid Dynamics are carried out to shed light on the effect of H2 addition on the combustion process occurring in condensing boilers equipped with perforated cylindrical burners. To this purpose, multi-hole geometries emulating a portion of a perforated burner are analyzed. Since the burner holes are positioned very close to each other, the interaction of the adjacent laminar premixed flames is observed to occur with influence on the flow and thermo-chemical fields which differ from those of a single premixed flame. The addition of hydrogen was found to lead to an anticipation of the reaction zone, although the general features observed with the G222 gas (23% H2, 77% CH4 ) were alike those of the G20 gas (100% CH4).
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Qin, Zuo Dong, G. J. Duns, Zhang Lin i Ji Shuang Chen. "Flame Retardant Properties of Fiber-Based Decorative Wallboard". Advanced Materials Research 487 (marzec 2012): 739–47. http://dx.doi.org/10.4028/www.scientific.net/amr.487.739.
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In this study, bamboo pulp is utilized as the main raw material for the production of compression-molded, fiber-based decorative wallboard panels which have three-dimensional geometric structure and possess environmentally compatible “green” flame retardant properties. The effectiveness of several flame retarding agents, including the Al(OH)3 single component system, the Al(OH)3/Mg(OH)2 mixed system and the Al(OH)3/Mg(OH)2/Zinc Borate mixed system are examined in terms of the resulting flame resistance, physical properties and oxygen indexes of the fiber-based decorative wallboard. The results show that the Al(OH)3/Mg(OH)2/Zinc Borate multicomponent mixed system is the most ideal flame retardant system for such applications. Results indicate that the optimal formulation consist of: 30% Mg(OH)2/25% Al(OH)2 /15% Zinc borate (relative mass ratio). Under such conditions, the oxygen index of the fiber decorates wallboard is 34.4, and the level of formaldehyde release reaches a value of E0.
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Hammack, Stephen, Tonghun Lee i Campbell Carter. "Microwave Plasma Enhancement of Various Flame Geometries at Atmospheric Pressure". IEEE Transactions on Plasma Science 40, nr 12 (grudzień 2012): 3139–46. http://dx.doi.org/10.1109/tps.2012.2195034.
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Kryukov, Aleksey, i Vladimir Malinin. "PRESSURE DEPENDENCE OF FLAME ZONE SIZE OF SINGLE ALUMINIUM PARTICLES". Perm National Research Polytechnic University Aerospace Engineering Bulletin, nr 60 (2020): 45–54. http://dx.doi.org/10.15593/2224-9982/2020.60.05.
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Mathematical modeling of geometric dimensions and thermodynamic parameters of flame around single aluminium under combustion in the 79 % Ar + 21 % O2 atmosphere was implemented. The modeling was carried out on the basis of summarizing of experimental data and results of thermodynamic analysis. The dependencies of temperature and oxidizer (oxygen) concentration on the flame boundary and pressure of surrounding medium on particle size were determined. Also relation of flame radius with particle radius was established. The calculations was realized according to model of diffusion mode combustion with taking into account quasistationarity and thermodynamic equilibrium of processes, from the assumption of spherical symmetry of the flame. The flame boundary, oxidizer concentration and temperature on the boundary are determined on the basis of condition of predetermined completeness of aluminium transformation into ultrafine oxide Al2O3. The relative size of flame zone is established to decrease from 4.5 to 6.8 when surrounding medium pressure changes from 0.1 to 6 MPa. The relative size of flame zone and oxidizer concentration on the flame boundary increase as the particle burn out. As the particle radius decreases the part of radiative heat exchange decreases in total balance of it’s energy. And the part of radiative heat exchange does not exceed 8 % for industrial aluminium powders with particles diameter less than 50 m. The surrounding medium pressure influences on values of parameters calculated essentially with the exception of part of radiation heat flow.
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Liu, Zhi-Qi, Zhi Li, Yun-Xian Yang, Yan-Ling Zhang, Xin Wen, Na Li, Can Fu, Rong-Kun Jian, Li-Juan Li i De-Yi Wang. "A Geometry Effect of Carbon Nanomaterials on Flame Retardancy and Mechanical Properties of Ethylene-Vinyl Acetate/Magnesium Hydroxide Composites". Polymers 10, nr 9 (14.09.2018): 1028. http://dx.doi.org/10.3390/polym10091028.
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This study was aimed at investigating the effects of carbon nanomaterials with different geometries on improving the flame retardancy of magnesium hydroxide–filled ethylene-vinyl acetate (EM). The thermal stability and flame retardancy were studied by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 test, and cone calorimeter test (CCT). The in situ temperature monitoring system and interrupted combustion offered direct evidence to link flame retardancy and composite structure. Results demonstrated that carbon nanomaterials enhanced the thermal stability and fire safety of EM. The geometry of carbon nanomaterials played a key role in synergistic flame retardancy of EM, with the flame-retardant order of carbon nanotube > nanoscale carbon black > graphene. Based on an online temperature monitoring system and interrupted combustion test, one-dimensional carbon nanotube was more inclined to form the network structure synergistically with magnesium hydroxide in ethylene-vinyl acetate, which facilitated the generation of more continuous char structure during combustion. In parallel, the mechanical property was characterized by a tensile test and dynamic mechanical analysis (DMA). The incorporation of carbon nanomaterials presented a limited effect on the mechanical properties of the EM system.