Symposium (International) on Combustion最新文献

{"title":"Transient local extinction and reignition behavior of diffusion flames affected by flame curvature and preferential diffusion","authors":"Kenji Yoshida,&nbsp;Toshimi Takagi","doi":"10.1016/S0082-0784(98)80461-X","DOIUrl":"10.1016/S0082-0784(98)80461-X","url":null,"abstract":"<div><p>Experimental and numerical studies are made of transient H₂/N₂-air counterflow diffusion flames unsteadily strained by an impinging micro jet. Two-dimensional temperature measurements by the laser Rayleigh scattering method and numerical computations taking into account detailed chemical kinetics are conducted, paying attention to transient local extinction and reginition in relation to the unsteadiness, flame curvature, and preferential diffusion effects. The results are as follows: (1) Transient local flame extinction is observed where the micro jet impinges. However, the transient flame can survive instantaneously in squite of quite high stretch rate where the steady flame cannot exist. (2) Reignition is observed after the local extinction due to the micro air jet impingement. the temperature after reignition becomes significantly higher than that of the original flame. This high temperature is induced by the concentration of H₂ species due to the preferential diffusion in relation to the concave curvature. The predicted behaviors of the local transient extinction and reignition are well confirmed by the experiments. (3) The reignition is induced after the formation of combustible premixed gas mixture and the consequent flame propagation. (4) The reignition is hardly observed after the extinction by micro fuel jet impingement. This is due to the dilution of H₂ species induced by the preferential diffusion in relation to the convex curvature. (5) The maximum flame temperature cannot be rationalized by the stretch rate but changes widely, depending on the unsteadiness and the flame curvature in relation with preferential diffusion.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 685-692"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80461-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"107519179","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An augmented reduced mechanism for methane oxidation with comprehensive global parametric validation","authors":"C.J. Sung ,&nbsp;C.K. Law ,&nbsp;J.-Y. Chen","doi":"10.1016/S0082-0784(98)80416-5","DOIUrl":"10.1016/S0082-0784(98)80416-5","url":null,"abstract":"<div><p>Using a computer algorithm for automatic generation of reduced chemistry, an augmented reduced mechanism, consisting of 16 species and 12 lumped reaction steps, has been developed for methane oxidation from GRI-Mech 1.2. Because the present mechanism consists of a larger number of non-steady-state intermediates than the conventional four- or five-step reduced mechanisms, it exhibits good to excellent performance in predicting a wide range of combustion phenomena under extensive thermodynamical parametric variations. Specifically, the phenomena tested include perfectly stirred reactor responses, autoignition and shock-tube ignition delay times, laminar flame propagation speeds, and ignition-extinction limits of counterflowing systems, whereas the thermodynamical parametric variations include those of temperature, pressure, and composition. It is recognized that, with the anticipated increase in computing capability in the foreseeable future, use of the present four- to five-step mechanisms will be unnecessarily limiting. Consequently, it is suggested that efforts should be expended toward development of augmented reduced mechanisms for more comprehensive description of combustion phenomena and for their potential implementation in the computational simulation of complex flows and systems.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 295-304"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80416-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"93666199","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical analysis of ignition of fuel droplet array in hot stagnant air","authors":"Megumi Goto ,&nbsp;Yiguang Ju ,&nbsp;Takashi Niioka","doi":"10.1016/S0082-0784(98)80040-4","DOIUrl":"10.1016/S0082-0784(98)80040-4","url":null,"abstract":"<div><p>Numerical analysis was conducted to simulate the ignition phenomena of a fuel droplet array in hot stagnant air. Previous experimental results showed that ignition times of an <em>n</em>-heptane droplet array quickly put into quiescent hot air were less than the ignition time of a single droplet. The objective of the present study was to clarify this interesting behavior of ignition time by numerical analysis. We assumed that a heptane droplet array with a droplet diameter of 0.75 to 1.25 mm and spacing of 4 to 20 mm was immersed in hot air with a temperature of 1123 K at time zero. The unsteady equation set for the array system was solved numerically by means of the finite-difference method. The results showed that ignition times became shorter than that of a single droplet as the droplet spacing decreased and that ignition times increased rapidly when the spacing further decreased. These ignition time behaviors were consistent with experimental results. Time-dependent temperature distributions indicated that the first ignition position(s) was located between droplets when the ignition time was less than that of a single droplet. When the spacing was smaller, an intense reaction region surrounded the array as a cylindrical tube. The basic mechanism of the shorter ignition time of a droplet array is a slight decrease of the vaporized fuel mass flux due to the suppression of the increase in droplet surface temperature in the array.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 1959-1966"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80040-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"94416224","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Oscillatory stretch effects on the structure and extinction of counterflow diffusion flames","authors":"T.M. Brown ,&nbsp;R.W. Pitz ,&nbsp;C.J. Sung","doi":"10.1016/S0082-0784(98)80463-3","DOIUrl":"10.1016/S0082-0784(98)80463-3","url":null,"abstract":"<div><p>The effects of oscillatory stretch on atmospheric laminar counterflow diffusion flames are investigated both numerically and experimentally. Measurements indicate that, at high excitation frequencies, the peak extinction strain rates of oscillating CH₄+N₂ versus air flames can be extended well beyond steady-state extinction limits. Hydroxyl radical concentrations are measured in a CH₄+N₂ versus air flame excited at moderate frequencies and are compared to numerical simulations including complex chemistry and detailed transport. Measurements and simulations of OH concentration oscillations show similar phase delays. However, the measurements indicate a larger variation of OH concentration. AT moderate frequencies, the time-dependent OH variation is quasi-steady where the time-dependent flame can be described by a series of steady-state flames. However, the time-dependent flame does not quite recover to its steady-state structure at the low-strain-rate extreme.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 703-710"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80463-3","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"107446775","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Non-premixed hydrocarbon ignition at high strain rates","authors":"Fokion N. Egolfopoulos ,&nbsp;Paul E. Dimotakis","doi":"10.1016/S0082-0784(98)80456-6","DOIUrl":"10.1016/S0082-0784(98)80456-6","url":null,"abstract":"<div><p>We report on the results of numerical-simulation investigations of ignition characteristics of hydrocarbon-fuel blends expected from thermal cracking of typical jet fuels, at conditions relevant to high-Mach-number, air-breathing propulsion. A two-point-continuation method was employed, with a detailed description of molecular transport and chemical kinetics, focusing on the effects of fuel composition, reactant temperature, additives, and imposed strain rate. It captured the entire S-curve that describes the processes of vigorous burning extinction, and ignition. The results demonstrate that ignition of such fuel blends is dominated by the synergistic behavior of CH₄ and C₂H₄. A fuel temperature of <em>T</em>_fuel=950 K was employed throughout. At higher air temperatures (<em>T</em>_air=1200 K), addition of small amounts of CH₄ to C₂H₄ molerately inhibits C₂H₄ ignition, while at lower <em>T</em>_air=1050 K, CH₄ promotes ignition. Large amounts of CH₄, however, inhibit C₂H₄ ignition at all <em>T</em>_airs. Ignition promotion was also investigated through the independent addtion of H₂ and F₂ in the reactant streams. H₂ addition (e.g., 2–10%) produces a two-stage ignition and sustains higher ignition strain rates. Small amounts of F₂ (1%) result in F-radical production, contributing to efficient fuel consumption, enhancing ignition characteristics. Ignition strain rates of σ_ign≅4000 s⁻¹, as compared to σ_ign≅250 s⁻¹ for pure C₂H₄, can be attained with such additives at lower temperatures (<em>T</em>_air=1050 K).</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 641-648"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80456-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"111961447","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Measurement of the resolved flame structure of turbulent premixed flames with constant reynolds number and varied stoichiometry","authors":"Armin Soika,&nbsp;Friedrich Dinkelacker,&nbsp;Alfred Leipertz","doi":"10.1016/S0082-0784(98)80473-6","DOIUrl":"10.1016/S0082-0784(98)80473-6","url":null,"abstract":"<div><p>Wire-stabilized premixed methane-air flames have been studied in a grid-generated homogeneous turbulent flow field in order to identify different burning regimes. The planar Rayleigh scattering technique was used with two parallel laser light sheets, which allows the detection of three-dimensional temperature gradients. For a detailed investigation of the flame structure and topology, the modification of the local temperature gradients at different progress variables <em>c</em> due to the turbulent motion was studied by varying the flame stoichiometry and thereby the Karlovitz number <em>Ka</em> while keeping the turbulent Reynolds number <em>Re_t</em> constant at 87 or 134. Because of a nearly Gaussian shaped statistical distribution of the thermal gradients, the 50% median and the width of the distribution are suitable measures used to characterize the flame response. Compared with laminar unstrained calculations, especially very lean flames (&lt;0.55) marked with the highest Karlovitz number (<em>Ka</em>=4.6) revealed a reduction of the flame thickness of about 30%. This is in contrast to the expected burning regime but fits well with laminar strained calculations. Subsequently, detailed investigations were made to examine the influence of curvature on local thermal gradients. It was found that negatively curved cusps (concave toward the reactants) show a steepening of the flame-temperature profile, while positively curved flame elements can be identified by a retardation of the overall reaction process. In terms of a statistical examination, the widths of the thermal gradient distribution conditioned at different reaction progress variables <em>c</em> were regarded, finding a decrease of the spread with increasing <em>Ka</em> independent of <em>Re_t</em> and <em>c</em>. Based on different curvature radii and perturbation frequencies of the detected flames, we assume that in our experiments the flame response depends more on flame curvature than on effects caused by modification of <em>Ka</em>.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 785-792"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80473-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"112016128","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Detonation wave propagation through a single orifice plate in a circular tube","authors":"G. Ciccarelli,&nbsp;J.L. Boccio","doi":"10.1016/S0082-0784(98)80072-6","DOIUrl":"10.1016/S0082-0784(98)80072-6","url":null,"abstract":"<div><p>Detonation behavior associated with the propagation of a detonation wave through an orifice plate located within a circular tube is investigated. The tube and orifice diameter used in the study are 27.3 cm and 10 cm, respectively. The test gas used is hydrogen-air at 1 atmosphere and at various initial temperatures up to 650 K. Immediately after the orifice, the detonation wave decouples and either fails or reinitiates. The reinitiation process is characterized by either spontaneous initiation, initiation due to shock reflection, or deflagration-to-detonation transition (DDT). In the case of DDT, transition is preceded by the degeneration of the decoupled detonation wave to a velocity consistent with a CJ deflagration. Delineation between these various propagation regimes could not be correlated with the detonation cell size, λ, and orifice diameter, <em>d</em>. The data, although limited, demonstrate for the first time that the <em>d_c/λ</em>=13 critical tube criterion obtained at room temperature may not apply at elevated temperature conditions. The evidence for this is data obtained at 500 K that shows no detonation transmission for 30% hydrogen in air that corresponds to <em>d/λ</em>=16.7. The tests also indicate that a simple <em>d/λ</em> correlation cannot be used to determine when reinitiation due to shock reflection is possible. For example, at 650 K detonation wave failure was observed for <em>d/λ</em>&lt;7.4, and at 300 K failure was observed for <em>d/λ</em>&lt;11.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2233-2239"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80072-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"106669386","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On pulsating and cellular forms of hydrodynamic instability in liquid-propellant combustion","authors":"Stephen B. Margolis","doi":"10.1016/S0082-0784(98)80089-1","DOIUrl":"10.1016/S0082-0784(98)80089-1","url":null,"abstract":"<div><p>An extended Landau-Levich model of liquid-propellant combustion, one that allows for a local dependence of the burning rate on the (gas) pressure at the liquid-gas interface, exhibits not only the classival hydrodynamic cellular instability attributed to Landau but also a pulsating hydrodynamic instability associated with sufficiently negative pressure sensitivities. Exploiting the realistic limit of small values of the gas-to-liquid density ratio <em>p</em>, analytical formulas for both neutral sability boundaries may be obtained by expanding all quatities in appropriate powers of <em>p</em> in each of three distinguished wave-number regimes. In particular, composite analytical expressions are derived for the neutral stability boundaries <em>A_p(k)</em>, where <em>A_p</em> is the pressure sensitivity of the burning rate and <em>k</em> is the wave number of the disturbance. For the cellular boundary, the results demonstrate explicitly the stabilizing effect of gravity on long-wave disturbances, the stabilizing effect of viscosity (both liquid and gas) and surface tension on short-wave perturbations, and the instability associated with intermediate wave numbers for negative values of <em>A_p</em>, which is characteristic of many hydroxylammoninum nitrate-based liquid propellants over certain pressure ranges. In contrast, the pulsating hydrodynamic stability boundary is insensitive to gravitational and surface-tension effects but is more sensitive to the effects of liquid viscosity because, for typical nonzero values of the latter, the pulsating boundary decreases to larger negative values of <em>A_p</em> as <em>k</em> increases through O(1) values. Thus, liquid-propellant combustion is predicted to be stable (that is, stealy and planar) only for a range of negative pressure sensitivities that lie below the cellular boundary that exists for sufficiently small negative values of A_<em>p</em> and above the pulsating boundary that exists for larger negative values of this parameter.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2375-2386"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80089-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"106785722","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spatial distributions of H, CN, and C2 in a diamond-growing oxyacetylene flame","authors":"R.J.H. Klein-Douwel,&nbsp;J.J. Ter Meulen","doi":"10.1016/S0082-0784(98)80100-8","DOIUrl":"10.1016/S0082-0784(98)80100-8","url":null,"abstract":"<div><p>Two-dimensional laser-induced fluorescence (2D-LIF) measurements are applied to the chemical vapor deposition (CVD) of diamond by an oxyacetylene flame to visualize the distributions of atomic hydrogen, C₂, and CN in the gas phase during diamond growth. Experiments are carried out in laminar flames and reveal that atomic hydrogen is ubiquitous at and beyond the flame front. Its presence extends to well outside the diamond deposition region, whereas the C₂ distribution is limited to the flame front and the acetylene feather. CN is found to be present mostly at the outer edge of the flame, where ambient air interacts with flame gases. The diamond layers obtained are characterized by optical as well as scanning electron microscopy (SEM) and cathodoluminescence topography (CL). Clear relations are observed between the local variations in growth rate of the diamond layer and the distribution of H, C₂, and CN in the boundary layer just above the substrate. Further relations between CN and the morphology and the nitrogen incorporation as identified by CL of the deposited diamond layer are found as well. These relations agree with theoretical models describing the importance of the mentioned species in (flame) deposition processes of diamond. Three separate regions can be discerned in the flame and the diamond layer, where the gas phase and diamond growth are predominantly governed by the flame source gases, the ambient atmosphere, and the interaction of both, respectively.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2477-2483"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80100-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"97233106","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Asymptotic flame shapes and speeds of hydrodynamically unstable laminar flames","authors":"Li-Zheng Ma,&nbsp;Jerzy Chomiak","doi":"10.1016/S0082-0784(98)80445-1","DOIUrl":"10.1016/S0082-0784(98)80445-1","url":null,"abstract":"<div><p>The self-induced baroclinic instability of flames, the Landau-Darrieus instability, is studied numerically in the nonlinear range. A level set (<em>G</em> equation) based approach accounting for heat-release effects is used to follow the flame response to initial perturbation and shape evolution. It is shown that the instability leads to the development of product bubbles moving into the unburned mixture and cold mixture spikes penetrating into the burned gases similar to the bubble-spike configuration produced by the nonlinear Rayleigh-Taylor instability of interfaces in a gravitational field. Independently of the initial perturbation, the flame bubble approaches asymptotically a shape close to a paraboloid. The substantial growth of the flame-surface area due to the instability increases the flame propagation speed to the asymptotic value;<span><math><mrow><mo>+</mo><mn>0.29</mn><msqrt><mrow><mi>α</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow></msqrt><msub><mi>S</mi><mi>l</mi></msub></mrow></math></span>where <em>α</em> is the density ratio and <em>S_l</em> the laminar burning velocity. The asymptotic amplitude of the flame is approximately<span><math><mrow><mi>A</mi><mo>=</mo><mn>0.37</mn><mi>d</mi><msqrt><mrow><mi>α</mi><mo>−</mo><mn>1</mn></mrow></msqrt></mrow></math></span>, where <em>d</em> is the flame width. The burning velocity has a minor effect on the asymptotic shape of the flames. When the turbulence scale is much smaller than the size of the combustion apparatus, the results can be directly applied to turbulent flames by replacing <em>S₁</em> by the turbulent burning velocity.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 545-553"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80445-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"102168032","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}