Symposium (International) on Combustion最新文献

{"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":"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":"The effect of radiation on the combustion wave propagation in a heterogeneous system","authors":"Igor Filimonov","doi":"10.1016/S0082-0784(98)80096-9","DOIUrl":"10.1016/S0082-0784(98)80096-9","url":null,"abstract":"<div><p>The behavior of integral curves has been theoretically investigated in the problem of combustion wave propagation through a heterogeneous model system. The effect of radiation heat transfer on the steadystate (possibly nonstationary) combustion modes has been considered. At sufficiently high but limited spaces between the plates in the system with quasi-homogeneous temperature distribution, the effect of radiation heat transfer can be significant at low retardation by the growing product layer, and the combustion velocity can be much increased by the decrease in the characteristic time of radiation. At the same parameters of heat transfer in the mode of high retardation, the effect of radiation is much weaker and the increase in the combustion velocity is negligibly small if the chemical reaction maximum appears at low temperatures and indexes of the initial substance conversion.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2441-2450"},"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)80096-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"100616860","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":"Extinction processes during a non-premixed flame-vortex interaction","authors":"D. Thévenin,&nbsp;P.H. Renard,&nbsp;J.C. Rolon,&nbsp;S. Candel","doi":"10.1016/S0082-0784(98)80465-7","DOIUrl":"10.1016/S0082-0784(98)80465-7","url":null,"abstract":"<div><p>Studies of flame-vortex interactions are quite valuable in the analysis of turbulent combustion. As turbulence may be viewed as a collection of vortices with different scales and intensities, the interaction of isolated vortical structures with flames defines the elementary process by which turbulence acts on flames. Experiments and interpretation are thus simplified because the unperturbed flame and the incoming vortex may be controlled with precision. We here investigate the influence of vortex velocity (directly related to its induced strain rate) and of global mixture ratio on the extinction limits. Three vortex types with different velocities interact with a non-premixed diluted hydrogen-air flame. The global mixture ratio of this flame has been varied between 0.5 and 1.2. Four different kinds of interaction are described, and the limits of the connected-flame regime, relevant for flamelet modeling, are identified. The growth of the flame surface during the interaction is also examined, showing very different effects depending on vortex velocity and global mixture ratio. The increase in flame surface area is maximum for slow vortices and intermediate values of the mixture ratio. The main features of the interaction and the relative importance of the increase in flame surface are then explained in the light of characteristic times and extinction strain rates obtained by asymptotic analysis. The extinction of the flame front is finally examined using direct numerical simulations of flame-vortex interactions, including complex chemistry, detailed thermodynamics, and multicomponent diffusion velocities. The relative importance of the strain rate acting on the flame front and of mixing effects is assessed, proving that unmixedness is not responsible for the extinction.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 719-726"},"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)80465-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"100834729","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":"CCl, CH, and NO LIF measurements in methane-air flames seeded with chlorinated species: Influence of CH3Cl and CH2Cl2 on CCl and NO formation","authors":"P. Devynck,&nbsp;P. Desgroux,&nbsp;L. Gasnot,&nbsp;E. Therssen,&nbsp;J.F. Pauwels","doi":"10.1016/S0082-0784(98)80435-9","DOIUrl":"10.1016/S0082-0784(98)80435-9","url":null,"abstract":"<div><p>In this work, the laser-induced fluorescence (LIF) technique is used to detect minor species (CCl, NO, and CH) in premixed stoichiometric methane-air flames seeded with monochloromethane or dichloromethane. Quenching data are extracted from time-resolved fluorescence lifetime measurements for all the excited species. First quenching measurements of CCl under flame conditions are reported. It is shown that LIF measurements are strongly perturbed by the presence of background emissions issued from the radiative relaxation of photolytic fragments (HCl^*, CCl^*, CH^*, and C₂^*) formed upon laser excitation. The parent molecules that are partly responsible for these emissions are C₂H₃Cl (for HCl^*, CH^*) and CHCl₂ (for CCl^*).</p><p>Profiles of both photolytic fragments and species directly measured by LIF are used to study the influence of CH₃Cl and CH₂Cl₂ addition on CCl and NO formation in methane-air flames. CCl radical is found to be formed in the reaction zone of the flames. The reaction path leading to CCl appears to be dependent on the nature of the chlorinated hydrocarbon (CHC) seeded in the flame. The suggested reaction paths may preferentially involve the contribution of CHCl₂ in case of CH₂Cl₂ degradation and CH₂Cl in case of CH₃Cl degradation. An important increase of NO in presence of CHC is pointed out for the first time. The NO formation in flames containing CHC appears to occur in the reaction zone of the flames, and [NO] is found to be constant in the burned gases: This suggests a predominance of the prompt-NO mechanism in this kind of flame as confirmed experimentally by the observed [CH] increase. Reaction paths involving the degradation of CHCs, particularly CHCl₂, should largely contribute to the formation of CH in flames seeded with CHCs.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 461-468"},"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)80435-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"112756235","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":"Two-dimensional direct numerical simulation of opposed-jet hydrogen-air diffusion flame","authors":"C.E. Frouzakis,&nbsp;J. Lee,&nbsp;A.G. Tomboulides ,&nbsp;K. Boulouchos","doi":"10.1016/S0082-0784(98)80448-7","DOIUrl":"10.1016/S0082-0784(98)80448-7","url":null,"abstract":"<div><p>Opposed-jet diffusion flame experiments are routinely analyzed with one-dimensional models obtained by assuming a specific form for the velocity field. In this study, two-dimensional simulations of the hydrogen-air laminar opposed-jet counterflow diffusion flame using detailed chemical kinetics and realistic transport were performed for parabolic and uniform inflow velocity profiles at the exits of the nozzles. Two-dimensional simulations allow for the detailed examination of the hydrodynamics and the assessment of the validity of the assumptions made in the traditional one-dimensional simulations. Using typical nozzle size and separation distance employed in experiments, we analyzed the effects of nozzle outflow boundary conditions, finite size, and finite separation distance on the structure of the strained laminar diffusion flame. We also analyzed the variations of the divergence of the velocity field (compressibility due to chemical reaction) and that of the hydrodynamic pressure. The two-dimensional simulation results show that the cost-effective one-dimensional model provides an accurate description of the flame structure even for low-strain hydrogen-air flame provided that the velocity profiles at the nozzle exits are uniform. Although in the one-dimensional model, the nozzle size to separation ratio is assumed to be large, our two-dimensional results show that a ratio of 1 is adequate. Finally, we observed that the velocity gradient (the axial derivative of the axial velocity component along the axis of symmetry) measured in experiments at a point just before the flame region is inadequate in describing the characteristic strain rate “seen” by the flame.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 571-577"},"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)80448-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"95528618","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"C60, C60O, C70 and C70O fullerene formations in premixed benzene-oxygen flames","authors":"Mohamed Hammida ,&nbsp;Antonio Fonseca ,&nbsp;Roger Doome ,&nbsp;Edmond De Hoffmann ,&nbsp;Paul A. Thiry ,&nbsp;Janos B. Nagy","doi":"10.1016/S0082-0784(98)80005-2","DOIUrl":"https://doi.org/10.1016/S0082-0784(98)80005-2","url":null,"abstract":"<div><p>The use of hydrocarbons for fullerenes synthesis has been described in the literature. In this study, the formation of fullerenes C₆₀, C₆₀O, C₇₀, and C₇₀O is investigated in premixed benzene-oxygen flames operated under a pressure of 7.5 kPa by systematically varying two physicochemical parameters: the initial velocity of the fresh gas mixture (at 298 K) at the burner, which is varied between 40 and 50 cm s⁻¹, and the atomic C/O ratio, which is varied from 0.7 to 1.15. The objective of running each flame at different sets of conditions is to assess the sensitivity of reaching an optimum in the process of fullerenes production in flames.</p><p>A higher production rate of fullerenes C_<em>n</em> under different conditions is achieved at an optimal level of C/O ratio of 1.05 and 45 cm s⁻¹ of gas velocity. In addition, the highest production rate of fullerenes is 786.7 mg/h, and the highest yield of carbon transformed to fullerenes, obtained is 0.22%. Flame synthesis of fullerenes would seem to offer potential for large-scale production. Different patterns for the production of fullerene and fullerenes oxide are obtained. This result seems to challenge the notion of complexity of the combustion, which accompanies the formation of these carbon molecules in flames. The mass spectrometer shows that heavy fullerenes containing more than 150 atoms are present in the production process. Peaks of PAH at m/e smaller than 500 amu suggest that the reaction of combining the polycyclic aromatic hydrocarbons in burned gases may play an important role in the formation of fullerenes in burned gas flames.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 1663-1668"},"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)80005-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72278418","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":"Pulsating instability in near-limit propagation of rich hydrogen/air flames","authors":"E.W. Christiansen,&nbsp;C.J. Sung,&nbsp;C.K. Law","doi":"10.1016/S0082-0784(98)80446-3","DOIUrl":"10.1016/S0082-0784(98)80446-3","url":null,"abstract":"<div><p>The adiabatic and radiation-affected unsteady planar propagation of rich hydrogen/air flames of nearlimit concentrations in the doubly infinite domain is computationally simulated with detailed chemistry and transport. Results for the adiabatic propagation show that, with progressive increase in the fuel richness, the mode of propagation changes from steady state to oscillatory with a single period, to oscillatory with double periods, and to oscillation separated by increasingly long periods of dormant chemical reactivity. In the presence of radiative loss, propagation with the first three modes are minimally affected, whereas extinction readily occurs, with precipitous drop in the flame temperature, during the dormant period of the last mode. Because the state for the onset of the last mode is at a leaner concentration than that of the nonadiabatic steady-state propagation limit the use of the steady-state result provides a conservative estimate for the rich fundamentall flammability limit. The study also shows that, by using appropriately extracted Lewis and Zeldovich numbers characterizing the steady, adiabatic flame propagation, the transition boundary from steady to pulsating propagation can be adequately described by the criterion derived by Sivashinsky based on one-step chemistry.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 555-562"},"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)80446-3","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"104642950","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":"in situ measurements of the thermal conductivity of ash deposits","authors":"Allen L. Robinson,&nbsp;Steven G. Buckley,&nbsp;Larry L. Baxter","doi":"10.1016/S0082-0784(98)80013-1","DOIUrl":"10.1016/S0082-0784(98)80013-1","url":null,"abstract":"<div><p>Ash deposits reduce heat transfer rates to furnace walls, superheater tubes, and other heat transfer surfaces in coal-fired power plants. The effective thermal conductivity of a porous ash deposit is one important parameter for determining the magnitude of this reduction. In this paper, we report <em>in situ</em>, time-resolved measurements of the effective thermal conductivity of ash deposits formed under conditions that closely replicate those found in the convective pass of a commercial boiler. Experiments were conducted using an Illinois #6 coal and a blend of Illinois #6 coal and wheat straw to determine the thermal conductivity of highly porous, unsintered deposits and to examine the influence of the initial stages of sintering on these deposits. For deposits formed while firing both fuels the measured thermal conductivity of loose, unsintered deposits is 0.15 W/(m K), almost a factor of three greater than that of air under these conditions. The initial stages of deposit sintering and densification are accompanied by a substantial increase in deposit thermal conductivity. Subsequent sintering continues to densify the deposit but has little effect on deposit thermal conductivity. These trends correspond to anticipated effects of sintering on the development of a layered deposit structure and on particle contact efficiency. Measured values of thermal conductivity are also observed to lie between rational theoretical bounds based on deposit porosity and structure.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 1727-1735"},"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)80013-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"101629192","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":"Mineral-char interactions during char combustion of a high-volatile coal","authors":"Melissa M. Lunden ,&nbsp;Nancy Y.C. Yang ,&nbsp;Thomas J. Headley ,&nbsp;Christopher R. Shaddix","doi":"10.1016/S0082-0784(98)80009-X","DOIUrl":"https://doi.org/10.1016/S0082-0784(98)80009-X","url":null,"abstract":"<div><p>We report on recent investigations of the role of inorganic mineral matter on the evolution of char structure during carbon burnout. Char samples collected in a carefully controlled, laminar flame-supported entrained flow reactor have been characterized using a number of microscopy tools. Observations of the inorganic structure of chars produced at a variety of combustion conditions are coupled with <em>in situ</em> particlesizing pyrometry measurements of the char particle population with an eye toward identifying the mechanism of mineral interaction and its effects on carbon burnout kinetics during pulverized coal char combustion. No evidence of a macroscopic ash film which has been hypothesized to retard char oxidation kinetics, was found on the chars. High-resolution electron microscopy, however, shows a surprising amount of inorganic mineral in solid solution within the carbonaceous matrix. This intimate mixing of organic and inorganic constituents may affect reactivity by both blocking oxygen access to active carbon sites and influencing the microscopic carbon structure that evolves during combustion.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 1695-1702"},"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)80009-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72292791","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}