Symposium (International) on Combustion最新文献

{"title":"A numerical study of unsteady self-propagating reactions in multilayer foils","authors":"Swaminathan Jayaraman ,&nbsp;Adrian B. Mann ,&nbsp;Timothy P. Weihs ,&nbsp;Omar M. Knio","doi":"10.1016/S0082-0784(98)80098-2","DOIUrl":"10.1016/S0082-0784(98)80098-2","url":null,"abstract":"<div><p>Self-propagating reactions in multilayer foils are analyzed using an unsteady computational model. The reactions are described in terms of the energy conservation equation and the evolution equation for a conserved scalar. The model is applied to analyze combustion waves in reacting foils that consist of alternating layers of Ni and Al. The individual layers have thicknesses, 2δ, in the range 20 to 200 nm, and the foils are 1 to 100 μm thick. The interfaces between the layers are assumed to be diffuse, with a characteristic mixed-zone thickness of 4Ω. The propagation of the flame is analyzed in terms of δ and Ω. Consistent with experimental observations and steady-state calculations, computed results show that the flame speed increases with decreasing δ, until a critical value, δ_c, is reached. Below δ_c, the trend is reversed—that is, the flame speed decreases with δ. Meanwhile, the flame speed increases monotonically with decreasing Ω. However, the calculations show that propagation of the reaction occurs in an unsteady fashion. Periodic and quasi-periodic, large-amplitude oscillations in the burning rate and the flame width are observed. As the flame speed increases, the amplitude of the oscillations increases and their characteristic period decreases. The occurrence of superadiabatic temperatures within the flame suggests that the oscillations result in an average propagation speed that is larger than the steady-state prediction.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2459-2467"},"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)80098-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"100745741","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":"Statistics of flame displacement speeds from computations of 2-D unsteady methane-air flames","authors":"N. Peters ,&nbsp;P. Terhoeven ,&nbsp;Jacqueline H. Chen ,&nbsp;Tarek Echekki","doi":"10.1016/S0082-0784(98)80479-7","DOIUrl":"10.1016/S0082-0784(98)80479-7","url":null,"abstract":"<div><p>Results of two-dimensional numerical computations of turbulent methane flames using detailed and reduced chemistry are analyzed in the context of a new theory for premixed turbulent combustion. This theory defines the thin reaction zones regine, where the Kolmogorov scale is smaller than the preheat zone thickness but larger than the reaction zone thickness. The two numerical computations considered in this paper fall clearly within this regime. A lean and a stoichiometric flame are considered. The former is characterized by a large ratio of the turbulence intensity to the laminar burning velocity and the latter by a smaller value of that ratio.</p><p>The displacement speed of the reaction zone relative to the flow is defined as the displacement speed of the isoscalar line at a fuel mass fraction corresponding to 10% of the upstream value. The three different mechanisms that are contributing to the displacement of the reaction zone, namely, normal and tangential diffusion and reaction, are analyzed and their probability density functions are evaluated. Although these contributions fluctuate considerably, the mean value of the overall displacement speed is found to be only around 40% different from the burning velocity of a plane premixed flame at the same equivalence ratio. Furthermore, the contribution of tangential diffusion, which can be expressed as a curvature term, cancels as far as the mean overall displacement speed is concerned, while the contributions of normal diffusion and reaction are large but have opposite signs. These contributions depend implicitly on curvature. This dependence is small for the lean flame but considerable for the stoichiometric flame where it leads to an enhanced diffusivity. This diffusivity is compared to the Markstein diffusivity that describes the equivalent curvanture effect in the corrugated flamelet regime.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 833-839"},"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)80479-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"113329395","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 recombination of hydrogen atoms with nitric oxide at high temperatures","authors":"Peter Glarborg ,&nbsp;Martin Østberg ,&nbsp;Maria U. Alzueta ,&nbsp;Kim Dam-Johansen ,&nbsp;James A. Miller","doi":"10.1016/S0082-0784(98)80408-6","DOIUrl":"10.1016/S0082-0784(98)80408-6","url":null,"abstract":"<div><p>The rate constant for the H+NO+N₂ reaction (R1,N₂) has been determined in the temperature range 1000–1170K from flow-reactor experiments on the CO/O₂/H₂O/N₂ system perturbed with different amounts of NO. The initiation temperature of this system is highly sensitive to reaction R1, which is the rate-controlling step in the nitric oxide catalyzed removal of hydrogen atoms. Based on the flow-reactor results and the limited amount of data reported in literature, a rate constant for the H+NO+N₂ reaction of 4.0×10²⁰<em>T</em>^−1.75 cm⁶/(mol²<em>s</em>) was determined. This value is in good agreement with the recent result of Allen and Dryer at 1000K but significantly lower at high temperatures than the recommendation of Tsang and Herron. With the recently determined value of ΔH_{<em>f,298</em>} (HNO) of 26.0 kcal/mol, which is 2 kcal/mol higher than previous estimates, our results correspond to a rate constant of 1.7×10¹⁹<em>T</em>^−1.5 exp(−23,400/<em>T</em>) cm³/(mol s) for the HNO+N₂ dissociation reaction in the 1000–2500 K range. The sharp drop-off in the rate constant for H+NO+M at high temperatures suggested by the flow-reactor results are supported by reinterpretation of data reported in literature on H₂/O₂/N₂ flames doped with NO. Theoretical considerations suggest that the effect can be attributed to weak-collision effects.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 219-226"},"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)80408-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"107470421","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":"Vorticity generation and flame distortion induced by shock flame interaction","authors":"Yiguang Ju ,&nbsp;Akishi Shimano ,&nbsp;Osamu Inoue","doi":"10.1016/S0082-0784(98)80467-0","DOIUrl":"10.1016/S0082-0784(98)80467-0","url":null,"abstract":"<div><p>The vorticity generation and flame distortion by the shock propagation through a cylindrical H₂/air flame are investigated numerically with detailed chemistry. it is shown that flame distortion and the appearance of the second shock waves greatly affects the total circulation. For strong shock wave, the results show that the flame distortion and interaction of the second shock waves yield subscale vortices. A comparison between the present prediction and the theory reveals that the predicted total circulation is lower than that given by theory. The results also show that the shock flame interaction results in significant distortion and break-up of the flame. The effects of shock strength on the flame distortion, the length of flame front, and the mass burning velocity are examined. The results show that both the total mass burning velocity and the length of the flame front increase dramatically with the shock Mach number. The mean local burning velocity is obtained by normalizing the total burning velocity with the length of the flame front. A good agreement between the mean local burning velocity and the burning velocity of laminar H₂/air flame is obtained. It is concluded that the flame distortion induced by the shock flame interaction is very close to the laminar flamelet regime.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 735-741"},"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)80467-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"102604380","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":"Evidence for a unified pathway of dioxin formation from aliphatic hydrocarbons","authors":"Philip H. Taylor ,&nbsp;Sukh S. Sidhu ,&nbsp;Wayne A. Rubey ,&nbsp;Barry Dellinger ,&nbsp;Andreas Wehrmeier ,&nbsp;Dieter Lenoir ,&nbsp;K.-W. Schramm","doi":"10.1016/S0082-0784(98)80018-0","DOIUrl":"10.1016/S0082-0784(98)80018-0","url":null,"abstract":"<div><p>Acetylene is readily converted to perchlorinated gas-phase intermediates including hexachlorobenzene, hexachlorobutadiene, and tetrachloroethylene and heavier perchlorinated species via heterogeneous gas-solid reactions with HCl and cupric oxide on borosilicate under postcombustion conditions. Experiments were conducted using an integrated gas-solid flow-reactor and analytical system at temperatures ranging from 150 to 500°C for gas-phase residence times of 2.0 s and total reaction times of 60 min. Chlorine addition and chlorine net substitution mechanisms mediated by the conversion of Cu(II)Cl₂ to Cu(I)Cl are proposed to account for the observed or inferred C₂ reaction products including tetrachloroethylene, trichloroethylene, and dichloroacetylene. The formation of condensation products including tetrachlorovinylacetylene, hexachlorobutadiene, and hexachlorobenzene are proposed to be catalyzed by copper chloride species and involve the following steps: (1) chemisorption of a chlorinated ethylene or acetylene by HCl elimination or 1,2-Cu−Cl addition, respectively: (2) physisorption of additional chlorimated ethylenes or acetylenes followed by <em>cis</em>-insertions: and (3) carbon-to-copper chlorine transfer followed by desorption of the molecular growth product. The mechanism accounts for product isomer distributions and branching desorption of the higher molecular weight products, and regeneration of the copper chloride catalyst.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 1769-1775"},"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)80018-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"99608915","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 thermal explosion of a cool spray in a hot gas","authors":"Igor Goldfarb ,&nbsp;Vladimir Goldshtein ,&nbsp;Grigory Kuzmenko ,&nbsp;J. Barry Greenberg","doi":"10.1016/S0082-0784(98)80088-X","DOIUrl":"10.1016/S0082-0784(98)80088-X","url":null,"abstract":"<div><p>The effect of a flammable spray on thermal explosion in a preheated combustible gas mixture is investigated using a simplified model that contains the essentials of the basic physical processes at work. The study represents a re-examination of the question of the ignition of a spray of droplets from the viewpoint of an explosion problem, in which the droplets are taken to be a source of endothermicity. Use is made of various methods for the qualitative analysis of systems of differential equations in order to examine the dynamics of the system. Possible types of dynamical behavior of the system are looked into and parametric regions of their existence are determined analytically. Peculiarities, of these dynamical regimes are investigated, and their dependence on the physical system parameters are analyzed. In particular, analytical formulas are developed for ignition delay times by exploiting the sensitivity of the process to the chemical activation energy. A qualitative comparison of predicted ignition times with independent experimental measurements from the literature yields good order of magnitude agreement.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2367-2374"},"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)80088-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"109674795","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":"A re-evaluation of the means used to calculate transport properties of reacting flows","authors":"Phillip Paul ,&nbsp;Jürgen Warnatz","doi":"10.1016/S0082-0784(98)80439-6","DOIUrl":"10.1016/S0082-0784(98)80439-6","url":null,"abstract":"<div><p>Simulations of laminar combustion and other reactive flow processes (like chemical vapor deposition, plasma etching, etc.) are presently carried out in most cases using the transport code TRANFIT attached to the CHEMKIN package. The approach used is based on experimental data from 1975 and is now outdated, especially in view of recent work presented in the literature.</p><p>The new approach described here seeks to remove the deficiencies of former transport models by using the following features: (1) representation of transport data of light species at high temperature by switching to an exponential repulsive potential, (2) use of effective potential parameters to handle the intermolecular forces in an easy and elegant way, if polar molecules are considered, and (3) use of a simplified formula for binary thermal diffusion factors, based on an expansion for large values of the mass ratio of the species included.</p><p>This paper presents the new transport model in terms of a complete set of equations. The molecular parameters provided allow a complete treatment of the oxidation of H₂ and H₂/CO mixtures (data for species taking place in the oxidation of hydrocarbons and in other reaction systems are not yet available). To demonstrate the consequences of the new transport model for combustion processes, results have been generated by implementing the model in a code for the simulation of premixed laminar flames.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 495-504"},"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)80439-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"112526270","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 effects of equivalence ratio on the formation of polycyclic aromatic hydrocarbons and soot in premixed methane flames","authors":"Tyler R. Melton,&nbsp;Antonio M. Vincitore,&nbsp;Selim M. Senkan","doi":"10.1016/S0082-0784(98)80001-5","DOIUrl":"https://doi.org/10.1016/S0082-0784(98)80001-5","url":null,"abstract":"<div><p>The formation of polycyclic aromatic hydrocarbons (PAH) and soot has been investigated in atmospheric pressure, laminar, methane/oxygen/argon premixed flames as a function of mixture equivalence ratio. Mole fraction profiles of major products, trace aromatic, substituted aromatic, and PAH were quantified by <em>direct</em> gas chromatography/mass spectrometry. In addition, soot-particle diameters, number densities, and volume fractions were determined using classical light scattering. The dependencies of flame species on equivalence ration, using the expression <em>X_i^max=A_iⁿⁱ</em> were also determined; results reveal that the sensitivity parameter <em>n</em> for stable aliphatic species exhibit the following rank order: c-C₅H₆ (4.2)&gt;C₃H₄ (3.9)&gt;C₄H₆ (3.3)&gt;C₄H₄ (2.8)&gt;C₄H₂ (2.2)&gt;C₂H₂ (1.8). For aromatic species, the values of <em>n</em> were in the following order: phenylacetylene (10.8)&gt;benzene (10.2)&gt;indene (7.5)&gt;toluene (5.5). In comparison, PAH species were extremely sensitive to flame equivalence ratios, with the following <em>n</em> values: acenaphthylene (14.2)&gt;fluoranthene (14.1)&gt;pyrene (13.2)&gt;anthracene (13.1)&gt;phenanthrene (11.7)&gt;naphthalene (10.8). Similarly, the sensitivity of soot volume fraction to equivalence ratio was about 13. These results suggest that PAH and soot formation are closely related and their levels are not strongly influenced by the levels of acetylene present in the flame under the conditions investigated.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 1631-1637"},"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)80001-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72278417","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":"Experimental and computational study of CH, CH*, and OH* in an axisymmetric laminar diffusion flame","authors":"K.T. Walsh,&nbsp;M.B. Long,&nbsp;M.A. Tanoff,&nbsp;M.D. Smooke","doi":"10.1016/S0082-0784(98)80453-0","DOIUrl":"10.1016/S0082-0784(98)80453-0","url":null,"abstract":"<div><p>In this study, we extend the results of previous combined numerical and experimental investigations of an axisymmetric laminar diffusion flame in which difference Raman spectroscopy, laser-induced fluorescence (LIF), and a multidimensional flame model were used to generate profiles of the temperature and major and minor species. A procedure is outlined by which the number densities of ground-state CH (<em>X²II</em>), excited-state CH (<em>A²δ</em>, denoted CH^*), and excited-state OH (A²Σ, denoted OH^*) are measured and modeled. CH^* and OH^* number densities are deconvoluted from line-of-sight flame-emission measurements. Ground-state CH is measured using linear LIF. The computations are done with GRI Mech 2.11 as wel as an alternate hydrocarbon mechanism. In both cases, additional reactions for the production and consumption of CH^* and OH^* are added from recent kinetic studies. Collisional quenching and spontaneous emission are responsible for the de-excitation of the excited-state radicals.</p><p>As with our previous investigations, GRI Mech 2.11 continues to produce very good agreement with the overall flame length observed in the experiments, while significantly under predicting the flame liftoff height. The alternate kinetic scheme is much more accurate in predicting lift-off height but overpredicts the overall flame length. Ground-state CH profiles predicted with GRI Mech 2.11 are in excellent agreement with the corresponding measurements, regarding both spatial distribution and absolute concentration (measured at 4 ppm) of the CH radical. Calculations of the excited-state species show reasonable agreement with the measurements as far as spatial distribution and overall characteristics are concerned. For OH^*, the measured peak mole fraction, 1.3×10⁻⁸, compared well with computed peaks, while the measured peak level for CH^*, 2×10⁻⁹, was severely underpredicted by both kinetic schemes, indicating that the formation and destruction kinetics associated with excited-state species in flames require further research.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 615-623"},"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)80453-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"103770672","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":"The influence of evaporation on the autoignition-delay of n-heptane air mixtures under gas turbine conditions","authors":"M. Cano Wolff,&nbsp;J. Meisl,&nbsp;R. Koch,&nbsp;S. Wittig","doi":"10.1016/S0082-0784(98)80048-9","DOIUrl":"10.1016/S0082-0784(98)80048-9","url":null,"abstract":"<div><p>In this work, autoignition-delay times of liquid fuel sprays for flow situations similar to those in premixing ducts are calculated. An intensive parameter study was conducted to identify the influence of the evaporating spray on autoignition delay. The parameter variation covers duct conditions relevant to gas turbines. Three monodisperse sprays with droplet sizes of 10,50, and 100 <em>μ</em>m and two sprays with Rossin-Rammler droplet size distribution are investigated. A full 3-D Navier-Stokes code is used for the prediction of the turbulent flow. It is coupled to a code based on a Lagrangian formulation for the prediction of the motion and evaporation of the droplets. The evolution of the chemical kinetics is predicted with the CHEMKIN package for <em>n</em>-heptane, which is selected as fuel. A detailed <em>n</em>-heptane low-temperature mechanism including 168 species and 904 reactions describes the chemical kinetics.</p><p>For initial temperatures inside the negative temperature coefficient region (NTC), the only spray parameter influencing autoignition delay is the spray evaporation time. If the initial temperature is on the lower boundary of the NTC region, the strong temperature dependence of autoignition in this region leads to a substantially longer autoignition delay due to the cooling of the gas phase caused by evaporation. A delaying effect of evaporation time is only present if the evaporation time is higher than the first induction time. Generally, the safety margin between autoignition and the end of evaporation is enhanced by utilization of a spray with small droplets and a narrow droplet size distribution. Also, a minimum autoignition delay for lean conditions at <em>Φ</em>=0.5 is identified.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2025-2031"},"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)80048-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"98460158","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}