Symposium (International) on Combustion最新文献

{"title":"HCO concentration in flames via quantitative laser-induced fluorescence","authors":"Eric W.-G. Diau ,&nbsp;Gregory P. Smith,&nbsp;Jay B. Jeffries,&nbsp;David R. Crosley","doi":"10.1016/S0082-0784(98)80434-7","DOIUrl":"10.1016/S0082-0784(98)80434-7","url":null,"abstract":"<div><p>Quantitative laser-induced fluorescence (LIF) measurements of the concentration of HCO are made in three 25-torr methane-oxygen-nitrogen flames: fuel lean (<em>φ</em>=0.81), near stoichiometric (<em>φ</em>=1.07), and fuel rich (<em>φ</em>=1.28). LIF is excited in the (000)-(000) band of the B-X system near 258 nm. The LIF signal from the flame is calibrated against nonflame measurements of a known HCO concentration produced by laser photolysis of acetaldehyde. The LIF signal is adjusted for the variation in the fraction of the population of the laser-excited level as the measured temperature changew with position in the flame and for the measured variation in quenching. The resulting concentration measurements agree well with model predictions for the fuel-lean and near-stoichiometric flame. The measurements in the fuel-rich flame are significantly larger than the model predictions: however, these measurements are subject to increased uncertainty due to the large, broadband background in the rich flame.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 453-460"},"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)80434-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"100405203","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":"Sulfur Transformation in a South Australian Low-Rank Coal during pyrolysis","authors":"Dong-Ke Zhang,&nbsp;Marnie Telfer","doi":"10.1016/S0082-0784(98)80010-6","DOIUrl":"10.1016/S0082-0784(98)80010-6","url":null,"abstract":"<div><p>Sulfur transformation during pyrolysis of a high sulfur low-rank coal from South Australia has been studied. Three experimental techniques covering a wide range of conditions, namely, temperature-programmed pyrolysis, fixed-bed pyrolysis, and fluidized-bed pyrolysis, have been employed to investigate the effect of pyrolysis conditions on the interactions between different forms of sulfur and mechanisms of sulfur evolution during coal pyrolysis. Both chemical analysis method following Australian Standards and SEM with an energy dispersive X-ray detector are used for sulfur analysis of the char. The results reveal that sulfur evolution is a net result of organic and inorganic sulfur decomposition and interaction. The presence and conversion of inorganic sulfur into complex organic sulfur compounds provide a major mechanism for sulfur retention in char during pyrolysis. The difference in heating rates in the different pyrolysis experiments does not change the natural of the sulfur transformations but affects the extent to which they occur. Faster heating rates do not necessarily imply greater sulfur evolution due to formation of complex organic sulfur. Coal samples pretreated by acid washing and Ca and Na ion exchange are also used to examine the role of inorganic matter in sulfur transformation. At low temperatures (&lt;400°C) acid washing shows little effect on sulfur retention, but at higher temperatures, sulfur retention is greatly reduced. While Na ion exchange enhances sulfur retention compared to the acid washed coal particularly at high temperatures (&gt;400°C), Ca ion exchange shows the opposite trend. An increase in sulfide formation in the Ca ion-exchanged coal at high temperatures is observed, indicating that organic sulfur decomposition is enhanced in the presence of Ca. The effect on sulfur retaining of potential reactions involving Ca ions with sulfur may be offset by the catalyzing influence of Ca ions on organic sulfur decomposition.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 1703-1709"},"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)80010-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"108242998","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":"Thermodynamic and kinetic analysis using AB initio calculations on dimethyl-ether radical+O2 reaction system","authors":"Takahiro Yamada,&nbsp;Joseph W. Bozzelli,&nbsp;Tsan Lay","doi":"10.1016/S0082-0784(98)80406-2","DOIUrl":"10.1016/S0082-0784(98)80406-2","url":null,"abstract":"&lt;div&gt;&lt;p&gt;Reaction pathways and kinetics are analyzed on CH&lt;sub&gt;3&lt;/sub&gt;OC·H&lt;sub&gt;2&lt;/sub&gt;+O&lt;sub&gt;2&lt;/sub&gt; reaction system using &lt;em&gt;ab initio&lt;/em&gt; calculations to determine tehrmodynamic properties of reactants, intermediate radicals, and transitionstate (TS) compounds. Enthalpies of formation (&lt;em&gt;ΔH&lt;sub&gt;f298&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;&lt;/em&gt;) are determined using the CBS-q//MP2(full)/6-31G(d,p) method with isodesmic reactions. Entropies (&lt;em&gt;S&lt;/em&gt;&lt;sub&gt;298&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;) and heat capacities (&lt;em&gt;C&lt;sub&gt;p&lt;/sub&gt;(T)&lt;/em&gt; 300≤&lt;em&gt;T/K&lt;/em&gt;≤1500) are determined using geometric parameters and vibrational frequencies obtained at the MP2(full)/6-31G(d,p) level of theory. Quantum Rice-Ramsperger-Kassel (QRRK) analysis is used to calculated energy-dependent rate constants, &lt;em&gt;k(E)&lt;/em&gt;, and the master equations is used to account for collisional stabilization. The dimethyl-ether radical CH&lt;sub&gt;3&lt;/sub&gt;OC·H&lt;sub&gt;2&lt;/sub&gt; (&lt;em&gt;ΔH&lt;sub&gt;f298&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;&lt;/em&gt;=0.1 kcal/mol) adds to O&lt;sub&gt;2&lt;/sub&gt; to form a peroxy radical CH&lt;sub&gt;3&lt;/sub&gt;OCH&lt;sub&gt;2&lt;/sub&gt;OO·(&lt;em&gt;ΔH&lt;sub&gt;f298&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;&lt;/em&gt;=−33.9 kcal/mol). The peroxy radical can undergo dissociation back to reactants or isomerize via hydrogen shift (&lt;em&gt;E&lt;sub&gt;a,rxn&lt;/sub&gt;&lt;/em&gt;=17.7 kcal/mol) to form a hydroperoxy alkyl radical C·H&lt;sub&gt;2&lt;/sub&gt;OCH&lt;sub&gt;2&lt;/sub&gt;OOH, (&lt;em&gt;ΔH&lt;sub&gt;f298&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;&lt;/em&gt;=−26.5 kcal/mol). This alkyl radical can undergo β-scission reaction to formaldehyde (CH&lt;sub&gt;2&lt;/sub&gt;O)+hydroperoxy methyl radical (C·H&lt;sub&gt;2&lt;/sub&gt;OOH), (&lt;em&gt;E&lt;sub&gt;a, rxn&lt;/sub&gt;&lt;/em&gt;=24.7 kcal/mol). The hydroperoxy methyl radical rapidly decomposes to a second CH&lt;sub&gt;2&lt;/sub&gt;O plus OH. The reaction barriers for CH&lt;sub&gt;3&lt;/sub&gt;OCH&lt;sub&gt;2&lt;/sub&gt; +O&lt;sub&gt;2&lt;/sub&gt; to 2 CH&lt;sub&gt;2&lt;/sub&gt;O+OH are lower than the energy needed for reaction back to CH&lt;sub&gt;3&lt;/sub&gt;OC·H&lt;sub&gt;2&lt;/sub&gt;+O&lt;sub&gt;2&lt;/sub&gt;, and provide a low-energy chain propagation path for dimethyl-ether oxidation.&lt;span&gt;&lt;span&gt;&lt;span&gt;&lt;math&gt;&lt;mtable&gt;&lt;mtr&gt;&lt;mtd&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;→&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;mo&gt;⋅&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mtd&gt;&lt;/mtr&gt;&lt;mtr&gt;&lt;mtd&gt;&lt;munder&gt;&lt;mrow&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;mo&gt;⋅&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;→&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;/mrow&gt;&lt;mo&gt;¯&lt;/mo&gt;&lt;/munder&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mtd&gt;&lt;/mtr&gt;&lt;mtr&gt;&lt;mtd&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;→&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;/mtd&gt;&lt;/mtr&gt;&lt;/mtable&gt;&lt;/math&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;Comparison of calculated fallof","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 201-209"},"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)80406-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"104412710","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":"Nonlinear instabilities leading to rapid mixing and combustion in confined supersonic double-shear-layer flow","authors":"Akira Umemura,&nbsp;Yoichi Takihana","doi":"10.1016/S0082-0784(98)80061-1","DOIUrl":"10.1016/S0082-0784(98)80061-1","url":null,"abstract":"<div><p>Direct numerical simulations conducted in the present study show that a slow fuel gas stream issued between supersonic high-temperature air streams confined in a constant-area channel can mix with air quickly to cause explosive combustion along the following processes: (1) linear flaw instability excitation, (2) eddy formation without shocks, fuel flow acceleration to supersonic speed and enhanced mixing with air, associated with fuel layer meandering, (3) explosive combustion, and (4) thermally choked burnt gas flow. The underlying physics of the supersonic instabilities involved are revealed by interpreting the simulation results in an attempt to find an effective mixing enhancement technique.</p><p>The basic flow configuration consists of a confined, plane, double shear/mixing layer flow with forcing fluctuations at the inlet. The difference in velocities between inlet air and fuel streams is supersonic. The reflection condition imposed at the walls serves to disturb acoustically the double shear layer flow in such a way that the walls reflect Mach waves radiated from the inlet disturbance. The most unstable wave excited downstream is skew-symmetric with respect to the centerline, thus leading to the meandering of fuel layer accompanied by Karman-vortex-like eddies. A series of instability excitations couples with the fuel layer meandering in a confined flow region, enhances the exchange of momentum and species between the fuel and air streams, thus accelerating the mixture to a supersonic speed within a short distance prior to explosive combustion. The behavior of the flame front resembles that of lifted turbulent-jet flames. Flame flashback, stationary flame front and flame blowout take place, depending on the inlet condition. Their criteria are provided in terms of the Chapman-Jouguet detonation wave speed.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2135-2142"},"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)80061-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"113187041","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 of stretched spray flames with nonunity Lewis numbers in a stagnation-point flow","authors":"Shuhn-Shyurng Hou ,&nbsp;Ta-Hui Lin","doi":"10.1016/S0082-0784(98)80046-5","DOIUrl":"10.1016/S0082-0784(98)80046-5","url":null,"abstract":"<div><p>The extinction of stretched premixed flames under the influence of dilute fuel sprays is studied using activation energy asymptotics. A completely prevaporized mode and a partially prevaporized mode of flame propagation are identified. Three parameters for flame extinction in the analysis consist of the mass fraction of liquid fuel and the initial droplet size of the spray, indicating the internal heat loss and heat gain for rich and lean sprays, respectively, and the flow stretch coupled with Lewis number (Le) that intensifies and weakens the burning strength of the Le&lt;1 and Le&gt;1 flame, respectively. The study presents sample calculations on lean ethanol-spray flames (Le&gt;1), rich ethanol-spray flames (Le&gt;1), and rich methanol-spray flames (Le&lt;1). Results show that the burning intensity of a spray flame with Le&gt;1 is weakened by the flow stretch: however, it is enhanced (further reduced) when the lean (rich) spray has a larger amount of liquid fuel loading or a smaller initial droplet size. It is generally found that the external heat loss associated with the flow stretch dominates the trend for flame extinction. The coupling effects of flow stretch and internal heat gain result in that there exists flame flashback instead of flame extinction for rich methanol-spray flames (Le&lt;1).</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2009-2015"},"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)80046-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"100793353","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":"Detection of extremely fine carbonaceous particles in the exhausts of diesel and spark-ignited internal combustion engines, by means of broad-band extinction and scattering spectroscopy in the ultraviolet band 190-400 NM","authors":"Antonio Borghese,&nbsp;simona S. Merola","doi":"10.1016/S0082-0784(98)80057-X","DOIUrl":"https://doi.org/10.1016/S0082-0784(98)80057-X","url":null,"abstract":"<div><p>Recent studies have shown that organic matter found in fine aerosol or sampled in flames can be only partially speciated, the major part being unidentified. Instrumental limitations of chemical analysis at very high molecular masses and of particle detectors at very low sizes leave unexplored the nanometric size range, where organic molecular clusters might accumulate.</p><p>This work reports on the detection of organic extremely fine particles in the exhausts of both diesel <em>and</em> spark-ignited engines, by means of broad-band extinction and scattering spectroscopy in the ultraviolet 190–400 nm band.</p><p>The detection techniques rely on a light source, resulting from the laser-induced optical breakdown of air, which features “blackbody” ultraviolet-visible emission, duration of few tens of nanoseconds and tighly confined spot volume.</p><p>Samples of internal combustion (IC) engines' emissions have been analyzed in two forms:(a) ordinarily air-diluted exhausts, for extinction measurements and (b) solution/suspension of condensed combustion water, which proved to increase the trapped species concentrations to levels suitable for spectral scattering measurements.</p><p>Extinction and scattering spectral data have led to characterize the scatters in terms of: (1) their complex index of refraction in the ultraviolet band 190–450 nm: (2) their average size, in the order of few nonometers and (3) their volume fraction <em>f</em>_v (hundreds of ppm) in the water-trapped exhausts.</p><p>The spectral shapes of the extinction coefficient α(λ) in the ultraviolet band have been interpreted in the framework of the solid-state physics, by relating the spatial structures of organic molecular clusters to the value <em>E</em>_g of the optical gap, derived experimentally by the Tauc relationship.</p><p>Resulting optical gaps are very low (<em>E</em>_g=0.2 eV) for air-diluted diesel exhausts, involving the presence of soot, as expected, whereas, in all the other cases explored, <em>E</em>_g spans over values greater than 3 eV, associated with carbon-containing nanoparticles.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2101-2109"},"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)80057-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"137402257","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":"Effect of hardware geometry on gas and drop behavior in a radial mixer spray","authors":"A. Ateshkadi,&nbsp;V.G. McDonell,&nbsp;G.S. Samuelsen","doi":"10.1016/S0082-0784(98)80043-X","DOIUrl":"10.1016/S0082-0784(98)80043-X","url":null,"abstract":"<div><p>The demands on current and future aero gas turbine combustors are requiring a greater insight into the role of the injector/done design and manufacturing tolerances. This paper systematically isolates manufacturing tolerances and focuses on hardware design. The target is the structure of the two-phase flow and combustion performance associated with practical injector/dome hardware. A spray injector with two radial inflow swirlers was custom designed to (1) maintain tight tolerances and strict assembly protocol and (2) thereby isolate the sensitivity of performance to hardware design. Although it represents practical hardware, the custom set is a unique modular design that (1) accommodates parametric variation in geometry, (2) retains symmetry, and (3) maintains effective area. Swirl sense and the presence of a venturi were found to be the most influential. The venturi acts as a fuel prefilming surface and constrains the highest fuel mass concentration to an annular ring near the centerline. Coswirl enhances the radial dispersion of the continuous phase, and counterswirl increases the level of mixing that occurs in the downstream region of the mixer. The combined effect of the two parameters (swirl sense and venturi) revealed that the largest drop sizes, which penetrate the continuous phase flow, are formed with coswirl and without venturi. The smallest drop size distributions were found to occur for the counterswirl configuration with venturi. In the case of counterswirl without venturi, the high concentration of fluid mass is found in the center region of the flow. The lean blowout (LBO) equivalence ratio was lower for counterswirl configurations for reasons that involved the coupling of the centerline recirculation zone with the location of high fuel concentration emanating from smaller droplets. In the coswirl configuration, a lack of fuel drops exists in the reaction anchoring region, thereby leading to poor stability characteristics.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 1985-1992"},"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)80043-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"112082628","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":"Transient combustion response of homogeneous solid propellant to acoustic oscillations in a rocket motor","authors":"Tae-Seong Roh,&nbsp;Sourabh Apte,&nbsp;Vigor Yang","doi":"10.1016/S0082-0784(98)80084-2","DOIUrl":"10.1016/S0082-0784(98)80084-2","url":null,"abstract":"<div><p>Interactions between acoustic waves and the transient combustion response of a double-base homogeneous propellant in a rocket motor have been analyzed numerically. The analysis extends the previous work on gas-phase flame dynamics to include the coupling with condensed-phase processes. Consequently, a more complete description of propellant combustion response to imposed acoustic oscillations can be obtained. Emphasis is placed on the near-surface flame-zone physiochemistry and its coupling with unsteady propellant burning in an oscillatory environment. The formulation treats complete conservation equations and the finite-rate chemical kinetics in both the gas-phase and subsurface regions. The instantaneous propellant burning rate is predicted as part of the solution. Various distinct features of unsteady heat release arising from propellant combustion response in a motor with forced oscillations are studied systematically. As in the pure gas-phase dynamics of the previous case, the dynamic behavior of the luminous flame plays a decisive role in determining the motor stability characteristics. However, the propellant combustion response may qualitatively modify the temporal evolution of heat-release distribution in the luminous flame and as a result exerts a significant influence on the global stability behavior. The primary flame structure adjacent to the propellant surface is usually little affected by flow oscillation. This may be attributed to the large thermal inertial of the condensed phase, which tends to restrain the temperature variation in the near-surface zone in the present study of laminar flows. The situation with a turbulent flow may be drastically different, as turbulence may penetrate directly into the, primary flame and substantially change the local flame dynamics and transport phenomena.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2335-2341"},"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)80084-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"107419699","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 study of low- and high-temperature silane combustion","authors":"V.I. Babushok,&nbsp;W. Tsang,&nbsp;D.R. Burgess Jr.,&nbsp;M.R. Zachariah","doi":"10.1016/S0082-0784(98)80095-7","DOIUrl":"10.1016/S0082-0784(98)80095-7","url":null,"abstract":"<div><p>Self-ignition and flame propagation properties of silane combustion systems have been studied through computer simulations using a database of kinetic and thermodynamic information that is consistent with current understanding of the elementary processes. These new inputs include the mechanism for chain branching through the SiH₃ radical, rate constants for the reactions of HO₂ with silane and its breakdown products, and the reaction of SiO with oxygen. Over the entire temperature range, the simulations show two distinct mechanisms. At low temperatures, the kinetics of SiH₃ is controlling, whereas at high temperatures, SiH₂ chemistry is of key importance. The results demonstrate that the upper explosion limit and ignition at room temperature and 1 bar can be described by the same set of reactions. With the new database, many of the experimental observations can be reproduced, and predictions are made regarding dependencies on process parameters. These include the critical conditions for chain ignition, the dependence of the critical pressure on the ratio of silane and oxygen concentration, and the temperature dependence of the critical ratio of silane to oxygen concentration. A scenario for low-temperature ignition is presented. At high temperatures, the importance of condensation processes for accurate prediction of flame velocities is clear. For very lean flames, the maximum reaction rate occurs at the lower temperature region of the flame zone.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2431-2439"},"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)80095-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"93951360","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":"Computational and experimental study of a forced, timevarying, axisymmetric, laminar diffusion flame","authors":"Rahima K. Mohammed,&nbsp;Michael A. Tanoff ,&nbsp;Mitchell D. Smooke,&nbsp;Andrew M. Schaffer,&nbsp;Marshall B. Long","doi":"10.1016/S0082-0784(98)80462-1","DOIUrl":"10.1016/S0082-0784(98)80462-1","url":null,"abstract":"<div><p>Forced, time-varying flames are laminar systems that help bridge the gap between laminar and turbulent combustion. In this study, we investigate computationally and experimentally the structure of an acoustically forced, axisymmetric laminar methane-air diffusion flame, in which a cylindrical fuel jet is surrounded by a coflowing oxidizer jet. The flame is forced by imposing a sinusoidal modulation on the steady fuel flow rate. Rayleigh scattering and spontaneous Raman scattering of the fuel are used to generate the temperature profile. Particle image velocimetry (PIV) is used to measure the fuel tube exit velocity over a cycle of the forcing modulation. CH flame emission measurements have been done to predict the excitedstate CH (CH^*) levels. Computationally, we solve the transient equations for the conservation of total mass, momentum, energy, and species mass with detailed transport and finite-rate C₂ chemistry submodels to predict the pressure, velocity, temperature, and species concentrations as a function of the two independent spatial coordinates and time. The governing equations are written in primitive variables. Implicit finite differences are used to discretize the governing equations and the boundary conditions on a nonstaggered, noniumiform grid. Modified damped Newton's method nested with a Bi-CGSTAB iteration is utilized to solve the resulting system of equations. Results of the study include a detailed description of the fluid dynamic-thermochemical structure of the flame at a 20-Hz frequency. A comparison of experimentally determined and calculated temperature profiles and CH^* levels agree well. Calculated mole fractions of species indicative of soot production (C₂H₂, CO) are compared against those levels in the corresponding steady flame and are observed to increase in peak concentration values and spatial extent. Analysis of acetylene production rates reveals additional significant production in the downstream region of the flame at certain times during the flame's cyclic history.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 693-702"},"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)80462-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"98323575","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}